Influence of organic coatings on the stability of macrodefect-free cements exposed to water

Abstract It is known that macrodefect-free (MDF) cements show instability in water, with swelling and reduction in strength. The weight and dimensional changes of three MDF cements, formulated from different aluminous cements, during immersion in quiescent tap water, were evaluated. The results show that the cement with the highest Al2O3 percentage had the lowest degradation after prolonged immersion. Hence, this material was selected for further analysis. As the time taken for water to diffuse into the body of MDF composites is considered a key factor in the collapse of their mechanical properties, the effect of organic coatings with different barrier properties on the composite behaviour, when exposed to water, was studied. The water permeability of seven surface coatings was evaluated by electrochemical impedance spectroscopy (EIS). Three of them were chosen for application to the selected MDF cement. The data presented show that the application of organic coatings, not necessarily characterised by extremely low water permeabilities, improves the stability of the composite when subjected to different conditions of exposure to water.

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