EFFECT OF MOISTURE ON FRACTAL DIMENSION AND SPECIFIC SURFACE OF HARDENED CEMENT PASTE BY SMALL-ANGLE X-RAY-SCATTERING

Finely divided fumed silica (Aerosil) has been used as a model substance to interpret the change in fractal dimension and specific surface of hardened cement paste (hcp) with relative humidity. Hcp is essentially a surface fractal at relative humidities below ca. 40% where the specific surface diminishes as surface area is lost around the gel particle contact points during adsorption. A ''smoother'' surface of lower fractal dimension results. Above ca. 40 %rh the disjoining pressure opens up the entangled hcp gel structure to produce a more mass fractal structure of higher internal surface area.