高温（火灾）作用后微纳米尺度现代水泥基材料力学性能的研究

Cement-based material exhibits itself a multiscale nature. The mechanical properties of cement-based material at the macro-scale depend on the material structure and mechanical properties at the micro-scale. The study on the microstructural mechanical properties of cement-based material is essential to the understanding and prediction of the macroscopic mechanical properties of cement-based material. This work plans to study the effects of water to cement ratio, mineral admixtures, heated temperature, cooling way and resting time on the chemical composition, microstructure, and microstructural mechanical properties of cement-based material, through comprehensively investigating the mechanical properties of cement pastes without/with the incorporation of fly ash, slag and silica fume. Multiple techniques and the self-developed image analysis method are used to quantitively characterize the evolution and distribution of material phases, and build the model of evolution of hardened cement paste. Within the framework of micromechanics and theory of porous media, based on the macroscopic mechanical testing results, we shall propose a model to predict the macroscopic mechanical properties of cement-based based materials after thermal damage. The research findings of this work can reveal the mechanism of damage and failure of modern cement-based materials after the exposure to high temperature (fire), can also set a solid basis for the structure stability evaluation and the renovation.

水泥基材料具有结构多尺度特性，宏观性能的变化源于其微结构和微观性能的改变。研究高温（火灾）作用后微纳米尺度现代水泥基材料的力学性能是揭示其宏观力学性能演变机理和实现科学预测的基础。本项目拟通过对纯水泥浆体及掺有粉煤灰、矿粉和硅灰的水泥浆体在高温（火灾）前后微纳米尺度力学性能的系统研究，获得水胶比、掺合料、火灾温度、冷却方式、静置时间等对水泥基材料微观组成、结构、微观力学行为、物相变化等的影响规律；通过多种测试手段和自主研发的图像分析技术实现物相演化和空间分布的定量表征，建立高温（火灾）作用后硬化水泥浆体结构演化模型；基于微观力学框架和多孔介质理论，结合宏观试验结果，提出基于微结构演化的高温（火灾）作用后现代水泥基材料宏观力学性能预测模型，以揭示现代水泥基材料在高温和火灾作用后力学性能损失及失效的机理，从而为火灾后结构可靠性分析和维修加固工作提供重要的理论依据。

本课题以解决水泥基材料高温（火灾）后力学性能评估和预测为切入点，采用DSC-TG、SEM、纳米压痕等研究了水泥基材料各组成物相（氢氧化钙、C-S-H凝胶、水泥颗粒、粉煤灰、矿粉、硅灰等）随温度发生物相变化、结构变化和微观力学性能变化的规律；然后采用SEM/ESEM、EDS、XRD等研究了不同条件高温（火灾）作用后水泥基材料中水化产物的物相和微结构变化，实现了高温（火灾）作用后水泥基材料微结构定量表征并探索了其微结构演变机理；样品同时采用纳米压痕技术和MTS研究了不同条件高温（火灾）作用后水泥基材料的微观力学性能和宏观力学性能，并基于微观力学框架和多孔介质理论建立了宏微观性能的联系。在前述研究的基础上，提出了现代水泥基材料高温（火灾）作用后宏观力学性能预测模型，并通过实验数据对理论计算结果进行了验证。本项目的多项研究成果在国内外均未见公开报道。研究成果为火灾后结构可靠性分析和维修加固工作提供重要理论依据和实验数据。