July 2002
Roller compacted concrete proves its strength and durability at New Jersey demonstration
Relatively new, roller compacted concrete has earned a reputation for strength and durability, and lived up to its reputation at Kerr Pipe’s heavily-trafficked entranceway at its Folsom plant.
Project Planning
The New Jersey Concrete Promotion Council (NJCPC) joined forces with Kerr Pipe and contractor R.E. Pierson Construction Company to demonstrate 18,000 sq. ft. of roller compacted concrete being placed last December. December is not the typical month to hold a roller compacted demonstration, however a warm fall and a slow start to winter provided perfect conditions for the demonstration scheduled on Dec. 14 — until it rained.
Earlier that week, the weather was sunny and mild in New Jersey, cooperating fully with the demo plans. Seventy registrants, from the DOT and other transportation authorities to county engineers, architects, engineers, and suppliers, were signed up to watch the roller compacted concrete be placed at Kerr Pipe, until plans were foiled by a recalcitrant Mother Nature.
“Roller compacted concrete can be placed in extreme climates, however, rain or even the threat of rain is not one of them,” said Tom Mackleer of Hercules Cement Co. “Excess moisture in the sub-base or on the surface can cause a sharp reduction in this product’s service life.”
Paving team members anxiously watched weather forecasts, looking for an opportunity to do the project. A small weather window opened and the paving team worked very quickly to reschedule the event for the following week.
Tuesday and Wednesday of the following week were ideal for the project to commence; mid-40s with light winds. Preparation and test pours were completed on Tuesday, and the demo was held on Wednesday. Twenty-five of the original 75 registrants came out for the roller compacted concrete demo.
“On the first day, we placed approximately 100 cu. yds. on a section adjacent to the office,” said Mackleer. “We wanted to give R.E. Pierson’s paving crew and Kerr Pipe’s batching personnel a chance to get familiar with the product and determine the quantity of material that could be batched.”
The day of the demonstration proceeded smoothly. The balance of the roller compacted concrete was placed in straight runs 14- to 16-ft. wide. R.E. Pierson’s crew was finished by mid-afternoon.
Concrete mix design
Roller compacted concrete is a zero-slump concrete mixture placed and compacted with the same equipment used for asphalt. For the Kerr Pipe project, the mix design was created by Scott Frantz of Hercules Cement Co. The mix design consisted of 1,725 lbs. of sand, 1,725 lbs. of 3/8-in. aggregate, and 525 lbs. of cement at a 0.42 water/cement ratio.
“After running various mix designs in our lab, this mix design provided the best results,” said Frantz. “It produces a smooth, dense surface that looks very similar to a finished course of asphalt, but can stand up to all types of traffic. Because of its low water-cement ratio, roller compacted concrete typically has compressive strengths greater than conventional concrete at the same cement factor.”
The roller compacted concrete at Kerr was placed at a depth of 7 in. and compacted down to 5 in. with a 10-ton Ingersoll-Rand roller. Immediately after the compacting operation, a concrete curing compound was applied. The roller compacted concrete process requires no additional finishing, as well as no forms, surface texturing, or scaling.
While R.E. Pierson supplied the labor and equipment from their paving crews, Kerr supplied the zero-slump concrete
for the entire project using two Besser mixers located in the central batching plant.
Pavement Performance
Several months later, Mackleer is pleased to report that the roller compacted concrete is performing well. “It is holding up great,” said Mackleer. “The amount of traffic it receives daily is incredible and it gets scraped daily by front-end loaders, but it is performing great.”
Mackleer initially proposed roller compacted concrete for Kerr Pipe because he felt that it was the best product for the area. “Being that Kerr Pipe is a pipe manufacturing facility, it gets a tremendous amount of truck traffic, heavy forklift traffic and industrial grade equipment running on it all the time,” said Mackleer. “During the summer in New Jersey, the asphalt has a tendency to get a little soft when it gets very hot. The turning patterns of the trucks tend to push the asphalt a bit. Roller compacted concrete is used for its strength and durability.”
Rex Busa, of Kerr Pipe and NJCPC, said that he feels the roller compacted concrete is living up to its reputation. “The sheer volume of traffic demands a durable, high-strength, long-lasting product. A minimum of seventy 80,000-lb. dump trucks, pipe trailers, and heavy industrial traffic transverse this location daily. After careful consideration and research, we were convinced the roller compacted concrete would not only meet, but exceed our requirements.”
Because roller compacted concrete could be considered as a hybrid between cement treated granular material and vibrated concrete, roller compacted concrete pavements are able to carry traffic directly on the finished surface. This was a definite bonus to Kerr Pipe, as they were able to have trucks rolling over the project two days after the material was put down.
The roller compacted concrete demo was carried off without a hitch — aside from the weather. The roller compacted concrete entranceway at Kerr Pipe is performing well and living up to its reputation of strength and durability. Mackleer was pleased to participate on the fourth roller compacted concrete project in New Jersey, and added, “Without the cooperation of Kerr Pipe and their willingness to try new and innovative things, we wouldn’t have got it done.”
Information provided by the New Jersey Concrete Promotion Council. Angie Moehlman, assistant editor for AggMan, contributed to this article.