Open -graded cold asphalts

OGCAs provide high air voids to drain water through the mixture. They have been used successfully for base courses and surface courses. 

The aggregate property requirements are similar to those for dense-graded cold mixtures. 

The grading is such as to produce an open-graded mixture. Table 6.3 shows the gradations proposed by the Asphalt Institute (Asphalt Institute MS-19 2008). 

Source Adapted from Asphalt Institute. Basic Asphalt Emukhn Manual, Manual Series No. 19 (MS-19), 4th Edition, Lexington, KY Asphalt Institute, 2008. With permission. 

The bituminous emulsion, typically medium-setting cationic type with paving grade bitumen, should satisfy the requirements of the respective specification used. 

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As with any dense-graded mixture, DGCAs possess greater stability and stiffness, and are far less permeable to water, when compared to open-graded cold asphalts (OGCAs). 

Construction processes may be more challenging. For example, gap and open graded RA has to be compacted at higher temperatures than conventional dense graded asphalt because the rubber stiffens the binders. The RA mixtures can also be difficult to hand work due to this stiffening, and the construction must be completed 48 h after mixing. Also, construction in cold temperatures, in the wet, and over pavements with severe cracks can cause problems. 

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