Significance of water/solid ratio and temperature on the physico-mechanical characteristics of hydrating 4CaO.Al₂O₃.Fe₂O₃

Abstract

Tetracalcium alumino-ferrite in paste form, at water/solid (W/S) ratios of 0.3, 0.4, 0.5 and 1.0, and in pressed form at effective water/solid ratios of 0.13 and 0.08 has been hydrated for up to 45 days at temperatures of 23 and 80° C. Some prehydrated samples have also been subjected to autoclave treatment at 216° C. Of all the samples studied, that hydrated at a W/S=0.13 at 80° C indicated the highest ratio of cubic phase to hexagonal phase; that hydrated at a W/S=0.08 at 23° C showed the lowest.

Thermograms gave evidence of the formation of hexagonal phases, although X-ray diffraction patterns did not. The specific surface area values depended on the degree of hydration and the nature of the product, autoclaved samples giving the lowest values. During the four days of hydration the specimen hydrated at 80° C expanded more than that hydrated at 23° C, but after that time the rates of expansion were reversed: that of the sample hydrated at 80° C was much lower than that of the sample hydrated at 23° C. Microstructural examination of the material formed at higher temperatures and lower water/solid ratios indicated a closely welded, continuous network of cubic phase. Such a structure yields a product of higher strength than that of a loose structure formed at higher water/solid ratios. A reasonably linear relation was found between porosity and logarithm of microhardness.