The potential use of two raw clays (Clay A: kaolin; Clay B: calcareous montmorillonite) as supplementary cementitious material (SCM) in blended cements was investigated. Cement replacement in mortars by 20% calcined Clay A and Clay B resulted in a considerable 28 day compressive strength improvement. The pozzolanic reactivity of Clay A and B is explained by characterization of the structural changes upon calcination with XRD, ICP-MS, FT-IR, 27Al-NMR, Mössbauer spectroscopy and SEM. At the temperature giving highest pozzolanic reactivity, kaolinite and montmorillonite were completely dehydroxylated, while calcite from Clay B was not completely decomposed. FT-IR, 27Al-NMR and Mössbauer spectroscopy revealed considerable structural deformations of kaolinite in Clay A and montmorillonite in Clay B resulting in an amorphous, reactive state. Oxidation of iron in Clay B during calcination contributed to strong distortions of the octahedral sheet in the montmorillonite structure. Additionally, the formation of a glass phase due to reaction of coccoliths (CaCO3) and montmorillonite was observed.

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Packing materials used in biofiltration of gaseous pollutants represent a key design parameter, as a proper selection might not only determine the adequate performance of the system but also its cost-effectiveness. This study systematically assessed and compared the performance of a conventional plastic carrier with that of two novel clay-based materials from SAINT GOBAIN for the abatement of a model odorous stream composed of H2S, methylmercaptan and toluene. The packing materials were tested in biotrickling filters, biofilters and a two-phase biotrickling filter. SAINT GOBAIN materials exhibited a higher adsorption potential under abiotic conditions, a higher buffer capacity and a superior performance compared to conventional plastic rings when implemented in biotrickling filters operating at gas residence times as low as 7.5 s. Among the materials tested in biofilters, Filtralite Air AC supported almost complete H2S and toluene removals at a gas residence time of 20 s, while successfully eliminating methylmercaptan at values of ~80%. Interestingly, under most of the conditions tested, clay-based materials also showed comparable pressure drop values than those of plastic rings.

The hydration of cement pastes with addition of a kaolinite rich clay (Clay A) and a calcareous smectite rich clay (Clay B) was investigated with isothermal calorimetry, in-situ XRD, PXRD, TGA and EPMA. Portland cement was replaced by 20, 35 and 50 weight% calcined clay in cement pastes and mortars. Both clays showed good pozzolanic reactivity. However, clay A having a higher amount of metakaolin and higher specific surface was more reactive in terms of CH consumption and mortar strength development. 50% replacement of PC by calcined Clay A resulted in increased 28 day compressive strength while mortars with 50% calcined Clay B showed almost equal 28 day compressive strength compared to the reference. With increasing addition of calcined clay, the second aluminate reaction (formation of AFm phase) of cement hydration was accelerated and the cement pastes became under sulphated. This resulted in a stronger and earlier sulphate depletion peak, especially in pastes with calcined Clay A. Due to 3% calcite in the used cement the main hydration product found was carboaluminate hydrate. The favoured formation of carboaluminate hydrate stabilised ettringite in the cement pastes.