Investigation On The Rheological Properties Of Concrete With Fly Ash

Good Workability of concrete is the prerequisite to achieve the concrete quality goal,which is related to the construction progress, the intensity of labor and the construction quality. It also seriously influences the physical mechanical performance and durability at late age of concrete. Rheological parameter is an important index to indicate the performance of flow ability and Workability of cementitious materials (cement paste, mortar and flesh concrete), which is significant for guiding the engineering application, controlling the workability of fresh concrete and ensuring the engineering quality. As a mineral admixture in concrete industry, fly ash has a wide development, and concrete with fly ash is here and there in present engineering practice. Therefore, this paper is aim to analyze the rheological properties of concrete with fly ash, and set up a set of scientific research approaches to analyze the influence of mineral admixture on cementitious materials, and explore the correlation between the rheological properties of cementitious materials and the macroscopic mechanical properties.As for the cement paste system, the effect of the fly ash on the rheological properties of paste was analyzed by the hydration of cement,particles accumulation of fly ash, morphology and so on in this paper. In addition, the influence of polycarboxylate and naphthalene superplasticizer on paste was also studied. The results indicated that:ground fly ash could accelerate early hydration of cement, consume more free water, and lower paste plasticity capacity, which had a negative effect on the rheological properties. However, ground fly ash would fill with the defects within, release more free water, which was helpful to spread around the cement particles and play a positive role on the rheological properties. The higher ground fly ash roundness was, the better ball phenomenon and rheological property was. Fly ash had a good effect on the rheological properties of cement paste containing superplasticizer, but the influence of changes in fly ash size distribution on the rheological properties of cement paste containing superplasticizer would be different. Naphthalene superplasticizer will have a better effect due to improved gradation, but polycarboxylate superplasticizer has no obvious effect.In the part of mortar, this paper found that the influence of grounded fly ash and superplasticzer on the rheological properties of mortar was the same as cement paste system.In the parts of flesh concrete, this paper made a qualitative analysis to concrete particle gradation, then represented concrete particle gradation in different proportioning of concrete, and found that the influence of fly ash particle gradation to flesh concrete was consistent with cement paste and mortar, so was the effect of superplasticizer to the rheological properties of fly ash cement.According to the analysis of relation between water binder ratio and rheological parameters in cement pastes, mortar and fresh concrete, a mathematical formula was inferred:f=Ae-Rn,in this formula f is yield stress, n is water binder ratio, and A, B are coefficient. According to the analysis of relation between concrete strength and rheological parameters in different water binder ratio and different amount of superplasticizer, a mathematical formula was inferred:R=Aln(f)+B,in this formula R is compression strength, f is yield stress, and A, B is coefficient. According to the analysis of relation between slump and rheological parameters in different situation, a mathematical formula was inferred:S=300 -A(f+B)/ρsg,in this formula S is slump, f is yield stress,ρsg is relatively density of concrete, and A, B is coefficient.According to research, this article has revealed the influence mechanism on rheological properties of material based on cement by the fly ash and the superplasticizer, established mathematical relation between the rheological parameter and the macroscopic performance of concrete, founded the mathematical relation between the tradition test method for slump test and the rheological parameter, set up a set of relatively complete scientific method about mineral admixture affect rheological properties of material based on cement, will lay a foundation for researching relation between the working performance of fresh concrete and the macroscopic durability.