Deterioration of natural hydraulic lime mortars, I: Effects of chemically accelerated leaching on physical and mechanical properties of uncarbonated materials

Masonry using lime binders is very common in all regions of the world. Models for the future climate in northern regions suggest more intense rainfall which will result in the materials used in mass masonry being saturated for longer periods and therefore at higher risk of binder leaching and consequent deterioration. In this first study of lime binder leaching, ammonium nitrate leachant was used to accelerate the deterioration of mortars containing natural hydraulic lime binders. Loss of binder reduced the alkalinity and strength of the mortar and increased its sorptivity. The leached depth followed diffusion-controlled kinetics with the rate constant increasing in line with the increasing free calcium hydroxide content of the binder. A predictive model was developed for uncarbonated mortars, such as those of all ages (historic or modern) found deep in mass masonry and those at early age in new construction or repairs.