Experiment and molecular dynamics simulation of functionalized cellulose nanocrystals as reinforcement in cement composites. (25th July 2022)

• Record Type: Journal Article
• Authors: Fan, Qichang; Meng, Xue; Li, Zhendong; Ma, Guangyuan; Wang, Zhanpeng; Zhang, Kun; He, Chang; Meng, Dan
• Is Part Of: Construction & building materials. Volume 341(2022)
• Publication Date: 2022-07-25
• Subjects: Cellulose nanocrystal -- Surface functionalized -- Molecular dynamics simulation -- CNC coated fiber -- PE fiber; Building materials -- Periodicals; 624.18
• DOI: 10.1016/j.conbuildmat.2022.127879
• Languages: English
• ISSNs: 0950-0618

Abstract

Highlights: Polyethylene fiber enhanced the flexural strength and reduced compressive strength of mortar. Two surfaces functionalized CNCs have opposite impacts on the mechanical properties of mortar. Coating CNC improved fiber-cement interaction. Molecular dynamics simulation results are consistent with the mechanical experiment results. Abstract: This study evaluated the potential effect of cellulose nanocrystal and coated polyethylene fiber on the mechanical properties of mortar. Two kinds of cellulose nanocrystals (CNC) directly as Nano-materials, and indirectly as film coated onto the polypropylene fibers were employed as cement-based reinforcement materials. The fluidity, flexural and compressive strength, and the microstructure of each specimen were measured. In the direct method, mortar mixed with the CNC containing carboxyl groups (CNC-C) showed superior properties compared to the CNC containing sulfo groups (CNC-S). The addition of CNC impacted the process of hydration and compactness of hydration products. The results of X-Ray polycrystalline diffractometer (XRD) and heat of hydration showed that CNC accelerated hydration process. Energy spectrum analysis (EDS) measured ratio of calcium to silicon (C/S) of calcium silicate hydrate (C-S-H) and proved that CNC-C increased the tightness of C-S-H while CNC-S decreased. The results of scanning electron microscopy (SEM) indicated that cellulose nanocrystals were interspersed in C-S-H, forming Nano-bridge and arresting Nano-crack. In the indirect method, the maximum increase in flexural strength of sample between all groups was the specimen that adding 0.3% (volume ratio of fiber to mortar) of CNC-C coated polypropylene fibers. The flexural and compressive strength of the mortar were increased by 22.81% and 10.65% compared to the control, respectively. The results of SEM indicated that coating enhanced bond of the fibers/matrix. Molecular dynamics simulation (MD) analyzed the binding energy, microstructure, dynamic characteristics and adsorption conformation between two CNCs and C-S-H at the molecular scale. MD presented clearly that the adsorption energy between CNC-S and C-S-H was much smaller than CNC-C and C-S-H. This was identical with CNC-C enhancing the mechanical properties of the mortar and CNC-S reducing the mechanical properties.