Microstructural characterisation and physical properties of cured thermally activated clay-lime blends

The microstructure of cured mixes consisting of thermally activated clay and lime (up to 20 wt.%) was investigated using X-ray diffraction, Fourier transform infrared spectrometry and scanning electron microscopy. Additionally, changes of bending strength, density and water absorption against curing time and lime addition were followed. The results showed that calcium silicate hydrate (C–S–H) and monocalcium aluminate decahydrite (CAH10) together with calcite formed. The occurrence of C–S–H and CAH10 involved chemical reactions between hydrated lime, micaceous species and quartz, and metakaolin respectively. The development of the cementitious products, favoured by the increase of lime admixture and ageing time, contributed to the increase of the mechanical resistance, but its impact on the remaining physical properties was somewhat irregular. Regarding water absorption, it was found that the kinetic of the process obeyed a pseudo-first order equation and the constant was in the range (10.6–16.2) × 10−2 min−1.

► Hydration of heated clay-lime blends resulted in the formation of C–S–H and CAH10.
► Mica/illite and metakaolin were involved in the neoformation processes.
► The bending strength increased with the increase of lime content and ageing time.
► The later operating factors had mitigated impacts on density and water absorption.