4 INCH CONCRETE OVERLAY

The Strata Corporation Gomaco slip-form paver sits waiting for the first mix
to arrive to construct the 4" concrete overlay on the Main Entrance Road to
Camp Grafton.

Ready Mix came to the rescue for this 4" concrete overlay project at the North Dakota National Guard Camp Grafton near Devils Lake. Paving was started around 10:30 a.m. on Tuesday, August 31st. At a production of 27 feet of pavement per 9 cubic yard load of concrete, about 900 c.y. of concrete provided 2700 l.f. of pavement by 7 p.m. that evening.

The contractor on the project was Strata Corporation - Construction Division with ready mix supplied by the Strata plant located in Devils Lake. This is the thinnest pavement the Strata group has ever paved, so there were some concerns prior to start of paving. However, within 100 feet of placement from the paving header, worries disappeared and production was at full speed.

Ready Mix Concrete is dumped in front of the paver on the milled
asphalt surface.

The overlay project was constructed on the main entrance road to Camp Grafton located on the southeast side of the main facility. Paving started at the northwest end of the project on the main base and proceeded south, with mix delivered through the alternate north camp gate. After the paving train rounded the corner and started east, the mix was delivered through the main gate. The second day of slip-form paving was on Wednesday, September 8th, with remaining pours being hand pours for fill-ins and driveway extensions.

The overlay was constructed on a milled surface on 20 year old asphalt varying from 5 to 9 inches in thickness. The milling operation removed anywhere from just scratching the surface to 1.5 inches of the pavement surface depth in order to provide a suitable surface for concrete bonding and to ensure uniform thickness control of concrete material quantities. Project was bid with cubic yard and square yard bid items. A 15% overrun was allowed for the cubic yard quantities.

Some of the paving crew members from left to right: Duane Hulst,
Lance Allard, Billy Lubitz, Stuart Henry, Shawn Hall, Tomas Flores, and
Greg Parisien on the paver.

The overlay was designed for moderate truck traffic conditions. The overlay was necessary due to the deteriorating condition of the asphalt, including depressed cracks and alligator cracking. Some alligator cracking was patched prior to milling, but other weak areas were left to be covered with the concrete.

Based on concrete removal operations at the header, a very good bond was achieved, as the failure plane at removal of concrete was in the asphalt, not at the material interface. Combining the thin concrete overlay with the old asphalt now provides a very substantial pavement section which will handle expected truck traffic and last for years.

Saws await sufficient strength gain to start the 6' by 6' sawing pattern
for the thin overlay. New pavement is in background.

Mixes for the project were typical NDDOT paving mixes with well graded aggregates, 564 lbs of cementitious, but with 20% direct replacement of cement with fly ash for fall paving conditions instead of the normal 29% replacement.

One week after the first day paving operations, only a few joints had cracked. Cracks were noted about every 7 joints or 42 feet. Due to the short 6' joint spacing (normal for concrete overlays), many of the joints will only crack when traffic is placed on the pavement. Consideration was given to leave joints unfilled, but a decision was made to have the joints filled with hot-pour at the completion of the paving work. No widening of joint cuts will be made, but the initial 1/8" sawcuts will be cleaned and filled from top to bottom verses using a backer rod for a concrete seal system.

Mike Baltzer, P.E. and Cale Wegener provided design, construction
engineering and inspection.

The project was designed by Swenson Hagen & Co. Engineers in Bismarck. Mike Baltzer, P.E. is the engineer of record on the project. Cale Wegener was the site engineer and inspector.

For information on concrete overlays, please contact Dave Sethre at the North Dakota Ready Mix & Concrete Products Association at 701-371-4497. Mike Baltzer can be contacted at 701-223-2600.

Paver train reaching the corner of the Main Entrance Road where the pavement turns to go straight east to Highway 20.

Final surface texture of the pavement was provided by a broom mounted on a bridge across the pavement. Speeds on the access road will be less than 40 mph.

Note small balls of mix paste pulled up by the broom. These will readily be removed by aggressive brooming or just by normal traffic wear.

Photo shows typical milling depths at the east end of the project near the Guard House. This area will be removed to the saw cut to provide a thickened edge for the concrete at the asphalt/concrete transition location.

Some alligator cracking will not be removed, but will provide a base for the 4" concrete overlay.

4" Concrete Overlay - 2010