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This study aims to explore the dynamic response of ultra-high performance engineered cementitious composites (UHP-ECC) incorporating waste crumb rubber (CR) at various temperatures, focusing on its potential to enhance the resilience and sustainability of civil infrastructures against low-velocity impacts. To date, the impact behaviour of UHP-ECC under low temperatures has rarely been explored. Firstly, natural river sand and waste tyre CR was utilized to prepare the UHP-ECC. Then, a series of mechanical tests, including compression test, flexural test and uniaxial tensile test were carried out to investigate the static mechanical properties of rubberised UHP-ECCs. In addition, the effects of different waste CR incorporations (0%, 5%, 10%, and 15%) and various temperatures (25 °C, −5 °C, −30 °C, −50 °C, −100 °C and −196 °C) were comprehensively investigated by low-velocity impact tests with constant impact energy. Lastly, the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) model was introduced to evaluate the overall performance of UHP-ECC. It was found that the use of river sand and CR significantly enhanced the tensile ductility and impact toughness of UHP-ECC. Impact energy primarily dissipates through damage such as matrix crack initiation, propagation, and fibre pull-out/rupture within the specimen. Adding CR notably decreased stress fluctuations during impact at room temperature, facilitating steady state energy absorption. Moreover, the time to reach peak impact force decreased with decreasing temperature across all UHP-ECC groups. At room temperature during impact process, fibre failure mode is dominated by pull-out failure, while lower temperatures lead to increased fibre rupture at the cracking surface. In low-temperature conditions, the impact response of rubberised UHP-ECC necessitates a comprehensive consideration of the synergistic effects, including material contraction, fibre bridging capacity, rubber phase transition, and water freezing. [ABSTRACT FROM AUTHOR]

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]

This study investigated 3D concrete printing of permanent formwork for concrete column construction. The effect of different hydroxypropyl methyl cellulose (HPMC) contents (0, 0.0003 and 0.0006 by mass of binder) and the water-to-binder (W/B) ratios (0.27, 0.29 and 0.31) on the rheological properties, structural build-up and mechanical performance were studied using several mixtures for manufacture of the permanent formworks. The results showed that the mixture with the HPMC = 0.0006 and the W/B = 0.27 showed the maximum static yield stress, largest thixotropy and maximum green strength, and thereby selected as the optimum mixture. The plastic failure of the optimum mixture was also predicted using a thixotropy model and was compared with the experimental results. Subsequently, three concrete columns with different longitudinal steel reinforcement ratios (0.0%, 1.9% and 2.5%) were constructed using the printed concrete as the permanent formwork and tested in compression. Good bonding was observed at the interface of the cast-in-place concrete and the printed concrete permanent formwork. In addition, it was observed that the initial stiffness, the maximum bearing capacity and the corresponding longitudinal displacement of the concrete columns increased, as the longitudinal reinforcement ratio increased. The counterpart concrete columns using the conventional formworks were also constructed and tested for comparison. In comparison, the concrete columns made using the printed concrete as the permanent formwork obtained a higher stiffness and bearing capacity than the counterpart conventional concrete columns. The reasons for the differences are explained. [ABSTRACT FROM AUTHOR]