A review on the performance of concrete with pretreated coarse aggregates from agricultural waste

By using agricultural by-products, especially palm kernel shells (PKS) and coconut shells (CS), as lightweight coarse aggregates that can reduce structural dead load, improve thermal performance, and divert waste from hazardous disposal pathways, this study addresses the growing need to lessen the environmental burden of conventional aggregates in concrete. The results of numerous experimental studies on PKS- and CS-based concretes and different pretreatment methods are dispersed and lack a cohesive framework that quantitatively connects pretreatment parameters to aggregate characteristics, the behaviour of fresh concrete, and long-term performance, particularly for durability and geopolymer systems. Therefore, this review’s goal is to determine how pretreatment affects the physical and chemical properties of PKS and CS as well as how it affects the workability, mechanical strength, and durability-related aspects of concretes that contain these aggregates. To enable a rigorous comparison of treated and untreated aggregates and mixtures, a systematic literature analysis was conducted utilising structured keyword searches in major databases with defined inclusion and exclusion criteria and structured data extraction. According to the review, chemical immersion, surface coatings, heat treatment, and controlled pre-soaking significantly reduce water absorption and porosity, improve the quality of the interfacial transition zone, and increase compressive, split tensile, and flexural strengths (about 6–13 MPa for high PKS replacement and 20–40 MPa for moderate CS replacement), while decreasing sorptivity, water absorption, and permeability when compared to untreated shells. These findings suggest that PKS and CS that have been properly pretreated can be used as sustainable lightweight aggregates in both structural and non-structural concretes. Nevertheless, there is currently no unified framework that quantitatively links particular pretreatment parameters, replacement level, and binder type to aggregate properties and both short- and long-term concrete performance, despite new research on geopolymer systems and multi-factor optimisation of mix design and pretreatment.