Timing is critical in preventive maintenance,
as "preventive maintenance is a program strategy
intended to arrest light deterioration, retard progressive
failures, and reduce the need for corrective maintenance
and service activities."[N]
Preventive strategies for flexible pavements include
seal coats such as chip seals, slurry seals, micro
surfacing, thin overlays, and crack sealing. Rubberized
asphalt concrete (RAC) usage can extend pavement life
and help to address waste and landfill issues while
providing a smoother ride, better resistance to cracking
than other types of pavement surfaces, and less frequent
maintenance. In addition, RAC has the potential to
reduce noise levels to a point where a soundwall may
not be needed in some locations. Preventative maintenance
(PM) treatments for concrete pavements include crack
and joint sealing, dowel bar retrofit, partial depth
slab repairs, and diamond grinding for smoothness and
improved pavement texture. All of these treatments
reduce the amount of water that may infiltrate the
pavement, slow the rate of deterioration, or correct
surface roughness. Timely application can maintain
or extend a pavements service life five to ten years
or longer before significant maintenance effort is
required. Surface treatments also help prevent raveling
and improve surface friction properties, but can accelerate
vapor action and stripping when applied to aged and
open pavements.[N]
Caltrans determined that for every $1 spent on Preventative
Maintenance or Capital Preventative Maintenance (CAPM),
$3 to $20 is saved if the treatment is applied at the
right time, before the pavement deteriorates into a
major rehabilitation or reconstruction project. In
addition, reconstruction in urban areas is more expensive.
Instead of the estimated $200,000 per lane mile, the
costs may exceed $1 million per lane mile. In contrast,
a PM strategy will typically cost $50,000 to $100,000
per lane mile, covering many more miles for the equivalent
dollar. A significant savings for PM comes from a reduction
in time spent in design and construction. Prior to
PM, for example, Caltrans did as much Corrective Major
Maintenance as the limited budget allowed until full
rehabilitation, or, in the worst-case, reconstruction
was needed. Time spent waiting until the pavement can
by fully rehabilitated allows time for the pavement
condition to deteriorate further. Since PM projects
are pavement only, they require less design time and
can be delivered faster. During construction, pavement
surfaces are renovated, using thinner treatments, which
contributes to faster production rates. Also, less
construction working days reduces the disruption to
the traveling public and less disturbance to roadside
environments.[N]
The factors affecting pavement life include a variety
of site conditions, including traffic, climate, and
paving material. Condition surveys help predict the
occurrence of distress (including density of cracking
and the average level of crack edge deterioration),
select appropriate maintenance, and program such activities
before further deterioration occurs. When crack densities
are low to moderate, crack sealing is effective; however,
as densities progress from moderate to high, surface
treatments are more effective. There are three basic
techniques for surface treatment of cracked pavements:
slurry, chip seals, and thin hot mix overlays. Selection
of the best treatment is a function of the existing
pavement condition. Results from the Strategic Highway
Research Program (SHRP) suggest the following: [N]
- Slurry seals perform best when applied to pavements
with little or no cracking.
- Chip seals perform well on cracked pavements, but
add no structure and do not improve rideability.
- Thin hot mix overlays perform better than other
treatments on pavements with higher roughness and/or
rutting. They are also effective as a seal, and they
prevent raveling.
The Federation of Canadian Municipalities and the
Canadian National Research Council also have developed Guidelines
for Sealing and Filling Cracks in Asphalt Concrete
Pavement: A Best Practice by the National Guide to
Sustainable Municipal Infrastructure. Other publications
included in their National Guide are Timely
Preventive Maintenance for Municipal Roads, a primer
on preventative maintenance methods, setting priorities,
and cost analysis; Priority
Planning and Budgeting Process for Pavement Maintenance
and Rehabilitation, a n eight-step approach to
budgeting and timely maintenance; and Alberta Transportation's Guidelines
for Assessing Pavement Preservation Strategies.
Pavement management systems have helped DOTs prioritize
improvements and document the cost-effectiveness of
preventative maintenance. In a shift to a more pro-active
road maintenance strategy, Nevada DOT is prioritizing
projects based on how quickly roads are deteriorating
or prediction models, not on the basis of their current
condition. Prevention strategies are ranked by life-cycle
cost, not initial cost. NDOT deployed cold-in-place
recycling based on a sophisticated lifecycle cost comparison;
the state optimized its projects by assigning roads
to five categories based on volume and environmental
conditions. [N]
Caltrans is among the state DOTs publishing a State
of the Pavement Survey. Pavement condition is evaluated
using ride score (IRI) and the pavement surface condition.
The PMS provides a systematic, objective evaluation
of pavement condition for identification of maintenance
and rehabilitation needs and projects, and then prioritization
of those projects. The tool can help a DOT track progress
toward reducing total pavement needs to specified target
levels as well as in improving pavement conditions
overall.
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