Cement-less and/cement-like geopolymer mortars were made with pulverised fuel ash (PFA) or ground granulated blast furnace slag (GGBS) activated by alkali with different alkali moduli (AM) and alkali dosage (AD). Once synthesised the samples were cured at 20°C and 70°C up to 28 days. The flexural and compressive strengths of these samples at early ages up to 28 days were tested conforming to BS EN196-1:2005. The electrical resistivity of these materials was monitored using a set of non-contacting electrodes to the age up to 7 days to characterise the geopolymerisation process from a physical phenomenon point of view.