Study On Compressive And Fracture Behaviour Of Silica Fume And Crumb Rubber Reinforced Recycled Aggregate Concrete With Steel Fibre

With the rapid development of the economy in China, a large number of solid waste are produced each year, such as crumb rubber and construction waste because of demolition and earthquake. It is one of the hot research topics about urban sustainable development on recycling the solid waste efficiently, which can reduce the environmental pollution and consumption of raw material. In order to recycle the waste rubber and concrete, a new environmental construction material—silica fume and crumb rubber reinforced recycled aggregate concrete with fibre (SRSRAC) was developed in this study. A series of test were conducted to study the compressive and fracture behaviour of this new kind of concrete. The main content and conclusion are as followed:(1)In order to fulfill the purpose of evironmental protection, energy conservation and cyclic utilization, recycled concrete aggregate (RCA) was introduced into the concrete mixture by substitution of natural coarse aggregate (NCA), and fibre was added into the concrete mixture. In addition, sand and cement were substituted by crumb rubber and silica fume, respectively. Based on a series of test, a new environmental recycled aggregeat concrete was proposed—silica fume and crumb rubber reinforced recycled aggregate concrete with fibre (SRSRAC). The results indicate that this new kind of materal has good mechanical properties, which matches with the development trend of energy conservation and emission reduction in China; silica fume and steel fiber show good coupling effect, which can improve the compressive and fracture behaviour of SRSRAC.(2)The crumb rubber content was at levels of 0%、 5%、 10%、15% and 20% by volume substitution of sand, and the silica fume content was at levels of 0%、 5% and 10% by quantity substitution of cement or at level of 3% in addition. Based on a series of axial compression test, which included 87 specimens in 29 groups, the compressive strength, stiffness, modulus of elasticity and energy dissipation capacity were analyzed. The results indicate that silica fume can improve the compressive strength of natural concrete and recycled aggregate concrete, but the SRSRAC with 5% silica fume or 3% in addition an not obviously improve the compressive behavior. Compared with steel fiber, the incorporation of polypropylene fibre can improve the compressive strength better. Take the compressive indices into consideration, the SRSRAC with 1% steel fiber,10% silica fume and 5% crumb rubber can gain the best compressive behaviour.(3)A total of 57 SRSRAC beams (φ 150mm × 300mm) which were devided into 19 groups were prepared. Based on a series of three-point bending tests, the influence of the method of silica fume incorporation and incorporation of rubber on the fracture behaviour of SRSRAC were studies. The relationship of the load-deplacement and load-CMOD of SRSRAC were measured, and then the fracture energy, fracture toughness, initiation toughness and unstable fracture toughness were calculated. The results show that as the rubber content increases, the fracture toughness decrease, but the fracture energy of SRSRAC increases firstly and then decreases.5%-10% is the best rubber incorporation for the fracture behaviour of SRSRAC. Compared with the polypropylene fiber, the union of steel fiber and silica fume can improve the fracture bahaviour of concrete more effectively. As the content of silica fume increases, the fracture behaviour of steel fiber reinforced concrete improves obviously. The methd of adding 3% silica fume in SRSRAC is as good as that of substituting 10% cement of SRSRAC with silica fume.(4) Based on the compressive and fracture test of SRSRAC, the failure mechanism of axial compressive test and fracture of SRSRAC were investigated. The results show that the silica fume can improve the compactness of recycled aggregate concrete, improve the bonding effect between steel fiber and recycled aggregate concrete. During the compressive process of SRSRAC, the incorporation of rubber can decrease stress concentration at the crack tip, steel fibre has the effect of crack resistance. During the fracture process of SRSRAC, the cracks propagate across the aggregate, and the steel fiber is pulled out; the stress is carried by steel fiber after the fracture of concrete, the propagation of cracks can be divied into 3 stages, including initiation, stable and unstable stage.