What is a Cement Concrete Road?
o A cement concrete road is a type of road construction where the surface is made of a solid layer of cement concrete. As such, such roads are also called Rigid pavements.
o It is a durable and long-lasting option for road infrastructure.
o The construction process involves placing a carefully designed mixture of cement, aggregates, water, and additives onto a prepared sub-base.
o The mixture is then compacted and cured to create a rigid and sturdy road surface.
o Cement concrete roads offer several advantages, including high strength, resistance to heavy traffic loads, low maintenance requirements, and excellent durability in various weather conditions. They are commonly used for highways, major roads, and areas with high traffic volume.
Structural Components of Cement Concrete Road
Starting from the bottom, cement concrete road layers are:
o subgrade
o Sub-base
o Concrete Slab
Subgrade
o The subgrade is a critical component in the construction of a cement concrete road. It is the natural or prepared surface on which the road is constructed.
o This layer provides support to the layers above it. These layers include the base, sub-base, and the pavement itself.
o The quality and characteristics of the subgrade significantly impact the performance and longevity of the road.
o The subgrade must possess adequate strength, stability, and drainage properties to ensure the overall stability and durability of the road structure.
Sub-base
o The sub-base is a layer above the subgrade and below the concrete pavement.
o It acts as a transition layer and distributes loads from the traffic.
o It provides additional support to the road structure.
o The sub-base is typically constructed using granular materials like crushed stone, gravel, or sand.
o This layer enhances the load-bearing capacity of the road and prevents the upward movement of moisture.
o It is important for promoting effective drainage.
Concrete Slab
o Concrete slab is the topmost layer and the actual riding surface of the road.
o It is constructed directly on top of the sub-base and is responsible for providing a smooth and durable driving surface.
o The concrete slab is typically made of a mixture of cement, aggregates, water, and sometimes additives.
o It offers excellent strength, durability, and resistance to heavy traffic loads.
o Notably, the Concrete slab is designed to withstand the stresses and strains imposed by vehicles.
Advantages of Cement Concrete Road
The multitude of advantages of cement concrete roads are:
o The life span of such roads is more.
o Such roads provide an impervious layer of cement.
o Cement concrete roads are strong and durable and are unaffected by weathering agencies.
o They give good visibility at night.
o Cement concrete roads provide dustless and sanitary surfaces.
o Cement concrete roads do not develop corrugations and hence it grants a noiseless surface.
o It can be designed more accurately for load distribution.
o Cement concrete roads are practically unaffected by weather and temperature.
o It is possible to use old concrete roads as a foundation for new concrete roads or for bituminous roads.
Disadvantages of Cement Concrete Road
Following are the disadvantages of a cement concrete road :
o Initial cost of construction is high, especially when suitable aggregate is not locally available.
o It is liable to crack, warp and twist.
o Skilled supervision, as well as skilled workmanship, is required for their construction.
o It becomes noisy under iron tyred traffic.
o Cement concrete roads can only be opened to traffic after a long curing time.
o In the case of such pavements, it is very difficult to locate and repair sewers and water mains that are lying under them.
o They are less resilient than W.B.M road or bituminous road.
Methods of Construction of Cement Concrete Roads
There are three methods to construct cement construct roads.
1. Alternate Bay Method
2. Continuous Bay Method
3. Expansion Joint and Strip Method
Alternate Bay Method:
Case 1: For Single Lane
Fig 1: Alternate Bay Method
If the road is a single lane, it is divided into suitable bays of 6 m to 8 m in length. The construction is then carried out in alternate bays.
Case 2: For Double Lane
Fig 2: Double Lane
The construction work is carried out in old bays of one lane and even bays of the other lane. The construction of the next bay is commenced after the concrete laid earlier is dried out.
Advantages of Alternate Bay Method
o Joints can be constructed easily and their width can be kept as desired.
o The bays which have been cured can serve as an additional working platform.
Disadvantages of Alternate Bay Method
o During rains, the water collects on the surface of the bays, which are not constructed.
o More time is required to complete the work.
o It requires a large number of transverse joints.
o The construction is spread over the full width of road pavement and due to this, the traffic will have to be completely diverted.
Continuous Bay Method
This is also known as the strip method or full-width method. In this method of construction, all the slabs or bay of a strip are constructed continuously without any break from one end to the other.
Fig: Continuous bay Method
o In the continuous bay method, construction joints are provided when the day’s work is not finished at the specified joint.
o Moreover, in addition to construction joints, dummy joints are also provided at 5 m intervals in the transverse direction. They are provided to check the planes of weakness and to control cracking.
Construction of Cement Concrete Road
The construction of cement concrete road involves the following operations:
1.Preparation of subgrade:
o Subgrade is natural soil on which the concrete slab is laid.
o It is cleaned, shaped and levelled.
o After cleaning, it is prepared to the required grade and profile.
o It should be seen that the subgrade has uniform strength over its entire width.
o If any local weak spots are found, they should be removed and strengthened by placing new material which is compacted.
o When concrete is to be directly placed on the subgrade, the surface should be saturated with water for 6 to 20 hrs in advance of placing the concrete.
o This is done to ensure that the subgrade does not absorb water from the concrete.
2.Provision of Sub-base:
o When the natural subgrade is not very firm, a sub-base over the subgrade is provided.
o Depending upon the type of soil, design load, intensity of traffic and economic consideration, the decision for providing the sub-base is taken.
o The sub-base serves the following three purposes:
o It provides a capillary cut-off, and the damage caused by mud pumping is prevented.
o It also provides a strong supporting layer.
o It reduces the thickness of the concrete slab and thus leads to a lower cost of construction.
o The sub-base may consist of any one of the following layers:
o A layer of well-graded soil-gravel mixture of maximum thickness 15 cm.
o Brick soling with one layer of Water Bound Mecadam of maximum total thickness 10 cm.
o Two layers of W.B.M. of maximum total thickness 15 cm.
o A layer of lean cement concrete of maximum thickness 10 cm.
o When subgrade soil is very poor, the sub-base should be placed over a blanket of some granular material or stabilised soil.
3.Placing the Forms in Cement Concrete Road:
o The forms may be made up of steel or timber.
o The steel forms are of mild steel channel sections and their depth is equal to the thickness of the pavement.
o Forms are properly braced and fixed to the ground by means of stakes.
o Forms are fixed in position by 3 stakes at the back of each 3 m length.
o When the forms are fixed, they must be checked for their trueness.
o The maximum deviations permissible in the vertical plane is 3 mm and in the horizontal plane 5 mm in the 3 m length of the form.
o The forms are oiled before placing concrete in them.
4.Watering the Prepared subgrade or Sub-base:
o After the forms are fixed, the prepared surface to receive concrete is made moist.
o If the subgrade is dry, it should be sprinkled with as much quantity of water as it can absorb.
o It is advisable to wet the surface at least 12 hrs in advance of placing the concrete.
o When an insulating layer of water-proof paper is provided, the moistening of the surface prior to placing the concrete is not required.
5.Batching of Materials and Mixing:
o After determining the proportions of ingredients for the Concrete mix, the fine and coarse aggregates are properly proportioned by weight in the weight-batching plant.
o They are then fed into the hopper along with the necessary quantity of cement, which is also measured by weight.
o The ingredients of concrete are mixed in proper proportions in a dry state. The mixing should preferably be done in a concrete mixer.
o The measured quantity of water is added so that the desired water-cement ratio is obtained.
6.Transporting and Placing of Concrete:
o After mixing, the concrete is transported to the site in wheel burrows or in pans which are manually carried.
o The mixed concrete is deposited rapidly on the subgrade in layers of thickness not more than 50 mm to 80 mm or about two or three times the size of aggregates.
o The concrete should be placed over the entire width of the bay in successive batches as a continuous operation and the topmost layer should be laid about 10 mm higher than the actual profile for further tamping.
o The top layer should also be laid to the required camber and gradient. While placing the concrete, it is compacted to eliminate voids.
o Segregation of concrete is avoided during transportation and placing. When reinforcement has been specified in the road slab, concrete is placed in two stages.
o In the first stage, concrete is placed and compacted to the depth corresponding to the level of reinforcement shown in the drawings.
o Reinforcement is then placed on top of compacted concrete and the remaining thickness of the slab is then completed in the second stage.
7.Compaction of Cement Concrete Road:
o After the concrete is placed in its position, it should be brought into its proper position by heavy screed or tamper fitted with suitable handles.
o The wooden tamper is at least 75 mm wide, and its underside is shaped to the finished cross-section of the slab.
o Its weight is about 10 kg/m.
o It should have sufficient strength to retain its shape under all working conditions
o Its length is equal to the length of the bay plus 60 mm.
o The underside of the tamper is provided by a metal plate of 5 mm thickness.
o The tamper is placed on the side form and its handles are gripped by the personnel who use the tamper.
o Concrete is also compacted by means of a power-driven finishing machine or by vibrating hand screed.
o Up to 12.5 cm thickness of slabs screed vibrators alone can be used for compaction.
o For greater thickness, an immersion vibrator is used.
8.Floating:
o After compaction, the entire slab surface is floated longitudinally with a wooden float board.
o The purpose of floating is to provide an even surface free from corrugations.
9.Belting:
o After floating, the surface is further finished by belting just before the concrete becomes hard.
o The purpose of belting is to make the road surface non-slippery and skid resistant. This operation is sometimes omitted.
10.Brooming:
o After belting, brooming is done by drawing brushes at right angles to the centerline of the road from edge to edge.
o Brooming is done just before the concrete becomes non-plastic.
o This operation is also sometimes omitted.
11.Edging:
After brooming, the edges of the slab are carefully finished with an edging tool before the concrete is finally set.
12.Curing Process of Cement Concrete Road:
o Curing consists of checking the loss of water from the concrete slab, and keeping the fresh concrete slab moist during the hardening period.
o Initial curing is done for 24 hrs.
o By this time, the concrete becomes hard enough to walk upon and then wet mats are removed and final curing done for 2 to 3 weeks.
o Final curing is done by any one of the following methods – Ponding Method, By covering the slab with 4 to 8 cm thick layer of wet sand or earth, and by Spraying a suitable chemical such as sodium or calcium chloride on the concrete surface.
13.Fillings of Joints and Edging:
o After curing, the surface is cleaned and washed.
o The joints are then properly filled-in attains with a suitable sealing compound.
14.Opening to Traffic:
Concrete road is opened to traffic when it attains the required strength or after 28 days of curing.
CC road: Construction process
The construction of a CC road involves the following steps:
1. Site preparation: The site for the road is cleared, and the ground is levelled to provide a stable foundation for the road.
2. Subgrade preparation: A subgrade layer of compacted soil is laid to provide a stable base for the concrete.
3. Formwork: Formwork is set up to create the shape of the road.
4. Reinforcement: Steel reinforcement bars are placed in the formwork to provide strength to the road.
5. Concrete placement: The concrete is mixed and poured into the formwork, which is then levelled and compacted to remove any air bubbles.
6. Curing: The concrete is left to cure for a few days to achieve its maximum strength.
7. Finishing: The surface of the road is finished by using trowels to create a smooth surface.
CC road: Benefits
There are many benefits of constructing CC roads, which are as follows:
1. Durability: CC roads have a longer lifespan than asphalt roads, as they are less prone to damage caused by heavy traffic, extreme weather conditions, and wear and tear. The superior durability of CC roads is due to the high strength and stiffness of concrete, which makes it resistant to damage caused by heavy vehicles and repeated loading. Unlike asphalt, which can soften and deform in high temperatures, CC roads maintain their shape and surface integrity, even in extreme heat. They are also resistant to water damage, as the concrete mixture is impermeable to water, preventing moisture from seeping into the underlying layers of the road, which can cause damage and deterioration over time.
1. Low maintenance: CC roads require minimal maintenance, as they do not need to be resurfaced frequently. They are also easy to clean, which makes them a popular choice for urban areas. Unlike asphalt roads, which require frequent resurfacing to maintain their surface integrity, CC roads can last for decades without the need for significant repairs or maintenance. This not only reduces the overall cost of maintaining the road network but also minimises the disruption to traffic flow caused by road closures and repairs.
2. Smooth surface: CC roads provide a smooth and even surface, reducing vehicle wear and tear, and resulting in less maintenance costs for car owners. This is particularly beneficial for commercial vehicles, such as trucks and buses, which are subject to frequent use and high levels of stress on their tires and suspension systems. The smooth surface of CC roads also reduces noise pollution caused by vehicle traffic, making them an ideal choice for residential areas and other noise-sensitive environments.
3. Environmentally friendly: The use of CC roads reduces the carbon footprint of the transportation sector. They are made from locally sourced materials, which reduces transportation costs and energy consumption. Concrete is made from locally sourced materials, such as aggregates and cement, which reduces the transportation costs and energy consumption associated with importing materials from distant locations. This not only reduces carbon emissions but also supports local businesses and economies.
4. Cost-effective: Although the initial cost of constructing a CC road is higher than an asphalt road, the long-term cost is lower due to its durability and low maintenance requirements. CC roads require less frequent repairs and maintenance, resulting in lower costs over their lifespan compared to asphalt roads, which require regular resurfacing and other maintenance activities.
COMPARISON BETWEEN BITUMINOUS CONCRETE ROADS AND CEMENT CONCRETE ROADS
It will be interesting to summarise the two important types of ad surfaces in common use, namely, flexible pavement in the form of bituminous concrete roads and rigid pavement in the form of cement concrete roads.
Table 1 shows the comparison of these types of roads with respect to specific items.
Table1. COMPARISON BETWEEN BITUMINOUS CONCRETE ROADS AND CEMENT CONCRETE ROADS
No. | Item | Bituminous concrete road | Cement Concrete roads |
1 | Compaction | It is achieved by rolling with usual precautions. | It is done by the use of vibrators. |
2 | Curing | Not necessary. | Necessary. |
3 | Formwork | Not necessary. | Required for edges and near joints. |
4 | Initial Cost | Less. | More |
5 | Joints | Note to be provided | To be invariably provided |
6 | Maintenance Cost | More | Less |
7 | Method of placing | The premix is prepared in hot mix plant and it is to be placed in hot condition. | The concrete is prepared by mixing cement, aggregates and water and it is to be deposited before cement starts to set. No heating is required. |
8 | Opening of underground trenches | Can be easily opened up. | Difficult to open. |
9 | Opening to traffic | After 24 hours. | After 15 to 20 days. |
10 | Salvage value | Practically nil. | Can serve as a base or foundation for the new bituminous surface. |
11 | Tractive resistance | More | Less |
12 | Useful life | Less | More |
13 | Utility | Less durable for heavy traffic, cost of repair an maintenance more. | More durable and reliable for heavy traffic. |
14 | Visibility at night | Bad | Good |
15 | Wear of surface | more | Less |
FAQs
What are the advantages of CC roads over asphalt roads?
CC roads have several advantages over asphalt roads, including longer lifespan, low maintenance, smooth surface, and environmental friendliness.
Are CC roads more expensive than asphalt roads?
Yes, the initial cost of constructing a CC road is typically higher than that of an asphalt road. However, the long-term cost savings associated with their durability and low maintenance requirements make them a cost-effective option in the long run.
How long do CC roads last?
CC roads can last from 20 to 30 years or more, depending on several factors, such as traffic volume, weather conditions, and maintenance.
Are CC roads suitable for all types of traffic?
Yes, CC roads are suitable for all types of traffic, including heavy commercial vehicles, buses, and cars.
How do you maintain CC roads?
CC roads require minimal maintenance, mainly periodic cleaning, and occasional repairs of surface defects such as cracks or spalling.