Introduction
Roller compacted concrete (RCC) is best described as a zero slump concrete that can support roller vibrator while being compact. The method developed and demonstrated in 1970 s for gravity dam constructions
RCC has evolved throughout the time due to its low construction cost, easiness in handling, simple method and durability advantages for various types of constructions.
Features of Roller Compacted Concrete
The most important feature in RCC is its dryness of the mix. RCC mix contains all the major ingredients similar to conventional concrete. However, the mix proportions of materials are different. As an example, the water content of the mixture is minimized to prepare a dry mix. Some of the major characteristics are as follows
Low cement content
Since the water content is less in the concrete mix, water to cement ratio (W/C) can maintain similar to conventional concrete (CVC) using much less cement content. Mix designs contain cement 75 kg – 120 kg per concrete cubic meter. This makes RCC a more sustainable construction method because cement holds the highest embodied energy in the production.
High usage of supplementary cementitious materials
Fly ash and granulated blast furnace slag are common supplementary cementitious materials for RCC. Optimizing packing and replacing cement up to 50% will economize the mix design.
Possible with large size aggregates
No need to stick with smaller size aggregates because you don’t have to pump the RCC mix to the site. 63 mm maximum aggregate size is commonly using in the mixes
Economical mix design
As a result of low cement and water contents, RCC mix designs are economical than CVC. Coarse and fine aggregate contents are optimized to achieve the best possible packing. Therefore minimum cement paste is required to fill the volume of the voids.
Low heat of hydration
Hydration heat is less compared to normal concrete (CVC) due to less cement content using. This minimizes the risk of thermal cracks which is ideal for water retaining structures like dams.
Fast construction
With less amount of forms and no reinforcement, this method requires less labor involvement. RCC can place continuously and open for traffic after the final setting time thanks to its dryness. Consequently the most valuable advantage in construction. Dry-mix of RCC can support the roller which is compacting the mix with the help of interlocking of aggregates.
Conventional concrete (CVC) requires time to harden and limits are available to govern the layer heights. Also, continuous placement saves the time taken for layer surface preparation. However, parameters like RCC production rate and setting time of concrete should match with the requirement for continuous work.
Simple construction procedure
Compared to other concreting methods RCC holds a simple construction procedure. Mixes are transported using conveyor belts, dump trucks and laid by the dozers. Concrete compacts using steel drum rollers as in road construction.
Tough and durable
RCC holds good resistance to rutting and ideal to withstand heavy concentrated loads. The mixtures are develop-able to reach even 70 MPa compressive strength. Required time to time maintenance are low with these structures.
Applications of Roller Compacted Concrete
Nowadays RCC is applying in many situations.
- Dam construction
- Sub-base construction of airports, ports and large storage facilities
- Pavement construction
- Parking spaces
Watch out for..
The degree of compaction is very important for the performance of RCC. When compacted poorly RCC may lead to less durable and high seepage. This reduces the design life of the structure and occurs costly repairs. Satisfying the desired compaction requirement is a must in roller compacted concrete.
If the mix contains more air, you can encounter bulging during the compaction. Controlling air entertainment in the mix can solve this problem. Finishing the placement process within the initial setting time ensures a good bond between RCC layers. Otherwise cold joints may appear in the finished work and structure will fail in performing designed capacity. Introducing a mortar layer on the dried surface will make suitable to place the next layer.
Read more about quality control in roller compacted concrete constructions and steps involve in RCC placements.
