Construction steps for laying of cement concrete Pavement slab
The various construction steps for laying of cement concrete pavement slab are describe below:-
- Preparation of sub grade
- Preparation of base course
- Placing of form work
- Watering of surface
- Mixing and placing of concrete
- Compaction and finishing
- Belting, Brooming and Edging
- Opening to traffic
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Preparation of sub grade
The sub grade is the natural soil which is properly compact by rollers and is brought to require camber and gradient. The cross and longitudinal profile should be check by suitable templates.
Preparation of base course
Over the prepare subgrade, base course or sub base course is sometimes providing. In certain cases, where the bearing capacity of subgrade soil is high, base or sub base layer may be omitting. The base for a concrete road may be WBM surface, compact granular material layer or stabilise soil base. The base or sub base layer not only provides a smooth level surface and a supporting layer, but it also reduces the thickness of concrete slab.
Placing of form work
After preparing the base, form work for concrete slab pavement is lay. The forms can be of steel or timber. The depth of form work should be equal to the thickness of slab. Form work should be rigidly fix in position and must be well in advance from the point where concrete mix is to be place. It should be oil properly from inside and must be check to line and grade.
Watering of surface
After laying form work, the surface of base or subgrade must be wet with water before placing of concrete mix. Water should not be allowed to stand on the surface during wetting operation. The main function of watering is to saturate the surface completely so that it should not absorb any water from the concrete mix.
Mixing and placing of concrete
The ingredients of concrete such as cement, sand and coarse aggregates are mix in a dry state in the ratio 1 2: 4. The mixing should be doing preferably in a concrete mixer. The water should be adding in a measure quantity to obtain the design water cement ratio.
The concrete mix is place in the lay form works by manual labour and it should be deposit in layers of thickness not more than 50 mm to 80 mm. The concrete mix should be lay on the entire width of the form work and always proceed lengthwise. The technique of construction may be alternate bay or continuous bay method. The top most layer should be lay 6 mm to 12 mm higher than the specify profile for further tamping work. The require transverse and longitudinal joints should be provide and it should be ensure that the top layer is lay to the desired camber and gradient.
Compaction and finishing
After placing of concrete mix, it should be compact by vibrating hand screeds or hand tampers. For large scale construction work, power drive vibrators or machines may be use. The hand tampers are use across the bay and tamping of the surface is doing along the length of the bay.
For finishing the concrete surface, wooden hand floats are usually used. The main function on floating is to develop a uniform and even surface pavement devoid of any waves or corrugations. The floating is always doing in longitudinal direction. Float is held in position parallel to the centre line of pavement and move gradually from one side to the other. Straight edge with 2 handles is use to check the finish pavement surface for its grade and level in longitudinal direction.
Belting, Brooming and Edging:
Belting is do in transverse direction to the carriage way by a 150 to 300 nm wide strip of canvas or rubber fit with handles at both ends. The belting is doing to finish the surface of concrete just before the concrete sets or hardens.
After belting, brooming of pavement surface is carrying out immediately with a fibre broom brush. Brooming is carrying out, to make the pavement surface rough and non-slippery having skid resistance. After brooming, edging tool is use for rounding the transverse and longitudinal edges of the pavement slab. The process of edging is carrying out before the concrete mix develops initial Setting.
Initial curing of finish pavement is carry out after 12 hours by covering the surface with gunny bags which are keep wet for at least one day. For final curing, gunny bags are removing and surface is cover with a sandy layer which is keep wet for at least 14 days.
Curing of finish pavement may also be carry by:
- Application of liquid impervious membrane.
- Ponding method in which whole surface is dividing into small bays by forming earthen banks which are fill with water. After curing is complete, a surface is clean properly and washes.
Opening to traffic
Road pavement is open to traffic after 28 days of curing slab or even earlier when the concrete has attained require strength. During this period, brick edging is constructing to protect the slab. Earth may be spread on the berms up to the top of brick edging to disallow the traffic.