Resistance of mortar containing unprocessed pulverised fuel ash (PFA) to sulphate attack

An investigation was carried out to establish the physical, mechanical and chemical characteristics of an unprocessed pulverised fuel ash (PFA) from a former landfill site at the Power Station Hill near Church Village, South Wales, United Kingdom. This was aimed at establishing the suitability of the ash in road construction (embankment and pavement) and also in concrete to be used in the construction of a proposed highway. This paper reports on mortar blends made using the unprocessed PFA as cement replacement. The resistance of the mortar was tested by observing sulphate attack during soaking in a standard BS sodium sulphate solution, for soaking periods of up to 504 days. Mortar cylinders of various mix designs were subjected to splitting tensile strength tests, after curing in water for up to 28 days. Thermogravimetric and derivative thermogravimetric (TG/DTG) analyses were carried out on the unhydrated ingredients, in order to assess the degree of hydration and rate of, and portlandite formation in the cement paste after soaking in either water or sodium sulphate solution environment. The binary PC–PFA mortar shows good sulphate resistance under a sulphatic environment with the exception of one trial pit ash (Trail Pit No. 6). The tensile splitting strength decreases as the cement replacement increases.