Nanosilica (NS) has the potential to enhance the performance of cement-based materials through improvements in pore structure, hydration product content, and the properties of calcium–(aluminum)–silicate–hydrate (C–(A)–S–H) gel, ultimately increasing resistance to sulfate attack. However, the underlying mechanisms of these enhancements remain incompletely understood, particularly with respect to the presence of unhydrated NS particles in blended cementitious materials under sulfate attack. C3A (tricalcium aluminate) is one of the main components of cement and a major source of aluminum phases during sulfate attack. This study aims to investigate the effects of NS on the hydration of the C3A–gypsum system and the subsequent reaction between the hydration products and sulfates. The investigation involves qualitative and quantitative analyses of the reaction products, and microscopic morphology, as well as tests on ion concentrations, zeta potentials, and sulfate concentrations in the reaction solution. Findings suggest that NS inhibits the formation of ettringite during the C3A–gypsum hydration process, but does not exert a notable influence on the final hydration product content. Furthermore, residual NS particles in the C3A–NS hydration system further impede the reaction between hydrogarnet and sulfate, thereby reducing ettringite formation. NS also impedes the dissolution of hydrogarnet, resulting in lower concentrations of Ca2+ and Al3+ ions and limited consumption of SO42−. Based on the analysis of the research results, this inhibitory effect is attributed to the adsorption of NS particles onto the hydrogarnet surface, which attracts Ca2+, SO42−, or CaS ion pair complexes, leading to surface ion overcharging and reduced hydrogarnet dissolution. In addition, NS particles may adsorb onto the surface of ettringite, preventing the adsorption of Ca2+, SO42−, or CaS ion pair complexes, thereby inhibiting the formation and growth of ettringite.

中文翻译：

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纳米二氧化硅对铝酸三钙水合的影响及其与硫酸盐溶液的反应


纳米二氧化硅 （NS） 有可能通过改善孔隙结构、水合产物含量和钙-（铝）-硅酸盐-水合物 （C-（A）-S-H） 凝胶的性能来提高水泥基材料的性能，最终提高对硫酸盐侵蚀的抵抗力。然而，这些增强的潜在机制仍不完全清楚，特别是关于硫酸盐侵蚀下混合胶凝材料中存在未水合的 NS 颗粒。C3A（铝酸三钙）是水泥的主要成分之一，也是硫酸盐侵蚀过程中铝相的主要来源。本研究旨在探讨 NS 对 C3A-石膏系统水化的影响以及水化产物与硫酸盐之间的后续反应。该研究涉及反应产物的定性和定量分析、微观形态，以及反应溶液中离子浓度、zeta 电位和硫酸盐浓度的测试。研究结果表明，NS 在 C3A-石膏水化过程中抑制钙矾石的形成，但对最终水化产物含量没有显着影响。此外，C3A-NS 水合系统中残留的 NS 颗粒进一步阻碍了水柘榴石和硫酸盐之间的反应，从而减少了钙矾石的形成。NS 还阻碍了水柘榴石的溶解，导致 Ca2+ 和 Al3+ 离子的浓度降低，SO42− 的消耗受到限制。根据对研究结果的分析，这种抑制作用归因于 NS 颗粒吸附到水柘榴石表面，从而吸引 Ca2+、SO42− 或 CaS 离子对复合物，导致表面离子过度充电和水柘榴石溶解减少。 此外，NS 颗粒可能会吸附到钙矾石表面，阻止 Ca2+、SO42− 或 CaS 离子对复合物的吸附，从而抑制钙矾石的形成和生长。