Sustainable concrete without chloride limits

An article published in the Boston Globe in October 2014 titled “For concrete, climate change may mean a shorter lifespan” pointed out to the general public some pessimistic, but still worth noting, predictions: collapse of reinforced concrete structures due to steel reinforcement corrosion could be the most immediate vulnerability resulting from climate change. In marine environments, chlorides present in seawater cause de-passivation of the steel and consequent corrosion phenomena. To prevent the risk of premature degradation in new concrete constructions, whenever it makes sense, non-corrosive reinforcement in the form of composites or stainless steels should be adopted. In the past decades, the scientific community, industry, owners and regulators have addressed the problem of steel reinforcement corrosion by focusing on: the physico-mechanical properties of concrete, the use of strict limits for admixed chlorides and prevention of chloride penetration by low permeability. If reinforcement corrosion were not the most compelling concern, some of these sought-after properties would have no reason to be implemented and, without detrimental effects on durability, concrete itself could become a more sustainable material. This paper presents the preliminary results of a research aimed at changing the current perspective: by using proper types of corrosion resisting reinforcement, it becomes possible to produce concrete without chloride limits that can include seawater instead of freshwater for mixing and curing, and recycled concrete aggregate (RCA) that may already be chloride-contaminated replacing natural aggregate. If successful, this “greener” concrete would also allow the use of cements without chloride restriction; thus, giving cement manufacturers the opportunity to use solid waste as kiln fuel (co-generation) as well as adding kiln dust (byproduct that currently requires disposal) back to the clinker.