Yizheng Cao;Jason Weiss;Jeffrey Youngblood;Robert Moon;Pablo Zavattieri;
<正>Cellulose nanocrystals(CNCs) are added into cement paste(CP) as a modification at the nano-scale to improve the mechanical performance.Isothermal calorimetry(IC) shows direct evidence that the degree of hydration(DOH) of CP is improved with CNCs. The first mechanism brought up to explain this phenomenon is the steric stabilization, which is the same mechanism some types of superplasticizer(SP) increase the workability in cement mixing.Rheological and heat flow rate measurements are taken to support this mechanism.Parallel investigations of DOH and flexural strength on the CP with SP show that the steric stabilization is not the only or the dominating mechanism in improving DOH.Another new mechanism,called short circuit diffusion,is proposed as a complementary for the CNCs to help cement hydration,in which mechanism the CNCs can transport the water from the capillary pores outside the hydration products shell to the unhydrated cement cores and hence cause extra hydrations.For the flexural strength, a ball-on-three-ball test is performed and the results show a maximum increase in strength of about 30%with only 0.2%of CNCs with respect to cement.The strength, however,decreases with further increasing the CNC concentrations,which is explained by the agglomerations of CNCs and verified with rheological measurements. Originaliry The cellulose nanocrystal(CNC) is the crystalline part of the cellulose fibers extracted from plants such as trees.It has been successfully utilized as reinforcements in the composites research such as polymers.In this paper,the CNC is added into cement pastes to modify the microstructure and improve the macroscopic mechanical performance.The degree of hydration(DOH) is found to be increased with CNCs.The flexural strength ofCNC-cemenl pastes is also improved at 4 different ages:3,7,21 and 28 days.As a result,the successful utilization of CNC in cement composites is the first originality. The reason for the improved flexural strength is attributed to the increase in DOH.As for the DOH improvement,it is found to be from two origins:(1) The steric stabilization, which is the same mechanism that polyarboxylate-based superplasticizer(SP) improve the workability of cement mixtures.This is verified by the heat flow and rheological measurements.(2) A new proposed mechanism short-circuit diffusion,which is verified by a parallel investigation on the cement pastes with SP.The verification of the mechanisms for CNC improving the DOH of cement pastes is the second originality.
cellulose nanocrystal;;isothermal calorimetry;;degree of hydration;;short-circuit diffusion;;ball-on-three-ball test
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