Modeling the microstructure change of high performance cement paste at elevated temperatures

It is commonly understood that the microstructure of cement paste controles the water expulsion from the concrete at high temperature. The pore structure at high temperature has a considerable influence on the spalling behavior. The accumulatieve pore pressure mechanism has become a widely accepted explanation for the explosive spalling in concrete structures. Modeling the physical-chemical changes induced microstructure or micro-cracking evolution of concrete during fire is of great important for engineering practice. In this paper, the influence of the physicochemical change of paste on the microstructure and on explosive spalling is studied qualitatively and quantitatively. In order to examine the consequence of dehydration or decomposition on the various properties of microstructure, a series of experiments were performed, which include thermal analysis, scanning electron microscopy and mercury intrusion porosimetry on different mixes at high temperatures. A numerical model to describe the change of the microstructure of high performance cement paste during heating is proposed. In the model, the consequences of dehydration or decomposition on the various properties of microstructure are modelled. The simulated degradation of materials with heating is validated and calibrated by experiments. The developed model is applied to investigate the influence of some factors such as the degree of hydration, the water/cement ratio and the limestone contents in high performance concrete. This research shows that computational material science is an effective method to provide insights about material behaviour.