PHASE-RELATIONS IN THE SYSTEM CAO-AL2O3-SIO2-H2O RELEVANT TO METAKAOLIN - CALCIUM HYDROXIDE HYDRATION

The persistence of metastable phases, notably of C-S-H and C-A-S-H gels dominates phase assemblages in the ''cement'' portion of the CaO-Al2O3-SiO2-H2O system at 25-degrees-C-85-degrees-C. Nevertheless, the coexistence of gels with more crystalline phases gives a pattern of coexistence which fulfils many of the requirements of a phase equilibrium diagram. Metakaolin - Ca(OH)2 mixes have been reacted for 6-10 months at 25-degrees-85-degrees-C and the results of 'warm' cures, at 55-degrees-C and 85-degrees-C, are combined into a phase diagram. Its most notable features are (i) the formation of an extensive series of silica-containing and possibly alumina deficient hydrogarnets, (ii) development of C-A-S-H gels and, (iii) at 85-degrees-C, crystallization of gismondine, CAS2H4.