Grooving & Grinding
By John Roberts, International Grooving & Grinding Association
January/ February 2001
Options for maintaining pavement smoothness at reduced costs
As airport sponsors look for ways to maintain pavement surfaces that are within their operating budgets, others are exploring ways to make that happen. Here, a representative of the Int'l Grooving and Grinding Association shares some insights on developing technologies.
Osan
Air Base in the Republic of Korea is home of the U.S.
Air Force's 7th Air Force command and 51st Fighter Wing.
The main runway was constructed in the 1950s and went
through several modifications, including a concrete
overlay, extension, replacement of a portion of the
keel section, and several major patching contracts.
There was probably some
roughness built in initially, but significant complaints
from pilots began after a major patching contract in
the mid-1980s. Two-thirds of the runway surface on the
east end is 40 years old and has considerable patching.
The bumps were generally less than a half-inch high,
but there were so many that it transmitted considerable
vibration to the aircraft.
One option considered
was total replacement of the runway, or at least the
center 75 feet for the entire runway length. However,
the downtime and cost were prohibitive, so the Air Force
patched the center portion, then diamond-ground a 100-ft.
wide section along the entire runway length.
The diamond grinding process
gently abrades saw cuts through the top surface of the
pavement close enough together so the fins between the
cuts break away, leaving longitudinal lines in a pattern
resembling corduroy.
Following the grinding,
the surface was re-grooved and the joints and cracks
were resealed. The contract allowed 40 calendar days
for total closure, plus 10 nights at the beginning and
30 nights at the end of the contract.
The diamond grinding was
completed in 20-hour shifts by Mass Grinding & Grooving,
McHenry, IL, using one modified Cushion Cut PC 5000-A
grinding machine during the 40-day total closure.
A California profilograph
was used to measure the roughness both before and after
the grinding. The initial profile had test sections
ranging in roughness from 14 inches per mile to as high
as 92 inches per mile. Every test section produced either
a 70 percent improvement or a profile index of less
than seven inches per mile.
Air Force pilots reported
they were very pleased with the end result, noting how
much more control they felt during takeoffs and landings
on the improved runway surface.
History of Diamond Grinding
Diamond grinding was first
used to correct roughness on airfield concrete pavements
in 1956 at Davis Monthan Air Base in Tucson, AZ. A constructed,
16-in. thick taxiway failed to meet the straight-edge
requirements. Rather than remove and replace the pavement,
the high spots were ground with a Concut bumpcutter,
which was invented by Cecil Hatcher for the project.
The project was brought into tolerance at considerable
savings to the paving contractor.
In the more than 44 years
since the advent of grinding and grooving, the process
has been used on numerous airfield surfaces to improve
ride quality and skid resistance. A sampling of other
projects include:
• Davis Monthan Air
Base, Tucson, AZ. (1956). A new portland cement (PCC)
concrete taxiway was ground to meet a straight-edge
test. The project spared the cost of removal and replacement
of major pavement sections.
• Cigli Air Base,
Izmir, Turkey (1962). A 100-ft. wide runway keel section
was ground for a length of 5,000 feet to reduce vibration
damage to surveillance instruments.
• King Khalid Military
City, Saudi Arabia (1982). Blisters were removed from
a new PCC runway and ramp to create a durable, uniform,
damage-free surface.
• Rochester International
Airport, MN. (1992). To restore a 25-year old PCC pavement
on the airport's main runway, grooving and grinding
were used as the final step in this CPR project to extend
pavement life and enhance the high level of service.
• Pittsburgh International
Air-port. (1993). Two runways were relieved of shallow
grooves and minor roughness, thereby improving ride
quality and safety.
• Lahore International
Airport, Pakistan (1994). The keel of the five-year
old main runway was smoothed along a 100x7,000-ft. section.
The process corrected built-in roughness from a PI of
70 to a PI of 10.
• Varna Airport,
Bulgaria (1996). The main runway was smoothed and sealed
to correct roughness from use and initial construction.
• LaGuardia International
Air-port, N.Y. (1997). Shallow grooves and minor roughness
were removed from one runway end to increase safety
and improve ride quality.
In addition to these projects,
hundreds of grinding projects have been completed on
airfield pavements around the world.
Runway Rideability
Runway rideability is
a controversial subject. Many argue there is no proof
that a rough runway compromises safety appreciably.
Still, it would be difficult to find a pilot or airport
owner that would claim any benefits from rough runways.
In highway construction
and rehabilitation, smooth pavements are acknowledged
to be safer, longer lasting, and preferred by road users.
The International Roughness Index (IRI) has been accepted
by many agencies in an attempt to standardize the test
method, if not ride quality, worldwide. Because of the
vast differences in wheel-base and operating speeds
of aircraft and motor vehicles, however, it is illogical
to simply adopt highway standards or test methods.
There are technical task
groups of well-respected, third-party organizations
currently working on the feasibility of requiring a
maximum level of runway rideability for commercial aircraft
operations. Recommenda-tions to the airport/airfield
community are expected in the next few years.
This report was submitted by John Roberts of the International Grooving & Grinding Association, based in Coxsackie, N.Y. The American Concrete Pavement Association, based in Skokie, IL, facilitated its publication.
Benefits of a Smooth Runway
There are many possible benefits associated with smooth runways, according to John Roberts of the International Grooving and Grinding Association. Among them ...
•
Increased passenger safety due to better aircraft
control;
• Increased
life of the runway pavement because of reduced
impact-loading;
• Reduction
in vibration, which can cause damage and errors
in instruments;
• Reduced stopping
distance, based on consistent tire-to-pavement
contact;
• Reduced aircraft
maintenance caused by rollout and takeoff vibrations;
• Less concern
expressed by passengers about aircraft shaking
and associated noise (e.g., overhead bins shaking);
• Increased
pilot and passenger comfort from improved ride
quality.
Many
of the benefits noted apply directly or indirectly
to military operations, too. Two major benefits
that are germane to military aircraft operations
are:
• Reduced "hook
skip" problems when using Basic Aeronautical
Knowledge (BAK) procedures, due to a more regular
runway surface;
• Reduced damage
to surveillance instruments due to vibrations.
Both military and
commercial airport users have responded favorably
to diamond grinding. As we learn more about how
to measure airfield pavement roughness and address
"how rough is too rough," we expect
a significant increase in the use of grooving
and grinding technology on airport runways and
taxiways worldwide.
