Mechanical properties and microstructure of low carbon high-strength engineered cementitious composites with supplementary cementitious material

The carbon emissions associated with concrete production remain a significant unresolved issue. One effective approach to mitigate this problem is to partially substitute cement with supplementary cementitious materials. The aim of the present study was to develop low-carbon, high-strength Engineered Cementitious Composites (HSECC) by incorporating low-hydration active solid waste in the form of coal gangue powder. To investigate the mechanical properties and underlying microscopic mechanisms of these composites, comprehensive testing was conducted, including assessments of compressive strength, tensile strength, single-crack tensile behaviour, three-point flexural performance, and scanning electron microscopy. The test results reveal that the integrity of the damaged compressive specimen was high. Compared with the test group without coal gangue powder, the incorporation of coal gangue powder significantly reduced the compressive strength, decreasing by 27.2 % and 32.5 %, respectively. The tensile strain hardening phenomenon appeared in all experimental groups. The inclusion of an optimal amount of coal gangue powder enhanced the tensile strain capacity, with the maximum tensile strain capacity reaching 4.15 %. Increasing fibre length substantially reduced crack width; for instance, the crack width in the 18 mm fibre test group was 31μm, which is only 33.6 % of the crack width observed in the 12 mm fibre group. Additionally, the incorporation of coal gangue powder significantly contributed to the reduction of crack width. In the context of embodied energy and embodied carbon in HSECC, PVA fibres and cement were found to be the primary contributors. Substituting a portion of the cement with coal gangue powder and silica powder significantly reduced both embodied energy and embodied carbon. The present study provides a novel utilisation method for coal gangue, a solid waste byproduct, which significantly mitigates its environmental impact. Additionally, the high-strength ECC produced using exclusively local materials demonstrates potential for broader implementation, particularly in applications such as concrete for bridge expansion joint anchorage zones and seismic retrofitting of external masonry walls.