Mechanical behaviour of Portland cement mortars with incorporation of Al-containing salt slags

Abstract

Recovery of a salt cake slag produced from aluminum scrap re-melted in rotary furnaces, at the lowest cost, while complying with all environmental laws is the main objective of this study. The characterisation of the slag residue involved determinations of the water leaching conditions, toxicological analysis, chemical analysis of the leaching waste, and mineralogical composition. A two-phase study was made to determine the effect of waste additions on mechanical properties of cement mortars, involving partial replacements of either sand or cement. SEM characterisation of fracture surfaces was also made. Partial substitution of cement, which is the most expensive component of the mortar, by salt slag has both environmental and economical advantages. However, only small amounts (up to 10 wt.%) can be replaced by washed slag without significant damage to mortar characteristics. Sand substitution by slag is less problematic and 30±50 wt.% replacement levels are easily achieved. However, the direct economical impact is less relevant. The incorporation of unwashed slag in impracticable, as a result of noxious gases released and significant volumetric expansion effects.