Lattice-based Simulation On Distribution Of Temperature Field Of Concrete

When concrete structures are subjected to the high temperature during their service life,their internal structures will be changed,resulting variations in thermos-physical and mechanical properties.It can be easily illustrated from the current research that the non-uniform distribution of the temperature within concrete is crucial to the durability and service life of concrete structures.Therefore,a more systemic numerical simulation about the thermal conduction is worth to be conducted for the evaluation of damage of concrete.To investigate the thermal conduction within the concrete at evaluated temperature,a lattice-based simulation from a mesoscopic perspective was conducted in the present work.In the project,concrete is regarded as a three-phase composite material containing of the coarse aggregate,hardened mortar matrix and the Interfacial Transition Zones(ITZs)between them.Besides,a model,with consideration of the thermal resistance,the water content and other factors,will be proposed to predict the thermal conductivity of concrete on the basis of classical models of thermal conductivity.Based on the lattice network model,a model with the consideration of crack is built to predict the thermal conduction within the concrete and the associated numerical simulation are conducted for further analyses.The detailed contents and conclusions are summarized as follows:(1)With consideration of the non-homogeneous characteristic of the material composition,a mesoscale approach,in which concrete is described as a three-phase composite consisting of the coarse aggregate,hardened cement mortar matrix and the interfacial transition zone(ITZ)between them,is adopted to develop the thermal conductivity of the mortar and ITZ components with in concrete in terms of the composite model.Compared with the experimental results existed in the literature,effect of various factors,such as the water-cement ratio,volume fraction of aggregate,sand ratio,saturation degree and the interfacial thermal resistance,on the thermal conductivity was discussed.The results show that thermal conductivity of concrete increases with an increase of saturation and aggregate volume fraction,but decreases with the increase of water-cement ratio.The influence of water saturation degree on thermal conductivity is well presented by means of the proposed model taking into account the interfacial thermal resistance.(2)It is of great importance for investigating the effect of temperature variation on the stress distribution of concrete in a real environment.The gradient of temperature is one of the important factors to cause cracking of concrete.By analyzing the mesoscale properties of thermal conduction in concrete,effect of the non-homogeneous characteristic of concrete on the thermal conduction process was discussed.Based on the nonlinear equation of thermal conduction,which was discretized by the Galerkin weighted residual and finite difference method,the mesoscale lattice network model was used to carry out the numerical simulation of thermal conduction,taking mortar,the granite and concrete for examples.Numerical results showed that the mesoscale lattice network model of concrete can effectively present the thermal conduction and reasonably predict the temperature distribution of internal concrete.(3)In this study,the lattice network is used to conduct the simulation of thermal conduction within the concrete.Besides,the lattice-based simulation is validated by the comparison between the numerical results and the experimental ones.Based on the calibrated method,thermal conductivity and temperature field in concrete subjected to the fire can be calculated accurately and the paramedic research is conducted to study the influence crack.Finally,based on the related numerical simulation,a conclusion is draw that the coarse aggregate shape,thermal conductivity of ITZ and crack width are less important for the thermal conduction of concrete.In contrast,the crack length and the distribution of coarse aggregate are the significant parameters affecting the heat transport in concrete.