Hydrating cement pastes as a complex disordered system

Abstract

In small-angle neutron scattering (SANS) experiments, realized on the MURN facility of the pulsed reactor IBR-2 of the Frank Laboratory of Neutron Physics at the Joint Institute for Nuclear Research, Dubna, the hydration processes in samples of ordinary Portland cement (OPC) and single clinker minerals are studied. The measured scattering curve contains information about the fractal behaviour of the interfaces and the size distribution of the scattering particles. Furthermore, a variation of the heavy and light water composition for the hydration water supports the selection of the observable microstructural objects. In dependence on the size distribution of the clinker grains a various time-dependent behaviour of the potential law of the scattering curve is shown. Considering the SANS results of hydrating OPC the exponents of the scattering curve in a given Q-range are varying in dependence on the hydration time and sample thickness. They lie in an interval from about −2 to −4. This is believed to be associated with fractal behaviour. A set of four hydrating C3S-samples is divided into 2 parts after an under water storage of 53 days. Then 2 samples were stored in an H2O/D2O-mixture for reducing the variety of the several hydration products by changing the neutron optical contrast. Considering the time-dependent change of the potential law of the scattering curves of hydrating C3S-samples some differences in contrast to hydrating OPC powder are visible. Within about 100 days after mixing the dry C3S powder with water the exponents of the SANS curves in the measured Q-range are higher than −3. If the hydration products of C3S are forming fractal structures then volume or mass fractals of some nanometers are shown.