SGER-Nanoscale Study of Cement Hydration by Nuclear Resonant Reaction Analysis

University Of Connecticut, Storrs CT

Investigators

Abstract

Nanoscale Investigation of Cement Hydration by Nuclear Resonant Reaction Analysis Nuclear Resonant Reaction Analysis (NRRA) has been applied to study cement hydration. Through the use of this technique, the change in hydrogen concentration on a few nanometer scale (corresponding to a few unit cells) can be studied as a function of time during the induction period. Initial results have demonstrated that the surface layer formed during the induction period on the tricalcium silicate grains (used in this study) is consistent with a tobermorite-like material, based on the absolute value of the observed hydrogen concentration and the measured thickness of the surface layer. The use of a very narrow nuclear resonant reaction (in this case the 1 H (15 N?) 12 Creaction at 6.4 MeV), when performed with a beam of nitrogen ions that has excellent energy resolution, is capable of measuring the hydrogen concentration of a thin layer. Optimum beam energy resolution is a critical parameter as the spatial resolution of the measurement is defined largely by the energy resolution of the incident ion beam. Therefore, the Dynamitron Tandem accelerator at the Ruhr Universitat, Bochum, Germany is being used for the experimental studies as this machine has had extensive work done over the last fifteen years to generate the best possible energy resolution for ion beams. By raising the beam energy, progressively deeper layers can be investigated. Thus, by using nitrogen beams of successively higher energies from the 6.4 MeV resonance, a profile of the hydrogen concentration as a function of time in the hydration process can be determined. The hydrogen concentration is obtained over a depth of a few nanometers at the surface of the grains and can be measured continuously to a depth of about 2 microns into the grains. A study of the hydration process of tricalcium silicate at 20 o C determined an induction time of 4.25 hours with a statistical precision of 0.07 hours. Temperature dependent results form an Arrhenius plot yielding and activation energy of 69 kJ/mol.