Efect Of Flexural Load And Chloride Salt Corrosion On Frost Resistance Of Thermal Insulation Concrete With Recycled Aggregates

Recycled Aggregate Thermal Insulation Concrete(RATIC)provides a new idea for the popularization and utilization of recycled concrete,which can not only realize the recycling of resources but also improve the efficiency of building energy saving.However,compared with ordinary concrete,the durability of concrete containing recycled aggregate is relatively poor.It serious constraints on the development of recycled concrete.At present,the research on the durability of recycled concrete is mostly a single factor,and the research on the durability of recycled concrete under the coupling of various factors is relatively lacking.At the same time,the complex porous multi-interface structure has a great influence on the durability of concrete because of the addition of recycled coarse aggregates and glazed hollow beads(GHBs).Therefore,this paper selects the adverse external conditions suitable for the cold areas in the north,designs the test scheme of multiple failure factors,and carries out the test of antifreeze durability of RATIC under multi-factor action.The performance indexes under unfavorable external factors,determines the environmental factors were analyzed.The deterioration characteristics and mechanism of RATIC under the combined action of load and environment were analyzed.At the same time,the antifreeze performance of RATIC is improved by enhancement properties of recycled coarse aggregates.The main research contents of this paper include:(1)The durability test of ordinary concrete and RATIC with different recycled coarse aggregates at replacement rates(0%,30%,50%,70%,and 100%)with 100% insulation aggregates content was carried out under the coupling action of chlorine salt erosion and freeze-thaw cycle.The compressive strength and splitting tensile strength of concrete specimens after different freezing and thawing cycles(0,25,50,75 and 100)were tested,and the law of mechanical properties of RATIC was obtained.After 100 freeze-thaw cycles,the compressive strength and splitting tensile strength of concrete specimens(RATIC-0%)decreased by 16.8% and 24.3% respectively,while the RATIC-100% specimens decreased by 48.3% and 57.7% respectively.Compared with ordinary concrete specimens,the test results show that the insulation aggregates can effectively inhibit the denudation effect of coupling on concrete specimens.Through the mesoscopic and microscopic level test,the RATIC specimen after the coupling between chlorine salt erosion and freeze-thaw cycle is observed,and the results show that the old interfacial transition zones(ITZs)inside the concrete is the most direct cause of the damage of concrete specimens under coupling action.(2)The effects of different replacement rates(0%,30%,50%,70%,and 100%)and different bending load levels(15%,30% and 45%)on the durability of RATIC under the coupling of bending load and freeze-thaw cycle were carried out.The results show that the replacement rate of coarse aggregate under coupling effect has a great influence on the durability of insulating concrete,and the brittle failure will occur suddenly with the concrete specimen of freeze-thaw cycle.The load level has a great influence on the durability of RATIC when the specimen loads 45% of the bending load,the durability of the concrete specimen is very poor,and the damage of the specimen after 30 freeze-thaw cycles is carried out.Comparing the test results with ordinary concrete,the influence of the insulation aggregate on the durability of the concrete specimen under the coupling action is obtained,and the mixing of the insulating aggregate can obviously delay the brittle fracture time of the concrete.On the basis of the pre-test,a microscopic test of the regenerated insulating concrete after coupling was carried out by means of CT fault sweep surface,and its internal porosity and crack development were observed.The deterioration of the internal interface of concrete is observed by a fluorescence microscope,and the failure mechanism of regenerative insulating concrete under coupling action is revealed.(3)In the course of the study,it is found that the performance of recycled coarse aggregate has a great influence on the antifreeze performance of recycled concrete,so the effect of enhancement properties of recycled coarse aggregate on the frost resistance of concrete is carried out.The properties of recycled coarse aggregate carbonization and nano-silica slurry wrapped with recycled coarse aggregate were strengthened,and the physical properties of recycled coarse aggregate before and after enhancement were compared to the enhanced effect.A 100% replacement ratio of RATIC specimens was made by using the enhanced recycled coarse aggregate,and the compressive strength,splitting tensile strength and antifreeze performance were tested,and the test results were compared with those of concrete specimen without reinforced.The results show that the mechanical properties of the reinforced RATIC are slightly improved,but the durability of the specimens under the coupling of chlorine salt erosion and freeze-thaw cycle is more obvious.