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而导致的混凝土干燥、收缩和膨胀对于混凝土构件的耐久性、弹性和结构设计非常重要。即使在相对湿度较低的情况下，液态水也已经存在于微孔中并作为 C-S-H 相内的层间水存在。在具有不同成分的几种类型的硬化水泥浆体中，经常观察到低湿度下明显的水蒸气吸附滞后和固体结构的体积变化。通过比较普通波特兰水泥和钙铝水泥经过不同处理和制备的硬化水泥浆的行为，我们能够确认低湿度下的滞后现象，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吸水的膨胀和收缩滞后的联系。该模型能够重现与微孔数量相关的吸附等温线的重要拓扑特征，以及低水蒸气压下不同类型的水蒸气和氮气吸附等温线。实验吸附图的建模和解释以及硬化水泥浆体在整个湿度范围内的膨胀和收缩需要考虑微孔和中孔，以及不同水泥中狭缝孔壁化学细节的改进建模通过计算机模拟粘贴。在该项目的延续中，用于计算吸附、膨胀、收缩和滞后的部分开发模型的理论基础将通过包含基于测量的孔径分布的相应滞后效应来完成。将在不同的固化条件下生产具有多种水灰比的高炉矿渣水泥的其他类型的水泥浆。它们的水和氮吸附特性以及相关的膨胀/收缩将作为相对湿度的函数进行测量。相应的孔径分布将通过高压压汞孔隙率测定法和SAXS来测定。计划对改进的水泥模型的真实层结构上的水蒸气吸附进行直接计算机模拟。特别是，要分析二价离子（例如钙离子）对水泥浆中毛细管力的影响。这里，需要确定冷凝物和微孔壁之间的力（壁应变）以及闭孔壁的粘附能。模拟结果为水蒸气吸附模型和水泥浆中产生的体积变化提供了额外的一致性测试。