A VEDA simulation on cement paste: using dynamic atomic force microscopy to characterize cellulose nanocrystal distribut
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Research Letters
A VEDA simulation on cement paste: using dynamic atomic force microscopy to characterize cellulose nanocrystal distribution Yizheng Cao, SSCI, Albany Molecular Research Inc., West Lafayette, IN 47906, USA Kho Pin Verian, Solidia Technologies, Piscataway, NJ 08854, USA Address all correspondence to Yizheng Cao at [email protected] (Received 5 May 2017; accepted 13 July 2017)
Abstract Cellulose nanocrystal (CNC) enhances mechanical performance of cement composites via short-circuit diffusion (SCD). CNCs transport water along their hydrophilic surface into the unhydrated cement cores to induce extra hydration. It is important to characterize CNC distribution because it determines the SCD pathways. This study for the first time, employs virtual environment dynamic atomic force microscopy, an atomic force microscopy computational tool to investigate CNC distribution in both fresh and hardened cement pastes. The methods not only provide insights in a static context (hardened sample), but also offer opportunities to evaluate the interaction of CNCs with calcium-silicate-hydrate growth during the kinetic early ages of hydration. Terms Glossary: ω, real-time frequency, ωd, driving frequency, ωn, natural frequency, ω0, resonant frequency of the oscillator in vacuum, ρ, density, η, viscosity, K, constant for a given cantilever, p1, p2, q1, q2, q3, q4, fitting coefficients, C, CNC concentration.
Introduction The advancement of nanotechnology in the last two decades has enabled the control of materials properties at the extremely small scale. Recent successes of using nanotechnology to improve cement composites have been achieved by introducing nanofillers with high aspect ratios, such as carbon nanotubes (CNTs)[1] and cellulose nanocrystals (CNCs)[2] into the cement matrix. Compared with CNTs, CNCs possess major advantages, including low cost, high abundance, biodegradability, and insignificant environmental and health impacts.[3] Cao et al. improved the flexural strength of cement paste by ∼30% and 50% by incorporating 0.2 vol% of raw CNCs and 1.5 vol% ultrasonicated CNCs into the mixture, respectively.[4] This performance enhancement with such small loadings originates from the increase in degree of hydration (DOH). The authors identified two mechanisms for the DOH increase: (1) steric stabilization by which CNCs separate the cement particles and increase the interfacial area between cement and water; (2) short-circuit diffusion (SCD) in which CNCs, due to their hydrophilic nature, transport water passing through the dense hydration products shell to induce more hydration in the unhydrated cement cores. The SCD is a new route of hydration kinetics and opens up opportunities for alternative possibilities for hydration, especially at late ages. The distribution of CNCs in cement paste is key because: (1) they form a pathway to convey water from the pore solution to the unhydrated cement cores; and (2) a non-uniform distribution may cause agglomerates that act as stress concentrators
compromising mechanica
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