Study On Hydration And Shrinkage Characterization Of Cement Pastes Using Electrical Resistivity Measurement

The electrical resistivity measurement can be employed to monitor the change of electrical resistivity during the hydration of cement and thus can be used to study the hydration characterization of cement-based materials. Chemical shrinkage and autogenous shrinkage caused by cement hydration are the important factors that can affect the volume stability of cement-based materials. In addition, mineral admixtures and chemical admixtures can also play an important role in the volume stability of concrete. The electrical resistivity measurement was employed as a basic testing method. The main content and conclusions can be summarized as follows.(1) Chemical shrinkage of Portland cement pastes was measured by volumetric method according to ASTM Standard C1608-07. The results obtained show that the relationship between chemical shrinkage and degree of hydration is linear. The relationship between chemical shrinkage and electrical resistivity appears to be roughly linear after12h. It is noticed that the electrical resistivity after12h can be used to determine the degree of hydration.(2) The evolution of electrical resistivity and autogenous shrinkage of Portland cement pastes with different dosages of fly ash was investigated. The results show that the electrical resistivity of the cement paste increased before setting and decreased after hardening with the increase of dosage of fly ash. The autogenous shrinkage of the hardened cement paste decreased with the increase of dosage of fly ash.(3) The setting process and evolution of electrical resistivity of Portland cement pastes with different dosages of naphthalene superplasticizer was investigated. The results show that the addition of superplasticizer to the pastes with a fixed water to cement ratio (W/C) can cause longer setting time and delay the evolution of electrical resistivity. The final setting time and the occurring time of maximum rate of electrical resistivity were both delayed when the dosage of superplasticizer was increased. The compressive strength at28days and the ultimate electrical resistivity show a same tendency for the cement pastes with different dosages of superplasticizer.(4) The evolution of electrical resistivity of calcium sulfoaluminate cement (CSA) paste within1440minutes was investigated. The results show that the electrical resistivity versus time curve occurs two peaks up to1440min. The occurring time of the two peaks seems to have no relationship with W/C. The reason for the occurring of the two peaks can be due to the process of ettringite formation and ettringite transformation to monosulfate in the CSA hydration system. The relationship between W/C and electrical resistivity at1hour follows a negative linear trend but a positive linear trend observed at24hours. The relationship between the compressive strength and the electrical resistivity at24hours for the hardened cement paste with different W/C ratios follows a negative linear equation.