Grooving & Grinding

Grooving & Grinding

By John Roberts, International Grooving & Grinding Association

January/ February 2001

Options for maintaining pavement smoothness at reduced costs

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.