Pozzolans rich in silica and alumina react with lime to form cementing compounds and are incorporated into portland cement as supplementary cementitious materials (SCMs). However, pozzolanic reactions progress slower than portland cement hydration, limiting their use in modern construction due to insufficient early-age strength. Hence, alternative SCMs that enable faster pozzolanic reactions are necessary including synthetic zeolites, which have high surface areas and compositional purity that indicate the possibility of rapid pozzolanic reactivity. Synthetic zeolites with varying cation composition (Na-zeolite, H-zeolite), SiO2/Al2O3 ratio, and framework type were evaluated for pozzolanic reactivity via Ca(OH)2 consumption using ion exchange and in-situ X-ray diffraction experiments. Na-zeolites exhibited limited exchange reactions with KOH and Ca(OH)2 due to the occupancy of acid sites by Na+ and hydroxyl groups. Meanwhile, H-zeolites readily adsorbed K+ and Ca2+ from a hydroxide solution by exchanging cations with H+ at Brønsted acid sites or cation adsorption at vacant acid sites. By adsorbing cations, the H-zeolite reduced the pH and increased Ca2+ solubility to promote pozzolanic reactions in a system where Ca(OH)2 dissolution/diffusion was a rate limiting factor. High H-zeolite reactivity resulted in 0.8 g of Ca(OH)2 consumed per 1 g of zeolites after 16 h of reaction versus 0.4 g of Ca(OH)2 consumed per 1 g of Na-zeolite. The H-zeolite modulated the pore fluid alkalinity and created a low-density amorphous silicate phase via mechanisms analogous to two-step C-S-H nucleation experiments. Controlling these reaction mechanisms is key to developing next generation pozzolanic cementitious systems with comparable hydration rates to portland cement.

中文翻译：

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增强的氢型沸石作为补充胶凝材料中的火山灰反应性


富含二氧化硅和氧化铝的火山灰与石灰反应形成胶结化合物，并作为补充胶凝材料 （SCM） 掺入波特兰水泥中。然而，火山灰反应的进展比硅酸盐水泥水化慢，由于早期强度不足，限制了它们在现代建筑中的应用。因此，需要能够实现更快火山灰反应的替代 SCM，包括合成沸石，它们具有高表面积和成分纯度，表明快速火山灰反应的可能性。使用离子交换和原位 X 射线衍射实验，通过 Ca（OH）2 消耗评估具有不同阳离子组成（Na-沸石、H-沸石）、SiO2/Al2O3 比率和框架类型的合成沸石的火山灰反应性。Na 分子筛与 KOH 和 Ca（OH）2 表现出有限的交换反应，因为 Na+ 和羟基占据了酸位点。同时，氢分子筛通过在 Brønsted 酸位点与 H+ 交换阳离子或在空酸位点进行阳离子吸附，很容易从氢氧化物溶液中吸附 K+ 和 Ca2+。通过吸附阳离子，H-沸石降低了 pH 值并增加了 Ca2+ 溶解度，从而在 Ca（OH）2 溶解/扩散是速率限制因素的系统中促进火山灰反应。高 H 分子筛反应性导致反应 0.8 小时后每 1 克沸石消耗 2 克 Ca（OH）16，而每 0.4 克钠沸石消耗 2 克 Ca（OH）2。H-沸石调节了孔隙流体的碱度，并通过类似于两步 CSH 成核实验的机制产生了低密度的非晶硅酸盐相。控制这些反应机制是开发具有与波特兰水泥相当的水化速率的下一代火山灰水泥系统的关键。