Issue 18

G. Ferro et alii, Frattura ed Integrità Strutturale, 18 (2011) 34-44; DOI: 10.3221/IGF-ESIS.18.04 42 Figure 13 : Possible interaction between COOH-MWCNTs and water molecules during cement hydration process [17]. CNT S IDEAL CONTENT hah et al. [20] found that, after dispersion in water using surfactant and ultrasonic energy, small amounts of CNTs (0.048 wt.% and 0.08 wt.%) produced a significant (50 %) increase in the Young’s modulus of cement pastes (Fig. 14). Further investigation using nanoindentation found that CNTs modified the C–S–H, increasing the quantity of high stiffness C–S–H, reinforcing the cement paste matrix at the nanoscale, and decreasing the porosity [21, 26]. Fig. 15 indicates the ideal carbon nanotubes content in function of their aspect ratio. Figure 14 : Flexural behaviour of cement paste with 0.08 wt% MWCNTs and plain cement paste. Figure 15 : Optimum amount of MWCNTs and superplasticizer according to the aspect ratio of CNTs for reinforcement in cement based materials [30]. S