United States Department of Transportation
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Abstract:This report describes a research project in which aspects of transit mixed concrete were studied. Phase I describes the work performed in evaluating the effects of extended retention of concrete in a transit mix truck for three hours. Four mixes were evaluated. These were (1) sand and gravel concrete with no admixtures, (2) sand and gravel concrete with admixtures, (3) lightweight coarse aggregate and sand with the moisture content of the coarse aggregate maintained at approximately 15 percent, and (4) the same mix with the moisture content of the coarse aggregate maintained at approximately 30 percent. Phase II describes the work performed in the field to determine yield, slump loss, loss of entrained air, water requirements and a comparison of field manufactured specimens to laboratory manufactured specimens. These tests were performed on concrete as was being used on construction projects throughout the State. The conclusion reached from Phase I of this study were that sand and gravel concrete without admixtures is affected more by long retention in a transit mixed truck than is sand and gravel concrete with admixtures. If necessary as much as two hours retention could be tolerated without severely damaging the properties of the concrete. Lightweight concrete with 15 percent moisture in the coarse aggregate performed better than lightweight concrete with 30 percent moisture in the coarse aggregate. Phase II indicated that slump loss, loos of entrained air and yield are not as large of a problem as has been indicated in the past.
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