Setting behaviour of waste-based cements estimated by impedance spectroscopy and temperature measurements

This work describes the study of phase development during the setting of various clinker formulations prepared with industrial wastes or by-products, namely sludges (generated in the Al-anodising and surface coating industrial processes, in potable water filtration/ cleaning operations and in the cutting process of natural marble) and foundry sand. For comparison, similar formulations were also prepared with commercial high purity grade raw materials and processed in identical conditions. To circumvent the experimental restrictions imposed by the use of Vicat's needle (i.e. large amount of material), electrical resistivity measurements were conducted by alternate current (a.c.) impedance spectroscopy to follow the hydration process and setting behaviour. During setting, the temperature evolution of the water/cement pastes was also recorded. Impedande spectroscopy (IS) studies were found to be a reliable method and, in some systems, can be a more sensitive technique to detect on-going hydration reactions.