Alessandro Nardinocchi

Reuse of recycled glass in mortar manufacturing

This work is aimed at studying the possibility of reusing waste glass from crushed containers as aggregate for preparing mortars. At present, this kind of reuse is still not common due to the risk of alkali–silica reaction (ASR) between alkalis of the cement and silica of the waste glass. This expansive reaction can cause great problems of cracking and, consequently, it can be extremely deleterious for the mortar durability. The influence of both size and colour of recycled glass coming from crushed containers on the durability of mortars is studied. The attention is focused on both mechanical behaviour, investigated by means of bending and compression tests, as well as durability, studied by means of accelerated tests for evaluating the tendency to expand under alkaline environment due to ASR. Several mortars are prepared by replacing at different rate the quartz sand with coarse glass cullet of different colours: clear (i.e. uncoloured), green and amber. Then, pulverised clear glass is added to the mortar mixtures, also in the presence of class F fly ash. Results obtained show that by using both green and amber glass cullet the mortars are stable, as well as by using powder glass, which also shows a significant pozzolanic effect. On the other hand, considerable expansion due to ASR is detected by using clear glass cullet.

Study of physical and elasto-mechanical behaviour of fiber-reinforced concrete made of cement containing biomass ash

In this work, the influence of different kinds of fibres on Fibre-reinforced concrete (FRC) cracking behaviour is examined. Several FRC mixtures are designed, in which cement is partially replaced at 20% by weight of cement by a biomass ash coming from paper mill sludge incineration. These FRCs are prepared by alternatively using steel fibres, polypropilene macro-fibres, glass macro-fibres, as well as hybrid or bicomponent synthetic fibres. The dosage of fibres is always equal to .55% by concrete mixing volume. As reference, also a mixture with the same mixture proportions but without fibre reinforcement is prepared and tested. Ring test according to ASTM C 1581-04 and free shrinkage test are carried out in the same exposure conditions: 21 °C and 50% relative humidity. Moreover, compressive and tensile strengths of FRCs, as well as their elastic modulus, are evaluated on cubic specimens up to 28 days of curing, and, in particular, also at the time of ring cracking. In this way, other important information could be extrapolated by introducing these experimental data in suitable numerical model of the ring concrete specimens available in the literature. This procedure enables to study the influence of the kind of fibres on the potential for early-age cracking of concrete, as well as to identify the effect of tensile creep on concrete cracking. Results obtained show the effectiveness of the randomly dispersed fibres in counteracting the early cracking of FRC.