Pastes Prepared with Sulfonate, Chalcedony and Sugar

Papers presented at ICPIC 2010, Madeira Island, Portugal, dealing with the use of polymers in cementitious materials, show the need to combine different admixtures to optimize the properties of cement. This work is a continuation of a paper presented at NOCMAT 2010, Cairo-Egypt, about the incorporation of several materials in Portland cement to increase mechanical properties and workability. The best performance admixtures were chosen and they were combined considering the superposition of effects. Cement pastes were prepared with chalcedony and sulfonate (to increase compressive strength) and sugar (to increase workability). Two percent of cement was replaced by the admixtures. The water/cement ratio was constant and equal to 0.44. Results show that the combination of 0.05% of sugar and 1.95% of sulfonate and 0.10% of sugar and 1.90% of chalcedony produced a paste with the greatest compressive strength and good workability. Compression strength was respectively 27.4 MPa and 36.6 MPa, which represent increases of 33.5% and 78.6%, respectively, relative to the reference paste without admixtures. While increasing the paste compression strength with sulfonate has been significant, the results of the paste with chalcedony were the more surprising because the water/cement ratio of pastes was kept constant. The chalcedony is a type of crystalline silica, which shows deformation in their structure. So because of crystalline structure of chalcedony, there should be, probably, no significant reactivity of it with the cement hydrates, just the fact that its structure be deformed can explain this reactivity. The most important conclusion concerns is that the combinations of admixtures can improve a lot the properties of Portland cement paste.