A Probabilistic Model to predict the Durability of Surface Treatments

Water repellent or consolidating surface treatments for brick and stone facing walls cannot be carried out in presence of salts due to the possible formation of cryptoefflorescence. Nevertheless, an attempt has been made within an EC contract, to establish the maximum salt content below which the surface treatments does not fail. Crystallization tests were carried out on treated and non-treated masonry materials and a suitable damage parameter describing the material deterioration process has been chosen. The parameter assumed is the loss of surface material at each measurement carried out with a laser device along chosen profiles on the sample surface. Some results of the on-going tests are presented. The high randomness connected with the material characteristics and decay in a natural environment suggests assuming the deterioration process L(λ) as a stochastic process of the random variable λ (where λ is the loss of surface material). Consequently, the probability of reaching or exceeding a given damage over time can be described by the corresponding fragility curve. By using this approach the magnitude of the expected damage over time as well as the occurrence time can be predicted. λ E. Garavaglia, G. Cardani and L. Binda