Experimental Research On The Performance Of Steam Curing Low-quality Recycled Fine Aggregate Concrete

Steam curing is an important production process for precast concrete components.It can greatly improve the early strength of concrete and shorten the demoulding time,but to a certain extent,it will reduce the mid-to late-stage strength and durability of concrete.The resource utilization of low-quality recycled fine aggregates is essential to achieve the harmless disposal of waste concrete.It can alleviate the relative shortage of non-renewable resources such as natural river sand,but it has a certain deteriorating effect on the macro performance of concrete.Its application is restricted,and it is difficult to realize effective resource utilization.In response to this,this article focuses on the effects of steam curing parameters(resting time,constant temperature temperature,constant temperature time)and low-quality recycled fine aggregate content on the work,mechanics and durability of concrete,as well as the microstructure characteristics of concrete.The research results obtained have important theoretical and practical guiding significance for the application of steam-cured low-quality recycled fine aggregate concrete.The main results of this paper are as follows:(1)The effect of the replacement rate of low-quality recycled fine aggregate on the flow properties and dry apparent density of concrete has been systematically studied.The research results show that as the replacement rate of low-quality recycled fine aggregate increases,the concrete slump gradually decreases,that is,when the use is low-quality recycled fine aggregate will reduce the fluidity of concrete;in addition,the use of low-quality recycled fine aggregate will reduce the apparent density of concrete.This is due to the performance characteristics of low-quality recycled fine aggregates(containing more old cement paste,soil,broken bricks and tiles,glass and other impurities,higher porosity,more surface edges and corners).In addition,through indepth and systematic research on the influence of steam curing parameters and the replacement rate of low-quality recycled fine aggregate on the compressive strength,splitting tensile strength and flexural strength of concrete cubes,the steam-cured lowquality recycled fine aggregate concrete has been mastered.The change law of mechanical properties basically determines the best steam curing parameters and the low-quality recycled fine aggregate content under the condition of meeting the basic mechanical properties of concrete.(2)The effect of steam curing parameters and low-quality recycled fine aggregate content on the anti-carbonization,anti-chloride ion penetration and capillary water absorption properties of concrete and the sulfate attack resistance of cement mortar has been deeply studied,and the relationship between steam curing parameters and the content of low-quality recycled fine aggregates and the above-mentioned durability was investigated,and the deterioration characteristics of the durability of steam-cured lowquality recycled fine aggregate concrete were mastered.(3)Using scanning electron microscopy(SEM)and mercury intrusion porosimetry(MIP)to conduct in-depth and systematic research on the microscopic morphology and pore structure characteristics of steam-cured low-quality recycled fine aggregate concrete,and mastered the characteristics of the microstructure the steamcured low-quality recycled fine aggregate concrete,and the analysis of the relationship between it and the macroscopic properties of concrete reveal the macroscopic performance degradation mechanism of steam-cured low-quality recycled fine aggregate concrete from the microscopic level.At the same time,the pore structure characteristics of the surface layer of the steam-cured low-quality recycled fine aggregate concrete,such as the bubble spacing coefficient,the pore specific surface area,and the average radius,were tested by the TR-AH hardened concrete pore structure analyzer,so that the reasons for the deterioration of durability of steam-cured low-quality recycled fine aggregate concrete are explained from the meso-scale.