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OCR for page 47
48
Rolling Time
Roller Weight
Speed Limits
Rolling Patterns
No. of Passes
0% 20% 40% 60% 80% 100%
North America AU, NZ, UK, SA
FIGURE 51 Typical rolling requirements.
with pneumatic rollers (McLeod 1969). A survey respondent excess chips that can dislodge and strike windshields causing
from the United Kingdom indicated that steel-wheeled rollers damage. Sweeping operations need to be properly executed
had been used primarily to assist with the rideability of the chip because the sweeping process itself can dislodge embedded
seal, that this had been discontinued in favor of using rubber- chips (Shuler 1990). However, sweeping the loose aggregate
clad steel rollers. When steel-wheeled rollers are being used, from the roadway immediately following rolling is a critical
they should be lightweight models of 6 to 8 tons, as heavier mistake, for the residual binder has not yet cured enough to
rollers will likely break down the aggregate (Asphalt Surface bond to the aggregate and underlying road surface.
Treatments--Specifications undated). Because degradation of
aggregate is a serious concern with steel-wheeled rollers, The time frame for sweeping depends on how long it
those rollers should be operated only in static mode. If any takes the binder to cure to a point sufficient to retain the
fracturing or crushing of the aggregate becomes evident, the aggregate. As the temperature declines into the evening,
operation should immediately stop the use of such rollers. As aggregate retention will be higher if sweeping is done at this
mentioned earlier, steel-wheeled rollers will have difficulties time. The WSDOT recommends that final brooming occur
when the underlying pavement is rutted, for they will bridge "during the cool period of the day (early morning)" and that
over the ruts and fail to properly seal the aggregate in the ruts. "if rock is dislodged (by the broom), that brooming be
Steel-wheeled rollers should never be used alone (1) because delayed until the asphalt has cured further or the weather is
they will not orient the particles into their least dimension cooler" (Asphalt Seal Coats 2003). Typically three passes
and (2) because of contour bridging (riding on the high spots are required to adequately sweep each driving lane (Seal
while spanning over the low spots), they will not contact the Coats . . . 2003). Figure 52 illustrates the typical number of
entire width. When achieving embedment becomes a con- sweeping passes as identified by the survey respondents. Of
cern, and the aggregate is not hard enough to sustain rolling note is that in spite of the number of sweeping passes
with a steel-wheeled roller, larger pneumatics such as 10-ton, required, the objective should be to remove all excess aggre-
11-wheeled pneumatic rollers may be an option to consider gate from the surface of the chip seal. Logically, the sweep-
(Wegman 1991). ing operation should direct dust away from the traveling
public. In areas where loose aggregate cannot be swept off
SWEEPING AND BROOMING the side of the road, a pickup sweeper should be used.
Sweeping is performed to remove the excess chips from the Sweeping should be started in the center of the pave-
roadway. With adhesion of the aggregate to the binder, sweep- ment and progress to the edges (Seal Coat . . . 2003). Post-
ing commences. Adequate sweeping is crucial to remove the construction sweeping may occur for several days after the
TABLE 9
MINIMUM ROLLING TIME
Traffic Volume (vehicles/lane/day)
Aggregate Size 1,200
[yd2/h (m2/h)]
1/4 in. (57 mm) 4,780 (4,000) 5,975 (5,000) 7,170 (6,000)
3/8 in. (10 mm) 3,585 (3,000) 4,180 (3,500) 5,380 (4,500)
9/16 in. (14 mm) 2,990 (2,500) 3,585 (3,000) 4,180 (3,500)
Source: Bituminous . . . 2003.
