Synergistic use of waste marble and brick powder in sustainable concrete: achieving strength-workability synergy with eco-efficiency

This study investigates a novel synergistic blend of waste marble powder (WMP) and waste brick powder (WBP) as a supplementary cementitious material (SCM) system in concrete. Mortar and concrete specimens containing 5–15% cement replacement with a 1:1 WBP–WMP blend were evaluated using flow, slump, compressive strength, ultrasonic pulse velocity, Schmidt rebound, scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA), with at least three specimens tested for mean results. The combined WBP–WMP system improved flowability, density, and compressive strength more effectively than either material alone. In concrete, slump increased from 13.25 mm at 5% replacement to 70 mm at 15% due to reduced internal friction and improved particle lubrication. Although early-age strength decreased slightly at higher replacement levels, compressive strength at 180 days exceeded the reference concrete by 10%. SEM analysis confirmed synergistic behaviour, where the pozzolanic action of WBP compensated for voids caused by WMP particle clustering. TGA results indicated improved thermal stability. At 15% replacement, approximately 48 kg of waste-derived material was utilised per cubic metre of concrete, corresponding to an estimated reduction of 40–43 kg CO₂ emissions from cement production.