Flexural behavior of two-layer beams made with normal and lightweight concrete layers

Abstract

In this paper, twelve concrete beams with two different layers of concrete were evaluated as a simply supported beam under four-points loading. The beams assembled of two different types of concrete layers, one of which was normal-weight concrete (NWC) and the other was lightweight aggregate concrete (LWAC). The investigated parameters were the thickness of the lightweight concrete to the overall depth of beams (hLW/h), and the compressive strength of normal and lightweight concrete. Due to the weak lightweight aggregates used, lightweight aggregate concrete exhibits more brittleness and lower stiffness. Therefore, the viability of compensating for this degradation and providing a layer of normal concrete seems to be very interesting in such beams. The behavior of beams was evaluated based on cracking, failure mode, flexural strength, maximum deflection, stiffness, and toughness. The results showed slight variations on the majority of the above-mentioned performance aspects of two-layer beams compared to fully normal concrete beams. While there were great enhancements compared to fully LWAC beams. The variants were mainly attributable to the efficacy of using LWAC in providing lower stiffness and lower tensile strength. The experimental results have been compared to predicted values using the ACI 318-19, with some modifications for the equations to be matched with two-layer beams, the comparison was in terms of the deflection due to service load, moment capacity, and cracking moment.