16.3.3 ROLLERS
Rollers are used for breakdown and intermediate rolling, compaction, and finish rolling to remove
roller marks. Available drum widths (rolling widths) range from 3 to 7 ft, approximately. Generally,
a vibratory or static steel-wheel roller, with the first drum as the driver, is used for breakdown. The
contact pressure that ensures compaction can be altered by changing the ballast load or dynamic
force (in the case of a vibratory roller) or the tire pressure (for a rubber-tired roller). Rollers
(Figure 16.14) can be rubber tired (these rollers are usually 15–20 ton in weight, and their tire
pressure is generally around 90 psi, with 4500 lb per tire), a vibratory steel-wheel roller (usually
10 ton in weight, with high-frequency and low-amplitude vibrations), and a static steel-wheel roller
(10–12 ton).