Mesoscale modeling of concrete at elevated temperature

Abstract

The mesoscale study of nominal strength concrete with focus on its tensile and compressive behaviour under monotonic loading both at room temperature and elevated temperature is the scope of this work. Diverse mechanical and thermal properties of aggregates and mortar matrix along with the Interfacial Transition Zone (ITZ) stems the need for its mesoscale level research. Conventionally the research on the concrete at mesoscale have been limited to concrete at room temperature. The present work emphasizes on the study of the behaviour of conrete at elevated emperature. A 150mm×150mm×150mm concrete space embedded with randomly placed non-overlapping and non-touching aggregates in the form of ellipsoids form the 3D geometry under investigation. A corresponding 2D geometry with ellipses is primarily used in this study with solid finite thickness elements adopted to model ITZ . The mechanical and thermal properties of aggregates and concrete composition for this study are caliberated based on the experimental data published in the literature. Aggregates are modelled with linear elastic material properties and Concrete Damaged Plasticity (CDP) model is assigned for mortar matrix and ITZ. The CDP model is adopted as a material property with suitable strength and failure parameters to closely resemble the actual behaviour of ITZ. The transient thermal strain of concrete at mesoscale is studied. The specimen is subjected to elevated temeperature and the thermal strain is calculated under free as well as loaded condition. The transient thermal strain (TTS) is also calculated, studied and compared with the available experimental results. A parametric study is performed on the two dimensional specimen to gauge the effect of parameters like nature of aggregate, initial compressive force in load induced thermal strain study. The compressive behaviour of concrete at elevated temperature is also studied. The specimen is heated to various temperature ranging from 20oCto 600oC and subjected to compressive load in ‘hot’ condition. The reduction in compressive strength with increase in temperature is studied. Present study establishes the potential of mesoscale modelling to predict the tensile and compressive behaviour of concrete including the initiation of crack and its propogation and can satisfactorily capture the behaviour of concrete at elevated temperature. Overall, the proposed mesoscale model, validated against the reported experimental results, is one of a kind computational model of concrete capable of predicting its intricate zehaviour at different operative regime with equal robustness.