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Influence of Chloride Permeability Test Parameters on Results for Silica Fume and Nonsilica Fume Concrete

During bridge construction, an early prediction of the permeability of the concrete overlay is always desirable. However, the field-extracted rapid chloride permeability test (RCPT) specimens often have a thickness that differs from the ASTM (AASHTO) standard (50.8 mm). The need may arise to test specimens at an earlier age for an early prediction of the overlay’s performance. It has also been documented that thinner specimens may exhibit an increase in temperature during the RCPT progress. This study investigates the impact of the RCPT parameters on concrete made with and without silica fume. Silica fume and nonsilica fume concrete specimens were prepared with two compaction techniques. Test specimens were also prepared at various thicknesses and subjected to the RCPT. The coulomb charge passing each specimen was recorded every 30 min during test progress. A supplementary group of specimens was prepared 6 months later using the same constituents to strengthen some of the findings. Results reveal that the relation between the coulomb charge and specimen thickness is nonlinear. Also, strong indications exist for a possible prediction of the 56-day coulomb value for the silica fume concrete based on 28-day results and of a more-or-less trend for the coulomb value with time. Results indicate that the relation between the coulomb charge and time while testing is in general a linear one, at least for good-quality concrete. Specimen compaction technique seems to have little effect on the measured coulomb charge.