Study On Mechanical Properties Of Thermal Insulation Concrete With Recycled Aggregates After Elevated Temperatures

Thermal insulation concrete with recycled aggregates(RATIC) solved two main problems together, including reuse of construction resources and building energy conservation, which provides a practical and feasible way for the sustainable development of China’s construction industry. RATIC shows good thermal insulation performance. At the same time, it also behaves well in mechanical and durability properties, which can meet the requirements for load-bearing. In this paper, based on previous results of RATIC, experimental researches were conducted on mechanical properties of RATIC after elevated temperatures. Calculation method was established for mechanical properties of RATIC after elevated temperatures, which can provide references for fire resistance designs of RATIC structures. The main works of this research are as follows:1. Based on the high temperature test, the appearance and mass loss of RATIC are studied. The appearance and mass loss ratio of RATIC with different replacement ratio of recycled aggregates are similar. Color change of RATIC are as follows: little-grayâ†'gray brownâ†'gray whiteâ†'white red. At 300-400 °C, a few number of fine cracks developed and grow in number. At 500-600°C, the surface of the specimen exhibited more cracks. At 700-800°C, more remarkable cracks occurred and the width of cracks significantly increased. The mass loss ratio of RATIC enlarged with temperature increase. The higher replacement ratio of recycled aggregates of RATIC, the larger mass loss ratio of RATIC is.2. Preliminary study on the cracking performance of RATIC was performed, and the effects of different water content, heating rate and specimen size on the explosive spalling performance of RATIC are studied. The experimental results show that the critical moisture content of RATIC is 1.76%-2.22%, and the explosive spalling of RATIC is mainly due to the coupling effect of steam pressure and thermal stress.3. Basic mechanical properties of RATIC with different replacement ratio of recycled aggregates after elevated temperatures were investigated, including compressive strength, tensile strength and elastic modulus. The effect of replacement ratio of recycled aggregates on mechanical properties of RATIC after elevated temperatures was also studied. The results show that the compressive strength of RATIC increased at first, then decreased with increasing temperature. Unlike compressive strength, tensile strength of RATIC decreased at first, then suddenly increased, finally once again decreased. The elastic modulus of RATIC after elevated temperatures decreased with the increasing temperature. No significant impact of different recycled aggregates replacement ratio on residual compressive strength and residual elastic modulus, however great difference show on residual tensile strength of RATIC after elevated temperatures. The higher replacement ratio of recycled aggregates, the smaller residual tensile strength of RATIC after elevated temperatures. Based on regression analysis, the calculation formula of compressive strength, tensile strength and elastic modulus of RATIC after elevated temperatures are established.4. The axial compressive stress-strain relationship of RATIC after elevated temperatures was obtained. It shows that the stress-strain curves of RATIC become flatter with temperature increases, and the peak points of stress-strain curve move right and downwards. The peak strain and ultimate strain increased with temperature increasing. With the increasing of replacement ratio of recycled aggregates, the descending branch of stress-strain curves becomes steeper. It means that the ductility of RATIC get worse. Based on experimental data, the peak strain, ultimate strain and stress- strain curve equations of RATIC with different replacement ratio of recycled aggregates were developed.