Abstract
Polyvinyl alcohol (PVA) and calcium sulphoaluminate (CSA) cement were used to prepare repair mortar for the restoration of the walls of a building built with bricks. The preparation, hydration, and properties of the PVA-modified CSA cement repair mortar were studied. Besides this, the mechanism by which PVA improves the bonding strength is also discussed. The results demonstrate that PVA prolongs the setting time of CSA cement, which is ascribed to PVA inhibiting the dissolution of C4A3$ (4CaO·3Al2O3·SO3) and the precipitation of AFt (3CaO·Al2O3·3CaSO4·26H2O) within the hydration age of 0~60 min. PVA lowers the mechanical strength of CSA cement repair mortar at the hydration age of 6 h. After 6 h, the mechanical strength is improved. PVA could also improve the bonding strength between CSA repair mortar and bricks. This is mainly ascribed to the Al ions in both the hydration products of CSA cement and the clay bricks reacting with the hydroxyl group of PVA and forming the chemical bond C-O-Al. Therefore, a tighter combination between CSA cement repair mortar and the clay bricks forms, thereby improving the bonding strength.
Highlights
Due to their direct exposure to the natural environment, the buildings in service are inevitably subjected to external mechanical forces and environmental corrosion
The tensile bonding strength between the calcium sulphoaluminate (CSA) cement repair mortar and the bricks was determined according to Chinese standard JGJ/T 70-2009 using a universal testing machine MTS CMT 5504
To achieve perfect mechanical interlocking between the CSA cement repair mortar and the bricks, good fluidity—which has close ties with the free water content—of the CSA cement repair mortar is required
Summary
Due to their direct exposure to the natural environment, the buildings in service are inevitably subjected to external mechanical forces and environmental corrosion. Structural damage arises, which poses a great threat to personal safety and shortens the service life [1,2,3,4]. Buildings with structural damage are in urgent need of repair. In China, most of the walls of residential buildings were built with bricks in the twentieth century. Because of the porous structure of the bricks, the wall structure exhibits strong water absorption, which makes repair mortars fall off due to water loss, leading to the failure of repair. To achieve the goal of perfect restoration of a wall structure built with bricks, the repair mortar should have good water retention and high bonding strength. To shorten the duration of repair works, the repair mortars must have the rapid hardening property [5,6,7]
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