Material's Monday
Roller-compacted concrete (RCC)
Roller-compacted concrete (RCC) or Rolled concrete is a special blend of concrete that has essentially the same ingredients as conventional concrete but in different ratios, and increasingly with partial substitution of fly ash for Portland cement. RCC is a mix of cement/fly ash, water, sand, aggregate and common additives, but contains much less water. The produced mix is drier and essentially has no slump. RCC is placed in a manner similar to paving; the material is delivered by dump trucks or conveyors, spread by small bulldozers or specially modified asphalt pavers, and then compacted by vibratory rollers.
Process of Generation and Use of Roller-compacted Concrete
RCC derives its name from the method used to lay it
- Mix – An RCC mixing facility, such as a pug mill, tilt drum, or dry batch ready-mixed plant, must have the efficiency to evenly disperse the relatively small amount of water present in the stiff, dry mix which resembles damp gravel.
- Transport – Dump trucks transport the RCC mix from the plant to the conventional or high-density asphalt pavers.
- Placement – The mix is placed in layers (or lifts) 4-9 inches thick.
- Compaction – Steel drum vibratory rollers are used to compact the concrete.
Compaction is the most important step in RCC construction because it helps in improving density, strength, placement , and helps in rendering a smooth surface texture. The process begins immediately after placement and continues until the pavement meets density requirements. The pavement must be cured to ensure proper strength gain.
Benefits
Sustainability
Roller Compacted Concrete pavements are environmentally friendly. Supplementary cementitious materials such as fly ash and ground granulated blast furnace slag can be used, reducing the amount of Portland cement and thus lowering the embodied energy of a Roller Compacted Concrete mix.
Roller Compacted Concrete’s lighter color provides greater light reflectivity, which means brighter and safer surroundings as well as lower lighting requirements. In fact, Roller Compacted Concrete pavement can reduce energy consumption by as much as 37% by either reducing the number of light fixtures needed or by allowing lower wattage light.
The lighter color of Roller Compacted Concrete also means less heat is absorbed, resulting in cooler communities. Utilizing such lighter colored pavements can reduce ambient air temperatures by as much as 7-10 degrees.
Roller Compacted Concrete pavements have a solar reflectance index (SRI) greater than the minimum 29 that is necessary to obtain the appropriate credits for heat island mitigation – non-roof in the USGBC’s LEED Green Building Rating System.
Speed of Construction
Perhaps the biggest benefit of Roller Compacted Concrete pavement is that it can be constructed more quickly and cost-effectively than conventional concrete or most asphalt pavements. Roller Compacted Concrete is placed with conventional or high-density asphalt-type paving equipment and compacted with rollers, eliminating the need for forming and finishing. In most cases, Roller Compacted Concrete can be completed in one pass. Extremely heavy-duty pavements requiring thicknesses greater than 10 inches may require two lifts. Because of its density and compaction, Roller Compacted Concrete can achieve sufficient load carrying capacity quickly and has, in some instances, been open to traffic within 24 hours after placement
Durability
Roller Compacted Concrete is a rigid pavement which will easily withstand the load from repetitive traffic. Because it can carry heavy loads more evenly, Roller Compacted Concrete will not rut from heavy axle loads, nor will it shove or tear from turning or braking vehicles. Additionally, Roller Compacted Concrete has all of the durability of conventional concrete pavement including resistance to fuels, oils, solvents and other fluids, and the ability to withstand the extremes of summer heat and winter cold. A properly designed Roller Compacted Concrete pavement will easily provide 20+ years of service.
Low Maintenance
Similar to conventional concrete, Roller Compacted Concrete has fewer repairs over its service life. There is no seal coating or resurfacing required. Aside from an occasional cleaning with a sweeper/vacuum, Roller Compacted Concrete maintenance requirements are minimal.
Competitive Cost
There are numerous cost savings associated with Roller Compacted Concrete. Historically, Roller Compacted Concrete has been comparable in cost to asphalt pavement. With rising oil/asphalt costs, Roller Compacted Concrete may actually be lower in initial paving costs. When compared to conventional concrete paving costs, Roller Compacted Concrete can provide savings of 25% to 30%. And owners will appreciate the lower Life-Cycle cost associated with Roller Compacted Concrete’s low maintenance requirements.
Solutions Provided by Roller Compacted Concrete :
- Low initial cost – RCC is competitive with alternative pavement options on a first-cost basis.
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High durability – Resists rutting and will not deform under heavy, concentrated loads.
- Resists deterioration from fuel and hydraulic fluid spills
- Performs well in freeze-thaw climates
- Supports heavy, repetitive loads without failure and spans localized, soft subgrade areas.
- Low maintenance - Fewer associated costs; No need for surface sealing or overlays
- Reduces downtime – Fast return to service and minimizes elevation changes for rehab projects
Applications
Logging Facilities, Composting Areas, and Storage Yards
Roller Compacted Concrete was first used for log handling facilities in Canada in the mid-1970’s. This type of application requires pavement strength and durability to support the heavy loads. Surface appearance, texture, and smoothness are of lesser importance for these applications; therefore, coarser aggregates can be used. Road graders and dozers are sometimes used to place the Roller-Compacted Concrete in the most basic applications.
Ports, Intermodal Facilities, and Heavy Industrial Facilities
Ports and heavy industrial facilities are large, open areas with few obstructions that may delay the construction process, making them ideal candidates for Roller Compacted Concrete. The heavy container handling equipment will often have point loads of 13 ton or higher. Traffic speeds are typically 30 mph or less.
Light Industrial Areas
Similar to heavy industrial areas, light industrial areas, such as warehouse facilities and auto manufacturing facilities, provide large uninterrupted areas that are ideal for Roller Compacted Concrete. Access roads within the industrial complex represent another application for Roller Compacted Concrete.
Local Streets
The speed of construction, economy and early opening to traffic are key reasons to use Roller Compacted Concrete for streets and local roads. In some cases, light traffic has been placed on the Roller Compacted Concrete pavement within 24 hours after construction to accommodate nearby businesses. In addition, using Roller Compacted Concrete for new residential developments provides a strong working platform during site work and construction. Surface treatments can be applied when the development nears completion.
Structural Design
How to Structurally Design Roller Compacted Concrete pavements?
Thickness design for Roller Compacted Concrete pavements employs the same basic strategy as for conventional concrete pavements. The strategy requires keeping the pavement’s flexural stress and fatigue damage caused by wheel loads within allowable limits. In the structural design, the pavement thickness is a function of the expected loads, concrete strength, and characteristics of supporting base and subgrade.
In RCC structural design, the pavement thickness is increased or the strength of the concrete is increased until the stress ratio is reduced sufficiently to provide for adequate fatigue performance.
Since the critical stresses in Roller Compacted Concrete are flexural, fatigue due to flexural stress in used for thickness design. Research has shown that Roller Compacted Concrete exhibits fatigue behavior very similar to that of conventional concrete. Therefore, the same design methodology used for conventional concrete can be applied to Roller Compacted Concrete pavements. The pavement thickness is a factor of the subgrade support, the Roller Compacted Concrete flexural strength and the anticipated vehicle loading.
Software that can be used for the same is RCC-PAVE. The RCC-PAVE program is based on PCA’s manual procedure. It can be used to design a new pavement or analyze an existing pavement. Users can select interior or edge loading and have the options of standard vehicle loading or user-defined loading. Similar to the manual procedure, the software was developed mainly for heavy-duty pavement applications.
