METHODOLOGY PAVEMENT QUALITY CONCRETE
(Acceptance Criteria: Ref. Sec 600 of MORT&H)
Scope
The work shall consist of construction of Dry Lean Concrete (DLC) Sub-base for Cement Concrete Pavement in accordance with the requirement of technical specifications and in conformity with approved lines, grades and cross-sections.
Equipment/Machinery Requirement:
- Batching & Mixing plant
- Slip form paver
- Texturing & curing machine
- Water tankers
- Tippers
- Concrete Saw
- Cement pump
- Front end loader
MATERIALS FOR PQC
Test certificates from manufacturer shall be presented for each lot of cement or cement testing shall be carried out in our site laboratory and result will be submitted. Joint test shall be carried out for the approval obtained from the engineer’s representative for every 200cum of material. Water shall be tested as per requirement of IS: 456 and approval obtained in advance.
Cement shall be procured in polyethylene bags and loaded manually in to hopper of cement pump. From hopper of pump it will be pumped to the Silo of the Batching Plant.
Combined grading of aggregates (Coarse & Fine) will be carried out at laboratory attached with the plant, at least daily and adjustments in Mix proportions will be made for aggregates components, accordingly.
All approved aggregate shall be stacked separately at plant site in stack 5.00 Meter clear distance apart and shall be identified by placards marked ‘APPROVED’ placed on top of the heap.
MIX DESIGN OF PQC
The Minimum Cement content in the PQC shall be not less than 360 kg/cum of Concrete without Fly ash. And Minimum Cement Content is 310 Kg in case of Fly Ash Material, which will be Not More than 20% and Max. W/C will be 0.50. If the Minimum Cement content is sufficient to achieve the desired strength, it will be increased as necessary. The average compressive & Flexure Strength of each consecutive group of 6 cubes & 6 Beams made in accordance with Clause 903.5.2.1. The compressive strength of Cubes will not be less than and 40 MPA at 28 Days. The Flexure strength of beams will not be less than and 4.5 MPA at 28 Days. Mix design as per the stipulations of ‘MORT&H’ and as per IS: 10262 will be carried out at the Laboratory and will be submitted to Engineer’s Representative for approval.
CONSTRUCTION PROCESS OF PQC
a) Preparation of surface Manual brooming shall done to clean DLC surface before laying separation membrane. Separation membrane will be laid for the first hour of paving before start of paving works and shall be continuous process thereafter ensuring sufficient membrane in place at all times of paving. Separation membrane will be fixed on DLC surface by concrete nails. Separation membrane will be prevented from damage by aggregates falling from tippers carrying concrete by manual brooming, ensured by close supervision.
b) Concrete production Concrete shall be produced in the batching plant, which is capable of proportioning the material, by weight, with each type of material being weighted separately. The Batching and mixing shall be carried out in a forced action central batching and mixing plant, which has automatic control. The control fully computerized so as to ensure accurate proportioning and mixing. The accuracy of weighing scales of the batching plant will be within +/- 2 per cent in the case of the aggregates and +/- 1 per cent in the case of cement water and Admixture will be introduced into the mixture in diluted form. Loaderswill be used to load aggregates from stacks of approved material into bins. Batch plant bins will have a storage capacity of 35 cum each. Water will be obtained from the bore wells at the plant site. Water will be stored in the water tank of 120 KL capacity. Mixing time shall be established to the Engineer’s representative. Concrete will not be produced when ambient temperature falls below 5 deg. centigrade or exceeds 35 deg. C. Following measures to control temperature within 30 deg. C will be adopted.
- Mechanically water will be sprinkled to cool the aggregate.
- Cover will be provided for aggregate to be used in next 24 hours.
Transportation OF PQC
Batching Plant mix concrete shall be discharged immediately from mixer, transported directly to the point where it is to be laid and protected from the weather by covering the tippers/dumpers. The concrete will be transported by sufficient numbers of tippers and dumpers. The number of the tippers will be adequate in number so as to feed the paver to work at a uniform speed of 1 RM/min. and in an uninterrupted manner.
PLACING OF PQC
a. The work will be carried out with Suitable Paver or ‘Wirtgen made Paver or equivalent Paver of laying capacity of 5-10. Meter. of main carriageway will be laid by Censer Paver and with manually.
b. Prepared sub-base course shall be checked before laying of PQC and Cracks wider than 5mm will be repaired with concrete prepared from aggregates lower than 10 mm size.
c. Surveyor will fix the alignment for every day’s work, one day in advance, and get it approved from Engineer’s Representative.
d. Prior to start of paving, string line will be set, approx. 200mm above PQC top levels on each side, on longitudinal profile, on stakes placed 10 met apart.
e. Air and concrete temperature shall be measured and recorded in the concrete docket, at the plant site as well as laying site. No concrete will be done when the concrete temperature cannot be maintained below 30 deg cent & when ambient temperature is more then. 35 deg. cent. Plant operation will be stopped based on feedback from laying site.
f. Test Station at Laying Site will be maintained 80 to 100 meter. Ahead of the Paver and will be shifted forward as the work progresses ahead.
g. Concrete production shall be stopped as per advice from paving site.
h. One copy of docket will be handed over to Engineer’s Representative at laying site and the other copy will retained by us.
i. Traceability of concrete received from the batching plant will be maintained by recording data as shown on Traceability form.
j. The concrete shall be deposited in front of Paver by the tippers.
k. Concrete shall be spread by JCB placed ahead of the Paver with in the paving area. Then it will be spread by plough of the Paver to the required level of surcharge..
L.Concrete will be vibrated and compacted by group of vibrators housed in the vibrator box at the spacing of 40cms. Capable of providing variable output for achieving required level of compaction.
m. Dowel bar location shall be identified by paint g on DLC. Tie bars shall be located by taking reference from the dowel bar marking. n. Dowel bars at transverse joints shall be inverted by vibration plastic
concrete and shall be placed at mid depth of the slab by dowel inserter. Similarly tie bars at longitudinal joints shall be inserted by vibration into plastic concrete and shall be placed at mid-depth of slab by Tie Bar inserter.
n.Concrete at all these location shall be simultaneously vibrated & finished.
o. Finishing of concrete surface at the required level shall be carried out by Oscillating Beam, which will be guided by the sensor.
p. Texturing shall be done by brush operated from texturing machine. Depth of the surface texture shall be maintained at 1.0 mm, which shall be tested with the Engineer’s Representative, and his approval shall be obtained.
q. Rate of evaporation from surface of concrete will be monitored at an interval of 01 hr. during laying. If rate of evaporation exceeds 01kg/M²/ Hr., evaporation retardant will be used to minimize the effect of surface evaporation. If rate of evaporation exceeds 2kg/M² / Hr., work will be stopped.
r. Barriers will be provided at each end of the paving site to prevent entry of vehicles. Entry points will be guarded during day and night.
CURING of pqc
Curing shall commence as soon as the completion of finishing operations of concrete surface. Curing shall be carried out, by spaying approved curing compound at the spray rate recommended by manufacturer. After 3 hour of spraying of curing compound, moist Hessian shall cover concrete surface without causing damage to curing compound film. Hessian shall be used and will be kept moist for 14 days by regular sprinkling of water from flexible pipe attached with a water tanker. Water tankers will be deployed round the clock for providing water for curing. Water will be available from the bore wells along the length of the road. Hessian of 16-guage thickness will used and stock to cover 40000 M² areas will be maintained.
JOINT CUTTING & FILLING
a. Joint cutting will commence at the earliest possible after paving. (When the pavement can withstand the weight of concrete saw and saw cutting does not dislodge particles/aggregates from the side of the joint)
b. Initial cut shall be with 3 mm thick diamond saw blade. This cut will be washed out immediately and a temporary seal shall be installed. 4mm thick Armour board shall be used as a temporary seal.
c. Widening of the joint to a width of 12 mm will be taken after 2 to 3 weeks by cutting with 10 mm thick saw blade operated by concrete saw. Widened joints shall be washed immediately after the cut.
Joints shall be cleaned with compressed air and shall be dried completely before filling with sealing compound. 15 mm thick Armour board shall be provided at the bottom of the groove and masking tape shall be fixed on each side of the joint.
d. Sealant shall then be filled specified depth and finished by tooling specified shape.
TRIAL PAVE OF PQC
a.Trail paving will be conducted at outside the road alignment and at our campsite.
b. Polyethylene film shall be spread over the prepared DLC surface. Paver shall be set up accordingly, by providing stakes guided sensor string line at the required target levels.
c. Mix shall be prepared as required by specification and as per approved Mix design.
d. Mix shall be carted to the laying site as per approved method in covered tippers.
e.Spreading, compacting & finishing shall be carried out in the manner
approved before.
f. Paving shall be carried out over two days and all transverse & longitudinal joints will be constructed as required by specification.
g. Curing shall be carried out as specified & as per approved method. Insertion of dowel bars 7 tie bars, surface texturing shall be done as specified and as per approved method statement.
h. Length of laboratory pave shall be kept as 60-70 meter.
i. Target level for the trial shall be fixed prior to paving.
j. Suitability of moisture content of mix shall be examined during the trial length construction to ensure that maximum density and compressive strength related to corresponding water content are achieved.
k. Achieve levels will be compared with the target levels.
l. Sealing of joints shall be done as specified and as per approved method.
m. Tests on trial shall be carried out as specified vide clause 602.10.5 of MOST specifications. Cores shall be taken to determine density of concrete & to check segregation.
n. Approval of engineer’s representative will be obtained before proceeding with the main work.
TESTING of pqc
Testing will be carried out as per table enclosed (encl. -III). Level conformance of finished DLC will be ensured by taking levels at specified grids and compared with the target levels. Concrete testing records will be maintained as per format enclosed (Encl- IV)
TOLERANCES IN PQC
The tolerances for surface regularity, level, thickness, density and strengthshall conform to the requirements given in clause 903.5. Control of quality of material and work shall conform to the specification as laid down in section 900 of MOST Specifications.
TRAFFIC
No heavy or light commercial vehicles like trucks, buses etc. shall be permitted on the PQC sub-base after its construction.
ENVIRONMENTAL SAFETY
I. Water will be obtained from the bore wells situated at our Camp Sites so that it will not affect nearby localities.
II. The Batching Plants are situated at our Camp Sites and water sprinklers will be installed to minimize Dust & Cement in the localities.
Fuel Storage and Refuelling Site are in the Camp Sites and Strict Supervision will be maintained to stop Spillage or Leakage to any nearby water bodies.
IV. Our Mechanical Staff will maintain Batching Plant & other related Equipment’s regularly to reduce Noise & Atmospheric Pollution.
V. The constructions Vehicles, Machineries and Equipment’s will move in our
designated area so it prevents compaction of any type of vegetation and plants.
VI. All workers will be suitably provided with safety guards &equipment’s at the site.
VII. Safety Signals & Sign boards will be provided at every 250 m at the Construction Site.
FAQS
pqc laying temperature
In concrete PQC shall be produced at batching plant by using chilled water. Maintaining the temperature of concrete within 30°C shall not be a problem.
pqc full form
Pavement Quality Concrete (PQC) is normally employed for providing a strong surface of rigid pavements. PQC is also used for construction of runways in airports in order to distribute the heavy impact load from wheel to sub- grade layers