Nuclear Resonant Reaction Analysis (NRRA) with the 15N(H,a) 12C reaction at 6.4 MeV has been applied to study cement hydration during the induction period. The change in hydrogen concentration on a few nanometer scale (roughly a unit cell) as a function of depth and time can be studied during and immediately after the induction period. By raising the beam energy above the resonance energy, measurements are made to depths of a few microns, comparable to the cement grain radius. Thus, the complete hydration process in the grains is determined as a function of depth. Results have shown that the surface layer formed during the induction period on C3S grains is consistent with a tobermorite-like material. Understanding the details of the hydration of cement will ultimately be the base for defining the transition from microscopic to macroscopic properties. The induction period of tricalcium silicate at 20 oC was 4.25 hours with a statistical precision of 0.07 hours. With measurements at 10 and 30 oC an Arrhenius plot yielded an activation energy of 69 4 kJ/mol. Subsequently, our work has begun to yield insight into other cement components and the effects of accelerators and retarders. Recently, we have begun to study the hydration of calcium aluminate and the effects of sodium gluconate, a commonly used retarder and have started to analyze components of concrete to understand their interaction with the cement. This proposal supports a detailed investigation of cement hydration, by using the NRRA technique. Specific experiments will investigate the effects of retarders and accelerators. This work will be performed with our industrial collaborators at W. R. Grace who will contribute their expertise and analytical capabilities in this area. Starting with their industrial techniques for determining material additives as retarders and accelerators, we will modify them to determine the underlying physical parameters to determine hydration behavior. These will be combined with analytical measurements that Grace can provide to develop theoretical models of hydration behavior. The experimental data provides clear insights into how different parameters, temperature, pH, and starting composition, affect the hydration process. This information will ultimately be used to improve the formulation of cements and concrete for construction and other purposes.
In addition to the education of students working on this project (typically 4-6 between the US, Germany and Spain), significant presentations are given at universities and scientific meetings. As the only group performing such experiments, we have begun to present results at international conferences and have begun working with researchers in even more countries in Asia and Europe on more aspects of concrete hydration.
