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Mechanical properties of engineered cementitious composites (ECC) are highly dependent on the pore structural characteristics and fibre-matrix interaction. The relationship between them has not been extensively explored. This paper proposes a practical micromechanical analytical model accounting for pore structure characteristics and crack-bridging properties to predict the strain-hardening and multiple microcracking behaviour of ECC. Using polyethylene fibre reinforced ECC (PE-ECC) as an example, Monte Carlo simulations were undertaken to investigate the tensile behaviour in terms of crack strength, fibre bridging strength and uniaxial tensile properties against heterogeneity of material property, which were validated with experimental data. A parametric study was then conducted to estimate the effects of fibre-matrix bond and fibre properties on stress-strain relationship and microcracking features of PE-ECC. Results indicate that the tensile properties of PE-ECC can be reasonably predicted. Under constant fibre dosages, the tensile ductility of PE-ECC is dominated by interfacial bond, followed by fibre location, orientation and diameter. Such insights are helpful to the design of ECC composites for practical applications. [ABSTRACT FROM AUTHOR]

The tensile behaviour of engineered cementitious composites (ECC) is highly dependent on their microstructure characteristics. To date, the strain-hardening behaviour of printed ECC in relation to its microstructure is not yet fully understood. This study presents a systematic investigation on the macroscopic mechanical properties of normal and printed ECC with various polyethylene (PE) fibre lengths (6 and 12 mm) in relation to their microstructural features in terms of pore structure characteristics, fibre orientation and fibre dispersion through a series of mechanical tests and X-ray computed tomography (CT) and backscattered electron (BSE) image acquisition, processing and analysis. Results indicate that it is desirable to use block specimens for mould-casting fabrication as contrast to printed ECC samples. The printed ECC containing 1.5 vol% 6 mm and 0.5 vol% 12 mm PE fibres by extrusion-based 3D printing exhibits unique tensile ductility of over 5% and average crack width of less than 100 μm. Regarding pore structure, normal ECC has a higher probability of large pores (over 1 mm3) than printed ECC, which would increase the risk of damage localization and lead to a significant variation in tensile properties. Besides, normal ECC with thickness of 30 mm and printed ECC possess a similar fist cracking strength as indicated by similar pore size and fracture toughness. Compared to normal ECC, printed ECC has a more uniform dispersion of PE fibres, the orientation of which is more perpendicular to the loading direction, resulting in a higher average tensile strength and strain capacity than normal ECC. [ABSTRACT FROM AUTHOR]