Thermally and mechanically treated Greek palygorskite clay as a pozzolanic material.

In view of the reduction of the environmental impact due to cement production and towards the attenuation of supplementary cementitious materials (SCMs) production cost, new, non-kaolin SCMs have been introduced. This work investigated the structural changes of the minerals present in two Greek palygorskite clays and the pozzolanic reactivity following calcination and grinding. The combination of x-ray diffraction (XRD), thermogravimetric (TG) analysis and Fourier-transform infrared (FTIR) techniques shed light on the effect of calcination and grinding time on minerals' structure and pozzolanic reactivity. The results showed that the thermal and mechanochemical dehydroxylation led to the structural disorganization of palygorskite crystal structure that commenced immediately following 3 h calcination and 15 min grinding. Thermally and mechanically treated clays demonstrated similar Ca(OH) 2 (CH) consumption, ranging between 665 and 755 and 577–761 mg CH/g clay respectively. Therefore, the pozzolanic reactivity of the treated clays was competitive with high-purity and commercial metakaolin, mechanically treated kaolin and higher than that of calcined zeolite suggesting that the thermal and mechanical treatment of palygorskite clay produced a SCM with enhanced pozzolanic reactivity, which may be an alternative to widely known pozzolanic materials. • Thermal and mechanical treatment induces the dehydroxylation of palygorskite. • Both treatments reduce or eliminate the palygorskite and smectite crystallinity. • Both treatments produce highly reactive pozzolans, competitive with metakaolins. • Palygorskite pozzolanic reaction produces tobermorite gel. [ABSTRACT FROM AUTHOR]