Roller Compacted Concrete For Pavement Applications

Roller Compacted Concrete is an innovative technology gaining popularity in the recent past due to some of the positive points like low cost of construction, speed in construction, and the possibility of using mineral admixtures obtained from industrial wastes like Fly Ash and Ground Granulated Blast furnace Slag (GGBS).

Dr. S. Krishna Rao, Professor and Head - Civil Engineering Department, Vignana Bharathi Institute of Technology, Hyderabad

Roller Compacted Concrete (RCC) has been developed as a new construction material during the 1960s for dam applications. ACI 325.10R defines Roller Compacted Concrete as concrete compacted by vibratory roller. By definition it is simply a concrete mix that has a stiff consistency (Zero Slump) which enables it to spread with a special type of paver and which can be compacted under the wheels of vibratory roller. RCC can be placed without formwork at large production rates and can be considered as more economical than conventional pavement quality concrete which is used in rigid pavement applications.

Material properties of RCC have a wider range of variation than the pavement quality concrete. Ordinary Portland cement of different grades, PPC and PSC, different mineral admixtures like Pulverised fuel Ash, Ground Granulated Blast Furnace Slag etc., and aggregates not satisfying the grading requirement usually for normal or conventional concrete can be used for its preparation. RCC can be used for pavement applications and this new paving method was proposed to be the best cost-effective and durable solution for rigid pavements and similar applications.

Roller Compacted Concrete Pavement (RCCP) material was successfully used in Canada in heavy industrial areas under severe frost conditions. The material had been doing well for carrying heavy traffic wheel loads with low construction cost. After that experience, several advances have been introduced to RCC. Most of these advances are focussed towards improving quality of the surface and durability. Also, an improvement in rideability came when special pavers were employed for placing the RCCP. With the advent of this procedure, RCC now unites the quality of concrete material and the low cost of bitumen and construction procedure of the bituminous pavements.


The low water-cement ratio varying between 0.30 to 0.40 assists in providing very high strengths. RCCP material is placed without formwork, with no surface texturing and no finishing. Hence it can be constructed very rapidly requiring less labour than traditional pavement quality concrete (PQC). With low water content used in the RCC mixture and low water-binder ratio, RCC usually has strengths greater than conventional concrete. To satisfy the economy of construction of RCC over PQC, smoothness and surface quality of RCCP suffer.

Applications
Considering the limitations of the Roller Compacted Concrete, its major application is for industrial pavements such as:

• Industrial access roads
• Parking areas
• Shipping yards and port terminals
• Truck terminals
• Bulk commodity storage yards
• Aircraft Apron
• Urban streets, rural roads and parking paths
• Heavy commercial parking lots (Surface Car Parking)

Advantages
Roller Compacted Concrete Pavement (RCCP) has the following advantages when compared to the conventional pavements.

• It has high flexural and compressive strength.
• Reduction in construction time.
• Little Maintenance costs
• High freeze-thaw durability
• Reduced cracking and shrinking
• Resists abrasion even under heavy traffic loads and volume
• It has more resistance for high temperature
• More Durability and high resistance to chemical attack

Limitations of Roller Compacted Concrete

• The surface of RCC is rougher than other pavements and not suitable for high speed traffic.
• The construction of adjacent slabs and also multiple horizontal lifts in same layer shall be placed within an hour to make sure the good bonding between layers.
• It is very difficult to compact the pavement layer towards the edges and hence most specifications are forced to limit the percent compaction to 96% modified proctor density.
• Generally, the use of admixture on RCC may be higher than conventional concrete pavements because of the dryness and stiffness of the mixture.
• In hot weather concreting of RCC for paving requires additional attention to decrease the possibility of water loss due to evaporation.

Considering the versatility of RCC over conventional pavements and its ease of application and its durability as compared to traditional bituminous pavements it becomes clear that the roller compacted concrete is a suitable paving material. Also, when considering the ever-increasing cost of petroleum-based products such as bitumen it becomes quite evident that RCC is likely to be the paving construction material of the future.

Roller Compacted Concrete Pavement Construction Procedure

Connectivity of rural roads is an important criterion in rural development. Low volume rural roads in India, including other district roads (ODR) and village roads (VR), occupies about 80% of the total roads of the country. At present these roads are provided with asphalt pavements. Most of these roads are potholed and distressed due to variety of reasons. Therefore, there is an urgent need to construct and maintain the rural roads in an optimal manner.

Alternative Solutions
A place where soil is soft and of poor strength, aggregate is costly and poor drainage conditions are prevailing; rigid pavement is best alternative to flexible pavement. Rigid pavement of following types is suggested in place of flexible pavements:

• Plain Cement Concrete Pavement (PCP) with M-30, M-35 & M-40 Grade concrete
• Continuously Reinforced Concrete Pavement (CRCP)
• Roller Compacted Concrete Pavement (RCCP)

Table: Some features of Rigid Pavements
Type of Rigid Pavement	Features
PCP	More number of joints and it causes inconvenient to the road user.
CRCP	Reduces the need of expansion and contraction joint and thus improves riding quality and reduces the maintenance cost. Construction is difficult. More costly and involves more man power.
RCCP	Overcomes the problems of traditional pavements. Much quicker to construct. Similar kind of ingredients as that of PCP. Higher percentage of Fine aggregate allows tight packing and consolidation.

Rigid pavements consist of a number of joints, which reduces stresses caused due to temperature changes and this is a principal cause for inconvenience to the road users. IRC: 101-1988 specifies technique of continuously reinforced concrete pavement which reduces the need of expansion and contraction joints; and thus improves riding quality and reduces the maintenance cost compared to plain cement concrete pavement (PCP). For the construction of conventional Continuously Reinforced Concrete Pavement (CRCP), percentage of steel required is 0.7-1.0%. Provision of steel reinforcement is important to arrest the cracks that occur in the concrete. Compared to flexible asphalt pavements construction, the process of construction of reinforced concrete pavements is difficult and costlier and involves more manpower.

RCC can overcome the problems usually encountered with flexible asphalt pavements or conventional plain or reinforced cement concrete pavements. RCC is the commercial name used for concrete placed with conventional hot mix asphalt paving equipment, then compacted with vibratory rollers. The strength properties of RCC are similar to that of a conventional concrete and consists of the same basic ingredients as conventional concrete; but RCC is dry mix made with lower water cement ratio and consists of mixture of dense graded aggregates, cement and water. The major difference between RCC mixtures and conventional concrete mixtures is that RCC has a higher percentage of fine aggregates, which allows for tight packing and consolidation.

The material is carried in dump trucks, placed into an asphalt-type paver equipped with a standard or high-density screed and then compacted under steel wheel rollers. Steel Drum Finish Roller with smooth rubber rear wheels and a vulcanized rubber drum is used to produce final surface texture. The time required for placing and compaction process is critical to obtain adequate density, strength, and smoothness of the finished RCC pavement. The concrete is placed and compacted fresh and at workable stage i.e., usually within 60 min of delivery. Due to stiff consistency it remains stable under vibratory rollers, yet wet enough to permit adequate mixing and distribution of paste without segregation.

Structural behavior of RCC is similar to that of conventional paving concrete, and so the design procedure follows the methodology used for concrete pavements.