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Microstructure characterization of Portland cement pastes influenced by lower curing pressures

机译：较低固化压力影响的硅酸盐水泥浆的微观结构表征

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Infrastructure constructions in highly mountainous areas (especially in Qinghai-Tibet Plateau with an average altitude close to 5000 m) are developed rapidly in recent years. Meanwhile, the lower atmospheric pressure effects caused by higher altitude on building material have to be carefully evaluated. In this study, the microstructure characterization during hydration behavior of Portland cement under applied low atmospheric pressures, i.e., 0.2, 0.5, 0.8, 0.9 times of 1.0 atmospheric pressure (P-0), was experimentally investigated using X-Ray diffraction (XRD), thermogravimetric analysis (TGA), and low temperature nitrogen adsorption techniques, in which the degree of hydration (DoH), the evolution of hydrates, and pore size distribution were assessed. Experimental results revealed that lower curing pressures had diminishing effects on the DoH, especially less than seven days. Although XRD cannot quantitatively identify the hydrate phases under lower curing pressures, TGA analysis provided evidences that both portlandite, ettringite, and calcium silica hydrate (CSH) phases decreased with reduced curing pressures from P-0 to 0.2P(0). Lower curing pressures caused increased cumulative volumes in micropores and mesopores, but have marginal effects on macropores based on nitrogen absorption evaluation on pore size distribution at 28 days of hydration. Moisture evaporation due to the lower curing pressure was confirmed by TGA measurement. The experimental results under lower curing pressures were served as inputs for thermodynamic simulation to predict hydrated products which confirmed the experiment data and indicated that the lower curing pressure caused more capillary pores in cement pastes. There were three concerns including DoH effect, w/c effect, and moisture evaporation effect that were considered as main reasons influencing the microstructures of cement paste cured under lower pressures. (C) 2019 Elsevier Ltd. All rights reserved.
机译：近年来，高山地区（尤其是青藏高原的平均海拔接近5000 m）的基础设施建设发展迅速。同时，必须仔细评估较高海拔对建筑材料造成的较低气压影响。在这项研究中，使用X射线衍射（XRD）通过实验研究了波特兰水泥在低气压（即1.0大气压（P-0）的0.2、0.5、0.8、0.9倍）下的水化过程中的微观结构表征。 ，热重分析（TGA）和低温氮吸附技术，其中评估了水合度（DoH），水合物的演变和孔径分布。实验结果表明，较低的固化压力对DoH的影响逐渐减弱，尤其是少于7天。尽管XRD无法在较低的固化压力下定量鉴定水合物相，但TGA分析提供的证据表明，随着固化压力从P-0降低至0.2P（0），钙铁矿，钙矾石和二氧化硅钙水合物（CSH）相均会降低。较低的固化压力会导致微孔和中孔的累积体积增加，但基于水化28天时对孔径分布的氮吸收评估，对大孔的影响很小。通过TGA测量确认了由于较低的固化压力引起的水分蒸发。在较低固化压力下的实验结果可作为热力学模拟的输入，以预测水合产物，从而证实了实验数据，并表明较低固化压力会导致水泥浆中更多的毛细孔。包括DoH效应，w / c效应和水分蒸发效应在内的三个问题被认为是影响在较低压力下固化的水泥浆的微观结构的主要原因。 （C）2019 Elsevier Ltd.保留所有权利。

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