A new technique to evaluate and quantify modified solution kinetics of calcareous materials after sulphuric acid pre-treatment and urban exposure

Carbonate building materials are prone to decay through natural processes of dissolution, which are often enhanced under acidic environmental conditions. A technique has been devised which links experimental laboratory quantification of dissolution rates with field exposure trials, allowing precise studies of the behaviour of natural stone under realistic conditions. A channel flow cell is used to investigate the dissolution kinetics of calcareous materials before and after 12 months exposure in an urban environment, with observations using scanning electron microscopy (SEM) and atomic force microscopy (AFM) allowing visualization of the dissolution process. This technique can be used to investigate and quantify the protection against dissolution provided by chemical pre-treatments. A pilot study using pre-treatment with sulphuric acid indicates that a gypsum covering (obtained by soaking samples in 0.1 M sulphuric acid for 21 hours) reduces the dissolution rate constant of calcite by almost one order of magnitude. This reduction is similar to that experienced as calcite undergoes natural weathering over 12 months in an urban environment.