Mortar damage due to airborne sulfur compounds in a simulation chamber

Abstract

The interaction between airborne sulfur compounds and mortars has been investigated. Simulation experiments were carried out in a flow chamber where temperature, relative humidity and SO2 concentration were controlled. Samples of lime, pozzolan and cement mortars were exposed for 90 days in air with 3 ppm of SO2 concentration, at 25°C temperature and 100% relative humidity. Following exposure, the mortar samples were studied by x-ray diffraction, infrared spectroscopy and high pressure liquid chromatography. The data obtained from bulk and surface analyses clearly show that the materials reacted with sulfur dioxide to form calcium sulfite hemi-hydrate and calcium sulfate dihydrate. The quantity of sulfite and sulfate measured depends on the physical and chemical properties of the three mortars, but is independent of their CaCO3 content. Formation of ettringite and thaumasite did not occur in the 90 day period taken into account in the present work.