NMR studies of hydrating cement: A spin-spin relaxation study of the early hydration stage

The early stages of cement hydration were investigated by proton spin-spin relaxation time (T c) measurements because these experiments can be performed much faster (in several seconds) than the characteristic time for a change in hydration evolution. In addition, comparing the free induction decays of nuclear magnetization and its spin echoes allows the separation of solid-like and liquid-like proton groups. The values of T 2 and the associated magnetization fractions were monitored for cement pastes with different water/cement ratios in the first 20 hours of hydration. Results show that already at the time of the first measurement, i.e. six minutes after mixing dry white cement powder with water, a quasi steady state is reached with protons distributed in three groups: loosely bound water (in the gel coatings and interstital spaces between coated clinker grains with T 2 of several ms), tightly bound water (T 2 ∼ 100 μs) and water/hydroxyl protons in crystalline structure (T 2 ∼ 10 μs). The values of T 2 and their associated magnetizations are fairly constant during the first several hours with the solid-like components only slowly growing at the expense of the liquid one. The fraction of the loosely bound water as well as the absolute value of its T 2 increases with increasing w/c ratio. These data indicate that although nothing vigorous is happening in the dormant period of cement hydration there is a continuous growth of the solid matrix.