RESEARCH OF ALTERATION OF PORTLANDITE CRYSTALS HABIT AS A FACTOR OF STRUCTURE FORMATION CONTROL FOR LIME-CONTAINING BINDERS

Abstract

The processes of CaO hydration have been investigated under various temperature conditions and while introducing of H3PO4, H2SO4,H2SiO3, H3BO3 and their sodium salts into water. The binding composites were obtained based on thin-grinded quicklime with 95.6 % of active CaO and MgO. The phase composition of the hydration products were clearly confirmed mainly by XRD and thermal analyses. Under cryogenic conditions (temperature –4˚C) the rate of the reaction between CaO and CO2 of the air increased and extra amount of calcite was formed. During CaO hydration with the introduction of additives containing SO42- and BO33- anions the formation of Portlandite crystals (mainly of lamellar habit) was observed. Rietveld method demonstrates the increase in half-width of 01–2, 02–1, 01–3, 022 and 122 reflections in Portlandite stone indicating the occurrence of stresses that alter the rate of crystals growth in definite directions. The formation of Ca(OH)2 fine crystals of hexagonal lamellae shape results in the increase of their surface, the contact area and bond strength that leads, in its turn, to the increase in mechanical strength of the structure.