Effects of Production Factors on the Physicochemical and Mechanical Properties of Compressed Earth Bricks Stabilized by Geopolymerization

Abstract

Geopolymerization presents an environmentally friendly and sustainable alternative to conventional construction materials, particularly in the production of compressed stabilized earth bricks (CSEB). This study investigates the influence of two key production factors which are the volcanic ash/laterite mass ratio (X1) and the amount of phosphoric acid (H₃PO₄) activating solution (X2), on the physicochemical and mechanical properties of CSEB. The raw materials, laterite and volcanic ash collected from the Adamaoua region in Cameroon, exhibit low porosity, high specific surface area, and are rich in silica and alumina oxides. The central composite design (CCD) was employed to model and optimize the CSEB production process, with compressive strength as the response variable. Results indicate that the compressive strength is predominantly governed by the mass ratio of volcanic ash to laterite, whose main effect is 49 times greater than that of the H₃PO₄ amount. However, due to the significant interaction effect between the volcanic ash/laterite mass ratio and the amount of H₃PO₄, and the important quadratic effect of the volcanic ash/laterite mass ratio, the variation in compressive strength is nonlinear. Optimal conditions were determined to be a volcanic ash/laterite mass ratio of 0.16 and an H₃PO₄ amount of 8.69 mL, yielding a compressive strength of 33MPa. The evaluation of the hydration behavior of CSEB under optimal conditions revealed minimal water absorption under capillary rise and full immersion. In the wet state, the compressive strength decreased by approximately 10% (full immersion) and 8% (partial immersion) compared to the dry state. Overall, geopolymerization significantly enhances both the compressive strength and water resistance of CSEB.