Hybrid effect of GNPs, GOs, and CNTs on the flexural and compressive strengths of cement paste

Abstract

This paper presents the individual and synergic effects of Graphene Nanoplatelets (GNPs), Graphene Oxides (GOs) and Carbon Nanotubes (CNTs) on the flexural and compressive strengths of cement paste. Mixes containing several nanoparticle types and weight fractions were prepared with Polycarboxylate ether (PCE) surfactant and tested after 90 days of curing. After that, the microstructure of the failed samples was studied using a Scanning Electron Microscope (SEM). Response Surface Methodologies (RSM) techniques were then employed to determine the strength functions' response to the nanofilaments' types and weight fractions. Finally, a cost analysis was done to evaluate the mixes' performance in-terms of strength and cost. Test results showed that the flexural strength of cement paste could be enhanced by 57.33% when using 0.04 wt % GOs. The results also showed that mixes containing 0.08 wt % GOs and 0.12 wt % CNTs improved the flexural strength by 47.03 and 44.38%, respectively when compared with the control cement paste mix. In-terms of compressive strength, mixes containing 0.04 wt % GNPs attained the highest compressive strength improvement of 15.7% when compared with the control mix. In hybrid mixes containing more than one nanoparticle type, the best synergistic action was generated between 50% CNTs and 50% GOs at a total dosage of 0.04% wt, where the compressive strength increased by 20.2%. The microstructural analysis showed good dispersion qualities and nanoparticles embedment within cement hydration products. On the other hand, RSM analysis showed that the maximum compressive and flexural strength functions' responses are obtained at the lowest nanofilaments’ weight fraction of 0.04 wt %. The desirability analysis confirmed that the compressive and flexural strengths of cement paste could be improved by 7 and 53%, respectively, using the predicted formulas. Finally, the cost analysis showed that GO-modified cement pastes are considerably more expensive than other mixes, yielding the lowest economic index.