Impact of induced rapid surface carbonation (IRS-C) treatment on the steel corrosion in reinforced concrete: a counterintuitive effect

Impact of induced rapid surface carbonation (IRS-C) treatment on the steel corrosion in reinforced concrete: a counterintuitive effect | 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 Impact of induced rapid surface carbonation (IRS-C) treatment on the steel corrosion in reinforced concrete: a counterintuitive effect Raquel Ruiz, Julio Ramirez, Mirian Velay-Lizancos This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9272577/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Corrosion of steel reinforcement in concrete is one of the main issues plaguing aging infrastructure worldwide. While concrete’s carbonation is usually associated with an increased risk of corrosion, this study proposes a counterintuitive method that uses carbonation of hardened elements to reduce corrosion risk: the induced rapid surface carbonation (IRS-C) treatment. Besides, this study analyzes the impact of IRS-C on the corrosion resistance of precast reinforced concrete elements and explains the mechanisms behind it. The IRS-C treatment consists of placing the hardened samples in a vacuum chamber, filling it with CO 2 after removing the air, and leaving them for 48 hours, which induces rapid carbonation of the samples' outer surfaces. 12 concrete beams, 8 with and 4 without reinforcement, and 12 cylinders were used. Half of the samples were treated with IRS-C, while the remaining served as a reference. ASTM G109 results showed that the IRS-C treated samples had lower total corrosion than the untreated samples. The phenolphthalein test confirmed that the treatment did not affect pH near the reinforcement and therefore did not lower the chloride threshold for corrosion. Furthermore, water absorption and titration tests confirmed that IRS-C formed a low-porosity surface layer that reduced water and chloride penetration. Thus, the IRS-C treatment is a promising method to improve the corrosion resistance of precast reinforced concrete elements. Materials Engineering Civil Engineering Carbonation treatment corrosion durability precast concrete reinforced concrete. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1. Introduction Aging infrastructure is a concern faced by many countries worldwide. The United States alone has 44.1% of bridges that show signs of deterioration, and 39% of roads are at risk of failure [ 1 , 2 ]. In an effort to combat its aging infrastructure, the United States has invested over $ 631 billion in repairing its bridges and roads through the Infrastructure Investment and Jobs Act. However, the American Society of Civil Engineers (ASCE) estimates that it would require an additional $ 875 billion to fully rehabilitate this infrastructure [ 1 , 2 ]. Corrosion of steel reinforcement is one of the main issues regarding the deterioration of aging concrete infrastructure [ 3 ]. As concrete ages, it begins to crack due to expected use, exposing the steel reinforcement to moisture, oxygen, and chlorides, which causes it to corrode [ 4 , 5 ]. Weathering carbonation is a phenomenon in which the hydration products and water in concrete react with atmospheric carbon dioxide, forming CaCO 3 , depleting calcium hydroxide [ 6 – 8 ], and therefore lowering the pH of the concrete pore solution [ 9 ]. This phenomenon is often associated with an increased risk of reinforcement corrosion, since a lower pH around the reinforcement lowers the threshold of chlorides required to initiate corrosion [ 6 , 7 ]. However, recent studies on the enhancement of bio-receptivity [ 11 ] and about CO 2 capture [ 12 , 13 ] indicated that induced surface carbonation via vacuum system treatment can reduce water penetration and surface porosity, and decrease surface pH. While a reduction in pH, if it reaches the reinforcement, will lower the chloride threshold for corrosion, a reduction in permeability will increase corrosion resistance, since it is known that reductions in permeability and porosity reduce the penetration of water and chlorides [ 14 – 16 ]. Thus, it is unclear what impact induced surface carbonation via a vacuum system has on the actual corrosion resistance of steel-reinforced concrete. This study proposes a counterintuitive method that uses carbonation of hardened elements to reduce corrosion risk: the induced rapid surface carbonation (IRS-C) treatment. Furthermore, this study analyzes the impact of IRS-C on the corrosion resistance of precast reinforced concrete elements and explains the underlying mechanisms. 2. Research Significance Steel reinforcement corrosion remains a major concern for infrastructure. Most methods to improve corrosion resistance involve additives to the concrete mix or applying protective epoxy coatings over the steel reinforcement. While carbonation is usually associated with increased corrosion risk, this study demonstrates the potential of induced rapid surface carbonation (IRS-C) treatment to reduce corrosion risk in reinforced concrete elements and advances understanding of IRS-C’s mechanisms for preventing corrosion. This counterintuitive method offers a novel approach to enhancing the long-term corrosion resistance of concrete in precast elements without modifying the mixture design. 3. Materials and Methods 3.1. Materials 3.1.1. Concrete The concrete’s mix proportioning is presented in Table 1 . The cement used was Type IL (Portland-Limestone Cement, PLC), and the mixture used a water-to-cement ratio of 0.48. The coarse aggregate was a crushed limestone aggregate with a maximum nominal size of 2.54 cm. The coarse aggregate had a specific gravity of 2.75 and a water absorption of 1.39%. The fine aggregate used was a natural sand with a specific gravity of 2.65 and a water absorption of 1.54%. Table 1 Mix Proportions (per m 3 of concrete) Material Weight (kg) Cement PLC 360.9 Coarse aggregate 1120.4 Fine aggregate 780.9 Water 173.2 3.1.2. Reinforcement The reinforcing bars used in this study were grade 60, No. 4 uncoated steel bars with a diameter of 1.27 cm [0.5 in]. For the 8 reinforced beams, a total of 36 reinforcing bars were used. The reinforcing bars were prepared using the ASTM G109 standard method [ 17 ]. The mill scale on the surface was removed using a bench grinder and a wire wheel brush until the surface was near white metal. One end of the bar was then drilled and tapped to attach an M4 (8–32) screw and two nuts. The bar was then soaked in hexane for 24 hours. Each end of the bar was then taped with electroplater’s tape, so only a 20.3 cm (8 in) portion of the bar was exposed in the middle. An 8.9 cm (3.5 in) neoprene tube was then placed over the electroplater’s tape on each side and filled with two-part waterproof epoxy. Finally, each bar was weighed and placed in the beam molds, orientation and dimensions shown in Fig. 1 . 3.1.3. Batching and Specimen Preparation Before mixing, the aggregates were dried out and then stored in closed containers with their corresponding absorption water for 24 hours at laboratory conditions to ensure proper temperature and moisture. The coarse aggregate was added to the mixer. Once the mixer started, the sand, cement, and water were added. Once all the mix components were added, the mixer ran for 3 minutes, stopped, rested for 3 minutes, and finished with 2 minutes of mixing. Then, the slump test was performed, and samples were cast. The target slump was 5 ± 1 inch (12.7 cm ± 2.54 cm) A total of 12 cylinders, 4 unreinforced beams, and 8 reinforced beams were used in this experiment. The dimensions of the beam and cylinder specimens were 27.9 x 11.4 x 15.2 cm (11 x 4.5 x 6 in) and 20.3 x 10.2 cm (8 x 4 in), respectively. The detailed dimensions of the reinforced beam are displayed in Fig. 1 . Each specimen with reinforcement contained 3 bars, each 38.1 cm (15 in) long. The specimens were prepared following ASTM C192 [ 18 ]. After the slump was verified, the fresh concrete was placed into the beam and cylinder molds using a scoop in two equal layers. The cylinder molds were consolidated using a metal rod and a rubber mallet. Each layer was rodded 25 times, and the mold was tapped lightly on the outside 10 times with a rubber mallet. Since the beam molds had reinforcement, a vibration table was used for consolidation. Each layer vibrated for 1 minute. After consolidation, the concrete surface was trowelled to the edge of the mold, and covered with a plastic tarp for the first 24 hours. Since the volume of concrete required to produce the 12 beams and 12 cylinders exceeded the mixer's capacity (1.15 m 3 ), the concrete was mixed in two batches. The first batch had a slump of 14 cm (5.5 in) and the second had a slump of 10.2 cm (4 in). From each batch, a total of 6 beams and 6 cylinders were cast. To ensure any variation between batches does not affect the analysis of the treatment effect, the samples from each batch were divided into two groups: half were used as references, while the other half from each batch was treated with IRS-C. 3.2. Methods 3.2.1. Curing procedure and Induced Rapid Surface Carbonation Treatment (IRS-C treatment) Figure 2 summarizes the curing conditions and treatment duration of each sample. A total of 4 unreinforced samples, 8 reinforced samples, and 12 cylinders, were produced and kept for the first day in the molds. After one day, all specimens were cured for 27 days in a temperature and humidity-controlled room (95 ± 5% RH and 25 ± 1°C), then moved to a 50% relative humidity (RH) chamber for another 14 days. At 42 days, half of the samples (the treated group) were exposed to IRS-C treatment for 2 days, while the untreated samples remained in the 50% RH chamber. After treatment, the samples were returned to the 50% RH chamber. All samples were kept in the 50% RH chamber until 56 days of age. Depending on the sample type, each sample will be subject to its corresponding tests, as explained in the following sections, and presented in Fig. 2 . The IRS-C treatment was applied to half of the samples (treated samples) by placing each sample to be treated in the vacuum chamber. When the pressure gauge (PG) reading is 0 kPa, it corresponds to atmospheric pressure. After closing the lid, the air inside the chamber was vacuumed, with the pressure gauge reading (PRG) from 0 kPa in the PG to -101 kPa (-30 inHg). Then, another valve connecting the vacuum chamber to a CO 2 bottle was opened to add CO 2 until the PGR reached − 17 kPa (-5 inHg), which is below atmospheric pressure, since at atmospheric pressure the gauge reads 0 kPa, and the CO 2 valve was also closed. The samples were exposed for a total of 48 hours to this CO 2 -rich environment, with refills of CO 2 at 2, 3, 4, 20, and 44 hours to ensure availability of CO 2 during the full exposure time, considering that concrete carbonation would reduce the CO 2 available. 3.2.2. Flexural Strength Test and Initial Cracking Load Determination The four beams without bars were tested in 42 days to determine their flexural strength (2 untreated and 2 treated), in accordance with ASTM C293 [ 19 ]. A Forney flexural testing machine with a load capacity of 133 kN (30,000 lb) was used for these tests. The results from this testing were used to determine the force needed to induce initial cracking in the concrete of the beams with reinforcement. All beams were cracked under the same load to allow comparison of the results across the different groups. To ensure cracking, the pre-crack load was set to 1.4 times the maximum load measured across all unreinforced samples. 3.2.3. Carbonation Depth Test The phenolphthalein test was used to determine the carbonation depth of the flexural strength test specimens. Phenolphthalein is a pH indicator used to assess the pH of cementitious materials, as it appears dark pink at pH values above 10. The typical pH of concrete is between 12 and 13.8, and when carbonated, the range drops to below 9 [ 20 ]. To conduct this test, a phenolphthalein solution was sprayed on a freshly broken piece of concrete. After 30 minutes, the color change was observed and documented. The areas of carbonated concrete should remain colorless, while the non-carbonated concrete should be dark pink. The distance from the top surface to the dark pink area is the depth of carbonation. The average depth of carbonation was calculated by averaging the depths of color change at 10 evenly spaced points along the specimen edge, excluding measurements where an aggregate was present at the surface. 3.2.4. Compressive Strength Test A Forney compression testing machine with a load capacity of 356 kN (80,000 lb) was used to test 6 cylinders, 3 from each type (untreated and treated). The cylinders were tested at 90 days following the ASTM C39 standard [ 21 ] to assess the long-term compressive strength of both treated and untreated samples. This test was used to determine the effect of the IRS-C treatment on the compressive strength of the concrete. 3.2.5. Corrosion Test The corrosion test was performed in accordance with ASTM G109 [ 17 ] to determine the effect of the IRS-C treatment on the corrosion rate of reinforcing bars embedded in concrete specimens. A total of 4 beams with reinforcement (2 untreated for reference and 2 treated) were first pre-cracked as described in section 3.2.2, to simulate a scenario in which the structural element had already been loaded, and therefore some cracks had appeared. Then, the 4 reinforced beams were prepared for corrosion testing by securing a 15.2 x 7.6 x 7.6 cm (6 x 3 x 3 in) 3D printed plastic dam to the top of the beam over the cracked surface, as shown in Fig. 3 , with a silicone caulk. The top and side surfaces of the specimen (outside the dam) were then sealed with an epoxy sealer and allowed to dry according to the manufacturer’s recommendations. Testing began one month after the specimens were removed from 95 ± 5% RH, at 56 days. The prepared beam specimens were placed onto non-electrically conducting supports within a 50% RH chamber. The specimens were ponded with 450 mL of a 3% NaCl solution, with a loose-fitting cover to reduce evaporation. The solution was removed after 2 weeks, and the specimens were dried for the next 2 weeks, repeating this cycle until the total corrosion reached 150 coulombs (C). The macrocell voltage was measured over a 10Ω resistor connecting the top and bottom reinforcement. Every 4 weeks, beginning 1 week after the specimens were initially ponded. The corrosion potential was also measured at the same time as the voltage, following ASTM C876 [ 22 ]. The corrosion potential was measured against a copper sulfate reference electrode. A wet sponge was placed between the reference electrode and the concrete surface to reduce the fluctuations in corrosion potential reading. The corrosion potential was measured in two locations within the dam for each of the reinforcing bars. Using the measured voltage, the total corrosion of the specimen will be calculated using Eq. 1 and Eq. 2 [ 17 ]. \(\:{I}_{j}=\frac{{V}_{j}}{10}\) Eq. 1 \(\:{TC}_{j}={TC}_{j-1}+\frac{\left({t}_{j}-{t}_{j-1}\right)x({I}_{j}+{I}_{j-1})}{2}\) Eq. 2 Where V j is voltage over a 10Ω resistor (volts), TC is the total corrosion (coulombs), t j is the time (seconds) at which the measurement of the macrocell current is carried out, and I j is the macrocell is current (amps) at time, t j . During the corrosion testing, the specimens not subjected to corrosion are kept in the same 50% RH chamber until the end of the testing. 3.2.6. Void Content & Absorption Tests 3 cylindrical concrete specimens, 10 x 5 cm (4 x 2 in), were used for the void content and water absorption tests. Each specimen was cut from the bottom of a molded 20.3 x 10.2 cm (8 x 4 in) cylinder, to have the carbonation on the cross-sectional area. The mass of the specimens was measured after they were vacuum saturated in water for 18 hours, following ASTM C1202 [ 23 ]. The specimens were then placed in an oven at 60°C and measured every 24 hours until the change in mass was less than 0.2%. The void content was then calculated using Eq. 3. \(\:v\left(\%\right)=\:\frac{({M}_{sat}-{M}_{dry})}{{\rho\:}_{w}\bullet\:Vol}\bullet\:100\) Eq. 3 Where v(%) is the percent of voids in the sample, M sat is the mass of the saturated sample (g), M dry is the mass of the dried sample, ρ w is the density of water (g/cm), and Vol is the total volume of the sample (cm 3 ). The absorption procedure followed ASTM C1585 [ 24 ], where the specimen sides were sealed with electrical tape. The specimens were placed in water-filled containers, with the original bottom surface of each specimen submerged. The specimen was covered with a plastic sheet to prevent water loss. The specimens were measured for initial absorption over the first 6 hours, and for secondary absorption over the following 7 days. 3.2.7. Titration of Acid-Soluble Chlorides Titration was performed on corrosion specimens to determine the acid-soluble chloride content of the concrete matrix. This testing followed the ASTM C1152 standard, looking at the 2.54 cm (1 in) clear cover of concrete above the top reinforcing bar [ 25 ]. Four layers of concrete were tested per sample. Using a mill and diamond core bit to grind each 0.64 cm (0.25 in) layer of concrete into powder. Over 20 grams of powder from each layer were collected and stored in airtight containers to prevent contamination. 1.5 g of each layer was mixed with 10 g of boiling deionized water in a 250 mL beaker. 3 g of nitric acid was added to the solution, which was then boiled for 1 minute. The solution was cooled entirely before being placed in the OMNIS automatic titration machine. The sample was titrated with a standard 0.01 N silver nitrate solution, and the voltage was recorded. 4. Results and Discussion 4.1. Flexural and Compressive Strength and initial Crack Loading Four unreinforced beams were tested for flexural strength. The average flexural strength of untreated samples was 5.46 MPa, while that of treated samples was 5.52 MPa, corresponding to a load of 42.3 kN and 42.7 kN, respectively. The difference between the two groups is within the variation between samples of the same type (Table 2 ); thus, the accelerated carbonation treatment did not modify the flexural strength of the samples significantly. The maximum 3-point load recorded among all tested samples was 49 kN. The compressive strength of the untreated samples was 44.26 MPa and 44.47 MPa, respectively. Both the 3-Point flexural and compressive strengths differed by 5% and 0.5%, respectively, indicating that the IRS-C treatment did not affect the concrete's strength. Table 2 Flexural and Compressive Strength of Unreinforced Concrete Beams Property Untreated Treated 3-point Maximum Load (kN) 48.93 40.86 35.58 44.59 Average 3-point Maximum Load (kN) 42.29 42.72 3-point Flexural Strength (MPa) 6.32 5.28 4.60 5.76 Average 3-point Flexural Strength (MPa) 5.46 5.52 Compressive Strength (MPa) 43.61 44.70 44.98 43.95 44.28 44.85 Average Compressive Strength (MPa) 44.26 44.47 4.2. Carbonation Depth It was determined that the average carbonation depth of the treated samples was 1.41 mm ± 0.039 mm (Fig. 4 ), whereas the untreated samples had negligible carbonation. The steel bar in the samples is covered by 25.4 mm of concrete, meaning the carbonation reaches less than 6% of the total concrete cover. According to previous literature [ 26 ], if the carbonation depth is less than 80% of the total cover of the reinforcing bar, the carbonation will not affect the corrosion risk of the steel reinforcement. Thus, since the IRS-C treatment does not lower the pH level of the concrete around the steel reinforcement and the carbonation depth is less than 6% of the concrete cover, the treatment is expected not to affect the chloride threshold for corrosion of the reinforcement. 4.3. Corrosion A total of 8 reinforced beams were tested for 126 days in accordance with ASTM G109. Figure 5 shows the progression of total corrosion (TC) during the testing period. The final average total corrosion of the untreated samples was 1439 C, while that of the treated samples was 739 C. The treated samples have a lower average total corrosion than the untreated samples, and this difference becomes more pronounced after 75 days. In addition, Fig. 6 shows the average corrosion potential of the reinforcement where the treated specimens had overall lower corrosion potentials than the untreated samples. The data in Fig. 5 and Fig. 6 suggest that the IRS-C treatment reduces the total amount of corrosion over time. This is a counterintuitive idea, as usually carbonation is linked to an increased risk of corrosion [ 27 ]; However, the phenolphthalein results showed that the IRS-C treatment did not affect the pH of the concrete near the reinforcement, and therefore, the reduction of pH did not play a role in increasing the corrosion risk. Still, the mechanism behind the increase in corrosion resistance cannot be explained by that. Thus, further testing was performed to elucidate the mechanisms underlying IRS-C's enhancement of corrosion resistance. 4.4. Void Content and Water Absorption Table 3 shows the results of the void content and water absorption testing. The average void content for the untreated samples was 8.40%, and for the treated samples, 8.19%. Thus, the IRS-C treatment did not produce a significant reduction in the total void content. This result was expected, as the carbonation layer accounts for less than 3% of the specimens' total volume and would have little effect on the void content, except in that small layer. The similar void content between the untreated and treated samples also explains the negligible difference in their flexural and compressive strengths. Figure 7 presents the average time-dependent water absorption based on ASTM C1585. Note that only the initial rates of absorption were calculated, as only the initial absorption data followed a linear relationship with a correlation coefficient R 2 greater than 0.98 [ 24 ]. Table 3 summarizes the results of the test, including also the initial and secondary absorption. The average initial rate of water absorption was reduced by IRS-C by over 11%, while the initial and secondary absorption were reduced by over 13% and 6%, respectively (Table 3 ). These results are consistent with previous studies that found that calcium carbonate formation due to carbonation of surface Ca(OH) 2 reduced permeability in concrete [ 29 , 30 ]. The differences in water absorption and the initial rate of absorption, along with the phenolphthalein results, indicate that IRS-C produced a thin surface layer with low permeability that could explain the lower corrosion risk observed in the treated samples compared to the untreated samples. Table 3 Average Density, Void Content, and Water Absorption of Concrete Condition Density (kg/m 3 ) Void Content (%) Initial Absorption (mm) Secondary Absorption (mm) Initial Rate of Absorption (x10 -3 mm/s 1/2 ) Untreated 2373 8.40 1.61 4.24 10.3 Treated 2387 8.19 1.40 3.97 9.1 Reduction Due to Treatment (%) - 2.47% 13.04% 6.37% 11.65% 4.5. Titration of Acid-Soluble Chlorides The results from the titration of acid-soluble chlorides are shown in Fig. 8 . The percentage above the bars indicates the percent decrease in chloride from the untreated to the treated samples. These show that the percentage of chloride in each layer is lower in the treated samples than in the untreated samples. Since treated samples exhibit lower water absorption than untreated samples, their lower water penetration reduces chloride penetration. The top layer showed the largest difference in chloride percentage. The absorption and titration results indicate that IRS-C treatment forms a lower-porosity layer at the concrete surface. This layer is formed by the carbonation of Ca(OH) 2 that forms calcium carbonate, reducing the permeability of concrete to water and chlorides, since CaCO 3 occupies more pore space than calcium hydroxide. Thus, the carbonated layer has a denser concrete matrix, thereby reducing the amount of chlorides able to penetrate the concrete. Furthermore, the phenolphthalein tests showed that this carbonated layer with a lower pH is less than 2 mm thick, thus the concrete around the reinforcement is not affected by the reduction of pH, and therefore, the threshold of chlorides that will induce corrosion is not affected. 5. Conclusions This study proposed and analyzed the effect of the novel induced rapid surface carbonation (IRS-C) treatment to improve the corrosion resistance of precast concrete elements. The results of the corrosion test show that the IRS-C treatment reduces the risk of corrosion in precast reinforced elements, particularly under long-term exposure to salts and water. The reduction in the permeability of concrete to water and chlorides produced by IRS-C without negatively affecting the strength or the pH around the bars explains the observed counterintuitive positive effect of IRS-C in reducing corrosion risk. This counterintuitive method, which utilizes rapid carbonation to reduce corrosion risk, offers a novel approach to enhancing the long-term corrosion resistance of hardened concrete in precast elements without modifying the mixture design or their initial curing process. Declarations Funding. The authors gratefully acknowledge the funding (RLR, MV-L) from the Office of Naval Research (ONR) Award No. N000142512311. The experiments reported in this study were performed in the Pankow Materials Laboratories at Lyles School of Civil Engineering (Purdue University). Data availability statement The data from this paper will be available upon reasonable request. References Bridges ASCE’s 2025 Infrastructure Report Card |. Accessed: Feb. 05, 2026. [Online]. Available: https://infrastructurereportcard.org/cat-item/bridges-infrastructure/ Roads ASCE’s 2025 Infrastructure Report Card |. Accessed: Feb. 05, 2026. [Online]. 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Int J Electrochem Sci 4(8):1178–1195. 10.1016/S1452-3981(23)15216-3 Fuhaid AFA, Niaz A (May 2022) Carbonation and Corrosion Problems in Reinforced Concrete Structures. Buildings 12(5):586. 10.3390/buildings12050586 Water absorption (Jun. 2019) and chloride diffusivity of concrete under the coupling effect of uniaxial compressive load and freeze–thaw cycles. Constr Build Mater 209:566–576. 10.1016/j.conbuildmat.2019.03.091 Influence of (Oct. 2017) freeze-thaw cycles on capillary absorption and chloride penetration into concrete. Cem Concr Res 100:60–67. 10.1016/j.cemconres.2017.05.018 Experimental (Oct. 2025) predictive assessment of carbonation behavior in concrete with integrated electronic waste fibers. Mater 9:101346. 10.1016/j.nxmate.2025.101346 Tavakoli D, Saradar A, Langaroudi MAM, Moein MM, Karakouzian M (2025) The influence of calcium carbonate on the mechanical properties and durability of ultra-high-performance concrete with varying silica fume content. MATEC Web Conf 409:12003. 10.1051/matecconf/202540912003 Additional Declarations The authors declare no competing interests. Cite Share Download PDF Status: Posted Version 1 posted 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. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-9272577","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":617316238,"identity":"18afbd79-f125-4655-8a05-b6985102fe27","order_by":0,"name":"Raquel Ruiz","email":"","orcid":"","institution":"Purdue University","correspondingAuthor":false,"prefix":"","firstName":"Raquel","middleName":"","lastName":"Ruiz","suffix":""},{"id":617316239,"identity":"09195123-7b70-456d-94ce-c61d4362907a","order_by":1,"name":"Julio Ramirez","email":"","orcid":"","institution":"Purdue University","correspondingAuthor":false,"prefix":"","firstName":"Julio","middleName":"","lastName":"Ramirez","suffix":""},{"id":617316240,"identity":"a792a822-e9d4-4d0e-81d2-0deb517393f9","order_by":2,"name":"Mirian Velay-Lizancos","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3UlEQVRIiWNgGAWjYHACxgMMDBY8/CAmD1gggbAeoBYJHskGUrUwGBwgVovujOQDB362ScgY3+4x+/C2zYaBnz3HAK8WsxtpCQd72yR4zO6cMZ45ty2NQbLnDQEtZ84YHOAFabmRY8zM23aYweAGIVvOnP9w8C9Qi/EMsJb/DPYEtRzvYTgMssVAAqzlAAOQQUhLm8FhmXMSPBJ3jhUzzjmXzCNx5lkBfi2HmR8+fFNmY88/u3kzw5syOzn+9uQNeLWAASMbAyhqwICHsHIw+IPQMgpGwSgYBaMAAwAAy6NF3olHt6YAAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0002-1539-7923","institution":"Purdue University","correspondingAuthor":true,"prefix":"","firstName":"Mirian","middleName":"","lastName":"Velay-Lizancos","suffix":""}],"badges":[],"createdAt":"2026-03-31 00:32:07","currentVersionCode":1,"declarations":{"humanSubjects":false,"vertebrateSubjects":false,"conflictsOfInterestStatement":false,"humanSubjectEthicalGuidelines":false,"humanSubjectConsent":false,"humanSubjectClinicalTrial":false,"humanSubjectCaseReport":false,"vertebrateSubjectEthicalGuidelines":false},"doi":"10.21203/rs.3.rs-9272577/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9272577/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":106914952,"identity":"470faeda-966f-46c2-aede-7456ed8c801f","added_by":"auto","created_at":"2026-04-14 17:41:08","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":90798,"visible":true,"origin":"","legend":"\u003cp\u003eBeam specimen dimensions cm [in] with reinforcement\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-9272577/v1/0950d87eed0138e4b69e3a98.png"},{"id":106961238,"identity":"a43e1cc3-a89b-489f-8c1a-63e2b4a94c8b","added_by":"auto","created_at":"2026-04-15 09:24:47","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1076974,"visible":true,"origin":"","legend":"\u003cp\u003eDiagram summary of curing conditions, treatment, and testing program for each sample\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-9272577/v1/c999d06a63daa1b4d8e9eb96.png"},{"id":106961253,"identity":"8f4138d9-b757-43b1-8a56-8ac527d83822","added_by":"auto","created_at":"2026-04-15 09:24:51","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":231449,"visible":true,"origin":"","legend":"\u003cp\u003eConcrete beam specimen prepared for corrosion testing (a) diagram (b) picture of samples with the dam\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-9272577/v1/419a2443e61d264e4fec1cc9.png"},{"id":106961251,"identity":"0f8a4756-98c8-4720-b42a-d26d291354e4","added_by":"auto","created_at":"2026-04-15 09:24:51","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":585464,"visible":true,"origin":"","legend":"\u003cp\u003eBroken specimens (after flexural strength test) with phenolphthalein for carbonation depth examination\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-9272577/v1/8372ee4e38d3da7fe594c526.png"},{"id":106961244,"identity":"61ed5b47-41b4-4c01-bca1-5edb5cb65dce","added_by":"auto","created_at":"2026-04-15 09:24:49","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":37318,"visible":true,"origin":"","legend":"\u003cp\u003eTotal corrosion in specimens over a 126-day period\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-9272577/v1/7bf154e3389bbb84debc94f6.png"},{"id":106961910,"identity":"6f1f9062-6bbb-4ca5-b130-aec6d2b83dfc","added_by":"auto","created_at":"2026-04-15 09:27:41","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":162796,"visible":true,"origin":"","legend":"\u003cp\u003eCorrosion potentials of the reinforcing bars over a 126-day period\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-9272577/v1/7b11f3ed437d2736eccbf020.png"},{"id":106960341,"identity":"ac8f50fa-5ea8-474b-80a0-2a691cf4c93e","added_by":"auto","created_at":"2026-04-15 09:20:20","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":84099,"visible":true,"origin":"","legend":"\u003cp\u003eAverage time-dependent water absorption based on ASTM C1585 [24]\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-9272577/v1/d82dbd74b6f2a45a3e352384.png"},{"id":106960329,"identity":"ad570c69-e3f0-487a-a4b7-80dfba0ae5d4","added_by":"auto","created_at":"2026-04-15 09:20:15","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":267124,"visible":true,"origin":"","legend":"\u003cp\u003eChloride (per m\u003csup\u003e3\u003c/sup\u003e of concrete) by penetration depth, and the percent decrease\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-9272577/v1/da38c6be1f4523e8e66758e7.png"},{"id":106963529,"identity":"d7f443ba-4e4c-4b44-aaec-15cc7ec62e0c","added_by":"auto","created_at":"2026-04-15 09:45:00","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3374690,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9272577/v1/ed152a39-a8c3-485c-bde5-befc2127e272.pdf"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003eImpact of induced rapid surface carbonation (IRS-C) treatment on the steel corrosion in reinforced concrete: a counterintuitive effect\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eAging infrastructure is a concern faced by many countries worldwide. The United States alone has 44.1% of bridges that show signs of deterioration, and 39% of roads are at risk of failure [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. In an effort to combat its aging infrastructure, the United States has invested over \u003cspan\u003e$\u003c/span\u003e631\u0026nbsp;billion in repairing its bridges and roads through the Infrastructure Investment and Jobs Act. However, the American Society of Civil Engineers (ASCE) estimates that it would require an additional \u003cspan\u003e$\u003c/span\u003e875\u0026nbsp;billion to fully rehabilitate this infrastructure [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eCorrosion of steel reinforcement is one of the main issues regarding the deterioration of aging concrete infrastructure [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. As concrete ages, it begins to crack due to expected use, exposing the steel reinforcement to moisture, oxygen, and chlorides, which causes it to corrode [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eWeathering carbonation is a phenomenon in which the hydration products and water in concrete react with atmospheric carbon dioxide, forming CaCO\u003csub\u003e3\u003c/sub\u003e, depleting calcium hydroxide [\u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], and therefore lowering the pH of the concrete pore solution [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. This phenomenon is often associated with an increased risk of reinforcement corrosion, since a lower pH around the reinforcement lowers the threshold of chlorides required to initiate corrosion [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eHowever, recent studies on the enhancement of bio-receptivity [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] and about CO\u003csub\u003e2\u003c/sub\u003e capture [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] indicated that induced surface carbonation via vacuum system treatment can reduce water penetration and surface porosity, and decrease surface pH. While a reduction in pH, if it reaches the reinforcement, will lower the chloride threshold for corrosion, a reduction in permeability will increase corrosion resistance, since it is known that reductions in permeability and porosity reduce the penetration of water and chlorides [\u003cspan additionalcitationids=\"CR15\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Thus, it is unclear what impact induced surface carbonation via a vacuum system has on the actual corrosion resistance of steel-reinforced concrete.\u003c/p\u003e \u003cp\u003eThis study proposes a counterintuitive method that uses carbonation of hardened elements to reduce corrosion risk: the induced rapid surface carbonation (IRS-C) treatment. Furthermore, this study analyzes the impact of IRS-C on the corrosion resistance of precast reinforced concrete elements and explains the underlying mechanisms.\u003c/p\u003e"},{"header":"2. Research Significance","content":"\u003cp\u003eSteel reinforcement corrosion remains a major concern for infrastructure. Most methods to improve corrosion resistance involve additives to the concrete mix or applying protective epoxy coatings over the steel reinforcement. While carbonation is usually associated with increased corrosion risk, this study demonstrates the potential of induced rapid surface carbonation (IRS-C) treatment to reduce corrosion risk in reinforced concrete elements and advances understanding of IRS-C\u0026rsquo;s mechanisms for preventing corrosion. This counterintuitive method offers a novel approach to enhancing the long-term corrosion resistance of concrete in precast elements without modifying the mixture design.\u003c/p\u003e"},{"header":"3. Materials and Methods","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Materials\u003c/h2\u003e \u003cdiv id=\"Sec5\" class=\"Section3\"\u003e \u003ch2\u003e3.1.1. Concrete\u003c/h2\u003e \u003cp\u003eThe concrete\u0026rsquo;s mix proportioning is presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The cement used was Type IL (Portland-Limestone Cement, PLC), and the mixture used a water-to-cement ratio of 0.48. The coarse aggregate was a crushed limestone aggregate with a maximum nominal size of 2.54 cm. The coarse aggregate had a specific gravity of 2.75 and a water absorption of 1.39%. The fine aggregate used was a natural sand with a specific gravity of 2.65 and a water absorption of 1.54%.\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 \u003cp\u003eMix Proportions (per m\u003csup\u003e3\u003c/sup\u003e of concrete)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaterial\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eWeight (kg)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCement PLC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e360.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCoarse aggregate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1120.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFine aggregate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e780.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWater\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e173.2\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 \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003e3.1.2. Reinforcement\u003c/h2\u003e \u003cp\u003eThe reinforcing bars used in this study were grade 60, No. 4 uncoated steel bars with a diameter of 1.27 cm [0.5 in]. For the 8 reinforced beams, a total of 36 reinforcing bars were used. The reinforcing bars were prepared using the ASTM G109 standard method [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. The mill scale on the surface was removed using a bench grinder and a wire wheel brush until the surface was near white metal. One end of the bar was then drilled and tapped to attach an M4 (8\u0026ndash;32) screw and two nuts. The bar was then soaked in hexane for 24 hours. Each end of the bar was then taped with electroplater\u0026rsquo;s tape, so only a 20.3 cm (8 in) portion of the bar was exposed in the middle. An 8.9 cm (3.5 in) neoprene tube was then placed over the electroplater\u0026rsquo;s tape on each side and filled with two-part waterproof epoxy. Finally, each bar was weighed and placed in the beam molds, orientation and dimensions shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e3.1.3. Batching and Specimen Preparation\u003c/h2\u003e \u003cp\u003eBefore mixing, the aggregates were dried out and then stored in closed containers with their corresponding absorption water for 24 hours at laboratory conditions to ensure proper temperature and moisture. The coarse aggregate was added to the mixer. Once the mixer started, the sand, cement, and water were added. Once all the mix components were added, the mixer ran for 3 minutes, stopped, rested for 3 minutes, and finished with 2 minutes of mixing. Then, the slump test was performed, and samples were cast. The target slump was 5\u0026thinsp;\u0026plusmn;\u0026thinsp;1 inch (12.7 cm\u0026thinsp;\u0026plusmn;\u0026thinsp;2.54 cm)\u003c/p\u003e \u003cp\u003eA total of 12 cylinders, 4 unreinforced beams, and 8 reinforced beams were used in this experiment. The dimensions of the beam and cylinder specimens were 27.9 x 11.4 x 15.2 cm (11 x 4.5 x 6 in) and 20.3 x 10.2 cm (8 x 4 in), respectively. The detailed dimensions of the reinforced beam are displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Each specimen with reinforcement contained 3 bars, each 38.1 cm (15 in) long. The specimens were prepared following ASTM C192 [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. After the slump was verified, the fresh concrete was placed into the beam and cylinder molds using a scoop in two equal layers. The cylinder molds were consolidated using a metal rod and a rubber mallet. Each layer was rodded 25 times, and the mold was tapped lightly on the outside 10 times with a rubber mallet. Since the beam molds had reinforcement, a vibration table was used for consolidation. Each layer vibrated for 1 minute. After consolidation, the concrete surface was trowelled to the edge of the mold, and covered with a plastic tarp for the first 24 hours.\u003c/p\u003e \u003cp\u003eSince the volume of concrete required to produce the 12 beams and 12 cylinders exceeded the mixer's capacity (1.15 m\u003csup\u003e3\u003c/sup\u003e), the concrete was mixed in two batches. The first batch had a slump of 14 cm (5.5 in) and the second had a slump of 10.2 cm (4 in). From each batch, a total of 6 beams and 6 cylinders were cast. To ensure any variation between batches does not affect the analysis of the treatment effect, the samples from each batch were divided into two groups: half were used as references, while the other half from each batch was treated with IRS-C.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Methods\u003c/h2\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e3.2.1. Curing procedure and Induced Rapid Surface Carbonation Treatment (IRS-C treatment)\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e summarizes the curing conditions and treatment duration of each sample. A total of 4 unreinforced samples, 8 reinforced samples, and 12 cylinders, were produced and kept for the first day in the molds. After one day, all specimens were cured for 27 days in a temperature and humidity-controlled room (95\u0026thinsp;\u0026plusmn;\u0026thinsp;5% RH and 25\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u0026deg;C), then moved to a 50% relative humidity (RH) chamber for another 14 days.\u003c/p\u003e \u003cp\u003eAt 42 days, half of the samples (the treated group) were exposed to IRS-C treatment for 2 days, while the untreated samples remained in the 50% RH chamber. After treatment, the samples were returned to the 50% RH chamber. All samples were kept in the 50% RH chamber until 56 days of age. Depending on the sample type, each sample will be subject to its corresponding tests, as explained in the following sections, and presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe IRS-C treatment was applied to half of the samples (treated samples) by placing each sample to be treated in the vacuum chamber. When the pressure gauge (PG) reading is 0 kPa, it corresponds to atmospheric pressure. After closing the lid, the air inside the chamber was vacuumed, with the pressure gauge reading (PRG) from 0 kPa in the PG to -101 kPa (-30 inHg). Then, another valve connecting the vacuum chamber to a CO\u003csub\u003e2\u003c/sub\u003e bottle was opened to add CO\u003csub\u003e2\u003c/sub\u003e until the PGR reached\u0026thinsp;\u0026minus;\u0026thinsp;17 kPa (-5 inHg), which is below atmospheric pressure, since at atmospheric pressure the gauge reads 0 kPa, and the CO\u003csub\u003e2\u003c/sub\u003e valve was also closed. The samples were exposed for a total of 48 hours to this CO\u003csub\u003e2\u003c/sub\u003e-rich environment, with refills of CO\u003csub\u003e2\u003c/sub\u003e at 2, 3, 4, 20, and 44 hours to ensure availability of CO\u003csub\u003e2\u003c/sub\u003e during the full exposure time, considering that concrete carbonation would reduce the CO\u003csub\u003e2\u003c/sub\u003e available.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e3.2.2. Flexural Strength Test and Initial Cracking Load Determination\u003c/h2\u003e \u003cp\u003eThe four beams without bars were tested in 42 days to determine their flexural strength (2 untreated and 2 treated), in accordance with ASTM C293 [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. A Forney flexural testing machine with a load capacity of 133 kN (30,000 lb) was used for these tests. The results from this testing were used to determine the force needed to induce initial cracking in the concrete of the beams with reinforcement. All beams were cracked under the same load to allow comparison of the results across the different groups. To ensure cracking, the pre-crack load was set to 1.4 times the maximum load measured across all unreinforced samples.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003e3.2.3. Carbonation Depth Test\u003c/h2\u003e \u003cp\u003eThe phenolphthalein test was used to determine the carbonation depth of the flexural strength test specimens. Phenolphthalein is a pH indicator used to assess the pH of cementitious materials, as it appears dark pink at pH values above 10. The typical pH of concrete is between 12 and 13.8, and when carbonated, the range drops to below 9 [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. To conduct this test, a phenolphthalein solution was sprayed on a freshly broken piece of concrete. After 30 minutes, the color change was observed and documented. The areas of carbonated concrete should remain colorless, while the non-carbonated concrete should be dark pink. The distance from the top surface to the dark pink area is the depth of carbonation. The average depth of carbonation was calculated by averaging the depths of color change at 10 evenly spaced points along the specimen edge, excluding measurements where an aggregate was present at the surface.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e3.2.4. Compressive Strength Test\u003c/h2\u003e \u003cp\u003eA Forney compression testing machine with a load capacity of 356 kN (80,000 lb) was used to test 6 cylinders, 3 from each type (untreated and treated). The cylinders were tested at 90 days following the ASTM C39 standard [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] to assess the long-term compressive strength of both treated and untreated samples. This test was used to determine the effect of the IRS-C treatment on the compressive strength of the concrete.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e \u003ch2\u003e3.2.5. Corrosion Test\u003c/h2\u003e \u003cp\u003eThe corrosion test was performed in accordance with ASTM G109 [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] to determine the effect of the IRS-C treatment on the corrosion rate of reinforcing bars embedded in concrete specimens. A total of 4 beams with reinforcement (2 untreated for reference and 2 treated) were first pre-cracked as described in section 3.2.2, to simulate a scenario in which the structural element had already been loaded, and therefore some cracks had appeared. Then, the 4 reinforced beams were prepared for corrosion testing by securing a 15.2 x 7.6 x 7.6 cm (6 x 3 x 3 in) 3D printed plastic dam to the top of the beam over the cracked surface, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, with a silicone caulk. The top and side surfaces of the specimen (outside the dam) were then sealed with an epoxy sealer and allowed to dry according to the manufacturer\u0026rsquo;s recommendations.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTesting began one month after the specimens were removed from 95\u0026thinsp;\u0026plusmn;\u0026thinsp;5% RH, at 56 days. The prepared beam specimens were placed onto non-electrically conducting supports within a 50% RH chamber. The specimens were ponded with 450 mL of a 3% NaCl solution, with a loose-fitting cover to reduce evaporation. The solution was removed after 2 weeks, and the specimens were dried for the next 2 weeks, repeating this cycle until the total corrosion reached 150 coulombs (C). The macrocell voltage was measured over a 10Ω resistor connecting the top and bottom reinforcement. Every 4 weeks, beginning 1 week after the specimens were initially ponded. The corrosion potential was also measured at the same time as the voltage, following ASTM C876 [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. The corrosion potential was measured against a copper sulfate reference electrode. A wet sponge was placed between the reference electrode and the concrete surface to reduce the fluctuations in corrosion potential reading.\u003c/p\u003e \u003cp\u003eThe corrosion potential was measured in two locations within the dam for each of the reinforcing bars. Using the measured voltage, the total corrosion of the specimen will be calculated using Eq.\u0026nbsp;1 and Eq.\u0026nbsp;2 [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Taba\" border=\"1\"\u003e \u003ccolgroup cols=\"2\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{I}_{j}=\\frac{{V}_{j}}{10}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eEq.\u0026nbsp;1\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{TC}_{j}={TC}_{j-1}+\\frac{\\left({t}_{j}-{t}_{j-1}\\right)x({I}_{j}+{I}_{j-1})}{2}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eEq.\u0026nbsp;2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eWhere V\u003csub\u003ej\u003c/sub\u003e is voltage over a 10Ω resistor (volts), TC is the total corrosion (coulombs), t\u003csub\u003ej\u003c/sub\u003e is the time (seconds) at which the measurement of the macrocell current is carried out, and I\u003csub\u003ej\u003c/sub\u003e is the macrocell is current (amps) at time, t\u003csub\u003ej\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003eDuring the corrosion testing, the specimens not subjected to corrosion are kept in the same 50% RH chamber until the end of the testing.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e \u003ch2\u003e3.2.6. Void Content \u0026amp; Absorption Tests\u003c/h2\u003e \u003cp\u003e3 cylindrical concrete specimens, 10 x 5 cm (4 x 2 in), were used for the void content and water absorption tests. Each specimen was cut from the bottom of a molded 20.3 x 10.2 cm (8 x 4 in) cylinder, to have the carbonation on the cross-sectional area. The mass of the specimens was measured after they were vacuum saturated in water for 18 hours, following ASTM C1202 [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The specimens were then placed in an oven at 60\u0026deg;C and measured every 24 hours until the change in mass was less than 0.2%. The void content was then calculated using Eq.\u0026nbsp;3.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Tabb\" border=\"1\"\u003e \u003ccolgroup cols=\"2\"\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 \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:v\\left(\\%\\right)=\\:\\frac{({M}_{sat}-{M}_{dry})}{{\\rho\\:}_{w}\\bullet\\:Vol}\\bullet\\:100\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eEq.\u0026nbsp;3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eWhere v(%) is the percent of voids in the sample, M\u003csub\u003esat\u003c/sub\u003e is the mass of the saturated sample (g), M\u003csub\u003edry\u003c/sub\u003e is the mass of the dried sample, ρ\u003csub\u003ew\u003c/sub\u003e is the density of water (g/cm), and Vol is the total volume of the sample (cm\u003csup\u003e3\u003c/sup\u003e).\u003c/p\u003e \u003cp\u003eThe absorption procedure followed ASTM C1585 [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], where the specimen sides were sealed with electrical tape. The specimens were placed in water-filled containers, with the original bottom surface of each specimen submerged. The specimen was covered with a plastic sheet to prevent water loss. The specimens were measured for initial absorption over the first 6 hours, and for secondary absorption over the following 7 days.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e \u003ch2\u003e3.2.7. Titration of Acid-Soluble Chlorides\u003c/h2\u003e \u003cp\u003eTitration was performed on corrosion specimens to determine the acid-soluble chloride content of the concrete matrix. This testing followed the ASTM C1152 standard, looking at the 2.54 cm (1 in) clear cover of concrete above the top reinforcing bar [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Four layers of concrete were tested per sample. Using a mill and diamond core bit to grind each 0.64 cm (0.25 in) layer of concrete into powder. Over 20 grams of powder from each layer were collected and stored in airtight containers to prevent contamination. 1.5 g of each layer was mixed with 10 g of boiling deionized water in a 250 mL beaker. 3 g of nitric acid was added to the solution, which was then boiled for 1 minute. The solution was cooled entirely before being placed in the OMNIS automatic titration machine. The sample was titrated with a standard 0.01 N silver nitrate solution, and the voltage was recorded.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"4. Results and Discussion","content":"\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e4.1. Flexural and Compressive Strength and initial Crack Loading\u003c/h2\u003e \u003cp\u003eFour unreinforced beams were tested for flexural strength. The average flexural strength of untreated samples was 5.46 MPa, while that of treated samples was 5.52 MPa, corresponding to a load of 42.3 kN and 42.7 kN, respectively. The difference between the two groups is within the variation between samples of the same type (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e); thus, the accelerated carbonation treatment did not modify the flexural strength of the samples significantly. The maximum 3-point load recorded among all tested samples was 49 kN.\u003c/p\u003e \u003cp\u003eThe compressive strength of the untreated samples was 44.26 MPa and 44.47 MPa, respectively. Both the 3-Point flexural and compressive strengths differed by 5% and 0.5%, respectively, indicating that the IRS-C treatment did not affect the concrete's strength.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eFlexural and Compressive Strength of Unreinforced Concrete Beams\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eProperty\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eUntreated\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTreated\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e3-point Maximum Load (kN)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e48.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e40.86\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e35.58\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e44.59\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAverage 3-point Maximum Load (kN)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e42.29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e42.72\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e3-point Flexural Strength (MPa)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e6.32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.28\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.76\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAverage 3-point Flexural Strength (MPa)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5.46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.52\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eCompressive Strength (MPa)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e43.61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e44.70\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e44.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e43.95\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e44.28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e44.85\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAverage Compressive Strength (MPa)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e44.26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e44.47\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 \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e4.2. Carbonation Depth\u003c/h2\u003e \u003cp\u003eIt was determined that the average carbonation depth of the treated samples was 1.41 mm\u0026thinsp;\u0026plusmn;\u0026thinsp;0.039 mm (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e), whereas the untreated samples had negligible carbonation. The steel bar in the samples is covered by 25.4 mm of concrete, meaning the carbonation reaches less than 6% of the total concrete cover. According to previous literature [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e], if the carbonation depth is less than 80% of the total cover of the reinforcing bar, the carbonation will not affect the corrosion risk of the steel reinforcement. Thus, since the IRS-C treatment does not lower the pH level of the concrete around the steel reinforcement and the carbonation depth is less than 6% of the concrete cover, the treatment is expected not to affect the chloride threshold for corrosion of the reinforcement.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003e4.3. Corrosion\u003c/h2\u003e \u003cp\u003eA total of 8 reinforced beams were tested for 126 days in accordance with ASTM G109. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e shows the progression of total corrosion (TC) during the testing period. The final average total corrosion of the untreated samples was 1439 C, while that of the treated samples was 739 C. The treated samples have a lower average total corrosion than the untreated samples, and this difference becomes more pronounced after 75 days. In addition, Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows the average corrosion potential of the reinforcement where the treated specimens had overall lower corrosion potentials than the untreated samples. The data in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e suggest that the IRS-C treatment reduces the total amount of corrosion over time. This is a counterintuitive idea, as usually carbonation is linked to an increased risk of corrosion [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]; However, the phenolphthalein results showed that the IRS-C treatment did not affect the pH of the concrete near the reinforcement, and therefore, the reduction of pH did not play a role in increasing the corrosion risk.\u003c/p\u003e \u003cp\u003eStill, the mechanism behind the increase in corrosion resistance cannot be explained by that. Thus, further testing was performed to elucidate the mechanisms underlying IRS-C's enhancement of corrosion resistance.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003e4.4. Void Content and Water Absorption\u003c/h2\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the results of the void content and water absorption testing. The average void content for the untreated samples was 8.40%, and for the treated samples, 8.19%. Thus, the IRS-C treatment did not produce a significant reduction in the total void content. This result was expected, as the carbonation layer accounts for less than 3% of the specimens' total volume and would have little effect on the void content, except in that small layer. The similar void content between the untreated and treated samples also explains the negligible difference in their flexural and compressive strengths.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e presents the average time-dependent water absorption based on ASTM C1585. Note that only the initial rates of absorption were calculated, as only the initial absorption data followed a linear relationship with a correlation coefficient R\u003csup\u003e2\u003c/sup\u003e greater than 0.98 [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e summarizes the results of the test, including also the initial and secondary absorption.\u003c/p\u003e \u003cp\u003eThe average initial rate of water absorption was reduced by IRS-C by over 11%, while the initial and secondary absorption were reduced by over 13% and 6%, respectively (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). These results are consistent with previous studies that found that calcium carbonate formation due to carbonation of surface Ca(OH)\u003csub\u003e2\u003c/sub\u003e reduced permeability in concrete [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe differences in water absorption and the initial rate of absorption, along with the phenolphthalein results, indicate that IRS-C produced a thin surface layer with low permeability that could explain the lower corrosion risk observed in the treated samples compared to the untreated samples.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eAverage Density, Void Content, and Water Absorption of Concrete\u003c/p\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=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCondition\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDensity (kg/m\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eVoid Content (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eInitial Absorption (mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSecondary Absorption (mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eInitial Rate of Absorption\u003c/p\u003e \u003cp\u003e(x10\u003csup\u003e-3\u003c/sup\u003emm/s\u003csup\u003e1/2\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\u003eUntreated\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2373\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e8.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e4.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e10.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTreated\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2387\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e8.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e9.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eReduction Due to Treatment (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.47%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e13.04%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e6.37%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e11.65%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003e4.5. Titration of Acid-Soluble Chlorides\u003c/h2\u003e \u003cp\u003eThe results from the titration of acid-soluble chlorides are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. The percentage above the bars indicates the percent decrease in chloride from the untreated to the treated samples. These show that the percentage of chloride in each layer is lower in the treated samples than in the untreated samples. Since treated samples exhibit lower water absorption than untreated samples, their lower water penetration reduces chloride penetration. The top layer showed the largest difference in chloride percentage.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe absorption and titration results indicate that IRS-C treatment forms a lower-porosity layer at the concrete surface. This layer is formed by the carbonation of Ca(OH)\u003csub\u003e2\u003c/sub\u003e that forms calcium carbonate, reducing the permeability of concrete to water and chlorides, since CaCO\u003csub\u003e3\u003c/sub\u003e occupies more pore space than calcium hydroxide. Thus, the carbonated layer has a denser concrete matrix, thereby reducing the amount of chlorides able to penetrate the concrete. Furthermore, the phenolphthalein tests showed that this carbonated layer with a lower pH is less than 2 mm thick, thus the concrete around the reinforcement is not affected by the reduction of pH, and therefore, the threshold of chlorides that will induce corrosion is not affected.\u003c/p\u003e \u003c/div\u003e"},{"header":"5. Conclusions","content":"\u003cp\u003eThis study proposed and analyzed the effect of the novel induced rapid surface carbonation (IRS-C) treatment to improve the corrosion resistance of precast concrete elements.\u003c/p\u003e \u003cp\u003eThe results of the corrosion test show that the IRS-C treatment reduces the risk of corrosion in precast reinforced elements, particularly under long-term exposure to salts and water.\u003c/p\u003e \u003cp\u003eThe reduction in the permeability of concrete to water and chlorides produced by IRS-C without negatively affecting the strength or the pH around the bars explains the observed counterintuitive positive effect of IRS-C in reducing corrosion risk.\u003c/p\u003e \u003cp\u003eThis counterintuitive method, which utilizes rapid carbonation to reduce corrosion risk, offers a novel approach to enhancing the long-term corrosion resistance of hardened concrete in precast elements without modifying the mixture design or their initial curing process.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eFunding.\u003c/h2\u003e \u003cp\u003eThe authors gratefully acknowledge the funding (RLR, MV-L) from the Office of Naval Research (ONR) Award No. N000142512311. The experiments reported in this study were performed in the Pankow Materials Laboratories at Lyles School of Civil Engineering (Purdue University).\u003c/p\u003e\u003ch2\u003eData availability statement\u003c/h2\u003e \u003cp\u003eThe data from this paper will be available upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBridges ASCE\u0026rsquo;s 2025 Infrastructure Report Card |. Accessed: Feb. 05, 2026. [Online]. Available: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://infrastructurereportcard.org/cat-item/bridges-infrastructure/\u003c/span\u003e\u003cspan address=\"https://infrastructurereportcard.org/cat-item/bridges-infrastructure/\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRoads ASCE\u0026rsquo;s 2025 Infrastructure Report Card |. Accessed: Feb. 05, 2026. [Online]. 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Mater 9:101346. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.nxmate.2025.101346\u003c/span\u003e\u003cspan address=\"10.1016/j.nxmate.2025.101346\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTavakoli D, Saradar A, Langaroudi MAM, Moein MM, Karakouzian M (2025) The influence of calcium carbonate on the mechanical properties and durability of ultra-high-performance concrete with varying silica fume content. MATEC Web Conf 409:12003. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1051/matecconf/202540912003\u003c/span\u003e\u003cspan address=\"10.1051/matecconf/202540912003\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[{"identity":"05cf8613-c544-4982-aa29-512845e1906c","identifier":"10.13039/100000006","name":"Office of Naval Research","awardNumber":"N000142512311","order_by":0}],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"Purdue University West Lafayette","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Carbonation treatment, corrosion, durability, precast concrete, reinforced concrete.","lastPublishedDoi":"10.21203/rs.3.rs-9272577/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9272577/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eCorrosion of steel reinforcement in concrete is one of the main issues plaguing aging infrastructure worldwide. While concrete\u0026rsquo;s carbonation is usually associated with an increased risk of corrosion, this study proposes a counterintuitive method that uses carbonation of hardened elements to reduce corrosion risk: the induced rapid surface carbonation (IRS-C) treatment. Besides, this study analyzes the impact of IRS-C on the corrosion resistance of precast reinforced concrete elements and explains the mechanisms behind it. The IRS-C treatment consists of placing the hardened samples in a vacuum chamber, filling it with CO\u003csub\u003e2\u003c/sub\u003e after removing the air, and leaving them for 48 hours, which induces rapid carbonation of the samples' outer surfaces. 12 concrete beams, 8 with and 4 without reinforcement, and 12 cylinders were used. Half of the samples were treated with IRS-C, while the remaining served as a reference. ASTM G109 results showed that the IRS-C treated samples had lower total corrosion than the untreated samples. The phenolphthalein test confirmed that the treatment did not affect pH near the reinforcement and therefore did not lower the chloride threshold for corrosion. Furthermore, water absorption and titration tests confirmed that IRS-C formed a low-porosity surface layer that reduced water and chloride penetration. Thus, the IRS-C treatment is a promising method to improve the corrosion resistance of precast reinforced concrete elements.\u003c/p\u003e","manuscriptTitle":"Impact of induced rapid surface carbonation (IRS-C) treatment on the steel corrosion in reinforced concrete: a counterintuitive effect","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-14 17:41:03","doi":"10.21203/rs.3.rs-9272577/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"c5f48ae5-f899-437b-9311-b7b51b2e4e19","owner":[],"postedDate":"April 14th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":66115403,"name":"Materials Engineering"},{"id":66115404,"name":"Civil Engineering"}],"tags":[],"updatedAt":"2026-04-14T17:41:04+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-14 17:41:03","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9272577","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9272577","identity":"rs-9272577","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}