دانلود رایگان مقاله تاثیر نانوبلورهای سلولز در ساختار خمیر سیمان

abstract

This paper reports the influence of raw and sonicated cellulose nanocrystals (CNCs) on the microstructure of cement paste. A novel centrifugation method is designed to measure the concentrations of the adsorbed CNCs (aCNCs) on the cement surface, and the free CNCs (fCNCs) which are mobile in water. It is found that, the majority of the CNCs (>94%) are aCNCs. More importantly, sonication does not significantly reduce the amount of aCNCs (reduction of less than 2%). We surmise that, after sonication, the aCNCs are primarily dispersed over the cement surface, instead of becoming fCNCs via sonication. Isothermal calorimetry and energy-dispersive X-ray spectroscopy (EDX) results support this theory. The water desorption tests show that the total porosities of cement pastes with raw and sonicated CNCs are 14.8% and 14.4%, which showed a reduction from 16% for the plain cement paste. The porosity reduction is a result of an increase in the degree of hydration. The advantage of sonicated CNCs is they are dispersed, avoiding therefore agglomerates that can lead to pores, voids, and air entrapment. The nanoindentation results show that the reduced indentation modulus on the interfacial regions between cement particles and the low density CSH is increased when CNCs are used.

4. Conclusions

This paper studies how sonication influences the CNCs distribution in both fresh and hardened cement pastes and how it modifies the microstructures of the pastes. Although sonication can disperse the CNC agglomerates, the dispersed CNCs remain adsorbed on cement surface in the fresh cement paste. For the hardened cement paste, it is found that sonication helps reduce the large size porosity. The nanoindentation results show that the reduced modulus at the high density CSH is increased with CNC additions, possibly due to the high modulus of the CNCs.