United States Department of Transportation
i
Effect of Larger Sized Coarse Aggregates and of Microsilica on Environmental Properties of Portland Cement Concrete Pavements and Structures; Volume 1 of 2
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2006-04-01
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[PDF-769.45 KB]
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TRIS Online Accession Number:1036741
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Edition:Final Report
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Abstract:This project assesses the effects of aggregate type and size on the mechanical properties of concrete, viz., on the compressive and flexural strengths, and on the modulus of elasticity. Explored are three aggregate gradations (No. 57, No. 467, and No. 357) consisting of two aggregate types (natural and crushed). Concrete made according to the specification for the Ohio Department of Transportation (ODOT) standard Class C mix provides the baseline for mechanical properties. The properties of the six concrete mixes produced are compared, in order to determine if aggregate gradation and type have a significant effect, using the following tests at 3, 7, 28, 56 and 90 days: (a) Compression; (b) Modulus of rupture; and (c) Modulus of elasticity. A series of environmental tests are documented in a companion report submitted under this contract. Air content, slump and unit weight tests were conducted for each mix. For the most part, different coarse aggregate properties did not impact significantly the mechanical properties of concrete examined. When significant differences were observed, these were confounded by variability issues related to the testing protocols themselves, and by mineralogical distinctions among the various aggregate blends. It is, therefore, concluded that coarse aggregate gradation had little effect on the mechanical properties of concrete. These results indicate that larger sized coarse aggregates can be used for pavements and highway structures without significantly compromising the mechanical properties of the concrete, and afford concrete producers more flexibility in creating cost-effective and cement-efficient mixes. In view of the natural variability of concrete test results, it is recommended that the number of specimens tested be increased to five or six, in order to improve the confidence level. Conversely, the number of testing dates can be considerably curtailed without compromising the quality of the data obtained.
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