Electrochemical impedance spectroscopy as a probe of cement hydration and microstructure

Understanding the hydration and microstructural evolution of cement has been a controversial subject for many decades. As a result of this, different techniques have been used to assess cement hydration. One of the techniques which has demonstrated to be a sensitive and useful technique is Alternating Current Impedance Spectroscopy (ACIS). However, this technique is not yet fully accepted by the cement research community and industry. This has been particularly evident in many cement studies at early hydration ages (>24hrs) in which the ACIS information available at this time is very limited due to instrument and data interpretation limitations, and the complex chemical composition, and continuous pore solution and microstructural development of cement paste. In this project, a custom-cell design is proposed to perform ACIS measurements in cement paste at early ages (>24hrs). The selection of the custom-cell is systematically assessed through a rigorous selection process of the cell components and experimental protocol. To evaluate the performance of the custom-cell design and demonstrate the capabilities of ACIS as a probe of cement hydration and microstructural development at early ages, three techniques (i.e. isothermal calorimetry, Vicat needle test, and scanning electron microscopy) are used as a benchmark to support and complement ACIS data interpretation. The results show that ACIS measurement can be performed at early cement hydration ages by using the proposed custom-cell design (decreases parasitic effects at high frequencies). The benchmark techniques demonstrated that ACIS is a promising and capable characterisation technique to assess the characteristics of the pore solution, thermochemical and microstructural changes during cement hydration. However, further experimental work is required to take further the potential of ACIS.