Better Roads

May 2014

Better Roads Digital Magazine

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Better Roads May 2014 19 HighwayContractor M any contractors look to temperature when con- templating compaction needs. Yet, some off-site specifi cations also have a signifi cant impact on the jobsite. These include mix design and aggregate shape. Dense-graded mixes are produced with continuously graded aggregate. In other words, there are a variety of sizes of aggregates in the design. The design formula includes asphalt cement and fi nes. Typically, the larger aggregates are surrounded by a matrix of mastic composed of asphalt cement and fi nes. The asphalt cement may be modifi ed by materials such as polymer or latex rubber to develop ad- ditional stiffness. Because the larger aggregates are surrounded by the mixture of asphalt cement and fi nes, there is less danger of damaging aggregates through the use of high-compaction force. Depending on the layer thickness, medium to high amplitude is often selected when compacting dense- graded mixes. Whether it's dense-graded, open-graded or gap-graded mix or stone-matrix asphalt, don't forget their impact on compaction. Size Matters in Mix Grades and Aggregate Shapes

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