The Study On The Influence Of Quality Of Coarse Aggregates On The Properties Of High Strength Concrete

Formerly, we would like to improve the structure and composition of cement mortar to enhance the performance of concrete. However, with the application of high strength concrete and the enhanced the sensitivity of the influence of coarse aggregates on the performance of high strength concrete, some performance of concrete could not be solved very well merely by the improvement of cement mortar. Since then, there is an important practical significance to explicit the effect of coarse aggregates on high strength concrete. Nevertheless, the viscosity of high-strength concrete, the plastic shrinkage, cracking of concrete in early age are the common problems in engineering, and the reasonable use of coarse aggregates is expect to reduce the plastic shrinkage and cracking of concrete. It is advantageous to the economy and the long-term durability of concrete.This paper belong to the project named “The key technological research of highstrength and high-performance concrete on the application”, and mainly studies the effect of coarse aggregates, namely coarse aggregates size distribution fractal dimension, volume content of coarse aggregates, the types of coarse aggregates, elongated and flaky particle content on the influence of early plastic shrinkage and cracking resistance. The main laws revealed include that:1) Coarse aggregates grading can be simply and quantitatively characterization by fraction dimension, and the void fraction of(5~26.5)mm coarse aggregates has a minimum value with the variation of grading distribution fraction dimension from 2.0 to 2.8. Through the study of the concrete that used with different coarse aggregates size fraction dimension, the slump and extension degree of fresh concrete increases with the decrease of the size distribution fraction dimension, but too low fraction dimension can cause poor adhesiveness and occur bleeding and reduce early cracking resistance of concrete. The optimum compressive strength of high strength concrete is obtained in the fraction dimension of 2.6.2) The content of the coarse aggregates in concrete should be reasonable. for(5~26.5) mm crushed limestone, The optimum content of coarse aggregates should be controlled at about 50%, then the comprehensive performances of high strength concrete will be better.3) Among the three types of coarse aggregates namely limestone, crushed pebble, basalt,the high strength concrete used by coarse aggregates of basalt has the highest compressive strength, but its ratio of rock strength and concrete strength grade is smallest, plastic shrinkage and cracking resistance in early age are poor.4) With the variation of the elongated and flaky particle content from 0 to 20%,It is harmful to the compressive strength and plastic shrinkage and cracking resistance of high strength concrete in early age when the elongated and flaky particle content is more than 10%.