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A progressive micromechanical damage-plasticity formulation is proposed to analyze the single hooked-end steel fiber pullout energy from the surrounding cement-based matrix within the context of hooked-end steel fiber-reinforced cementitious composites (HSFRCC). As the hooked-end steel fiber has a unique fiber geometry, its fiber pullout energy from the cement-based matrix consists of the interfacial fiber-matrix debonding, the frictional sliding and pullout energy, and the elastoplastic deformation energy of the steel fiber hooked end. The aforementioned energy components are analytically derived first, and the superposition principle is subsequently employed to obtain the total energy dissipation during the fiber pullout process. Good agreement is obtained for comparisons between the experimental results of single hooked-end steel fiber pullout tests and the proposed analytical predictions. This satisfactory verification supports the validity and applicability of the proposed damage-plasticity energy prediction formulation, and suggests the applicability of this methodology to further investigation on micromechanical fracture energy prediction of HSFRCC during flexural macro-cracking.

Since pullout behaviors of fibers intersecting a fracture plane of cementitious composite are similar to those in a single-fiber pullout test, micromechanical model of fracture energy for hooked-end steel fiber-reinforced cementitious composite (HSFRCC) is developed on the basis of single hooked-end steel fiber pullout test. The hooked-ends of steel fibers intersecting a fracture plane have various deformations which can be generally classified into hooked-end total deformation, partial deformation, and nondeformation. The pullout energy of steel fiber with deformed hooked-end is significantly different from that with nondeformed one; derivations of pullout energies of hooked-end steel fibers with deformed/nondeformed hooked-ends are carried out first. The fracture energy model of HSFRCC is proposed using probabilistic method accounting for energy contributions from all steel fibers intersecting the fracture plane. Experimental validation of the proposed micromechanical model is performed, and excellent agreements are observed in comparison with experimental data from uniaxial tensile tests. As the proposed fracture energy model is a function of physical and micro-geometric properties of hooked-end steel fibers and cementitious matrix, it can guide optimal design of HSFRCC.

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Incinerator fly ash is the material collected by the scrubber after incineration of municipal solid wastes (MSW). By composition it belongs to the CaO−SiO2−Al2O3−Fe2O3system, and it is similar to the slag and fly ash from electricity generating stations that is usually used. It may contain water-leachable heavy metals and so it is regarded as hazardous and must be immobilised/stabilised. The physical properties of fly ash were studied experimentally and its influence on the mechanical properties of the hardened cement paste, the hydration mechanism when the fly ash was added to the cement system and the pollution from heavy metals within the fly ash were also investigated. The feasibility of using the fly ash derived from the incineration of MSW as supplementary cementitious material was explored. It was shown that the reactivity of fly ash was lower and the addition of fly ash to cement may lead to retardation of cement hydration and, furthermore, that ettringite can be formed during the hydration process, which is beneficial for strength development. It was also shown that the immobilisation effect of cement on this fly ash is good and that heavy metals can be immobilised within the structure of the hydration phases through addition, substitution or sorption mechanisms.