Effect of NaOH Concentration and Curing Temperature on Geopolymers Incorporating Oyster Shell and Glass Waste

Abstract

This study investigates the influence of NaOH concentration, curing temperature, oyster shell powder (PC) and glass powder (PV) on the physical and mechanical properties of geopolymer cements based on calcined clay, aiming to enhance the performance of construction materials in Douala. Oyster shells and glass waste, rich in calcite and silica, respectively, are underutilized and contribute to environmental pollution in Cameroon. Geopolymers, a sustainable alternative to traditional Portland cement, were formulated by partially replacing metakaolin with PC and PV powders. The study focuses on key parameters such as density, water absorption, porosity, and compressive strength, evaluated at different curing temperatures (40°C–60°C) and NaOH concentrations (8 and 12 M). The results showed that the optimal formulation, obtained with 8 M NaOH and cured at 49°C, achieved a compressive strength of 3.29 MPa at 28 days, with an apparent density of 1.36, water absorption of 24.23%, and total porosity of 31.04%. The experimental design followed a full factorial 2 4 approach with a center point in order to evaluate the combined effects of NaOH concentration and curing temperature, and to establish predictive models for each property. Statistical analysis using ANOVA was used to evaluate the main effects and interactions of the factors studied, whereas optimization was performed using desirability functions to find the right balance between maximizing compressive strength and density, and minimizing porosity and water absorption. Although the maximum compressive strength achieved (6.44 MPa) is markedly lower than that of conventional geopolymers, which typically exceed 20 MPa, this material is particularly suitable for nonstructural applications such as lightweight masonry blocks or insulating panels. Future studies will focus on chemical and thermal characterizations, as well as on evaluating the flexural strength and long‐term durability of the material under tropical climatic conditions.