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11 FIGURE 5 Summary of survey responses. Aggregate selection is largely a cost function of availabil- Finally, different types of aggregate are more suited to certain ity and transportation distance. Local geography largely deter- binders as a result of electrostatic compatibility, and this fac- mines the quality of the aggregate, and it is common for agen- tor requires the chip seal designer to consider the electrostatic cies to opt for a marginal quality (i.e., at the low end of the compatibility of local aggregate during binder selection. specifications) local aggregate owing to cost considerations. The quality of aggregate is important to the overall success of CHIP SEAL--ART OR SCIENCE? the chip seal program. As aggregate quality decreases, a num- ber of constructability problems, such as dust and degradation Traditional thought in the United States has portrayed chip of the aggregate during handling, may arise from using poor- seals as an art rather than a science (Wegman 1991). Beliefs quality aggregates located within proximity to the project. The that chip seal design is simply a "recipe" prevail to this day. Australians have been known to be willing to pay for high- The reasoning behind this is that the majority of North Amer- quality aggregate imported from great distances to ensure the ican chip seal practice is based on local empirical experience quality of their chip seals (Austroads Provisional . . . 2001). rather than on sound engineering principles. The main reason