Low-Energy Recycled Cardboard Powder (RCP) as a Cement Substitute in Concrete: Strength-Based Assessment for Sustainable Construction

Production of cement is one of the major contributors to carbon dioxide emissions in the world, as such, there is motivation to come up with sustainable alternatives to cement production that would cut on the consumption of cement without affecting the structural performance. Out of all the municipal solid waste, cardboard waste is produced in huge amounts and has the potential to be reused in cementitious materials because it contains fibrous cellulose. The paper examines the possibility of recycled cardboard powder (RCP), which is a by-product of a low-energy soaking-drying-grinding procedure, as a partial cement replacement in M25 grade concrete. The concrete mixes with 0%, 0.5%, 1.0% and 1.5% of RCP (weight of cement) were tested regarding the workability and mechanical properties such as compressive strength, split tensile strength, and flexural strength after 7 days and 28 days. Findings have shown that the hygroscopic characteristics of cellulose residues make workability decrease gradually as the cellulose content in RCP increases. Nevertheless, the properties of strength increased with moderate levels of replacement, where 1% RCP mix had the highest compressive strength (31–32 MPa), split tensile strength (3.2 MPa) and flexural strength (4.8–5.0 MPa) at 28 days. The addition of RCP in the content to 1.5% led to a decrease in strength caused by cement dilution and the lower dispersion efficiency. The results indicate that recycled cardboard powder (RCP) can safely be used to a high degree of cement substitution at 1% of structural-grade concrete, which provides a perspective of low-energy and sustainable waste-valorization.