Study On Performance Of Green Recycled Concrete With Low Shrinkage

With the implementation of the national sustainable development policy and the strengthening of social environmental protection awareness,the research on the resource utilization of construction waste has attracted a lot of attention of many scholars.The application of recycled concrete can effectively solve the environmental pollution problem from construction waste,but due to the defects of high crushing index and high water absorption of recycled aggregate,the mechanical properties and shrinkage properties of the prepared recycled concrete are relatively poor,which restrict the development of recycled concrete to a certain extent.Therefore,the preparation technology of recycled aggregate is an important prerequisite to restrict the application and promotion of recycled concrete engineering.In this paper,based on the recycled coarse aggregate produced by the particle shaping aggregate strengthening method,the green low carbon cement is used to prepare green recycled concrete with low shrinkage,which not only effectively alleviates the scarcity situation of natural resource,but also significantly improves the performance of recycled concrete,which is of great significance for the multi-path resource utilization of construction waste.Under the financial support of the National Natural Science Foundation of China(51878366),in this paper,the green recycled concrete with low shrinkage is prepared by using recycled coarse aggregate after simple crushed and particle shaping treatment as the main raw material,high-belite sulfoaluminate cement as the basic cementitious material,and mixed with some blast furnace slag and fly ash,the effects of four variables including cementitious material system and content,quality of recycled coarse aggregate and replacement rate on working properties,mechanical properties and drying shrinkage properties are systematically researched.The main research work and conclusions are as follows:(1)Research on the preparation technology of recycled aggregate.Simple crushed,simple crushed-particle shaping and simple crushing-second particle shaping methods are respectively used to produce simple crushed recycled coarse aggregate,primary recycled coarse aggregate with particle shaping and secondary recycled coarse aggregate with particle shaping.The comparative study of the performance indexes of recycled coarse aggregate showed that the quality of secondary recycled coarse aggregate with particle shaping is the best,and the effect of strengthening technology of particle shaping aggregate is significant.(2)Research on workability of green recycled concrete.With the premise that green recycled concrete achieves the same workability,with the enhancement of recycled coarse aggregate quality and the reduction of replacement ratio,the water consumption of concrete mix gradually decreases.For simple crushed recycled coarse aggregate,its replacement ratio should not exceed 50%.The influence of the change of cementitious material system on the water consumption of green recycled concrete is relatively great,100% cement > 70% cement + 30% slag > 70% cement + 30% fly ash >70% cement + 15% slag + 15% fly ash in order.With the increase of the amount of cementitious material,the water consumption of concrete mix gradually increases.(3)Research on the mechanical property of green recycled concrete.The 1d compressive strength of green recycled concrete can reach about 80% of 28 d compressive strength,which shows the excellent performance of quick setting and hardening,high early strength and stable late strength,and gradually increases with the enhancement of the recycled coarse aggregate quality and the reduction of replacement ratio.The mechanical property of green recycled concrete are enhanced gradually with the increase of cementitious material content.The influence of the change of cementitious material system on its mechanical properties is: 100% cement > 70%cement + 30% slag > 70% cement + 15% slag + 15% fly ash > 70% cement + 30% fly ash.(4)Establishment on strength formula for green recycled concrete.According to the performance and mechanical properties of green recycled concrete,based on the main performance indexes of water absorption,crushing index and apparent density of recycled coarse aggregate,the multi factor Bolomey strength formula and the strength formula introducing with the influence factor of recycled coarse aggregate are established respectively.(5)Research on performance of green recycled concrete with drying shrinkage.By systematically studying the shrinkage variation of green recycled concrete,the shrinkage ratio of green recycled concrete is respectively reduced by 50%～95%and230%～340%compared with rapid-hardening sulfoaluminate cement and ordinary cement-based recycled concrete.Thus the excellent drying shrinkage resistance of green recycled concrete is significantly highlighted,which can be used to produce concrete with low shrinkage and related products.In this paper,high-belite sulfoaluminate cement-based recycled concrete is prepared by using construction waste and industrial solid waste synergistically,and the performance evolution law is explored and studied under the coupling effect of multiple factors.The obtained green recycled concrete with low shrinkage has an excellent performance and the error of established strength calculation formula is relatively smaller.The research achievement provide a new way for the resource utilization of construction waste,which has a certain guiding significance on the green cycle development of recycled concrete.