Cinque Anni Di Ricerca Al Politecnico Di Milano Sulla Capacità Di Autoriparazione Dei Materiali Cementizi.

Worldwide increasing consciousness for sustainable use of natural resources has made “overcoming the apparent contradictory requirements of low cost and high performance a challenging task” as well as a major concern. The importance of sustainability as a requisite which has to inform structure concept and design has been also recently highlighted in Model Code 2010. In this con-text, the availability of self-healing technologies, by controlling and repairing “early-stage cracks in concrete structures, where pos-sible”, could, on the one, hand prevent “permeation of driving factors for deterioration”, thus extending the structure service life, and, on the other hand, even provide partial recovery of engineering properties relevant to the application. The author’s research group has undertaken a comprehensive research project, focusing on both experimental characterization and numerical predictive modelling of the self healing capacity of a broad category of cementitious composites, ranging from normal strength concrete to high performance cementitious composites reinforced with different kinds of industrial (steel) and natural fibres. Both autogenous healing capacity has been considered and self-healing engineered techniques, including the use of presaturated natural fibres as well as of tailored admixtures. Tailored methodologies have been employed to characterize the healing capacity of the different investigated cement based materials. These methodologies are based on comparative evaluation of the mechanical performance measured through 3- or 4- point bending tests. Tests have been performed to pre-crack the specimens to target values of crack opening, and after scheduled conditioning times to selected exposure conditions, ranging from water immersion to wet and dry cy-cles to exposure to humid and dry climates. As a further step a predictive modelling approach, based on modified microplane model, has been formulated. The whole experimental and numerical investigation represents a comprehensive and solid step to-wards the reliable and consistent incorporation of self healing concepts and effects into a durability-based design framework for engineering applications made of or retrofitted with self healing concrete and cementitious composites.