Roller Compacted Concrete
1. What is Roller Compacted Concrete?
As its name indicates, Roller Compacted Concrete (RCC) is a concrete which uses rollers to consolidate the concrete into a durable surface.
2. How is it different from Conventional Concrete?
RCC has the same basic ingredient as conventional concrete: cement, water, and aggregates.
Also, the method of compaction is different with the RCC being compacted by vibratory or pneumatic-tired rollers.
3. How is the mix for RCC different from the mix of Conventional Concrete?
The objective of mix design is to produce an RCC mixture that has sufficient paste volume to coat the aggregates in the mix and to fill in the voids between them.
Any of the basic RCC proportioning methods like those based on concrete consistency testing, the solid suspension model, the optimal paste volume method, and soil compaction testing may be used for mix design.
Roller-Compacted Concrete (RCC) uses aggregate sizes often found in conventional concrete. However, the blending of aggregates will be different than that done in case of conventional concrete.
Gap-graded mixes that are dominated by two or three aggregate sizes are not desirable for RCC.
The content of fine particles required is typically higher than that of conventional concrete.
Washed aggregates are not required for this type of concrete since a small quantity of non-plastic fines present (2% to 8% material passing a No. 200 sieve) can enhance its properties. This produces a mix that is stable during rolling.
Various Standards /institutes like ACI recommend particular gradings for different roller compacted structures like pavements. Generally use of dense, well-graded blends with a nominal maximum size aggregate (NMSA) not exceeding ¾-inch (19 mm) is recommended in order to help minimize segregation and produce a smooth finished surface.
The moisture content in the mix should be such that the mix is dry enough to support the weight of a vibratory roller yet wet enough to ensure an even distribution of the cement paste.
Compared with conventional concrete, RCC pavement mixes have:
- A lower water content
- A lower paste content
- No air-entrainment, although some admixtures may be used to increase workability and control set time.
- More finer aggregates
- Smaller maximum size coarse aggregate.
4. Does the RCC mix require curing?
Curing is very important for RCC also.
Normally surface of RCC is kept moist for 7 days, or until a curing compound is applied. Due to more open texture surface of RCC, the curing compound application rates are 1.5 to 2 times the application rates used for conventional concrete.
Due to large surface area of structures like RCC pavement curing techniques such as plastic sheeting and wet burlap may not be used due to higher cost involved.
5. Basic Construction Sequence for Roller Compacted Concrete
- Produced in a pug mill or central batch plant
- Transported by dump trucks
- Placed with an asphalt paver : The thickness of layers generally varies from 8” to 10”
- May be compacted by vibratory or pneumatic-tired rollers
6. Performance of Roller Compacted Concrete
The table below (source PCA) illustrates the features & benefits of RCC:
|High flexural strength
(500 to 1000 psi) (3.5 MPa to 7.0 MPa)
|Supports heavy, repetitive loads without failure and spans localized soft subgrade areas, which reduces maintenance costs and down time.|
|High compressive strength (4,000 to 10,000 psi) (28 MPa to 69 MPa)||Withstands high concentrated loads and impacts from heavy industrial, military, and mining applications.|
|High shear strength||Eliminates rutting and subsequent repairs.|
|High density, low absorption||Provides excellent durability, even under freeze-thaw conditions; eliminates seepage through pavement.|
|Low water content, low water/cement ratio||Increases strength, reduces permeability, and enhances durability and resistance to chemical attack.|
|Aggregate interlock||Provides high shear resistance at joints and uncontrolled cracks to prevent vertical displacement or faulting.|
|No steel reinforcing or dowels||Speeds and simplifies construction, reduces costs.|
|No forms or finishing||Speeds construction, reduces cost, minimizes labor.|
|No formed or sawed joints||Speeds construction, reduces cost. (To enhance appearance, joints can be sawn into RCC pavement.)|
|Hard, durable, light-colored surface||Resists abrasion, eliminates need for surface course and reduces cost. The light color reduces lighting requirements for parking and storage areas.|
Photograph on the right is a sample cut from RCC pavement. It is seen that this sample is tightly compacted from top to bottom
- Aesthetics – RCC does not have the same appearance as other types of concrete. It is NOT as pretty and smooth as regular concrete.
- Rougher Surface Texture – The mix design and construction methods that make roller compacted concrete so fast, easy, cheap, and durable also create a surface texture that gives it a characteristic coarse finish.
- Limited to low-speed traffic – Due to the nature of its surface, RCC is not appropriate for all types of traffic. Vehicles traveling at high speeds would experience a bumpy ride. That makes it better for applications where strength and durability are needed instead of speed.
8. Typical application areas
The use of RCC for pavements at industrial facilities such as port and intermodal container terminals is particularly appropriate because of the ability to construct low-cost concrete pavements over large areas; typical applications areas are:
- bulk material storage
- general cargo storage
- container terminals
- road / rail transfer facilities
- Ro-Ro terminals
- truck parks
- tank roads and parking
- sewage sludge stacking
- composting slabs
- Pre-casting yards
Parking Lot made with Roller Compacted Concrete
Container Handling Depot made with Roller Compacted Concrete
Picture Sources: www.watanabesato.co.jp & Mississippi Concrete Industries Association