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.