Deleterious Chemical Effects of Concentrated Deicing Solutions on Portland Cement Concrete. Implementation Guide; Final rept. for Sep 02-Apr 08

摘要

This research project investigated the effects of concentrated brines of magnesium chloride, calcium chloride, sodium chloride, and calcium magnesium acetate on Portland cement concrete. Although know to be effective at deicing and anti-icing, the deleterious effects these chemicals may have on concrete have not been well documented. As a results of this research, it was determined that there is significant evidence that magnesium chloride and calcium chloride chemically interact with hardened Portland cement paste in concrete resulting in expansive cracking, increased permeability, and a significant loss in compressive strength. Although the same effects were not seen with sodium chloride brines, it was shown that sodium chloride brines have the highest rate of ingress into hardened concrete. This latter fact is significant with respect to corrosion of embedded steel. The mechanism for attack of hardened cement paste varies with deicer chemical but in general, a chemical reaction between chlorides and cement hydration products results in the dissolution of the hardened cement paste and formation of oxychloride phases, which are expansive. The chemical attack of the hardened cement paste is significantly reduced if supplementary cementitious materials are included in the concrete mixture. Both coal fly ash and ground granulated blast furnace slag were found to be effective at mitigating the chemical attack caused by the deicers tested. In the tests performed, ground granulated blast furnace slag performed better as a mitigation strategy as compared to coal fly ash.