concrete pavement.docx - Materials for Portland Concrete Pavement Portland cement concrete(PCC pavements(or rigid pavements consist of a PCC slab that

concrete pavement.docx - Materials for Portland Concrete...

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Materials for Portland Concrete Pavement Portland cement concrete (PCC) pavements (or rigid pavements) consist of a PCC slab that is usually supported by a granular or stabilized base, and a subbase. In some cases the PCC slab may be overlaid with a layer of asphalt concrete. CONCRETE ASPHALT MATERIALS FOR CONCRETE PAVEMENT Basic components of PCC include coarse aggregate (crushed stone or gravel), fine aggregate (usually natural sand), Portland cement, and water. The aggregate functions as a filler material, which is bound together by hardened Portland cement paste formed by chemical reactions (hydration) between the Portland cement and water. In addition to these basic components, supplementary cementitious materials and chemical admixtures are often used to enhance or modify properties of the fresh or hardened concrete. Sand Aggregates Coarse Water Cement COARSE AGGREGATE Coarse aggregate most frequently used in Portland cement concrete include crushed stone, gravel, and blast furnace slag. Other similar insert materials may also be used, and listed
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materials may be used singly or in combination with one another. Specific requirements related to coarse aggregations to be used for this purpose may be divided into five groups: deleterious subtances, percentage of wear, soundness, weight per cubic foot(slug), and grading. In certain areas, considerable difficulty has been experienced with aggregate containing deleterious subtances that react harmfully with the alkalies present in the cement. Such reactions generally result in abnormal expansion of the concrete. Methods have been devised (ASTM Method C227 and C289) for detecting aggregates with these harmful characteristics, and suitable stipulations are included in typical specifications (for example, ASTM C33). The ability of the coarse aggregate to resist abrasion is generally controlled by inclusion of the specifications of maximum permissible percentage of wear in the Los Angeles abrasion test. Maximum permissible percentages of wear in this test (AASHTO Designation T96) range from as low as 30 to as high as 65 in specifications of various state highway departments. On the average ,however, the maximum permissible loss varies from 40 to 50 percent of all three of the principle types of coarse aggregate, although many specifications do not contain a requirement related to the percentage of wear of slag. The soundness test used is an accelerated weathering test. The weighted loss in the sodium sulfate sound test (AASHTO T104) may generally be said to have maximum permissible value ranging from 10 to 15 percent, as measured at the end of five cycles of alternate wetting and drying. A small number of states use a freezing and thawing test for the same purpose. The material is generally required to be well graded from coarse to fine, with the maximum size of coarse aggregate permitted by most highway organizations being from 3 to 2 in (75-50mm).
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  • Spring '16
  • Engr. Manuntag

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