Models for Predicting Strength Reduction Factors for Concrete that Utilizes Palm Kernel Shells and Waste Automobile Tires as Aggregates

Palm kernel shells (PKS) and waste automobile tires do not only enhance the properties of concrete (e.g. damping ratio, ductility, impact resistance etc.), but also their rational utilization can significantly reduce carbon footprints and environmental pollution globally. In this study, a multivariate regression analysis was carried out to develop models for predicting the reduction factors and thereafter the strengths (compressive strength, flexural tensile strength, split tensile strength and bond strength) of concrete that utilizes PKS and waste automobile tire chips as partial to full replacement of the conventional crushed granite stones as coarse aggregates. The strength reduction factors, , were modelled as a function of the total aggregate replacement level (TAR), and the volume of PKS (P) and tire (T) particles in a given concrete mix whilst the performance of the models was assessed using the Mean Squared Error (MSE) and the Coefficient of Determination () techniques. After studying several mathematical functions, it was found that a single linear regression model can be used to predict the strength reduction factors for all the mechanical properties of the concrete tested but with different function parameters. The values of the ranged from 0 to 1 depending on the aforementioned factors. However, a of 0.53 (53%) can be achieved at the 50% optimum replacement where P50T50 for any of the mechanical properties. Furthermore, for each of the concrete properties, the was positively correlated with the volume of PKS but negatively correlated with the TAR level and volume of tire particles in the concrete matrix. Thus, an increase in the TAR level or tire content decreases the and vice versa. In conclusion, the proposed models can be used to establish the target strengths of PKS.