Mechanical Properties and Microcosmic Properties of Self-Compacting Concrete Modified by Compound Admixtures

It has become a research hotspot to explore raw material substitutes of concrete. It is important to research the mechanical properties of self-compacting concrete (SCC) with slag powder (SP) and rubber particle (RP) replacing cement and coarse aggregate, respectively. 12 kinds of composite modified self-compacting concrete (CMSCC) specimens were prepared by using 10%, 20% and 30% SP and 30%, 40%, 50% and 60% RP. The rheological properties, mechanical properties and microstructure of the CMSCC were investigated. Results indicate that the workability, compressive strength, splitting tensile strength and flexural strength of CMSCC prepared by 20% SP and less than 40% RP are improved. In order to maximize the utilization of waste materials, 20% SP and 40% RP can be used as the optimal ratio of the combined modifier. The microstructure shows that the addition of proper amount of SP is conducive to the formation of increasingly more uniform C-S-H gel. C-S-H gel can fill the internal pores of the sample and enhance the adhesion between the aggregate, thus improving the mechanical properties of CMSCC. RP has a rougher surface and lower density and stiffness, which inhibits the workability and mechanical properties of CMSCC. The above research results have important theoretical and practical significance for the selection of raw materials of self-compacting concrete and the rational use of industrial wastes.