The influence of mineral admixture and superplasticizer on the rheological behavior of cement paste
Student thesis: Master's Thesis
Self-compacting concrete has gained wide use as a high-performance concreting material for civil engineering construction. Since self-compacting concrete is generally proportioned with small-sized aggregate and high fines content, the rheological behavior of its cementitious materials is a major influencing factor on the fresh and hardened properties of self-compacting concrete. To better produce self-compacting concrete effectively, it is pertinent to study the rheological behaviour of cement paste in-depth. The objective of this research is to examine the rheology of cement pastes incorporated with superplasticizer and pulverized fly ash. Empirical tests such as slump flow test, V-funnel test and flow cone test on different mixes of cement pastes at a water-binder ratio of 0.2 were undertaken. Dosage of superplasticizer and the replacement level of cement by pulverized fly ash were varied. The results indicated that at a fixed water-binder ratio, there is an optimum superplasticizer content for maximum performance which was found to increase with the amount of cement replaced by pulverized fly ash. The rheological properties of cementitious materials were investigated using a Brookfield rheometer with a serrated coaxial cylinder. Rheological parameters were then determined by Herschel Buckley model. Cement paste exhibited a shear-thickening behaviour which the apparent viscosity increases with an increase in the shear rate. When pulverized fuel ash are used, the intensity of this phenonmenon was amplified. Nonetheless, the shear thickening behavior is shown to decrease with an introduction of SP. Plastic viscosity and the exponent is found to reduce as the dosage of SP increases. Secondly, the above empirical test results appear to be appropriate in characterizing the rheological behaviour of self-compacting cement paste instead of a rheometer. Yield stress, plastic viscosity and the exponent are in good correlation with the empirical test results.
- Testing, Additives, Cement