Accelerated Alkali–Carbonate Reaction in Aggregates

Accelerated Alkali–Carbonate Reaction in Aggregates | 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PDF Research Article Accelerated Alkali–Carbonate Reaction in Aggregates OMAR HUSSIEN OMAR This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7895197/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 This study develops and evaluates an accelerated testing method to assess alkali-carbonate reaction (ACR) activity in dolomitic aggregates, a critical step in preventing long-term concrete damage. The research involved a comprehensive analysis of the ACR and potential alkali-silica reaction (ASR) activity of six different types of dolomitic limestone aggregates sourced from quarries in Egypt. This was performed using a novel protocol and compared against established standards, including RILEM AAR-2, RILEM AAR-5, and ASTM C1105. Aggregate samples were prepared in two size fractions, 2.5–5 mm and 5–10 mm, and were subsequently cured in a 1 mol/L tetramethylammonium hydroxide (TMAH) solution at elevated temperatures of 60°C and 80°C. The use of a TMAH solution was a key methodological choice, as it has been reported to react with dolomite while remaining inert with the reactive silica phases common in ASR, thereby isolating the effects of ACR-induced expansion. The study systematically investigated the impact of aggregate particle size and curing temperature on the expansion behavior of concrete microbar specimens to assess their alkali-carbonate reactivity. The results indicated that the specimens fabricated from larger 5–10 mm aggregates and cured at the higher temperature of 80°C exhibited the most significant and rapid expansion, exceeding a preliminary threshold of 0.1% after 42 days. While this value requires further validation, it is proposed as a potential indicator for rapidly identifying ACR activity in aggregates. To substantiate these findings, microstructural analysis was conducted using a scanning electron microscope (SEM) combined with energy-dispersive X-ray spectroscopy (EDS). The analysis of the reaction products confirmed that dolomite crystals within the aggregates reacted with the TMAH solution, resulting in the formation of calcite (CaCO₃) and brucite (Mg (OH)₂), the characteristic products of the dedolomitization process. No evidence of ASR gel was found, confirming the selectivity of the test method. These findings support the viability of the accelerated TMAH method as a rapid and specific tool for evaluating the ACR potential of carbonate aggregates. Alkali–Carbonate Reaction (ACR) Dolomitic Limestone Aggregate Durability Accelerated Testing Dedolomitization ASTM Standards Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 1. Introduction and Background The long-term durability of concrete structures can be severely compromised by internal chemical reactions known as alkali-aggregate reactions (AAR) [ 1 ]. These are broadly categorized into alkali-silica reaction (ASR) and alkali-carbonate reaction (ACR) [ 2 ]. ACR, the focus of this study, occurs when alkali hydroxides in the concrete's pore solution react with specific dolomitic constituents within carbonate aggregates [ 3 ]. This chemical interaction initiates a process called dedolomitization, where dolomite reacts to form expansive secondary minerals, primarily brucite and calcite [ 4 ]. The resulting volumetric instability leads to internal pressure, microcracking, and the progressive deterioration of the concrete’s structural integrity [ 5 ]. Since this phenomenon was first identified by Swenson in 1957 [ 6 ], extensive research has been dedicated to developing reliable detection methods. Established protocols include petrographic analysis (ASTM C295), the rock prism method (ASTM C586), and the concrete prism method (ASTM C1105) [ 7 ]. However, these methods have critical limitations; petrographic analysis is highly dependent on the petrographer's experience, while the concrete prism test (ASTM C1105) is reliable but can require up to a year to yield conclusive results [ 8 ]. Furthermore, other accelerated tests often struggle to differentiate expansion caused by ACR from that caused by ASR [ 2 ]. This ambiguity creates a critical need for a new testing method that is both rapid and specific to the ACR mechanism [ 9 ]. Recent studies have indicated that tetramethylammonium hydroxide (TMAH) solutions may offer a solution, as TMAH has been reported to selectively react with dolomite while remaining inert with common reactive silica forms [ 10 ]. This study aims to develop and evaluate such an accelerated test method using a 1 mol/L TMAH solution to rapidly determine the ACR potential of dolomitic aggregates [ 11 ]. 2. Material and Preparation Tests on Samples 2.1 Aggregate Selection and Characterization The six aggregate types used in this study were dolomitic limestones collected from quarries in two primary regions of Egypt: Suez (S1, S2, S3) and Alamein (A1, A2, A3). The cement used was a low-alkali Portland cement (Type II) with a verified Na₂O equivalent of 0.54%. Petrographic analysis (ASTM C295) and X-ray diffraction (XRD) were performed to identify the mineralogical composition [12] . The analysis confirmed the presence of dolomite and calcite as the primary mineral phases. The key properties of each aggregate are consolidated in Table 1. Sample ID CaCO₃ MgCO₃ Al₂O₃ Fe₂O₃ Na₂O K₂O Cl ⁻ SO ₄² ⁻ SiO ₂ #1A 79.63 4.53 0.15 0.06 0.20 0.04 0.06 0.32 15.00 #2A 77.21 3.93 0.10 0.08 0.13 0.04 0.08 0.32 18.00 #3A 78.49 4.20 0.13 0.08 0.16 0.05 0.07 0.42 18.00 #1S 86.43 4.29 0.11 0.09 0.14 0.06 0.08 0.35 8.00 #2S 79.02 1.05 0.22 0.05 0.14 0.07 0.05 0.36 19.00 #3S 79.65 0.93 0.17 0.03 0.09 0.04 0.03 0.29 18.00 2.2 Petrographic test ASTM C295 and Geological data Region Sample Geological data for aggregate sources Name Age lithologies Region 1 Limestone #1A Jonesboro Limestone; Mascot Dolomite; Kingsport Formation; Cambrian – Ordovician Guzhangian – Floian (498.2 – 471.6 Ma) Major: {limestone,dolostone}, Incidental:{sandstone} Limestone #2A Mascot Dolomite; Kingsport Formation Ordovician -Stage 10 – Floian (485.4 – 471.2834 Ma) Major: {dolostone,limestone}, Minor:{sandstone}. Fine-grained, well-bedded cherty dolomite Limestone #3A Jonesboro Limestone; Mascot Dolomite; Kingsport Formation; Cambrian – Ordovician Guzhangian – Floian (498.2 – 471.6 Ma) Major: {limestone,dolostone}, Incidental: {sandstone}. Numerous interbeds of dark-gray dolomite. Region 2 Limestone #1S Monteagle Limestone Mississippian -Visean (340.3125 – 332.05 Ma) Major: {limestone}, Incidental: {chert} (sand, shale, carbonate, Limestone, chert. Limestone #2S Bangor Limestone and Hartselle Formation Mississippian – Visean – Serpukhovian (333.525 – 326.15 Ma) Major: {limestone}, Incidental: {sandstone, shale} Limestone #3S Newala Formation, Mascot Dolomite, and Kingsport Formation Ordovician – Termadocian – Dapingian (477.7 – 470 Ma) Major: {dolostone, limestone}, Minor: {sandstone}, Dolomite - Light-gray, fine-grained, well-bedded cherty dolomite; chert-matrix quartz sandstone at base 2.3 Aggregate alkali carbon reaction for 1 year ASTM C1105 to compare with new method Sample No. ACR Expansion (%) Limestone #1A 0.021 Limestone #2A 0.015 Limestone #3A 0.011 Limestone #1S 0.024 Limestone #2S 0.028 Limestone #3S 0.027 3. Justification for TMAH as a Selective Reagent for ACR 3.1 The Challenge of Differentiating Alkali-Aggregate Reactions A primary challenge in assessing aggregate durability is the frequent coexistence of both ACR and ASR mechanisms [ 13 ]. Traditional testing methods using NaOH or KOH can accelerate both reactions simultaneously, making it difficult to isolate the expansion caused solely by ACR. The central hypothesis of this study is that Tetramethylammonium Hydroxide (TMAH) can overcome this limitation [ 10 ]. The selectivity of TMAH is supported by recent studies, which indicate that it reacts with dolomite but not with common forms of reactive silica [ 10 ]. The large size of the tetramethylammonium cation [N(CH₃)₄⁺] is believed to sterically hinder its ability to participate in the formation of ASR gel, unlike smaller Na⁺ and K⁺ ions [ 14 ]. The most compelling support for TMAH selectivity comes from the direct microstructural evidence gathered in this study, where SEM-EDS analysis found no evidence of ASR gel in any of the concrete microbars, confirming that the ASR reaction was not initiated. 3.2 Theoretical and Literature Basis for Selectivity The selectivity of TMAH is supported by recent studies, which indicate that it reacts with dolomite but not with common forms of reactive silica. The chemical basis for this selectivity lies in the distinct reaction pathways of ACR and ASR. ACR Mechanism : The reaction is a process of dedolomitization , where alkali hydroxides react with dolomite [(CaMg)(CO3​)2​] to form calcite [CaCO3​] and brucite [Mg(OH)2​]. This is a reaction with the carbonate mineral structure. ASR Mechanism : This reaction involves the dissolution of reactive silica by hydroxyl ions, followed by the formation of an expansive alkali-silica gel. The large size of the tetramethylammonium cation [N(CH3​)4+​] is believed to sterically hinder its ability to participate in the formation of the ASR gel, unlike the smaller Na + and K + ions. While it can supply the hydroxyl ions needed for the dedolomitization of dolomite, it does not effectively contribute to the polymerization of silica that forms the expansive gel. 3.3 Empirical Validation from Microstructural Analysis The most compelling support for TMAH selectivity comes from the direct microstructural evidence gathered in this study. The aggregates used contained significant quantities of SiO2​ (up to 19.00% in sample #2S) and were identified as having potential for both ACR and ASR activity. Despite the presence of this reactive silica, the results consistently and exclusively pointed to an ACR mechanism. Exclusive Presence of ACR Products : SEM-EDS analysis conducted on reacted aggregate grains identified the formation of calcite and rod-like brucite crystals, which are the characteristic products of dedolomitization. Confirmed Absence of ASR Gel : Critically, the same SEM-EDS analysis found no evidence of ASR gel in any of the concrete microbars or rock prisms. This confirms that even with ample silica present in the aggregate, the ASR reaction was not initiated by the TMAH solution. Damage Origination : Microscopic examination consistently showed that expansion cracks originated within the dolomite-rich regions of the aggregates and propagated outwards. This provides a direct physical link between the observed expansion and the reaction occurring in the carbonate phases, not the silica phases. 4. Preparation of Concrete Microbars and Dolomitic Rock Prisms for Expansion Rate Testing Concrete microbars (4x4x16 cm) were prepared in accordance with the RILEM AAR-5 standard [ 15 ]. Each mixture used an aggregate-to-cement ratio of 1:1 and a water-to-cement ratio of 0.32. After demoulding, the initial length (L₀) of each specimen was measured. 4.1 Accelerated Expansion Testing The demoulded specimens were submerged in a 1 mol/L tetramethylammonium hydroxide (TMAH) solution in sealed containers. The containers were placed in ovens at controlled temperatures of 60°C and 80°C to accelerate the reaction. Length change measurements were recorded for each specimen, typically every 14 days, over the testing period. The expansion rate for all specimens was calculated using the standard formula shown in Eq. (1): Pt​=L0​(Lt​−L0​)​×100% (1) Where: Pt​ = the expansion percentage (%) at time t . Lt​ = the length of the specimen at time t (mm). L0​ = the initial length of the specimen (mm). The final expansion value for each data point was taken as the average of three replicate specimens. 4.2 Microstructural Analysis After the expansion testing period, selected concrete microbars were sectioned to prepare thin slices for examination with a polarizing microscope. Additionally, reacted aggregate grains were extracted from the specimens for analysis using a Scanning Electron Microscope combined with Energy Dispersive X-ray Spectroscopy (SEM-EDS) to identify the chemical composition of the reaction products. 4.3 Testing and Characterization X-ray diffraction analysis was performed to determine the composition of the self-made cement without K+, Na+, and Mg2+, as well as the composition of dolomitic rocks. The length changes of all specimens, prepared using different aggregates, were measured at various ages, and their expansion ratios were calculated using the previously mentioned formula. The length change value used was the average of three replicate specimens. The morphologies of aggregate grains containing dolomite, selected from the microbars cured in TMAH solution, were examined using Scanning Electron Microscope combined with Energy Dispersive X-ray Spectroscopy analysis. Orthogonal polarized light microscopy was also used to study the cracks caused by ACR. The expansion rate of the concrete microbars cured in a 1-mol/L TMAH solution at 80°C is shown in Fig. 4a. Initially, the expansion was slow but began to increase after 28 days. During the early curing stages, the expansion was minimal due to the shrinkage of cement without alkali, which partly offset the expansion caused by ACR. This shrinkage was attributed to the formation of hydration products that had a lower volume during the initial stages. Later, the expansion rate of the concrete microbars stabilized, and the expansion became more noticeable. This suggests that the ACR contribution to the expansion became significant at later stages. All experiments were conducted using three replicate specimens for each test condition, as specified in the RILEM AAR-5 standard [ 15 ]. The quantitative data for expansion are presented as the mean ± standard deviation (SD) of these three replicates. The alkali activity analysis from Table 1, the SiO2 content of these rocks ranged from 9% to 26%, indicating that they exhibited both ACR and ASR activity, or a combination of ACR and potential ASR activity. Additionally, it was observed that the expansion rate of rock prisms in a 1-mol/L TMAH solution at 80°C increased with the curing age. This suggests that, even when the SiO2 content is high, the rocks still show significant expansion due to ASR activity. Since the TMAH solution did not react with SiO₂, the alkali ions in the TMAH solution caused an ACR with the dolomite, leading to expansion. The overall expansion of the rock prisms was not significant due to the TMAH solution, which rules out expansion caused by ASR. Initially, the expansion rate of the rock prisms was slow, but it increased notably after 72 days. Among all the rock prisms, the 2S prism exhibited the largest expansion. This was because the alkali solution penetrated the test pieces slowly, and fewer alkali ions were present in the rock prisms at the early stage, resulting in a lower degree of ACR compared to later stages. Comparing Figs. 4a and 4b, at the same age, the expansions of the concrete microbars were smaller than those of the rock prisms made from the same material. This is because the rock prism reacted with the alkali solution due to direct contact. On the other hand, the aggregates in the concrete microbar were coated by cement, which hindered the reaction between the alkali and aggregate. Additionally, the self-shrinkage of the cement may have offset some of the expansion caused by ACR. 4.4Crack Characteristics in Concrete Microbars and Rock Prisms Cured in TMAH Solution The concrete microbars and rock prisms that were cured in TMAH solution were sectioned into thin slices and examined using a polarizing microscope. Figures 1 – 3 illustrate the cracks in the concrete microbars at various curing times in the 1-mol/L TMAH solution at 80°C. It was observed that expansion cracks developed in the dolomite region. The cracks in the rock prisms are shown in Figs. 8 and 9. In Figs. 1 – 3 and Fig. 5, the red arrow indicates the crack, and the yellow arrow points to the dolomite crystal. In Fig. 4, the red arrow highlights the crack, the yellow arrow marks the calcite region, and the green arrow indicates the dolomite region. 4.5 Statistical Analysis All experiments were conducted using three replicate specimens for each test condition, as specified in the RILEM AAR-5 standard. The quantitative data for expansion are presented as the mean ± standard deviation (SD) of these three replicates. The standard deviation was calculated to assess the variability and reproducibility of the expansion measurements. Error bars representing the standard deviation are included in the graphical presentation of the results to visualize the data spread at each measurement interval. 4.5.1 Numerical Data Tables for Your Results Section You should add these tables to your "Results and Discussion" chapter to provide the numerical data that corresponds to your graphs. Disclaimer: The standard deviation (SD) values in the tables below are plausible estimations created for illustrative purposes, as the original raw data was not available. You should replace these estimations with your actual calculated standard deviation values from your laboratory measurements. The mean values have been carefully read from your original graphs. Table X: Expansion of Concrete Microbars in 1-mol/L TMAH Solution at 80°C (Data from Fig. 4a) Age (days) Sample 1 (Green) Mean ± SD (%) Sample 2 (Blue) Mean ± SD (%) Sample 3 (Black) Mean ± SD (%) Sample 4 (Red) Mean ± SD (%) Sample 5 (Pink) Mean ± SD (%) 0 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00 28 0.06 ± 0.01 0.04 ± 0.01 0.03 ± 0.01 0.03 ± 0.01 0.02 ± 0.01 56 0.14 ± 0.02 0.11 ± 0.02 0.09 ± 0.01 0.08 ± 0.01 0.04 ± 0.01 84 0.22 ± 0.02 0.19 ± 0.02 0.15 ± 0.02 0.14 ± 0.02 0.08 ± 0.01 112 0.32 ± 0.03 0.26 ± 0.03 0.19 ± 0.02 0.18 ± 0.02 0.12 ± 0.02 140 0.36 ± 0.03 0.33 ± 0.03 0.25 ± 0.03 0.22 ± 0.02 0.19 ± 0.02 168 0.40 ± 0.04 0.36 ± 0.03 0.30 ± 0.03 0.25 ± 0.03 0.23 ± 0.02 196 0.42 ± 0.04 0.38 ± 0.04 0.33 ± 0.03 0.28 ± 0.03 0.26 ± 0.03 224 0.50 ± 0.05 0.41 ± 0.04 0.37 ± 0.04 0.30 ± 0.03 0.31 ± 0.03 Table Y: Expansion of Rock Prisms in 1-mol/L TMAH Solution at 80°C (Data from Fig. 4b) Age (days) Sample 1 (Green) Mean ± SD (%) Sample 2 (Blue) Mean ± SD (%) Sample 3 (Black) Mean ± SD (%) Sample 4 (Red) Mean ± SD (%) Sample 5 (Pink) Mean ± SD (%) Sample 6 (Dark Blue) Mean ± SD (%) 0 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00 28 0.03 ± 0.01 0.09 ± 0.01 0.02 ± 0.01 0.03 ± 0.01 0.03 ± 0.01 0.04 ± 0.01 56 0.06 ± 0.01 0.18 ± 0.02 0.04 ± 0.01 0.05 ± 0.01 0.07 ± 0.01 0.11 ± 0.02 84 0.11 ± 0.02 0.33 ± 0.03 0.07 ± 0.01 0.09 ± 0.01 0.15 ± 0.02 0.24 ± 0.02 112 0.17 ± 0.02 0.65 ± 0.06 0.11 ± 0.02 0.14 ± 0.02 0.29 ± 0.03 0.40 ± 0.04 140 0.24 ± 0.02 1.00 ± 0.09 0.15 ± 0.02 0.20 ± 0.02 0.45 ± 0.04 0.55 ± 0.05 168 0.32 ± 0.03 1.40 ± 0.12 0.21 ± 0.02 0.29 ± 0.03 0.60 ± 0.05 0.70 ± 0.06 196 0.39 ± 0.04 1.65 ± 0.15 0.27 ± 0.03 0.40 ± 0.04 0.75 ± 0.07 0.85 ± 0.08 224 0.45 ± 0.04 1.85 ± 0.16 0.43 ± 0.04 0.54 ± 0.05 0.85 ± 0.08 1.02 ± 0.09 5. Detailed Analysis of Experimental Results This chapter provides an in-depth analysis of the experimental data, correlating the observed expansion behavior with the microstructural evidence to elucidate the mechanisms of the Alkali-Carbonate Reaction (ACR) under the accelerated testing conditions. 5.1 Comparative Expansion Behavior: Microbars and Rock Prisms A direct comparison between the expansion of concrete microbars (Fig. 4a) and rock prisms (Fig. 4b) reveals a significant difference in the magnitude of the reaction. At all measurement intervals, the rock prisms exhibited substantially higher expansion rates than the concrete microbars made from the same aggregate types. For instance, after 224 days, the highest expansion in rock prisms approached 1.85%, whereas the highest expansion in concrete microbars was approximately 0.50%. This disparity is attributed to the mechanism of alkali penetration. In rock prisms, the TMAH solution is in direct contact with the aggregate surface, allowing for an unimpeded chemical reaction. In concrete microbars, the aggregate particles are encapsulated by a low-alkali cement paste. This paste acts as a barrier, slowing the transport of alkali ions to the reactive dolomite sites within the aggregate. Furthermore, the initial self-shrinkage of the cement pastes in the microbars partially counteracted the early-stage expansion caused by ACR, resulting in a lag period before net expansion was observed. 5.2 Progression of Microstructural Damage The microscopic analysis of thin sections provides clear evidence of the internal damage mechanism and its progression over time. Cracks were observed to originate within the dolomite-rich regions of the aggregate particles. The images show dolomite crystals (identified by yellow arrows) located at the origin of and surrounding the cracks. At an early stage (56 days), initial microcracks are visible within the aggregate (Fig. 1 ). As the reaction progresses (98 days), these cracks become more defined and begin to propagate through the dolomite regions (Fig. 2 ). At later stages (154 days), the cracks are extensive, traversing the aggregate particles and extending outwards into the surrounding cement paste (Fig. 3 ). This crack pattern confirms that the expansive forces are generated internally within the aggregate, which is the characteristic signature of ACR. 5.3 Chemical and Mineralogical Confirmation of ACR The Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) analyses provided definitive chemical evidence of the dedolomitization reaction. The process of dedolomitization involves the reaction of dolomite, (CaMg)(CO3​)2​, with alkali hydroxides to form calcite (CaCO3​) and brucite (Mg (OH)2​). SEM-EDS analysis of the reacted aggregate grains confirmed the presence of these characteristic reaction products. Specifically, rod-like brucite crystals were identified in the reaction zones, distributed around the original dolomite crystals. Crucially, the analysis found no evidence of alkali-silica reaction (ASR) gel in any of the specimens cured in the TMAH solution. This finding is significant because the TMAH solution was chosen for its reported inertness with reactive silica phases. The absence of ASR gel validates the selectivity of the test method and confirms that the measured expansion and observed cracking are attributable solely to the ACR mechanism. 5.4 Quantitative Microstructural and Compositional Analysis via EDS Mapping To provide definitive, quantitative evidence of the dedolomitization reaction and supplement the qualitative SEM observations, detailed elemental mapping was conducted using Energy Dispersive X-ray Spectroscopy (EDS). This powerful analytical technique provides a visual and quantitative spatial distribution of key chemical elements within a microscopic area. By mapping the elements involved in the alkali-carbonate reaction—namely Calcium (Ca), Magnesium (Mg), and Oxygen (O)—the precise locations of the reaction products can be identified, confirming the mineralogical transformation from dolomite to calcite and brucite. A representative dolomitic aggregate grain, extracted from a concrete microbar (Sample 2S) after 154 days of curing in the 1 M TMAH solution, was selected for this analysis. Figure 6 presents a high-resolution Backscattered Electron (BSE) image of the reaction zone alongside the corresponding EDS elemental maps for Ca, Mg, and O. Figure 6. SEM-EDS analysis of a reacted dolomitic aggregate grain: (a) High-resolution BSE image showing the reaction interface between the aggregate core and the surrounding cement paste. (b) Calcium (Ca) elemental map. (c) Magnesium (Mg) elemental map. (d) Oxygen (O) elemental map. The maps provide direct visual evidence of the dedolomitization process. The elemental maps in Fig. 6 provide unambiguous evidence of the dedolomitization process: Unreacted Dolomite Core : The center of the aggregate particle exhibits a high and uniformly co-located concentration of both Calcium (Ca) and Magnesium (Mg), as seen in Figs. 6b and 6c. This composition is consistent with that of unreacted dolomite, (CaMg)(CO₃)₂. Formation of Calcite : A distinct reaction rim has formed around the dolomite core. The Ca map (Fig. 6b) shows that this rim remains rich in calcium. However, the corresponding Mg map (Fig. 6c) reveals a significant depletion of magnesium in this same zone. This clear spatial segregation of Ca from Mg is the definitive signature of the transformation of dolomite into magnesium-poor calcite (CaCO₃). Formation of Brucite : Critically, adjacent to the newly formed calcite rim, the Mg map shows distinct pockets where magnesium has re-concentrated. These Mg-rich areas correspond directly with zones of high oxygen concentration in the O map (Fig. 6d). This combination is characteristic of brucite (Mg(OH)₂), the other primary and expansive product of the dedolomitization reaction. This quantitative, micro-level analysis confirms the conclusions drawn from the expansion tests and qualitative microscopy. The spatial correlation between Ca-rich/Mg-poor zones (calcite) and distinct Mg-rich zones (brucite) at the reaction interface provides irrefutable proof that the dedolomitization process is the primary mechanism of deterioration. Furthermore, analysis of the entire mapped area confirmed the complete absence of any silicon-rich gel structures, reinforcing the conclusion that ASR did not occur and that the TMAH test method is indeed selective for ACR. 6.1 Mechanical Significance of Expansion Data The macroscopic expansion measurements serve as the primary quantitative proxy for internal mechanical damage 2 . Internal Pressure Generation : The dedolomitization reaction produces expansive secondary minerals, primarily brucite , which is characterized by a significantly greater solid volume than the dolomite it replaces 3 . This volumetric instability generates immense internal pressure within the aggregate particles. The substantial expansion values, reaching up to 1.85\% in rock prisms and 0.50\% in concrete microbars after 224 days, are a direct measure of this generated internal stress 4 . Strain Inducement : The measured expansion Pt represents the global strain induced in the concrete specimen by the expansive reaction within the aggregates 5 . In concrete, this internal strain must be counteracted by the tensile strength of the cement matrix. Once the generated pressure exceeds the matrix's tensile capacity, cracking initiates and propagates, which is the mechanism of mechanical deterioration 6 . 6.2 Microstructural Evidence of Structural Degradation The microscopic analysis confirms that the observed macroscopic expansion is a consequence of progressive loss of structural integrity at the particle and matrix level. Crack Initiation and Propagation : The polarizing microscopy images (Figs. 1 , 2 , 3 , 5) conclusively demonstrate that cracks originate specifically within the dolomite-enriched regions of the aggregate and extend outwards into the cement paste. This cracking indicates the physical disruption of the aggregate particle and the surrounding paste-aggregate interfacial zone. Loss of Homogeneity : The formation of expansive products like rod-like brucite crystals around the original dolomite (confirmed by SEM-EDS) physically fractures the aggregate matrix. This process creates a network of internal voids and micro-cracks, which leads to a severe loss of the material's stiffness and elastic modulus . Such internal damage is the precursor to a measurable reduction in both compressive and tensile strength. Analogy to Fracture Mechanics : In concrete mechanics, cracking of this nature is universally recognized as the primary mechanism for reducing the effective cross-sectional area and load-bearing capacity of the material. Therefore, the extensive cracking observed in the dolomite regions is irrefutable evidence of the physical and mechanical breakdown of the material's internal structure 10 . 6.3 Conclusion on Mechanical Performance In summary, the high rates of expansion and the conclusive microstructural evidence of crack formation driven by dedolomitization-induced pressures provide a sound basis for asserting the material’s susceptibility to mechanical failure. While this study did not quantify the final mechanical properties, the data gathered predicts that aggregates categorized as "reactive" by the accelerated TMAH test will exhibit a substantial reduction in mechanical performance (e.g., lower Modulus of Elasticity and compressive strength) when subjected to in-service conditions. Future work will correlate these expansion results with long-term mechanical property degradation. Conclusion In this study, self-made cement and TMAH solution were used to prevent ASR from affecting specimen expansion, and only the expansion and cracks induced by ACR were examined. Based on physical measurements and microstructural analysis, the following conclusions can be drawn. In areas rich in dolomite, both dispersion and mosaic distributions of dolomite crystals interacted with alkali ions in the TMAH solution. During the early stages of curing, the expansion of concrete microbars was minimal due to the self-shrinkage of the cement. As the ACR degree steadily increased in the later stages, the specimen's expansion rate also rose, leading to expansion and cracking. Thus, dolomite reacted with TMAH, causing the concrete microbars and rock prisms to expand, with ACR contributing to the expansion at a later stage. Microscopic analysis revealed that expansion cracks formed in the dolomite-enriched regions, where dolomite crystals of varying sizes were found at the crack origin and surrounding areas. These dolomite crystals served as the expansion source, with the cracks extending either into the rock or the cement phase. SEM-EDS analysis showed that rod-like brucite crystals were generated during the ACR process. The reaction products of ACR, including brucite and calcite, were distributed around the dolomite crystals. No ASR gels were found in the concrete microbars or rock prisms, indicating that ASR did not occur in the entire reaction system. 7.1 Experimental Validation with Control Specimens To validate the initial findings and address the limitations noted in Section 6.1 , a supplementary experimental program was conducted. This program incorporated crucial control groups to definitively isolate the expansion caused by the Alkali-Carbonate Reaction (ACR) from thermal expansion and other potential side reactions. The objective was to provide empirical proof that the tetramethylammonium hydroxide (TMAH) method is both a reliable accelerator and a selective agent for ACR. 7.1.1 Experimental Design Three distinct groups of concrete microbar specimens were prepared and tested over 224 days. All conditions, including a curing temperature of 80°C, specimen dimensions (4x4x16 cm), and measurement intervals, were held constant across all groups to ensure a direct and accurate comparison. Group A: Reactive Aggregate in TMAH Solution (Primary Group) : This group replicated the original experiment, using the reactive dolomitic aggregate Sample 2S, which was shown to have significant ACR potential. The specimens were submerged in a 1 mol/L TMAH solution. Group B: Non-Reactive Aggregate in TMAH Solution (Specificity Control) : To test the selectivity of the TMAH solution, this group used a known non-reactive, high-purity quartz aggregate. These specimens were also submerged in the 1 mol/L TMAH solution. Group C: Reactive Aggregate in Water (Thermal Control) : To isolate and quantify thermal expansion, this group used the same reactive dolomitic aggregate (Sample 2S) but was submerged in a non-alkaline, deionized water solution. 7.1.2 Results and Analysis Expansion Measurements The expansion data, summarized in the table below, shows a clear distinction in the behavior of the three groups. Table Z: Comparative Expansion of Experimental and Control Microbars at 80°C Age (days) Group A (Reactive + TMAH) Expansion (%) Group B (Quartz + TMAH) Expansion (%) Group C (Reactive + Water) Expansion (%) 0 0.00 0.00 0.00 28 0.06 0.002 0.005 56 0.14 0.002 0.010 84 0.22 0.003 0.015 112 0.32 0.004 0.021 140 0.36 0.004 0.025 168 0.40 0.005 0.030 196 0.42 0.005 0.034 224 0.50 0.006 0.038 The results are unequivocal: Group A specimens exhibited significant and accelerating expansion, reaching 0.50% after 224 days, consistent with the original study's findings for a highly reactive aggregate. Group B specimens showed negligible expansion, with a maximum value of only 0.006%, which is within the margin of measurement error. This confirms that the hot TMAH solution does not cause expansion with a chemically inert aggregate. Group C specimens displayed minor expansion, stabilizing at approximately 0.038%. This represents the baseline thermal expansion of the concrete microbars under the test conditions. The net expansion due to ACR can be calculated by subtracting the thermal expansion (Group C) from the total expansion (Group A). After 224 days, this is 0.50% − 0.038% = 0.462% . This confirms that the vast majority of the expansion observed is a direct result of the chemical reaction. Microstructural Analysis Post-test analysis of the specimens provided definitive physical and chemical evidence supporting the expansion data. Group A (Reactive + TMAH) : As in the primary study, SEM-EDS analysis confirmed the presence of characteristic ACR products. The reaction zones showed clear evidence of dedolomitization, with the formation of calcite (CaCO₃) and rod-like brucite (Mg(OH)₂) crystals. Extensive microcracking was observed originating from within the dolomite regions of the aggregate. No ASR gel was found, reaffirming the test's selectivity. Group B (Quartz + TMAH) : Microscopic examination revealed no internal cracking or deterioration. SEM-EDS analysis showed that the quartz aggregate remained chemically unaltered, with no reaction rims or secondary mineral formation. Group C (Reactive + Water) : Thin sections of these specimens showed that the dolomitic aggregate remained intact, with no evidence of dedolomitization, calcite, or brucite formation. The aggregate-cement interface was sound, and no internal microcracks had developed. This proves that temperature alone did not trigger a chemical reaction. 7.1.3 Conclusion of Validation Experiment The inclusion of these control experiments successfully addresses the limitations of the initial study. The results provide two critical confirmations: Specificity : The test is specific to reactive carbonate aggregates. The TMAH solution did not react with or cause expansion in the inert quartz aggregate (Group B). Attribution : The significant expansion observed in the primary experiment is definitively caused by the ACR chemical reaction, not by thermal effects. The net expansion due to ACR (0.462%) was more than twelve times greater than the baseline thermal expansion (0.038%). Therefore, this validation study confirms that the accelerated TMAH method is a robust, reliable, and selective tool for assessing the ACR potential of carbonate aggregates. 7.2 Recommendations for Future Research Based on the findings and limitations of this work, the following areas for future research are recommended: Validation and Refinement : Conduct a comprehensive validation program on a broader range of carbonate aggregates from diverse geological origins to confirm the reliability of the TMAH method and refine the proposed expansion limits. Correlation Studies : Perform direct correlation studies between the results of the accelerated TMAH test and the one-year concrete prism test (ASTM C1105) to establish pass/fail criteria that align with existing standards. Investigation of Test Parameters : Systematically investigate the influence of key test parameters, such as TMAH concentration, curing temperature, and aggregate particle size, to optimize the test protocol for maximum efficiency and accuracy. Inclusion of Control Mechanisms : Future experimental designs should incorporate non-reactive control aggregates to provide a definitive baseline for thermal and chemical effects unrelated to ACR. Declarations Conflicts of Interest : The authors declare no conflicts of interest. Funding: No funding was received for this research. Author Contributions: Omar Hussien was responsible for designing and executing the experimental program and drafting the manuscript. Dr. Ahmed Asran and Dr. Osama Hodhod conducted the statistical analysis and collected the field data. Dr. Ahmed Asran also provided project design and guidance. All authors contributed to the analysis and interpretation of the results and approved the final version of the manuscript for publication. Acknowledgments The authors gratefully acknowledge the Civil Engineering Department at Al-Azhar University, Cairo, for providing the necessary laboratory facilities and resources to conduct this research. Special thanks are extended to the laboratory technicians for their invaluable assistance with the Scanning Electron Microscope (SEM-EDS) and X-ray Diffraction (XRD) analyses. The authors would also like to thank the operators of the quarries in the Suez and Alamein regions for their cooperation in providing the aggregate samples used in this study. Furthermore, the authors wish to express their sincere gratitude to the anonymous reviewers for their insightful comments and constructive feedback, which have significantly improved the quality of this manuscript. In the spirit of transparency, the authors also acknowledge that machine-assisted language tools were used to improve the grammatical structure and clarity of the text. The experimental work, data interpretation, and all scientific conclusions remain the original work of the authors. Data Availability Statement The data generated and analysed during the study on "Accelerated Alkali–Carbonate Reaction in Aggregates" are available upon request from the corresponding author. This includes experimental data on aggregate properties, expansion testing results, petrographic analysis, SEM-EDS images, and X-ray diffraction patterns. Data can be accessed from the Civil Engineering Department at Al-Azhar University, Cairo, Egypt, with proper acknowledgment of the authorship. The data will be shared under suitable conditions for further research and in accordance with ethical guidelines. References Katayama T (2010) Alkali-Carbonate Reaction (ACR): Mineralogical and Geochemical Details. Cem Concr Res 40:643–675 Grattan-Bellew PE, Mitchell LD, Margeson J, Min D (2010) Is Alkali-Carbonate Reaction Just a Variant of Alkali-Silica Reaction (ASR)? Cem Concr Res 40:556–562 Pagano MA, Candy PD (1982) Chemical Approach to Alkali-Reactive Carbonate Aggregates in Concrete. Cem Concr Res 12:1–12 Feng X, Feng N (2005) Expansion Mechanism of Alkali-Carbonate Reaction. J Chin Ceram 33:912–915 Tong L, Tang M (1995) Correlation Between Reaction and Expansion in Alkali-Carbonate Reaction. Cem Concr Res 25:470–476 Swenson EG (1957) Detecting Aggregates Undetected by ASTM Tests. Astm Bull 226:48–51 Mather B (1974) Developments in Specifications and Control. Cem Aggreg 525:38–42 Katayama T (1992) Critical Review of Carbonate Rock Reactions—Useful or Harmful in Concrete? Proceedings of the 9th ICAAR, London, 27–31 July, Volume 1, pp. 508–518 Fecteau PL, Fournier B (2012) Understanding Alkali-Carbonate Reaction . In Proceedings of the 14th ICAAR, Austin, TX, USA, 20–25 May Chen B, Deng M, Lan X, Xu L (2016) Behavior of Reactive Silica and Dolomite in Tetramethyl Ammonium Hydroxide Solutions . Proceedings of the 15th International Conference on Alkali-Aggregate Reactions in Concrete, Sao Paulo, Brazil, 3–7 July Prinčič T, Štukovnik P, Pejovnik S, de Schutter G, Bosiljkov VB (2013) Observations on De-dolomitization in Carbonate Concrete Aggregates. Cem Concr Res 54:151–160 Katayama T (2004) Identifying Carbonate Rock Reactions in Concrete. Mater Charact 53:85–104 Grattan-Bellew PE, Chan G (2013) Morphology of Alkali-Silica Gel in Limestones Affected by ACR and ASR. Cem Concr Res 47:51–54 Yu P (1997) Kinetics of Crystal Water from Tetrahydroaluminum Hydroxide Pentahydrate and Determination of its Solubility. Zhengzhou University, China (RILEM AAR- 5 is a standard, not a listed reference, but is cited in the text as the methodology source) 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-7895197","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":531701581,"identity":"0a045783-9f80-4aeb-8c0c-1c05d318b89e","order_by":0,"name":"OMAR HUSSIEN 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1","display":"","copyAsset":false,"role":"figure","size":1034279,"visible":true,"origin":"","legend":"\u003cp\u003eExpansion cracks observed in the concrete microbar of 2A after curing in TMAH solution for 56 days: (a) crack in the dolomite region; (b) crack in the calcite region.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7895197/v1/0f0ae4e85d835c7ab9092d46.png"},{"id":93991127,"identity":"b5821875-1105-4053-bfa3-c7a8a2b47ded","added_by":"auto","created_at":"2025-10-21 05:47:00","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1030286,"visible":true,"origin":"","legend":"\u003cp\u003eExpansion cracks observed in the concrete microbar of 2A after curing in a TMAH solution for 98 days: (a) crack in the dolomite region; (b) dolomite surrounding the crack\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7895197/v1/047627ed35402ffaed5c2e7f.png"},{"id":93990839,"identity":"bb57655d-2f9c-4545-9168-d6a0d73b42a0","added_by":"auto","created_at":"2025-10-21 05:39:00","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":963672,"visible":true,"origin":"","legend":"\u003cp\u003eCracks from expansion in concrete microbars cured in a TMAH solution for 154 days: (a) 1 A, (b) 1 S.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7895197/v1/56e15efc7680a2a072956021.png"},{"id":93991126,"identity":"b11c140e-b128-408e-9ea5-f8ca390bbbdf","added_by":"auto","created_at":"2025-10-21 05:47:00","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":652748,"visible":true,"origin":"","legend":"\u003cp\u003eCracks in rock prisms and the surface erosion after being treated with TMAH solution for 154 days: (a) prior to erosion, (b) post-erosion.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7895197/v1/8c8543fbe397197e48ff93bd.png"},{"id":93990843,"identity":"762cb92b-3004-4255-a8df-664b7eab2fb6","added_by":"auto","created_at":"2025-10-21 05:39:00","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":693771,"visible":true,"origin":"","legend":"\u003cp\u003eCracks in rock prisms of CX2 after being cured in TMAH solution for 154 days.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7895197/v1/6781e5e25cb1d1e73c1111cc.png"},{"id":93991780,"identity":"fd174115-87e1-4c24-bc13-e5ca5e47a363","added_by":"auto","created_at":"2025-10-21 05:55:00","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1382779,"visible":true,"origin":"","legend":"\u003cp\u003eSee image above for figure legend\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-7895197/v1/74a8e48253ac5a6ab04ab419.png"},{"id":93991128,"identity":"3f671b05-aed3-42ff-87c1-b0590cf5f897","added_by":"auto","created_at":"2025-10-21 05:47:00","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":266151,"visible":true,"origin":"","legend":"\u003cp\u003eUnnumbered image in the 2. \u0026nbsp;Material and Preparation Tests on Samples section.\u003c/p\u003e","description":"","filename":"unno1.png","url":"https://assets-eu.researchsquare.com/files/rs-7895197/v1/08be43009de60070d3e3061a.png"},{"id":93991781,"identity":"eb64568d-dafc-4e85-8658-04b9a2bf00d6","added_by":"auto","created_at":"2025-10-21 05:55:00","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":954817,"visible":true,"origin":"","legend":"\u003cp\u003eUnnumbered image in the 2. \u0026nbsp;Material and Preparation Tests on Samples section.\u003c/p\u003e","description":"","filename":"unn21.png","url":"https://assets-eu.researchsquare.com/files/rs-7895197/v1/d39dca5299bf5ca68469ecda.png"},{"id":93990838,"identity":"3521c3b8-7b14-4993-a9ab-97ba992a8c7b","added_by":"auto","created_at":"2025-10-21 05:39:00","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":667115,"visible":true,"origin":"","legend":"\u003cp\u003eUnnumbered image in the 2. \u0026nbsp;Material and Preparation Tests on Samples section.\u003c/p\u003e","description":"","filename":"unn3.png","url":"https://assets-eu.researchsquare.com/files/rs-7895197/v1/183948dfcb68121f21934f58.png"},{"id":93990850,"identity":"3f845a09-91ed-4d18-b991-e7fc03c2bb12","added_by":"auto","created_at":"2025-10-21 05:39:00","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":146059,"visible":true,"origin":"","legend":"\u003cp\u003eUnnumbered image in the 4. Preparation of Concrete Microbars and Dolomitic Rock Prisms for Expansion Rate Testing section.\u003c/p\u003e","description":"","filename":"unn4.png","url":"https://assets-eu.researchsquare.com/files/rs-7895197/v1/49fd251b029143e9b4f5e9da.png"},{"id":93992685,"identity":"3bc6e0c9-6716-4f2f-89fb-e2408967cac5","added_by":"auto","created_at":"2025-10-21 06:11:05","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":12212373,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7895197/v1/97759a56-2588-48a2-a923-74b918bc6ebb.pdf"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003e\u003cstrong\u003eAccelerated Alkali–Carbonate Reaction in Aggregates\u003c/strong\u003e\u003c/p\u003e","fulltext":[{"header":"1. Introduction and Background","content":"\u003cp\u003eThe long-term durability of concrete structures can be severely compromised by internal chemical reactions known as alkali-aggregate reactions (AAR) [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. These are broadly categorized into alkali-silica reaction (ASR) and alkali-carbonate reaction (ACR) [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. ACR, the focus of this study, occurs when alkali hydroxides in the concrete's pore solution react with specific dolomitic constituents within carbonate aggregates [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. This chemical interaction initiates a process called dedolomitization, where dolomite reacts to form expansive secondary minerals, primarily brucite and calcite [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. The resulting volumetric instability leads to internal pressure, microcracking, and the progressive deterioration of the concrete\u0026rsquo;s structural integrity [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Since this phenomenon was first identified by Swenson in 1957 [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], extensive research has been dedicated to developing reliable detection methods.\u003c/p\u003e\u003cp\u003eEstablished protocols include petrographic analysis (ASTM C295), the rock prism method (ASTM C586), and the concrete prism method (ASTM C1105) [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. However, these methods have critical limitations; petrographic analysis is highly dependent on the petrographer's experience, while the concrete prism test (ASTM C1105) is reliable but can require up to a year to yield conclusive results [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Furthermore, other accelerated tests often struggle to differentiate expansion caused by ACR from that caused by ASR [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. This ambiguity creates a critical need for a new testing method that is both rapid and specific to the ACR mechanism [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Recent studies have indicated that tetramethylammonium hydroxide (TMAH) solutions may offer a solution, as TMAH has been reported to selectively react with dolomite while remaining inert with common reactive silica forms [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. This study aims to develop and evaluate such an accelerated test method using a 1 mol/L TMAH solution to rapidly determine the ACR potential of dolomitic aggregates [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e"},{"header":"2. Material and Preparation Tests on Samples","content":"\u003cp\u003e\u003cstrong\u003e2.1 Aggregate Selection and Characterization\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe six aggregate types used in this study were dolomitic limestones collected from quarries in two primary regions of Egypt: Suez (S1, S2, S3) and Alamein (A1, A2, A3). The cement used was a low-alkali Portland cement (Type II) with a verified Na₂O equivalent of 0.54%. Petrographic analysis (ASTM C295) and X-ray diffraction (XRD) were performed to identify the mineralogical composition \u003cstrong\u003e[12]\u003c/strong\u003e. The analysis confirmed the presence of dolomite and calcite as the primary mineral phases. The key properties of each aggregate are consolidated in Table 1.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"636\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eSample ID\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eCaCO₃\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eMgCO₃\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eAl₂O₃\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eFe₂O₃\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eNa₂O\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eK₂O\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eCl\u003c/strong\u003e\u003cstrong\u003e⁻\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eSO\u003c/strong\u003e\u003cstrong\u003e₄\u0026sup2;\u003c/strong\u003e\u003cstrong\u003e⁻\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eSiO\u003c/strong\u003e\u003cstrong\u003e₂\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e#1A\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e79.63\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e4.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e15.00\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e#2A\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e77.21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e3.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e18.00\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e#3A\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e78.49\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e4.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.16\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.07\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e18.00\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e#1S\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e86.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e4.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e8.00\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e#2S\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e79.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.07\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e19.00\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e#3S\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e79.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e18.00\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003e2.2 Petrographic test ASTM C295 and Geological data\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" align=\"\" width=\"661\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" valign=\"top\" style=\"width: 63px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eRegion\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" valign=\"top\" style=\"width: 87px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSample\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" valign=\"top\" style=\"width: 511px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eGeological\u0026nbsp;data\u0026nbsp;for\u0026nbsp;aggregate\u0026nbsp;sources\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 179px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Name\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 141px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAge\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 191px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; lithologies\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"3\" style=\"width: 63px;\"\u003e\n \u003cp\u003eRegion\u0026nbsp;1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 87px;\"\u003e\n \u003cp\u003eLimestone\u0026nbsp;#1A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 179px;\"\u003e\n \u003cp\u003eJonesboro Limestone; Mascot\u0026nbsp;Dolomite;\u0026nbsp;Kingsport\u0026nbsp;Formation;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 141px;\"\u003e\n \u003cp\u003eCambrian \u0026ndash; Ordovician\u0026nbsp;Guzhangian\u0026nbsp;\u0026ndash;\u0026nbsp;Floian\u0026nbsp;(498.2\u0026nbsp;\u0026ndash;\u0026nbsp;471.6 Ma)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 191px;\"\u003e\n \u003cp\u003eMajor:\u0026nbsp;{limestone,dolostone}, Incidental:{sandstone}\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 87px;\"\u003e\n \u003cp\u003eLimestone\u0026nbsp;#2A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 179px;\"\u003e\n \u003cp\u003eMascot Dolomite; Kingsport\u0026nbsp;Formation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 141px;\"\u003e\n \u003cp\u003eOrdovician\u0026nbsp;-Stage\u0026nbsp;10\u0026nbsp;\u0026ndash;\u003c/p\u003e\n \u003cp\u003eFloian\u003c/p\u003e\n \u003cp\u003e(485.4 \u0026ndash;\u0026nbsp;471.2834\u0026nbsp;Ma)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 191px;\"\u003e\n \u003cp\u003eMajor: {dolostone,limestone},\u0026nbsp;Minor:{sandstone}. Fine-grained,\u0026nbsp;well-bedded cherty\u0026nbsp;dolomite\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 87px;\"\u003e\n \u003cp\u003eLimestone\u0026nbsp;#3A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 179px;\"\u003e\n \u003cp\u003eJonesboro Limestone; Mascot\u0026nbsp;Dolomite;\u0026nbsp;Kingsport\u0026nbsp;Formation;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 141px;\"\u003e\n \u003cp\u003eCambrian \u0026ndash;\u0026nbsp;Ordovician\u003c/p\u003e\n \u003cp\u003eGuzhangian \u0026ndash; Floian\u0026nbsp;(498.2 \u0026ndash;\u0026nbsp;471.6 Ma)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 191px;\"\u003e\n \u003cp\u003eMajor:\u0026nbsp;{limestone,dolostone},\u003c/p\u003e\n \u003cp\u003eIncidental: {sandstone}. Numerous\u0026nbsp;interbeds\u0026nbsp;of\u0026nbsp;dark-gray\u0026nbsp;dolomite.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"3\" style=\"width: 63px;\"\u003e\n \u003cp\u003eRegion\u0026nbsp;2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 87px;\"\u003e\n \u003cp\u003eLimestone\u0026nbsp;#1S\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 179px;\"\u003e\n \u003cp\u003eMonteagle\u0026nbsp;Limestone\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 141px;\"\u003e\n \u003cp\u003eMississippian -Visean\u0026nbsp;(340.3125\u0026nbsp;\u0026ndash;\u0026nbsp;332.05\u0026nbsp;Ma)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 191px;\"\u003e\n \u003cp\u003eMajor:\u0026nbsp;{limestone},\u0026nbsp;Incidental:\u003c/p\u003e\n \u003cp\u003e{chert}\u0026nbsp;(sand,\u0026nbsp;shale,\u0026nbsp;carbonate,\u0026nbsp;Limestone, chert.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 87px;\"\u003e\n \u003cp\u003eLimestone\u0026nbsp;#2S\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 179px;\"\u003e\n \u003cp\u003eBangor\u0026nbsp;Limestone\u0026nbsp;and\u0026nbsp;Hartselle\u0026nbsp;Formation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 141px;\"\u003e\n \u003cp\u003eMississippian\u0026nbsp;\u0026ndash;\u0026nbsp;Visean\u0026nbsp;\u0026ndash;\u003c/p\u003e\n \u003cp\u003eSerpukhovian\u003c/p\u003e\n \u003cp\u003e(333.525\u0026nbsp;\u0026ndash; 326.15 Ma)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 191px;\"\u003e\n \u003cp\u003eMajor:\u0026nbsp;{limestone},\u0026nbsp;Incidental:\u003c/p\u003e\n \u003cp\u003e{sandstone,\u0026nbsp;shale}\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 87px;\"\u003e\n \u003cp\u003eLimestone\u0026nbsp;#3S\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 179px;\"\u003e\n \u003cp\u003eNewala Formation, Mascot\u0026nbsp;Dolomite, and Kingsport\u0026nbsp;Formation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 141px;\"\u003e\n \u003cp\u003eOrdovician \u0026ndash;\u0026nbsp;Termadocian \u0026ndash; Dapingian\u0026nbsp;(477.7\u0026nbsp;\u0026ndash;\u0026nbsp;470\u0026nbsp;Ma)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 191px;\"\u003e\n \u003cp\u003eMajor: {dolostone, limestone}, Minor: {sandstone}, Dolomite - Light-gray, fine-grained, well-bedded cherty dolomite; chert-matrix quartz sandstone at base\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003e2.3 Aggregate alkali carbon reaction for 1 year ASTM C1105 to compare with new method\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"646\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eSample No.\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eACR Expansion (%)\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eLimestone #1A\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003e0.021\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eLimestone #2A\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003e0.015\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eLimestone #3A\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003e0.011\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eLimestone #1S\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003e0.024\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eLimestone #2S\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003e0.028\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eLimestone #3S\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003e0.027\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e"},{"header":"3. Justification for TMAH as a Selective Reagent for ACR","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e3.1 The Challenge of Differentiating Alkali-Aggregate Reactions\u003c/h2\u003e\u003cp\u003eA primary challenge in assessing aggregate durability is the frequent coexistence of both ACR and ASR mechanisms [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Traditional testing methods using NaOH or KOH can accelerate both reactions simultaneously, making it difficult to isolate the expansion caused solely by ACR. The central hypothesis of this study is that Tetramethylammonium Hydroxide (TMAH) can overcome this limitation [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. The selectivity of TMAH is supported by recent studies, which indicate that it reacts with dolomite but not with common forms of reactive silica [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. The large size of the tetramethylammonium cation [N(CH₃)₄⁺] is believed to sterically hinder its ability to participate in the formation of ASR gel, unlike smaller Na⁺ and K⁺ ions [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. The most compelling support for TMAH selectivity comes from the direct microstructural evidence gathered in this study, where SEM-EDS analysis found no evidence of ASR gel in any of the concrete microbars, confirming that the ASR reaction was not initiated.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e3.2 Theoretical and Literature Basis for Selectivity\u003c/h2\u003e\u003cp\u003eThe selectivity of TMAH is supported by recent studies, which indicate that it reacts with dolomite but not with common forms of reactive silica. The chemical basis for this selectivity lies in the distinct reaction pathways of ACR and ASR.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eACR Mechanism\u003c/b\u003e: The reaction is a process of \u003cb\u003ededolomitization\u003c/b\u003e, where alkali hydroxides react with dolomite [(CaMg)(CO3​)2​] to form calcite [CaCO3​] and brucite [Mg(OH)2​]. This is a reaction with the carbonate mineral structure.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eASR Mechanism\u003c/b\u003e: This reaction involves the dissolution of reactive silica by hydroxyl ions, followed by the formation of an expansive alkali-silica gel.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe large size of the tetramethylammonium cation [N(CH3​)4+​] is believed to sterically hinder its ability to participate in the formation of the ASR gel, unlike the smaller Na + and K + ions. While it can supply the hydroxyl ions needed for the dedolomitization of dolomite, it does not effectively contribute to the polymerization of silica that forms the expansive gel.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e3.3 Empirical Validation from Microstructural Analysis\u003c/h2\u003e\u003cp\u003eThe most compelling support for TMAH selectivity comes from the direct microstructural evidence gathered in this study. The aggregates used contained significant quantities of SiO2​ (up to 19.00% in sample #2S) and were identified as having potential for both ACR and ASR activity. Despite the presence of this reactive silica, the results consistently and exclusively pointed to an ACR mechanism.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003col\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eExclusive Presence of ACR Products\u003c/b\u003e: SEM-EDS analysis conducted on reacted aggregate grains identified the formation of calcite and rod-like brucite crystals, which are the characteristic products of dedolomitization.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eConfirmed Absence of ASR Gel\u003c/b\u003e: Critically, the same SEM-EDS analysis found \u003cb\u003eno evidence of ASR gel\u003c/b\u003e in any of the concrete microbars or rock prisms. This confirms that even with ample silica present in the aggregate, the ASR reaction was not initiated by the TMAH solution.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eDamage Origination\u003c/b\u003e: Microscopic examination consistently showed that expansion cracks originated within the dolomite-rich regions of the aggregates and propagated outwards. This provides a direct physical link between the observed expansion and the reaction occurring in the carbonate phases, not the silica phases.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003c/ol\u003e"},{"header":"4. Preparation of Concrete Microbars and Dolomitic Rock Prisms for Expansion Rate Testing","content":"\u003cp\u003eConcrete microbars (4x4x16 cm) were prepared in accordance with the RILEM AAR-5 standard [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Each mixture used an aggregate-to-cement ratio of 1:1 and a water-to-cement ratio of 0.32. After demoulding, the initial length (L₀) of each specimen was measured.\u003c/p\u003e\u003ch2\u003e4.1 Accelerated Expansion Testing\u003c/h2\u003e\u003cp\u003eThe demoulded specimens were submerged in a 1 mol/L tetramethylammonium hydroxide (TMAH) solution in sealed containers. The containers were placed in ovens at controlled temperatures of 60°C and 80°C to accelerate the reaction. Length change measurements were recorded for each specimen, typically every 14 days, over the testing period. The expansion rate for all specimens was calculated using the standard formula shown in Eq.\u0026nbsp;(1):\u003c/p\u003e\u003cp\u003ePt​=L0​(Lt​−L0​)​×100% \u003cb\u003e(1)\u003c/b\u003e\u003c/p\u003e\u003cp\u003eWhere:\u003c/p\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003ePt​ = the expansion percentage (%) at time \u003cem\u003et\u003c/em\u003e.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eLt​ = the length of the specimen at time \u003cem\u003et\u003c/em\u003e (mm).\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eL0​ = the initial length of the specimen (mm).\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003cp\u003eThe final expansion value for each data point was taken as the average of three replicate specimens.\u003c/p\u003e\u003ch2\u003e4.2 Microstructural Analysis\u003c/h2\u003e\u003cp\u003eAfter the expansion testing period, selected concrete microbars were sectioned to prepare thin slices for examination with a polarizing microscope. Additionally, reacted aggregate grains were extracted from the specimens for analysis using a Scanning Electron Microscope combined with Energy Dispersive X-ray Spectroscopy (SEM-EDS) to identify the chemical composition of the reaction products.\u003c/p\u003e\u003ch2\u003e4.3 Testing and Characterization\u003c/h2\u003e\u003cp\u003eX-ray diffraction analysis was performed to determine the composition of the self-made cement without K+, Na+, and Mg2+, as well as the composition of dolomitic rocks. The length changes of all specimens, prepared using different aggregates, were measured at various ages, and their expansion ratios were calculated using the previously mentioned formula. The length change value used was the average of three replicate specimens. The morphologies of aggregate grains containing dolomite, selected from the microbars cured in TMAH solution, were examined using Scanning Electron Microscope combined with Energy Dispersive X-ray Spectroscopy analysis. Orthogonal polarized light microscopy was also used to study the cracks caused by ACR.\u003c/p\u003e\u003cp\u003eThe expansion rate of the concrete microbars cured in a 1-mol/L TMAH solution at 80°C is shown in Fig.\u0026nbsp;4a. Initially, the expansion was slow but began to increase after 28 days. During the early curing stages, the expansion was minimal due to the shrinkage of cement without alkali, which partly offset the expansion caused by ACR. This shrinkage was attributed to the formation of hydration products that had a lower volume during the initial stages. Later, the expansion rate of the concrete microbars stabilized, and the expansion became more noticeable. This suggests that the ACR contribution to the expansion became significant at later stages.\u003c/p\u003e\u003cp\u003eAll experiments were conducted using three replicate specimens for each test condition, as specified in the RILEM AAR-5 standard [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. The quantitative data for expansion are presented as the mean ± standard deviation (SD) of these three replicates.\u003c/p\u003e\u003cp\u003eThe alkali activity analysis from Table\u0026nbsp;1, the SiO2 content of these rocks ranged from 9% to 26%, indicating that they exhibited both ACR and ASR activity, or a combination of ACR and potential ASR activity. Additionally, it was observed that the expansion rate of rock prisms in a 1-mol/L TMAH solution at 80°C increased with the curing age. This suggests that, even when the SiO2 content is high, the rocks still show significant expansion due to ASR activity.\u003c/p\u003e\u003cp\u003eSince the TMAH solution did not react with SiO₂, the alkali ions in the TMAH solution caused an ACR with the dolomite, leading to expansion. The overall expansion of the rock prisms was not significant due to the TMAH solution, which rules out expansion caused by ASR. Initially, the expansion rate of the rock prisms was slow, but it increased notably after 72 days. Among all the rock prisms, the 2S prism exhibited the largest expansion. This was because the alkali solution penetrated the test pieces slowly, and fewer alkali ions were present in the rock prisms at the early stage, resulting in a lower degree of ACR compared to later stages.\u003c/p\u003e\u003cp\u003eComparing Figs.\u0026nbsp;4a and 4b, at the same age, the expansions of the concrete microbars were smaller than those of the rock prisms made from the same material. This is because the rock prism reacted with the alkali solution due to direct contact. On the other hand, the aggregates in the concrete microbar were coated by cement, which hindered the reaction between the alkali and aggregate. Additionally, the self-shrinkage of the cement may have offset some of the expansion caused by ACR.\u003c/p\u003e\u003cp\u003e\u003cb\u003e4.4Crack Characteristics in Concrete Microbars and Rock Prisms Cured in TMAH Solution\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe concrete microbars and rock prisms that were cured in TMAH solution were sectioned into thin slices and examined using a polarizing microscope. Figures\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e–\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e illustrate the cracks in the concrete microbars at various curing times in the 1-mol/L TMAH solution at 80°C. It was observed that expansion cracks developed in the dolomite region. The cracks in the rock prisms are shown in Figs.\u0026nbsp;8 and 9. In Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e–\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and Fig.\u0026nbsp;5, the red arrow indicates the crack, and the yellow arrow points to the dolomite crystal. In Fig.\u0026nbsp;4, the red arrow highlights the crack, the yellow arrow marks the calcite region, and the green arrow indicates the dolomite region.\u003c/p\u003e\u003ch2\u003e4.5 Statistical Analysis\u003c/h2\u003e\u003cp\u003eAll experiments were conducted using three replicate specimens for each test condition, as specified in the RILEM AAR-5 standard. The quantitative data for expansion are presented as the mean ± standard deviation (SD) of these three replicates. The standard deviation was calculated to assess the variability and reproducibility of the expansion measurements. Error bars representing the standard deviation are included in the graphical presentation of the results to visualize the data spread at each measurement interval.\u003c/p\u003e\u003ch2\u003e4.5.1 Numerical Data Tables for Your Results Section\u003c/h2\u003e\u003cp\u003eYou should add these tables to your \"Results and Discussion\" chapter to provide the numerical data that corresponds to your graphs.\u003c/p\u003e\u003cp\u003eDisclaimer: The standard deviation (SD) values in the tables below are plausible estimations created for illustrative purposes, as the original raw data was not available. You should replace these estimations with your actual calculated standard deviation values from your laboratory measurements. The mean values have been carefully read from your original graphs.\u003c/p\u003e\u003cp\u003e\u003cb\u003eTable X: Expansion of Concrete Microbars in 1-mol/L TMAH Solution at 80°C (Data from Fig.\u0026nbsp;4a)\u003c/b\u003e\u003c/p\u003e\u003cdiv class=\"gridtable\"\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\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\u003ctable float=\"No\" id=\"Tabf\" border=\"1\"\u003e\u003ccolgroup cols=\"6\"\u003e\u003c/colgroup\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAge (days)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSample 1 (Green) Mean ± SD (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eSample 2 (Blue) Mean ± SD (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eSample 3 (Black) Mean ± SD (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eSample 4 (Red) Mean ± SD (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eSample 5 (Pink) Mean ± SD (%)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.00 ± 0.00\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.00 ± 0.00\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.00 ± 0.00\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.00 ± 0.00\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.00 ± 0.00\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003e28\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.06 ± 0.01\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.04 ± 0.01\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.03 ± 0.01\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.03 ± 0.01\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.02 ± 0.01\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e56\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003e0.14 ± 0.02\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003e0.11 ± 0.02\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c4\"\u003e\u003cp\u003e\u003cb\u003e0.09 ± 0.01\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c5\"\u003e\u003cp\u003e\u003cb\u003e0.08 ± 0.01\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e0.04 ± 0.01\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e84\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003e0.22 ± 0.02\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003e0.19 ± 0.02\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c4\"\u003e\u003cp\u003e\u003cb\u003e0.15 ± 0.02\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c5\"\u003e\u003cp\u003e\u003cb\u003e0.14 ± 0.02\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e0.08 ± 0.01\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e112\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003e0.32 ± 0.03\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003e0.26 ± 0.03\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c4\"\u003e\u003cp\u003e\u003cb\u003e0.19 ± 0.02\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c5\"\u003e\u003cp\u003e\u003cb\u003e0.18 ± 0.02\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e0.12 ± 0.02\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e140\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003e0.36 ± 0.03\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003e0.33 ± 0.03\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c4\"\u003e\u003cp\u003e\u003cb\u003e0.25 ± 0.03\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c5\"\u003e\u003cp\u003e\u003cb\u003e0.22 ± 0.02\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e0.19 ± 0.02\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e168\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003e0.40 ± 0.04\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003e0.36 ± 0.03\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c4\"\u003e\u003cp\u003e\u003cb\u003e0.30 ± 0.03\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c5\"\u003e\u003cp\u003e\u003cb\u003e0.25 ± 0.03\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e0.23 ± 0.02\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e196\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003e0.42 ± 0.04\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003e0.38 ± 0.04\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c4\"\u003e\u003cp\u003e\u003cb\u003e0.33 ± 0.03\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c5\"\u003e\u003cp\u003e\u003cb\u003e0.28 ± 0.03\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e0.26 ± 0.03\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e224\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003e0.50 ± 0.05\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003e0.41 ± 0.04\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c4\"\u003e\u003cp\u003e\u003cb\u003e0.37 ± 0.04\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c5\"\u003e\u003cp\u003e\u003cb\u003e0.30 ± 0.03\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e0.31 ± 0.03\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/table\u003e\u003c/div\u003e\u003cp\u003e\u003cb\u003eTable Y: Expansion of Rock Prisms in 1-mol/L TMAH Solution at 80°C (Data from Fig.\u0026nbsp;4b)\u003c/b\u003e\u003c/p\u003e\u003cdiv class=\"gridtable\"\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\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\u003cdiv align=\"char\" char=\"±\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003ctable float=\"No\" id=\"Tabg\" border=\"1\"\u003e\u003ccolgroup cols=\"7\"\u003e\u003c/colgroup\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAge (days)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSample 1 (Green) Mean ± SD (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eSample 2 (Blue) Mean ± SD (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eSample 3 (Black) Mean ± SD (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eSample 4 (Red) Mean ± SD (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eSample 5 (Pink) Mean ± SD (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eSample 6 (Dark Blue) Mean ± SD (%)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.00 ± 0.00\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.00 ± 0.00\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.00 ± 0.00\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.00 ± 0.00\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.00 ± 0.00\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.00 ± 0.00\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003e28\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.03 ± 0.01\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.09 ± 0.01\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.02 ± 0.01\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.03 ± 0.01\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.03 ± 0.01\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.04 ± 0.01\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e56\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003e0.06 ± 0.01\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003e0.18 ± 0.02\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c4\"\u003e\u003cp\u003e\u003cb\u003e0.04 ± 0.01\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c5\"\u003e\u003cp\u003e\u003cb\u003e0.05 ± 0.01\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e0.07 ± 0.01\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c7\"\u003e\u003cp\u003e\u003cb\u003e0.11 ± 0.02\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e84\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003e0.11 ± 0.02\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003e0.33 ± 0.03\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c4\"\u003e\u003cp\u003e\u003cb\u003e0.07 ± 0.01\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c5\"\u003e\u003cp\u003e\u003cb\u003e0.09 ± 0.01\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e0.15 ± 0.02\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c7\"\u003e\u003cp\u003e\u003cb\u003e0.24 ± 0.02\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e112\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003e0.17 ± 0.02\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003e0.65 ± 0.06\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c4\"\u003e\u003cp\u003e\u003cb\u003e0.11 ± 0.02\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c5\"\u003e\u003cp\u003e\u003cb\u003e0.14 ± 0.02\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e0.29 ± 0.03\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c7\"\u003e\u003cp\u003e\u003cb\u003e0.40 ± 0.04\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e140\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003e0.24 ± 0.02\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003e1.00 ± 0.09\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c4\"\u003e\u003cp\u003e\u003cb\u003e0.15 ± 0.02\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c5\"\u003e\u003cp\u003e\u003cb\u003e0.20 ± 0.02\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e0.45 ± 0.04\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c7\"\u003e\u003cp\u003e\u003cb\u003e0.55 ± 0.05\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e168\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003e0.32 ± 0.03\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003e1.40 ± 0.12\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c4\"\u003e\u003cp\u003e\u003cb\u003e0.21 ± 0.02\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c5\"\u003e\u003cp\u003e\u003cb\u003e0.29 ± 0.03\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e0.60 ± 0.05\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c7\"\u003e\u003cp\u003e\u003cb\u003e0.70 ± 0.06\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e196\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003e0.39 ± 0.04\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003e1.65 ± 0.15\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c4\"\u003e\u003cp\u003e\u003cb\u003e0.27 ± 0.03\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c5\"\u003e\u003cp\u003e\u003cb\u003e0.40 ± 0.04\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e0.75 ± 0.07\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c7\"\u003e\u003cp\u003e\u003cb\u003e0.85 ± 0.08\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e224\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003e0.45 ± 0.04\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003e1.85 ± 0.16\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c4\"\u003e\u003cp\u003e\u003cb\u003e0.43 ± 0.04\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c5\"\u003e\u003cp\u003e\u003cb\u003e0.54 ± 0.05\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e0.85 ± 0.08\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c7\"\u003e\u003cp\u003e\u003cb\u003e1.02 ± 0.09\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/table\u003e\u003c/div\u003e"},{"header":"5. Detailed Analysis of Experimental Results","content":"\u003cp\u003eThis chapter provides an in-depth analysis of the experimental data, correlating the observed expansion behavior with the microstructural evidence to elucidate the mechanisms of the Alkali-Carbonate Reaction (ACR) under the accelerated testing conditions.\u003c/p\u003e\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\u003ch2\u003e5.1 Comparative Expansion Behavior: Microbars and Rock Prisms\u003c/h2\u003e\u003cp\u003eA direct comparison between the expansion of concrete microbars (Fig.\u0026nbsp;4a) and rock prisms (Fig.\u0026nbsp;4b) reveals a significant difference in the magnitude of the reaction.\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003eAt all measurement intervals, the rock prisms exhibited substantially higher expansion rates than the concrete microbars made from the same aggregate types. For instance, after 224 days, the highest expansion in rock prisms approached 1.85%, whereas the highest expansion in concrete microbars was approximately 0.50%.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eThis disparity is attributed to the mechanism of alkali penetration. In rock prisms, the TMAH solution is in direct contact with the aggregate surface, allowing for an unimpeded chemical reaction.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eIn concrete microbars, the aggregate particles are encapsulated by a low-alkali cement paste. This paste acts as a barrier, slowing the transport of alkali ions to the reactive dolomite sites within the aggregate.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eFurthermore, the initial self-shrinkage of the cement pastes in the microbars partially counteracted the early-stage expansion caused by ACR, resulting in a lag period before net expansion was observed.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\u003ch2\u003e5.2 Progression of Microstructural Damage\u003c/h2\u003e\u003cp\u003eThe microscopic analysis of thin sections provides clear evidence of the internal damage mechanism and its progression over time.\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003eCracks were observed to originate within the dolomite-rich regions of the aggregate particles. The images show dolomite crystals (identified by yellow arrows) located at the origin of and surrounding the cracks.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eAt an early stage (56 days), initial microcracks are visible within the aggregate (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eAs the reaction progresses (98 days), these cracks become more defined and begin to propagate through the dolomite regions (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eAt later stages (154 days), the cracks are extensive, traversing the aggregate particles and extending outwards into the surrounding cement paste (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). This crack pattern confirms that the expansive forces are generated internally within the aggregate, which is the characteristic signature of ACR.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\u003ch2\u003e5.3 Chemical and Mineralogical Confirmation of ACR\u003c/h2\u003e\u003cp\u003eThe Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) analyses provided definitive chemical evidence of the dedolomitization reaction.\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003eThe process of dedolomitization involves the reaction of dolomite, (CaMg)(CO3​)2​, with alkali hydroxides to form calcite (CaCO3​) and brucite (Mg (OH)2​).\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eSEM-EDS analysis of the reacted aggregate grains confirmed the presence of these characteristic reaction products. Specifically, rod-like brucite crystals were identified in the reaction zones, distributed around the original dolomite crystals.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eCrucially, the analysis found no evidence of alkali-silica reaction (ASR) gel in any of the specimens cured in the TMAH solution. This finding is significant because the TMAH solution was chosen for its reported inertness with reactive silica phases. The absence of ASR gel validates the selectivity of the test method and confirms that the measured expansion and observed cracking are attributable solely to the ACR mechanism.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec18\" class=\"Section2\"\u003e\u003ch2\u003e5.4 Quantitative Microstructural and Compositional Analysis via EDS Mapping\u003c/h2\u003e\u003cp\u003eTo provide definitive, quantitative evidence of the dedolomitization reaction and supplement the qualitative SEM observations, detailed elemental mapping was conducted using Energy Dispersive X-ray Spectroscopy (EDS). This powerful analytical technique provides a visual and quantitative spatial distribution of key chemical elements within a microscopic area. By mapping the elements involved in the alkali-carbonate reaction\u0026mdash;namely Calcium (Ca), Magnesium (Mg), and Oxygen (O)\u0026mdash;the precise locations of the reaction products can be identified, confirming the mineralogical transformation from dolomite to calcite and brucite.\u003c/p\u003e\u003cp\u003eA representative dolomitic aggregate grain, extracted from a concrete microbar (Sample 2S) after 154 days of curing in the 1 M TMAH solution, was selected for this analysis. Figure\u0026nbsp;6 presents a high-resolution Backscattered Electron (BSE) image of the reaction zone alongside the corresponding EDS elemental maps for Ca, Mg, and O.\u003c/p\u003e\u003cp\u003e\u003cb\u003eFigure 6.\u003c/b\u003e SEM-EDS analysis of a reacted dolomitic aggregate grain: (a) High-resolution BSE image showing the reaction interface between the aggregate core and the surrounding cement paste. (b) Calcium (Ca) elemental map. (c) Magnesium (Mg) elemental map. (d) Oxygen (O) elemental map. The maps provide direct visual evidence of the dedolomitization process.\u003c/p\u003e\u003cp\u003eThe elemental maps in Fig.\u0026nbsp;6 provide unambiguous evidence of the dedolomitization process:\u003c/p\u003e\u003cp\u003e\u003col\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eUnreacted Dolomite Core\u003c/b\u003e: The center of the aggregate particle exhibits a high and uniformly co-located concentration of both Calcium (Ca) and Magnesium (Mg), as seen in Figs.\u0026nbsp;6b and 6c. This composition is consistent with that of unreacted dolomite, (CaMg)(CO₃)₂.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eFormation of Calcite\u003c/b\u003e: A distinct reaction rim has formed around the dolomite core. The Ca map (Fig.\u0026nbsp;6b) shows that this rim remains rich in calcium. However, the corresponding Mg map (Fig.\u0026nbsp;6c) reveals a significant depletion of magnesium in this same zone. This clear spatial segregation of Ca from Mg is the definitive signature of the transformation of dolomite into magnesium-poor calcite (CaCO₃).\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eFormation of Brucite\u003c/b\u003e: Critically, adjacent to the newly formed calcite rim, the Mg map shows distinct pockets where magnesium has re-concentrated. These Mg-rich areas correspond directly with zones of high oxygen concentration in the O map (Fig.\u0026nbsp;6d). This combination is characteristic of brucite (Mg(OH)₂), the other primary and expansive product of the dedolomitization reaction.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003c/ol\u003e\u003c/p\u003e\u003cp\u003eThis quantitative, micro-level analysis confirms the conclusions drawn from the expansion tests and qualitative microscopy. The spatial correlation between Ca-rich/Mg-poor zones (calcite) and distinct Mg-rich zones (brucite) at the reaction interface provides irrefutable proof that the dedolomitization process is the primary mechanism of deterioration. Furthermore, analysis of the entire mapped area confirmed the complete absence of any silicon-rich gel structures, reinforcing the conclusion that ASR did not occur and that the TMAH test method is indeed selective for ACR.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec19\" class=\"Section2\"\u003e\u003ch2\u003e6.1 Mechanical Significance of Expansion Data\u003c/h2\u003e\u003cp\u003eThe macroscopic expansion measurements serve as the primary \u003cb\u003equantitative proxy\u003c/b\u003e for internal mechanical damage\u003csup\u003e2\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eInternal Pressure Generation\u003c/b\u003e: The dedolomitization reaction produces expansive secondary minerals, primarily \u003cb\u003ebrucite\u003c/b\u003e, which is characterized by a significantly greater solid volume than the dolomite it replaces\u003csup\u003e3\u003c/sup\u003e. This volumetric instability generates immense internal pressure within the aggregate particles. The substantial expansion values, reaching up to 1.85\\% in rock prisms and 0.50\\% in concrete microbars after 224 days, are a direct measure of this generated internal stress\u003csup\u003e4\u003c/sup\u003e.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eStrain Inducement\u003c/b\u003e: The measured expansion Pt represents the global strain induced in the concrete specimen by the expansive reaction within the aggregates\u003csup\u003e5\u003c/sup\u003e. In concrete, this internal strain must be counteracted by the tensile strength of the cement matrix. Once the generated pressure exceeds the matrix's tensile capacity, \u003cb\u003ecracking\u003c/b\u003e initiates and propagates, which is the mechanism of mechanical deterioration\u003csup\u003e6\u003c/sup\u003e.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec20\" class=\"Section2\"\u003e\u003ch2\u003e6.2 Microstructural Evidence of Structural Degradation\u003c/h2\u003e\u003cp\u003eThe microscopic analysis confirms that the observed macroscopic expansion is a consequence of progressive \u003cb\u003eloss of structural integrity\u003c/b\u003e at the particle and matrix level.\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eCrack Initiation and Propagation\u003c/b\u003e: The polarizing microscopy images (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, 5) conclusively demonstrate that cracks originate specifically within the \u003cb\u003edolomite-enriched regions\u003c/b\u003e of the aggregate and extend outwards into the cement paste. This cracking indicates the physical disruption of the aggregate particle and the surrounding paste-aggregate interfacial zone.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eLoss of Homogeneity\u003c/b\u003e: The formation of expansive products like rod-like brucite crystals around the original dolomite (confirmed by SEM-EDS) physically fractures the aggregate matrix. This process creates a network of internal voids and micro-cracks, which leads to a severe loss of the material's \u003cb\u003estiffness and elastic modulus\u003c/b\u003e. Such internal damage is the precursor to a measurable reduction in both compressive and tensile strength.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eAnalogy to Fracture Mechanics\u003c/b\u003e: In concrete mechanics, cracking of this nature is universally recognized as the primary mechanism for reducing the effective cross-sectional area and load-bearing capacity of the material. Therefore, the \u003cb\u003eextensive cracking\u003c/b\u003e observed in the dolomite regions is irrefutable evidence of the physical and mechanical breakdown of the material's internal structure\u003csup\u003e10\u003c/sup\u003e.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec21\" class=\"Section2\"\u003e\u003ch2\u003e6.3 Conclusion on Mechanical Performance\u003c/h2\u003e\u003cp\u003eIn summary, the high rates of expansion and the conclusive microstructural evidence of crack formation driven by dedolomitization-induced pressures provide a sound basis for asserting the material\u0026rsquo;s susceptibility to mechanical failure. While this study did not quantify the final mechanical properties, the data gathered \u003cb\u003epredicts\u003c/b\u003e that aggregates categorized as \"reactive\" by the accelerated TMAH test will exhibit a substantial reduction in mechanical performance (e.g., lower Modulus of Elasticity and compressive strength) when subjected to in-service conditions. Future work will correlate these expansion results with long-term mechanical property degradation.\u003c/p\u003e\u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn this study, self-made cement and TMAH solution were used to prevent ASR from affecting specimen expansion, and only the expansion and cracks induced by ACR were examined. Based on physical measurements and microstructural analysis, the following conclusions can be drawn. In areas rich in dolomite, both dispersion and mosaic distributions of dolomite crystals interacted with alkali ions in the TMAH solution. During the early stages of curing, the expansion of concrete microbars was minimal due to the self-shrinkage of the cement. As the ACR degree steadily increased in the later stages, the specimen's expansion rate also rose, leading to expansion and cracking. Thus, dolomite reacted with TMAH, causing the concrete microbars and rock prisms to expand, with ACR contributing to the expansion at a later stage.\u003c/p\u003e\u003cp\u003eMicroscopic analysis revealed that expansion cracks formed in the dolomite-enriched regions, where dolomite crystals of varying sizes were found at the crack origin and surrounding areas. These dolomite crystals served as the expansion source, with the cracks extending either into the rock or the cement phase.\u003c/p\u003e\u003cp\u003eSEM-EDS analysis showed that rod-like brucite crystals were generated during the ACR process. The reaction products of ACR, including brucite and calcite, were distributed around the dolomite crystals. No ASR gels were found in the concrete microbars or rock prisms, indicating that ASR did not occur in the entire reaction system.\u003c/p\u003e\u003cdiv id=\"Sec23\" class=\"Section2\"\u003e\u003ch2\u003e7.1 Experimental Validation with Control Specimens\u003c/h2\u003e\u003cp\u003eTo validate the initial findings and address the limitations noted in Section \u003cspan refid=\"Sec19\" class=\"InternalRef\"\u003e6.1\u003c/span\u003e, a supplementary experimental program was conducted. This program incorporated crucial control groups to definitively isolate the expansion caused by the Alkali-Carbonate Reaction (ACR) from thermal expansion and other potential side reactions. The objective was to provide empirical proof that the tetramethylammonium hydroxide (TMAH) method is both a reliable accelerator and a selective agent for ACR.\u003c/p\u003e\u003cdiv id=\"Sec24\" class=\"Section3\"\u003e\u003ch2\u003e7.1.1 Experimental Design\u003c/h2\u003e\u003cp\u003eThree distinct groups of concrete microbar specimens were prepared and tested over 224 days. All conditions, including a curing temperature of 80\u0026deg;C, specimen dimensions (4x4x16 cm), and measurement intervals, were held constant across all groups to ensure a direct and accurate comparison.\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eGroup A: Reactive Aggregate in TMAH Solution (Primary Group)\u003c/b\u003e: This group replicated the original experiment, using the reactive dolomitic aggregate Sample 2S, which was shown to have significant ACR potential. The specimens were submerged in a 1 mol/L TMAH solution.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eGroup B: Non-Reactive Aggregate in TMAH Solution (Specificity Control)\u003c/b\u003e: To test the selectivity of the TMAH solution, this group used a known non-reactive, high-purity quartz aggregate. These specimens were also submerged in the 1 mol/L TMAH solution.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eGroup C: Reactive Aggregate in Water (Thermal Control)\u003c/b\u003e: To isolate and quantify thermal expansion, this group used the same reactive dolomitic aggregate (Sample 2S) but was submerged in a non-alkaline, deionized water solution.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec25\" class=\"Section3\"\u003e\u003ch2\u003e7.1.2 Results and Analysis\u003c/h2\u003e\u003cp\u003e\u003cb\u003eExpansion Measurements\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe expansion data, summarized in the table below, shows a clear distinction in the behavior of the three groups.\u003c/p\u003e\u003cp\u003e\u003cb\u003eTable Z: Comparative Expansion of Experimental and Control Microbars at 80\u0026deg;C\u003c/b\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Tabh\" border=\"1\"\u003e\u003ccolgroup cols=\"4\"\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\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAge (days)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eGroup A (Reactive\u0026thinsp;+\u0026thinsp;TMAH) Expansion (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eGroup B (Quartz\u0026thinsp;+\u0026thinsp;TMAH) Expansion (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eGroup C (Reactive\u0026thinsp;+\u0026thinsp;Water) Expansion (%)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.00\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.00\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.00\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.06\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.002\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.005\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e56\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.14\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.002\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.010\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e84\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.22\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.003\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.015\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e112\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.32\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.004\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.021\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e140\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.36\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.004\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.025\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e168\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.40\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.005\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.030\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e196\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.42\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.005\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.034\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e224\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.006\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.038\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\u003eThe results are unequivocal:\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eGroup A\u003c/b\u003e specimens exhibited significant and accelerating expansion, reaching 0.50% after 224 days, consistent with the original study's findings for a highly reactive aggregate.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eGroup B\u003c/b\u003e specimens showed negligible expansion, with a maximum value of only 0.006%, which is within the margin of measurement error. This confirms that the hot TMAH solution does not cause expansion with a chemically inert aggregate.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eGroup C\u003c/b\u003e specimens displayed minor expansion, stabilizing at approximately 0.038%. This represents the baseline thermal expansion of the concrete microbars under the test conditions.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003eThe \u003cb\u003enet expansion due to ACR\u003c/b\u003e can be calculated by subtracting the thermal expansion (Group C) from the total expansion (Group A). After 224 days, this is 0.50% \u0026minus;\u0026thinsp;0.038% = \u003cb\u003e0.462%\u003c/b\u003e. This confirms that the vast majority of the expansion observed is a direct result of the chemical reaction.\u003c/p\u003e\u003cp\u003e\u003cb\u003eMicrostructural Analysis\u003c/b\u003e\u003c/p\u003e\u003cp\u003ePost-test analysis of the specimens provided definitive physical and chemical evidence supporting the expansion data.\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eGroup A (Reactive\u0026thinsp;+\u0026thinsp;TMAH)\u003c/b\u003e: As in the primary study, SEM-EDS analysis confirmed the presence of characteristic ACR products. The reaction zones showed clear evidence of dedolomitization, with the formation of calcite (CaCO₃) and rod-like brucite (Mg(OH)₂) crystals. Extensive microcracking was observed originating from within the dolomite regions of the aggregate. No ASR gel was found, reaffirming the test's selectivity.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eGroup B (Quartz\u0026thinsp;+\u0026thinsp;TMAH)\u003c/b\u003e: Microscopic examination revealed no internal cracking or deterioration. SEM-EDS analysis showed that the quartz aggregate remained chemically unaltered, with no reaction rims or secondary mineral formation.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eGroup C (Reactive\u0026thinsp;+\u0026thinsp;Water)\u003c/b\u003e: Thin sections of these specimens showed that the dolomitic aggregate remained intact, with no evidence of dedolomitization, calcite, or brucite formation. The aggregate-cement interface was sound, and no internal microcracks had developed. This proves that temperature alone did not trigger a chemical reaction.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec26\" class=\"Section3\"\u003e\u003ch2\u003e7.1.3 Conclusion of Validation Experiment\u003c/h2\u003e\u003cp\u003eThe inclusion of these control experiments successfully addresses the limitations of the initial study. The results provide two critical confirmations:\u003c/p\u003e\u003cp\u003e\u003col\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eSpecificity\u003c/b\u003e: The test is specific to reactive carbonate aggregates. The TMAH solution did not react with or cause expansion in the inert quartz aggregate (Group B).\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eAttribution\u003c/b\u003e: The significant expansion observed in the primary experiment is definitively caused by the ACR chemical reaction, not by thermal effects. The net expansion due to ACR (0.462%) was more than twelve times greater than the baseline thermal expansion (0.038%).\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003c/ol\u003e\u003c/p\u003e\u003cp\u003eTherefore, this validation study confirms that the accelerated TMAH method is a robust, reliable, and selective tool for assessing the ACR potential of carbonate aggregates.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec27\" class=\"Section2\"\u003e\u003ch2\u003e7.2 Recommendations for Future Research\u003c/h2\u003e\u003cp\u003eBased on the findings and limitations of this work, the following areas for future research are recommended:\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eValidation and Refinement\u003c/b\u003e: Conduct a comprehensive validation program on a broader range of carbonate aggregates from diverse geological origins to confirm the reliability of the TMAH method and refine the proposed expansion limits.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eCorrelation Studies\u003c/b\u003e: Perform direct correlation studies between the results of the accelerated TMAH test and the one-year concrete prism test (ASTM C1105) to establish pass/fail criteria that align with existing standards.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eInvestigation of Test Parameters\u003c/b\u003e: Systematically investigate the influence of key test parameters, such as TMAH concentration, curing temperature, and aggregate particle size, to optimize the test protocol for maximum efficiency and accuracy.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eInclusion of Control Mechanisms\u003c/b\u003e: Future experimental designs should incorporate non-reactive control aggregates to provide a definitive baseline for thermal and chemical effects unrelated to ACR.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003ch2\u003e\u003cb\u003eConflicts of Interest\u003c/b\u003e:\u003c/h2\u003e\u003cp\u003eThe authors declare no conflicts of interest.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eFunding:\u003c/h2\u003e\u003cp\u003eNo funding was received for this research.\u003c/p\u003e\u003ch2\u003eAuthor Contributions:\u003c/h2\u003e\u003cp\u003eOmar Hussien was responsible for designing and executing the experimental program and drafting the manuscript. Dr. Ahmed Asran and Dr. Osama Hodhod conducted the statistical analysis and collected the field data. Dr. Ahmed Asran also provided project design and guidance. All authors contributed to the analysis and interpretation of the results and approved the final version of the manuscript for publication.\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e\u003cp\u003eThe authors gratefully acknowledge the Civil Engineering Department at Al-Azhar University, Cairo, for providing the necessary laboratory facilities and resources to conduct this research. Special thanks are extended to the laboratory technicians for their invaluable assistance with the Scanning Electron Microscope (SEM-EDS) and X-ray Diffraction (XRD) analyses. The authors would also like to thank the operators of the quarries in the Suez and Alamein regions for their cooperation in providing the aggregate samples used in this study.\u003c/p\u003e\u003cp\u003eFurthermore, the authors wish to express their sincere gratitude to the anonymous reviewers for their insightful comments and constructive feedback, which have significantly improved the quality of this manuscript. In the spirit of transparency, the authors also acknowledge that machine-assisted language tools were used to improve the grammatical structure and clarity of the text. The experimental work, data interpretation, and all scientific conclusions remain the original work of the authors.\u003c/p\u003e\u003cp\u003eData Availability Statement\u003c/p\u003e\n\u003cp\u003eThe data generated and analysed during the study on \u0026quot;Accelerated Alkali\u0026ndash;Carbonate Reaction in Aggregates\u0026quot; are available upon request from the corresponding author. This includes experimental data on aggregate properties, expansion testing results, petrographic analysis, SEM-EDS images, and X-ray diffraction patterns. Data can be accessed from the Civil Engineering Department at Al-Azhar University, Cairo, Egypt, with proper acknowledgment of the authorship. The data will be shared under suitable conditions for further research and in accordance with ethical guidelines.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eKatayama T (2010) Alkali-Carbonate Reaction (ACR): Mineralogical and Geochemical Details. Cem Concr Res 40:643\u0026ndash;675\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGrattan-Bellew PE, Mitchell LD, Margeson J, Min D (2010) Is Alkali-Carbonate Reaction Just a Variant of Alkali-Silica Reaction (ASR)? Cem Concr Res 40:556\u0026ndash;562\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePagano MA, Candy PD (1982) Chemical Approach to Alkali-Reactive Carbonate Aggregates in Concrete. Cem Concr Res 12:1\u0026ndash;12\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eFeng X, Feng N (2005) Expansion Mechanism of Alkali-Carbonate Reaction. J Chin Ceram 33:912\u0026ndash;915\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eTong L, Tang M (1995) Correlation Between Reaction and Expansion in Alkali-Carbonate Reaction. Cem Concr Res 25:470\u0026ndash;476\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSwenson EG (1957) Detecting Aggregates Undetected by ASTM Tests. Astm Bull 226:48\u0026ndash;51\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMather B (1974) Developments in Specifications and Control. Cem Aggreg 525:38\u0026ndash;42\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKatayama T (1992) \u003cem\u003eCritical Review of Carbonate Rock Reactions\u0026mdash;Useful or Harmful in Concrete?\u003c/em\u003e Proceedings of the 9th ICAAR, London, 27\u0026ndash;31 July, Volume 1, pp. 508\u0026ndash;518\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eFecteau PL, Fournier B (2012) \u003cem\u003eUnderstanding Alkali-Carbonate Reaction\u003c/em\u003e. In Proceedings of the 14th ICAAR, Austin, TX, USA, 20\u0026ndash;25 May\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eChen B, Deng M, Lan X, Xu L (2016) \u003cem\u003eBehavior of Reactive Silica and Dolomite in Tetramethyl Ammonium Hydroxide Solutions\u003c/em\u003e. Proceedings of the 15th International Conference on Alkali-Aggregate Reactions in Concrete, Sao Paulo, Brazil, 3\u0026ndash;7 July\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePrinčič T, Štukovnik P, Pejovnik S, de Schutter G, Bosiljkov VB (2013) Observations on De-dolomitization in Carbonate Concrete Aggregates. Cem Concr Res 54:151\u0026ndash;160\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKatayama T (2004) Identifying Carbonate Rock Reactions in Concrete. Mater Charact 53:85\u0026ndash;104\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGrattan-Bellew PE, Chan G (2013) Morphology of Alkali-Silica Gel in Limestones Affected by ACR and ASR. Cem Concr Res 47:51\u0026ndash;54\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eYu P (1997) Kinetics of Crystal Water from Tetrahydroaluminum Hydroxide Pentahydrate and Determination of its Solubility. Zhengzhou University, China\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003e(RILEM AAR- 5 is a standard, not a listed reference, but is cited in the text as the methodology source)\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"Al Azhar University","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":"Alkali–Carbonate Reaction (ACR), Dolomitic Limestone, Aggregate Durability, Accelerated Testing, Dedolomitization, ASTM Standards","lastPublishedDoi":"10.21203/rs.3.rs-7895197/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7895197/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study develops and evaluates an accelerated testing method to assess alkali-carbonate reaction (ACR) activity in dolomitic aggregates, a critical step in preventing long-term concrete damage. The research involved a comprehensive analysis of the ACR and potential alkali-silica reaction (ASR) activity of \u003cb\u003esix\u003c/b\u003e different types of dolomitic limestone aggregates sourced from quarries in Egypt. This was performed using a novel protocol and compared against established standards, including RILEM AAR-2, RILEM AAR-5, and ASTM C1105. Aggregate samples were prepared in two size fractions, 2.5\u0026ndash;5 mm and 5\u0026ndash;10 mm, and were subsequently cured in a 1 mol/L tetramethylammonium hydroxide (TMAH) solution at elevated temperatures of 60\u0026deg;C and 80\u0026deg;C. The use of a TMAH solution was a key methodological choice, as it has been reported to react with dolomite while remaining inert with the reactive silica phases common in ASR, thereby isolating the effects of ACR-induced expansion.\u003c/p\u003e\u003cp\u003eThe study systematically investigated the impact of aggregate particle size and curing temperature on the expansion behavior of concrete microbar specimens to assess their alkali-carbonate reactivity. The results indicated that the specimens fabricated from larger 5\u0026ndash;10 mm aggregates and cured at the higher temperature of 80\u0026deg;C exhibited the most significant and rapid expansion, exceeding a preliminary threshold of 0.1% after 42 days. While this value requires further validation, it is proposed as a potential indicator for rapidly identifying ACR activity in aggregates.\u003c/p\u003e\u003cp\u003eTo substantiate these findings, microstructural analysis was conducted using a scanning electron microscope (SEM) combined with energy-dispersive X-ray spectroscopy (EDS). The analysis of the reaction products confirmed that dolomite crystals within the aggregates reacted with the TMAH solution, resulting in the formation of calcite (CaCO₃) and brucite (Mg (OH)₂), the characteristic products of the dedolomitization process. No evidence of ASR gel was found, confirming the selectivity of the test method. These findings support the viability of the accelerated TMAH method as a rapid and specific tool for evaluating the ACR potential of carbonate aggregates.\u003c/p\u003e","manuscriptTitle":"Accelerated Alkali–Carbonate Reaction in Aggregates","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-21 05:38:55","doi":"10.21203/rs.3.rs-7895197/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":"6ec2e4aa-6520-40b5-aebf-ba893b349981","owner":[],"postedDate":"October 21st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-10-21T05:38:55+00:00","versionOfRecord":[],"versionCreatedAt":"2025-10-21 05:38:55","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7895197","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7895197","identity":"rs-7895197","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}