Analysis of aluminum concentrations in the pore solution during hydration of tricalcium silicate

- The presence of aluminum can reduce the reactivity of C3S.
- Release of aluminum from C3S does not affect Al-ion concentrations.
- The retarding effect can be compensated by the addition of gypsum.

The hydration of two batches of tricalcium silicate was followed by isothermal heat conduction calorimetry and analysis of pore solution composition. These two samples were different in Al2O3-content and free lime concentration. It was observed that the material containing aluminum reacts slower than the pure one. The reactivity was also analyzed in the presence of ettringite, gypsum and tricalcium aluminate, respectively.The aluminum concentration in the pore solution was always below the limit of detection during hydration of the samples independent of the presence of aluminum in tricalcium silicate or the addition of most supplementary phases. Elevated aluminum concentrations were only observed in the presence of tricalcium aluminate.The experimental investigations confirm earlier results that aluminum can reduce the reactivity of tricalcium silicate. It is shown in this study that this mechanism is not based on elevated aluminum concentrations in the pore solution.