Experimental Study On Basic Properties Of Recycled Coarse Aggregate Sand-free Permeable Concrete

Due to the complex composition of construction waste,the strength of different components varies greatly.Using two kinds of recycled coarse aggregates to prepare sand-free permeable concrete,not only can realize the recycling of construction waste,but also improve the problem of urban rainfall infiltration.The influences of water cement ratio,aggregate size and cement content on the permeability coefficient,compressive strength and frost resistance of recycled concrete coarse aggregate sand-free permeable concrete are analyzed by comprehensive test.The influences of three factors on the flexural resistance of recycled concrete coarse aggregate sand-free permeable concrete are analyzed by orthogonal test.The influences of water cement ratio and cement content on the permeability coefficient and compressive strength of the sand-free permeable concrete of recycled clay brick are analyzed by comprehensive test,and the influences of water cement ratio,cement content and polypropylene fiber content on the flexural resistance of the sand-free permeable concrete of recycled clay brick are analyzed by orthogonal test.The main conclusions are as follows:(1)With the decrease of cement dosage and the increase of recycled coarse aggregate size,the permeability coefficient of recycled coarse aggregate sand-free permeable concrete gradually increases,the effective porosity of recycled coarse aggregate sand-free permeable concrete is 14.8% ~ 31.6%,and the permeability coefficient is 0.8 ~ 3.1cm/s.(2)When the water cement ratio and target porosity are constant,sand-free permeable concrete is prepared by using recycled concrete coarse aggregate with size of 13.2~16mm,and the compressive strength reaches the maximum value.With the decrease of the target porosity,the compressive strength of sand-free permeable concrete prepared by two kinds of recycled coarse aggregate increases gradually.When the water cement ratio changes slightly,the compressive strength of sand-free permeable concrete prepared by two kinds of recycled coarse aggregate increases with the increase of water cement ratio.Adding a proper amount of evenly dispersed polypropylene fiber can improve the flexural performance of recycled clay brick coarse aggregate sand-free permeable concrete,but the flexural strength is lower than that of the sand-free permeable concrete of coarse aggregate of recycled concrete.(3)As recycled coarse aggregate of small size contains more elongated and flaky components,the water absorption rate of recycled concrete coarse aggregate sand-free permeable concrete is higher,resulting in the loss rate of compressive strength of recycled coarse aggregate sand-free permeable concrete is 4.1% ~ 70.2%.With the increase of aggregate particle size and cement,the strength loss rate decreases gradually.When the water cement ratio is 0.35,the strength loss rate is the smallest.