Study On Mechanics And Impermeability Of Fully Recycled Coarse Aggregate Concrete

The waste concrete fragments in construction waste are processed by a series of processes such as crushing,cleaning and screening to form recycled aggregates.The recycled aggregates are divided into coarse aggregates and fine aggregates according to the particle size.The recycled aggregates are all instead of sand and gravel.The concrete mixed with cement and water is called fully recycled concrete.The fully recycled concrete is studied to improve the utilization rate of construction waste concrete resources and engineering economy.Taking the coarse aggregate in construction waste as the research point,the mechanical properties and impermeability of fully recycled coarse aggregate concrete are studied by preparing fully recycled coarse aggregate concrete,which provides reference for practical engineering application.The specific research contents and results are as follows.(1)Raw materials and their properties : The particle size of recycled aggregate and natural aggregate was screened to determine the particle size distribution.The basic performance tests of apparent density,bulk density,water content,water absorption and crushing index were carried out to compare the basic properties of recycled aggregate and natural aggregate.The chemical composition of standard sand,cement,admixture and fly ash was explored.(2)The influence of aggregate particle size and pretreatment process on concrete performance : The working performance of concrete was measured by particle size test,and the optimum coarse aggregate particle size was determined to be5mm-20 mm.Recycled aggregate has high water absorption and special surface properties.The pretreatment of recycled aggregate is pretreated by saturated surface dry treatment and paste wrapped stone method.Recycled aggregate by saturated surface dry treatment makes the mixing process is not easy to absorb water,to ensure the workability of recycled concrete.The interface layer structure between coarse aggregate and hardened cement paste is improved by the method of paste wrapping stone,and the performance of recycled concrete is improved.(3)Study on the mechanical properties of fully recycled coarse aggregate concrete :According to the design specification of concrete mix ratio,the mix ratio was calculated,and the effective water-cement ratio was introduced to prepare the compressive and flexural specimens of fully recycled coarse aggregate concrete.By changing the water-cement ratio,the amount of polycarboxylate superplasticizer,age and curing conditions,the compressive and flexural tests were carried out.The results show that the mechanical properties of fully recycled coarse aggregate concrete increase first and then decrease with the water-cement ratio.The mechanical properties of fully recycled concrete with water reducer are significantly higher than those without water reducer.When the water-cement ratio is 0.45 and the amount of polycarboxylate superplasticizer is 0.4 % under standard curing.The compressive strength reaches the maximum value of 49.1 MPa,and the flexural strength is 5.02 MPa.At this time,the reasonable water-cement ratio should be 0.45,and the suitable water reducing agent content is 0.4 %.(4)Study on impermeability of fully recycled coarse aggregate concrete : When the water-cement ratio increases from 0.3 to 0.5,the impermeability of recycled concrete gradually weakens.Adding an appropriate amount of polycarboxylate superplasticizer and fly ash can better improve the performance of recycled concrete.Continuous incorporation of fly ash,impermeability water pressure gradually reduced.With 0.5 %water reducing agent and 10 % fly ash,recycled concrete has good impermeability.