Study On Test Of Mixed Sand Concrete Early Age Shrinkage Cracking Performance

Early cracks of concrete reduce the performance of structure, directly affect the durability of concrete and shorten the service life of concrete. The use of fine sand concrete, cementitious material consumption, resulting in the hydration process release a lot of heat of hydration, increase the possibility of cracking in concrete at early age. In this paper, the mixed sand concrete, experimental study on early cracking resistance of mixed sand concrete, and the tensile strength, the elastic modulus of concrete to the analysis of the early age cracking tendency.To determine the reasonable mixing ratio by calculating the mixed sand fineness modulus, the fineness modulus of sand mixing control in 2.3~3 range. Mixed sand can save the cementitious material content, improve the density of concrete. Experimental study on working properties and mechanical properties of the concrete with different mixing ratio of mixed sand under the same conditions, showed that the mechanism of sand on concrete strength is enhanced, but the concrete mixture water retention and cohesiveness decreased.Through the C40 mixed sand concrete mix ratio test, the change of concrete water cement ratio, sand ratio and mixing ratio of mixed sand experiment, effects of these three parameters, the mixed sand concrete early cracking resistance and mechanical properties, analysis of the relationship between the mechanical properties and mixed sand concrete early age cracking tendency, and put forward the mixed sand concrete early crack resistance good mix. The test results show that: the mechanism of sand mixing ratio of mixed sand concrete total cracking area is 80% 299mm2/m2, the mechanism of sand mixing ratio of 60% units total crack area of 687 mm2/m2, the mechanism of sand mixing ratio of mixed sand concrete ratio of 80% sand mixing ratio is reduced to 60% of the maximum crack width, concrete the crack is reduced to a, anti cracking performance of early increased from grade to grade, the mechanism of sand ratio of 80% mixed sand concrete early crack resistance performance is better. Water binder ratio of mixed sand concrete anti cracking performance is better than the 0.42 water to binder ratio of 0.38 mixed sand concrete, but its mechanical properties are less than 0.38 of the mixed sand concrete water cement sand ratio; early anti cracking properties of mixed sand concrete 40% the ratio of the sand ratio 36% of the early cracking resistance. Mixed sand concrete early compression ratio increases with the decrease of water cement ratio of concrete, the brittleness increases, increase the early age cracking tendency of concrete; mix sand concrete fsp/fsp28 and E/E28 within the 1d growth rate, and the early static elastic modulus growth rate higher than the growth rate of splitting tensile strength of concrete, resulting in the constraint condition of the tensile stress of the growth rate was significantly higher than that of tensile strength growth rate, thus increasing the early age cracking tendency of concrete.Through the surface microscopic observation and SEM scanning electron microscope test, the proportion of the study found that the mechanism of sand is 60% time, the internal structure of mixed sand concrete early cracking of many pores its surface is more serious; mixed sand mechanism sand ratio is 80%, the total crack area of concrete is small, dense internal structure of cement stone, low porosity, good anti cracking performance of concrete.