Effect Of Mineral Admixture On Shrinkage And Mechanics Of Concrete At Early Age

Mineral admixtures have become an important component of modern concrete, and is highly related to much performance of concrete. This paper has discussed the effect of fly ash, phosphate slag.and silica fume on autogenous shrinkage, drying shrinkage, mechanics and crack of cement-based materials at early age. The author report a device which could test the autogenous shrinkage of cement-based materials on the basis of summing up the testing equipment and methods of autogenous shrinkage at home and abroad. The device can not only measure the early autogenous shrinkage of mortar consecutively, but also it can be used circulatly.The results indicate that fly ash and phosphate slag can reduce the autogenous shrinkage and drying shrinkage of mortar at early age, but silica fume increase the both. Compared to the norm, the mixture of above-mentioned mineral admixtures increase autogenous shrinkage at early age. The mixture of mineral admixtures makes the drying shrinkage of mortar at early age become large except the mixture of fly ash and phosphate slag. Fly ash and phosphate slag could degrade mechanics and brittleness factor of mortar at early age,which is good to anti- crack. The utilization of silica fume can optimize mechanics of mortar, but produces little influence on the brittleness factor. In addition, The cubic compressive strength, tensile strength, splitting tension strength, modulus of elasticity and ultimate tension of concrete at 1 day, 2 days, 3 days, 5 days and 7 days are tested and analyzed respectively in this paper. The effect of mineral admixtures on anti-crack performance of concrete and mortar was studied by the method of improved flat slab and ring. Combination of correlation analysis method, we research the correlativity among the autogenous shrinkage of concrete, the time when crack come up in concrete and mortar, the square of crack of concrete. The test results show that the autogenous shrinkage of cement-based materials is closely related to the crack of concrete; the greater the autogenous shrinkage at early age, the earlier crack croping up, the more area cracked. The research results and testing apparatus developed in this parper can be used in mineral admixture selecting and the optimization of mixing-ratio on crack at early age.