Effect of free water on the flowability of cement paste with chemical or mineral admixtures

Abstract The particle packing state in cement paste and the characterization methods of free water were studied. The changes of free water in cement paste by adding mineral admixture and chemical admixture were measured, and the relationship between flowability and internal structure of cement paste was analyzed. The results showed that: water in cement paste can be classified by plastic limit test and liquid limit test. Excess water over the plastic limit which was the surplus water after filling the accumulate void of cement particles can only achieve the purpose of separating cement particles. When water exceeded the liquid limit, the free water caused the flow of paste under gravity. The improvement of flowability by adding superplasticizer was not only due to dispersion of flocculation structure, but mainly because of lower adsorption force field of cement particles to water. Superplasticizer reduced the thickness of water diffusion layer, and increased the flowability of the paste. The mineral admixture influenced the packing state and water adsorption capacity of particle materials.