Enhancing concrete strength and durability of normal and high- strength concrete: Exploring combined effects of optimized silica fume and slag

Enhancing concrete strength and durability of normal and high- strength concrete: Exploring combined effects of optimized silica fume and slag | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Enhancing concrete strength and durability of normal and high- strength concrete: Exploring combined effects of optimized silica fume and slag Davood Mostofinejad, Mohsen Nasrollahi, Hadi Bahmani, Zahra Zajshoor, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4414385/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 10 Aug, 2024 Read the published version in Iranian Journal of Science and Technology, Transactions of Civil Engineering → Version 1 posted 9 You are reading this latest preprint version Abstract The utilization of supplementary cementitious materials (SCMs) in concrete attracted significant attention worldwide due to both environmental benefits and the potential for enhancing concrete's mechanical properties and durability. This study investigates the interaction effects of silica fume and ground granulated blast furnace slag (GGBFS) on the behavior of normal and high-strength concrete in terms of steel corrosion resistance, carbonation depth, and compressive strength. Fifty-two concrete specimens were prepared in four groups with different combinations of water-to-cementitious materials ratio (w/cm), slag content, and silica fume content and were tested. A method was employed to compare the corrosion initiation times of different concrete specimens. The results demonstrated that silica fume improves the concrete's resistance to steel corrosion by enhancing the density, strength, and durability of the cement matrix. The specimen with a w/cm ratio of 0.3 containing 35% slag and 10% silica fume achieved a 33% reduction in carbonation depth and a compressive strength of 118 MPa, representing a 20% increase compared to the similar specimen without slag. Furthermore, the specimen with a w/cm ratio of 0.3 containing 35% slag and 15% silica fume exhibited a 44% increase in steel corrosion resistance compared to the similar specimen without silica fume. While optimizing the combined content of slag and silica fume, this study highlights that their individual effects are less significant than their combined effect when used as partial replacements for cement. Durability Slag Silica fume Carbonation depth Steel corrosion Chloride ion penetration Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 1. Introduction The durability of concrete has long been a fundamental aspect of concrete technology, as it must endure the environmental conditions for which it is designed throughout its structural lifespan. When assessing the durability of concrete structures, particularly in corrosive environments, experts emphasize that resistance alone is insufficient. Concrete design must account for various environmental conditions [ 1 ]. Concrete structures can encounter a range of issues during their service life due to external factors induced by the surrounding environment and internal factors that can compromise concrete durability. These factors generally fall into three categories: physical, such as freeze-thaw action; mechanical, like abrasion; and chemical, including sulfate attack and acid corrosion of reinforcements [ 2 ]. The alkaline environment of concrete fosters the formation of a temporary and unstable microscopic iron oxide layer on the metal surface, providing corrosion protection. However, as concrete's alkalinity decreases and ion attacks occur, this protective coating on the steel's surface deteriorates [ 3 ]. Carbonation is the most common mechanism responsible for reducing the alkalinity of concrete [ 1 ]. Furthermore, the penetration of chloride ions into steel rebar surfaces leads to corrosion, diminishing the durability of reinforced concrete structures [ 1 ]. To address this, the production of low-permeability concrete has gained attention to enhance its durability and corrosion resistance [ 2 – 4 ]. Consequently, extensive research has been conducted to explore steel corrosion prevention methods, such as cathodic protection [ 2 ], corrosion inhibitors [ 3 ], and epoxy coatings [ 4 ], but these methods are expensive and have limited effectiveness. Alternatively, the use of supplementary cementitious materials, partially replacing Portland cement, holds promise for sustainable and effective corrosion resistance improvement [ 5 , 6 ]. Notably, pozzolanic admixtures, like silica fume (SF), fly ash (FA), and granulated blast furnace slag (GBFS), are among the most commonly used supplementary cementitious materials to prepare dense and robust concrete [ 7 – 10 ]. The advent of new construction materials and techniques has made the production of high-performance concrete feasible, achieved through the incorporation of silica fume additives, superplasticizers, and low w/cm ratios, resulting in better compaction and viscosity. High-performance concrete exhibits low permeability, which plays a crucial role in minimizing the ingress of contaminants like chloride, carbon dioxide, and humidity, known to initiate corrosion [ 11 – 18 ]. The increasing utilization of high-performance concrete in tall buildings, bridges, and structures exposed to harsh environments necessitates further research into its durability. In recent years, there has been a rise in the use of alternative pozzolanic materials, such as fly ash and slag, due to economic factors and their favourable effects on workability in high-performance concrete. From an economic perspective, a significant cost difference between cement and alternative cementitious materials has been observed. Moreover, using these materials as partial replacements for cement reduces the consumption of expensive superplasticizers. Additionally, slag and fly ash contribute to the development of durability and strength in concrete, as they are not chemically inert in the concrete environment [ 19 – 22 ]. Silica fume serves two critical roles in concrete. First, its pozzolanic properties lead to a chemical reaction with calcium hydroxide (CH) to generate additional hydrated calcium silicate (C-S-H), enhancing concrete strength. Second, due to its minute particle size, silica fume fills all the microscopic pores in the cement paste, reducing its permeability [ 10 , 19 ]. Consequently, adding silica fume to the concrete mixture in appropriate proportions significantly decreases concrete permeability and corrosion rate while improving its strength and durability [ 23 – 26 ]. Despite extensive research on concrete durability, a comprehensive understanding of how different proportions of slag and silica fume influence overall durability remains elusive. The quest to identify the optimal combination of these supplementary cementitious materials (SCMs) to enhance concrete's resistance to steel rebar corrosion is an ongoing endeavor. This study delves into the specific impact of incorporating silica fume, slag, and their various combinations at different proportions and water-to-cement (w/c) ratios on critical durability factors, including steel corrosion, carbonation penetration, and compressive strength. While previous studies have explored the individual effects of these SCMs, their combined influence and the optimal proportions for enhancing concrete durability remain largely unknown. The overarching objective of this investigation is to unravel the intricate interplay between silica fume, slag, and w/c ratio, providing valuable insights into their synergistic effects on concrete durability, particularly in terms of resisting steel rebar corrosion. The ultimate goal is to formulate practical guidelines for the optimal utilization of these SCMs in the production of robust and reliable concrete structures. Concrete specimens were prepared with three different w/cm ratios of 0.5, 0.4, and 0.3. Each w/cm ratio included varying percentages of slag (10%, 20%, 30%, and 50%) as a replacement for cement while for each case the silica fume replacements were also varied at 0%, 5%, 10%, and 15%. Cubic concrete specimens containing four rebars at each corner were employed to assess the steel corrosion using the half-cell potential measurement method. The specimens were subjected to alternating wet and dry conditions while immersed in a chloride ion solution for five days and exposed to open air for two days to accelerate the corrosion of steel rebars. Furthermore, carbonation penetration and compressive strength tests were conducted at 28-day and 91-day intervals. 2. Materials and methods 2.1. Preparation of specimens This study involved testing four distinct types of specimens to assess their performance. The first set of specimens involved incorporating silica fume as a partial replacement for cement, with w/cm ratios of 0.25, 0.3, 0.4, and 0.5. The purpose of these specimens was to investigate the influence of silica fume on steel corrosion in concrete exposed to chloride penetration. The second, third, and fourth sets of specimens were composed of concrete mixes containing 20%, 30%, and 50% slag content, respectively, as cement substitutes, with varying percentages of silica fume. The w/cm ratios for these three sets of concrete specimens were 0.5, 0.4, and 0.3. The intention was to examine the effects of slag, as well as the combined effects of slag and silica fume, on steel corrosion in a chloride-rich concrete environment. For each mix design, three specimens were designated for assessing steel corrosion through the measurement of half-cell potential. Furthermore, three specimens were devoted to determining the compressive strength at 28 days, and another three for measuring the compressive strength at 91 days. Additionally, two specimens were employed to evaluate the depth of carbonation. To fulfill specific testing requirements, three additional cubic specimens measuring 70 mm in dimension were prepared. Consequently, a total of 728 specimens were manufactured, with 159 specimens designated for half-cell potential measurement, 15 specimens for carbonation depth assessment, and the remaining specimens allocated to evaluate the compressive strength at 28 and 91 days. 2.2. Materials The mechanical properties and durability of High-Performance Concrete (HPC) are profoundly influenced by the characteristics of cement, aggregate, and pozzolanic materials. Consistent with prior research, the following materials, selected based on specific criteria, were employed: Coarse broken limestone, adhering to the ASTM-C33 [ 27 ] grading standard, with a maximum particle size of 12.5 mm, a dry density of 1950 kg/m², and a water absorption rate of 0.55%. Fine limestone, meeting the prescribed ASTM-C33 grading, with a density of 2.51 and a water absorption rate of 1%. Type 1 cement, in compliance with the ASTM-C150 [ 28 ] standard. Silica fume in powdered form, characterized by a density of 2.2. Slag of the type ground granulated blast furnace slag (GGBFS). Melamine-formaldehyde sulfate superplasticizer, following the specifications outlined in ASTM-C494 [ 29 ]. 2.3. Mix design 2.3.1. Specimens with silica fume as a partial cement replacement This set of specimens was specifically designed to investigate the impact of silica fume on the corrosion of steel rebars exposed to chloride ions. Different proportions of silica fume (0%, 5%, 10%, and 15%) were utilized as partial replacements for the cement content in each specimen at each w/cm ratio. The control specimen, in each w/cm ratio, contained 0% silica fume, serving as a reference against which the corrosion behavior of steel in other specimens was compared. A systematic coding system was employed to represent these specimens, using the letter 'A' to signify concrete with silica fume and no slag, followed by the respective w/cm ratio. Additionally, the proportion of silica fume incorporated in each specimen was indicated in the code. For instance, the code 'A 0.4-5' denoted a specimen with silica fume (without slag) at a w/cm ratio of 0.4, wherein 5% of the cement content was replaced by silica fume. Detailed mix designs for this group of specimens are presented in Table 1 . Notably, the quantity of coarse aggregate in all specimens was kept constant at 1020 kg/m² to eliminate its influence on chloride ion penetration and subsequent steel corrosion. 2.3.2. Specimens with slag and silica fume as cement replacements This set of specimens was specifically designed to investigate the effects of both slag and a combination of slag and silica fume on steel corrosion in the presence of chloride ions. Cement was partially replaced with slag in these specimens at percentages of 20%, 35%, and 50%, respectively. Concurrently, for each percentage of slag replacement, silica fume was introduced as a substitute for cement at proportions of 0%, 5%, 10%, and 15%. To designate these specimens, employed the letters 'B,' 'C,' and 'D' to represent concrete specimens containing 20%, 35%, and 50% slag content, respectively. The respective w/cm ratio was indicated, followed by the proportion of silica fume utilized. For example, the code 'D 0.3–10' referred to a specimen with 50% slag content and 10% silica fume, replacing a portion of the cement, with a w/cm ratio of 0.3. In this instance, Portland cement constituted only 40% of the total cementitious materials. The quantities of materials used in these specimens were consistent with those listed in Table 1 , with the distinction being that groups B, C, and D incorporated 20%, 35%, and 50% slag replacement for cement, respectively. Table 1 Concrete mix design variations (kg/m 3 ). Specimen Silica fume * Added water Superplasticizers ** Cement + Slag Limestone powder (A, B, C, D) 0.5-0 0 202 1.1 380 692 (A, B, C, D) 0.5-5 19 202 1.1 361 685 (A, B, C, D) 0.5–10 38 202 1.1 342 679 (A, B, C, D) 0.5–15 57 202 1.1 323 672 (A, B, C, D) 0.4-0 0 184 1.5 430 692 (A, B, C, D) 0.4-5 21.5 184 1.5 408 685 (A, B, C, D) 0.4–10 43 184 1.5 387 679 (A, B, C, D) 0.4–15 64.5 184 1.5 365 672 (A, B, C, D) 0.3-0 0 174 1.8 540 629 (A, B, C, D) 0.3-5 27 174 1.8 513 620 (A, B, C, D) 0.3–10 54 174 1.8 486 611 (A, B, C, D) 0.3–15 81 174 1.8 459 602 A 0.25-0 0 162 2.8 600 605 A 0.25-5 30 162 2.8 570 595 A 0.25-10 60 162 2.8 540 585 A 0.25-15 90 162 2.8 510 575 * Water addition is based on specific w/cm ratio and using almost dry aggregate ** Cement and slag contents are based on the specimen group (A, B, C, or D). 2.4. Corrosion tests of steel in concrete 2.4.1. Half-cell potential measurement device In this study, the corrosion of steel in concrete specimens was assessed using the half-cell potential measurement method, following the ASTM C876-91 standard [ 30 ]. As prescribed by this standard, if the potential measured concerning the copper-copper sulfate electrode exceeded 200 mV, there was a 90% probability that the steel rebars were free from corrosion. For potential values between 200 and 350 mV, the corrosion condition of the steel remained uncertain. Finally, if the measured potential fell below 350 mV, there was a 90% probability that corrosion had occurred in the steel rebars. The potential difference of the steel electrodes was compared to a copper-copper sulfate reference electrode, and the corrosion status of the steel was determined based on this potential difference. The half-cell potential measurement device (see Fig. 1 ) comprises various components that must be assembled before utilization. These components include a voltmeter with high internal resistance, a reference electrode cylinder, a reference electrode, a surfactant tank, a base for supporting the voltmeter on the surfactant tank, and connecting wires. Adhering to the manufacturer's instructions for the half-cell potential measurement device employed in this research, copper sulfate crystals were initially added to the antifreeze solution and thoroughly mixed. The resulting solution was then poured into the designated cylinder for the reference electrode. It is crucial to ensure that this solution always contains some insoluble copper sulfate. Subsequently, the reference electrode was positioned inside this cylinder and securely fastened with a screw at its end. The surfactant tank was filled with contact electric solution, which was obtained by mixing 90 ml of contact electric material with 19 liters of water. The solution needed to fill at least 75% of the tank's height. Following this, the cylinder containing the reference electrode was submerged in the solution within the surfactant tank, firmly closed, and secured with a screw at the end of the cylinder. The voltmeter base was then affixed to the end of the reference electrode cylinder outside the surfactant tank using a screw, and the voltmeter was placed atop it. The voltmeter was connected to the reference electrode through a connecting wire fixed to the base of the voltmeter. Additionally, the voltmeter base was connected to the reference electrode via the same screw beneath it. To measure the half-cell potential, the reference electrode was linked to the voltmeter using a connecting wire, while another connecting wire was employed to connect the steel rebar in the concrete specimen to the voltmeter. After a designated period, a steady numerical value was displayed on the digital voltmeter, indicating the potential of the rebar within the specimen relative to the reference electrode. 2.4.2 Environmental conditions and test duration in corrosion testing To create a chloride-rich environment conducive to corrosion, a seven-percent-by-weight NaCl solution was employed. The use of distilled water for preparing the NaCl solution ensured the exclusion of extraneous substances that could influence steel corrosion. Additionally, to expedite the corrosion of steel rebars embedded in the specimens, a cyclic wetting and drying regime was implemented. This regime involved subjecting the specimens to 48 hours of exposure to ambient air once a week, facilitating water evaporation from their surfaces and pores. This process provided the necessary oxygen supply for steel corrosion. To compare the initiation times of corrosion among the specimens, the half-cell potential was measured for all fabricated specimens. The measurements were continued until their potentials dropped below 350 mV, indicating a 90% probability of steel corrosion. The test duration spanned approximately fifteen weeks, with weekly measurements conducted throughout this period. This comprehensive approach allowed for a meticulous assessment of the corrosion behavior and initiation times of the individual specimens. 2.5. Measurement of carbonation depth In this research, an experiment was conducted to ascertain the depth of carbonation in various specimens and investigate the influence of key parameters, such as the w/cm ratio, silica fume percentage, slag percentage, and their combination, on carbonation depth. Since carbonation typically occurs at a slow rate under normal environmental conditions, an autoclave was employed to expedite the process (see Fig. 2 ). The concrete specimens were carefully placed in the autoclave tank, and the lid was securely fastened using screws to ensure a complete seal. Subsequently, a CO 2 gas capsule was connected to the tank through a hose, and the specimens were subjected to a closed chamber saturated with CO 2 gas under a pressure of 1.5 atmospheres, which was the maximum reliable pressure for the autoclave device. This accelerated carbonation process lasted for one day. The pressure gauge on the chamber's lid indicated an increase in gas pressure. Once the pressure reached 1.5 atmospheres, the valve of the CO 2 gas capsule was closed. Over several days, the gas pressure gradually decreased, and it was periodically readjusted by opening and closing the valve of the capsule. After 10 days, the specimens were removed from the autoclave and subsequently cut in half using a press. To determine the depth of carbon dioxide penetration, a phenolphthalein reagent was applied to the fractured surfaces of the specimens. The reagent, prepared by dissolving one gram of phenolphthalein powder in one liter of ethyl alcohol, facilitated the identification of regions of the concrete specimens that retained alkalinity (turning the colorless solution of phenolphthalein purple) and regions that had undergone carbonation (remaining unchanged in color). The depth of carbonation was measured after one hour of applying the reagent to the fractured surfaces of the specimens, with gas penetration measured on all four sides of each specimen with a precision of 1 mm. The average penetration depth represented the carbonation depth for the respective mix design. Due to the limited volume of the autoclave device, two specimens were used for carbonation testing for each mix design, and the average penetration depth was considered as the carbonation depth for that specific mix design. 2.6. Compressive strength analysis The compressive strength analysis involved the use of seventy-mm-cubic specimens, as depicted in Fig. 3 . These specimens were subjected to compressive strength testing at two distinct time intervals: 28 days and 91 days. To ensure statistical validity and accuracy, three specimens were prepared for each mixing design, resulting in a total of 312 specimens specifically designated for compressive strength measurements. Moreover, additional specimens were made for each mixing design, serving as replacements in the event that the original specimens were deemed unsuitable or compromised. 3. Results 3.1. Results of half-cell potential measurement 3.1.1. Specimens without slag Figure 4(a) shows the results of monitoring the electrochemical potential of rebars in concrete specimens devoid of slag content (referred to as type A specimens). These specimens contain varying proportions of silica fume, with a constant w/cm ratio of 0.5. The figure depicts temporal variations in potential. The control specimen, which denotes the absence of silica fume, consistently exhibits lower potential values than specimens with silica fume, suggesting higher corrosion in the rebars of the control specimen. As shown, the control concrete experienced a more rapid decline in potential below the 350 mV threshold, which indicates a 90% probability of steel rebar corrosion according to ASTM C876. In contrast, the specimens containing silica fume showed a longer delay period before corrosion initiation, suggesting improved corrosion resistance. Consequently, the control concrete exhibits a shorter time to initiate corrosion, resulting in a higher corrosion rate. It is noteworthy that corrosion initiation in concrete containing 5% silica fume is superior to other silica fume proportions, thereby enhancing resistance to steel reinforcement corrosion. Figure 4(b) illustrates the potential measurements within concrete specimens containing varying proportions of silica fume and a w/cm ratio of 0.4. Over a period exceeding three months, the internal rebar potential in the control specimen consistently remains lower compared to specimens containing silica fume. This disparity highlights the superior corrosion resistance exhibited by silica fume-incorporated specimens. Notably, the control specimen experiences a more rapid decline below the 350 mV threshold compared to concrete containing 10% silica fume. Therefore, substituting 10% of cement with silica fume in the 0.4 w/cm ratio effectively optimizes steel corrosion resistance. This enhanced resistance is likely attributed to the pozzolanic reaction of silica fume, which consumes calcium hydroxide, a byproduct of cement hydration, to form additional calcium silicate hydrate (C-S-H), the primary binding phase in concrete responsible for strength and durability. Additionally, increasing silica fume content to 5% and 10% within w/cm ratios of 0.4 and 0.5, respectively, reduces the concrete's resistance to steel corrosion. This could be attributed to the formation of a denser microstructure at these ratios, which hinders the diffusion of oxygen towards the steel rebar, essential for passivation. Conversely, raising silica fume content to 15% within the 0.15 w/cm ratio enhances the concrete's steel corrosion resistance. This is likely due to the reduced availability of free water for cement hydration at this lower ratio, leading to decreased calcium hydroxide production. The silica fume can effectively utilize this limited calcium hydroxide to form additional calcium silicate hydrate (C-S-H), thereby improving the concrete's durability. Consequently, the optimal silica fume proportion for achieving peak concrete durability against steel corrosion varies dynamically in response to w/cm ratio adjustments. This dynamic relationship is crucial not only for enhancing corrosion resistance but also from an economic standpoint, considering the higher cost of silica fume compared to cement. The following analysis, presented in Fig. 4(c), focuses on type A concrete specimens with a w/cm ratio of 0.3. As silica fume proportions increase, the potential difference between control concrete and silica fume-containing specimens widens. This is accompanied by a larger temporal separation in potential-time diagrams, indicating improved concrete performance against steel corrosion with increasing silica fume content. In this category, higher silica fume percentages simultaneously enhance the corrosion durability of the concrete. This could be attributed to the pozzolanic reaction of silica fume, which consumes calcium hydroxide, a byproduct of cement hydration, to form additional calcium silicate hydrate (C-S-H), the primary binding phase in concrete that imparts strength and durability. Notably, the time required for corrosion initiation in the 15% silica fume specimen exceeds that of other specimens, demonstrating superior corrosion resistance. With a w/cm ratio of 0.25, as shown in Fig. 4(d), increasing silica fume content improves concrete's performance and durability against steel corrosion. Specifically, the specimen with 15% silica fume consistently exhibits higher potential values across most measurement intervals, indicating superior corrosion resistance. Notably, reducing the w/cm ratio while increasing silica fume content further widens the gap in potential values between silica fume-infused concrete and the control, suggesting reduced susceptibility to corrosion in the former. The reduction of the w/cm ratio significantly impacts rebar potential, hindering the migration of ions essential for corrosion initiation and thereby limiting corrosion susceptibility. This phenomenon arises from the denser and less permeable structure of the concrete. Notably, the extended time required for corrosion initiation enhances the longevity of the concrete structure. Additionally, increasing silica fume content and decreasing w/cm ratios further widen the potential gap between control and silica fume-incorporated concrete specimens, distinctly influencing corrosion resistance enhancement. In conclusion, the interplay between a fixed proportion of silica fume and manipulated w/cm ratios dynamically influences rebar potential. This interaction plays a pivotal role in shaping concrete's corrosion susceptibility, with implications for its durability and structural longevity. 3.1.2. Specimens containing 20% slag Figure 5(a) presents the results of measuring the potential of rebars within concrete specimens (type B) containing 20% slag as a partial cement substitute, various proportions of silica fume, and a fixed w/cm ratio of 0.5. Notably, the potential of rebars in concrete containing silica fume exhibited higher values compared to concrete with no silica fume, indicating reduced corrosion tendencies. This demonstrates that incorporating silica fume enhances concrete durability against steel corrosion in the presence of steel reinforcement. The specimen with 5% silica fume demonstrated superior performance, exhibiting a shorter time to corrosion initiation, albeit still longer than other silica fume-containing specimens. The specimens with 10% and 15% silica fume exhibited lower potential values compared to the 5% specimen but higher values than the 0% silica fume concrete. Furthermore, when comparing these specimens to similar ones (with 0.5 w/cm ratios and containing silica fume without slag), the addition of slag significantly improved the concrete's durability against steel corrosion. This suggests that utilizing both pozzolans, silica fume, and slag, enhances concrete reliability against steel corrosion compared to using only silica fume. Figure 5(b) presents the results of measuring the potential of rebars within type B concrete specimens with various proportions of silica fume and a fixed w/cm ratio of 0.4. The potential of rebars in specimens containing silica fume was consistently higher than in specimens with only slag and no silica fume, indicating improved corrosion resistance. The concrete specimen with 10% silica fume required more time for the rebars' potential to drop below 350 mV, indicating superior performance. This suggests that optimizing the silica fume percentage can improve concrete performance. This is likely due to the pozzolanic reaction of silica fume, which consumes calcium hydroxide (a by-product of cement hydration) to form an additional calcium silicate hydrate (C-S-H). C-S-H is the primary binding phase in concrete that provides strength and durability. Reducing the w/cm ratio has a significant impact on concrete's resistance to steel corrosion, as it reduces concrete's permeability. This, in turn, reduces the availability of water and oxygen for electrochemical reactions, thereby reducing steel corrosion rates. Consequently, concrete design guidelines should consider the required resistance factors and environmental conditions when selecting an appropriate w/cm ratio. Figure 5(c) presents the results for type B concrete specimens with varying silica fume percentages and a w/cm ratio of 0.3. The corrosion potential of rebars embedded in concrete containing silica fume was consistently higher compared to rebars in concrete without silica fume. This difference in potential increased with higher silica fume percentages. The duration over which the potential remained above 200 mV served as an indicator of corrosion absence. In specimens with 10% and 15% silica fume, this period was approximately 1.5 and 2 times longer, respectively, compared to specimens without silica fume. Concrete with a 15% silica fume replacement exhibited superior performance, significantly delaying corrosion initiation. A plausible explanation for the observed outcomes is that the addition of silica fume reduces the concrete's permeability, thereby impeding the penetration of chloride ions, the primary instigators of corrosion in reinforced concrete. In practice, it is recommended to reduce the w/cm ratio to effectively utilize the properties of silica fume and slag to enhance concrete reliability against steel corrosion. Attention should be paid to proper compaction and curing during concrete construction, particularly when using silica fume, to prevent surface drying and cracking. In corrosive environments, cracks can facilitate the penetration of corrosive materials into the concrete. By carefully considering these factors, the durability and resistance of concrete against steel corrosion can be significantly improved. 3.1.3. Specimens containing 35% slag Figure 6(a) illustrates the results of evaluating the corrosion potential of rebars embedded in type C concrete specimens (with 35% slag as a partial cement replacement) containing varying amounts of silica fume while maintaining a constant w/cm ratio of 0.5. It is noteworthy that the concrete specimen containing 0% silica fume effectively represented a 35% slag replacement for cement. The findings demonstrate that the specimen incorporating 5% silica fume exhibited a delayed onset of steel corrosion compared to other specimens, suggesting a lower corrosion rate. Specimens with 10% and 15% silica fume displayed similar corrosion onset times, both outperforming the specimen with 0% silica fume. Hence, the addition of silica fume, in conjunction with the presence of 35% slag as a cement substitute, significantly enhances the concrete's resistance to steel corrosion. A comparison between type C specimens with a w/cm ratio of 0.5 and type A specimens containing no slag, but with the same w/cm ratio, highlights the superior performance of type C specimens. This advantage stems from the pozzolanic reaction of slag, which refines the concrete's microstructure, reduces permeability, and enhances its resistance against aggressive agents, including water and oxygen, essential for steel reinforcement corrosion. The pozzolanic reaction modifies the cement paste structure by converting calcium hydroxide crystals into hydrated calcium silicate (C-S-H), leading to denser concrete. Additionally, Fig. 6(b) illustrates the results of measuring the rebar potential in type C concrete specimens with varying proportions of silica fume and a fixed w/cm ratio of 0.4. Here, the specimen containing 10% silica fume exhibited delayed corrosion onset compared to other specimens, indicating enhanced durability against steel corrosion. Subsequently, the specimens with 5% and 15% silica fume demonstrated better performance than the specimens without silica fume. A comparison between the specimens containing 0% silica fume, which includes 35% slag as a cement substitute, and the specimen without slag and silica fume, illustrates the beneficial impact of slag alone on the concrete's corrosion resistance. It is worth noting that although slag decreases the alkalinity of the concrete environment, which could increase the risk of corrosion, its ability to improve the concrete structure and reduce permeability outweighs this factor, ultimately increasing resistance to steel corrosion. Similarly, silica fume's pozzolanic properties contribute to the conversion of calcium hydroxide into C-S-H, supporting the conclusion that the addition of silica fume to concrete specimens enhances their resistance against steel corrosion. Furthermore, Fig. 6(c) displays the results of measuring the rebar potential in type C concrete specimens with varying amounts of silica fume and a fixed w/cm ratio of 0.3. Notably, the specimen containing 10% silica fume exhibited delayed onset of steel corrosion compared to other specimens, followed by the specimens containing 5% and 10% silica fume, respectively, showing better performance than the specimen without silica fume. A closer examination of this figure reveals a reduced gap between the graph of the specimen without silica fume (with 35% slag substitution for cement) and those with silica fume, particularly in comparison to specimens containing 20% slag. This observation highlights the superior corrosion performance of concrete with higher slag substitution (up to 35%). Additionally, when comparing these specimens with type B specimens, the increase in slag content from 20–35% substantially improved the concrete's resistance to steel corrosion. This economic significance lies in the fact that slag, being a byproduct of the steel industry, incurs minimal cost, rendering it an affordable and cost-effective alternative to cement. Consequently, substituting cement with larger amounts of slag in concrete construction not only saves costs but also confers beneficial effects such as enhanced corrosion and sulfate attack resistance, reduced hydration temperature, increased compressive strength, and decreased super-lubricant consumption. 3.1.4. Specimens containing 50% slag In Fig. 7, the outcomes of assessing the rebar potential in type D concrete specimens (with varying percentages of slag as a cement substitute) with different proportions of silica fume and constant w/cm ratios of 0.5, 0.4, and 0.3, respectively, are presented. From Fig. 7(a), it is evident that the onset of corrosion in the concrete specimen containing 5% silica fume was delayed compared to other specimens. The corrosion onset time for concrete specimens containing 10% and 15% silica fume showed negligible differences between them, falling between the durations observed in the specimens with 5% and 0% silica fume. Figure 7(b) and (c) demonstrate that in type D specimens with w/cm ratios of 0.4 and 0.3, respectively, the incorporation of 10% and 15% silica fume yields the most favorable outcomes in terms of enhancing concrete durability against steel corrosion. Across all type D specimens with different w/cm ratios, the combined use of silica fume and slag significantly improves concrete's resistance to steel corrosion when compared to the use of slag alone in concrete production. It is worth noting that the potential difference between the specimens containing silica fume and slag decreased compared to cases where specimens solely contained silica fume, particularly evident at low w/cm ratios. This observation arises from the fact that the presence of slag in concrete enhances concrete's durability against steel corrosion. Although the addition of silica fume to the concrete mixture with slag increases its corrosion resistance, the effect of adding silica fume in this scenario is less pronounced than when silica fume is added to concrete without slag. Nevertheless, the combined use of silica fume and slag consistently exhibits a more substantial positive impact on improving concrete's resistance to steel corrosion compared to using silica fume or slag in isolation. The use of 50% slag as a cement substitute has adversely affected the durability of concrete against steel corrosion in most cases, as indicated by the shorter corrosion onset time compared to concrete with 20% slag. However, slag still provides some protection to concrete against steel corrosion relative to concrete without slag. The reason for this behavior is related to the impact of slag on the hydration and pore characteristics of the cement matrix, which determine the chloride transport and corrosion resistance of steel. Some studies have shown that slag can react with water and calcium hydroxide to produce more calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H), which enhance the density and strength of the concrete. On the other hand, slag can also consume calcium hydroxide, which lowers the pH value of the pore solution and reduces the alkalinity of the concrete. This can impair the passivation ability of the concrete and increase the vulnerability of steel to corrosion. Furthermore, slag can raise the porosity and permeability of the concrete at early ages, allowing more chloride ions and oxygen to penetrate into the concrete. These factors account for why concrete with 50% slag has poorer durability against steel corrosion than concrete with 20% slag or no slag. Nevertheless, concrete with 20% slag still outperforms concrete without slag, because the positive effects of slag on the hydration products and the pore refinement dominate over the negative effects of slag on the pH value and the porosity at later ages [ 31 – 34 ]. 3.1.5. Comparative analysis of time required for steel corrosion initiation In this study, the goal was to compare the time needed for steel corrosion to commence in different concrete specimens by establishing relationships between relevant variables. Consequently, a function was devised to express the initiation time of steel corrosion for two distinct concrete specimens based on the independent variables: w/cm ratio (W/CM), percentage of silica fume (SF/CM), and percentage of slag (Slag/CM) present in each of the compared specimens. Thus, this relationship involved six independent variables and one function (dependent variable), as described by Eq. ( 1 ). $$\frac{{{{\left( {{t_0}} \right)}_1}}}{{{{\left( {{t_0}} \right)}_2}}}=F\left\{ {{{(\frac{W}{{CM}})}_1},{{(\frac{W}{{CM}})}_2},{{(\frac{{SF}}{{CM}})}_1},{{(\frac{{SF}}{{CM}})}_2},{{(\frac{{Slag}}{{CM}})}_1},{{(\frac{{Slag}}{{CM}})}_2}} \right\}$$ 1 In Eq. ( 1 ), the indices 1 and 2 pertain to the first and second specimens under comparison, respectively. The other parameters in this equation are W/CM, SF/CM, Slag/CM, and t 0 , representing the time required for steel corrosion initiation. Employing logarithmic interpolation, we derived Eq. ( 2 ) to facilitate the comparison of the time required for corrosion initiation between two distinct concrete specimens. This equation was formulated based on 1128 comparisons, involving 1128 series of comparisons with the six independent variables and one dependent variable. $$\frac{{{{\left( {{t_0}} \right)}_1}}}{{{{\left( {{t_0}} \right)}_2}}}=1.346\left\{ {\frac{{\left( {\frac{W}{{CM}}} \right)_{2}^{{1.622}}}}{{\left( {\frac{W}{{CM}}} \right)_{1}^{{1.109}}}}.\frac{{\left( {\frac{{SF}}{{CM}}} \right)_{1}^{{0.056}}}}{{\left( {\frac{{SF}}{{CM}}} \right)_{2}^{{0.078}}}}.\frac{{\left( {\frac{{Slag}}{{CM}}} \right)_{1}^{{0.022}}}}{{\left( {\frac{{Slag}}{{CM}}} \right)_{2}^{{0.045}}}}} \right\}$$ 2 The above relationship allows for a preliminary estimation of the performance comparison of a concrete specimen against steel corrosion when compared to another concrete specimen, while considering variations in the parameters of the w/cm ratio, percentage of slag, and percentage of silica fume as a replacement for cement. If the effect of slag is disregarded in the observations, Eq. ( 3 ) is obtained. This relationship is based on 66 comparisons, which collectively encompass 66 series of comparisons. $$\frac{{{{\left( {{t_0}} \right)}_1}}}{{{{\left( {{t_0}} \right)}_2}}}=1.321\left\{ {\frac{{{{\left( {{{(\frac{W}{{CM}})}_2}+1} \right)}^{4.36}}}}{{{{\left( {{{(\frac{W}{{CM}})}_1}+1} \right)}^{3.403}}}}.\frac{{\left( {\frac{{SF}}{{CM}}} \right)_{1}^{{0.05}}}}{{\left( {\frac{{SF}}{{CM}}} \right)_{2}^{{0.05}}}}} \right\}$$ 3 Eq. ( 3 ) was derived from observations concerning concrete specimens containing only silica fume. Thus, when slag is not used in concrete production, and the parameters of w/cm ratio and the percentage of silica fume replacing cement are altered in two different specimens, Eq. ( 3 ) can be employed to compare the corrosion resistance performance of these two specimens. Similarly, if the impact of silica fume is disregarded in the observations, Eq. ( 4 ) is derived. This relationship is also based on 66 comparisons, representing 66 series of comparisons. $$\frac{{{{\left( {{t_0}} \right)}_1}}}{{{{\left( {{t_0}} \right)}_2}}}=0.976\left\{ {\frac{{{{\left( {{{(\frac{W}{{CM}})}_2}+1} \right)}^{5.099}}}}{{{{\left( {{{(\frac{W}{{CM}})}_1}+1} \right)}^{3.166}}}}.\frac{{\left( {\frac{{Slag}}{{CM}}} \right)_{1}^{{0.022}}}}{{\left( {\frac{{Slag}}{{CM}}} \right)_{2}^{{0.033}}}}} \right\} - 1$$ 4 Eq. ( 4 ) can be obtained by comparing the results of specimens containing only slag. Therefore, in cases where the w/cm ratio and the percentage of slag replacing cement vary, and no silica fume is present in the concrete, Eq. ( 4 ) can be used to estimate and compare the corrosion resistance performance of two different concretes. The following restrictions for Eqs. ( 2 ), ( 3 ), and (4) are essential to note: $$0{\text{ }} \leqslant {\text{ }}SF/CM{\text{ }} \leqslant {\text{ }}0.15,{\text{ }}0{\text{ }} \leqslant {\text{ }}Slag/CM{\text{ }} \leqslant {\text{ }}0.5,{\text{ }}0.3{\text{ }} \leqslant {\text{ }}W/CM{\text{ }} \leqslant {\text{ }}0.5.$$ 5 During the internal stage of deriving Eqs. ( 2 ), ( 3 ), and (4), in cases where either SF/CM or Slag/CM became zero, logarithmic interpolation necessitated replacing zero with the value 0.0001. Hence, when using the aforementioned equations, if the percentage of slag or silica fume replacing cement in the specimens is zero, it is imperative to substitute zero with the value 0.0001 to ensure accurate calculations. 3.2. Carbonation test The findings of the carbonation test (Fig. 8) indicate that the incorporation of silica fume generally results in a negligible increase in carbonation depth compared to the control concrete in specimens containing 0% slag and varying w/c ratios. However, for w/c ratios of 0.3 and 0.25, the impact of silica fume addition on carbonation depth diminishes compared to ratios of 0.5 and 0.4, resulting in a minimal disparity between specimens with and without silica fume in terms of carbonation depth. Conversely, when 20% of slag replaces cement, the carbonation depth decreases compared to similar specimens without slag. According to some research, slag can reduce the carbonation depth of concrete by enhancing the degree of hydration, refining the pore structure of the cement matrix, and raising the pH value and buffering capacity of the pore solution [ 35 , 36 ]. These effects, however, are more pronounced at lower slag contents (such as 20%) than at higher slag contents (such as 50%), as excess slag can increase the porosity and permeability of the concrete at early ages, facilitating carbon dioxide ingress and lowering the concrete's alkalinity. On the other hand, silica fume can improve the carbonation resistance of concrete by decreasing the porosity and permeability of the cement matrix, as well as by forming additional calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H), which increase the density and strength of the concrete. However, these effects are more significant in concrete without slag than in concrete with slag, because the slag already provides some benefits on the hydration products and the pore structure refinement. Thus, the addition of silica fume has a negligible impact on the carbonation depth when 20% of slag substitutes for cement. Conversely, when 50% of slag substitutes for cement, the carbonation depth increases compared to similar specimens without slag, and adding silica fume to the concrete composition slightly reduces the carbonation depth [ 37 , 38 ]. Increasing the slag content from 20–35% as a cement replacement leads to a reduction in carbonation depth, as compared to similar specimens containing 20% slag or no slag. Additionally, the inclusion of silica fume in the concrete mixture contributes to a decrease in carbonation depth, particularly when compared to specimens containing 20% slag. However, in concrete specimens with a slag content increased from 35–50%, the carbonation depth increases, in contrast to specimens containing 20% and 35% slag. Nevertheless, in these specimens, the addition of silica fume to concrete slightly decreases the carbonation depth when compared to concrete without silica fume. 3.3. Compressive strength Figure 9 displays the compressive strength of type A concrete specimens containing various proportions of silica fume while maintaining constant w/cm ratios of 0.5, 0.4, 0.3, and 0.25. By comparing the compressive strength of 91-day specimens with that of 28-day specimens, it becomes apparent that the majority of concrete's compressive strength is achieved by 28 days, with specimens containing silica fume consistently exhibiting higher compressive strengths than control specimens. Among the specimens with a w/cm ratio of 0.5, the specimen containing 10% silica fume demonstrated the highest compressive strength at both 28 and 91 days. In the case of a w/cm ratio of 0.25, while the 28-day compressive strength of the specimen with 10% silica fume was slightly superior to that with 15% silica fume, the 91-day compressive strength of the specimen containing 15% silica fume surpassed that of the 10% silica fume specimen. Therefore, for w/cm ratios, incorporating 15% silica fume in the concrete mixture leads to the highest compressive strength at 91 days, followed by specimens with 10% and 5% silica fume. Moreover, the research results indicate that when using limestone aggregates with w/cm ratios of 0.3 and 0.4, the substitution of 10% silica fume in cement yields the greatest increase in concrete's compressive strength. However, for concrete with a w/cm ratio of 0.25, replacing cement with 15% silica fume exhibits higher compressive strength compared to 10%. One possible reason for the results shown in Fig. 9 is that silica fume has a pozzolanic effect on the hydration of cement, which means that it reacts with the calcium hydroxide released by the cement hydration and forms additional calcium silicate hydrate (C-S-H), the main binding phase in concrete. This improves the density, strength, and durability of the cement paste, enhancing the compressive strength of concrete. The optimal dosage of silica fume depends on the w/cm ratios and the curing time of the concrete. Silica fume can increase the water demand and reduce the workability of fresh concrete, especially at higher dosages and lower w/cm ratios. This can affect the quality of compaction and consolidation, potentially reducing compressive strength. Therefore, for higher w/cm ratios, such as 0.5, a lower dosage of silica fume, like 10%, may suffice to achieve maximum compressive strength. Conversely, for lower w/cm ratios, such as 0.25, a higher dosage of silica fume, like 15%, may be necessary to counteract the negative effects of low water content and high cement content on the hydration process and pore structure of concrete. Silica fume can accelerate early strength development in concrete, but its long-term strength gain may be slower than that of plain concrete due to the reduced availability of calcium hydroxide for further pozzolanic reaction. For longer curing times, such as 91 days, a higher dosage of silica fume, like 15%, may be more beneficial than a lower dosage, like 10%, to achieve higher compressive strength, especially for lower w/cm ratios, such as 0.25. These factors may explain why, for w/cm ratios of 0.3 and 0.4, incorporating 10% silica fume in the concrete mixture leads to the highest compressive strength at both 28 and 91 days, while for a w/cm ratio of 0.25, replacing cement with 15% silica fume exhibits higher compressive strength at 91 days compared to 10%. [ 39 , 40 ]. A comparison of the optimum silica fume percentages in type A specimens with varying w/cm ratios indicates that reducing the w/cm ratio improves the performance of specimens with higher silica fume contents in terms of compressive strength. In Fig. 10, the compressive strength results of type B concrete specimens containing different percentages of silica fume are presented, with fixed w/cm ratios of 0.5, 0.4, and 0.3. The outcomes reveal that the inclusion of silica fume in concrete containing slag enhances the compressive strength of specimens. The order of increasing compressive strength in specimens with silica fume remains consistent across each w/cm ratio, mirroring the trend observed in type A specimens. Figure 11 demonstrates the compressive strength results of concrete specimens with varying silica fume percentages and w/cm ratios of 0.5, 0.4, and 0.3, respectively. Notably, the 28-day compressive strength of type C specimens was lower compared to similar specimens with 20% slag (type B) and even specimens without slag (type A). This discrepancy can be attributed to the slower hydration reaction of slag, resulting in reduced strength development in cement with slag compared to regular cement without slag. However, once the slag hydration reaction is completed, the microstructure of the concrete improves, leading to higher strength in concrete containing slag compared to concrete without slag. As seen in the results, the 91-day compressive strength of concrete containing slag (especially in the case of type C specimens) becomes comparable to specimens without slag and even to specimens with 20% slag. Thus, it can be inferred that the slag hydration reaction occurred before 28 days in type B specimens, resulting in higher 28-day compressive strength than in specimens without slag. However, in type C specimens, where the percentage of slag replacement increased, more time was required for the slag hydration reaction to complete in the concrete mixture. It is worth mentioning that the slow rate of slag hydration reaction contributes to reduced heat development in concrete, which may be advantageous during mass concreting. In type C specimens, the optimum percentages of silica fume in each w/cm ratio align with type B specimens, with the strength of specimens containing silica fume exhibiting improvement compared to those without it. The results suggest that the slag content in concrete influences the hydration process and the pore structure of the cement matrix, which affects the compressive strength of concrete. Some studies have shown that slag can react with water and calcium hydroxide to produce more calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H), enhancing the density and strength of the concrete. However, slag can also consume calcium hydroxide, lowering the pH value of the pore solution and reducing the alkalinity of the concrete. This can impair the passivation ability of the concrete and increase the vulnerability of steel to corrosion. Furthermore, slag can increase the porosity and permeability of the concrete at early ages, allowing more chloride ions and oxygen to penetrate into the concrete. These factors account for why concrete with slag (especially in the case of type C specimens) has poorer compressive strength than concrete without slag at 28 days. However, as the curing time progresses, the slag hydration reaction fills the pores in the cement matrix, improving the compressive strength of concrete. Therefore, at 91 days, concrete with slag becomes similar to or even higher than concrete without slag in terms of compressive strength. The addition of silica fume to the concrete mixture can further improve the compressive strength by decreasing the porosity and permeability of the cement matrix, as well as by forming additional C-S-H and C-A-H. The optimal dosages of silica fume depend on the w/cm ratios and the slag content in the concrete mixture [ 41 , 42 ]. Figure 12 illustrates the compressive strength results of type D concrete specimens containing different percentages of silica fume, with w/cm ratios of 0.5, 0.4, and 0.3, respectively. In this specimen type, 50% of cement was substituted with slag, and with the addition of silica fume to the concrete, the strength of type D specimens, similar to type A, B, and C specimens, increased compared to concrete without silica fume. Notably, the compressive strength and the rate of strength gain in concrete containing slag may significantly vary. 4. Conclusions This study investigated the influence of silica fume and slag, and their interaction effects, on steel corrosion, carbonation depth, and compressive strength of concrete. Four groups of concrete specimens were designed and cast. The first group contained only silica fume with different w/cm ratios (0.25, 0.3, 0.4, and 0.5). Groups two, three, and four incorporated 20%, 35%, and 50% slag as a cement replacement, respectively, along with varying percentages of silica fume and w/cm ratios of 0.3, 0.4, and 0.5. The key findings of the research are summarized as follows: 1- The incorporation of silica fume into concrete exhibited beneficial effects, including an increase in resistance against steel corrosion. Among specimens in the first category, A-0.25-15, with a 0.25 w/cm ratio and 15% cement replaced by silica fume, exhibited the highest corrosion resistance (91 days). This specimen did not exceed the threshold level of -350mV and showed a nearly 46.7% increase in corrosion resistance compared to a similar specimen without silica fume (A-0.25-0). 2- Among specimens containing slag, specimen C-0.3-15 exhibited the highest corrosion resistance, with a corrosion potential of -329 mV after 91 days. This specimen demonstrated a 19% and 44% increase in corrosion resistance compared to similar specimens without slag (A-0.3-15) and without silica fume (C-0.3-0), respectively. 3- Analysis of the results revealed that increasing slag content up to 35% led to a reduction in carbonation depth. Conversely, incorporating 50% slag resulted in a significant increase in carbonation depth compared to specimens containing lower slag contents, performing nearly similar to Group A (without slag) specimens. Furthermore, the results indicated that the inclusion of silica fume within 10–15% across all groups, with or without slag, decreased the carbonation depth. 4- Specimen C-0.3-10 exhibited the lowest carbonation depth, recording a value of 3.5 mm. Notably, this specimen demonstrated a 33% and 14.6% reduction in carbonation depth compared to specimens A-0.3-10 (similar concrete without slag) and C-0.3-0 (similar specimen without silica fume), respectively. 5- Specimen C-0.3-10 exhibited the highest compressive strength equal to 118 MPa. This value represented a 20.4% increase compared to the counterpart concrete specimen without slag (A-0.3-10), and an 18.4% enhancement in strength relative to the similar specimen lacking silica fume (C-0.3-0). 6- Increasing the slag replacement to 50% resulted in a remarkable decline in the performance of steel corrosion resistance, carbonation depth, and compressive strength, compared to specimens containing 35% slag, though the performance was comparable to similar specimens lacking any slag replacement. 7- The combined use of silica fume and slag as partial cement replacements showed a synergistic effect on the overall performance of concrete. 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Cite Share Download PDF Status: Published Journal Publication published 10 Aug, 2024 Read the published version in Iranian Journal of Science and Technology, Transactions of Civil Engineering → Version 1 posted Editorial decision: Revision requested 31 May, 2024 Reviews received at journal 27 May, 2024 Reviews received at journal 26 May, 2024 Reviewers agreed at journal 17 May, 2024 Reviewers agreed at journal 17 May, 2024 Reviewers invited by journal 17 May, 2024 Submission checks completed at journal 14 May, 2024 Editor assigned by journal 14 May, 2024 First submitted to journal 13 May, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4414385","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":305534420,"identity":"372ce71d-1ce6-4e1c-bf61-4a28f34bef95","order_by":0,"name":"Davood Mostofinejad","email":"","orcid":"","institution":"Isfahan University of Technology (IUT)","correspondingAuthor":false,"prefix":"","firstName":"Davood","middleName":"","lastName":"Mostofinejad","suffix":""},{"id":305534421,"identity":"e2025861-3873-4e74-bfe6-09a32c4f2a64","order_by":1,"name":"Mohsen Nasrollahi","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA9UlEQVRIie3RsYrCMBjA8a8U4vLZrgGL9wQHgUJFDPgqHoJTz3uBDtlc+gA+jEPKB3XyARxFcOqgWx0OjD23M1U3h/ynEL4fSRsAl+uNiwJA0EezYrcdfESQmZli2RD/BeL/jfnto5+qW5zOK4mssylIZgQB/9FQZxAN1H2S6GDaw8MMGc4nlJYEjE/By0vASNsIih5oMhdLBX2rWUOgqwC55WKGxOf6SsJK0PBGvN92knC8Em5O8ZRsiN96CmEyQm2+hVeiyEvzH3AvKCq5nazzeFtr2Q/DND7WGe9/LL52uyqTYxv59wjN02gAK3C5XC7XE10AO+ZG0AHa4eEAAAAASUVORK5CYII=","orcid":"","institution":"Isfahan University of Technology (IUT)","correspondingAuthor":true,"prefix":"","firstName":"Mohsen","middleName":"","lastName":"Nasrollahi","suffix":""},{"id":305534422,"identity":"3e669219-e45f-4fdb-8eb7-82323902fc66","order_by":2,"name":"Hadi Bahmani","email":"","orcid":"","institution":"Isfahan University of Technology (IUT)","correspondingAuthor":false,"prefix":"","firstName":"Hadi","middleName":"","lastName":"Bahmani","suffix":""},{"id":305534426,"identity":"dd0a6892-1346-4201-93ec-18159bb5c100","order_by":3,"name":"Zahra Zajshoor","email":"","orcid":"","institution":"Isfahan University of Technology (IUT)","correspondingAuthor":false,"prefix":"","firstName":"Zahra","middleName":"","lastName":"Zajshoor","suffix":""},{"id":305534428,"identity":"39d28b61-6263-46a5-bec0-baeda5732b01","order_by":4,"name":"Morteza Sadeghi","email":"","orcid":"","institution":"Isfahan University of Technology (IUT)","correspondingAuthor":false,"prefix":"","firstName":"Morteza","middleName":"","lastName":"Sadeghi","suffix":""}],"badges":[],"createdAt":"2024-05-13 16:06:38","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4414385/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4414385/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s40996-024-01573-9","type":"published","date":"2024-08-10T15:58:08+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":57430363,"identity":"debf6f22-2341-4968-9a5e-0ff51b481f53","added_by":"auto","created_at":"2024-05-30 14:53:33","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":318466,"visible":true,"origin":"","legend":"\u003cp\u003eHalf-cell potential measuring instruments\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4414385/v1/70df85c9583077b59c467f03.png"},{"id":57430368,"identity":"8d9177d6-aa89-477d-bb9b-a0b7405330ea","added_by":"auto","created_at":"2024-05-30 14:53:34","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":244570,"visible":true,"origin":"","legend":"\u003cp\u003eCarbonation depth measurement test device\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4414385/v1/13c3ff5f6aa8b4fab4ba875d.png"},{"id":57430365,"identity":"5a191dd3-7cf9-45c8-8276-d528e6e616b5","added_by":"auto","created_at":"2024-05-30 14:53:33","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":280144,"visible":true,"origin":"","legend":"\u003cp\u003eCompressive strength test device.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4414385/v1/b84bf7869c0bb0e86f32d9b3.png"},{"id":57430366,"identity":"f99433f4-54bf-44d6-97fa-1bca0883fc66","added_by":"auto","created_at":"2024-05-30 14:53:33","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":99162,"visible":true,"origin":"","legend":"\u003cp\u003eResults of corrosion potential within type A specimens with different percentages of silica fume and w/cm ratios: (a) w/cm=0.5; (b) w/cm=0.4; (c) w/cm=0.3; (d) w/cm=0.25.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4414385/v1/2de298025b9196318f3d522f.png"},{"id":57430364,"identity":"64ecd081-9548-4d5a-9b04-04364bc5ba02","added_by":"auto","created_at":"2024-05-30 14:53:33","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":75901,"visible":true,"origin":"","legend":"\u003cp\u003eResults of corrosion potential within type B specimens with different percentages of silica fume and w/cm ratios: (a) w/cm=0.5; (b) w/cm=0.4; (c) w/cm=0.3.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4414385/v1/e13bfa877b54a9e283d15d3f.png"},{"id":57430367,"identity":"f1d09aef-99c8-47bc-bde4-482e84bc2eb0","added_by":"auto","created_at":"2024-05-30 14:53:34","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":72618,"visible":true,"origin":"","legend":"\u003cp\u003eResults of corrosion potential within type C specimens with different percentages of silica fume and w/cm ratios: (a) w/cm=0.5; (b) w/cm=0.4; (c) w/cm=0.3.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-4414385/v1/cad20c59e2b61071018deb71.png"},{"id":57430374,"identity":"2786a2fc-7415-49a8-9273-4bebbf1f6e70","added_by":"auto","created_at":"2024-05-30 14:53:34","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":74245,"visible":true,"origin":"","legend":"\u003cp\u003eResults of corrosion potential within type D specimens with different percentages of silica fume and w/cm ratios: (a) w/cm=0.5; (b) w/cm=0.4; (c) w/cm=0.3.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-4414385/v1/a8731095467f51e22519191d.png"},{"id":57430370,"identity":"55ad4c5e-eb20-46a5-b557-1008a528597f","added_by":"auto","created_at":"2024-05-30 14:53:34","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":216277,"visible":true,"origin":"","legend":"\u003cp\u003eResults of carbonation depth in different types of concrete specimens with varying percentages of silica fume and w/cm ratios: (a) Type A; (b) Type B; (c) Type C; (d) Type D.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-4414385/v1/e1e397da19fa0e99b518d5c2.png"},{"id":57430371,"identity":"150e72fa-bc8f-41c1-bbe9-58bdcc93e638","added_by":"auto","created_at":"2024-05-30 14:53:34","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":74808,"visible":true,"origin":"","legend":"\u003cp\u003eCompressive strength of type A specimens with different percentages of silica fume and w/cm ratios: (a) w/cm=0.5; (b) w/cm=0.4; (c) w/cm=0.3; (d) w/cm=0.25.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-4414385/v1/a158c408ea76222e123e30a5.png"},{"id":57430373,"identity":"22f154db-dae5-4a63-a168-8e556f332d4b","added_by":"auto","created_at":"2024-05-30 14:53:34","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":67052,"visible":true,"origin":"","legend":"\u003cp\u003eCompressive strength of type B specimens with different percentages of silica fume and w/cm ratios: (a) w/cm=0.5; (b) w/cm=0.4; (c) w/cm=0.3.\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-4414385/v1/8cdacd3af55282c1272cdc14.png"},{"id":57430369,"identity":"f05d7681-b626-4d03-a114-2dc592c17aa8","added_by":"auto","created_at":"2024-05-30 14:53:34","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":67974,"visible":true,"origin":"","legend":"\u003cp\u003eCompressive strength of type C specimens with different percentages of silica fume and w/cm ratios: (a) w/cm=0.5; (b) w/cm=0.4; (c) w/cm=0.3.\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-4414385/v1/e6aece7fba2035a36817de7e.png"},{"id":57430375,"identity":"e0365bd4-2dd0-4329-8dd9-126691c4a9bf","added_by":"auto","created_at":"2024-05-30 14:53:34","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":57676,"visible":true,"origin":"","legend":"\u003cp\u003eCompressive strength of type D specimens with different percentages of silica fume and w/cm ratios: (a) w/cm=0.5; (b) w/cm=0.4; (c) w/cm=0.3.\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-4414385/v1/06c0be6617fe5021495e8443.png"},{"id":62298621,"identity":"5f450741-3224-4e91-8f3a-8ce8d678a489","added_by":"auto","created_at":"2024-08-12 16:15:23","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2278978,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4414385/v1/3834fe5a-756e-4553-b886-f0aca2bfc7f8.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eEnhancing concrete strength and durability of normal and high- strength concrete: Exploring combined effects of optimized silica fume and slag\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe durability of concrete has long been a fundamental aspect of concrete technology, as it must endure the environmental conditions for which it is designed throughout its structural lifespan. When assessing the durability of concrete structures, particularly in corrosive environments, experts emphasize that resistance alone is insufficient. Concrete design must account for various environmental conditions [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Concrete structures can encounter a range of issues during their service life due to external factors induced by the surrounding environment and internal factors that can compromise concrete durability. These factors generally fall into three categories: physical, such as freeze-thaw action; mechanical, like abrasion; and chemical, including sulfate attack and acid corrosion of reinforcements [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. The alkaline environment of concrete fosters the formation of a temporary and unstable microscopic iron oxide layer on the metal surface, providing corrosion protection. However, as concrete's alkalinity decreases and ion attacks occur, this protective coating on the steel's surface deteriorates [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Carbonation is the most common mechanism responsible for reducing the alkalinity of concrete [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Furthermore, the penetration of chloride ions into steel rebar surfaces leads to corrosion, diminishing the durability of reinforced concrete structures [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. To address this, the production of low-permeability concrete has gained attention to enhance its durability and corrosion resistance [\u003cspan additionalcitationids=\"CR3\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Consequently, extensive research has been conducted to explore steel corrosion prevention methods, such as cathodic protection [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], corrosion inhibitors [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], and epoxy coatings [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], but these methods are expensive and have limited effectiveness. Alternatively, the use of supplementary cementitious materials, partially replacing Portland cement, holds promise for sustainable and effective corrosion resistance improvement [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Notably, pozzolanic admixtures, like silica fume (SF), fly ash (FA), and granulated blast furnace slag (GBFS), are among the most commonly used supplementary cementitious materials to prepare dense and robust concrete [\u003cspan additionalcitationids=\"CR8 CR9\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe advent of new construction materials and techniques has made the production of high-performance concrete feasible, achieved through the incorporation of silica fume additives, superplasticizers, and low w/cm ratios, resulting in better compaction and viscosity. High-performance concrete exhibits low permeability, which plays a crucial role in minimizing the ingress of contaminants like chloride, carbon dioxide, and humidity, known to initiate corrosion [\u003cspan additionalcitationids=\"CR12 CR13 CR14 CR15 CR16 CR17\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. The increasing utilization of high-performance concrete in tall buildings, bridges, and structures exposed to harsh environments necessitates further research into its durability. In recent years, there has been a rise in the use of alternative pozzolanic materials, such as fly ash and slag, due to economic factors and their favourable effects on workability in high-performance concrete. From an economic perspective, a significant cost difference between cement and alternative cementitious materials has been observed. Moreover, using these materials as partial replacements for cement reduces the consumption of expensive superplasticizers. Additionally, slag and fly ash contribute to the development of durability and strength in concrete, as they are not chemically inert in the concrete environment [\u003cspan additionalcitationids=\"CR20 CR21\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Silica fume serves two critical roles in concrete. First, its pozzolanic properties lead to a chemical reaction with calcium hydroxide (CH) to generate additional hydrated calcium silicate (C-S-H), enhancing concrete strength. Second, due to its minute particle size, silica fume fills all the microscopic pores in the cement paste, reducing its permeability [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Consequently, adding silica fume to the concrete mixture in appropriate proportions significantly decreases concrete permeability and corrosion rate while improving its strength and durability [\u003cspan additionalcitationids=\"CR24 CR25\" citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eDespite extensive research on concrete durability, a comprehensive understanding of how different proportions of slag and silica fume influence overall durability remains elusive. The quest to identify the optimal combination of these supplementary cementitious materials (SCMs) to enhance concrete's resistance to steel rebar corrosion is an ongoing endeavor.\u003c/p\u003e \u003cp\u003eThis study delves into the specific impact of incorporating silica fume, slag, and their various combinations at different proportions and water-to-cement (w/c) ratios on critical durability factors, including steel corrosion, carbonation penetration, and compressive strength. While previous studies have explored the individual effects of these SCMs, their combined influence and the optimal proportions for enhancing concrete durability remain largely unknown.\u003c/p\u003e \u003cp\u003eThe overarching objective of this investigation is to unravel the intricate interplay between silica fume, slag, and w/c ratio, providing valuable insights into their synergistic effects on concrete durability, particularly in terms of resisting steel rebar corrosion. The ultimate goal is to formulate practical guidelines for the optimal utilization of these SCMs in the production of robust and reliable concrete structures.\u003c/p\u003e \u003cp\u003eConcrete specimens were prepared with three different w/cm ratios of 0.5, 0.4, and 0.3. Each w/cm ratio included varying percentages of slag (10%, 20%, 30%, and 50%) as a replacement for cement while for each case the silica fume replacements were also varied at 0%, 5%, 10%, and 15%. Cubic concrete specimens containing four rebars at each corner were employed to assess the steel corrosion using the half-cell potential measurement method. The specimens were subjected to alternating wet and dry conditions while immersed in a chloride ion solution for five days and exposed to open air for two days to accelerate the corrosion of steel rebars. Furthermore, carbonation penetration and compressive strength tests were conducted at 28-day and 91-day intervals.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Preparation of specimens\u003c/h2\u003e \u003cp\u003eThis study involved testing four distinct types of specimens to assess their performance. The first set of specimens involved incorporating silica fume as a partial replacement for cement, with w/cm ratios of 0.25, 0.3, 0.4, and 0.5. The purpose of these specimens was to investigate the influence of silica fume on steel corrosion in concrete exposed to chloride penetration. The second, third, and fourth sets of specimens were composed of concrete mixes containing 20%, 30%, and 50% slag content, respectively, as cement substitutes, with varying percentages of silica fume. The w/cm ratios for these three sets of concrete specimens were 0.5, 0.4, and 0.3. The intention was to examine the effects of slag, as well as the combined effects of slag and silica fume, on steel corrosion in a chloride-rich concrete environment.\u003c/p\u003e \u003cp\u003eFor each mix design, three specimens were designated for assessing steel corrosion through the measurement of half-cell potential. Furthermore, three specimens were devoted to determining the compressive strength at 28 days, and another three for measuring the compressive strength at 91 days. Additionally, two specimens were employed to evaluate the depth of carbonation. To fulfill specific testing requirements, three additional cubic specimens measuring 70 mm in dimension were prepared. Consequently, a total of 728 specimens were manufactured, with 159 specimens designated for half-cell potential measurement, 15 specimens for carbonation depth assessment, and the remaining specimens allocated to evaluate the compressive strength at 28 and 91 days.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Materials\u003c/h2\u003e \u003cp\u003eThe mechanical properties and durability of High-Performance Concrete (HPC) are profoundly influenced by the characteristics of cement, aggregate, and pozzolanic materials. Consistent with prior research, the following materials, selected based on specific criteria, were employed:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eCoarse broken limestone, adhering to the ASTM-C33 [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] grading standard, with a maximum particle size of 12.5 mm, a dry density of 1950 kg/m\u0026sup2;, and a water absorption rate of 0.55%.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eFine limestone, meeting the prescribed ASTM-C33 grading, with a density of 2.51 and a water absorption rate of 1%.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eType 1 cement, in compliance with the ASTM-C150 [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e] standard.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eSilica fume in powdered form, characterized by a density of 2.2.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eSlag of the type ground granulated blast furnace slag (GGBFS).\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eMelamine-formaldehyde sulfate superplasticizer, following the specifications outlined in ASTM-C494 [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Mix design\u003c/h2\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003e2.3.1. Specimens with silica fume as a partial cement replacement\u003c/h2\u003e \u003cp\u003eThis set of specimens was specifically designed to investigate the impact of silica fume on the corrosion of steel rebars exposed to chloride ions. Different proportions of silica fume (0%, 5%, 10%, and 15%) were utilized as partial replacements for the cement content in each specimen at each w/cm ratio. The control specimen, in each w/cm ratio, contained 0% silica fume, serving as a reference against which the corrosion behavior of steel in other specimens was compared. A systematic coding system was employed to represent these specimens, using the letter 'A' to signify concrete with silica fume and no slag, followed by the respective w/cm ratio. Additionally, the proportion of silica fume incorporated in each specimen was indicated in the code. For instance, the code 'A 0.4-5' denoted a specimen with silica fume (without slag) at a w/cm ratio of 0.4, wherein 5% of the cement content was replaced by silica fume. Detailed mix designs for this group of specimens are presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Notably, the quantity of coarse aggregate in all specimens was kept constant at 1020 kg/m\u0026sup2; to eliminate its influence on chloride ion penetration and subsequent steel corrosion.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e2.3.2. Specimens with slag and silica fume as cement replacements\u003c/h2\u003e \u003cp\u003eThis set of specimens was specifically designed to investigate the effects of both slag and a combination of slag and silica fume on steel corrosion in the presence of chloride ions. Cement was partially replaced with slag in these specimens at percentages of 20%, 35%, and 50%, respectively. Concurrently, for each percentage of slag replacement, silica fume was introduced as a substitute for cement at proportions of 0%, 5%, 10%, and 15%.\u003c/p\u003e \u003cp\u003eTo designate these specimens, employed the letters 'B,' 'C,' and 'D' to represent concrete specimens containing 20%, 35%, and 50% slag content, respectively. The respective w/cm ratio was indicated, followed by the proportion of silica fume utilized. For example, the code 'D 0.3\u0026ndash;10' referred to a specimen with 50% slag content and 10% silica fume, replacing a portion of the cement, with a w/cm ratio of 0.3. In this instance, Portland cement constituted only 40% of the total cementitious materials. The quantities of materials used in these specimens were consistent with those listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, with the distinction being that groups B, C, and D incorporated 20%, 35%, and 50% slag replacement for cement, respectively.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e\u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"6\" nameend=\"c6\" namest=\"c1\"\u003e \u003cp\u003eConcrete mix design variations (kg/m\u003csup\u003e3\u003c/sup\u003e).\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSpecimen\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSilica fume\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003csup\u003e*\u003c/sup\u003eAdded water\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSuperplasticizers\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003csup\u003e**\u003c/sup\u003eCement\u003c/p\u003e \u003cp\u003e+\u003c/p\u003e \u003cp\u003eSlag\u003c/p\u003e\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eLimestone\u003c/p\u003e \u003cp\u003epowder\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e(A, B, C, D) 0.5-0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e202\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e380\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e692\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e(A, B, C, D) 0.5-5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e202\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e361\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e685\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e(A, B, C, D) 0.5\u0026ndash;10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e202\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e342\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e679\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e(A, B, C, D) 0.5\u0026ndash;15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e202\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e323\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e672\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e(A, B, C, D) 0.4-0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e184\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e430\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e692\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e(A, B, C, D) 0.4-5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e21.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e184\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e408\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e685\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e(A, B, C, D) 0.4\u0026ndash;10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e184\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e387\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e679\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e(A, B, C, D) 0.4\u0026ndash;15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e64.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e184\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e365\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e672\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e(A, B, C, D) 0.3-0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e174\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e540\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e629\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e(A, B, C, D) 0.3-5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e27\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e174\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e513\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e620\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e(A, B, C, D) 0.3\u0026ndash;10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e54\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e174\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e486\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e611\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e(A, B, C, D) 0.3\u0026ndash;15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e81\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e174\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e459\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e602\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eA 0.25-0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e162\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e605\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eA 0.25-5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e162\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e570\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e595\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eA 0.25-10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e162\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e540\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e585\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eA 0.25-15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e162\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e510\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e575\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"6\" nameend=\"c6\" namest=\"c1\"\u003e \u003cp\u003e* Water addition is based on specific w/cm ratio and using almost dry aggregate\u003c/p\u003e \u003cp\u003e** Cement and slag contents are based on the specimen group (A, B, C, or D).\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.4. Corrosion tests of steel in concrete\u003c/h2\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e2.4.1. Half-cell potential measurement device\u003c/h2\u003e \u003cp\u003eIn this study, the corrosion of steel in concrete specimens was assessed using the half-cell potential measurement method, following the ASTM C876-91 standard [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. As prescribed by this standard, if the potential measured concerning the copper-copper sulfate electrode exceeded 200 mV, there was a 90% probability that the steel rebars were free from corrosion. For potential values between 200 and 350 mV, the corrosion condition of the steel remained uncertain. Finally, if the measured potential fell below 350 mV, there was a 90% probability that corrosion had occurred in the steel rebars. The potential difference of the steel electrodes was compared to a copper-copper sulfate reference electrode, and the corrosion status of the steel was determined based on this potential difference.\u003c/p\u003e \u003cp\u003eThe half-cell potential measurement device (see Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) comprises various components that must be assembled before utilization. These components include a voltmeter with high internal resistance, a reference electrode cylinder, a reference electrode, a surfactant tank, a base for supporting the voltmeter on the surfactant tank, and connecting wires. Adhering to the manufacturer's instructions for the half-cell potential measurement device employed in this research, copper sulfate crystals were initially added to the antifreeze solution and thoroughly mixed. The resulting solution was then poured into the designated cylinder for the reference electrode. It is crucial to ensure that this solution always contains some insoluble copper sulfate. Subsequently, the reference electrode was positioned inside this cylinder and securely fastened with a screw at its end.\u003c/p\u003e \u003cp\u003eThe surfactant tank was filled with contact electric solution, which was obtained by mixing 90 ml of contact electric material with 19 liters of water. The solution needed to fill at least 75% of the tank's height. Following this, the cylinder containing the reference electrode was submerged in the solution within the surfactant tank, firmly closed, and secured with a screw at the end of the cylinder. The voltmeter base was then affixed to the end of the reference electrode cylinder outside the surfactant tank using a screw, and the voltmeter was placed atop it. The voltmeter was connected to the reference electrode through a connecting wire fixed to the base of the voltmeter. Additionally, the voltmeter base was connected to the reference electrode via the same screw beneath it.\u003c/p\u003e \u003cp\u003eTo measure the half-cell potential, the reference electrode was linked to the voltmeter using a connecting wire, while another connecting wire was employed to connect the steel rebar in the concrete specimen to the voltmeter. After a designated period, a steady numerical value was displayed on the digital voltmeter, indicating the potential of the rebar within the specimen relative to the reference electrode.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e2.4.2 Environmental conditions and test duration in corrosion testing\u003c/h2\u003e \u003cp\u003eTo create a chloride-rich environment conducive to corrosion, a seven-percent-by-weight NaCl solution was employed. The use of distilled water for preparing the NaCl solution ensured the exclusion of extraneous substances that could influence steel corrosion. Additionally, to expedite the corrosion of steel rebars embedded in the specimens, a cyclic wetting and drying regime was implemented. This regime involved subjecting the specimens to 48 hours of exposure to ambient air once a week, facilitating water evaporation from their surfaces and pores. This process provided the necessary oxygen supply for steel corrosion.\u003c/p\u003e \u003cp\u003eTo compare the initiation times of corrosion among the specimens, the half-cell potential was measured for all fabricated specimens. The measurements were continued until their potentials dropped below 350 mV, indicating a 90% probability of steel corrosion. The test duration spanned approximately fifteen weeks, with weekly measurements conducted throughout this period. This comprehensive approach allowed for a meticulous assessment of the corrosion behavior and initiation times of the individual specimens.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e2.5. Measurement of carbonation depth\u003c/h2\u003e \u003cp\u003eIn this research, an experiment was conducted to ascertain the depth of carbonation in various specimens and investigate the influence of key parameters, such as the w/cm ratio, silica fume percentage, slag percentage, and their combination, on carbonation depth. Since carbonation typically occurs at a slow rate under normal environmental conditions, an autoclave was employed to expedite the process (see Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The concrete specimens were carefully placed in the autoclave tank, and the lid was securely fastened using screws to ensure a complete seal. Subsequently, a CO\u003csub\u003e2\u003c/sub\u003e gas capsule was connected to the tank through a hose, and the specimens were subjected to a closed chamber saturated with CO\u003csub\u003e2\u003c/sub\u003e gas under a pressure of 1.5 atmospheres, which was the maximum reliable pressure for the autoclave device. This accelerated carbonation process lasted for one day. The pressure gauge on the chamber's lid indicated an increase in gas pressure. Once the pressure reached 1.5 atmospheres, the valve of the CO\u003csub\u003e2\u003c/sub\u003e gas capsule was closed. Over several days, the gas pressure gradually decreased, and it was periodically readjusted by opening and closing the valve of the capsule. After 10 days, the specimens were removed from the autoclave and subsequently cut in half using a press.\u003c/p\u003e \u003cp\u003eTo determine the depth of carbon dioxide penetration, a phenolphthalein reagent was applied to the fractured surfaces of the specimens. The reagent, prepared by dissolving one gram of phenolphthalein powder in one liter of ethyl alcohol, facilitated the identification of regions of the concrete specimens that retained alkalinity (turning the colorless solution of phenolphthalein purple) and regions that had undergone carbonation (remaining unchanged in color). The depth of carbonation was measured after one hour of applying the reagent to the fractured surfaces of the specimens, with gas penetration measured on all four sides of each specimen with a precision of 1 mm. The average penetration depth represented the carbonation depth for the respective mix design. Due to the limited volume of the autoclave device, two specimens were used for carbonation testing for each mix design, and the average penetration depth was considered as the carbonation depth for that specific mix design.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e2.6. Compressive strength analysis\u003c/h2\u003e \u003cp\u003eThe compressive strength analysis involved the use of seventy-mm-cubic specimens, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. These specimens were subjected to compressive strength testing at two distinct time intervals: 28 days and 91 days. To ensure statistical validity and accuracy, three specimens were prepared for each mixing design, resulting in a total of 312 specimens specifically designated for compressive strength measurements. Moreover, additional specimens were made for each mixing design, serving as replacements in the event that the original specimens were deemed unsuitable or compromised.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Results of half-cell potential measurement\u003c/h2\u003e \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e \u003ch2\u003e3.1.1. Specimens without slag\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;4(a) shows the results of monitoring the electrochemical potential of rebars in concrete specimens devoid of slag content (referred to as type A specimens). These specimens contain varying proportions of silica fume, with a constant w/cm ratio of 0.5. The figure depicts temporal variations in potential. The control specimen, which denotes the absence of silica fume, consistently exhibits lower potential values than specimens with silica fume, suggesting higher corrosion in the rebars of the control specimen.\u003c/p\u003e \u003cp\u003eAs shown, the control concrete experienced a more rapid decline in potential below the 350 mV threshold, which indicates a 90% probability of steel rebar corrosion according to ASTM C876. In contrast, the specimens containing silica fume showed a longer delay period before corrosion initiation, suggesting improved corrosion resistance. Consequently, the control concrete exhibits a shorter time to initiate corrosion, resulting in a higher corrosion rate. It is noteworthy that corrosion initiation in concrete containing 5% silica fume is superior to other silica fume proportions, thereby enhancing resistance to steel reinforcement corrosion.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;4(b) illustrates the potential measurements within concrete specimens containing varying proportions of silica fume and a w/cm ratio of 0.4. Over a period exceeding three months, the internal rebar potential in the control specimen consistently remains lower compared to specimens containing silica fume. This disparity highlights the superior corrosion resistance exhibited by silica fume-incorporated specimens. Notably, the control specimen experiences a more rapid decline below the 350 mV threshold compared to concrete containing 10% silica fume. Therefore, substituting 10% of cement with silica fume in the 0.4 w/cm ratio effectively optimizes steel corrosion resistance. This enhanced resistance is likely attributed to the pozzolanic reaction of silica fume, which consumes calcium hydroxide, a byproduct of cement hydration, to form additional calcium silicate hydrate (C-S-H), the primary binding phase in concrete responsible for strength and durability.\u003c/p\u003e \u003cp\u003eAdditionally, increasing silica fume content to 5% and 10% within w/cm ratios of 0.4 and 0.5, respectively, reduces the concrete's resistance to steel corrosion. This could be attributed to the formation of a denser microstructure at these ratios, which hinders the diffusion of oxygen towards the steel rebar, essential for passivation. Conversely, raising silica fume content to 15% within the 0.15 w/cm ratio enhances the concrete's steel corrosion resistance. This is likely due to the reduced availability of free water for cement hydration at this lower ratio, leading to decreased calcium hydroxide production. The silica fume can effectively utilize this limited calcium hydroxide to form additional calcium silicate hydrate (C-S-H), thereby improving the concrete's durability. Consequently, the optimal silica fume proportion for achieving peak concrete durability against steel corrosion varies dynamically in response to w/cm ratio adjustments. This dynamic relationship is crucial not only for enhancing corrosion resistance but also from an economic standpoint, considering the higher cost of silica fume compared to cement.\u003c/p\u003e \u003cp\u003eThe following analysis, presented in Fig.\u0026nbsp;4(c), focuses on type A concrete specimens with a w/cm ratio of 0.3. As silica fume proportions increase, the potential difference between control concrete and silica fume-containing specimens widens. This is accompanied by a larger temporal separation in potential-time diagrams, indicating improved concrete performance against steel corrosion with increasing silica fume content. In this category, higher silica fume percentages simultaneously enhance the corrosion durability of the concrete. This could be attributed to the pozzolanic reaction of silica fume, which consumes calcium hydroxide, a byproduct of cement hydration, to form additional calcium silicate hydrate (C-S-H), the primary binding phase in concrete that imparts strength and durability. Notably, the time required for corrosion initiation in the 15% silica fume specimen exceeds that of other specimens, demonstrating superior corrosion resistance.\u003c/p\u003e \u003cp\u003eWith a w/cm ratio of 0.25, as shown in Fig.\u0026nbsp;4(d), increasing silica fume content improves concrete's performance and durability against steel corrosion. Specifically, the specimen with 15% silica fume consistently exhibits higher potential values across most measurement intervals, indicating superior corrosion resistance. Notably, reducing the w/cm ratio while increasing silica fume content further widens the gap in potential values between silica fume-infused concrete and the control, suggesting reduced susceptibility to corrosion in the former.\u003c/p\u003e \u003cp\u003eThe reduction of the w/cm ratio significantly impacts rebar potential, hindering the migration of ions essential for corrosion initiation and thereby limiting corrosion susceptibility. This phenomenon arises from the denser and less permeable structure of the concrete. Notably, the extended time required for corrosion initiation enhances the longevity of the concrete structure. Additionally, increasing silica fume content and decreasing w/cm ratios further widen the potential gap between control and silica fume-incorporated concrete specimens, distinctly influencing corrosion resistance enhancement.\u003c/p\u003e \u003cp\u003eIn conclusion, the interplay between a fixed proportion of silica fume and manipulated w/cm ratios dynamically influences rebar potential. This interaction plays a pivotal role in shaping concrete's corrosion susceptibility, with implications for its durability and structural longevity.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e \u003ch2\u003e3.1.2. Specimens containing 20% slag\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;5(a) presents the results of measuring the potential of rebars within concrete specimens (type B) containing 20% slag as a partial cement substitute, various proportions of silica fume, and a fixed w/cm ratio of 0.5. Notably, the potential of rebars in concrete containing silica fume exhibited higher values compared to concrete with no silica fume, indicating reduced corrosion tendencies. This demonstrates that incorporating silica fume enhances concrete durability against steel corrosion in the presence of steel reinforcement. The specimen with 5% silica fume demonstrated superior performance, exhibiting a shorter time to corrosion initiation, albeit still longer than other silica fume-containing specimens. The specimens with 10% and 15% silica fume exhibited lower potential values compared to the 5% specimen but higher values than the 0% silica fume concrete. Furthermore, when comparing these specimens to similar ones (with 0.5 w/cm ratios and containing silica fume without slag), the addition of slag significantly improved the concrete's durability against steel corrosion. This suggests that utilizing both pozzolans, silica fume, and slag, enhances concrete reliability against steel corrosion compared to using only silica fume.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;5(b) presents the results of measuring the potential of rebars within type B concrete specimens with various proportions of silica fume and a fixed w/cm ratio of 0.4. The potential of rebars in specimens containing silica fume was consistently higher than in specimens with only slag and no silica fume, indicating improved corrosion resistance. The concrete specimen with 10% silica fume required more time for the rebars' potential to drop below 350 mV, indicating superior performance. This suggests that optimizing the silica fume percentage can improve concrete performance. This is likely due to the pozzolanic reaction of silica fume, which consumes calcium hydroxide (a by-product of cement hydration) to form an additional calcium silicate hydrate (C-S-H). C-S-H is the primary binding phase in concrete that provides strength and durability.\u003c/p\u003e \u003cp\u003eReducing the w/cm ratio has a significant impact on concrete's resistance to steel corrosion, as it reduces concrete's permeability. This, in turn, reduces the availability of water and oxygen for electrochemical reactions, thereby reducing steel corrosion rates. Consequently, concrete design guidelines should consider the required resistance factors and environmental conditions when selecting an appropriate w/cm ratio.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;5(c) presents the results for type B concrete specimens with varying silica fume percentages and a w/cm ratio of 0.3. The corrosion potential of rebars embedded in concrete containing silica fume was consistently higher compared to rebars in concrete without silica fume. This difference in potential increased with higher silica fume percentages. The duration over which the potential remained above 200 mV served as an indicator of corrosion absence. In specimens with 10% and 15% silica fume, this period was approximately 1.5 and 2 times longer, respectively, compared to specimens without silica fume. Concrete with a 15% silica fume replacement exhibited superior performance, significantly delaying corrosion initiation. A plausible explanation for the observed outcomes is that the addition of silica fume reduces the concrete's permeability, thereby impeding the penetration of chloride ions, the primary instigators of corrosion in reinforced concrete.\u003c/p\u003e \u003cp\u003eIn practice, it is recommended to reduce the w/cm ratio to effectively utilize the properties of silica fume and slag to enhance concrete reliability against steel corrosion. Attention should be paid to proper compaction and curing during concrete construction, particularly when using silica fume, to prevent surface drying and cracking. In corrosive environments, cracks can facilitate the penetration of corrosive materials into the concrete. By carefully considering these factors, the durability and resistance of concrete against steel corrosion can be significantly improved.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section3\"\u003e \u003ch2\u003e3.1.3. Specimens containing 35% slag\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;6(a) illustrates the results of evaluating the corrosion potential of rebars embedded in type C concrete specimens (with 35% slag as a partial cement replacement) containing varying amounts of silica fume while maintaining a constant w/cm ratio of 0.5. It is noteworthy that the concrete specimen containing 0% silica fume effectively represented a 35% slag replacement for cement.\u003c/p\u003e \u003cp\u003eThe findings demonstrate that the specimen incorporating 5% silica fume exhibited a delayed onset of steel corrosion compared to other specimens, suggesting a lower corrosion rate. Specimens with 10% and 15% silica fume displayed similar corrosion onset times, both outperforming the specimen with 0% silica fume. Hence, the addition of silica fume, in conjunction with the presence of 35% slag as a cement substitute, significantly enhances the concrete's resistance to steel corrosion. A comparison between type C specimens with a w/cm ratio of 0.5 and type A specimens containing no slag, but with the same w/cm ratio, highlights the superior performance of type C specimens. This advantage stems from the pozzolanic reaction of slag, which refines the concrete's microstructure, reduces permeability, and enhances its resistance against aggressive agents, including water and oxygen, essential for steel reinforcement corrosion. The pozzolanic reaction modifies the cement paste structure by converting calcium hydroxide crystals into hydrated calcium silicate (C-S-H), leading to denser concrete.\u003c/p\u003e \u003cp\u003eAdditionally, Fig.\u0026nbsp;6(b) illustrates the results of measuring the rebar potential in type C concrete specimens with varying proportions of silica fume and a fixed w/cm ratio of 0.4. Here, the specimen containing 10% silica fume exhibited delayed corrosion onset compared to other specimens, indicating enhanced durability against steel corrosion. Subsequently, the specimens with 5% and 15% silica fume demonstrated better performance than the specimens without silica fume. A comparison between the specimens containing 0% silica fume, which includes 35% slag as a cement substitute, and the specimen without slag and silica fume, illustrates the beneficial impact of slag alone on the concrete's corrosion resistance. It is worth noting that although slag decreases the alkalinity of the concrete environment, which could increase the risk of corrosion, its ability to improve the concrete structure and reduce permeability outweighs this factor, ultimately increasing resistance to steel corrosion. Similarly, silica fume's pozzolanic properties contribute to the conversion of calcium hydroxide into C-S-H, supporting the conclusion that the addition of silica fume to concrete specimens enhances their resistance against steel corrosion.\u003c/p\u003e \u003cp\u003eFurthermore, Fig.\u0026nbsp;6(c) displays the results of measuring the rebar potential in type C concrete specimens with varying amounts of silica fume and a fixed w/cm ratio of 0.3. Notably, the specimen containing 10% silica fume exhibited delayed onset of steel corrosion compared to other specimens, followed by the specimens containing 5% and 10% silica fume, respectively, showing better performance than the specimen without silica fume. A closer examination of this figure reveals a reduced gap between the graph of the specimen without silica fume (with 35% slag substitution for cement) and those with silica fume, particularly in comparison to specimens containing 20% slag. This observation highlights the superior corrosion performance of concrete with higher slag substitution (up to 35%). Additionally, when comparing these specimens with type B specimens, the increase in slag content from 20\u0026ndash;35% substantially improved the concrete's resistance to steel corrosion. This economic significance lies in the fact that slag, being a byproduct of the steel industry, incurs minimal cost, rendering it an affordable and cost-effective alternative to cement. Consequently, substituting cement with larger amounts of slag in concrete construction not only saves costs but also confers beneficial effects such as enhanced corrosion and sulfate attack resistance, reduced hydration temperature, increased compressive strength, and decreased super-lubricant consumption.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section3\"\u003e \u003ch2\u003e3.1.4. Specimens containing 50% slag\u003c/h2\u003e \u003cp\u003eIn Fig.\u0026nbsp;7, the outcomes of assessing the rebar potential in type D concrete specimens (with varying percentages of slag as a cement substitute) with different proportions of silica fume and constant w/cm ratios of 0.5, 0.4, and 0.3, respectively, are presented. From Fig.\u0026nbsp;7(a), it is evident that the onset of corrosion in the concrete specimen containing 5% silica fume was delayed compared to other specimens. The corrosion onset time for concrete specimens containing 10% and 15% silica fume showed negligible differences between them, falling between the durations observed in the specimens with 5% and 0% silica fume.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;7(b) and (c) demonstrate that in type D specimens with w/cm ratios of 0.4 and 0.3, respectively, the incorporation of 10% and 15% silica fume yields the most favorable outcomes in terms of enhancing concrete durability against steel corrosion. Across all type D specimens with different w/cm ratios, the combined use of silica fume and slag significantly improves concrete's resistance to steel corrosion when compared to the use of slag alone in concrete production.\u003c/p\u003e \u003cp\u003eIt is worth noting that the potential difference between the specimens containing silica fume and slag decreased compared to cases where specimens solely contained silica fume, particularly evident at low w/cm ratios. This observation arises from the fact that the presence of slag in concrete enhances concrete's durability against steel corrosion. Although the addition of silica fume to the concrete mixture with slag increases its corrosion resistance, the effect of adding silica fume in this scenario is less pronounced than when silica fume is added to concrete without slag. Nevertheless, the combined use of silica fume and slag consistently exhibits a more substantial positive impact on improving concrete's resistance to steel corrosion compared to using silica fume or slag in isolation.\u003c/p\u003e \u003cp\u003eThe use of 50% slag as a cement substitute has adversely affected the durability of concrete against steel corrosion in most cases, as indicated by the shorter corrosion onset time compared to concrete with 20% slag. However, slag still provides some protection to concrete against steel corrosion relative to concrete without slag. The reason for this behavior is related to the impact of slag on the hydration and pore characteristics of the cement matrix, which determine the chloride transport and corrosion resistance of steel. Some studies have shown that slag can react with water and calcium hydroxide to produce more calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H), which enhance the density and strength of the concrete. On the other hand, slag can also consume calcium hydroxide, which lowers the pH value of the pore solution and reduces the alkalinity of the concrete. This can impair the passivation ability of the concrete and increase the vulnerability of steel to corrosion. Furthermore, slag can raise the porosity and permeability of the concrete at early ages, allowing more chloride ions and oxygen to penetrate into the concrete. These factors account for why concrete with 50% slag has poorer durability against steel corrosion than concrete with 20% slag or no slag. Nevertheless, concrete with 20% slag still outperforms concrete without slag, because the positive effects of slag on the hydration products and the pore refinement dominate over the negative effects of slag on the pH value and the porosity at later ages [\u003cspan additionalcitationids=\"CR32 CR33\" citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section3\"\u003e \u003ch2\u003e3.1.5. Comparative analysis of time required for steel corrosion initiation\u003c/h2\u003e \u003cp\u003eIn this study, the goal was to compare the time needed for steel corrosion to commence in different concrete specimens by establishing relationships between relevant variables. Consequently, a function was devised to express the initiation time of steel corrosion for two distinct concrete specimens based on the independent variables: w/cm ratio (W/CM), percentage of silica fume (SF/CM), and percentage of slag (Slag/CM) present in each of the compared specimens. Thus, this relationship involved six independent variables and one function (dependent variable), as described by Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\frac{{{{\\left( {{t_0}} \\right)}_1}}}{{{{\\left( {{t_0}} \\right)}_2}}}=F\\left\\{ {{{(\\frac{W}{{CM}})}_1},{{(\\frac{W}{{CM}})}_2},{{(\\frac{{SF}}{{CM}})}_1},{{(\\frac{{SF}}{{CM}})}_2},{{(\\frac{{Slag}}{{CM}})}_1},{{(\\frac{{Slag}}{{CM}})}_2}} \\right\\}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eIn Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), the indices 1 and 2 pertain to the first and second specimens under comparison, respectively. The other parameters in this equation are W/CM, SF/CM, Slag/CM, and t\u003csub\u003e0\u003c/sub\u003e, representing the time required for steel corrosion initiation.\u003c/p\u003e \u003cp\u003eEmploying logarithmic interpolation, we derived Eq.\u0026nbsp;(\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) to facilitate the comparison of the time required for corrosion initiation between two distinct concrete specimens. This equation was formulated based on 1128 comparisons, involving 1128 series of comparisons with the six independent variables and one dependent variable.\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\frac{{{{\\left( {{t_0}} \\right)}_1}}}{{{{\\left( {{t_0}} \\right)}_2}}}=1.346\\left\\{ {\\frac{{\\left( {\\frac{W}{{CM}}} \\right)_{2}^{{1.622}}}}{{\\left( {\\frac{W}{{CM}}} \\right)_{1}^{{1.109}}}}.\\frac{{\\left( {\\frac{{SF}}{{CM}}} \\right)_{1}^{{0.056}}}}{{\\left( {\\frac{{SF}}{{CM}}} \\right)_{2}^{{0.078}}}}.\\frac{{\\left( {\\frac{{Slag}}{{CM}}} \\right)_{1}^{{0.022}}}}{{\\left( {\\frac{{Slag}}{{CM}}} \\right)_{2}^{{0.045}}}}} \\right\\}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe above relationship allows for a preliminary estimation of the performance comparison of a concrete specimen against steel corrosion when compared to another concrete specimen, while considering variations in the parameters of the w/cm ratio, percentage of slag, and percentage of silica fume as a replacement for cement.\u003c/p\u003e \u003cp\u003eIf the effect of slag is disregarded in the observations, Eq.\u0026nbsp;(\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) is obtained. This relationship is based on 66 comparisons, which collectively encompass 66 series of comparisons.\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$$\\frac{{{{\\left( {{t_0}} \\right)}_1}}}{{{{\\left( {{t_0}} \\right)}_2}}}=1.321\\left\\{ {\\frac{{{{\\left( {{{(\\frac{W}{{CM}})}_2}+1} \\right)}^{4.36}}}}{{{{\\left( {{{(\\frac{W}{{CM}})}_1}+1} \\right)}^{3.403}}}}.\\frac{{\\left( {\\frac{{SF}}{{CM}}} \\right)_{1}^{{0.05}}}}{{\\left( {\\frac{{SF}}{{CM}}} \\right)_{2}^{{0.05}}}}} \\right\\}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eEq.\u0026nbsp;(\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) was derived from observations concerning concrete specimens containing only silica fume. Thus, when slag is not used in concrete production, and the parameters of w/cm ratio and the percentage of silica fume replacing cement are altered in two different specimens, Eq.\u0026nbsp;(\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) can be employed to compare the corrosion resistance performance of these two specimens.\u003c/p\u003e \u003cp\u003eSimilarly, if the impact of silica fume is disregarded in the observations, Eq.\u0026nbsp;(\u003cspan refid=\"Equ4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) is derived. This relationship is also based on 66 comparisons, representing 66 series of comparisons.\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e\n$$\\frac{{{{\\left( {{t_0}} \\right)}_1}}}{{{{\\left( {{t_0}} \\right)}_2}}}=0.976\\left\\{ {\\frac{{{{\\left( {{{(\\frac{W}{{CM}})}_2}+1} \\right)}^{5.099}}}}{{{{\\left( {{{(\\frac{W}{{CM}})}_1}+1} \\right)}^{3.166}}}}.\\frac{{\\left( {\\frac{{Slag}}{{CM}}} \\right)_{1}^{{0.022}}}}{{\\left( {\\frac{{Slag}}{{CM}}} \\right)_{2}^{{0.033}}}}} \\right\\} - 1$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eEq.\u0026nbsp;(\u003cspan refid=\"Equ4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) can be obtained by comparing the results of specimens containing only slag. Therefore, in cases where the w/cm ratio and the percentage of slag replacing cement vary, and no silica fume is present in the concrete, Eq.\u0026nbsp;(\u003cspan refid=\"Equ4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) can be used to estimate and compare the corrosion resistance performance of two different concretes.\u003c/p\u003e \u003cp\u003eThe following restrictions for Eqs.\u0026nbsp;(\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), (\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), and (4) are essential to note:\u003cdiv id=\"Equ5\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ5\" name=\"EquationSource\"\u003e\n$$0{\\text{ }} \\leqslant {\\text{ }}SF/CM{\\text{ }} \\leqslant {\\text{ }}0.15,{\\text{ }}0{\\text{ }} \\leqslant {\\text{ }}Slag/CM{\\text{ }} \\leqslant {\\text{ }}0.5,{\\text{ }}0.3{\\text{ }} \\leqslant {\\text{ }}W/CM{\\text{ }} \\leqslant {\\text{ }}0.5.$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e5\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eDuring the internal stage of deriving Eqs.\u0026nbsp;(\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), (\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), and (4), in cases where either SF/CM or Slag/CM became zero, logarithmic interpolation necessitated replacing zero with the value 0.0001. Hence, when using the aforementioned equations, if the percentage of slag or silica fume replacing cement in the specimens is zero, it is imperative to substitute zero with the value 0.0001 to ensure accurate calculations.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Carbonation test\u003c/h2\u003e \u003cp\u003eThe findings of the carbonation test (Fig.\u0026nbsp;8) indicate that the incorporation of silica fume generally results in a negligible increase in carbonation depth compared to the control concrete in specimens containing 0% slag and varying w/c ratios. However, for w/c ratios of 0.3 and 0.25, the impact of silica fume addition on carbonation depth diminishes compared to ratios of 0.5 and 0.4, resulting in a minimal disparity between specimens with and without silica fume in terms of carbonation depth.\u003c/p\u003e \u003cp\u003eConversely, when 20% of slag replaces cement, the carbonation depth decreases compared to similar specimens without slag. According to some research, slag can reduce the carbonation depth of concrete by enhancing the degree of hydration, refining the pore structure of the cement matrix, and raising the pH value and buffering capacity of the pore solution [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. These effects, however, are more pronounced at lower slag contents (such as 20%) than at higher slag contents (such as 50%), as excess slag can increase the porosity and permeability of the concrete at early ages, facilitating carbon dioxide ingress and lowering the concrete's alkalinity.\u003c/p\u003e \u003cp\u003eOn the other hand, silica fume can improve the carbonation resistance of concrete by decreasing the porosity and permeability of the cement matrix, as well as by forming additional calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H), which increase the density and strength of the concrete. However, these effects are more significant in concrete without slag than in concrete with slag, because the slag already provides some benefits on the hydration products and the pore structure refinement. Thus, the addition of silica fume has a negligible impact on the carbonation depth when 20% of slag substitutes for cement.\u003c/p\u003e \u003cp\u003eConversely, when 50% of slag substitutes for cement, the carbonation depth increases compared to similar specimens without slag, and adding silica fume to the concrete composition slightly reduces the carbonation depth [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIncreasing the slag content from 20\u0026ndash;35% as a cement replacement leads to a reduction in carbonation depth, as compared to similar specimens containing 20% slag or no slag. Additionally, the inclusion of silica fume in the concrete mixture contributes to a decrease in carbonation depth, particularly when compared to specimens containing 20% slag.\u003c/p\u003e \u003cp\u003eHowever, in concrete specimens with a slag content increased from 35\u0026ndash;50%, the carbonation depth increases, in contrast to specimens containing 20% and 35% slag. Nevertheless, in these specimens, the addition of silica fume to concrete slightly decreases the carbonation depth when compared to concrete without silica fume.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003e3.3. Compressive strength\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;9 displays the compressive strength of type A concrete specimens containing various proportions of silica fume while maintaining constant w/cm ratios of 0.5, 0.4, 0.3, and 0.25. By comparing the compressive strength of 91-day specimens with that of 28-day specimens, it becomes apparent that the majority of concrete's compressive strength is achieved by 28 days, with specimens containing silica fume consistently exhibiting higher compressive strengths than control specimens. Among the specimens with a w/cm ratio of 0.5, the specimen containing 10% silica fume demonstrated the highest compressive strength at both 28 and 91 days. In the case of a w/cm ratio of 0.25, while the 28-day compressive strength of the specimen with 10% silica fume was slightly superior to that with 15% silica fume, the 91-day compressive strength of the specimen containing 15% silica fume surpassed that of the 10% silica fume specimen. Therefore, for w/cm ratios, incorporating 15% silica fume in the concrete mixture leads to the highest compressive strength at 91 days, followed by specimens with 10% and 5% silica fume.\u003c/p\u003e \u003cp\u003eMoreover, the research results indicate that when using limestone aggregates with w/cm ratios of 0.3 and 0.4, the substitution of 10% silica fume in cement yields the greatest increase in concrete's compressive strength. However, for concrete with a w/cm ratio of 0.25, replacing cement with 15% silica fume exhibits higher compressive strength compared to 10%. One possible reason for the results shown in Fig.\u0026nbsp;9 is that silica fume has a pozzolanic effect on the hydration of cement, which means that it reacts with the calcium hydroxide released by the cement hydration and forms additional calcium silicate hydrate (C-S-H), the main binding phase in concrete. This improves the density, strength, and durability of the cement paste, enhancing the compressive strength of concrete.\u003c/p\u003e \u003cp\u003eThe optimal dosage of silica fume depends on the w/cm ratios and the curing time of the concrete. Silica fume can increase the water demand and reduce the workability of fresh concrete, especially at higher dosages and lower w/cm ratios. This can affect the quality of compaction and consolidation, potentially reducing compressive strength. Therefore, for higher w/cm ratios, such as 0.5, a lower dosage of silica fume, like 10%, may suffice to achieve maximum compressive strength. Conversely, for lower w/cm ratios, such as 0.25, a higher dosage of silica fume, like 15%, may be necessary to counteract the negative effects of low water content and high cement content on the hydration process and pore structure of concrete.\u003c/p\u003e \u003cp\u003eSilica fume can accelerate early strength development in concrete, but its long-term strength gain may be slower than that of plain concrete due to the reduced availability of calcium hydroxide for further pozzolanic reaction. For longer curing times, such as 91 days, a higher dosage of silica fume, like 15%, may be more beneficial than a lower dosage, like 10%, to achieve higher compressive strength, especially for lower w/cm ratios, such as 0.25. These factors may explain why, for w/cm ratios of 0.3 and 0.4, incorporating 10% silica fume in the concrete mixture leads to the highest compressive strength at both 28 and 91 days, while for a w/cm ratio of 0.25, replacing cement with 15% silica fume exhibits higher compressive strength at 91 days compared to 10%. [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eA comparison of the optimum silica fume percentages in type A specimens with varying w/cm ratios indicates that reducing the w/cm ratio improves the performance of specimens with higher silica fume contents in terms of compressive strength. In Fig.\u0026nbsp;10, the compressive strength results of type B concrete specimens containing different percentages of silica fume are presented, with fixed w/cm ratios of 0.5, 0.4, and 0.3. The outcomes reveal that the inclusion of silica fume in concrete containing slag enhances the compressive strength of specimens. The order of increasing compressive strength in specimens with silica fume remains consistent across each w/cm ratio, mirroring the trend observed in type A specimens.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;11 demonstrates the compressive strength results of concrete specimens with varying silica fume percentages and w/cm ratios of 0.5, 0.4, and 0.3, respectively. Notably, the 28-day compressive strength of type C specimens was lower compared to similar specimens with 20% slag (type B) and even specimens without slag (type A). This discrepancy can be attributed to the slower hydration reaction of slag, resulting in reduced strength development in cement with slag compared to regular cement without slag. However, once the slag hydration reaction is completed, the microstructure of the concrete improves, leading to higher strength in concrete containing slag compared to concrete without slag. As seen in the results, the 91-day compressive strength of concrete containing slag (especially in the case of type C specimens) becomes comparable to specimens without slag and even to specimens with 20% slag. Thus, it can be inferred that the slag hydration reaction occurred before 28 days in type B specimens, resulting in higher 28-day compressive strength than in specimens without slag. However, in type C specimens, where the percentage of slag replacement increased, more time was required for the slag hydration reaction to complete in the concrete mixture. It is worth mentioning that the slow rate of slag hydration reaction contributes to reduced heat development in concrete, which may be advantageous during mass concreting. In type C specimens, the optimum percentages of silica fume in each w/cm ratio align with type B specimens, with the strength of specimens containing silica fume exhibiting improvement compared to those without it.\u003c/p\u003e \u003cp\u003eThe results suggest that the slag content in concrete influences the hydration process and the pore structure of the cement matrix, which affects the compressive strength of concrete. Some studies have shown that slag can react with water and calcium hydroxide to produce more calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H), enhancing the density and strength of the concrete. However, slag can also consume calcium hydroxide, lowering the pH value of the pore solution and reducing the alkalinity of the concrete. This can impair the passivation ability of the concrete and increase the vulnerability of steel to corrosion. Furthermore, slag can increase the porosity and permeability of the concrete at early ages, allowing more chloride ions and oxygen to penetrate into the concrete. These factors account for why concrete with slag (especially in the case of type C specimens) has poorer compressive strength than concrete without slag at 28 days. However, as the curing time progresses, the slag hydration reaction fills the pores in the cement matrix, improving the compressive strength of concrete. Therefore, at 91 days, concrete with slag becomes similar to or even higher than concrete without slag in terms of compressive strength. The addition of silica fume to the concrete mixture can further improve the compressive strength by decreasing the porosity and permeability of the cement matrix, as well as by forming additional C-S-H and C-A-H. The optimal dosages of silica fume depend on the w/cm ratios and the slag content in the concrete mixture [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;12 illustrates the compressive strength results of type D concrete specimens containing different percentages of silica fume, with w/cm ratios of 0.5, 0.4, and 0.3, respectively. In this specimen type, 50% of cement was substituted with slag, and with the addition of silica fume to the concrete, the strength of type D specimens, similar to type A, B, and C specimens, increased compared to concrete without silica fume. Notably, the compressive strength and the rate of strength gain in concrete containing slag may significantly vary.\u003c/p\u003e "},{"header":"4. Conclusions","content":"\u003cp\u003eThis study investigated the influence of silica fume and slag, and their interaction effects, on steel corrosion, carbonation depth, and compressive strength of concrete. Four groups of concrete specimens were designed and cast. The first group contained only silica fume with different w/cm ratios (0.25, 0.3, 0.4, and 0.5). Groups two, three, and four incorporated 20%, 35%, and 50% slag as a cement replacement, respectively, along with varying percentages of silica fume and w/cm ratios of 0.3, 0.4, and 0.5. The key findings of the research are summarized as follows:\u003c/p\u003e \u003cp\u003e1- The incorporation of silica fume into concrete exhibited beneficial effects, including an increase in resistance against steel corrosion. Among specimens in the first category, A-0.25-15, with a 0.25 w/cm ratio and 15% cement replaced by silica fume, exhibited the highest corrosion resistance (91 days). This specimen did not exceed the threshold level of -350mV and showed a nearly 46.7% increase in corrosion resistance compared to a similar specimen without silica fume (A-0.25-0).\u003c/p\u003e \u003cp\u003e2- Among specimens containing slag, specimen C-0.3-15 exhibited the highest corrosion resistance, with a corrosion potential of -329 mV after 91 days. This specimen demonstrated a 19% and 44% increase in corrosion resistance compared to similar specimens without slag (A-0.3-15) and without silica fume (C-0.3-0), respectively.\u003c/p\u003e \u003cp\u003e3- Analysis of the results revealed that increasing slag content up to 35% led to a reduction in carbonation depth. Conversely, incorporating 50% slag resulted in a significant increase in carbonation depth compared to specimens containing lower slag contents, performing nearly similar to Group A (without slag) specimens. Furthermore, the results indicated that the inclusion of silica fume within 10\u0026ndash;15% across all groups, with or without slag, decreased the carbonation depth.\u003c/p\u003e \u003cp\u003e4- Specimen C-0.3-10 exhibited the lowest carbonation depth, recording a value of 3.5 mm. Notably, this specimen demonstrated a 33% and 14.6% reduction in carbonation depth compared to specimens A-0.3-10 (similar concrete without slag) and C-0.3-0 (similar specimen without silica fume), respectively.\u003c/p\u003e \u003cp\u003e5- Specimen C-0.3-10 exhibited the highest compressive strength equal to 118 MPa. This value represented a 20.4% increase compared to the counterpart concrete specimen without slag (A-0.3-10), and an 18.4% enhancement in strength relative to the similar specimen lacking silica fume (C-0.3-0).\u003c/p\u003e \u003cp\u003e6- Increasing the slag replacement to 50% resulted in a remarkable decline in the performance of steel corrosion resistance, carbonation depth, and compressive strength, compared to specimens containing 35% slag, though the performance was comparable to similar specimens lacking any slag replacement.\u003c/p\u003e \u003cp\u003e7- The combined use of silica fume and slag as partial cement replacements showed a synergistic effect on the overall performance of concrete. This combination significantly enhanced corrosion resistance, reduced carbonation depth, and improved compressive strength. Among the groups studied, Group C which contained 35% slag, demonstrated better overall performance; while the specimens with 10\u0026ndash;15% silica fume in this group showed the best performance underscoring the positive interaction between these supplementary cementitious materials at optimized levels.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eConceptualization and design of the study: (Davood Mostofinejad ), (Mohsen Nasrollahi)Data collection: (Morteza Sadeghi), (Zahra Zajshoor)Analysis and interpretation of results: (Mohsen Nasrollahi), (Hadi Bahmani), Drafting the initial manuscript: (Mohsen Nasrollahi)Review and final editing: (Davood Mostofinejad ), (Mohsen Nasrollahi)Supervisor:(Davood Mostofinejad )\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eK.E. Kurtis, K. Mehta, A critical review of deterioration of concrete due to corrosion of reinforcing steel, Spec. 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Mater. 235 (2020) 117485.\u003c/li\u003e\n\u003cli\u003eS.A. Dadvar, D. Mostofinejad, H. Bahmani, Strengthening of Reinforced Concrete Columns with Combined Ultra-High-Performance Fiber-Reinforced Concrete and Glass Fiber-Reinforced Polymer Jacketing., ACI Struct. J. 118 (2021).\u003c/li\u003e\n\u003cli\u003eM. Hajiaghamemar, D. Mostofinejad, H. Bahmani, High volume of slag and polypropylene fibres in engineered cementitious composites: microstructure and mechanical properties, Mag. Concr. Res. 75 (2022) 607\u0026ndash;624.\u003c/li\u003e\n\u003cli\u003eJ.M. Scanton, M.R. Sherman, Fly ash concrete: An evaluation of chloride penetration testing methods, Concr. Int. 18 (1996) 57\u0026ndash;62.\u003c/li\u003e\n\u003cli\u003eJ.H. Luciano, C.K. Nmai, J.R. Delgado, Novel Approach to Developing High-Strength Concrete, Concr. Int. 13 (1991) 25\u0026ndash;29.\u003c/li\u003e\n\u003cli\u003eR. Gagn, A. Boisvert, M. 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Hamidah, M.S. Muhd Norhasri, I. Noorli, Effect of clay as a nanomaterial on corrosion potential of steel reinforcement embedded in ultra-high performance concrete, in: InCIEC 2015 Proc. Int. Civ. Infrastruct. Eng. Conf., Springer, 2016: pp. 679\u0026ndash;687.\u003c/li\u003e\n\u003cli\u003eA. Standard, Standard specification for concrete aggregates, ASTM Int. 1 (2003) 11.\u003c/li\u003e\n\u003cli\u003eA. Standard, Standard specification for Portland cement, ASTM Int. West Conshohocken, PA. (2009).\u003c/li\u003e\n\u003cli\u003eC. ASTM, Standard specification for chemical admixtures for concrete, Annu. B. ASTM Stand. (2013).\u003c/li\u003e\n\u003cli\u003eC. ASTM, Standard test method for half-cell potentials of uncoated reinforcing steel in concrete, ASTM C 876-91. (1999).\u003c/li\u003e\n\u003cli\u003eJ. Wang, J. Xie, C. Wang, J. Zhao, F. Liu, C. Fang, Study on the optimum initial curing condition for fly ash and GGBS based geopolymer recycled aggregate concrete, Constr. Build. Mater. 247 (2020) 118540.\u003c/li\u003e\n\u003cli\u003eY. Cao, C. Gehlen, U. Angst, L. Wang, Z. Wang, Y. Yao, Critical chloride content in reinforced concrete\u0026mdash;An updated review considering Chinese experience, Cem. Concr. Res. 117 (2019) 58\u0026ndash;68.\u003c/li\u003e\n\u003cli\u003eV. Marcos-Meson, A. Michel, A. Solgaard, G. Fischer, C. Edvardsen, T.L. Skovhus, Corrosion resistance of steel fibre reinforced concrete-A literature review, Cem. Concr. Res. 103 (2018) 1\u0026ndash;20.\u003c/li\u003e\n\u003cli\u003eM. Otieno, H. Beushausen, M. Alexander, Chloride-induced corrosion of steel in cracked concrete\u0026ndash;Part I: Experimental studies under accelerated and natural marine environments, Cem. Concr. Res. 79 (2016) 373\u0026ndash;385.\u003c/li\u003e\n\u003cli\u003eA.M. Zeyad, A.H. Khan, B.A. Tayeh, Durability and strength characteristics of high-strength concrete incorporated with volcanic pumice powder and polypropylene fibers, J. Mater. Res. Technol. 9 (2020) 806\u0026ndash;818.\u003c/li\u003e\n\u003cli\u003eA.M. Tahwia, G.M. Elgendy, M. Amin, Durability and microstructure of eco-efficient ultra-high-performance concrete, Constr. Build. Mater. 303 (2021) 124491.\u003c/li\u003e\n\u003cli\u003eY. Wei, P. Chen, S. Cao, H. Wang, Y. Liu, Z. Wang, W. Zhao, Prediction of Carbonation Depth for Concrete Containing Mineral Admixtures Based on Machine Learning, Arab. J. Sci. Eng. (2023) 1\u0026ndash;15.\u003c/li\u003e\n\u003cli\u003eJ. Skibsted, R. Snellings, Reactivity of supplementary cementitious materials (SCMs) in cement blends, Cem. Concr. Res. 124 (2019) 105799.\u003c/li\u003e\n\u003cli\u003eM.A. Uddin, M.T. Bashir, A.M. Khan, F. Alsharari, F. Farid, R. Alrowais, Effect of Silica Fume on Compressive Strength and Water Absorption of the Portland Cement\u0026ndash;Silica Fume Blended Mortar, Arab. J. Sci. Eng. (2023) 1\u0026ndash;9.\u003c/li\u003e\n\u003cli\u003eR.A.I. Albattat, Z. Jamshidzadeh, A.K.R. Alasadi, Assessment of compressive strength and durability of silica fume-based concrete in acidic environment, Innov. Infrastruct. Solut. 5 (2020) 1\u0026ndash;7.\u003c/li\u003e\n\u003cli\u003eW. Chen, H.J.H. Brouwers, The hydration of slag, part 2: reaction models for blended cement, J. Mater. Sci. 42 (2007) 444\u0026ndash;464.\u003c/li\u003e\n\u003cli\u003eT.C. Powers, T.L. Brownyard, Studies of the physical properties of hardened Portland cement paste, in: J. Proc., 1946: pp. 101\u0026ndash;132.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"iranian-journal-of-science-and-technology-transactions-of-civil-engineering","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"istc","sideBox":"Learn more about [Iranian Journal of Science and Technology, Transactions of Civil Engineering](http://link.springer.com/journal/40996)","snPcode":"40996","submissionUrl":"https://submission.nature.com/new-submission/40996/3","title":"Iranian Journal of Science and Technology, Transactions of Civil Engineering","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Durability, Slag, Silica fume, Carbonation depth, Steel corrosion, Chloride ion penetration","lastPublishedDoi":"10.21203/rs.3.rs-4414385/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4414385/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe utilization of supplementary cementitious materials (SCMs) in concrete attracted significant attention worldwide due to both environmental benefits and the potential for enhancing concrete's mechanical properties and durability. This study investigates the interaction effects of silica fume and ground granulated blast furnace slag (GGBFS) on the behavior of normal and high-strength concrete in terms of steel corrosion resistance, carbonation depth, and compressive strength. Fifty-two concrete specimens were prepared in four groups with different combinations of water-to-cementitious materials ratio (w/cm), slag content, and silica fume content and were tested. A method was employed to compare the corrosion initiation times of different concrete specimens. The results demonstrated that silica fume improves the concrete's resistance to steel corrosion by enhancing the density, strength, and durability of the cement matrix. The specimen with a w/cm ratio of 0.3 containing 35% slag and 10% silica fume achieved a 33% reduction in carbonation depth and a compressive strength of 118 MPa, representing a 20% increase compared to the similar specimen without slag. Furthermore, the specimen with a w/cm ratio of 0.3 containing 35% slag and 15% silica fume exhibited a 44% increase in steel corrosion resistance compared to the similar specimen without silica fume. While optimizing the combined content of slag and silica fume, this study highlights that their individual effects are less significant than their combined effect when used as partial replacements for cement.\u003c/p\u003e","manuscriptTitle":"Enhancing concrete strength and durability of normal and high- strength concrete: Exploring combined effects of optimized silica fume and slag","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-05-30 14:53:29","doi":"10.21203/rs.3.rs-4414385/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-05-31T06:45:09+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-05-27T18:43:08+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-05-26T04:25:53+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"330573797187470618871811015820600024590","date":"2024-05-17T13:55:45+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"15688257384848145822986823719293198061","date":"2024-05-17T09:47:06+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-05-17T09:43:43+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-05-14T14:44:10+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-05-14T14:44:10+00:00","index":"","fulltext":""},{"type":"submitted","content":"Iranian Journal of Science and Technology, Transactions of Civil Engineering","date":"2024-05-13T16:03:48+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"iranian-journal-of-science-and-technology-transactions-of-civil-engineering","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"istc","sideBox":"Learn more about [Iranian Journal of Science and Technology, Transactions of Civil Engineering](http://link.springer.com/journal/40996)","snPcode":"40996","submissionUrl":"https://submission.nature.com/new-submission/40996/3","title":"Iranian Journal of Science and Technology, Transactions of Civil Engineering","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"7a9fd274-71f6-46f7-a3c5-59be50dff72a","owner":[],"postedDate":"May 30th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-08-12T16:06:18+00:00","versionOfRecord":{"articleIdentity":"rs-4414385","link":"https://doi.org/10.1007/s40996-024-01573-9","journal":{"identity":"iranian-journal-of-science-and-technology-transactions-of-civil-engineering","isVorOnly":false,"title":"Iranian Journal of Science and Technology, Transactions of Civil Engineering"},"publishedOn":"2024-08-10 15:58:08","publishedOnDateReadable":"August 10th, 2024"},"versionCreatedAt":"2024-05-30 14:53:29","video":"","vorDoi":"10.1007/s40996-024-01573-9","vorDoiUrl":"https://doi.org/10.1007/s40996-024-01573-9","workflowStages":[]},"version":"v1","identity":"rs-4414385","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4414385","identity":"rs-4414385","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}