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42 The above-mentioned tests are hardly scientific in that they Post-Treatments require an experienced person to conduct them with some degree of reproducibility. This points to the need for research The ISSA inspector's manual (ISSA 2010a) contains infor- to develop a suite of field tests that allow an inspector to test mation on two post-microsurfacing treatments that are the microsurfacing mix after it has been laid as well as tests cogent to the discussion. The first is sweeping to remove to identify when the mix has cured to a sufficient degree to excess stone on heavily trafficked roads, which ISSA recom- open it to traffic without fear of damaging it. mends be done with a suction broom if possible and com- pleted before opening the road to traffic. Sweeping is also Microsurfacing can normally handle rolling traffic without needed if excessive stone loss is experienced after opening damage less than one hour after placement (Price 2010). a heavily trafficked road. The second treatment is sanding, However, in areas such as intersections where stop and go which can be used to furnish extra protection for special traffic is prevalent, additional curing time may be needed, areas such as intersections. Wet spots can also be sanded to especially during unexpectedly hot or cold weather (National permit their opening to traffic. Sanding can commence as Highway Institute 2007). Microsurfacing emulsions can soon as the microsurfacing can support traffic without pick retain some water for several weeks. If during this period up (Caltrans 2009). freezing temperatures are experienced, the binder film will rupture and the surface will ravel. As a result the Caltrans Maintenance Technical Advisory Guide (MTAG) recom- SUMMARY mends that projects "not be started" unless there is a "2-week window" without freezing weather in the forecast (Caltrans This chapter reviewed the microsurfacing construction process 2009). Another concern is that asphalt emulsions "cannot re- from concept to traffic opening. Two types of spreader boxes emulsify if not fully cured, but they can be tender enough to were discussed in detail, but these are mere appurtenances re-disperse under the effects of traffic loading and excessive that are attached to other pieces of construction equipment, water, especially ponded water. In this process, broken aggre- and that is the subject of the next chapter. One effective prac- gates or asphalt particles that have not fully coalesced into tice was developed: films are dispersed in water, which disintegrates the emul- sion" (Caltrans 2009). Microsurfacing can typically withstand a light rain 3 h after application. However, a heavy rain and Scratch coat and full lane-width microsurfacing can use heavy traffic will damage the surface, especially in areas with the same size aggregate with no apparent difference in shear resulting from turning movements (Caltrans 2009). performance.