Better Roads

May 2014

Better Roads Digital Magazine

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Better Roads May 2014 21 friction. Once they are moved into contact with each other, angular aggregates produce high pavement strength. More force and heavier compactors are needed to overcome the internal friction between the fractured faces of crushed stone aggregate. Most high-traffi c mix designs specify the use of crushed aggregates with a certain number and shape of fractured faces. The role of thickness No matter what type of mix or what type of project, an important factor is the ratio between the size of the largest aggregate in the mix and the thickness of the layer. This ratio strongly affects the ability of the mat to accept compaction energy and reach the specifi ed density. For example, a layer thickness of 10 cm (4 inch) and a maximum aggregate size of 25 mm (1 inch) are relatively easy to compact. You can use high compaction forces and not worry about damaging aggregates. With a 4:1 ratio, there is ample space for aggregate movement allowing the aggregates to re-orient. Many public works departments specify a 3:1 ratio as a minimum for high-traffi c mix design. When the ratio of layer thickness to aggregate size is less than 3:1, the compaction process is much more diffi cult. In particular, when there are angular aggregates in the layer, it is likely that those aggregates will not move into the proper compacted orientation without being damaged. The compactor operator is more likely to notice drum bouncing or the appearance of uncoated rock at the surface of the mat. Lack of density and damaged aggregates will lead to premature mat failure. When the ratio of layer thickness to ag- gregate size is less than 3:1, low compaction energy is needed. In summary, crews will always need to monitor tempera- tures. But, don't forget that what happens before the mix even reaches the jobsite has an impact, too. Article and photos courtesy of Cat Paving. (Editor's note: This excerpt fi rst appeared in "The Cat Paving Products Guide to Asphalt Compaction." The book is available on Amazon.com and through participating Cat dealers.) NEAR YOU! COMING TO A LOCATION Technology is constantly changing. Understanding how these changes impact your business and boost profitability is now more important than ever. With our "we'll bring it to you" concept, the Topcon Technology Roadshow makes it convenient for anyone to learn how these industry innovations can help your business increase productivity in an ever-changing environment. REGISTER TODAY AT TOPCONROADSHOW.COM LEARN MORE ABOUT 7H[W,1)2WRRUYLVLWZZZEHWWHUURDGVFRPLQIR

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