Performance characterization of the concrete subjected to fire in terms of sustainability

The research, in a context of a sustainability of the building process, that should consider adequately the problem of building waste disposal, has the objective of determining the performance characteristics of concrete under the effect of fire, in order to evaluate the possibility of reutilization, and in positive case, what could the best uses be, considering the current regulations. The experimentation, carried out on cubic samples with a side of 15 cm (according to UNI EN 12390, using aggregates with Dmax= 30 mm), with Portland cement of mixture 42,5 in two types (one with Pozzolana CEM II/B-P 42.5 and one with limestone CEM II/A-LL 42.5), with class of resistance C25/30, is based on the following parameters: increase of temperature, nature of fire, heating speed, time of exposition. The tests that have been carried out were both destructive (sclerometric, ultrasounds, Sonreb) and non-destructive (crushing and thermogravimetric), and the experimental results obtained also show that: - the concretes present a remaining mechanical resistance that is lower than 50% of the initial one, after they have been subjected to the full cycle of temperature increase; - between 200°C and 600°C, there is a significant decomposition of the binding component (hydrated cement), while that of limestone is predictable for temperatures higher than 700°C; - the phenomenon of the “explosive spalling” – verified on two samples – has far more devastating consequences than the simple decay of the mechanical characteristics as, considered in a structural element, it causes a reduction of the resisting section, with a consequential increase of tensions in the remaining part, and direct exposition of the reinforcement without protection, situations which can cause the structural collapse of the element. Some uses in the field of transport have been hypothesized, also basing on the indications of the current regulations and on the detected statistics of the current uses.