Mechanical Properties and 3D Fractal Analysis of Engineered Cementitious Composites with Shape Memory Alloy Fibres

This paper presents a systematic experimental study on the effect of shape memory alloy (SMA) fibres (0.25-1% by volume) on microstructure and engineering properties, in particular mechanical properties of polyvinyl alcohol (PVA) fibre (2% by volume) reinforced engineered cementitious composites (ECC). A series of tests were performed to characterise the flowability, compressive properties and flexural and uniaxial tensile behaviour in terms of strain/deflectionhardening and multiple microcracking performance and flexural and tensile strengths, as well as the 3D fractal crack analysis and microstructural evolution of ECC. Results indicate that the presence of more SMA fibres diminished the flowability of ECC, which can be ascribed to the higher surface roughness of SMA fibres as confirmed by the atomic force microscopy analysis but did not result in any change in the self-compacting characteristics of ECC. The highest compressive strength was achieved at the ECC mix with 0.5% SMA inclusion as 62.5 and 72.1 MPa for ambient curing of 28 and 56 days. Although the presence of 1% SMA fibre reduced the compressive strength of ECC due to the increased interfacial porosity and fibre cluster, the residual flexural crack width of ECC containing 1% SMA fibre was effectively reduced by about 54.3% as compared with the reference ECC mix, consistent with its best tensile performance. Accordingly, the failure patterns of ECC changed from the tensile failure with more uniformly distributed cracks and the highest dissipated fractal fracture energy (Ws/Gf=167.7) to the tensile failure along with less tortuous crack path and fractal fracture energy (Ws/Gf=80.2).