METHOD STATEMENT OF PAVEMENT QUALITY CONCRETE (PQC) CONSTRUCTION
It is very important to have a good construction method of Pavement quality concrete (PQC) for Durable concrete.So let’s know what we should keep in mind at the time of Pavement quality concrete (PQC) construction.
The work shall consist of Construction of un-reinforced, dowel jointed, plain cement concrete pavement in accordance to the requirements of MOSRT&H specifications and in conformity with lines, grades and cross sections as shown in drawing.
Advantages of PQC
PQC is used as a Top layer of Cement concrete road.
• Good friction and drainage characteristics.
• High strengths and stability to withstand the shear stress induced by heavy wheel loads and high tyre pressures.
• A durable, hard-wearing, weather-proof surface free from loose material.
• Facilitate economic maintenance.
• More life of Pavement.
MATERIALS AND MIX PROPORTION
- Aggregate Proportions
- PQC Mix Design for 1 Cum.
BATCHING & MIXING
For the batching and mixing of PQC, RMC plants capacity of batching plant and laying speed of paver shall be maintained as per clause 602.9.1 and 602.9.3 of MORH specifications under good supervision. Batching & Mixing shall be done as per design mix proportions in RMC Plant.
PROCEDURE OF PAVEMENT QUALITY CONCRETE CONSTRUCTION
- If the DLC is found damaged at any place or it has cracks wider than 10 mm, it shall be repaired wit fine cement concrete or bituminous concrete before laying of the separation membrane.
- The laying of PQC by paver with Mechanized or Manually method.
- As per MORTH clause 602.11, we carry out trial length of 100 mts (Minimum) before executing the PQC laying for permanent works. And finishing of the PQC laying should be completed in 120 Minutes after the addition of water in the batching plant.as per clause 602.9.4.2 of MORTH specification.
- A Separation Membrane shall be used between the PQC and DLC. Separation Membrane shall be 125 micron thick laid flat without creases. Prior to laying of Separation, it shall be ensured that the position is correct, the same is clean of dirt or other extraneous materials and free from any damage.
- The temperature of concrete should be between 5 to 30 Degree centigrade to be maintained at the time laying.
- The ambient temperature shall not be more than 35-degree centigrade to maintain at the time of laying of PQC as per clause 602.7.2.
- FRL of PQC shall be maintained by guide wires/ shuttering on both sides as per approved drawings.
- Transporting of concrete shall be done by dumper/transit mixtures after completion of batching and mixing.
- As shown in drawings of Contraction Joint, Mild steel round bars confirming IS: 432 & IS: 1139 shall be used as Dowel bars as per Drawings. Dowel bars shall be supported on cradles/dowel chairs to hold the position in mid with the tolerance of + 20 mm. Dowel bars shall be covered by a thin plastic sheath for at least 2/3 of the length or half plus 50 mm.
- As shown in drawings of Longitudinal Joint, Fe 415 / 500 deformed steel bars confirming IS: 1786 shall be used.
- Workability of Concrete shall be 25 + 15 mm at the time of placing or it shall be modified depending upon the site requirements.
- Surface vibrator shall be used to level the top and after completion of finishing works, texturing works shall be start with texture brush without delay.
- Immediately after the surface texturing, the surface and sides of slab shall be cured by spraying curing compound to prevent against evaporation losses.
- Stopper shall be provided at the end of the construction of day.
JOINTS IN PQC
The location and type of joints shall be shown in the drawing and it shall be constructed as per functional requirements as described as under.
Transverse joints: Transverse joints shall be Expansion and Contraction Joints. Expansion joint shall be used where cement concrete pavement is designed with Structures like Box Culverts, Bridges, etc. The Contraction Joint shall be provided at interval of 4.5 m of slab. The Contraction joint shall be cut as soon as possible as the concrete has undergone initial hardening by mechanical sawn joint groove, 3 to 5 mm wide 1/4 or 1/3 depth of slab. Before opening the traffic, Contraction joint shall be widened 10 to 11 mm and 20 mm depth to apply Poly sulphaid sealant.
Longitudinal joints: The Longitudinal joints shall be provided throughout the lane axis of paving width where continuous groove or key / tie bars are provided. The groove may be cut after final set of the concrete at least 1/3 depth of slab. Before opening the traffic Longitudinal joint shall be widened 6 to 8 mm and 15 mm depth to apply Poly sulphid sealant as shown in drawings.
Surface texture are very important in pavement quality concrete (PQC) Surface texture shall be measured by sand patch method as per MOSRT&H specifications before opening the traffic.
CURING OF PQC
The next day of laying the surface shall be covered by moist hessian clothes or pond curing or other any other suitable method. The surface of PQC shall be kept damp minimum 14 days.
PRECAUTIONS FOR PQC CONSTRUCTION
- Care shall be taken for workability of concrete.
- Surface texturing shall be done before hardening of the concrete.
- Curing of PQC is most essential to prevent cracks.
- Joint construction shall be under good supervision to prevent spall of concrete.
QUALITY CONTROL & ASSURANCE
6 cubes and 6 beams shall be cast to assure the design compressive and flexural strength. Tolerance in surface level for PQC shall be +5 mm to -5 mm. Texture depth shall meet criteria as per MOSRT&H Table 600-2. Concrete slump value shall be 25 + 15 mm.14 Health, safety and environment
All employees working within the limit of this project shall follow the guidelines/rules & regulations as mentioned in HSE PLAN.
Read more : Compressive strength of Concrete Core specimen
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