Dispersion Stability and the Reaction Mechanism of Boron Nitride Nanosheets in a Cementitious Alkaline Environment: An Experimental and Computational Study

Boron nitride nanosheets (BNNSs) have attracted the attention of researchers for their extraordinary mechanical properties, large surface areas, and strong interactions with the host matrix, making them ideal candidates as supplementary materials for the construction industry. However, the major challenge associated with the incorporation of BNNSs in cement-based materials is their unfavorable dispersion in a cementitious alkaline environment. In this work, experimental and computational methods were employed to trace the influential factors that hindered the proper dispersion of BNNSs within cementitious composites. The results showed that the BNNS dispersion remained stable in mild alkaline environments with pH values ranging from 7.5 to 12.2, but high alkalinity (pH = 13.1) reduced the BNNS dispersion. Among the various cations, Ca2+ is the most reactive cation for BNNS agglomeration in a cementitious alkaline environment. To protect BNNS against these influential factors, polycarboxylate ether-based superplasticizer (PCE) was selected as a suitable treatment to improve the dispersion stability of BNNS within cementitious composites. The formation of covalent bonds between calcium silicate hydrate and BNNS resulted in enhanced charge transfer and consequently improved the load transfer from the matrix to the BNNS. Finally, based on the mechanical tests, with the addition of only 0.01 wt % PCE-treated BNNSs, the compressive and flexural strengths of the cement samples improved by 43 and 13%, respectively, which clearly showed the significance of stable BNNS dispersion using PCE on the performance of the final cement composite. The results of this study could improve the fundamental understanding of BNNS-containing cementitious nanocomposites.