LONG-TIME MONITORING OF THE MICROSTRUCTURAL CHANGE IN HARDENING CEMENT PASTE BY SANS

Hydrating cement paste is an essential part of concrete because its st ructure largely determines the physical properties of concrete (e.g. i ts strength and durability). Small-angle neutron scattering (SANS) inv estigations were used to obtain a non-destructive description of stati stically representative microstructures (nanometre and micrometre scal e). The results obtained illustrate the possibilities of using SANS to monitor the time-dependent microstructural changes that occur during the hydration process. All samples were made from ordinary Portland ce ment (OPC) with a water/cement ratio of 0.38. By controlling the volum e ratio of D2O in the hydration water (C-dw), a variation in contrast is achieved. In the special case of C-dw = 0.38 the scattering length densities of the hydration products are nearly homogeneous and the con trast between them is drastically reduced. In order to study the influ ence of the hydration conditions, the sample thickness, temperature, t he size fraction of the cement clinker and C-dw were varied. The hydra tion products and inner surfaces formed by the separated microstructur al objects were found to show a fractal behaviour. The fractal dimensi on obtained from the scattering curves reflects the microstructural ch anges that occur during the hydration process within the size range of a few nanometres up to a few micrometres, depending on the chosen hyd ration parameters. In this size range the SANS effect is dominated by the hydration products.