Corrosion Resistance on Recycled Aggregate Concrete Incorporating Slag

Abstract

Ann discusses Al-Yaqout et al's paper about the corrosion resistance of steel in concrete containing recycled aggregate incorporated with slag. Their concrete mixture proportions seem misleading. The authors set the water-binder ratio (w/b) as 0.35 for all mixtures: the binder content was 410.0 kg/m3 and water was 143.5 kg/m3, irrespective of mixture type. Portland cement was solely admixed as binder in some mixtures, while portland cement (307.5 kg/m3) and slag (102.5 kg/m3) were combined in the other mixtures. Simultaneously, the content of natural sand was 705.0 kg/m3. With no information on these specific gravities, it could be easily expected that the specific gravity for portland cement usually ranges 3.10 to 3.15, while slag is 2.85 to 2.90. Depending on the mixtures, recycled aggregate was used as coarse aggregate, at 0, 50, and 100%. Fortunately, the specific gravity for natural aggregate and recycled aggregate was given in the paper: the value for natural aggregate was 2.69 and for recycled was 2.39. Then, the total weight of coarse aggregate was commonly 1100.0 kg/m3 in all mixtures. The authors substantially designed concrete mixtures with an equated weight for each material including binder, water, sand, and coarse aggregate, neglecting their different specific gravities. This mixture design, in fact, imposes potentially erroneous proportioning.