Using Polymer Modified Asphalt Emulsions in Surface Treatments A ...

espect to each specific treatment type, and where applicable, compared to the
performance of non-modified asphalt emulsions.
2.5.2 Chip Seals
Chip seals (sometimes called seal coats or bituminous surface treatments) consist of an
asphalt emulsion which is applied to the pavement surface which is subsequently
overlain by one or more layers of stone chip aggregate up to one-inch in total thickness,
and then rolled. Chips seals are commonly employed as an inexpensive treatment for
minor forms of pavement surface distress such as cracking or raveling.
The advantages of using polymer modified asphalt emulsions in chip seal applications
over non-modified mixtures include:
1. Better stone retention;
2. Projects can usually be opened to traffic sooner;
3. Reduced rates of flushing and bleeding;
4. More effective on higher volume roadways (due to improved stone retention);
and,
5. Greater design tolerance for chip and asphalt emulsion quantities and aggregate
embedment factor (14).
Takamura (2003) demonstrates the impact of polymer modifiers on improving stone
retention in chip seals (66). Figure 20 presents a comparison of retained aggregate
percentages between modified and unmodified variants of eight mixtures - each
containing different aggregates – from an early strength sweep test. As Figure 20
illustrates, improvements in aggregate retention range from modest to dramatic in the
polymer modified (i.e., BASF’s Butonal NX1118) chip seal mixes in all eight test
cases, with percentages near or above 90%.
57