Studio dell'effetto delle fessure sulla durabilità del calcestruzzo armato

Corrosion of embedded steel rebar - due to carbonation or to the penetration of chlorides from the environment - is one of the main causes of degradation of reinforced concrete structures. The durability design is therefore commonly aimed at preventing corrosion of steel reinforcement. Currently available durability models allow to evaluate the evolution in time of corrosion process, and to estimate the service life as a function of several parameters, related both to the materials properties and to the environmental exposure conditions. All the most accredited models available today, however, are based on a significant assumption, i.e. they consider concrete in uncracked condition. This condition rarely occurs in practice, but the knowledge on the effects of cracks on concrete durability is not deep enough to allow an update of the current durability models. In this paper, the main aspects characterizing the literature on cracks in concrete and their effects on reinforced concrete durability are presented, and, afterwards, preliminary results concerning the effects of micro-cracking on concrete chloride penetration resistance are shown. In this study, six different concretes are considered, obtained with three cement types (Ordinary Portland, Portland-Limestone and Pozzolanic) and two w/c ratios (0.45 and 0.55), both in sound and micro-cracked configurations. Through an accelerated testing procedure, the effects of micro-cracking on chloride penetration and chloride migration coefficient are assessed.