Pub Date : 2025-08-09DOI: 10.1016/j.cemconres.2025.108009
Zixian Su, Zengliang Yue, Alastair T.M. Marsh, Marco Di Michiel, Timothy L. Burnett, John L. Provis, Partha P. Paul, Susan A. Bernal, Philip J. Withers
In situ synchrotron X-ray diffraction computed tomography (XRD-CT) and micro-tomography (μCT) are used to determine the effects of accelerated carbonation on sodium silicate- and carbonate-activated slag cement pastes, focusing on changes in crystalline and semi-crystalline phases, and pore structures. Accelerated carbonation leads to decalcification of the interlayer of aluminium-substituted calcium silicate hydrate (C-(A)-S-H), resulting in reduced interlayer distance, volume shrinkage, and increased porosity with larger pore volumes. The hydrotalcite-like Mg-Al LDH phase acts as a CO2 sink, mitigating the increased concentration of CO32− in pore solution via interlayer anion exchange of OH− for CO32−, playing a more significant role in sodium silicate slag cement paste. Additionally, sodium silicate-activated slag cement is found to have a finer, more tortuous pore distribution and higher carbonation resistance than sodium carbonate-activated slag cement, as evidenced by a smaller degree of carbonation-induced C-(A)-S-H shrinkage, and a smaller increase in porosity volume during carbonation.
采用原位同步加速器x射线衍射计算机断层扫描（XRD-CT）和微断层扫描（μCT）研究了加速碳化对水玻璃和碳酸盐活化矿渣水泥浆体的影响，重点研究了矿渣水泥浆体的晶相、半晶相和孔隙结构的变化。碳化加速导致铝取代水合硅酸钙（C-(A)- s - h）夹层脱钙，导致层间距离减小，体积收缩，孔隙率增大，孔隙体积增大。类水滑石Mg-Al LDH相作为CO2汇，通过层间OH -阴离子交换CO32 -，减缓孔溶液中CO32 -浓度的增加，在水玻璃渣水泥浆中发挥更大的作用。与碳酸钠活化矿渣水泥相比，硅酸钠活化矿渣水泥具有更细、更弯曲的孔隙分布和更高的抗碳化能力，表现为碳化引起的C-(a)- s - h收缩程度更小，碳化过程中孔隙体积的增加也更小。
{"title":"4D quantification of C-(A)-S-H and Mg-Al LDH phase alterations and microstructural evolution during accelerated carbonation of alkali-activated slag pastes","authors":"Zixian Su, Zengliang Yue, Alastair T.M. Marsh, Marco Di Michiel, Timothy L. Burnett, John L. Provis, Partha P. Paul, Susan A. Bernal, Philip J. Withers","doi":"10.1016/j.cemconres.2025.108009","DOIUrl":"https://doi.org/10.1016/j.cemconres.2025.108009","url":null,"abstract":"In situ synchrotron X-ray diffraction computed tomography (XRD-CT) and micro-tomography (μCT) are used to determine the effects of accelerated carbonation on sodium silicate- and carbonate-activated slag cement pastes, focusing on changes in crystalline and semi-crystalline phases, and pore structures. Accelerated carbonation leads to decalcification of the interlayer of aluminium-substituted calcium silicate hydrate (C-(A)-S-H), resulting in reduced interlayer distance, volume shrinkage, and increased porosity with larger pore volumes. The hydrotalcite-like Mg-Al LDH phase acts as a CO<sub>2</sub> sink, mitigating the increased concentration of CO<sub>3</sub><sup>2−</sup> in pore solution via interlayer anion exchange of OH<sup>−</sup> for CO<sub>3</sub><sup>2−</sup>, playing a more significant role in sodium silicate slag cement paste. Additionally, sodium silicate-activated slag cement is found to have a finer, more tortuous pore distribution and higher carbonation resistance than sodium carbonate-activated slag cement, as evidenced by a smaller degree of carbonation-induced C-(A)-S-H shrinkage, and a smaller increase in porosity volume during carbonation.","PeriodicalId":266,"journal":{"name":"Cement and Concrete Research","volume":"20 1","pages":""},"PeriodicalIF":11.4,"publicationDate":"2025-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144802858","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Dicalcium silicate is a key carbonatable mineral in Portland cement. Typically, pure C2S is synthesized through high-temperature solid-phase reactions above 1400 °C, but such temperatures can negatively affect its carbonation behavior, with the underlying mechanisms remaining unclear. This study investigated the effect of calcination temperatures (600 °C to 1400 °C) on C2S carbonation. Results show that high calcination temperatures significantly reduce carbonation reactivity and CO2 uptake. This is primarily due to the increase in particle size, the transformation from fibers to particles, and a decrease in specific surface area. Additionally, the internal crystal defects in low-temperature calcined C2S contribute to its high reactivity. However, the temperature-induced reduction in mesoporosity, increase in crystal size, decrease in defects, and phase transition from β-C2S to γ-C2S also affect carbonation reactivity. These factors also influence the polymorphs and morphology of CaCO3. This study offers guidance for developing low-temperature synthesis methods for low-calcium cement.
{"title":"Insights into the carbonation behavior of polymorphs of Ca2SiO4 (C2S): the role of calcination temperature","authors":"Miao Ren, Peiliang Shen, Yi Jiang, Jionghuang He, Qinglong Qin, Chi-sun Poon","doi":"10.1016/j.cemconres.2025.108005","DOIUrl":"https://doi.org/10.1016/j.cemconres.2025.108005","url":null,"abstract":"Dicalcium silicate is a key carbonatable mineral in Portland cement. Typically, pure C<sub>2</sub>S is synthesized through high-temperature solid-phase reactions above 1400 °C, but such temperatures can negatively affect its carbonation behavior, with the underlying mechanisms remaining unclear. This study investigated the effect of calcination temperatures (600 °C to 1400 °C) on C<sub>2</sub>S carbonation. Results show that high calcination temperatures significantly reduce carbonation reactivity and CO<sub>2</sub> uptake. This is primarily due to the increase in particle size, the transformation from fibers to particles, and a decrease in specific surface area. Additionally, the internal crystal defects in low-temperature calcined C<sub>2</sub>S contribute to its high reactivity. However, the temperature-induced reduction in mesoporosity, increase in crystal size, decrease in defects, and phase transition from β-C<sub>2</sub>S to γ-C<sub>2</sub>S also affect carbonation reactivity. These factors also influence the polymorphs and morphology of CaCO<sub>3</sub>. This study offers guidance for developing low-temperature synthesis methods for low-calcium cement.","PeriodicalId":266,"journal":{"name":"Cement and Concrete Research","volume":"173 1","pages":""},"PeriodicalIF":11.4,"publicationDate":"2025-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144802857","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Elucidating the impact of nitrate anions on sulfate balance mechanism of cement is essential for optimizing the hydration performance of cementitious systems. This knowledge provides fundamental insights into regulating cementitious systems under varying service conditions. This study investigated how varying SO₃ content and nitrate anions affect sulfate balance in C3S/C3A pastes and the impact of these alterations on the hydration process. The influence of nitrate anions from Mg(NO₃)₂ on sulfate balance was determined by calorimetry, ICP-OES, TG, XRD and SEM. It was found that nitrate anions counteract Mg2+ inhibition of C3S and C3A hydration by enhancing mineral dissolution, liberating Ca2+ into pore solutions to accelerate hydration. Accelerating the formation process of ettringite (AFt) increased demand for sulfate. This Ca2+ enrichment promotes portlandite supersaturation, which shortens the hydration induction period and accelerates C-S-H growth. The sulfate content significantly influences C-S-H growth kinetics at fixed nitrate concentrations.
{"title":"Effect of nitrate anions on sulfate balance and hydration kinetics in C3S/C3A systems","authors":"Lei Lu, Xiao Liu, Jian Wang, Simai Wang, Yuhan Yao, Yurui Xu, Minghui Jiang, Yanzhen Xiao, Yanxi Li, Ziming Wang, Suping Cui","doi":"10.1016/j.cemconres.2025.108008","DOIUrl":"https://doi.org/10.1016/j.cemconres.2025.108008","url":null,"abstract":"Elucidating the impact of nitrate anions on sulfate balance mechanism of cement is essential for optimizing the hydration performance of cementitious systems. This knowledge provides fundamental insights into regulating cementitious systems under varying service conditions. This study investigated how varying SO₃ content and nitrate anions affect sulfate balance in C<sub>3</sub>S/C<sub>3</sub>A pastes and the impact of these alterations on the hydration process. The influence of nitrate anions from Mg(NO₃)₂ on sulfate balance was determined by calorimetry, ICP-OES, TG, XRD and SEM. It was found that nitrate anions counteract Mg<sup>2+</sup> inhibition of C<sub>3</sub>S and C<sub>3</sub>A hydration by enhancing mineral dissolution, liberating Ca<sup>2+</sup> into pore solutions to accelerate hydration. Accelerating the formation process of ettringite (AFt) increased demand for sulfate. This Ca<sup>2+</sup> enrichment promotes portlandite supersaturation, which shortens the hydration induction period and accelerates C-S-H growth. The sulfate content significantly influences C-S-H growth kinetics at fixed nitrate concentrations.","PeriodicalId":266,"journal":{"name":"Cement and Concrete Research","volume":"290 1","pages":""},"PeriodicalIF":11.4,"publicationDate":"2025-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144802870","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-08-06DOI: 10.1016/j.cemconres.2025.108006
Lupesh Dudi, Shashank Bishnoi
This study investigates why mass transport properties differ between Portland cement (PC) and low-clinker binders before and after carbonation by examining their underlying microstructural characteristics. Mass transport parameters (sorption rate, oxygen permeability, and chloride migration) were evaluated for non‑carbonated and carbonated mortars made with PC and low-clinker binders (fly ash, slag, limestone-calcined clay, and fly ash–slag composites) at water-to-binder ratios of 0.4, 0.5, and 0.6. Complementary microstructural analyses included mercury intrusion porosimetry (MIP), N₂ adsorption, saturation degree, pore-connectivity factor, and water-accessible porosity. For non‑carbonated mortars, no generalized correlation was found between transport properties and microstructure due to the varying effects of different SCMs on critical/threshold pore diameter, pore-connectivity, and pore surface/solution interaction with transporting media. However, incorporating material coefficients (based on transport mechanism) alongside porosity resulted in a strong correlation across different mixes. After carbonation, low-clinker binders exhibited increased transport due to coarsened pore structures, higher connectivity, and reduced interaction of transporting media with pore surface/solution. Furthermore, a generalized correlation was found between mass transport properties and microstructural parameters in carbonated mortars across all mass transport mechanisms, indicating that microstructural differences from SCMs addition diminish after carbonation. Carbonation results in homogenizing key features such as hygroscopicity and pore surface/solution interaction with transporting media. Additionally, in carbonated mortars, pore-connectivity, bulk conductivity, and critical/threshold pore diameter can be treated as functions of total porosity, enabling the development of cement-independent mass transport models.
{"title":"Revealing the relationships between transport properties and microstructure characteristics in low-clinker binders before and after carbonation","authors":"Lupesh Dudi, Shashank Bishnoi","doi":"10.1016/j.cemconres.2025.108006","DOIUrl":"10.1016/j.cemconres.2025.108006","url":null,"abstract":"<div><div>This study investigates why mass transport properties differ between Portland cement (PC) and low-clinker binders before and after carbonation by examining their underlying microstructural characteristics. Mass transport parameters (sorption rate, oxygen permeability, and chloride migration) were evaluated for non‑carbonated and carbonated mortars made with PC and low-clinker binders (fly ash, slag, limestone-calcined clay, and fly ash–slag composites) at water-to-binder ratios of 0.4, 0.5, and 0.6. Complementary microstructural analyses included mercury intrusion porosimetry (MIP), N₂ adsorption, saturation degree, pore-connectivity factor, and water-accessible porosity. For non‑carbonated mortars, no generalized correlation was found between transport properties and microstructure due to the varying effects of different SCMs on critical/threshold pore diameter, pore-connectivity, and pore surface/solution interaction with transporting media. However, incorporating material coefficients (based on transport mechanism) alongside porosity resulted in a strong correlation across different mixes. After carbonation, low-clinker binders exhibited increased transport due to coarsened pore structures, higher connectivity, and reduced interaction of transporting media with pore surface/solution. Furthermore, a generalized correlation was found between mass transport properties and microstructural parameters in carbonated mortars across all mass transport mechanisms, indicating that microstructural differences from SCMs addition diminish after carbonation. Carbonation results in homogenizing key features such as hygroscopicity and pore surface/solution interaction with transporting media. Additionally, in carbonated mortars, pore-connectivity, bulk conductivity, and critical/threshold pore diameter can be treated as functions of total porosity, enabling the development of cement-independent mass transport models.</div></div>","PeriodicalId":266,"journal":{"name":"Cement and Concrete Research","volume":"198 ","pages":"Article 108006"},"PeriodicalIF":13.1,"publicationDate":"2025-08-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144780386","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-08-01DOI: 10.1016/j.cemconres.2025.108003
Fei Meng , Kaidong Han , Tengfei Guo , Xin Shu , Yandong Guo , Lei Dong , Jingshun Cai , Qianping Ran
The bulk modification of cementitious materials by hydrophobic agents is an effective strategy to reduce the water absorption. However, the decrease in compressive strength has been one of the most significant problems. We reported in this paper the synthesis of a sustained-release capsule (OTES@SC) with n-octyltriethoxy silane (OTES) as core material and silica shell. The capsule (containing 70.0 % of OTES) enabled the continuous release of OTES within days. The addition of OTES@SC reduced the water absorption while improved the compressive strength of hardened cement paste. Both the effects would be more pronounced at higher capsule dosages (~70.6 % water absorption reducing and 17.4 % increase of compressive strength at 0.5 wt% capsule dosage). The sustained release of OTES from OTES@SC enabled the continuous surface modification by OTES both already in cement paste and newly formed. Compared with the direct addition of OTES (average thickness of the hydrophobic layer decreased from ~10 nm to ~0 nm during hydration), the hydrophobic layer had reached a thickness of a few molecules layer at 28 d, exhibiting significantly improved uniformity on cement paste particle surfaces. The thinner layer and the normal hydration of part of reactive sites of clinkers greatly reduced the inhibition effect of OTES on hydration. Additionally, the pozzolanic effect and nano-size of silica further promoted hydration. Thus, OTES@SC improved hydration degree and refined pore structure of paste.
{"title":"Elucidating the effects and mechanisms of OTES@silica nano capsules on water resistance and compressive strength of cement paste","authors":"Fei Meng , Kaidong Han , Tengfei Guo , Xin Shu , Yandong Guo , Lei Dong , Jingshun Cai , Qianping Ran","doi":"10.1016/j.cemconres.2025.108003","DOIUrl":"10.1016/j.cemconres.2025.108003","url":null,"abstract":"<div><div>The bulk modification of cementitious materials by hydrophobic agents is an effective strategy to reduce the water absorption. However, the decrease in compressive strength has been one of the most significant problems. We reported in this paper the synthesis of a sustained-release capsule (OTES@SC) with n-octyltriethoxy silane (OTES) as core material and silica shell. The capsule (containing 70.0 % of OTES) enabled the continuous release of OTES within days. The addition of OTES@SC reduced the water absorption while improved the compressive strength of hardened cement paste. Both the effects would be more pronounced at higher capsule dosages (~70.6 % water absorption reducing and 17.4 % increase of compressive strength at 0.5 wt% capsule dosage). The sustained release of OTES from OTES@SC enabled the continuous surface modification by OTES both already in cement paste and newly formed. Compared with the direct addition of OTES (average thickness of the hydrophobic layer decreased from ~10 nm to ~0 nm during hydration), the hydrophobic layer had reached a thickness of a few molecules layer at 28 d, exhibiting significantly improved uniformity on cement paste particle surfaces. The thinner layer and the normal hydration of part of reactive sites of clinkers greatly reduced the inhibition effect of OTES on hydration. Additionally, the pozzolanic effect and nano-size of silica further promoted hydration. Thus, OTES@SC improved hydration degree and refined pore structure of paste.</div></div>","PeriodicalId":266,"journal":{"name":"Cement and Concrete Research","volume":"198 ","pages":"Article 108003"},"PeriodicalIF":13.1,"publicationDate":"2025-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144750250","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-07-24DOI: 10.1016/j.cemconres.2025.108002
Zuobang Yao , Ram Pal , Haemin Song , Arthur Van de Keere , Ali Kashani , Elke Gruyaert , Taehwan Kim
This paper presented the experimental results of investigating chloride resistance and the microstructure of alkali-activated concrete (AAC). To show the reliable and efficient chloride transport analyses for AAC, a modified rapid chloride penetration test using 10 V was validated, and the conventional chloride profile methods were compared with the newly developed micro X-ray fluorescence (μXRF) profile method. Six AAC mixtures incorporating different precursors were evaluated for mechanical strength, water absorption, chloride diffusion, and binding. At the same content of ground granulated blast furnace slag in mixtures, the precursor incorporating calcined bauxite tailings and rice husk ash increased porosity and reduced chloride resistance compared to that containing fly ash. This study revealed that chloride binding in all AAC used in this study was predominantly physical and reversible, contrasting with Portland cement systems. μXRF technique provided reliable and spatially resolved chloride profile data for AAC. This study provides valuable insights into AAC performance and testing, emphasising the importance of precursor selection for sustainable AAC.
{"title":"Chloride transport, binding, and microstructure in alkali-activated concrete with different types of precursor combinations","authors":"Zuobang Yao , Ram Pal , Haemin Song , Arthur Van de Keere , Ali Kashani , Elke Gruyaert , Taehwan Kim","doi":"10.1016/j.cemconres.2025.108002","DOIUrl":"10.1016/j.cemconres.2025.108002","url":null,"abstract":"<div><div>This paper presented the experimental results of investigating chloride resistance and the microstructure of alkali-activated concrete (AAC). To show the reliable and efficient chloride transport analyses for AAC, a modified rapid chloride penetration test using 10 V was validated, and the conventional chloride profile methods were compared with the newly developed micro X-ray fluorescence (μXRF) profile method. Six AAC mixtures incorporating different precursors were evaluated for mechanical strength, water absorption, chloride diffusion, and binding. At the same content of ground granulated blast furnace slag in mixtures, the precursor incorporating calcined bauxite tailings and rice husk ash increased porosity and reduced chloride resistance compared to that containing fly ash. This study revealed that chloride binding in all AAC used in this study was predominantly physical and reversible, contrasting with Portland cement systems. μXRF technique provided reliable and spatially resolved chloride profile data for AAC. This study provides valuable insights into AAC performance and testing, emphasising the importance of precursor selection for sustainable AAC.</div></div>","PeriodicalId":266,"journal":{"name":"Cement and Concrete Research","volume":"198 ","pages":"Article 108002"},"PeriodicalIF":10.9,"publicationDate":"2025-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144694944","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-07-22DOI: 10.1016/j.cemconres.2025.107999
Yun Chen , Jiayi Chen , Mayank Gupta , Xuhui Liang , Luiz Miranda de Lima , Zhiyuan Xu , Yibing Zuo , Suhong Yin , Qijun Yu , Guang Ye
This study presents an extended numerical approach based on GeoMicro3D to simulate the reaction kinetics and three-dimensional (3D) microstructure evolution of alkali-activated fly ash (AAFA). Dissolution experiments were conducted under varying NaOH concentrations and temperatures to formulate predictive rate functions for Si and Al release. These experimentally derived kinetic functions, alongside a thermodynamic dataset for N-(C-)A-S-H gels, were incorporated into the GeoMicro3D model to capture the chemical reactions and 3D microstructure evolution of AAFA. The model well captured reaction degree of fly ash, formation of solid products, evolution of pore solution compositions, and porosity over time. Notably, it is the first to predict the time-dependent spatial distribution of phases within the 3D AAFA microstructure by integrating kinetic and microstructural modeling. Dual validation using both dissolution data and microstructural metrics demonstrates the model's reliability and robustness. This integrated framework provides new insights into the coupled chemical–microstructural evolution of alkali-activated materials.
本文提出了一种基于GeoMicro3D的扩展数值方法来模拟碱活化粉煤灰（AAFA）的反应动力学和三维（3D）微观结构演化。在不同的NaOH浓度和温度下进行了溶解实验，以建立Si和Al释放的预测速率函数。这些实验导出的动力学函数，以及N-(C-) a - s - h凝胶的热力学数据集，被整合到GeoMicro3D模型中，以捕捉AAFA的化学反应和3D微观结构演变。该模型较好地捕捉了粉煤灰的反应程度、固体产物的形成、孔隙溶液组成的演变以及孔隙度随时间的变化。值得注意的是，这是第一个通过整合动力学和微观结构建模来预测三维AAFA微观结构中相的时空分布的研究。使用溶解数据和微观结构指标的双重验证证明了模型的可靠性和稳健性。这一综合框架为碱活化材料的化学-微观结构耦合演化提供了新的见解。
{"title":"An experimental and numerical study of alkali-activated fly ash paste – from dissolution kinetics to microstructure formation","authors":"Yun Chen , Jiayi Chen , Mayank Gupta , Xuhui Liang , Luiz Miranda de Lima , Zhiyuan Xu , Yibing Zuo , Suhong Yin , Qijun Yu , Guang Ye","doi":"10.1016/j.cemconres.2025.107999","DOIUrl":"10.1016/j.cemconres.2025.107999","url":null,"abstract":"<div><div>This study presents an extended numerical approach based on GeoMicro3D to simulate the reaction kinetics and three-dimensional (3D) microstructure evolution of alkali-activated fly ash (AAFA). Dissolution experiments were conducted under varying NaOH concentrations and temperatures to formulate predictive rate functions for Si and Al release. These experimentally derived kinetic functions, alongside a thermodynamic dataset for N-(C-)A-S-H gels, were incorporated into the GeoMicro3D model to capture the chemical reactions and 3D microstructure evolution of AAFA. The model well captured reaction degree of fly ash, formation of solid products, evolution of pore solution compositions, and porosity over time. Notably, it is the first to predict the time-dependent spatial distribution of phases within the 3D AAFA microstructure by integrating kinetic and microstructural modeling. Dual validation using both dissolution data and microstructural metrics demonstrates the model's reliability and robustness. This integrated framework provides new insights into the coupled chemical–microstructural evolution of alkali-activated materials.</div></div>","PeriodicalId":266,"journal":{"name":"Cement and Concrete Research","volume":"198 ","pages":"Article 107999"},"PeriodicalIF":10.9,"publicationDate":"2025-07-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144678281","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This article explains the vibrational modes in the SiO stretching range in the IR spectra of synthetic C-S-H phases with varying C/S ratios. These are compared with selected in situ spectra of hydrates of OPC, and those of synthetic crystalline hydrates. The assignments were supported by 29Si NMR and trimethylsilylation (TMS) data. IR and Raman polarized spectra of oriented crystals of 14 Å tobermorite, jennite and jaffeite enabled direct observation of the SiO vibrational modes. They were successfully resolved based on the involvement of specific silicon (paired, bridging) and oxygen (bridging, non-bridging) atoms, and were compared with existing theoretical data. The resemblance between the IR spectra of synthetic C-S-H and those formed upon hydration of OPC, proves the suitability of model C-S-H phases for understanding hydration processes. Some uncertainties in the assignment of the C-S-H bands observed in existing in situ IR experiments are discussed, and potential sources of error identified.
本文解释了不同C/S比的合成C-S- h相在红外光谱中SiO拉伸范围内的振动模式。这些与选择的OPC水合物和合成晶体水合物的原位光谱进行了比较。29Si核磁共振和三甲基硅基化（TMS）数据支持了这些指派。14 Å tobermorite， jennite和jaffeite取向晶体的红外和拉曼偏振光谱可以直接观察SiO的振动模式。基于特定硅原子（配对的、桥接的）和氧原子（桥接的、非桥接的）的参与，它们被成功地解决了，并与现有的理论数据进行了比较。合成C-S-H的红外光谱与OPC水化后形成的红外光谱相似，证明了模型C-S-H相对理解水化过程的适用性。讨论了现有原位红外实验中观测到的C-S-H波段分配中的一些不确定性，并确定了潜在的误差来源。
{"title":"Assignment of SiO vibrational modes in the IR spectra of C-S-H phases based on single-crystal polarized IR and Raman spectra of 14 Å tobermorite, jennite, and jaffeite","authors":"Krassimir Garbev , Biliana Gasharova , Angela Ullrich , Günter Beuchle , Peter Stemmermann","doi":"10.1016/j.cemconres.2025.108000","DOIUrl":"10.1016/j.cemconres.2025.108000","url":null,"abstract":"<div><div>This article explains the vibrational modes in the Si<img>O stretching range in the IR spectra of synthetic C-S-H phases with varying C/S ratios. These are compared with selected <em>in situ</em> spectra of hydrates of OPC, and those of synthetic crystalline hydrates. The assignments were supported by <sup>29</sup>Si NMR and trimethylsilylation (TMS) data. IR and Raman polarized spectra of oriented crystals of 14 Å tobermorite, jennite and jaffeite enabled direct observation of the Si<img>O vibrational modes. They were successfully resolved based on the involvement of specific silicon (paired, bridging) and oxygen (bridging, non-bridging) atoms, and were compared with existing theoretical data. The resemblance between the IR spectra of synthetic C-S-H and those formed upon hydration of OPC, proves the suitability of model C-S-H phases for understanding hydration processes. Some uncertainties in the assignment of the C-S-H bands observed in existing <em>in situ</em> IR experiments are discussed, and potential sources of error identified.</div></div>","PeriodicalId":266,"journal":{"name":"Cement and Concrete Research","volume":"198 ","pages":"Article 108000"},"PeriodicalIF":10.9,"publicationDate":"2025-07-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144678275","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-07-21DOI: 10.1016/j.cemconres.2025.108001
Zhaoheng Guo , Cheng Liu , Xu Luo , Gaofeng Chen , Huixia Wu , Zhenhai Xu , Shujun Li , Jianming Gao , Yasong Zhao , Hongjian Du
The incorporation of nanoscale or microscale silica into cementitious materials has been demonstrated to markedly enhance resistance to sulfate attack. Despite this benefit, the exact mechanisms responsible for these improvements are not yet fully understood, particularly concerning the role of unhydrated silica particles in blended cement under sulfate exposure. Tricalcium aluminate (C3A), a key component of cement, contributes a substantial proportion of the aluminum phases that are vulnerable to sulfate attack. The present study investigated how silica particles of varying sizes influence the interactions between C3A hydrates and sulfate solutions. By conducting qualitative and quantitative analyses of the reaction products, microstructural morphology, ion concentrations, zeta potentials, and sulfate concentrations in the solution, a new impact mechanism model was developed. These findings reveal that nanoscale silica (NS) particles in the C3A hydrates and the sulfate system impede the reaction between hydrogarnet and sulfate, thereby reducing ettringite formation. NS mainly suppresses hydrogarnet dissolution, resulting in lower concentrations of Ca2+ and Al3+ ions and reduced consumption of SO42− ions. This suppression is attributed to the adsorption of NS on the hydrogarnet surface, and NS attracts Ca2+, SO42− ions, or CaS ion pairs, leading to surface ion overcharging and thereby reducing hydrogarnet dissolution. In addition, NS particles adhere to the surface of ettringite, preventing the adsorption of Ca2+, SO42−, or CaS ion pairs, thereby inhibiting ettringite formation and growth. This effect is notably dependent on the presence of NS, as microscale silica or insufficient quantities of NS lessen or eliminate the impact. These findings provide insights into the use of nanomaterials to enhance the durability of cement-based materials and establish a foundational basis for future research in this area.
{"title":"Inhibition of tricalcium aluminate hydrate–sulfate interactions by size and content-dependent silica particles","authors":"Zhaoheng Guo , Cheng Liu , Xu Luo , Gaofeng Chen , Huixia Wu , Zhenhai Xu , Shujun Li , Jianming Gao , Yasong Zhao , Hongjian Du","doi":"10.1016/j.cemconres.2025.108001","DOIUrl":"10.1016/j.cemconres.2025.108001","url":null,"abstract":"<div><div>The incorporation of nanoscale or microscale silica into cementitious materials has been demonstrated to markedly enhance resistance to sulfate attack. Despite this benefit, the exact mechanisms responsible for these improvements are not yet fully understood, particularly concerning the role of unhydrated silica particles in blended cement under sulfate exposure. Tricalcium aluminate (C<sub>3</sub>A), a key component of cement, contributes a substantial proportion of the aluminum phases that are vulnerable to sulfate attack. The present study investigated how silica particles of varying sizes influence the interactions between C<sub>3</sub>A hydrates and sulfate solutions. By conducting qualitative and quantitative analyses of the reaction products, microstructural morphology, ion concentrations, zeta potentials, and sulfate concentrations in the solution, a new impact mechanism model was developed. These findings reveal that nanoscale silica (NS) particles in the C<sub>3</sub>A hydrates and the sulfate system impede the reaction between hydrogarnet and sulfate, thereby reducing ettringite formation. NS mainly suppresses hydrogarnet dissolution, resulting in lower concentrations of Ca<sup>2+</sup> and Al<sup>3+</sup> ions and reduced consumption of SO<sub>4</sub><sup>2−</sup> ions. This suppression is attributed to the adsorption of NS on the hydrogarnet surface, and NS attracts Ca<sup>2+</sup>, SO<sub>4</sub><sup>2−</sup> ions, or Ca<img>S ion pairs, leading to surface ion overcharging and thereby reducing hydrogarnet dissolution. In addition, NS particles adhere to the surface of ettringite, preventing the adsorption of Ca<sup>2+</sup>, SO<sub>4</sub><sup>2−</sup>, or Ca<img>S ion pairs, thereby inhibiting ettringite formation and growth. This effect is notably dependent on the presence of NS, as microscale silica or insufficient quantities of NS lessen or eliminate the impact. These findings provide insights into the use of nanomaterials to enhance the durability of cement-based materials and establish a foundational basis for future research in this area.</div></div>","PeriodicalId":266,"journal":{"name":"Cement and Concrete Research","volume":"198 ","pages":"Article 108001"},"PeriodicalIF":10.9,"publicationDate":"2025-07-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144671016","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-07-21DOI: 10.1016/j.cemconres.2025.107982
Imane Koufany , Jaime Fernandez-Sanchez , Ana Cuesta , Isabel Santacruz , Eric P. Bescher , Miguel A.G. Aranda , Angeles G. De la Torre
This study investigates the early-age hydration behavior of eight belite calcium sulfoaluminate (BCSA) cement batches with nearly identical compositions and physical properties, yet exhibiting significantly different hydration kinetics. Two clusters were identified: relatively fast-setting cements with a final setting time of 22 min and a main calorimetric peak at 2 h, and relatively slow-setting cements with 28-minute setting times and peaks at 3 h. These values can be retarded by adding citric acid. The fast-setting cements displayed higher early concentrations of soluble potassium (149 mM) and sulfate (76 mM) than slow-setting cements (107 mM and 57 mM, respectively), attributed to greater potassium sulfate content. Higher alkaline content accelerates ye'elimite dissolution and hasten ettringite crystallization. Isothermal calorimetry and in-situ laboratory X-ray powder diffraction (analyzed via Rietveld refinement) confirmed that the differences in dissolution and crystallization kinetics underlie the observed variability. The addition of citric acid extended both initial and final setting times by approximately 1.8 h. Its retarding effect was most pronounced for anhydrite dissolution, with a smaller impact on ye'elimite dissolution and AFt crystallization. Pore solution analysis revealed that citric acid increased calcium and sulfate concentrations while reducing potassium levels, supporting a retardation mechanism involving calcium complexation and preferential sorption/deposition of citrate onto anhydrous phases. These findings underscore the importance of early-age phase-specific dissolution behavior in governing BCSA cement performance, particularly for applications requiring rapid setting and early strength development.
{"title":"Understanding early hydration in belite calcium sulfoaluminate cements: Impacts of minor elements and citric acid","authors":"Imane Koufany , Jaime Fernandez-Sanchez , Ana Cuesta , Isabel Santacruz , Eric P. Bescher , Miguel A.G. Aranda , Angeles G. De la Torre","doi":"10.1016/j.cemconres.2025.107982","DOIUrl":"10.1016/j.cemconres.2025.107982","url":null,"abstract":"<div><div>This study investigates the early-age hydration behavior of eight belite calcium sulfoaluminate (BCSA) cement batches with nearly identical compositions and physical properties, yet exhibiting significantly different hydration kinetics. Two clusters were identified: relatively fast-setting cements with a final setting time of 22 min and a main calorimetric peak at 2 h, and relatively slow-setting cements with 28-minute setting times and peaks at 3 h. These values can be retarded by adding citric acid. The fast-setting cements displayed higher early concentrations of soluble potassium (149 mM) and sulfate (76 mM) than slow-setting cements (107 mM and 57 mM, respectively), attributed to greater potassium sulfate content. Higher alkaline content accelerates ye'elimite dissolution and hasten ettringite crystallization. Isothermal calorimetry and in-situ laboratory X-ray powder diffraction (analyzed via Rietveld refinement) confirmed that the differences in dissolution and crystallization kinetics underlie the observed variability. The addition of citric acid extended both initial and final setting times by approximately 1.8 h. Its retarding effect was most pronounced for anhydrite dissolution, with a smaller impact on ye'elimite dissolution and AFt crystallization. Pore solution analysis revealed that citric acid increased calcium and sulfate concentrations while reducing potassium levels, supporting a retardation mechanism involving calcium complexation and preferential sorption/deposition of citrate onto anhydrous phases. These findings underscore the importance of early-age phase-specific dissolution behavior in governing BCSA cement performance, particularly for applications requiring rapid setting and early strength development.</div></div>","PeriodicalId":266,"journal":{"name":"Cement and Concrete Research","volume":"198 ","pages":"Article 107982"},"PeriodicalIF":10.9,"publicationDate":"2025-07-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144669782","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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