T. Spillane

Heavy ion beam measurement of the hydration of cementitious materials.

The setting and development of strength of Portland cement concrete depends upon the reaction of water with various phases in the Portland cement. Nuclear resonance reaction analysis (NRRA) involving the (1)H((15)N,alpha,gamma)(12)C reaction has been applied to measure the hydrogen depth profile in the few 100 nm thick surface layer that controls the early stage of the reaction. Specific topics that have been investigated include the reactivity of individual cementitious phases and the effects of accelerators and retarders.

Progress in Nanoscale Studies of Hydrogen Reactions in Construction Materials

Nuclear resonance reaction analysis (NRRA) has been applied to measure the nanoscale distribution of hydrogen with depth in the hydration of cementitious phases. This has provided a better understanding of the mechanisms and kinetics of cement hydration during the induction period that is critical to improved concrete technology. NRRA was also applied to measure the hydrogen depth profiles in other materials used in concrete construction such as fly ash and steel. By varying the incident beam energy one measures a profile with a depth resolution of a few nanometers. Time-resolved measurements are achieved by stopping the chemical reactions at specific times. Effects of temperature, sulfate concentration, accelerators and retarders, and superplasticizers have been investigated. Hydration of fly ashes has been studied with synthetic glass specimens whose chemical compositions are modeled on those of actual fly ashes. A combinatorial chemistry approach was used where glasses of different compositions are hydrated in various solutions for a fixed time. The resulting hydrogen depth profiles show significant differences in hydrated phases, rates of depth penetration and amount of surface etching. Hydrogen embrittlement of steel was studied on slow strain rate specimens under different corrosion potentials.

Recent results on the 12C+12C reactions

The set of fusion reactions 12C+12C play a critical role in several astrophysical processes. In a recent experiment, the fusion reactions 12C+12C have been studied at ECM = 2.10 to 4.75 MeV by γ‐ray spectroscopy using a C target of ultra‐low hydrogen contamination. The deduced astrophysical S(E) factor exhibits previously unknown resonances at E⩽3.0 MeV, in particular a strong and narrow resonance at E = 2.14 MeV, the high‐energy tail of the Gamow peak. Current extrapolations of the reaction rate, which assume that the astrophysical S(E) factor varies smoothly with energy within the Gamow window, are thus subject to significant uncertainty.