CA Ratio Guidelines NMPS CA Ratio NMPS New CA Ratio COARSE IN CONTROL
{"Image DocumentName": "CA Ratio Guidelines NMPS CA Ratio NMPS New CA Ratio COARSE IN CONTROL", "Image ImageDescription": "25.0mm. 19.0mm. 12.5mm. 9.5mm. 4.75mm. CA Ratio \u2013 \u2013 \u2013 \u2013 FINE IN CONTROL. As the CA ratio increases, VMA increases, because interceptors decrease packing of the pluggers, which in turn decreases packing of the fine fraction. If the CA ratio is too low, there is an excess of pluggers and even if the mix meets VMA or Voids, it will generally be susceptible to segregation. As the CA ratio approaches the high end of the suggested range (see next slide), the coarse fraction becomes balanced and neither sized material (interceptors or pluggers) controls the overall coarse fraction, which makes it difficult to lock up, especially in the field where the mix generally isn\u2019t confined as it is in the lab compaction mold. High CA ratios generally occur with S shaped combined blend gradations that have gained notoriety in Superpave because they can be difficult to compact in the field. We generally don\u2019t recommend blends with CA ratios above the high end of the corresponding range because of this, but they do exist. As the CA ratio exceeds the range, the interceptors start to control the coarse fraction. In addition to difficulties with field compaction, other issues with having a CA ratio above the high end of the corresponding range are: - Eventually the void size in the coarse fraction (plus PCS) will decrease to the point where the PCS actually changes to the next smaller sieve. First, this causes a shift in the volume of coarse and fine. Second, if the PCS is different, all three ratios that are used to evaluate the combined blend need to reference different sieves. - Segregation susceptibility will likely begin to increase again at some point, probably in inverse proportion to the corresponding range. NMPS. All Sizes. New CA Ratio", "Image XResolution": "37", "Image YResolution": "37", "Image ResolutionUnit": "Pixels/Centimeter", "Image Software": "SlidePlayer", "Image YCbCrPositioning": "Centered"}