Recycling of calcined clay as an alternative precursor in geopolymers: A study of durability

The alkali-activated materials have properties like commonly used cementitious materials, however, it does not have burning steps at high temperatures that emit large amounts of CO2 into the atmosphere. The main precursor used in the production of activated alkali materials is metakaolin, which in general has a heterogeneous chemical and mineralogical composition and high shrinkage. Therefore, the objective of this research is to evaluate the production potential of an alternative precursor based on calcined clay, aiming to standardize the material's shrinkage parameters. The properties of mechanical strength to bending and linear shrinkage, in the face of exposure to degradation cycles such as wetting/drying in saline environment and ice and thaw cycles, were analyzed to simulate and predict real application situations. The results indicate that the calcined clay has a lower mechanical strength than the composition containing metakaolin, due to its lower reactivity. However, in degradation simulations, it is observed that the calcined clay has greater durability than the composition with metakaolin, since it has less shrinkage. The compositions with calcined clay reached a maximum content of 1.2%, while compositions with metakaolin reached shrinkage of around 6%. In function, it is concluded that it is possible to use the alternative precursor based on calcined clay in alkali activated materials.