Study On The Properties And The Improvement Of Recycled Fine Aggregate Concrete

With the rapid development of construction industry and the gradual reduction of non-renewable resources, the recycling utilization of construction waste has already become an important research topic at home and abroad. The durability of recycled concrete is related with the service life, economy and safety of buildings. To promote the engineering application of recycled concrete, the basic properties of recycled fine aggregate concrete are studied in this thesis.The main research work and results are as follows:(1) The basic properties of recycled fine aggregate are studied by experiments. Experiments show that recycled fine aggregate has different characteristics from natual sand, such as lower apparent density, lower bulk density, larger water absorption ratio, and higher crushing value. Morover, the fineness modulus of recycled fine aggregate is greater than the upper limit of Sand for Building(GB/T14684-2011). Hence, it is not feasible to replace natural sand with recycled fine aggregate totally in engineering practice. The optimal replacement rate of recycled fine aggregate is 0~20%.(2) The basic properties of recycled fine aggregate concrete are studied by experiment. The C35 recycled fine aggregate concrete is made based on free water-cement ratio, and the effect of two kinds of mixing process(traditional mixing technology and two-time mixing technology) and recycled fine aggregate replacement ratio(0, 10%, 20%, 30%, 40%, 50%) on the mechanical properties and carbonation properties of the prepared recycled fine aggregate concrete are analyzed. Test results show that the basic performance of recycled fine aggregate concrete is decreased with the increase of recycled fine aggregate replacement ratio in traditional mixing technology, and recycled fine aggregate replacement ratio should be controlled between 0 and 30%. In general, the basic properties of recycled fine aggregate concrete in two-time mixing technology are superior to that in traditional mixing technology. Hence, it is feasible to apply 50% recycled fine aggregate in recycled concrete.(3) The effect of three factors, namely water-cement ratio, recycled fine aggregate replacement ratio and fly ash replacement ratio, on the mechanical properties and carbonation properties of recycled fine aggregate concrete when applying two-time mixing technology are studied through orthogonal test. The effect weight of each factor is analyzed and the carbonization prediction model is obtained based on the regression fitting of the experimental data. Test results reveal that the performance of recycled fine aggregate concrete will decline with the increase of water-cement ratio, recycled fine aggregate replacement ratio and fly ash replacement ratio, and water-cement ratio is the major influencing fator. Moreover, the relationship of the effect weight of such three factors is: water-cement ratio > fly ash replacement ratio > recycled fine aggregate replacement ratio. Furthermore, the carbonation depth calculated by using the established carbonization prediction model is in good agreement with the measured carbonation depth, which verifies the feasibility of the established carbonization prediction model.