How the Keyhole Process Works

Step 1 - The Coring Process:

The coring truck or skid steer mounted coring unit, sets up and cores a 12", 18" or 24" diameter hole, up to 22" in depth, through the sidewalk or roadway in just minutes. For a proper reinstatement, the coring unit must be adjustable to ensure that the core is cut perpendicular to the horizon and not the pavement surface. Count on a coring rate of around 1" per minute through asphalt, concrete, or composite pavements.

Minicor coring attachment

Series 500 Coring Truck

MD-200 Coring Truck

Step 2 - The Coring Process:

Using a specially designed Utilicor core puller, which securely holds the core through the center pilot hole that was simultaneously cut during the coring process, the core is extracted from the roadway and safely set aside for future reinstatement.

Remove core

Set core to the side

Step 3 - Vacuum excavation, repair and backfill:

With clear access through the hard surface, vacuum excavation to expose the infrastructure and subsequent repair or inspection portion of the work can now go ahead. Once this done, the hole is backfilled and compacted an inch or two below the base of the pavement using either native fill or engineered fill (as per your local municipal specifications / standards) and the core is readied for reinstatement.

Vacuum

Repair or inspect

Backfill and compact

Step 4 - Core Reinstatement - dry fit:

To ensure a level fit and compensate for any irregularities on the bottom of the core, add an inch or so layer of pea gravel to the bottom of the hole and using the core itself, tamp it down so that the top of the core is level with the pavement and about half an inch below the surface. If it is not, adjust the layer of pea gravel. This is called "dry-fitting" and is a very important step in reinstating the core. Once the core is level with the roadway, remove the core, and set it aside.

Level base and pea gravel

Step 5 - Mixing the Utilibond:

Fill the empty Utilibond pail with clean water to the bottom of the line marked on the outside of the Utilibond pail (precisely 2 Litres of clean water for 44 lb. of dry Utilibond powder), or use the one litre container found in the Twin Pack size to add one or two litres of water depending on the thickness and diameter of the core to be reinstated. (Refer to Twin Pack instructions for more information. Click HERE to download the Utilibond Twin Pack   ). InstructionsGradually add in dry Utilibond powder to the water and mix with an Utilicor recommended mixing paddle, powered by a hand held 1/2" chuck drill. Mix for 2-3 minutes, or until you get a smooth "pancake batter" consistency with no lumps.

Mix Utilibond

Step 6 - Pouring Utilibond:

Carefully pour the Utilibond bonding compound slowly into the hole, in a way that does not to disturb the bed of pea gravel used to level the core.

Pour Utilibond

Step 7 - Reinserting the Core:

Using the core puller, slowly lower the core into the hole, making sure to allow the Utilibond to flow up around the entire core (the kerf area). By gently rocking the core back and forth and applying gentle downward pressure, you will force the Utilibond to ooze up through the kerf to completely surround the core.

Once the Utilibond has flown up around the complete circumference of the core, remove the core puller and the remaining Utilibond will come out through the center pilot hole as you carefully level the surface of the core to the existing pavement. Slowly and gently does it.

Clean up excess Utilibond from the road surface using a flat 8" trowel.

Make sure that you do not press the core below the surface of the road or you will have to start all over again.  Clean up any excess Utilibond around the hole with the trowel, and using a soft, wet, plasterer’s brush carefully smooth out the surface of the joint.

Insert core

Push down until level

Wiping down top of core

Step 8 - Clean Up:

After 15-20 minutes (at 70° F) the area is ready for an initial power washing. Do not apply direct spray to the kerf or the center pilot hole, to avoid washing out the Utilibond, but do wash away all the excess Utilibond on the paved surfaces adjacent. Wash all tools immediately after using.

Wash site

Step 9 - Virtually Invisible Repair Completed!

After 30 minutes (at 70° F) the Utilibond will have reached its full strength gain capable of supporting a single wheel load of more than 50,000 lbs (5 times the AASHTO H-25 Standard) and the roadway can be safely re-opened to traffic.

After the repair is complete the reinstatement is virtually invisible, and the roadway has been restored to its pre excavation strength and load sharing abilities in accordance with its original design.

The repair is both permanent and final.

Perfectly reinstated roadway