Research On Preparation And Mechanisms Of Super High Strength Concrete

With the rapid development of the national civil engineering, the ordinary strength concrete can not completely meet their requirements. The super high strength concrete has many advantages, such as high specific strength, load capacity and low consumption of resource and energy, which can gradually meet the building's demands of lightweight, high-rise and large span, so the study of super high strength concrete has a great importance.There are two preparation targets of super high strength concrete in this paper, one is 100 MPa grade, and the other is 150 MPa grade, which have been achived by different ways, and the different influence factors on the properties of super high strength concrete have been researched; And after that, X-ray diffraction and scanning electronic microscope have been taken to study the hydration and the interface structure of concrete, which can explain the mechanism of strength development of super high strength concrete.The results have shown that:①"Portland cement+reactive mineral admixture +superplasticizer " have prepared the super high strength concrete with the 28d compressive strength of more than 107MPa and the slump of more than 100mm. The optimum content of silica fume is 10%, and the best water to cementitious materials ratio is 0.20. When standard curing can't be adopted, the concrete can be curing in the nature environment sealed with plastic bags, and 28d compressive strength at this time can still be more than 100MPa;②Based on the preparation method of 100 MPa grade super high strength concrete, removal of coarse aggregates, quartz sands with 0.15 mm to 0.6 mm instead of river sands, and the introduction of S95 steel slag and copper wire cut fiber, and then a 3-day 90℃steam curing, the super high strength concrete with the 28d compressive strength of more than 160MPa have been prepared. The optimum content of silica fume is 0.25, and the lowest water to cementitious materials ratio is 0.18. The introduction of an appropriate amount of GBFS can reduce the amount of silica fume and cement without decreasing the strength of concrete, the optium content of GGBS is 0.30. Steam curing time had better to be 3 days. If not particularly stringent requirements on the compressive strength, the quartz sand can be replaced with a graded river sand, and its compressive strength can be more than 140MPa, whereas the cost will be reduced.③The secondary reaction (pozzolanic reaction) can happen between silica fume and Ca(OH)2 produced by the hydration of cement clinker, and then the hydrated calcium silicate gel will generate, which can lead to a more compact structure. Steam curing can accelerate the process of cement hydration and pozzolanic reaction, and can improve the micro-structure, which will promote the rapid formation of strength. The interface between sand and cement and between steel fiber and cement are all very compact, and the interfacial transition region is not obvious.