Behavior to Salt Crystallization of Repointing by Ready-Mix Mortars: Experimental Data and Application of a Probabilistic Model

Abstract

During their life Cultural Heritage buildings suffer different attacks due to the changes induced to the surrounding environment along the years. Each attack causes damages of different magnitude which are, often, time dependent. Salt crystallization is one of the highest causes of damage in masonry connected with an aggressive environment. Mortar joints as brick and stone can be a vehicle of the water and salts coming from capillary rise or sea spray. The maintenance against damages consists in replacing (re-pointing) the joint using a new mortar. The commercial mortars for repair, present nowadays on the market, give rise to a question: how durable is the mortar once it has been used to repair masonry? In the chapter, to investigate durability of these materials, and the eventual damage that they induce at the interface mortar/brick, a procedure based on salt crystallization tests is described and the development of a simple probabilistic damage model introduced. The salt crystallization tests were carried out on brick masonry specimens prepared with the same type of bricks and six types of commercial mortars based on natural hydraulic binders (NHL). During the test the loss of material from the surface was measured and assumed as parameter of damage. The loss is referred to the vertical section of the specimen and quantified through a computer code starting from successive readings of the surface decay along defined profiles using a laser profilometer device. The randomness affecting the damage due to the salt crystallization and the consequent continuing loss of material suggests studying the deterioration under a probabilistic point of view where the continuous deterioration of specimens can be assumed to be a stochastic process.