Experimental Analysis And Simulation Research On Thermal Distribution Of Recycled Aggregate Concrete Members At Elevated Temperatures

Recycled aggregate concrete(RAC)is a kind of concrete mixed with coarse or fine recycled concrete aggregate(RCA),which is obtained by crushing,screening and cleaning construction waste and demolition waste.The use of RAC can not only alleviat the resource and environmental problems caused by waste concrete disposal effectively but also solve the resource shortage due to the rapid consumption of building materials.Therefore,RAC is a new type of green building material and has become a hot spot in building material research.In recent years,researches on RAC mainly focus on its properties at normal temperatures.Fire,as a kind of disaster with high frequency,seriously affects the safety of people and buildings.Therefore,fire resistance and residual capacities of RAC structures under and after fire exposure need to be studied.The thermal distribution is a precondition of stress analysis,which directly affects the accuracy of stress analysis.Thus it is necessary to study the thermal distribution of RAC members at elevated temperatures through experiments and finite element methods,and compare the thermal distribution with that of normal concrete.This thesis conducted a experimental study and finite element analysis on the thermal distribution of RAC members at elevated temperatures.The main contents are as follows:(1)Fire tests of 9 RAC slabs and 9 RAC columns at elevated temperatures were conducted to investigate the influence of coarse RCA replacement percentage(0%?50%?100%)and fine RCA replacement percentage(0%?50%?100%)on thermal distributions of RAC members.The temperatures of key points in the cross-section were recorded.The spalling of concrete in fire tests was described and possible causes of it were discussed.The characteristics of thermal distributions were analyzed and the influences of coarse RCA and fine RCA replacement percentage were discussed.The results show that the temperature decreases with the increase of coarse RCA replacement percentage and fine RCA replacement percentage.(2)A finite element model of RCA members was developed for investigating heat treasfer of this kind of member.The accuracy of the proposed model was evaluated using the available test results.Based on the model,a parametric analysis was carried out to investigate the influence of RCA replacement percentage and crosssection dimension on thermal distributions of RAC members.The RCA replacement has the greatest influence on the thermal distributions.Based on the simulation results,simplified equations were proposed for predicting the temperatures of RAC members.(3)Based on the existing thermo-hygro models,an improved thermo-hygro model was established considering non-local thermal equilibrium.The thermal distribution results using thermo-hygro model were more consistent with the test results compared with normal thermal distribution model.Besides,the temperature plateau could be simulated using thermo-hygro model.The influences of intrinsic permeability and condensation rate on the thermal distributions of RCA were analyzed.Permeability mainly affects the generation of the temperature plateau,and changing the condensation rate has little effect on the thermal distributions.