PAVEMENT QUALITY CONCRETE FOR ROADS

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..

1. Ordinary Portland Cement (IS 269), Portland Pozzolana Cement (IS 459) & Portland Slag Cement (IS 1489) Can be used for PQC.
2. Crushed Aggregates with Max size 32mm can be used as per IS:383.
3. Clean Coarse river sand to be used for PQC conforming to IS:383.
4. 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.
5. 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.

DRY LEAN CONCRETE FOR ROADS

DLC or Dry Lean Concrete is cement concrete with low slump value to be laid for rigid pavement over sub-base and rolled & compacted by mechanical means.

·    Ordinary Portland cement, Portland PozzolanaCement or Portland Slag Cement be used for DLC.

·   Coarse aggregate shall consist of Clean, hard, strong, dense, non-porous and durable pieces of crushed stone or crushed gravel and shall be devoid of pieces of disintegrated stone, soft, flaky, elongated, very angular or splintery pieces. The maximum size of the coarse aggregate shall be 25 mm.

·    The fine aggregate shall consist of clean, natural sand or crushed stone sand or a combination of the two and shall conform to IS : 383. Fine aggregate shall be free from soft particles, clay, shale, loam, cemented particles, mica, organic and other foreign matter.

·      The coarse and fine aggregates may be obtained in either of the following manner:

(i) In separate nominal sizes of coarse and fine aggregates and mixed together intimately before use.

(ii) Separately as 25 mm nominal single size, 12.5 mm nominal size graded aggregates - and Fine

Aggregate of crushed stone dust or sand or a combination of these two.

                       

AGGREGATE GRADATION FOR DRY LEAN CONCRETE:-

Sl No	Sieve Sizes	Percentage passing the sieve by weight
1	26.50 mm	100%
2	19.00 mm	80-100%
3	9.50 mm	55-75%
4	4.75 mm	35-60%
5	600.00 micron	10-35%
6	75.00 micron	0-8%

·   Water for mixing and curing of concrete shall be clean and free from injurious amounts of oil, salt, acid, vegetable matter or other substances harmful to the finished concrete.

·   The mix shall be proportioned with a maximum aggregate cement ratio of 15 : 1.

·   The minimum cement content is 150 kg/cu.m. of concrete.

·   The average compressive strength of each consecutive group of 5 cubes made shall not be less than 10 MPa at 7 days. In addition, the minimum compressive strength of any individual cube shall not be less than 7.5 MPa at 7 days.

·   The batching plant shall be capable of proportioning the materials by weight, each type of material being weighed separately. The cement from the bulk stock shall be weighed separately from the aggregates. The batching and mixing shall be carried out preferably in a forced action central batching and mixing plant having necessary automatic controls to ensure accurate proportioning and mixing. Other types of mixers shall be permitted subject to demonstration of their satisfactory performance during the trial length. The type and capacity of the plant shall be got approved by the Engineer before commencement of the trial length. The (weighing balances shall be calibrated by weighing the aggregates, cement, water and admixtures physically either by weighing with large weighing machine or in a weigh bridge. The accuracy of weighing scales of the batching plant shall be within ± 2 per cent in the case of aggregates and ±1 per cent in the case of cement and water.

·   Plant mix lean concrete shall be discharged immediately from the mixer, transported directly to the point where it is to be laid and protected from the weather by covering the tippers/ dumpers with tarpaulin during transit. The concrete shall be transported by tipping trucks, sufficient in number to ensure a continuous supply of material to feed the laying equipment to work at a uniform speed and in an uninterrupted manner. The lead of the batching plant to paving site shall be such that the travel time available from mixing to paving.

·   Lean concrete shall be laid/placed mechanically /manually. The concrete shall be laid in one layer in an even manner without segregation, so that after compaction the total thickness is as specified. The laying of the two- lane road sub-base may be done either in full width or lane by lane. Preferably the lean concrete shall be placed and compacted across the full width of the road, by constructing it in one go or in two lanes running forward simultaneously.

Rolling & Compaction; Spreading of DLC

·   The compaction shall be carried out immediately after the material is laid and leveled with 8 -10 Tonne Static Roller. In order to ensure thorough compaction which is essential, rolling shall be continued on the full width till there is no further visible movement under the roller and the surface is closed.          

·    As soon as the lean concrete surface is compacted, curing shall commence. Curing shall be done by covering the surface by gunny bags/hessian, which shall be kept continuously moist for 7 days by sprinkling water.

·   The minimum dry density obtained shall be 97% of the dry density achieved during trial length construction and the density achieved at the edges (i.e. upto 0.5m from the edge) shall be not less than 95% of the MDD.

WBM ROAD CONSTRUCTION

      WBM Stands for Water Bound Macadam which is the most commonly used road construction procedure for over more than 190 years.Pioneered by Scottish Engineer John Loudon McAdam around 1820 Macadam is a type of Road Construction. The broken stones of base and surface course,if any are bound by the stone dust is presence of moisture is called WBM Roads.
Macadam means the pavement base course made of crushed or broken aggregate mechanically interlocked by rolling and the voids filled with screening and binding material with the assistance of water.WBM may be used as a sub-base,base or a surface course.The thickness of each compacted layer of WBM ranges from 10cm to 7.5cm depending on size and the gradation of aggregate used.

Construction Procedure:
1.Prepare the foundation for receiving the WBM course. 
2.Lateral confinement may be done by compacting the shoulder to advance,to a thickness equal to that of the compacted WBM layer and by trimming the inner side vertically.
3.Spreading of Coarse Aggregate.

4.Compaction of coarse aggregate is done by wheeled power roller of capacity 6 to 10 tonnes or alternately by an equivalent vibratory roller.

5.Dry screening is applied gradually over the surface to fill the interstices in these.
6.The surface is sprinkled with water,swept and rolled.
7.Binding material is applied at a uniform and slow rate at two and more layers.
8.WBM Coarse is allowed to set overnight.