Construction materials face growing pressure to balance environmental sustainability with structural performance requirements. This investigation examines waste carbon black (WCB) as a partial cement replacement. Multiple ultrasonic evaluation approaches are deployed to monitor periodic strength development during curing. Mortar specimens containing 2.5% and 5% WCB by weight of cement were tested using conventional and advanced ultrasonic methods. Testing included ultrasonic pulse velocity (UPV), higher-harmonic β parameter, Sideband Peak Count Index (SPC-I), and Spectral Dissipation Index (SDI). Results demonstrate that 2.5% WCB incorporation yields a marginal improvement in both compressive strength (39.3 ± 1.96 MPa versus 37.46 ± 1.87 MPa for control, approximately 5% higher) and flexural strength (4.43 ± 0.22 MPa versus 4.25 ± 0.21 MPa for control, approximately 4% higher) changes largely within experimental variability. Scanning electron microscopy (SEM) reveals a slightly denser microstructure and reduced pore coverage in 2.5% WCB sample compared to control sample. However, increasing WCB content to 5% causes particle agglomeration, compromising mechanical properties with compressive strength dropping to 23.12 ± 1.16 MPa. Ultrasonic monitoring revealed distinct microstructural evolution patterns, with UPV values reaching 3333 ± 100.05 m/s for optimal 2.5% WCB mixtures. The β parameter effectively detected early-stage particle agglomeration induced micro-cracking at 5% WCB prior to strength degradation, while hybrid parameters, i.e. SPC-I and SDI, provided sensitive indicators of internal structural changes throughout curing. Life cycle assessment confirmed environmental benefits, showing modest 2–3% reductions in global warming potential and resource depletion. This integrated approach establishes a comprehensive framework linking mechanical performance monitoring with environmental impact assessment, advancing sustainable concrete technology through industrial waste utilization.
Amjad et al. (Thu,) studied this question.