Porosity investigation of metakaolin based geopolymers

Ordinary Portland Cement (OPC) is widely used in construction and is responsible for 5–8% of global CO₂ emissions. To date, the challenge is to find alternative sustainable solutions to traditional binders. Alkali-activated materials (AAMs) and geopolymers (GP) are among the most promising ones for this purpose, due to their fast-hardening at room temperature curing. This study aims to evaluate the correlation between microstructure and mechanical properties of geopolymeric binders based on metakaolin (MK) and ceramic tile waste (R), exploiting two different techniques such as mercury intrusion porosimetry (MIP) and 1H time domain-nuclear magnetic resonance (1H TD-NMR) for porosity investigations. The results highlight a significant increase in compressive strength development between 2 and 7 days, regardless the presence of ceramic waste. However, ceramic waste promotes lower compressive strengths than MK-based geopolymers for all the curing times in agreement with a broader pore size distribution in the range between 0.01-300 mm. 1H TD-NMR technique highlights that gel pore formation is delayed when ceramic waste is used as co-precursor, but similar refined nanopores structure are obtained after 2 days of curing, regardless the presence of ceramic waste.