Abstract
The state of water in bound-disperse structures formed in the course of cement hardening and the effect of surfactants [polyethylene glycol (PEG), polypropylene glycol (PPG), and hexanol] on this state and also the state of water in freely-disperse structures in hydrated cements in the presence of the same surfactants at different extents of their adsorption were studied by the NMR relaxation technique. It is established that, in the semilog scale, the envelope of spin-echo signals from protons in the samples with a water-to-cement ratio of 0.3 can be decomposed into three components (for samples containing PPG or hexanol additives, into four components) corresponding to protons of different water fractions varying in the course of formation of the structure of cement stone. The maximum change with time was found for the occupancy of the shortest T2 component. During several hours of cement hardening, the occupancy of this water fraction ranged up to 96 - 97% (from the total signal of water protons). Consideration of adsorption isotherms and NMR relaxation data for samples containing PPG and hexanol additives suggests that the mobility of water molecules, which determine the intermediate T2 components, is associated with the behavior of water near the interface in the presence of adsorbed substances. It is shown that, in the presence of additives, boundary layers of water are changed. At the end of the second week of the hardening process, the fraction of the short T2 component ranged up to 78 - 84% from the total proton signal. A scheme of the water distribution in pores of cement stone in the presence of additives and its interrelation with relaxation processes are discussed.