J F MARTIRENA1, R L DAY2, D BETANCOURT1 and Y DIAZ
Universidad Central de Las Villas, Santa Clara, Cuba
Schulich School of Engineering, University of Calgary, Canada
Calcium carbonate as a source of calcite has been used as an admixture in fired clay bricks. The research aims at decreasing the firing temperature and dwell-time for production of clay bricks. The presence of small amounts of calcium carbonate improves the compressive strength of the bricks at firing temperatures around 900oC, apparently because of the fluxing effect associated with the presence of calcite, which basically enables the sintering reaction to take place at lower temperature in clays rich in kaolin. The tests were performed on cylindrical specimens and on practical-size bricks, and include SEM observation and EDS/EDX mapping, XRD, porosimetry and compressive strength measurement. Bricks having between 2% and 5% calcium carbonate showed the best performance when fired at 900oC for 2-3 hours; these bricks show a 40% increase in compressive strength. The resulting bricks are denser and stronger. The slight increase in porosity observed is apparently related to the presence of cracks produced by the release of CO2 during the decomposition of the calcite. The specimens made with calcite performed well under wet/dry cycles and salt crystallization tests when compared to normal bricks made without calcium carbonate.