Preparation And Early Mechanical Properties Research Of Recycled Concrete Based On EMV Method

With the continuous progress of modernization,a large amount of construction waste will be produced in the process of urban construction.The rationalization of construction waste has become one of the hot social issues.As an important way of recycling construction waste resources,recycled concrete can help to build an environment-friendly society.It is of great significance to promote the economic and sustainable development of the construction industry.The coarse aggregate in recycled concrete plays an important role in the overall performance of concrete,and the strengthening of recycled coarse aggregate can effectively improve its physical properties.The optimization of concrete mix ratio design can improve the working performance,mechanical performance and durability of concrete.The study of early mechanical properties is of great significance for construction safety,construction quality and structural reliability.Based on the latest technological achievements at home and abroad,this paper has done the following experiments:1.Recycled coarse aggregate enhancement test is divided into two parts,the first part is to remove the residual mortar of recycled coarse aggregate surface,which is designed to strengthen the three different methods;the second part is the completion of the first part of the test,the recycled coarse aggregate internal micro cracks design different enhancement methods.Performance of recycled coarse aggregate through index test,analysis and comparison of experimental data of different recycled coarse aggregate strengthening processing method,the optimal enhancement of recycled coarse aggregate: Immersion in 5% oxalic acid solution for 24 hours+ Mixer stirring 120s+ Immersion in 1.2% PVA solution for 24 hours.The water absorption rate of reinforcement,crushing index and apparent density index was to improve.2.On the basis of ordinary concrete mix ratio,the effects of sand ratio,fly ash content,silica powder content,regenerated aggregate substitution ratio and fiber content on working performance and mechanical properties were studied by using equal volume mortar method and orthogonal test method.By measuring the slump and strength index of each group of recycled concrete mixture,and using the orthogonal test range analysis method to evaluate the influence of various factors on the recycled concrete and its easiness and mechanical properties,the optimum mix ratio of recycled concrete was obtained.3.On the basis of the optimum mix ratio,the compressive strength,flexural strength and splitting tensile strength of each group of concrete specimens were measured for 3 days,7 days,14 days and 28 days by taking the rate of replacement of recycled coarse aggregate as a variable.Based on the regression analysis of experimental data,the calculation formula of intensity and age and the mathematical model of intensity conversion are obtained.4.The microstructure of recycled concrete and ordinary concrete with different ages was studied by scanning electron microscope(SEM).The characteristics of the hydration products and the interfacial transition zone between coarse aggregate and cement mortar at the same age were analyzed.