As airports become increasingly busy, runway maintenance becomes more urgent - while, at the same time, closing runways for carrying out repairs gets more inconvenient.
Thus, the use of any materials that extend the maintenance schedule carries a great advantage. MacPave offers the possibility of substantially reducing the rate of runway deterioration caused by cracks in the asphalt overlays or reflective stemming from concrete joints. Such joints will often be reflected through new asphalt overlays within 1 - 2 years and expensive and time-consuming repairs will be needed.
MacPave offers a way of watersealing and closing the potential crack, the concrete blocks constituting an excellent base.
As increasingly larger aircraft become more common, wheel pressure on runways and taxiways likewise increases and can result in disturbed concrete blocks, compounded by water penetrating through cracks and flushing out the underlying gravel. A well-compacted subbase has become a high priority.
The in-service demands on a runway surface again differ from those on a roadway. The severest loading takes place when an aircraft is at the end of a runway awaiting take-off. (Some military airports, especially those used by cargo planes, tankers, bombers, etc., double their paving thickness at the ends of runways to compensate.)
The tugs that pull some planes into position often put more strain on the surface than the plane itself. Load release at take-off, and even more, impact loading on landing, impose stresses that are unknown on most highways. The MacPave mastic is sandwiched between layers of polyester fabric, one woven to add strength, energy absorption, resilience and stability to the system. Not only does the stress-relief inter-layer provide a durable protective covering over cracks in asphalt or concrete, it also prevents extension of the crack and water penetration to the runway/roadbed.
Macpave requires no special adhesive but can be installed with routine AC 20 or B 85-100 tack coat adhesive. The use of a stress-relief inter-layer for both types is to keep reflective cracking to a bare minimum and delay the redevelopment of cracks for as long as possible, thus providing substantial savings in maintenance costs.
An important Swedish development is a special concrete that can be injected under the blocks to stabilize the foundation. This has proved more enduring than bitumen oil. What is more, aircraft can continue to use the runway or taxiway while repairs proceed.
MacPave membrane is advantageously installed at night. As soon as the tackcoat is cured, aircraft, even loaded jumbojets, can use the runway for up to a week before the final asphalt paving. A wider MacPave membrane than that used for highways and roads is normally used for airport aprons to compensate for the heavy wheel loading. We also have a special MacPave membrane for laying around manholes.
MacPave has been installed at several airports around the world and has been specified for rapid runway repair for military airfields that could be subject to airstrikes. Studies have shown that a damaged runway could be restored to operation in 1½ hours and used for 10 - 20 days before final repairs are carried out.
Here (left) the cracks have been treated, and the runway is ready for overlaying the asphalt. During this process (overlaying of asphalt), the runway can continue to be used for take-off and landing operations for 14 days without any problems.
When this type of crack happens on a runway (right), stones are often loosened. These have to be removed before overlaying with MacPave.
As you can see, the airport is still under use as the repair is going on. This is the touch-down area, which has been moved in from the end of the runway. This work was done in May of 1990, when this photo was taken. In June of 2002, no cracks had returned - 12 years later. Landvetter Airport is owned and operated by the Swedish Aviation Authority.
For runways, the longest of which is 10 000 feet, temperatures below frezing are normal in many areas from November to April, with annual snowfall rarely less than 40 inches( 1 metre). Conversely, in the summer, the area is subjected to high hummidity and daily peak temperatures up to 100 F. These extremes result in contractions to distances of about two feet in runway length between summer and winter, leading to major longitudinal and transverse cracking problems, some more than three inches (6,5 cm) wide.
In August, the repair began on a 20,000 square foot highly used portion
of runway. A mastic/fabric interlayer system was used to reduce reflective and thermal cracking and moisture intrusion. The system consisted of a dense dimensionally stable mastic sandwiched between two high-strength
geo-textile fabrics. Scheduling the refurbishing project was a major problem. Since aircraft would be taking off and landing from 6 a.m. to 11 p.m. "We looked for a product that could be installed at night and used the next day," said a project supervisor.
The repair process in the repair area was milled, cracks were filled and the geotextile interlayer was placed over the cracks and pavement joints before final hot-mix asphalt was laid. A
hand-propelled dolly was specially designed for uniformly dispensing the interlayer on the milled surfaces. A
test-strip evaluation was completed before actual work began.
Because of traffic, the repair work was performed between 11 p.m. and 6 a.m. in just two nights during the project. Daytime pavement surface temperatures rose to 140 F and rain fell. Despite these obstacles, aircraft were able to land on the prepared runways even before final paving since the interlayer could
not be dislodged once in place.
The aircraft ranged from the biggest Jumbo Jet (he first aircraft in the morning was a freighter from Paris - Boeing 747) to normal sized jets. Four years later, the repair has proved successful, already extending runway life substantially.
REFLECTIVE AND ECONOMICAL TREATMENT
With costs escalating, use increasing and accessibility on the rise, airports, such as municipal, county and government facilities, are constantly facing demands to maintain their facilities with tighter and tighter budgets. A reflective and economical way to treat this problem that plagues different countries' infrastructures - airports and surfaces designed to support traffic - is MacPave, a high-denisity mastic, laminated for extra strength and flexibility and sandwiched between a woven and spun, bound polyester fabric. This tough petrochemical product will not deteriorate under debilitating factors associated with highway or runway conditions caused by the pressure, speed and heat of friction.
1. Both transverse and longitudinal cracks were treated with MacPave strips.
2. Finished application of MacPave before overlays. Note: you can still use the airport for landing and take-off as soon as the application tack has cured. This can be used up to two to three weeks, according to traffic situations. |
3. Cracks were cleaned, edges smoothed out and joint sealing filler placed before mastic material was applied. |
