to prevent bleeding problems and that the various size pieces of aggregate can be bound well enough to prevent aggregate loss problems. Polymer modification of the binder also probably would be helpful.
Smaller sizes (e.g., 0.25 inch) of chip seal aggregate perform well in the short term. They provide a tighter surface texture (improving noise) and require less weight of aggregate per square area to provide adequate coverage (reducing cost). Also, less binder is required to bind the aggregate to the surface, further reducing costs. Generally the literature suggests that chip seals constructed with smaller cover aggregate sizes will wear more quickly than larger sizes, especially under heavier traffic. The test sections placed for this study have not been observed long enough to confirm or to dispute this assertion.
Treatments with quartzite aggregate (e.g., quartzite-manufactured sand in the thin hot sand mix, which had very high SR despite the small aggregate size and smooth, tight surface) provided the best SR. However, other than the hot sand mix, quartzite surfaces used in this study also appear to have the greatest vulnerability to snowplow damage. Snowplow damage is not inevitable with quartzite aggregates, because several other roads exist with quartzite aggregate TMSs that have not exhibited snowplow damage to this extent. Several possible reasons for vulnerability to snowplow damage for the particular test sections include the following:
Because aggregate is hydrophilic, the aggregate may not have been well adhered to the binder (stripping). Adjusting the binder may mitigate this problem.
Because aggregate gradation lacks fine particles, the larger particles may have
stood up higher than the rest of the surface, so they were more vulnerable to being scraped away by the snowplow blade.
Because the aggregate gradation lacked fine particles, the aggregate may have lacked stability and was easily removed when hit from the side by snowplows.
Because the aggregate particles are hard, they may have been plucked out of the surface (rather than sheared 'oft) when hit by a snowplow blade. (Anecdotal evidence from the first author suggests that limestone chips in Iowa are often sheared by snowplow blades.)
Maintenance personnel in Iowa report that snowplow damage can be mitigated if "shoes" are used under snowplow blades to limit engagement between the blade and road surface. Limiting down pressure on blades to the extent possible is also helpful.
The gradual loss of quartzite manufactured sand aggregate on hot sand mix may provide a renewed surface with considerable microtexture. This phenomenon may account for its good SR performance. Because the aggregate particles are small, their gradual loss is not particularly problematic.
In general, TMSs should be considered as some of the many tools available in a tool kit for maintaining, upgrading, and building highway and road networks. They should be used in cases where they provide economic benefit by preserving roads and increase road user safety and satisfaction. For successful use, the type of treatment and the type of materials must be properly selected, and construction must be executed with an emphasis on quality.