Experimental Study on Properties of Hydraulic Mortars with Mixed in Crystallisation Inhibitors

Sodium chloride (NaCl) is one of the most commonly occurring weathering agents, responsible for a progressive damage in mortar. Current solutions to mitigate salt damage in mortar, such as the use of mixed-in water repellent additives, have often exhibited low compatibility with the existing building fabric. In the last years, research has shown promising results in mitigating salt decay by making use of crystallisation inhibitors. Sodium ferrocyanide is one of the inhibitors that has proven to be particularly effective to reduce damage due to sodium chloride crystallisation. In this research the possibility of developing hydraulic mortars with mixed-in inhibitor (sodium ferrocyanide) for an improved resistance to sodium chloride crystallisation damage is investigated. As a first step, the interaction between the inhibitor and the hydraulic binder: natural hydraulic lime (NHL), was studied; the results are presented in this paper. Various concentrations of sodium ferrocyanide were tested (0%, 0.1% and 1% by binder weight). The effect of the inhibitor on several physical (hydration, water absorption, pore size distribution) and mechanical (compressive and flexural strength) properties was experimentally assessed, using several complementary methods and techniques. The results show that the addition of the sodium ferrocyanide does not affect the fresh and hardened properties of mortar. These results are promising and open new possibilities for the application of inhibitors to improve the durability of hydraulic mortars.