Experimental Research On Flexural Stiffness Of Reinforced Concrete Beams With Recycled Coarse Aggregate

The use of recycled aggregate concrete brings forward a new approach for the reuse of the building waste materials. This could be an important breakthrough for our endeavor towards sustainable development. The studies on the use of recycled aggregates concrete have been going on for 50 years. In fact, none of the results show that recycled aggregate concrete is unsuitable for structure. Only having inadequate number of studies in durability aspects, made recycled aggregate concrete to be preferred just as stuffing material for road construction. In utilizing recycled aggregate concrete in structural aggregate, the inferiority in concrete quality is a major concern. The main reason is that recycled aggregate contains significant amount of porosity in clinging mortar. In recent year, some studies concerning concrete and reinforced concrete made of recycled aggregate have been performed. However, those are not sufficient for making clear behavior of structural members leading to establishing design method. Especially, few studies concerning flexural stiffness of reinforced concrete beams with recycled coarse aggregate were performed.The aim of this contribution is to investigate the applicability of recycled aggregate containing high amount of cement paste as a structural aggregate by comparing the flexural properties of reinforced concrete members produced from recycled aggregate concrete with those of reinforced concrete members with ordinary concrete. Based on the test of cubes and prisms, the relationship between cubic compressive strength, prism strength and Young's modules of recycled concrete are investigated. Flexural properties of 27 reinforced recycled concrete beams and 3 reinforced concrete beams are investigated experimentally. The major factors are compressive strength of recycled aggregate concrete and ratio of tension reinforcement. Flexural properties of reinforced recycled concrete beams, i.e. mid-span deflection under serviceable load and stiffness are discussed. The main conclusions are as following:1. Compared with ordinary aggregate concrete, the elastic modulus of recycled aggregate concrete is smaller by 20%.2. Under the same loadings, the strain of tensile steel and the strain of concrete in compression zone of recycled aggregate concrete beams are larger than that of natural aggregate concrete beams.3. The calculating method on bearing capability for natural aggregate concrete beam can satisfy the requirement of recycled aggregate concrete beams.4. The mid-span deflection of recycled coarse aggregate concrete beam was slightly larger than that of ordinary aggregate concrete beam by 11% under the same conditions.5. The calculating method on flexural stiffness of reinforced concrete beams with recycled coarse aggregate under service loading was obtained. The calculated values of mid-span deflection of recycled coarse aggregate beams are in good agreement with the test values and recycled coarse aggregate beam can satisfy the requirement under service loadings.