by Jon M. Casey

It goes without saying that asphalt pavement is a popular, reliable alternative to concrete pavement for roads, parking lots and sidewalks. Recently, with the increases in the cost of liquid asphalt, which adds significantly to the overall cost of asphalt paving material, consumers are considering bids on projects that can be completed with either material. Thus, for asphalt paving contractors who want to pave with concrete but don’t want to purchase more equipment, Roller Compacted Concrete (RCC) has become the perfect choice. If asphalt paving contractors are looking for new opportunities to bid more work, the addition of RCC to an existing lineup of asphalt paving materials, might be the ideal solution.

For some, it’s like comparing black to white. But for others who have looked into this innovative way of concrete installation, the “white” alternative to “black” paving material makes sense. They realize there are benefits to offering either concrete or asphalt paving to a customer. More importantly, “The Black and White of Paving,” can be profitable as well.

According to Ken Crank, Director of Concrete Promotion for the Pennsylvania Aggregates and Concrete Association, what makes RCC such an easy and desirable consideration is that the two paving applications require the same equipment, manpower and for the most part, the same techniques as conventional asphalt paving jobs. While DOTs and municipal authorities have yet to approve RCC for heavily traveled roadways, the use of RCC for parking lots, access roads and driveways, is becoming more common. Because RCC has the ability to withstand heavier loading than a similar thickness of asphalt paving material, this new, cost-effective alternative gives asphalt paving contractors the ability to bid concrete jobs that they might have otherwise passed up because of equipment considerations.

“Contractors are becoming more aware of how RCC can be used in place of conventional asphalt pavement,” said Crank in a recent conversation with Hard Hat News. “RCC has become a viable alternative in several applications. In Pennsylvania, over the past five years, approximately 40 projects have been completed with nearly 200,000 cubic yards of RCC being placed over that time.”

Crank said what makes RCC a desirable addition to the contractors “tool box” is that it requires no forms, no reinforcing steel and no finishing. Because it is a zero-slump material, consisting of a damp gravel concrete mix, it can be consolidated with vibratory rollers. “It’s concrete pavement, placed in a different way,” he said.

To aid in our “Black and White” discussion, we had the opportunity to attend a demonstration pour of RCC at a PACA workshop held in October 2013 at Center Concrete Company’s Plant 5 facility near Montoursville, PA. A paving crew from Glenn O. Hawbaker, Inc. used a conventional CAT AP600D asphalt paver followed by a Bomag 120D double drum compactor, to pave a prepared portion of the plant’s parking area. The paving was near the batch plant, in a highly-traveled area where equipment regularly travels to and from the loading area. The existing pavement had been removed, with the base graded and ready for concrete to be applied.

The following day, as a job of contrast, Hard Hat News observed an asphalt paving job that took place the following day, on PA Route 74 outside Carlisle, PA. There, as part of a 4.12-mile, $1.5 million paving contract, a Pennsy Supply crew used a CAT AP1000D paver, followed with a Volvo double drum compactor, to resurface this moderately traveled section of suburban highway. The accompanying photos of these two projects reveal the similarities of how the two paving methods could benefit paving contractors and their company’s bottom lines.

Crank said contractors are able to learn application methods quickly because the physical properties of RCC are more like asphalt paving material than conventional concrete pours, but without the high temperatures of hot asphalt mixes. He said the permeability varies with the mix proportions, placement method and degree of compaction.  The compressive strengths run from 4000-9000 psi and the flexural strength is from 450 to 1100 psi. Since the air content is less than two percent, the compacted wet density is 140-160 lb/cf.

“Large projects like the Norfolk Southern intermodal facility in Harrisburg, PA and the Baker-Hughes Distribution Center in Lock Haven, PA have benefitted from RCC,” he said. “Smaller projects like PP&L facilities in Allentown and Montoursville, PA and the Wenger’s Grocery Outlet in Mifflinburg, PA have concrete parking areas in place of asphalt as well. Local road projects like the one in Upper Nazareth Township, PA and the highway shoulder project in PennDOT District 11 near Pittsburgh, have this method of paving moving steadily into the thinking of project designers throughout the area.”

Crank said the materials for RCC are the same as for conventional concrete and can be prepared with existing concrete plants of various kinds. The mixes include coarse and fine aggregates, cementitious materials, water and admixtures. Aggregate selection is important because the choices affect mix workability, segregation issues and ease of consolidation. The mix designs differ from conventional pavements because they are not air-entrained, they have lower water and paste content, larger fine aggregate content with nominal maximum aggregate sizes at approximately 5/8-inch. Also, the w/c ratio runs between 0.3 and 0.45.

He added the current design procedures for parking lots, streets and roads with mixed traffic are found in the ACI 330 and ACI 325.12R tables and on StreetPave software. The Portland Cement Association’s RCC-Pave computer program is a resource as well. Notably, the Army Corps of Engineers approves RCC for single vehicles in similar applications.

Crank concluded by saying that there are loading, transporting and placing techniques common to both asphalt and RCC applications, but a few are somewhat different. Nevertheless these methods are not so different that they would pose a problem for paving crews. So, for paving contractors who are looking for a new way to bid on additional jobs, being able to offer “black and white” paving is the ideal solution. For more information on RCC, visit www.specifyconcrete.org or contact Ken Crank at ken@pacaweb.org.