Erosion of aerial lime and sticky rice mortars by cyclic wetting–drying and dilute sulfate acid actions

Lime mortar with organic additives is one of the most widely used building materials in ancient China and continues to play an important role in historic structure restoration. This study investigated the erosion of ordinary aerial lime and sticky-rice mortars under the cyclic actions of wetting–drying (WD) and dilute sulfate acid (DSA). Comprehensive experimental tests were conducted to study the mechanical properties, quality, microstructure and pore structure of the mortars according to cyclic WD and DSA actions. Results showed that both the WD and DSA actions can significantly degrade the compressive and shear strengths of the mortars. The DSA softens the mortar matrices more severely than the WD by a leaching mechanism. Apparently, sticky rice does not change the micro morphology, pore structure and packing pattern of the mortar matrices, but it inhibits the carbonation of the lime. Both the WD and DSA actions can erode the ordinary aerial lime and sticky-rice mortars, causing more porous matrices and coarser particles. The results of this study make it possible to clarify how the WD and DSA actions affect the durability of partially matured aerial lime mortars with or without sticky rice, with potential uses in the restoration of ancient buildings.