The Effect of Minnesota Aggregates on Rapid Chloride Permeability Tests

Status:  Complete
Report Date:  02/08/2005


This report investigates the effect of the type of coarse aggregate used in concrete on chloride ions penetrability as indicated by the rapid chloride penetration test (RCPT). Twelve coarse aggregate types, commonly used in Minnesota Department of Transportation highway construction projects, were identified and used for this study. The coarse aggregate types were subjected to laboratory testing to determine their physical properties and ambient chloride content. The aggregate types were used to prepare fresh concrete according to Mn/DOT specifications in which silica fume and fly ash were used. In order to characterize the concrete in terms of resistance to chloride ions penetration, concrete specimens made of these aggregate types were subjected to the rapid chloride permeability test at different ages. All mix parameters including gradation and quantities of different aggregates were held constant in different mixes. The only variable was the aggregate type. For concrete specimens tested at 28 days of age, the average total charge passed varied between 1,452 and 2,606 Coulombs, which can be described as low to moderate chloride ions penetrability, according to AASHTO designation. The average total charge passed decreased with time (age) for all of the concrete specimens tested. Considering specimens at 91 days of age, the average total charge passed ranged from 601 to 1,236 Coulombs, which can be characterized as very low to low chloride ions penetrability. The aggregate type has a noticeable influence on the RCPT results for the concrete mix design that was utilized.

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