Calcined kaolinite–bentonite clay blends as supplementary cementitious materials

• Published in: Applied clay science 2015-05, Vol.108, p.84-93
• Main Authors: Taylor-Lange, Sarah C., Lamon, Emily L., Riding, Kyle A., Juenger, Maria C.G.
• Format: Article
• Language: English
• Subjects: Amorphous material; Metakaolin; Pozzolan; Thermal treatment
• ISSN: 0169-1317; 1872-9053
• DOI: 10.1016/j.clay.2015.01.025

In an effort to limit the environmental impact of concrete materials, there is increasing interest in the development and use of a wider range of minerals as acceptable supplementary cementitious materials (SCMs). This study investigated calcined blended clays of kaolinite and bentonite, with impurities, to assess their feasibility as SCMs. The combined use of Rietveld quantitative x-ray diffraction (RQXRD) and thermogravimetric analysis (TGA) techniques proved useful in initially gauging amorphous content post-calcination, lending insight into the relationship between calcination temperature and pozzolanic reactivity. The results demonstrated that for the calcined blended clays, as the amorphous content increased, the SCM consumed more portlandite and the compressive strength of cement-SCM mortars increased. Blends of kaolinite–bentonite clays, containing initially 35wt.% crystalline kaolinite prior to calcination, achieved roughly 10% increase in compressive strength over samples containing 100wt.% cement, at 90days. Blended kaolinite SCMs may offer significant advantages as a low-cost alternative binder or cement replacement material, with the ability to maintain or enhance mechanical strength. •Clay with 35 wt% kaolinite has the potential to be a moderately reactive SCM.•RQXRD-TGA proved useful in gauging the amorphous content of calcined clay.•Pozzolanic reactivity is dependent upon the initial clay composition.•As amorphous content increases, the compressive strength increases.