Carrot-based covalently bonded saccharides as a new 2D material for healing defective calcium-silicate-hydrate in cement: Integrating atomistic computational simulation with experimental studies

Concrete is currently produced at a rate of 20 billion tonnes per year and contributes 5–10% of mankind's CO2 production. If the strength of the calcium-silicate-hydrate (C–S–H), the main binding material of concrete, could be improved, the volume of cementitious material needed for a given structure would be reduced and its environmental impact would be decreased. Here, we show that the constitutive behavior of C–S–H can be improved significantly by complexation with carrot-based cellulose nanosheets (CNSs). This environmentally friendly, reinforcing material heals the defective microstructure of C–S–H, which is responsible for structural deformation and failure at larger length scales. CNSs are built from repeating saccharide units that are covalently linked by a β-1-4 glycosidic (C–O–C) bond. The CNSs show remarkable affinity to C–S–H due to the interfacial Ca–O coordination and H-bond interaction. The functional groups on the surface of the CNS sheet act as a root network, cross-linking the neighboring silicate calcium layers and inhibiting the water dynamics at the silicate nanochannel, thereby significantly improving the interfacial properties of the C–S–H/CNS hybrid structure. The macro experimental results show that the mechanical properties of the composites increase with increasing the concentration of CNSs up to 0.4-wt%. At 28 days and CNS concentration of 0.20-wt%, the flexural strength increases by about 23.2% and the compressive strength increases by about 17.5%. The developed atomic-scale molecular dynamics simulations, combined with top-down experimental measurements of their mechanical properties reveal that the proposed C–S–H/CNS composites show significant enhancement in strength, stiffness and ductility, and provide a foundation for the development of new high-performance construction materials with lower carbon footprint.