Infrastructure is an obligation and an opportunity. It’s an obligation because we can’t live without it and an opportunity since there is always room for improvement. Of the many forms of infrastructure, paved surfaces – roads, bridges, parking lots, industrial yards – might be the least likely place to look for opportunity until you consider that low-maintenance longevity is almost always a top priority for the infrastructure investor. When it comes to durability, ease of maintenance, and uniformity of finished product, concrete is hard to beat. Yet our insistence on innovation persists.
“The majority of the paved surfaces in the world are asphalt, followed by conventional concrete,” begins Greg Halsted, Senior Director of Local Paving at the National Ready Mixed Concrete Association (NRMCA). Halsted has 39 years of heavy civil infrastructure experience across a career that includes roles with the Georgia Department of Transportation, The Portland Cement Association (PCA), and the Concrete Reinforcing Steel Institute (CRSI) before joining the NRMCA in 2023. Founded in 1930, the NRMCA supports the expansion and improvement of the ready-mixed concrete industry through leadership, advocacy, workforce development, and concrete technology advancements. “As a pavement engineer, I like the idea of coming up with pavement solutions that address specific situational needs while also being very durable and sustainable. Roller-compacted concrete (RCC) is now widely accepted and gaining ground on asphalt in the paving world and rightfully so.”
RCC uses the same basic ingredients as conventional concrete – cement, water, and aggregates – but does so in a drier mix more like damp aggregate than a slurry. RCC can also contain supplementary cementitious materials (SCMs) such as fly ash and slag cement as well as chemical admixtures that enhance the material’s fresh and hardened properties.
“RCC is a zero-slump – some even say a negative-slump – concrete that is consolidated by compacting it with vibratory rollers similar to paving asphalt,” says Halsted. “It is placed quickly because of its high production rates and the absence of formwork and reinforcing steel. It requires a lot less labor, as well as fewer types of equipment and materials to lay down. RCC’s durability is basically identical to conventional concrete. So, having it last for 40 to 60 years with minimal maintenance would not be uncommon.”
RCC was introduced commercially in the 1970s when the Canadian logging industry started engaging in environmentally cleaner, land-based log sorting methods requiring ultra-strong pavement to stand up to massive loads and specialized equipment. In a sense, RCC is the best of both worlds - the durability of concrete with asphalt’s ease of application. However, as Halsted points out, placement requires precise experience, specialized equipment, and ingrained attention to detail.
“People often ask if RCC is hard to place. My honest answer is ‘Not for people who know what they are doing,” Halsted says. Paving RCC involves placing equipment and techniques similar to those involved in paving asphalt, which helps to make RCC very competitive on a first-cost basis in many markets. Factoring in its durability and minimal maintenance requirements, RCC is the lower-cost paving material over its service life. Whereas much of the world is paved in asphalt, affording opportunities to many contractors of varying expertise, little of the world is paved in RCC. Best practices demand RCC-specific equipment and expertise in both concrete and asphalt paving.
Bridging the gap between progress and process, Halsted is joined in this conversation by Corey Zollinger, Chairman of the RCC Pavement Council, a volunteer-led industry trade association founded in 2014. A civil engineer by training, Zollinger and the Council are concentrating on increasing RCC’s market share by growing workforce expertise.
“The most critical element in the decision to use RCC is hiring a contractor who has the equipment, experience, and knowledgeable personnel this material requires,” says Zollinger. The Council’s members include contractors, engineers, and equipment and material suppliers. Membership tiers include Contractors, Contractors-in-Training, Associates, and Allies. “The biggest challenge with RCC is the learning curve. Our Contractor-in-Training program is open to businesses that have five RCC projects or less or may not have all the equipment or personnel in-house.”
Zollinger advises any pavement or concrete contractors thinking of adding RCC to their arsenal to join the Council and take advantage of the training, experience, and network of resources required to make RCC operationally efficient.
“There is no learning on the job. If you are new to this, it is going to take an investment. That’s not only money but your brain and your heart too,” says Zollinger, the son of a concrete pavement professor who cut his teeth in the industry as a soils lab technician. “RCC is not a forgiving material. As a no-slump concrete, there is no top-to-bottom movement. You must pay close attention to the mix design in production and placement requires high-density compaction pavers and vibratory rollers. RCC is compacted to a natural finish that looks like asphalt. It can be power-troweled or given a broom finish if desired. It is then sprayed with a curing compound that allows the concrete to maintain water content while it gains strength at an appropriate rate.”
Operationally, RCC’s advantage over conventional concrete is the speed of placement. Without formwork and reinforcing steel as part of the equation, pavers need little more than a string line to follow to lay down the surface. Because of RCC’s density, contractors can allow light traffic to cross it relatively soon after it is placed, meaning homeowners can access their driveways during construction.
“RCC will achieve 2,500 psi or more in three days, and it can be opened to traffic shortly after placement,” says Zollinger of a benefit that increases RCC’s appeal as a municipal roadway in urban areas. “We have seen instances where a major intersection was being paved at 10:30 in the morning and opened to traffic by 5 o’clock.”
As a trade association, the RCC Pavement Council strives to provide the leadership, resources, and direction the industry needs. As such, Zollinger and his colleagues are developing an amalgamated Environmental Product Declaration (EPD) based on member data from across a wide range of industry averages.
“Among pavements, due to the much lower cementitious content, RCC is less carbon intensive than either conventional concrete or asphalt,” finishes Zollinger. “Using sustainable building materials is important for owners. The EPD will demonstrate RCC’s sustainable advantages over conventional concrete or asphalt.”
Halsted agrees and stresses the importance of choosing the right pavement for functional needs and specific conditions.
“At this point, owners developing projects involving pavement should think of RCC pavement as an option along with asphalt and conventional concrete,” he says. “For example, an industrial lot requiring 14 inches of asphalt may only require 8 inches of RCC. That’s a big difference. When you consider the longevity of the pavement, RCC is far superior in the cost/benefit analysis.”
As for detractors, beyond some first costs and the need for highly experienced RCC contractors, the main knock against RCC pavement to this point has been surface smoothness.
“Fifteen years ago, RCC wasn’t being paved to the same level of smoothness as conventional concrete,” continues Halsted who is the Chair of the American Concrete Institute’s (ACI) Committee 327 to update the Guide to Roller Compacted Concrete Pavements. Meant to provide owners, contractors, material suppliers, and others with a thorough introduction to RCC, the Committee is working on documenting key changes in RCC science since the Guide’s original 2015 release (see inset). “For quite a long time now, RCC has been used to pave surfaces that support high traffic and heavy loads. With innovations in aggregate mixtures, compaction equipment, and additives, RCC is being used for DOT projects, regular parking lots, municipal roads, and even small applications like a golf course cart path. Just like any quality building material, RCC has gotten better over time.”
