Experimental and Modeling Explanations for Enhancing Mechanisms of Colloidal Nanoalumina in Calcite-Containing Cementitious Materials

This study investigated the properties of colloidal nanoalumina (CNA)-blended cementitious mixtures in the presence of calcite to promote better understanding of the enhancing mechanisms of nanoalumina in cementitious materials through experimental investigation and thermodynamic calculation. The rate of heat evolution, compressive strength, connected pore structure, and chloride binding capacity were investigated. The results show that CNA can accelerate cement hydration at early age, and therefore improve the 1-day strength of blended mixtures. The strength at 28 and 56 days can be maximized with 1% by weight CNA addition, but considerably reduced with 5% by weight CNA. Different from the mechanical properties, the connected pore structure and chloride binding capacity are improved straightforwardly with CNA addition, which benefits the ability to resist chloride attack. The experimental and modeling results demonstrate that CNA addition benefits the generation of carboaluminate, which has high efficiency to fill voids due to its higher volume, thus densifying the microstructure as well as improving the chloride resistance. However, these aluminate-ferrite-monosubstituent (AFm) phases demonstrate little cementing capacity relative to calcium silicate hydrate (C S H) gels, thus resulting in an obvious decrease of strength with a high amount of CNA addition even though the microstructure is further densified.