Validated concrete damage plasticity modelling of concrete incorporating domestic and industrial sewage sludge reinforced with disposable face mask fibers

This study investigated the compressive behaviour of concrete incorporating treated domestic sewage sludge (DSS), industrial sewage sludge (ISS), disposable face mask fibres (DFMF), and silica fume (SF), while evaluating the ability of the Concrete Damage Plasticity (CDP) model in ABAQUS to reproduce the observed mechanical response. The study addresses the valorisation of multiple waste streams while examining how sludge source influences cement-based composite performance. The experimental programme evaluated workability in accordance with SANS 5862-1:2006 and compressive strength in accordance with SANS 5863:2006 using triplicate 150 × 150 × 150mm cubes at 7,14,28 and 90-days. Physical, chemical and compositional characterisation was conducted to support interpretation of the differing behaviour of DSS and ISS in concrete. A finite element model based on the Concrete Damage Plasticity (CDP) approach was developed and calibrated against the experimental results to simulate the stress–strain response, damage evolution, and failure behaviour of the concrete composites. The optimum waste-utilisation mix containing 3.5% DSS, 17.5% DFMF and 5% SF achieved a mean 28-day compressive strength of 31.47 MPa. Under identical replacement conditions, the corresponding ISS mixture achieved 22.77 MPa, representing a 27.6% lower strength. These findings demonstrate that sludge source and composition are critical when selecting waste materials for concrete intended to meet medium-strength performance requirements. The numerical simulations closely reproduced the measured compressive response, with differences of approximately 1%, verifying the consistency of the adopted CDP framework within the investigated calibration range. Overall, DSS combined with DFMF and SF demonstrated potential for medium-strength concrete, whereas ISS requires further material and mix optimisation.