EVALUATING THE IMPACT OF SILICA FUME AND WASTE MARBLE DUST/POWDER ON CONCRETE DURABILITY CHARACTERISTICS

Abstract

Two of concrete's weaknesses share a single origin. Ordinary Portland cement (OPC) is carbon-intensive to produce and the calcium hydroxide left behind by its hydration is the phase most readily dissolved when concrete meets acids or sulfates. This study tests whether both can be addressed at once by combining silica fume (SF), which consumes calcium hydroxide pozzolanically with waste marble powder (WMP), which densifies the matrix physically in a single mix. A full factorial of sixteen mixes crossed four SF levels (0, 5, 10 and 15% of cement mass) with four WMP levels (0, 10, 20 and 30% of fine-aggregate mass) at a fixed 1:2:4 proportion and a water-to-binder ratio of 0.60, using materials locally sourced in Sindh, Pakistan. Slump was measured on every fresh mix. A total of 128 cubes of 100 mm were cured with water for 28 days and then immersed for a further 28 days in 5% sulfuric acid (ASTM C267) solution, after which residual compressive strength was determined. All replacements produced a monotonic reduction in slump from 85 mm for the control to 40 mm for SF15WMP30. However, all mixes retained cohesiveness and were placeable. The maximum residual strength after acid exposure (+22.116 MPa with +5.18% relative to the control mix on the exposed control or in acid exposure) was recorded for SF10WMP10, while the weakest mix SF15WMP30 experienced a loss of 11.78% in acid after 28days of immersion time. Performance was degraded beyond 10% of either material. Acid was the more aggressive medium throughout. On its own, marble powder contains carbonate which is acid soluble, this can limit the benefit of marble under acid attack. Recommended as the optimal combination: SF10WMP10.