Free and bound water in cement pastes

Quasi-elastic neutron scattering has been used to investigate the nature of the bonding of water molecules in cement pastes of various porosities. The experiments show that it is possible, to quite a good approximation, to speak of the water as being either ‘bound’ with negligible mobility, or ‘free’ with the full mobility of bulk water. There is no evidence for any hydration state of intermediate mobility. The ratio offree to total water in saturated specimens given by these experiments is considerably less than that obtained from conventional weight-loss measurements under controlled drying.