Microstructure-Driven Strength and Durability Optimization of Structural Concrete Incorporating Iron Ore Tailings

Le résumé fourni par la source

Unsustainable extraction of river sand has caused widespread ecological damage and created an urgent need for alternative fine aggregates. Iron Ore Tailings (IOT), generated in bulk during iron ore beneficiation and presently managed by stockpiling, constitute a candidate waste stream for valorisation in cementitious systems. This study evaluates IOT as a replacement for manufactured sand in mortar and structural concrete using a hierarchical mortar-to-concrete optimisation framework. Cement mortars were produced at IOT replacement levels of 0 to 100 per cent and water-cement ratios of 0.40, 0.50 and 0.60 at a 1:3 binder-to-aggregate ratio, and the optimum identified at mortar scale was transferred to M25 concrete cast at water-cement ratios of 0.50 and 0.60. Replacement of 40 per cent of the manufactured sand raised the 28-day compressive strength from 35.24 to 39.02 MPa at a water-cement ratio of 0.50, a gain of 10.7 per cent that remains statistically significant for any within-triplicate coefficient of variation up to 4.49 per cent. Flexural capacity was preserved rather than improved, and the reductions in splitting tensile strength of 8.4 and 7.6 per cent and in slump of 9.6 and 8.3 per cent, although consistent in direction, lie within the typical precision of those tests at three replicates. Charge passed decreased monotonically from 160 to 144 coulombs across 0 to 60 per cent replacement, all mixes remaining within the very low permeability class of ASTM C1202. A second-order response surface fitted to the mortar means places the stationary point at 27 to 30 per cent, and the optimum is accordingly reported as a range of 30 to 40 per cent rather than as a sharp maximum. The strength gain is attributed to packing densification and capillary void refinement rather than to pozzolanic reaction, an interpretation supported by the low calcium oxide and amorphous contents of the tailings and benchmarked against published pore structure and interfacial transition zone data for comparable IOT concrete. Cradle-to-gate assessment gives a 1.1 per cent reduction in global warming potential per cubic metre, a 10.7 per cent reduction in carbon intensity per megapascal and a 7.6 per cent reduction if the strength margin is reinvested as a binder reduction, with material cost falling 5.4 per cent per cubic metre within a break-even haul distance of about 200 km. IOT is therefore established as a technically competitive and environmentally preferable fine aggregate for structural concrete.

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