Micromechanical characterization of metakaolin-based geopolymers

The search for alternative cementitious materials is important for the continued development of the construction industry, particularly products with high levels of supplementary cementitious materials and polymer and geopolymer composites. Due to the environmental impact of its production, the construction industry is targeting the rational use of Portland cement through the development of more efficient materials and cements. Thus, this research aimed to prepare and characterize the mechanical properties of metakaolin-based geopolymers and mortars. Tests were conducted to determine the elastic modulus, hardness, compressive and flexural strength, as well the flexural modulus, while the microstructure was studied by scanning electron microscopy. The most influent variable was the concentration/composition of the alkaline activator. By using a Na2OSiO2/NaOH ratio of 1.6, samples showed maximal performance: compressive strength = 64 MPa, flexural strength = 17.6 MPa, and elastic modulus of about 10 GPa. This geopolymer was then used to produce mortars, and the maximal performance was achieved when mixed with sand (1:3 in mass): 59 MPa compressive strength and elastic modulus of 24.4 GPa. The micro-nanomechanical properties of the geopolymer were very similar to those obtained for Portland cement; however, the geopolymer revealed greater deformation capacity and tensile strength.