Understanding microstructure evolution of cast geopolymers based on metakaolin and ceramic tile waste

This study addresses the current lack of insight into the microstructure evolution of cast geopolymers produced by combining two different precursors. Detailed investigations of micro- and nano-porosity developed during geopolymerization as a function of curing time are carried out and, for the first time, 1 H Time-Domain Nuclear Magnetic Resonance is applied diffusely. The results show that the metakaolin replacement with 35% ceramic tile waste addition induces coarsening of pore size distributions in the 0.08-1 μm range and a reduction in gel content. Furthermore, although a delay in the development of the 3D network was observed, the gel formation process was still completed within 24 hours, in contrast to the 5–6 hours required for 100% metakaolin geopolymers. These differences in microstructural evolution are also reflected in the development of compressive strength. • Combined precursors influence early-age microstructure. • Integrated MIP, N 2 adsorption, and 1 H TD-NMR analyses provide detailed microstructural insight. • Mechanical property–microstructure correlations guide formulation optimization.