Sustainable masonry mortar for brick joint and plaster in the UK

Blended mixtures of ground granulated blastfurnace slag and Portland cement were used in making sustainable masonry mortars suitable for brick joints and for plastering, with Portland cement mortar as control. The testing programme included the determination of a relationship between the mortar flow value and mortar water demand for a wide range of mix compositions. The mortar tensile strength is not a very critical property due to the fact that brickwork mortar is not usually under tension when in service; however, this parameter was determined in the laboratory using a standard briquet towing/testing machine. Chemical durability of the control and blended mortar in aggressive sulfate-bearing exposure conditions was investigated. The relationship between compressive strength of the mortar cured in water and in sodium sulfate solution at room temperature (20 ± 2°C) for from 3 to 120 days was established. The results demonstrated that after a prolonged period of exposure, significant strength and weight loss in the control mortar was observed. This phenomenon is explained, due to calcium hydroxide production as a consequence of Portland cement hydration, change in mortar morphology, inhibition of reaction species and the final disruption of the mortar matrix, resulting in loss of strength and weight at late age. The results obtained suggest that ground granulated blastfurnace slag can be incorporated into Portland cement for the development of sustainable and durable mortars in the UK.