The effectiveness of di-ammonium hydrogen phosphate (DAP) consolidation treatment on lime-based mortars weathered by freeze-thaw cycles

Abstract

The present paper investigates the effectiveness of di-ammonium hydrogen phosphate (DAP) as a consolidation treatment for artificially weathered lime-based mortars. Laboratory prepared samples were exposed to repeated freeze-thaw cycles and then subjected to 2.0 M DAP solution via 24 h poultice. The microstructural variations due to freeze-thaw cycles and the effects induced by the subsequent DAP consolidation were assessed with the use of a multi-analytical approach combining optical observations, weight variations, dynamic elastic modulus change and peeling test outcomes. The results indicate that DAP treatment significantly restored the weathered mortars in terms of physical and cohesive properties. The correlation between the weight loss and surface degradation by the peeling test examination was projected. The new properties of weathered and consolidated mortars are critically discussed with an eye on their expected behaviour in the field of Built Heritage conservation. Lastly, as a chief outcome of this study, a novel protocol for the evaluation of surface cohesion through peeling tests combined with image analysis is proposed.