Fibre-Reinforced Concrete Pavement For NICE Road, Bangalore
Mr. KRS. Narayan
National Head-Market Development
Reliance Industries Ltd., Mumbai.
Road transportation is undoubtedly the lifeline of the nation and
its development is a crucial concern. The traditional bituminous
pavements and their needs for continuous maintenance and
rehabilitation coupled with frequent repairs, points towards the scope
for cement concrete pavements. There are several advantages of
cement concrete pavements over bituminous pavements. This paper
explains benefits of RECRON3S FIBRE REINFORCED CONCRETE
PAVEMENTS, which is a recent advancement in the field of Reinforced
Concrete Pavement design with a Case Study of NICE ROAD-Bangalore
which is India’s Longest White-topped Road using Recron3S Fibres is
In a developing country such as India, road networks form the arteries of the nation. A pavement is the layered structure on which vehicles travel. It serves two purposes, namely, to provide a comfortable
Mr. KRS. Narayanas it satisfies two of the much-demanded requirements of pavement material in India, economy and reduced pollution. It also has several other advantages like longer life, low maintenance cost, fuel efficiency, good riding quality, increased load carrying capacity and impermeability to water over flexible pavements. Fibre Reinforced Concrete Pavements are more efficient than ordinary cement concrete pavement. “FRC is defined as composite material consisting of concrete reinforced with discrete randomly but uniformly dispersed short length fibres.” The fibres may be of STEEL, SYNTHETIC or natural materials. FRC is a material of improved properties and not as reinforced cement concrete whereas reinforcement is provided for local strengthening of concrete in tension region. Fibres generally used in cement concrete pavements are Steel fibres and organic Synthetic Polymer fibres such as Polyester or Polypropylene.
National Head-Market Development,
Reliance Industries Ltd.
Fibre Reinforced Concrete
Concrete is well known as a brittle material when subjected to normal stresses and impact loading, especially, with its tensile strength being just one tenth of its compressive strength. It is only common knowledge that, concrete members are reinforced with continuous reinforcing bars to withstand tensile stresses, to compensate for the lack of ductility and is also adopted to overcome high potential tensile stresses and shear stresses at critical location in a concrete member. Even though the addition of steel reinforcement significantly increases the strength of the concrete, the development of microcracks must be controlled to produce concrete with homogenous tensile properties. The introduction of fibres was brought into consideration, as a solution to develop concrete with enhanced flexural and tensile strength, which is a new form of binder that could combine Portland cement in bonding with cement matrices. Fibres are generally discontinuous, randomly distributed throughout the cement matrices. Referring to the American Concrete Institute (ACI) committee 544, in fibre reinforced concrete there are four categories namely
1. SFRC - Steel Fibre Reinforced Concrete
2. GFRC - Glass Fibre Reinforced Concrete
3. SNFRC - Synthetic Fibre Reinforced Concrete
4. NFRC - Natural Fibre Reinforced Concrete
Fibre Reinforced concrete can be defined as a composite material consisting of mixtures of cement, mortar or concrete with discontinuous, discrete, uniformly dispersed suitable fibres. Continuous meshes, woven fabrics and long wires or rods are not considered to be discrete fibres. Fibre reinforced concrete (FRC) is concrete containing fibrous material, which increases its structural integrity. It contains short discrete fibres that are uniformly distributed and randomly oriented. Fibres may generally be classified into two: organic and inorganic. Inorganic fibres include Steel fibres and Glass fibres, whereas organic fibres include natural fibres like coconut, sisal, wood, bamboo, jute, sugarcane, etc., and synthetic fibres based on Acrylic, Carbon, Polypropylene, Polyethylene, Nylon, Aramid, and Polyester. Within these different fibres the character of fibre reinforced concrete changes with varying concretes, fibre materials, geometries, distribution, orientation and densities.
Fibres are usually used in concrete to control cracking in its Plastic and Drying states. They also lower the permeability of concrete and thus reduce bleeding of water. Some types of fibres produce greater impact, abrasion and shatter resistance in concrete. The amount of fibres added to a concrete mix is measured as a percentage of the total volume of the composite (concrete and fibres) termed volume fraction (Vf). Vf typically ranges from 0.1 to 3%. Aspect ratio (l/d) is calculated by dividing fibre length (l) by its diameter (d). Fibres with a non-circular cross section use an equivalent diameter for the calculation of aspect ratio. If the modulus of elasticity of the fibre is higher than the matrix (concrete or mortar binder), they help to carry the load by increasing the tensile strength of the material. Fibres that are too long tend to “ball” in the mix and create workability problems.
Polymer Synthetic Fibre Reinforced Concrete (PSFRC)
Polymeric fibres are gaining popularity because of its properties like zero risk of corrosion and cost effectiveness. The polymeric fibres commonly used are Recron3s--Polyester and Polypropylene. These fibres act as crack arresters, restricting the development of cracks and thus transforming a brittle material into a strong composite with superior crack resistance, improved ductility and distinctive post cracking behaviour prior to failure. Concrete pavements may be weak in tension and against impact, but PFRC is a suitable material, which may be used for cement concrete pavement as it possesses extra strength in flexural fatigue and impact etc. The usage of fibres in combination with concrete also results in a mix with improved early resistance to plastic shrinkage cracking and thereby protects the concrete from drying shrinkage cracks. It accomplishes improved durability and reduced surface water permeability of concrete. It reduces the risk of plastic settlement cracking over rebar. It enables easier and smoother finishing. It also helps to achieve reduced bleeding of water to surface during concrete placement, which inhibits the migration of cement and sand to the surface and the benefits of the above will be harder, more durable surface with better abrasion resistance. A uniform distribution of fibres throughout the concrete improves the homogeneity of the concrete matrix. It also facilitates reduced water absorption, greater impact resistance, enhanced flexural strength and tensile strength of concrete. The use of polymer fibres with concrete has been recognized by the Bureau of Indian Standards (BIS) and Indian Road Congress and is included in the following Standard documents:
- IS:456:2000 – Amendment No.7, 2007
- IRC:44-2008 – Cement Concrete Mix Designs for Pavements with fibres
- IRC:SP 46-2013—Guidelines for Design & Construction of Fibre Reinforced Concrete Pavements.
- ICI-Indian Concrete Institute-Technical Committee recommendation for Fibre Reinforced Concrete-TC-01
- IRC:SP:76:2008 – Guidelines for Ultra Thin White Topping with fibres
Polymer Fibre Reinforced Concrete has been Approved by National Bodies Like:
1. Central Public Works Department (CPWD) & Local State PWDs.
2. Airport Authority of India
3. Military Engineering Services
4. Defence Airfields
India’s Longest White-Topped Concrete Road Using Fibres
Project—Bangalore-Mysore Infrastructure Corridor Project (BMICP) – NECE Ltd.-Nandi Economic Corridor Enterprises Limited.
Salient Features of the Project
1. First White Topped Project in India – Completed in May 2013.
2. Longest White topped Concrete Road in India—90 Lane km.
3. First White topped project under PPP model.
4. Designed for 489 MSA.
5. Design Life of 60 years.
6. Project using Fibres for entire White topping of approx. 72,000 cu.m. of Concrete.
7. Project completed with least time & cost overrun, completed in 120 days using RMC.
8. Concrete Pavement is light in colour adding to luminosity during night, thereby saving Energy.
9. Project executed without cutting a single tree & saving environment.
10. Albedo effect—Surface being light in colour compared to Bitumen roads reduces surface temperature (Heat Island effect) having substantial effect in less heat radiation to the surroundings.
11. Savings in Natural Aggregates as Design life is 60 years. Design & Construction Features
- Composite Rigid Pavement Construction with M-40 grade of RMC with designed Flexural Strength of 5.2 N/mm2.
- Use of Fibre Reinforced M-40 grade of Concrete for entire 72,000 cu.m. with the aid of Site based RMC plant of high capacity of 120 cu.m./hr.
- Highly mechanized Paver operation used for laying concrete.
- Effective use of Curing compound replacing conventional water curing system for concrete.
- No use of Dowel bars/reinforcements for the entire 90 lane km.
- Laying of concrete with joints/grooves of 1m x 1m panels.
Mix Design Details
Sequence of Paving Operations
The base course of Dry Lean Concrete (DLC) serves as working platform for supporting PFRC slabs, which, by slab action distributes the wheel load to larger area. The DLC base layer rests on granular sub-base, which rests on subgrade. Over the well compacted sub-grade Granular Sub-base is constructed using big stone boulders and mud. Over that the Dry Lean Concrete of mix 1:4:8 is made, which is compacted, levelled and floated. Surface of DLC is also corrected for road camber. An antifriction separation membrane of 125-micron thickness is spread over the DLC surface to impart free movement of the upper slab caused due to temperature warping stresses. The separation membrane may be stuck to the lower layer with patches of adhesives or appropriate tape or concrete nails with washer so that polythene sheet does not move during placement of concrete. Many of the thickness design methods for cement concrete pavement adopted internationally derive their origin from the method evolved by Portland Cement Association (PCA). In this technology thickness of the pavement is assumed on trial basis. When dewatered concrete is provided on lean concrete, it has no problem of water being coming out on surface during compaction process but when it is done over WBM, a considerable amount of water is soaked by WBM and thus the concrete loses the water to WMB and the water which comes out during dewatering/ compaction process is not in same quantity as in case of lean concrete. It appears that it is better to provide base concrete than WBM as the base. Due to repeated application of flexural stresses by the traffic loads, progressive fatigue damage takes place in the cement concrete slab in the form of cracks especially when the applied stress in terms of flexural strength of concrete is high. The ratio between the flexural stress due to the load and the flexural strength is termed as the stress ratio (SR). If the SR is less than 0.45, the concrete pavement is expected to sustain infinite number repetitions. As the SR decreases the number of load
Requirements for Paving Operations
1. Use of microfilm or anti-friction layer of 125 micron in between PFRC and DLC layers.
2. The DLC layer is to be swept clean of all the extraneous materials before applying microfilm which may be nailed to the DLC layer without wrinkles and holes.
3. Concreting work in hot weather should be carried out in early or later hours.
4. The laying temperature of concrete should always be below 35°Celsius.
Membrane curing is applied with the help of texture-cum-curing machine. The resin-based curing compound is used at the rate of 300 ml per sq.m. of the slab area. After about 1.5 hours moist Hessian cloth is spread over the surface covered with curing compound spray.
Protection and Maintenance
The joint groove is to be protected from ingress of dirt or any foreign matter by inserting performed neoprene sealant. To exercise a very stringent quality control the tests are to be conducted on fine and coarse stone aggregates, water cement, granular sub base, DLC etc as per standards and specification published by Indian Roads Congress.
1. Water logging is a major reason for potholes in roads. WBM and Asphalt roads are permeable to water, which damages the road and sub grade. But PFRC roads are highly impermeable to water so they will not allow water logging and water coming out to the surface from sub grade.
2. Implementation of sensors in roads will be easier while using polymer fibres for concrete.
3. Environmental load of PFRC pavement was found to be significantly lower than the steel fibre reinforced pavement.
4. Maintenance activities related to steel corrosion will be reduced while using PFRC.
5. In fresh concrete polymer fibres reduce the settlement of aggregate particles from pavement surface resulting in an impermeable and more durable, skid resistant pavement.
6. Fibres reduce plastic shrinkage and substance cracking. Fibres also provide residual strength after occurrence of cracking.
7. The use of PFRC produces concrete of improved abrasion resistance and impact resistance.
8. PFRC also enhances ductile and flexural toughness of concrete.
9. All these advantages result in overall improved DURABILITY of PAVEMENT & ensuring design life with drastic reduction in long term maintenance costs.
The use of PFRC, being a relatively new technology poses a threat of a high initial cost of construction. Applications of PFRC
1. Slab On Grade: All types of pavements and overlays, industrial floors, roads, taxi ways, hangars, etc.
2. Structural Concrete: Foundations (deep and shallow), machine foundation, slabs, column beams and lintel, bridge decks and girders etc.
3. Water retaining Structures: RCC retaining walls, water tanks, cross drains, swimming pools, hydel projects, check dams, canal lining, ETPs, jetties, ports, spillways etc.
4. Water proofing in rooftops, sunken toilets, etc.
PFRC can be used advantageously over normal concrete pavement. Polymeric fibres such as polyester or polypropylene are being used due to their cost effective as well as corrosion resistance. PFRC requires specific design considerations and construction procedures to obtain optimum performance. The higher initial cost by 15-20% is counterbalanced by the reduction in maintenance and rehabilitation operations, making PFRC cheaper than flexible pavement by 30-35%. In a fast developing and vast country like India, roadnet works ensure mobility of resources, communication and in turn contribute to growth and development. Resistance to change, though however small, disturbs our society; hence we are always reluctant to accept even the best. It’s high time that we overcome the resistance and reach for the peaks. PFRC opens a new hope to developing and globalizing the quality and reshaping the face of the “True Indian Roads”.
Acknowledgement: The Author wishes to thankfully acknowledge the support, cooperation & technical inputs from NICE Site team & Ultratech RMC Plant / Lab staff.
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