COMPARATIVE-STUDY OF CA-SI GELS PRODUCTS OF ALKALI-AGGREGATE REACTIONIN HYDRAULIC CONCRETES AND SYNTHETIC TYPE GELS

Comparative study of Ca-Si gels products of alkali-aggregate reaction in hydraulic concretes and synthetic type gels. Morphological characte ristics and chemical compositions of natural Ca-Si gels are determined from samples taken from test cylinders (16 x 32 cm), altered 28 days at 60 degrees C under 100% H.R.. Synthetic gels which compositions are well known (fixed CaO/SiO2 ratio) are placed under the same condition s of evolution. Using a S.E.M., a comparison between morphological and chemical characteristics of both gels is performed. The main results are: after evolution both types of gels show that their CaO/SiO2 ratio values have characteristic values of 0.43 on an average; both types o f gel show the same domain of variation of their SiO2 and CaO content; under similar conditions, natural and synthetic gels present the same morphological characteristics; Na and K do not seem to be incorporate d into the structure of natural and synthetic gels. The study of physi co-chemical properties of synthetic gels seems to be a good way to und erstand the formation processes of gels products of alkali-aggregate r eactions.