Craig W. Hargis

Effect of Calcium Carbonate Fineness on Calcium Sulfoaluminate-Belite Cement

This study investigated the hydration characteristics and strength development of calcium sulfoaluminate-belite (CSAB) cements incorporating calcium carbonate (CC) powders with various particle size distributions and different gypsum amounts. In general, the CSAB hydration was accelerated by the CC powder, but the acceleration and resulting strength improvement were more effective with finer CC powder. Regardless of the fineness of the CC powder, it took part in the hydration of CSAB cement, forming hemicarboaluminate and monocarboaluminate phases. These hydration and nucleation effects compensated for the strength reduction from decreased cementing components (i.e., dilution effect) when finer CC powders were used, while they did not overcome the strength reduction when coarser CC powder was used. On the other hand, increasing the amount of gypsum for a given CC content improved the strength. The strength of CSAB cement had a clear inverse relationship with its total pore volume measured by mercury intrusion porosimetry (MIP). Thermodynamic modeling for CSAB cement hydration showed that the use of CC powder increased total volume of solid phases up to 6 wt % at a given amount of gypsum.

Aggregate Passivation: Lithium Hydroxide Aggregate Treatment to Suppress Alkali-Silica Reaction

Alkali-silica reaction (ASR) continues to be a concrete durability problem despite the many physical and chemical mitigation techniques known to successfully prevent it. The research presented herein tested a new method to limit ASR: aggregate passivation. A lithium silicate layer was created on reactive natural siliceous aggregate surfaces by treating the aggregates in a lithium hydroxide solution prior to use. A 4 M LiOH treatment was found to be superior to a 2 M LiOH treatment in producing a lithium silicate passivation layer and in reducing expansion due to ASR. The use of passivated aggregates greatly reduced expansion in accelerated mortar bar tests compared to nonpassivated aggregates and lithium-based admixtures.