Mechanical properties of lightweight concrete made with fiber reinforced fly ash pellets

Abstract

In this study, an extended experimental programme was conducted to investigate some physical and mechanical properties of lightweight concretes (LWCs) made with cold bonded fiber reinforced fly ash pellets and also tire chips as coarse aggregates. Crumb rubber and polypropylene fiber were used to reinforce the fly ash pellets. Lightweight concretes were investigated in two groups, namely lightweight aggregate concrete (LWAC) and lightweight rubberized concrete (LWRC) that contained both LWA and tire chips. Totally, 17 lightweight concrete (LWC) mixtures were produced with lightweight aggregates (LC, L1P, L5P and L1F) and tire chips at 0.40 w/c ratio and tested for mechanical properties such as compressive and splitting tensile strength, modulus of elasticity and so on. The findings of the study revealed that the compressive strength values of all LWAC series conformed to the limitation for structural use. The use of LWA and tire chips in concrete mixtures had negative effect on the basic engineering properties compared to the full use of crushed stone as coarse aggregate. The strength loss of LWAC and LWRC can be accounted firstly for the weakness of lightweight fly ash aggregate compared to the mortar phase and normalweight coarse aggregate and secondly for the adherence problem existing between tire chips and matrix zone of lightweight concrete with cold bonded pellets and for the extra void entrapped by tire chips, respectively. However, bond strength increased with no trend when LWA and crushed stone were used together in an equal part as coarse aggregate by volume. This positive contribution of LWAs may be accounted for a better coherence and interlocking of the LWA with the surrounding concrete those minimize the cracking and so utilize the adhesion between the concrete and rebar. When the concrete series with full use of different LWAs as coarse aggregates are compared to each other, it is seen that average flexural strength, failure impact energy and fracture toughness of L1F(4-16) type concrete series were the highest that may be attributed to the extra adherence between polypropylene fiber reinforced pellets and matrix phase by the help of polypropylene fibers existing on the surface of aggregates. Besides, the use of tire chips with LWA in an equal part of coarse aggregate by volume had a positive effect to increase toughness due to energy absorbing capacity.