Shear strength properties of structural lightweight reinforced concrete beams and two-way slabs using palm kernel shell course aggregates

In the last three decades, the use of Palm Kernel Shells (PKS) as coarse aggregate in concrete has continuously received increasing attention among researchers, especially in Africa. This is primarily due to its environmental and economic benefits. However, while considerable amount of research has been carried out to assist in understanding its concrete mix designs and associated mechanical properties, a limited amount of works have been carried out to assist in the current understanding with respect to its shear resistance. The main objective of this study was to investigate the shear strength properties of structural lightweight reinforced concrete shallow beams and two-way slabs using PKS coarse aggregates. A comparison between properties of PKS concrete and normal weight concrete (NWC) was made. The effect of types of cement on the mechanical properties of both PKS and NWC were also investigated. The materials phase of this research evaluated fresh concrete properties such as slump, and the key mechanical properties of hardened concrete, that is, compressive, flexural tensile strengths and density. The study employed a series of trial mixes, which resulted in casting and testing 216 cubes and 180 modulus of rupture beams at 7, 14, 21, 28, 56, and 90-days of curing, to obtain an optimum mix design. The third phase of the study consisted of testing 46 reinforced concrete beams to evaluate the flexural response of the reinforced PKS concrete and NWC beams, with and without shear reinforcement. The 46 beams consisted of 19 beams without shear reinforcement (15 PKS concrete and 4 NWC) and 27 beams with shear reinforcement (21 beams were cast with PKS and 6 beams were cast with granite aggregates). The variables of the third phase were the overall depth of the beams, longitudinal reinforcement, shear reinforcement, shear span-to-depth ratio and modes of loading. The fourth phase of the study investigated the flexural response of eight two-way slabs (four slabs were cast with PKS and four were cast with granite aggregates). The main variables were concrete strength and the modes of loading. The study revealed that the physical and mechanical properties of the PKS aggregate are satisfactory for producing structural lightweight aggregate concrete. The 28-day air-dry density of PKS concrete was within the range for structural LWAC. The 28-day compressive strength of the concrete produced in this study was found to satisfy the minimum strength requirements of a structural concrete based on BS 8110-1 and ASTM C330. It was found that PKS concrete beams with and without shear reinforcement behaved in a similar manner to those of NWC beams based on the range of parameters tested, including the cracking modes. PKSC two-way slabs mostly failed as a result of punching shear. The study further revealed that the design equations of the British Standards Institute, American Concrete Institute and Eurocode 2 can be used to safely predict the shear capacity of PKS concrete beams with and without shear reinforcement. It is further concluded that PKS aggregates can be used in the production of LWC for structural applications in Ghana.

Source: KNUST