The Phoenix Kart Racing Association (PKRA) recently finished the first stage its track resurfacing project. The track’s last major asphalt repairs were made in 2002 when the asphalt was completely removed and new asphalt was paved. Since 2002 the track’s surface began showing signs of fatigue cracking, and raveling in many areas along the track. The track also had some bumpy areas which posed a safety hazard, and also three concrete sections placed inside turns from a previous repair which had less than desirable grip for the karts. These were the areas focused on when the track’s resurfacing project began.
A racetrack has very different requirements from a regular roadway because of:
- High G forces in turns
- Very sticky tire compounds
- High pavement temperatures
- A smooth, non polishing surface for low non suspension karts
The asphalt needed to meet theses challenging requirements must be:
- Fine crushed aggregate for a smooth surface and good grip
- Stiff asphalt to hold the aggregate together. “Raveling” is a major failure on racetracks because the soft tires pull the aggregate out of the pavement.
- Performance grade asphalt to withstand the high temperatures
- Asphalt rich mix for low air voids, durability, and fatigue life.
Paving Work Schedule
Ace Asphalt conducted the work and the engineering firm “Speedie and Associates” provided on-site quality control and testing, and also, off-site lab testing. The work schedule included:
- Remove and replace asphalt near turn nine
- Increase the radius of turn four
- Profile grade high areas and seal existing cracks
- Thoroughly clean the track
- Spray entire track with an asphalt tack emulsion
- Pave the entire track with an average 1.5 inch compacted hot mix asphalt (HMA)
Day 1: Remove and Replace
- Cut and remove a one hundred foot section near the beginning of turn nine (clockwise direction) known as the “ski jump”. This bumpy section had a very poor sub grade and several feet of dirt was removed and replaced with an aggregate base coat (ABC) material to help stiffen the underlying ground.
- Established the desired grade profile of the removed section using three dimensional surveying. The profile was a challenge because it meets at the apex of a hill that leads into a slight banked turn. An adjoining banked turn also meets in the same area. There wasn’t a single distinct grade profile that could be matched and the profile needed to be blended to match the three distinct grades. This area is simply a characteristic of the track and will challenge the drivers.
- Remove the curbing of and widen turn four known as the “Rib Buster”. The curbing in turn four was part of the reason the corner was bumpy and removing and replacing it was necessary to correct the problem. Since the curb was being replaced, the opportunity to create a passing zone and increase the speed of the turn presented itself. Therefore, the turn was widened about five feet and a four inch aggregate base coat was placed in it.
- Areas of the track were profile graded to remove high areas, and also to tie in the entry and exit of the track using an asphalt milling machine.
Day 2: Intermediate Paving and Crack Filling
- A four inch base coat of a 3/4 inch hot mix asphalt (HMA) was placed as a base coat to bridge the removed section near turn nine.
- A four inch base coat of a 3/4 inch hot mix asphalt (HMA) was placed as a base coat to the widened area of turn four.
- Large cracks were filled with fine sand in preparation for the overlays. Using a geo-textile fabric over the cracks was proposed, however the cost outweighed the benefit. Even with the fabric, over time, reflective cracking from the underlying cracks will show through. Another option was the use of a crack sealant, however these sealants have a tendency to raise the asphalt and create a bump when a hot mix asphalt is overlaid on top of them, which was planned. Therefore, simply filling the cracks with sand was the best choice for this project. Crack sealing is part of an ongoing preventative maintenance program and in time, the track will need to be crack sealed.
- The track was thoroughly cleaned using a mechanical brush and air blower.
Day 3: Tack Emulsion and Paving
- The track was sprayed with an asphalt emulsion which serves as a binder to prevent the overlays from shifting along the old asphalt base. Asphalt emulsion is asphalt mixed with water and a surfactant. This allows the asphalt to be sprayed at low temperatures. When the water in the emulsion evaporates, the surface is extremely tacky and when the hot asphalt overlay is placed over it, a strong bond is formed.
- A high grade asphalt mix, engineered to meet our needs, was overlaid on the existing asphalt. The mix design was chosen by an independent engineering firm “Speedie and Associates”. The engineers provided on-site quality control and testing, as well as, off-site laboratory testing of asphalt samples.
- The existing asphalt was in good condition and served very well as a base substrate for the new overlays. Ace used an Ingersoll Rand PF-3172 highway class paver for the overlays. The paver could lay a 21 foot section and was able to place the asphalt as quickly as the convoy of dump trucks could deliver it. The asphalt crew worked continuously and in concert taking care to avoid seems, bumps, scrapes, or anything else that could mar the finish or upset a kart. Care was taken to blend in the seams and the only cold seam was near the middle of the back straight at the end of day three. Large strait edges were used to manage the seams throughout each pass with the paver. The quality assurance engineer took Nuclear Density Gauge (NDG) readings several times during each paved section. The NDG uses gamma radiation to indirectly measure the density of the HMA when it’s placed. The density reading helps determine if the asphalt was properly compacted during the paving process. Lab test were conducted to ensure the mix met the specifications in the design. The quality assurance engineer also monitored the entire asphalt paving process.
Day 4 Paving Continued
- Paving resumed from the back straight and finished up with the completion of the oval staging area. The track was inspected and some small areas were manicured to ensure the smoothest surface possible.
- Several areas of the track have a high edge, up to four inches in some places. Dirt will need to be back filled to support these edges and also make the track safer if a kart departs the prepared surface.
- The track will also need to be striped
- The curbing will need to be addressed later on and new curbs poured in some areas.
- A preventative maintenance program will need to be developed to ensure a long lasting, smooth track.
Attention to every detail was made to ensure the highest quality the club could afford. Track safety was the primary goal, followed by achieving the smoothest and fastest track possible for everyone’s enjoyment. No track is perfect, and ours will be no exception, however we believe we have achieved our goals. The track is smooth, bumps have been removed, and a high quality, long lasting pavement was placed over it, ensuring a great track for many more years. This has been a very long process and a lot of care went into getting this project right. This was money well spent, money saved by the members and money returned to the members in the form of a like new track. Every member of PKRA should be proud of their contribution to help make this track and this club the finest kart racing club in the United States!