Geopolymers from Olive Stone Bottom Ashes for Sustainable Construction: Influence of the Molding Method

The forming methodology influences the physicochemical, mechanical, and microstructural properties. In this study, which aims to develop a geopolymeric material for potential insulation applications in buildings such as vertical walls, geopolymers were developed using industrial wastes from different industries: slate stone cutting sludge (SSCS) and chamotte (CH) were used as precursors, and olive stone bottom ash (OSBA) and sodium silicate (Na 2 SiO 3 ) were used as alkaline activators. Two forming methods were evaluated: uniaxial pressing and casting of the material, varying the forming method and the liquid/solid ratio. The results showed that the pressed geopolymers achieved higher bulk densities (up to 2.13 g/cm 3 ) and significantly higher compressive strength (28.04 MPa at 28 days), attributable to a higher compactness and degree of geopolymer reaction. In contrast, the casting geopolymers exhibited surface efflorescence, related to slower curing and higher porosity, which reduced their compressive strength (17.88 MPa). In addition, the pressed geopolymers showed better thermal stability and fire performance. These results demonstrate that the variation of the forming method has a direct influence on the material properties of geopolymers, and that the pressing process allows for a reduction of the alkaline activator content, thus reducing its environmental footprint.