Study On Structure And Performance Of 300 ~ 400MPa Super High Strength Concrete

The reactive powder concrete (RPC) material of ultrahigh strength is a new type of inorganic non-metallic composite with the features of low density, high toughness, high strength and etc. In this paper, the author studies the structure and properties of reactive powder concrete (RPC) of ultrahigh strength, and obtains the main achievements in research as follows:Fine aggregate material is the main component of concrete subjects RPC, which accounts for 30-50% of total volume of RPC concrete. RPC fine aggregate in concrete not only has a technical role, but also has an economic significance. Aggregate performance contrasts are made by adding quartz sand, fused corundum, ceramic beads and etc.. When mixed with 12 mm steel fiber, with the increase of fine quartz sand aggregate content, flexural strength and compressive strength of RPC concrete gradually increase, and the bending strength and compressive strength reach the peak when fine quartz sand aggregate content is 1.1. The fused corundum of high strength, high hardness and high elastic modulus combined with RPC substrate interface has poor performance, and the RPC enhancement effect is not obvious. High strength, elastic modulus and ceramic beads which adapt to matrix can be made into reactive powder concrete of ultrahigh strength with stable compressive strength of 330 MPa, and the flexural strength of 40 MPa. Therefore, ceramic beads can significantly enhance the performance of the RPC concrete.The various types of fiber combinations of steel fiber shape, length-diameter ratio, chopped steel fiber and etc. have a significant impact on the performance of concrete RPC. By mixing large dosage of steel fiber, the experimental results are that with the increase of steel fiber content, breaking strength and compressive strength have improved significantly. When the total fiber volume fraction is unchanged,12mm long steel fibers have a large impact on folding strength; 6mm short steel fibers have a large impact on the compressive strength, and bending presents the characteristics of plastic damage. To increase the content of chopped steel fibers can obviously improve the compressive strength of RPC composite material, but can not improve the bending strength obviously, and bending presents the characteristics of brittle failure.In the RPC matrix used as the research object, using melting quartz powder as siliceous raw materials can eliminate the influence of quartz diffraction peak in the analysis of XRD phase of RPC substrate, and improve the analysis precision of XRD phase. By using the melting quartz powder instead of superfine quartz powder, and by cold isostatic pressing and the plastic molding, researches have been made on the micro hardness, compressive strength and the growing laws of the nucleation of hydration calcium silicate of hydration products under different growing space,. The study shows that the vickers hardness can demonstrate the mechanical properties and matrix structure of RPC matrix well, and can demonstrate that cold isostatic pressing forming can make matrix structure dense; fracture appears metallic luster; compressive damage presents the phenomenon of layer peeling, and matrix presents brittle failure. Under the condition of big water cement ratio, a diffraction peak can not be found in tobermorite RPC matrix. Through the SEM experiment, it can be found that the RPC substrate is very dense; the macroscopic defect is a small amount of air entraining pores, and amorphous hydration products generate at the side of air entraining pores. Therefore, the hydration product particle size is small, and the overall density is one of the important reasons for the ultrahigh strength of RPC concrete.Through researches on the phase and structure morphology of RPC substrate material, it can be found that the RPC hydration products are mainly C-S-H gel and partly unhydration cement clinker. Through the scanning electron microscope, it can be observed that the structure of RPC substrate is dense; hydration phase presents gel particles aggregation and half crystal fiber accumulation, and hydration phase accumulation presents the phenomenon of the internal stress of crystallization. Hexagonal columnar calcium hydroxide crystal has been found in the RPC substrate gap; calcium hydroxide crystallization precipitation increases the expanding internal stress; the internal stress can be enhanced under the constraint of steel fiber on expansion, and ultrahigh performance concrete of 101.2 MPa bending strength, and 406.4 MPa compressive strength can be configured.