▎ 摘　　要

The unique attractive properties that make graphene nanoplatelets (GNPs) effective nano-reinforcer for cement composites. Dispersion of GNPs with dispersant is a conventional method. In order to avoid the introduction of dispersant left in cement-based materials, water reducing agent was directly used to disperse GNPs. This article investigated GNPs were dispersed using different water reduced agents, the mechanical properties and toughening mechanism of modified GNPs reinforced cement composites. In this research, GNPs were dispersed well in aqueous solution using polycarboxylate superplasticizer (PS), naphthalene superplasticizer (NS) and melamine superplasticizer (MS) as dispersants with ultrasonication. Results showed that water reducers can improve the influence of GNPs on cement-based materials and a GNPs dosage of 0.06 wt% could make the GNPs/cement composites as flowable as the plain sample. The flexural strength of cement paste increased up to 16%, 13% and 20% with 0.06 wt% PS, NS and MS modified GNPs at 28d, it increased the compressive strength of the GNPs/cement composites by 8%, 5% and 11.2%. The ratio of compressive-bend strength of decline rates of PS and NS modified GNPs/cement composites were 7.4% and 8.2% at 0.06 wt% GNPs at 28d, while the ratio of compressive-bend strength of decline rates of MS modified GNPs/cement composites were 10.9% with 0.09 wt% GNPs at 28d. It found that GNPs could accelerate hydration process of cement composite, leading to more hydration products, finer CH crystals, longer mean chain length of C-S-H gel and lower porosity, and thus the propagation of cracks of the cement composites was inhibited. (C) 2019 Elsevier Ltd. All rights reserved.