Feasibility of Calcined Marl as an Alternative Pozzolanic Material
Calcareous clay rich in smectite was calcined at temperatures of 600–1000 °C using a pilot- and industrial scale rotary kiln. Compressive strength of mortars was tested between 1–365 days, when 20–65 % of OPC was replaced by calcined clay at equal w/c-ratios. With respect to reactivity as a pozzolan, the optimum calcination temperature was around 800 °C. With a replacement level of 50 % the 1-day strength was reduced but high enough for demoulding concrete infield practice, while after 28 days almost the same strength as with no replacement could be obtained. The raw and reactive calcined state of the clay was characterised using different methods like XRD, TG/DTG, SEM, FTIR, Al27-NMR and Mössbauer Spectroscopy. At the optimum calcination temperature calcium carbonate from the clay is only partly decomposed. The main calcium carbonate source is coccoliths which enabled the formation of a reactive Ca enriched glass phase together with the decomposing clay minerals. Oxidation of Fe2+ to Fe3+ resulted in a structural disordering increasing the reactivity of the calcined clay. Pozzolanic activity was tested in pastes of calcined clay and calcium hydroxide.
KeywordsCompressive Strength Clay Mineral Quadrupole Splitting Calcium Hydroxide Blended Cement
Unable to display preview. Download preview PDF.
- 1.Mehta, P.K.: Concrete technology for sustainable development. Concr. Int. 21(11), 47–53 (1999)Google Scholar
- 3.World Business Council for Sustainable Development (WBCSD): The cement sustainability initiative. Cement Industry Energy and CO2 Performance Getting the Numbers Right (2011)Google Scholar
- 4.World Business Council for Sustainable Development (WBCSD): Carbon emissions reduction up to 2050. Cement Technology Roadmap (2009)Google Scholar
- 5.Justnes, H.: Making cements with less clinker content. SINTEF, Trondheim (2007)Google Scholar
- 6.Justnes, H., Østnor, T.,: Durability and Microstructure of Mortar with Calcined Mark as Supplementary Cementitious Cementing Material. XIII DBMC, Sao Paulo (2014)Google Scholar
- 8.Murad, E., Cashion, J.: Mössbauer Spectroscopy of Environmental Materials. Kluwer Academic Press, New York (2004)Google Scholar
- 9.Takeda, M., Kawakami, O., Tominaga, T.: 57Fe mössbauer spectroscopic studies of structural changes of montmorillonite on heating in reduced atmosphere. J. Phys. Colloque C2 supplément au nr. 3(3), C2-472 (1979)Google Scholar