Lignosulfonates are being used as corrosion inhibitors in highway deicing salts. Corrosion reductions of 50 to 80% have been reported for mild steel. Lignosulfonates act as both cathodic and anodic inhibitors. They remove oxygen from solution, form insoluble material on the corroding surface, and use its reducing ability to prevent oxidation of ferrous iron to ferric. Although lignosulfonates in deicing salts would be expected to protect exposed rebar in concrete, experiments were run to measure corrosion inhibition on rebar exposed by microcracks in concrete, and in undamaged concrete where corrosionoccurs by chloride diffusion. Mortar blocks with cracks leading to the embedded mild steel electrodes were soaked in 3% sodium magnesium chloride solutions, with and without 0.75% Lignosulfonate. After 6weeks, electrochemical measurements showed a 70% reduction in corrosion for the solutions with lignosulfonates. Wiss-janey concrete test blocks were treated weekly for 1 year with 15% sodium and magnesium chloride solutions, with and without 3.75% Lignosulfonate. Chloride penetration data indicated substantially lower chloride levels forblocks treated with salt solutions containing lignosulfonate. This experiment was repeated using small mortar cylinders that were treated with 3% sodium, magnesium, and calcium chloride solutions, with and without 0.75% Lignosulfonates. Significant reductions in chloridelevels were observed for samples treated with lignosulfonates. The proposed mechanism is the precipitation of lignosulfonates on or with calcium hydroxide to seal the pores in the surface. Depending on conditions, the life span of undamaged reinforced concrete structurescould substantially increase if lignosulfonates were added to deicing salts. This paper appears in transportation research record no. 1268, Highway maintenance operations and research 1990.
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