Study On Performance Of Recycled Lightweight Aggregate Concrete With Waste Clay Bricks As Aggregates

With the development of urbanization,a lrage number of urban and rural buildings are demolished.and raw materials of those constructions mostly are clay bricks,so a mass of waste clay bricks should be dealt with properly.The lightweight and certain strength of clay bricks provides the possibility to make lightweight aggregate concrete(LAC)with clay bricks as aggregates.In this paper,the performance of clay brick aggregates and design of mix proportion were investigated to meet the requirements of strength and density of LAC.After that,the basic mechanical properties,physical properties,dry shrinkage and durability of LAC with clay bricks as aggregates were studied systematically.Those could provide a theoretical and experimental basis for engineering applications.The results of experiments show that the bulk density of coarse aggregates with clay bricks is 910kg/m3,which belongs to the category of lightweight aggregate,and coarse aggregates are optimized to meet the continuous gradation of 5-20mm,and fine aggregates with clay bricks belong to middle sand of area ?.The results of ESEM show that the surface of clay brick is rugged and multihole.The water absorption of clay brick is high and it could absorb water rapidly in the early time.The LAC with clay bricks as aggregates could meet constructional requirement by 24h pre-wetting.The best mix proportion of LAC with clay bricks as aggregates was obtained by optimization design The compressive strength of LAC could reach up to 40MPa,and the density degree?1800.The results of basic mechanical and physical properties of LAC with clay bricks as aggregates show that the compressive strength under different groups is quite different in the early age,but it will be stable at about 40MPa in the later stage.The flexural strength at 28d age is about 3.9MPa-4.7MPa,and split tensile strength at 28d age is about 2.0MPa?3.0MPa.The ratio of axial compressive strength and cubic compressive strength at 28d age is between 0.83 and 0.93,which is higher than the ordinary concrete and consistent with the LAC.Also,the static elastic modulus of 28d age is 20%?40%lower than the ordinary concrete.The mathematical models of mechanical properties of LAC with clay bricks as aggregates are built,and the stress-strain curve is analyzed and fitted by the cub-cubic function.The dry apparent density of LAC with clay bricks as aggregates is between 1700 kg/m3 and 1840 kg/m3,and the thermal conductivity ia between 0.5 W/(m·K)and 0.7 W/(m.K).The influence degree of factors to dry apparent density and thermal conducticity from high to low is:water/binder ratio>addition of fly ash>volume sand ratio.The saturated water absorptivity of LAC with clay bricks as aggregates is about 13%?18%,and the softening coefficient is about 0.85?0.95,which has met the requirement of water-resistant materials.The results of dry shrinkage and durability of LAC with clay bricks as aggregates show that LAC with clay bricks as aggregates has lager dry shrinkage and contractibility rate at 180d age is exceed 1000?m/m.Adding fly ash can inhibit the dry shrinkage,and the best dosage is 10%.JGJ 51 model can be used to fit the dry shrinkage well.The influence degree of factors to durability from high to low is:addition of fly ash>water/binder ratio>volume sand ratio.Adding 10%of fly ash can significantly enhance its resistance to freezing-thawing and Cl-permeability.But the addition fly ash will speed the carbonization,the higher of content,the faster of carbonization.Reducing the W/B will improve the durability significantly,and increasing the volume sand ratio can reduce the resistance to carbonization,LAC with 40%volume sand ratio has a better resistance of freeze-thaw and Cl-permeability.