Production of Agro-waste cement Composites: Influence of nutshells on mechanical and hardened properties

Different countries have been encountering significant obstacles in the disposal of agro-wastes in landfills, with a recent increase in landfill sites receiving inadequate or no treatment. Moreover, in addition to high disposal costs, several factors related to landfills pose a significant threat to human health and ecosystems - examples include leachates, toxins, and greenhouse gases, which constitute environmental problems. Nutshells are an example of agro-waste materials that can be utilized in different industrial and engineering applications to help save the environment. This study aims to evaluate and investigate the utilization of nutshells (from pistachios, walnuts, and hazelnuts) as a replacement material to produce an agro-waste cement composite. Different nutshell contents (0.5, 1, 1.5, 2, and 2.5% by weight of cement) were used in the preparation of the cement composite mixtures. The nutshells were characterized by X-ray diffraction and energy-dispersive X-ray spectroscopy, and scanning electron microscopy (SEM) was also implemented to observe the prepared cement mortar composites. The compressive strength, hardness, thermal conductivity, and water absorption of cementitious composites were investigated, highlighting that the addition of nutshells significantly enhances the compressive strength. Agro-waste cement composite specimens with a nutshell content of 2.5% exhibited the highest compressive strength. Other properties of the cement composites, such as the thermal insulation properties, were also enhanced by the inclusion of nutshells. For instance, thermal conductivity of all mortar composite samples reduced by 57, 48, and 45% for the addition of 2.5% walnut, pistachio, and hazelnut shells, respectively. This eco-friendly material represents a potential way to address the generation of waste products from agricultural activities and nature; suggested uses of such composites include their application in lightweight panels, thermal insulators, and sustainable building blocks, among several other materials.