CHARACTERIZATION OF MECHANICAL AND ELASTIC BEHAVIOUR OF CONCRETES MADE OF RECYCLED-CONCRETE AGGREGATES

摘要

An investigation is presented of mechanical behaviour and elastic properties of recycled-aggregate concretes. These concretes were prepared by alternatively using two different recycled aggregate fractions, both made of recycled concrete from rubble from demolition sites. The difference between the two recycled aggregate fractions was the grain size distribution, ranging either from 6 to 12 mm or from 11 to 22 mm. Several concrete mixtures were prepared using only virgin aggregates (as a reference mixture), 30% finer coarse recycled aggregate replacing fine gravel, and 30% coarse recycled aggregate replacing gravel. Several water to cement ratios were adopted: 0.40, 0.45, 0.50, 0.55, and 0.60. All the concrete mixtures showed the same fluidity level (slump S5). Compression tests were carried out after 28 days of wet curing. In addition, concrete elastic modulus as well as drying shrinkage were measured. Results obtained show that structural concrete up to C32/40 strength class can be manufactured by replacing 30% virgin aggregate with recycled-concrete aggregate. In addition, a correlation between elastic modulus and compressive strength of recycled-aggregate concrete was found. Finally, on the basis of drying shrinkage results it was observed that, particularly if fine recycled-concrete aggregate is added to the mixture, lower shrinkage strains were detected especially for shorter curing time. This aspect, together with a low elastic modulus, leads to a lower tendency to cracking of recycled-aggregate concrete when compared to concrete without recycled aggregates.