Exfoliation and dispersion of boron nitride nanosheets to enhance ordinary Portland cement paste

Exfoliation and dispersion of boron nitride nanosheets (BNNSs) is the key to achieving desired reinforcing effects for ordinary Portland cement (OPC). Few studies exist, however, of the dispersion of BNNSs in a cement-induced alkaline environment and their effect on the mechanical properties of normal OPC paste. In this study, protocols were developed to prepare BNNS-reinforced OPC paste. Ultrasonication was used to exfoliate BNNSs from h-BN in water based suspensions. The addition of surfactants in the suspension was found to hinder the exfoliation of the BNNSs. The surfactants were, however, found to be essential for the dispersion of the BNNSs in pore solution. Among the three surfactants used in this study, polycarboxylate based superplasticizer was most suitable as it maintained over 40% of the BNNSs stable in the pore solution for 4 hours and increased the hydration flow peak over 20%. Atomic force microscopy results indicated that the thickness of the BNNSs was mostly under 10 nm. With the addition of 0.003 wt% BNNSs, the compressive and tensile strengths of the cement were increased by 13% and 8%, respectively. Besides the nucleation effect as indicated by hydration heat, pore structure refinement and chemical bonding were also found as the main reinforcing mechanisms of BNNSs in OPC matrix.