A Framework for Evaluating the Physical-Mechanical Properties of Cementitious Composites


Student thesis: Doctoral Thesis

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Awarding Institution
  • Kim Meow LIEW (Supervisor)
  • Lu-Wen Zhang (External person) (External Co-Supervisor)
Award date10 Aug 2023


Cementitious composites have become the most fundamental building materials providing high quality living environments for the global population while maintaining a comparatively low cost. However, due to the inherent micro- and nano-scale flaws in their porous media, the internal micro-structure of cementitious composites progressively deteriorates in varies serving environment, resulting in the unreversible decrease of the mechanical properties. These nano and micro scale induced instabilities can hardly be captured or observed using experimental approaches, thereby hindering the uncovering of their failure behaviors. Thus, modelling techniques become promising tools for the understanding of the physical and mechanical properties cross-scale perspectives.

We first built up a phase-field based framework to evaluate the micro fracture evolution in fiber reinforced cement composites. A comprehensive constitutive model was proposed to describe both interfacial debonding and frictional slipping, which accounted for snubbing and bonding effects in fiber-reinforced composites. The proposed approach showed great potentials in predicting the fiber de-bonding and interfacial sliding as well as the micro-crack kinking path in complicated quasi-brittle materials, adding efficiency and robustness to the study of features and fracture mechanisms of fiber reinforcements in complex fiber–cement systems.

Besides, we constructed a molecular model to illustrate the fatigue behavior of the interface between fiber and hydraulic cement matrix. we show by atomic modelling that fiber, pore water, and calcium silicate hydrate (C-S-H) construct a solid-liquid-solid interface, which creates a dynamically balanced system, keeping the stability of cement matrix under cyclic loading. Particularly, the debonding and self-healing of the interface accompanied by the formation and breakage of H-bonds, thereby preventing the interfacial expansion and microcrack initiation.

To further evaluate the water effects on the atomic behaviors of cement hydrates, we investigated here the nanoscale wetting behaviors of C-S-H and reported a surface modification strategy to control its hydrophobicity. Molecular dynamic simulation results revealed that the surfactant, fluoroalkylsilane (FAS), furnishes superhydrophobic surfaces, which hinders ionic interactions and stabilizes the interlayer calcium to eliminate calcium leaching in C-S-H. Meanwhile, FAS layer provides a rougher and highly electronegative surface, blocking the chloride adsorption and invasion.

Finally, we focused on an original molecular pathway to predict the durability and analyze the environmental impact of fluoroalkyl-silane (FS) based additive modified cementitious composites in marine environment. Simulation results indicate that decalcification can be eliminated through FS surface modification, decreasing the porosity, and slowing down chloride accumulation. Then we map the simulation findings to their environmental impact by quantitatively analyzing the lifespan of a cement cover in marine environment. Our findings portray an atomic understanding for improving the durability of cement composites and propose strategies to predict their service life and environmental impact.

We adopted cross-scale modelling techniques to elucidate the nano to micro scale physical and mechanical behaviors cementitious composites. The micro fracture behaviors of fiber reinforced cement composites, and their fatigue are evaluated using phase-field methods and molecular simulations. The wetting behaviors, durability and lifespan assessment of cement composites are predict using a molecular inspired pathway. These works portrayed atomistic insights in C-S-H surface properties, improving the chemical and physical stability of cementitious composites in saline solutions and providing strategies for their surface modifications.