Early-age characterisation of Portland cement by impedance spectroscopy

Alternating current impedance spectroscopy (ACIS) was used to assess the effect of different sand, anhydrite and water contents on the electrochemical response of Portland cement paste in the early stages of hydration. Potential factors that may affect impedance measurements and data interpretation are also discussed, such as the complexity of the chemical composition of cement, its physical properties and hydration kinetics, and technique limitations. The impedance data obtained were benchmarked against different supporting techniques and literature data, showing a strong relationship among hydration rates as determined by thermochemistry, setting time measurements by physical approaches, pore fluid chemistry, electrical conductivity and the observed impedance behaviour. The results demonstrate that ACIS is a sensitive technique for assessing cement paste hydration, enabling differentiation of changes in the water and cement content, hydration degree and microstructural development during the first 24 h after mixing.