Effect of Additional Surfaces on Ordinary Portland Cement Early-Age Hydration

Early-age hydration of Ordinary Portland Cement (OPC) was studied in the presence of two additional surfaces. Additional surfaces are known to accelerate the early-age hydration of OPC. Autocatalytic reaction modelling was used to determine acceleration mechanism of additional surfaces. Heat development of the hydration was measured with semi-adiabatic calorimetry and the results were modelled with an autocatalytic reaction. Autocatalytic reaction modelling was able to determine number of initially active nucleation sites in early-age hydration. OPC hydration followed autocatalytic reaction principles throughout induction period and accelerating period. Both of the added surfaces, limestone filler and calcium-silicate-hydrate (C-S-H) coated limestone filler accelerated the early-age hydration. According to autocatalytic modelling, the C-S-H coated filler increased the number of initially active nucleation sites. Pristine limestone filler accelerated the early-age hydration by providing the additional nucleation sites throughout the early-age hydration. The difference was explained with common theories of nucleation and crystal growth. Autocatalytic model and measured calorimeter curve started to significantly deviate at the inflection point, where the reaction mode changed. The reaction mode change depended on the average particle distance. Early-age hydration, modelled as autocatalytic reaction was able to improve understanding of OPC early-age hydration and quantify the number of initially active nucleation sites. Understanding and quantifying the acceleration mechanisms in early-age hydration will aid larger utilization of supplementary cementitious materials where understanding the early-age strength development is crucial.

Contribution of CNTs/CNFs morphology to reduction of autogenous shrinkage of Portland cement paste

在这试验性的研究，碳 nanotubes (CNT ) 和碳 nanofibers (CNF ) 被集中的 sonication 面对 superplasticizer 在水里驱散并且随后与波特兰一起混合了水泥， water/ 水泥比率在 0.3 和 0.4 之间变化。在新鲜阶段的自然发生的收缩被调查。CNT 和 CNF 被扫描电子显微镜学(SEM ) 的高分辨率描绘，含水的粘贴被 X 光检查衍射和 SEM 学习。结果为包含 nanomaterials 的小数量(0.01 wt%) 的粘贴在 50% 显示出自然发生的收缩的减小。更高的增加显得是更少有效。收缩的最高的减小为长的碳 nanofibers 被观察、相当直、有约 200 nm 的直径。结果证明 nanomaterials 的增加特别在水和的早阶段加速了水和过程。效果在 functionalized nanotubes 的情况中是最显著的。导致自然发生的收缩的减小的建议机制是增强 nano 效果的联合，水和的改变和含水的矩阵的微观结构。