Influence Of Quality And Replacement Ratio Of Recycled Fine Aggregate On Mechanical Properties Of Recycled Concrete

Recycled concrete technology can achieve concrete waste reprocessing, so that both the limited resources can be reused, and some environmental problems can be solved. Due to wide range of sources of construction waste, its composition is more complex, resulting in a large difference in performance of recycled aggregate, which makes the recycling of waste concrete difficult. Therefore, the amount of different cementitious materials, different quality and replacement rate of recycled fine aggregate affect work performance and mechanical properties of concrete, for the study of systems of recycled concrete is of great significance.Funded by the National Natural Science Foundation of China(51378270,51208272) I did the following research:1. Prepare six different qualities of recycled fine aggregate, according to the "concrete and mortar with recycled fine aggregate"(GB / T 25176-2010) to determine the level of recycled fine aggregate, which are simple crushed recycled fine aggregate(class II); a particle shaping recycled fine aggregate(quasi class I),; secondary particle shaping recycled fine aggregate(class I); simple crushed recycled fine aggregate chemically strengthened(class II); a composite strengthening recycled fine aggregate(class I); secondary composite strengthening recycled fine aggregate(class I).2. Under the conditions of different amount of cementitious material, different quality and replacement rate of recycled fine aggregate affect work performance and mechanical properties of concrete.3. Based on the test results of multiple linear fit analysis, draw strength formula of regenerated concrete.4. Study the influence of cementitious material strength to recycled concrete strength by cement mortar strength test method(ISO method).The results are as follows:1. Physical strengthening can improve work performance and mechanical properties of recycled concrete. In cementitious material consumption 500kg/m3 as an example, water consumption of II class, quasi Class I and Class I recycled concrete increased by 4.7%, 2.8%,4.3% than ordinary concrete when completely replaced; compressive intensity decreased by 18.9%, 8.5%- 4.4%. Composite reinforcing can improve the working performance of recycled concrete to a greater extent, but reduce the mechanical properties to some extent. In cementitious material consumption 500kg/m3 as an example, water consumption of II class, quasi Class I and Class I recycled concrete increased by 3.8%, 2.1%, 1.9% than ordinary concrete when completely replaced; compressive intensity decreased by 23.9%, 14.5%, 9.3%.But optimizing of pore structure can improve the durability, which achieves the best overall performance.2. The quality and the replacement rate of recycled fine aggregate have a good linear relationship with recycled concrete, so the strength formula of recycled concrete can be established by ordinary concrete. When the replacement rate is 100%, compressive strength obtained by the strength formula of recycled concrete is close to the experimental values, II class, II class C, quasi Class I, Class I FC, Class I, Class I SC recycled concrete differ by 0.3%, 1.4%, 1.9%, 2.1%, 0.8% and 0.5% with experimental values, the error is small. When recycled fine aggregate replacement rate is 100%, gray water ratio is 3.47, the recycled fine aggregate quality is Class I, values by meta-analysis formulas verification theory differ 0.1% with experimental values. The strength formula of recycled concrete shows that advantageous affect on quality of recycled fine aggregate on the compressive strength of recycled concrete: Class I recycled fine aggregate> Associate class I recycled fine aggregate> Class I SC recycled fine aggregate= Class I FC recycled fine aggregate > Class II recycled fine aggregate> Class II C recycled fine aggregate.3. Cementitious materials for strength properties of recycled concrete impact significantly. Ordinary portland cement P.O32.5, P.O42.5 and P.O52.5 mixed by fly ash 0%, 10%, 20%, 30% and 40%, can prepare recycled concrete with the strength grade C20 ~ C70.