Relationship Between Fractal Gradation Of Recycled Concrete And Unconfined Compressive Strength

Construction waste is a misplaced resource.Realizing the recycling of construction waste can not only realize the value of construction waste itself,but also reduce environmental pollution and save construction materials.Therefore,in the process of rapid urban development,how to realize the resource utilization of construction waste and improve the utilization rate of construction waste is an urgent problem to be solved.Many scholars at home and abroad have joined the research field of construction waste recycling and have achieved some results.However,insufficient attention has been paid to the particle size composition of the aggregate in the application process after construction waste is broken.This paper first measured the basic physical properties of recycled concrete.Based on the fractal gradation composition,the recycled concrete aggregates composed of different ratios of coarse aggregate to fine aggregate were used as the research object.The full-graded aggregates bulk dry density,coarse-graded aggregates bulk dry density,Fine-graded aggregates bulk dry density tests were carry out.From the perspective of porosity,the ratio of coarse aggregate to fine aggregate,and the fractal dimension to analyze the test data,the best gradation is obtained to meet the smallest porosity,the largest bulk dry density and dry density compacted by vibration,and can form a skeleton— —The gradation of dense structure,and revise the value of n after comparing with the full curve.Secondly,under the condition of strictly controlling the mixing water-cement ratio,the test block is made of recycled concrete aggregates composed of different ratios of coarse aggregate to fine aggregate under the saturated surface dry state.Under standard curing conditions,measure the quality and compressive strength of test blocks of different ages(7d,14 d,28d,90d),analyze the compressive strength and the quality of test blocks,curing age,the ratio of coarse aggregate to fine aggregate,gradation,fractal dimension,The relationship between the bulk dry density.The composition of the ratio of coarse aggregate to fine aggregate of concrete with the highest compressive strength in each age is the best gradation,which is consistent with the conclusion drawn from the bulk density.The rationality of the optimal gradation is proved by comparison with the k method and the standard gradation,and the corresponding k value is proposed.Through the bulk dry density test and unconfined compressive strength test of recycled concrete,the research results obtained in this paper are as follows:(1)The fully-graded recycled concrete aggregate composed of 60% coarse aggregate and 40% fine aggregate has the highest natural and dry density compacted by vibration and the lowest porosity,which means it has reached the densest state--Skeleton-dense structure.(2)Both the natural bulk dry density and dry density compacted by vibration conform to the quadratic function mathematical model with The ratio of coarse aggregate to fine aggregate and the value of fractal dimension D.(3)The compressive strengths of recycled concrete test blocks of different grades at the same age(7d,14 d,28d,90d)all show a trend of first becoming stronger and then weaker.And the compressive strength of the test block composed of 60% coarse aggregate and 40%fine aggregate reaches the maximum value,and the compressive strength of the test block composed of this gradation has the largest increase in 28 d,and this gradation can be considered as the best Gradation.(4)The unconfined compressive strength,The ratio of coarse aggregate to fine aggregate and fractal dimension D value of recycled concrete test blocks at different ages conform to the quadratic function mathematical model.The compressive strength increases with the increase of the bulk dry density.With 60% coarse aggregate and 40% fine aggregate as the dividing line,the compressive strength is highly linearly related to the bulk dry density(natural bulk dry density and dry density compacted by vibration).