Fiber Effects on Brittleness Mitigation in Marble Dust Concrete

Abstract Concrete brittleness limits its use in bending-dominated elements. It also raises the cost of tensile reinforcement. A three-stage experimental program was carried out to address this limitation while also reducing the environmental burden associated with clinker production. In Stage I, marble dust (MD) was used to replace Portland cement at five levels, from 5% to 14% of binder mass. A 10% replacement gave the highest 28-day compressive strength, 49.64 MPa, and the highest modulus of rupture, 6.18 MPa, at a w/b of 0.364. In Stages II and III, polypropylene macro-fibers (PP), recycled PET bottle strips (rPET), and hooked-end steel fibers (SF) were added to the MD10 mixture, across twelve dosages in total. The brittleness index was reduced by up to 27.3% relative to the unreinforced MD10 mixture, which had an index of 8.03. Recycled PET fibers at a 1.00% volume fraction gave the lowest brittleness index of any mixture tested, 5.84, lower than every steel-fiber dosage. A cost and carbon assessment was then carried out, using validated emission factors and regional material prices. It showed that rPET fibers achieved this reduction for a material cost premium of only 1.68 USD per cubic meter and a carbon overhead of 7.66 kg CO 2 e per cubic meter. The resulting cost efficiency index, 0.77 USD/m 3 per unit of brittleness reduction, and environmental efficiency index, 3.50 kg CO 2 e/m 3 per unit of brittleness reduction, were substantially lower: the corresponding value for the best performing steel fiber dosage were approximately 79 and 36 times lower higher, respectively. Recycled PET fibers in a marble dust matrix are therefore a structurally effective, low-cost, and low-carbon route to brittleness reduction in sustainable concrete.