Long-Term Performance of Silica Fume Concrete in Soil Exposure of Marine Environments

Given the time-dependent microstructural modifications in cement matrix, long-term monitoring of concrete in natural exposures will be necessary. The present research addresses the long-term performance of concrete specimens embedded in coastal soil of a harsh marine environment for 88 months. Chloride ion diffusion, binding capacity, and effects of carbonation and surface coatings were investigated for concrete mixtures with up to 12.5% silica fume (SF) and water-to-cementitious materials ratios (w/cm) of 0.4 and 0.5. Three types of surface coatings, including bitumen and rubber emulsion, polymer modified cementitious coating, and polyurethane, were also incorporated. It was observed that concentration of bound chloride ion is decreasing as a result of an increase in SF content from 0 to 12.5% and increasing the w/cm from 0.4 to 0.5. Slight carbonation was observed at 88 months, with carbonation depths limited to 5.5 mm. Decrease in chloride binding capacity was observed in carbonated areas. Depth of concrete cover to reach 50 and 100 years of service life was calculated. It was observed that a concrete cover of 200 mm can secure 100 years of service life while incorporating a concrete mixture with w/cm of 0.5 and 100% portland cement. The required thickness of cover was reduced to 35 mm in the case of the mixture cast with 12.5% SF and w/cm of 0.4. Coating equivalency lines were developed to compare the efficiency of the investigated coatings with corresponding combinations of w/cm and SF replacement level.