RCC: Roller Compacted Concrete Is Here To Stay
What is roller compacted concrete?
Roller compacted concrete (RCC) is a tough, durable type of concrete pavement that is well suited for heavy industrial applications, as well as low-speed roads and arterial roads. Roller compacted concrete draws its name from the construction practices used to place and finish the material. Similiar to what the industry knows as conventional concrete(stone, sand, cement, and water), RCC however, is composed up of different proportions and placing methods. Roller compacted concrete pavement (RCCP) is a dry mix that is rigid enough to bear the weight of 20 ton rollers and stiff enough to be compacted by high density pavers. The standard means of placing RCCP is by first being placed through a standard or high density paver and subsequently compacted by a non-vibratory or vibratory roller. Most of the time, RCC is constructed without joints, formwork, finishing, steel reinforcement, or dowels. Making a significant economic impact in those areas for the job at hand.
RCC In Indiana
Roller compacted concrete in the State of Indiana has been a very successful application in heavy industrial roads to low speed/light traffic roads. Located in roughly 40 counties (out of Indiana’s 92 counties), from northern Indiana to southern Indiana, RCC usage is rising, with more in the future. Within the last 5 years, Indiana has seen a rise in the produciton of RCC because of it’s proven track record, as well as its other features; like high early strength (we’ve seen anywhere as high as 9000 psi), quicker construction times, and quicker opening times on paving projects. This product is created through the use of local components, produced by local ready mix producers, and applied by local contractors. The selling points of this product can go on and on, just like roller compacted concrete is able to. Take another hard look at this material when durability and longevity are your material needs.
RCC is NOT a new product…
In North America, RCC has been around since the 1960’s and was used primarily in the construction of dams. The use of RCC in dam building became so prevalent through the economic benefits that it brought to that application. Quicker, easier placement methods coupled with lower costs made RCC the standard practice for dam building in the 1960’s and 1970’s. The lower cement content in RCC, compared to that of conventional concrete, enable the construction process to be overhauled due to the lower heat of hydration that occurs in curing of the material. Meaning that one can place more RCC at a time than conventional concrete.
As a pavement application, the durable RCC was again called on for it’s quick placement, high strengths, and lower material costs. The target market of this primitive pavement was the logging industry of Canada and the northern United States. The need at hand was that of a strong pavement capable of bearing severe loads from logging trucks and other specialized equipment. The economic benefits that RCC brought were the perfect fit for the industry, the lower material costs and resources needed for placement helped spring RCC from the logging industry to other industrial applications around the world.
Dating back to the 1970’s, roller compacted concrete has been a successful product and continues to gain momentum in the United States. RCCP is a product that doesn’t fit any and all applications, but does excel when used in heavy load, low speed, and cold weather uses. With the material becoming more and more prominent in the marketplace, there is an increase in the use of RCCP in areas such as; industrial parking, local streets, highway shoulders, as well as other low volume roads. To go along with the above stated, RCCP has entered the urban paving market, with applications like low-maintenence roads, subdivision residential streets, and various other arterial roads. With the use of an asphalt overlay, RCC has been used in trucking roads, highway shoulder rehabilitation, as well as intersection approach lanes.
You have probably read much about the economic benefits that RCC possesses. So what are those benefits? Let’s identify them. Lower material costs. This refers to the lower cement content in RCC than that of conventional concrete, and in conventional concrete, cement is the most expensive ingredient. This is accomplished through the replacement of Portland cement with fly ash. Simpler construction practices. Again, compared to conventional concrete, RCC requires no materials for formwork, calls for no joints or dowels, significantly less manpower for the application, and time saved in opening a recently completed project. Once RCC is rolled and compacted fully, the material is capable of withstanding traffic and bearing stress immediately. Although not recommended, that is where one can save a considerable amount of time in the construction process. High strengths. RCC is one material of great strength and durability. These describing factors are also achieved in a short amount of time. Compressive strenghs for roller compacted concrete can be in the upwards of 9000 psi! The mix design of RCC will usually consist of a high amount of stone, Portland cement with a replacement of fly ash, a minimal amount of sand, and of course, water to hydrate the mix. The drier mix allows a high psi to form much quicker than that of a more fluid, hydrated mix.
RCCP calls for most of the same guidelines and procedures for subgrade preparation as that of conventional concrete pavement. The bottom line is that the subbase should provide sufficient strength throughout the entire thickness of the pavement to support the compaction process. Incorrect subbase preparation can cause inconsistent surface conditions and potentially shorten the life span of the pavement itself. The target density grade of RCCP after it has been compacted is right at 95% of the total compaction. Prior to paving, the subgrade should be adequately moistened, wet but no standing water or puddling, as well as kept free of foreign material like garbage or other debris. There are drawbacks from oversaturating the subbase or having the subgrade too dry. If the subbase is too dry, it can draw moisture from the RCC on top of it, causing improper compaction and a failed product. For a subgrade that is too wet, the RCC can swell and lead to another failed end result. Adequate time should be invested to ensure that the subbase is properly moistened, this is another aspect that can lead to a successful application of RCCP.
Moisture Content of RCC
Moisture content of roller compacted concrete is a vital component that ultimately decides if the material will be a successful application or not. An easy mental image to remember for properly proportioned RCC is a handful of damp gravel. The two variables that moisture content can directly affect to is:
- Adequate compaction
- Long-term performance
Some things to consider regarding moisture content along the construction process are:
- Verify the moisture content of the aggregates prior to mixing
- Monitor the moisture content of RCC on the job site before paving begins
- On the below moisture content curve, one ideally would like to be above the optimum moisture point to compensate for the loss of moisture during transportation and sitting time on the job site. This is another reason why proper planning and preparation are so crucial to the construction process of roller compacted concrete.
There are several results that can be attained from either an RCC mix that is either too wet or too dry. A mix with excessive moisture can lead to:
- Poor compaction
- Continous deformations during compaction
- Adhesion to roller drum, causing more deformed surface textures
The results that can be possible due to a drier mix are:
- Poor compaction
- Segregation of the mixture, leading to a weaker, inconsistent pavement
- Surface raveling, tears, and overall rough, open surface texture
The process of applying RCCP from production to construction to compaction, is one that requires a timely schedule and minimal interruptions. This cannot be said enough, following the basics can attribute to a succesful application of RCCP. To go along with the above stated, there are a few aspects of paving RCCP that one should keep in mind.
- Production rates should match that of paving rates
- Joint(fresh/cold) dimensions should be planned prior to construction
- RCCP should be compacted no longer than 60 minutes after hydration of cement
The compaction times should be noted that these times can vary with variables such as ambient temperatures, wind speed, and retarding/accelerating admixtures. The typical construction process of RCCP includes a typical ready mix concrete batch plant or RCC mixer(for more info see bottom), dump truck for transportation, and the standard “paving train” used for asphalt pavement. Roller compacted concrete can be processed and compacted through a standard asphalt paver or high-density paver. It should be noted that RCC should not and can not be applied through a conventional concrete paver or similar slip-form pavers.
Surface Texture – Note the difference in texture appearance
Below is a photo of a typical surface texture before roller compaction.
Below is a photo of a typical surface texture after roller compaction.
Construction Process Photos
RCC discharged from a transit mixer truck to a dumptruck prior to transporation. Note the “damp gravel” appearance.
Also note the discharge taking place ABOVE the dumptruck.
The “Paving Train”
10-ton roller in action, taking care of the compaction.
Roller compacting the fresh joint.
So there you have it, RCC is a versatile concrete application capable of achieving high early strength and saving the project owner valuable resources. Low cost continues to draw interest from the likes of engineers and owners, but ultimately, the performance has spoken for itself time and time again.
For more detailed information, reach out to the IRMCA;
Jerry Larson – Executive Director firstname.lastname@example.org
Justin Edwards – Promo Manager email@example.com
Jack Weiskittel – Promo Manager firstname.lastname@example.org