Figure 12.10 shows the results from tests of water permeability of an SMA mixtures with gradations 0/4.75, 0/9.5, and 0/12.5 mm (Cooley and Brown, 2003). All instances concern U. S. SMA, previously described in Chapters 6 and 7.
Figure 12.10 clearly shows the relationship between the maximum aggregate size of the SMA and the probability of its being permeable. The larger the maximum aggregate size of the SMA, the higher the probability of its being permeable. Thus the size of the maximum particle is a decisive factor for permeability of an SMA
![Подпись: 03 4 5 6 7 8 9 10 11 12 13 14 15 Air void content, % v/v FIGURE 12.10 Water permeability of SMA mixtures with gradation 0/4.75, 0/9.5, and 0/12.5 mm, depending on the size of the selected breakpoint sieve—the degree of gap gradation. (From Cooley, L.A. Jr. and Brown E.R., Potential of Using Stone Matrix Asphalt [SMA] For Thin Overlays. National Center for Asphalt Technology, Auburn University, NCAT Report 03-01, April 2003. With permission.)](/img/1312/image249_1.gif "Test Results") |
mixture and so is the gradation within the coarse aggregate fraction (driven by the breakpoint sieve using the U. S. definition). An increase in this factor is followed by the growth of the size of internal pores, and consequently, the probability of their connection (Cooley and Brown, 2003). It has been stated in research (Cooley et al., 2002) that SMA mixtures are characterized by a higher potential for permeability than AC mixtures with the same content of air voids. Investigations of permeable pavements in Florida in the United States led to a definition of permeable mixtures as those mixtures with field permeabilities greater than 100 x 10-5 cm/sec[71] (Choubane et al., 1998). SMA mixtures may be prone to this excessive permeability, particularly those with a nominal maximum aggregate size greater than 10 mm.
