Abstract
The Federal Highway Administration has funded several investigations to find and develop a deicing chemical to replace the chloride containing salts that have been so damaging to bridge decks in the United States. Calcium Magnesium Acetate (CMA) has been selected as the most promising of several studied and this paper reports on one part of a project devoted to develop an understanding of the corrosion behavior of various metals in CMA. One part of the corrosion study found CMA to be less corrosive to exposed steel and aluminum than sodium chloride. This paper reports on the behavior of steel embedded in concrete when exposed to CMA.
CMA changes the pore solution chemistry by precipitating hydroxyl ions as calcium hydroxide and magnesium hydroxide since calcium and magnesium ions are added with the CMA. The pH of simulated pore solutions shift from about 13.8 to values as low as 10.5 dependent upon the amount of CMA added. The potential of steel shifts from about -200 mV to about -600 mV, with respect to calomel, in this lower pH environment. The potential of steel in mortar cylinders soaked in CMA solution also shifted to the -600 mV level.
Steel in concrete slabs used in ponding tests also indicated the steel potential could be shifted in the negative direction when CMA diffused to the level of the steel.
These large shifts in potential could result in corrosion of steel in contact with CMA containing concrete because of the macrocells created. Further studies are recommended to accurately determine if this problem will be encountered if CMA is widely adopted for bridge decks.
