CONSTRUCTION

 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