Pavement Quality Concrete is a concrete which is used now a days for most type of Road Contraction works. Generally it is designed in High Grade (M-35 to M-50) and designed for 32mm size aggregates and low slump.
Materials Required:- The Following materials are required for Construction of PQC Road..
- Ordinary Portland Cement (IS 269), Portland Pozzolana Cement (IS 459) & Portland Slag Cement (IS 1489) Can be used for PQC.
- Crushed Aggregates with Max size 32mm can be used as per IS:383.
- Clean Coarse river sand to be used for PQC conforming to IS:383.
- Water conforming to IS:456-2000 to be used for PQC. In case of hot water concrete plant should have a arrangement for water cooling.
- Different types of admixtures conforming to IS:6925 & IS:9103 to be used for PQC.
Procedure:-
- For concrete road or rigid pavements, the concrete shall be laid in alternate panels to avoid development of shrinkage & thermal cracks.
- The base shall be sprayed with water to ensure no moisture is drawn from the concrete.
- If specified in the drawing, polythene sheet shall be spread on the entire area to limit the loss of moisture from the concrete. polythene sheet of 125 micron (with Lap of 300mm) shall be overlapped at the junctions.
- In case continuous casting is desired, the same can be carried with saw cutting arrangement of the concrete pavement.
- Such pavement shall be cut to 1/3rd the depth at every 6m within 24 Hours after laying the concrete. Any deviation in this can result in irregular formation of cracks.
Construction & Expansion Joints:-
A typical constriction joint consist of placing a stopper across the length & width without affecting the spacing or placing of rebar’s. Necessary holes shall be made in the stopper for ensuring the same. All stoppers shall be applied with form release agents and removed as soon as concrete attains final set.
- The concrete surface shall be made rough by chipping the same with chisel immediately after de-shuttering.
- For expansion joints, additional MS bar ( Dowel Bar ) shall be provided at half the depth of the pavement with 50 % of the length of the rod in the previous concrete & remaining in the next pour.
- Expansion joints of 25mm (or More) width and half of depth of pavement to be provided after required concrete length (as instructed in drawing or technical specifications) .
- Construction joints of 12mm to be provided after required length.
- One end of the MS bar shall be coated with grease & covered in plastic sleeve for easy movement.
- If required as per drawing, an expansion board made of bitumen impregnated fibre or polystyrene shall be placed at the expansion joint area.
- Tie bars as shown in drawing shall be inserted at the longitudinal joints where load transfer is minimal.
Concreting:-
- Concrete of minimum M-35 grade shall be used for laying the pavement.
- Concrete shall start only after all arrangements for laying were in place including crack preventive measures & curing mechanism.
- Concrete shall be differed in windy or rainy weather.
- Necessary protective covers and its spreading mechanism without disturbing the texture shall be made available for every pour.
- Concrete slump shall be controlled to 50mm & placement shall start from one end.
- Concrete shall be spread evenly & rough levelled using wooden screeds.
- The levelled concrete shall be vibrated by surface mounted vibrators and finished to rough texture.
- Slump should be 15 to 45mm for placing of this concrete.
Curing:-
- Curing of completed pavement shall start immediately after concrete final setting.
- Initial curing shall be carried by covering the surface with wet hessian & latter by ponding
Joint Sealing:-
Joints to be sealed with bitumen sealant of Grade-A of IS-1834 in every expansion and construction joints.
Testing:-
- Cubes (For Compressive Strength) & Beams (For Flexural Strength) to be taken for each 150 cum of concrete .If the volume of concrete done in one day is less than 150 cum, still 6 cubes & 6 Beams to be taken.
- These cubes & beams to be tested in 7 & 28 days of concreting and checked as per specifications.(Average strength of 3 cubes (28 days result) not to be less than Required Strength).
- Core test shall be carried out in case of failure of Cube or Beams as per engineer in charge.
