Micromechanical modeling of drying shrinkage of cement based on pore size distribution and on capillary forces

基于孔径分布和毛细管力的水泥干燥收缩的微机械建模

基本信息

批准号：
262927646
负责人：
Professor Dr.-Ing. Thomas A. Bier
金额：
--
依托单位：
Institut für Physikalische Chemie
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2014
资助国家：
德国
起止时间：
2013-12-31 至 2020-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/262927646?language=en
关键词：
Micromechanical modeling drying shrinkage cement

项目摘要

Drying, shrinkage, and swelling of concrete due to variations of the relative humidity are very important for durability, resilience, and the structural design of concrete members. Even at a low relative humidity, liquid water is already present in micropores and as interlayer water within the C-S-H phases. In several types of hardened cement pastes with different compositions, pronounced hysteresis of water vapor sorption and volume change of the solid structure at low humidity is frequently observed. By comparing the behavior of differently treated and prepared hardened cement pastes from Ordinary Portland- and Calcium Alumina Cement, we were able to confirm a hysteresis at low humidity which is linked to the presence of micropores. We developed a theoretical model that can explain water-vapor sorption hysteresis and its connection to hysteresis of swelling and shrinkage based on water sorption in micropores and interlayer water. The model is capable of reproducing important topological features of sorption isotherms in relation to the amount of micropores as well as the different types of isotherms of water vapor and nitrogen sorption for low water vapor pressures. Modelling and interpretation of experimental sorption diagrams as well as the swelling and shrinkage of hardened cement paste in the whole humidity range needs to take into account both micro- and mesopores as well as an improved modeling of chemical details of slit-pore walls in different cement pastes by computer simulations. In the project continuation, the theoretical foundations of a partially developed model for calculating sorption, swelling, shrinkage, and hysteresis are to be completed by inclusion of the corresponding hysteresis effects based on measured pore size distributions. Additional types of cement pastes from Blast-furnace slag cement with several water to cement ratios will be produced at different curing conditions. Their water- and nitrogen sorption properties and the associated swelling/shrinkage will be measured as a function of relative humidity. The corresponding pore size distribution will be determined by high-pressure mercury intrusion porosimetry and SAXS. Direct computer simulations of water vapor sorption on realistic layer structures of improved cement models are planned. In particular, the effect of divalent ions such as calcium ions on the capillary forces in cement pastes are to be analyzed. Here, the forces (wall strain) between the condensate and the micropore walls as well as the adhesion energy for the walls of closed pores are to be determined. The simulation results provide additional consistency tests for the models of water vapor sorption and the resulting volume changes in cement paste.

由于相对湿度的变化，干燥，收缩和混凝土肿胀对于耐用性，弹性和混凝土成员的结构设计非常重要。即使在低相对湿度下，液态水也已经存在于Micropores中，并且在C-S-H相中作为层间水。在具有不同组成的几种类型的硬化水泥糊中，经常观察到水蒸气吸附的明显滞后和低湿度下固体结构的体积变化。通过比较普通波特兰和钙氧化铝水泥的不同处理和制备的硬化水泥糊的行为，我们能够在低湿度下确认滞后，这与微孔的存在有关。我们开发了一个理论模型，可以解释水蒸气吸附滞后及其与基于微孔和层间水中水吸附的肿胀和收缩滞后的联系。该模型能够复制与微孔量以及低水蒸气压力的不同类型的水蒸气和氮吸附相关的吸附等温度的重要拓扑特征。实验吸附图的建模和解释以及整个湿度范围内硬化水泥糊的肿胀和收缩需要考虑到微孔和中孔以及通过计算机仿真不同水泥糊中缝隙孔壁的化学细节的改进建模。在项目延续中，应根据测量的孔径分布来纳入相应的滞后效应来完成一个部分开发的用于计算吸附，肿胀，收缩和滞后的模型的理论基础。在不同的固化条件下，将产生其他类型的水泥水泥水泥水泥水泥水泥的水泥水泥。它们的水和氮吸附特性以及相关的肿胀/收缩将是相对湿度的函数。相应的孔径分布将由高压汞入侵孔隙法和萨克斯群确定。计划在改进的水泥模型的逼真层结构上进行水蒸气吸附的直接计算机模拟。特别是，应分析二价离子（例如钙离子）对水泥糊中毛细作用的影响。在这里，要确定冷凝水和微孔壁之间的力（壁应力）以及封闭孔的壁的粘附能。模拟结果为水蒸气吸附模型和水泥糊的体积变化提供了其他一致性测试。