| With the rapid development of China’s urban construction,the amount of demolition of abandoned buildings is increasing,and the amount of waste concrete is increasing,how to effectively treat and utilize waste concrete has become one of the current research hotspots,for this reason,recycled concrete should be brought out,recycled concrete can make waste concrete recycling and reduce environmental pollution,which is of great significance to the sustainable development of our country.At present,recycled aggregate has defects such as microcracks and adhesion of old mortar,which limit the development of recycled concrete,and on the basis of relevant research at home and abroad,the self-compacting properties and mechanical properties of modified self-compacting recycled concrete are studied by two modification methods:modified recycled aggregate and fiber modified recycled concrete.The effects of microwave heating,mechanical grinding,slurry,hydrochloric acid solution immersion and sodium silicate solution immersion on the self-compacting properties and mechanical properties of modified self-compacting recycled concrete were studied through single-factor experiments.The effects of three factors:steel fiber content,recycled coarse aggregate substitution rate and recycled fine aggregate substitution rate on the self-compacting and mechanical properties of steel fiber self-compacting recycled coarse and fine aggregate concrete were studied through orthogonal tests.The effects of four factors,steel fiber content,basalt fiber content,recycled coarse aggregate substitution rate and confining pressure value,on the self-compacting properties and mechanical properties of triaxial compression modified selfcompacting recycled concrete were studied through single-factor experiments,and a triaxial compressive strength prediction model was established to provide some reference data for the application of modified self-compacting recycled concrete.The results of the study are as follows:(1)In the modified recycled aggregate test,different aggregate modification methods can improve the basic physical properties of recycled crude aggregate.The self-compacting performance of concrete in the test group was above the performance grade SF2 of self-compacting concrete.Microwave heating and mechanical grinding of recycled aggregates increased the most,with increases of 9.5%,12.0%,17.9%,19%,15.8%and 4.5%respectively compared with the benchmark group.Soaking recycled aggregates in hydrochloric acid solution increased the splitting strength the most.Coated recycled aggregates will slightly reduce the compressive strength;Soaking the recycled aggregate with sodium silicate solution will slightly reduce the splitting strength.(2)In the orthogonal test of steel fiber modified self-compacting recycled concrete,the selfcompacting performance of the test group can basically meet the technical requirements of selfcompacting concrete.With the increase of steel fiber content,the failure cracks of the test block gradually decreased.The 28d compressive,splitting and flexural strength of concrete in the orthogonal group was greater than that of the benchmark group,and the increase was 32.5%,36.4%and 40%respectively compared with the benchmark group.The effect of each factor level on compression,splitting and flexural strength was comprehensively evaluated by the power coefficient method,and the optimal mixing ratio was suggested:the replacement rate of recycled coarse aggregate was 70%,the replacement rate of recycled fine aggregate was 30%,and the volume content of steel fiber was 0.75%;The uniaxial force strength model established based on the test data has a high correlation with the measured value,and the error is basically within 5%,which can well predict the strength of steel fiber self-compacting recycled coarse and fine aggregate concrete.(3)In the triaxial compression test of modified self-compacting recycled concrete,the failure state of recycled concrete changed from vertical splitting failure to oblique shear failure with the increase of confining pressure.The confining pressure can significantly increase the peak stress and peak strain of recycled concrete.Under low confining pressure,steel fiber and basalt fiber have a certain crack blocking effect on the crack failure of recycled concrete,and under high confining pressure,the reinforcement effect of fiber on recycled concrete is not obvious.The strength prediction model of triaxial compression modified self-compacting recycled concrete based on octahedral stress spatial failure criterion and Rendulic plane failure criterion is highly correlated with the test data. |
