Prediction of the service life of brick/stone masonry damaged by salt crystallisation: application of a stochastic model

An attempt has been made within a EC Contract, to establish the maximum salt content in brick and stone masonry, below which the surface protection treatments do not fail. Crystallisation tests were carried out on treated and untreated brick and limestone masonry specimens. A large number of tests were previously carried out on the single units used for the masonry specimens. Salt solutions with two low concentrations of sodium sulphate were inserted in masonry wallettes treated with a water based water repellent or with a consolidant. On the basis of the recorded experimental data, a suitable damage parameter describing the material deterioration process has been chosen. The parameter assumed is the loss of surface material. The deterioration process could be interpreted as a stochastic process L(t,l), function of time t and damage l. In this way, for differen t damage levels l it is possible to build the fragility curve. By using this approach the magnitude of the expected damage over time and the occurrence time of it can be predicted. The results will allow for the investigation on the durability of materials with respect to the prediction treatments and on the decay process of single and composite materials.