Concrete roads, also known as Rigid Pavements, are the most preferred choice for engineers in terms of the life of the roads because of their superior quality and strength. The average life of concrete roads is more than 25 years. Concrete roads are able to withstand high traffic volume and heavy traffic loads because of their flexural strength. The steps followed in the construction of cement concrete roads are:
1. Preparation of Subgrade – The subgrade is firstly cleaned properly of any trees or root extensions. It is then shaped, leveled and prepared according to the design camber and gradient. It should be compacted properly, and any weak spots must be eliminated. The entire prepared soil for subgrade should have uniform strength. The subgrade should be watered for 6 -20hrs before placing concrete to avoid water seepage from the concrete mix into the subgrade.
2. Need for Sub-base – Sub-base is provided below the concrete layer. Materials used for sub-base are factory aggregates, granular fill, crushed rock, recycled concrete, crushed brick,
3. Placing of forms – Forms are fixed to the ground and properly supported. It can be made out of timber or mild steel channel sections of depth equal to the design depth of the concrete slab pavement. While fixing the forms it should be firm enough to support the concrete pour and should be checked for line and grading.
4. Watering – After putting the formwork in place, the base or subgrade should be wet with water before placing the concrete. It should ideally be done at least 12 hours in advance of placing concrete.
5. Batching and Mixing of Materials – The proportioned ingredients of the materials are properly weighed in weight- batching plant and fed into the hopper along with appropriate cement quantity. Mixing of materials in proportion is done in the dry state and generally done in a concrete mixer. The water is added at last as per the water cement ratio.
6. Transporting and Placing of concrete – At this stage, the concrete is transported with the help of manually carried pans or wheelbarrows on site. The entire bay must be filled thoroughly in successive batches as a continuous operation. The topmost layer should be laid to the prescribed camber and gradient. Voids must be eliminated by roding and vibrating the mix while placing.
7. Compacting the Concrete Slab –Concrete can also be compacted by a power-driven finishing machine or by vibrating hand screeds and for greater depths, immersion vibrators are used.
8. Floating– In order to provide an even surface free of corrugations throughout the pavement, the entire slab surface should be floated with wooden flat boards.
9. Brooming and Edging – The surface is broomed at right angles to the centre line of the road from edge to edge with drawing brushes. Edging is also done for finished edges on the sides of the road before the concrete sets.
10. Curing – The concrete slab must be checked for loss of water regularly and must be kept moist during the hardening period. Initial curing is for 24 hours. The surface can be walked upon by this time and the wet mats are removed after this for final curing of 2-3 weeks.
11. Open to traffic– After curing when the concrete slab attains the specified strength or after 28 days it is opened to traffic.
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