High-temperature Resistance Properties Of Recycled Aggregate Concrete And Fire Resistance Of Members

Recycled aggregate concrete(RAC)is a kind of green building material produced with crushed waste concrete instead of natural aggregates.The use of RAC can solve problems of shortage of natural resources and disposal of construction waste.To date,RAC has been a hot spot in building material research.However,most research focuses on properties of RAC at normal temperature.Few studies have been reported on thermal or mechanical properties of RAC at elevated temperatures,and researches on mechanical properties of RAC after high temperature exposure,thermal distributions and fire resistance of RAC members in fire and residual capacities after fire are also not perfect.In this context,this thesis intends to study the high-temperature material properties of RAC and the mechanical performance of three kinds of structure members(slab,beam and column)made with RAC in fire and after fire exposure.The main work is as follows:(1)Thermal properties of RAC containing three different coarse recycled concrete aggregate(RCA)content,including thermal conductivity,specific heat and thermal expansion,were measured in the temperature range of 20-800 oC.Based on the test results,simplified equations were proposed to express the elevated-temperature thermal conductivity,specific heat and thermal expansion of RAC.(2)Axial compression experiments of 90 RAC prisms were conducted to investigate the influence of temperature,coarse RCA replacement percentage and water to cement ratio on the compressive strength,elastic modulus,peak strain and complete stress-strain curves.Based on the test results,equations of compressive strength,elastic modulus and peak strain of RAC at elevated temperatures were suggested and a model was proposed for compressive stress-strain relationship of RAC at elevated temperatures.(3)Experiments of 360 RAC cubes were conducted to investigate the influence of temperature,coarse RCA replacement percentage,water to cement ratio and cooling method on residual strengths of RAC after high temperature exposure.Compressive strengths of RAC cubes under different cooling regimes and splitting tensile strengths of RAC cubes under natural cooling were obtained from tests.Based on the test results,equations of residual compressive strength(natural cooling,water cooling)and splitting tensile strength of RAC after exposure to elevated temperatures were suggested.(4)Axial compression experiments of 150 RAC prisms were conducted to investigate the influence of temperature,coarse RCA replacement percentage and water to cement ratio on the compressive strength,elastic modulus,peak strain and complete stress-strain curve.Based on the test results,equations of compressive strength,elastic modulus and peak strain of RAC after elevated temperatures were suggested and a model was proposed for compressive stress-strain relationship of RAC after elevated temperatures.(5)Based on the study of elevated-temperature thermal and mechanical properties of RAC,finite element models were developed using the software ABAQUS to investigate the thermal field and fire resistance of reinforced RAC members(slab,beam,column)under the ISO 834 standard fire condition and the residual performance of RAC members after the ISO 834 fire,including both heating and cooling phases.The models were validated with related tests.Simplified equations were proposed for predicting the temperatures of RAC members,by dividing the cross section into 1-D and 2-D heat transfer areas.Effects of coarse RCA replacement percentage on the thermal field and fire resistance of reinforced RAC members under fire and residual strength of reinforced RAC members after fire were analysed.