How Different is the Deteriorating Mechanism of Fired Clay Bricks Due to NaCl Salt Compared to the Highly Damaging Na<inf>2</inf>SO<inf>4</inf>?

Deterioration due to salt crystallization or physical salt attack is one of the crucial issues faced by the world’s architectural heritage. Sodium sulphate is known for its highly damaging nature and hence adopted universally as the deteriorating agent by various laboratory salt degradation tests. There exists a general disagreement in the research community regarding the damaging nature of NaCl to masonry structures, perhaps due to a lack of sufficient information regarding the mechanism of decay. The current paper analyses the degree of deterioration and mechanisms in various brick types in the presence of NaCl and compares that with the mechanism of Na2SO4 damages. Accelerated salt weathering tests were conducted as per the RILEM V 1.b test procedure followed by the micro-analytical characterization of samples post-degradation. The difficulty in attaining higher supersaturations was observed in the case of NaCl, which resulted in a much slower rate of degradation. The role of microstructure of the material in altering the damage mechanism is elucidated using data collected with Mercury Intrusion Porosimetry and Scanning Electron Microscopy. Also, a question on choosing the right protective treatment for the samples on various exposures- sodium sulphate and sodium chloride is addressed.