Roller Compacted Concrete

Roller-compacted concrete (RCC), which gets its name from the way it is made, is a type of concrete that does not slump when it is still wet. ACI 207.5R says that it is concrete that has been pressed down with a roller.

This would ensure good consolidation, which is important for getting the right density, strength (compressive strength can be more than 60MPa), smoothness, and surface texture. Roller-compacted concrete is made without joints, forms, finishing, steel reinforcement, or dowels.

Because of these things, roller-compacted concrete is easy, quick, and cheap to use. Roller-compacted concrete is often cheaper because it is built quickly and in large quantities.

RCC is used now when strength, durability, and cost are the most important factors. It is used to build dams, roads, airfields, parking lots, power plants, road shoulders, storage facilities, military bases, and other industrial complexes, and to fix them up. Depending on how thick and wide the installation is supposed to be, the concrete can be put down very quickly—from 60 to 120 meters per hour.

Placement, Production, and Materials

Roller-compacted concrete is made up of the same basic ingredients as traditional concrete: cement, water, and aggregates like gravel or crushed stone. Unlike traditional concrete, however, the mixture is drier and sufficiently stiff to be compacted by a vibratory roller.

RCC mix designs typically include a high percentage of stone, Portland cement with a fly ash replacement, a small amount of sand, and, of course, water to hydrate the mix.

The roller compacted concrete mixture must be dry enough to prevent the vibratory roller equipment from sinking, but wet enough to allow adequate distribution of the binder mortar in concrete during the mixing and vibratory compaction operations.

Earth and rockfill construction equipment are used to transport, place, and compact roller compacted concrete.

Preparation of Roller Compacted Concrete

• Using the right size and number of tools to meet the needs of the construction.
• On the construction site, make sure there is backup equipment.
• Sequence construction operations, such as access and routing for equipment, air and water support system, foundation preparation and joint treatment, setting up forms or precast work, setting up line and grade control, placing conventional concrete at contacts or in facings, and placing bedding mortar. The work of placing, spreading, and compacting RCC should be interrupted as little as possible by these tasks.

RCC placement

Roller compacted concrete mixture should be fresh at the time of compaction to achieve the best compaction results.

The bond between roller-compacted concrete lifts should be ensured by cleaning the lift surface, maintaining surface moisture, and using a bonding mixture such as fluid bedding mortar or concrete.

When placing the concrete mixture, it should be compacted and spread in a uniform lift thickness. Most rolling procedures begin with a static pass to even out the loosely placed concrete, followed by the application of the vibratory roller.

Number of Passes of Rollers

Before beginning construction work in the test section, the required number of passes must be specified. The number of passes required to achieve the desired density for the mixture within a given moisture content range should be correlated with the concrete placement.

Process of Compaction

Roller-compacted concrete should be compacted 15 minutes after placement and 45 minutes after mixing.

Concrete should be placed continuously from one dam abutment to the next. The following list should be placed on top of the previous lift.

High-Consistency Reinforced Concrete Compaction

A 10-ton dual drum roller can compact RCC with a Vibe consistency of 15 to 20 s in about 6 passes. A 30 cm thick loose lift of RCC will lose around 2.5 cm thickness at this consistency.

The density of the RCC increases dramatically after four to six passes but decreases slightly with additional passes. This is due to a rebound from the top surface behind the roller. One hour after the initial compaction, the surface can be tightened with static roller compaction.

RCC Low Consistency Compaction

RCC mixture with little or no measurement Vibe consistency necessitates more than six vibration roller passes to adequately compact. Concrete density may level out without a distinct peak.

At the end of the compaction process, the roller may bounce off the surface and fracture aggregate on the top surface. This demonstrates contacting particles rather than cement paste between them.

Sequence of Compaction

The roller operator must develop a rolling sequence based on the width of the RCC lift and placement sequence.

When placing and spreading a loose lane, the roller should keep a minimum distance of 15 cm to 30 cm from the lane’s edge.

The uncompacted portion will be compacted in conjunction with the adjacent lane.

Joints in construction

If the placement of RCC is interrupted before the completion of a lift due to plant or equipment failure, roll down and compact the loose material along the edge of the lift on a slope.

This compacted material is treated as a construction joint, and it should be cleaned of any loose material before being covered with RCC to finish the unfinished lift.

Application of Small-Sized Compaction Equipment

Due to inaccessibility, lack of restraint, and safety of unformed places such as upstream facing, etc., some dam structures cannot be compacted with large compaction machinery.

Small compaction equipment, such as a tamper, small roller, or a backhoe-mounted plate vibrator, is appropriate for RCC compaction in this situation. Small-size compaction equipment is required in the following areas of the dam project:

The area along the downstream and upstream sides.

• Adjacent to diversion and outlet works, as well as other conduits
• Dam foundation and abutment closure zones
• Localized compaction is used to repair lift surfaces that have been damaged by equipment operation.
• Around an instrument or another embedded item

Advantages Roller Compacted Concrete

The main advantage is reduced cost and time for construction (cost-effective and Fast construction). so, it can achieve high quality in terms of strength, durability, and surface finish at the relatively low device and personnel costs.

• Resistance to shoving and pushing
• Minimal maintenance required
• No rutting
• No pot holes
• Resistance to oil spills, fuels and/or hydraulic fluids
• Formwork costs are minimized or eliminated because of the layer placement method.
• Rebar is not required
• High Volume Placement
• It does not deform under heavy, concentrated loads
• Span soft localized subgrades
• Can withstand high temperatures
• Reduce cement consumption as the leaner concrete mix can be used.
• No concerns about high heat release while the concrete is drying

The cost of transporting, placement, and compaction of concrete are minimized because concrete can be hauled by dump trucks; spread by bulldozers, and compacted by vibratory rollers.

Disadvantages Roller Compacted Concrete

• Although it is used to efficiently design RCC dams to be the least expensive alternative to other types of dams, there are some conditions that may make RCC more expensive.
• When aggregate material is not reasonably available, the foundation rock is of poor quality or not close to the surface, or foundation conditions can lead to excessive differential settlement, RCC may not be appropriate.
• Dams repaired or built with roller-compacted concrete may experience water seepage. As a result, water stoppage layers must be considered.

FAQs

What precisely is roller-compacted concrete?

Roller-compacted concrete (RCC) is a type of concrete that can support a roller while being compacted in its unhardened state.

What is the significance of planning and preparation in the effectiveness of roller-compacted concrete?

RCC placement and compaction is a fast-paced construction process, so its success is dependent on pre-construction planning and coordination of all interrelated activities.

What types of machinery are used to compact roller-compacted concrete?

In most cases, static rollers are used to compact RCC lifts first, followed by a vibratory roller to complete the compaction process.
Because large-sized machinery cannot access the area or may damage the conduits, inaccessible areas in dam projects, such as those near abutments and around conduits, must be compacted with small-sized compaction equipment.