Nuclear Resonance Reaction Analysis and Wet Chemistry Investigation of the Hydration of Tricalcium Aluminate PhasesNuclear Resonance Reaction Analysis and Wet Chemistry Investigation of the Hydration of Tricalcium Aluminate Phases

摘要

The hydration of C3A was investigated with Nuclear Resonance Reaction Analysis (NRRA), to measure hydrogen concentrations at specific depths within the first 2 μm from the surface. Pellets of either cubic or orthorhombic C3A, were hydrated in solutions saturated with respect to both calcium hydroxide and calcium sulfate at 25oC. In some cases the retarder sodium gluconate was added to the solution. Individual specimens were removed from the solution at specified time intervals and analyzed by NRRA. In all cases, the region of the hydrogen depth profile closest to the surface showed a linear relationship with depth that is interpreted as a crystalline surface layer. For the two cubic C3A samples, the hydrogen depth profiles were significantly different beyond the linear region depending on whether sodium gluconate was added. Without sodium gluconate, the depth profiles showed a typical curve with the main peak, presumably CAH gel, at about 200 nm. With sodium gluconate the main peak was absent and the concentration of hydrogen at depth was much lower. This suggests that the sodium gluconate makes the surface layer more impermeable to water transport. For the orthorhombic samples, the depth profiles had similar shapes for the samples both with and without sodium gluconate, but the former showed a much deeper reacted zone. For all the samples, the depth profiles generally increased with time, except for the cubic C3A without sodium gluconate which steadily decreased over time. The dominant ions were Ca2+ and SO42-in the hydration solutions. Over time, the SO42-concentrations typically decreased, indicating precipitation of ettringite. For the solutions without sodium gluconate, the Ca2+ concentrations also decreased slightly. For those with sodium gluconate, the cubic specimen showed a 10-20% increase in Ca2+ while the orthorhombic specimen showed an increase of nearly 60%. For this specimen, the Al concentration nearly tripled. The increases in these ions may be due to the chelating effect of the gluconate ion.