Construction Methodology for Pavement Quality Concrete (PQC)
1. Name of activity:
Pavement Quality concrete Layer
2. Highway Activities (Rigid Pavement)
3. Description
of Activity:
The work shall consist of construction of unreinforced,
dowel jointed, plain cement concrete pavement in accordance with the
requirements of specifications and in
conformity with the lines, grades and cross sections shown on the drawings or
as directed by the engineer.
Acceptance
Criteria : Trial length complies with
specifications provided as per MORT&H clause 602.10.6
4. References:
a) Ref. to Technical Specification (MORT&H Spec. & Amendments)
a.1) Clauses: 602, 902.4, 903.5
a.2) Tables: 600-.
b) Ref. other related works prior to this activity:
b.1) Mix design approval, DLC 100 mm, and Level Recording.
c) Ref. to Drawing(s):
c.1) PQC Panel detail (Approved by Consultant)
d) IS/IRC Specifications
d.1) IS: SP:23, IS: 432, IS 1139, IS 1786
5. Scope
of Work:
This methodology shall be
applicable for construction of dowel jointed or plain cement concrete pavement
in accordance with the lines, grades, camber and thickness as shown in the
drawings using fixed forms.
6. Materials:
Cement:
These shall consist of
Ordinary Portland Cement from approved source. The minimum cement content shall
be 400 Kg/cum. However, optimum cement content shall be determined by carrying
out concrete mix design in accordance with IRC: 44-2008 and establishing a job
mix formula, approval of which shall be obtained from IE.
Admixtures:
The admixtures shall
confirm to IS 6925 and IS 9103 shall improve the workability of concrete or
extension of time and they will not have any effect on the properties of
concrete. The performance of these admixtures will be proved both on laboratory
trials and in trial paving works. The admixtures containing calcium chloride
shall not be used.
Aggregates:
The aggregates shall be of
crushed stone or Crushed gravel, confirming to IS 383. The coarse aggregate
shall be clean, hard, strong, dense and durable of crushed stone. The Los
Angeles Abrasion value shall not be more than 35%. The fine aggregate shall be
of clean natural sand or crushed stone sand or combination of both. These shall
be free from clay, shale, loam, mica and other organic matter. The limit of
deleterious material content shall not exceed the requirements set out in
IS:383. Coarse aggragates and fine aggregates shall satisfy all the
requirements specified in Sections 602.2.4.2 and 602.2.4.3 of MORTH (3rd
Rev.).
Water:
Water used for mixing and
curing of concrete shall be free from oil, salt, acid and other substances,
which are harmful to concrete. It shall meet the requirements stipulated in IS:
456.
Mild steel bars for dowel and tie bars:
Dowel bars shall confirm to
S 240 (with yield strength 840 Mpa) and tie bars (deformed or plain) to grade Fe500
deformed steel bars as per IS: 1786/IS: 432.
Pre-Molded joint filler:
This shall be used for
expansion joints abutting structures like bridges, culverts and at end of the
day work. These shall be of 20-25mm thickness or as shown in drawings,
complying to IS 1838. It shall be 25mm less in depth than the thickness of slab
provided in suitable lengths, which shall not be less than lane width. Holes
shall be made to accommodate dowel bars.
Joint sealing compound:
While carrying out joint
sealing, the provision made under codes viz. IRC: 57-2006, IRC: 15-2011 and
IRC: 58-2011 shall be taken into consideration. This shall be hot poured
Elastomeric type as per AASHTO M282 or cold poured Polysulphide type as per BS
5212-part2 having flexibility, resistance to age hardening and durability.
Separation membrane:
A separation membrane of
impermeable plastic sheeting 125 microns thick shall lay between the concrete
slab and sub-base by nailing with concrete nails to the lower layer. Where
overlap is necessary the same shall be laid by at least 300mm.
7. Procedure:
Mix:
The mix shall be designed
as per IRC: 44-2008. And the design shall be based on the flexural strength of
concrete. The water content shall be minimum required to provide workability
for full compaction of the concrete to the required density. The maximum free
water cement ratio shall be 0.5. The mix shall be proportioned to give an
average strength at 28 days exceeding the specified strength (4.8Mpa) by 1.65
times the standard deviation calculated from the flexural strength of the first
30 beams first during the trial length and then the job control test beams (during the actual
execution). The workability requirements at the batching plant and at site
shall be established by slump tests while doing trial length. A slump value of
30±15mm is reasonable for
slip form paving and 50±15mm for fixed form paving.
Avg. strength Ratio ® of
7days and 28 days compressive strength of cubes prepared from each batch shall
be determined periodically during construction. If R value so obtained is found
less than those determined as the time of mix design, 5% extra cement shall be
added to the mix.
Mixing:
The materials shall be
mixed in a mechanized batching plant consisting air-conditioned centralized
control cabin, minimum 4bins, weigh hoppers, separate scales for cement, fine
and coarse aggregate with weighing balances calibrated, aggregates being
proportioned by automatic weighing devices using load cells. The concrete
ingredients shall be mixed thoroughly by a mixer with automatic timing/alarm
device to mix and discharge (in case of failure of timing/alarm device concrete
shall be mixed as per Manufacturer’s recommendations) capable of mixing to get
a homogenous mix without being segregated while discharge.
Joints, dowel and tie bars:
The location and type of
joint shall be as shown in the drawings.
Contraction Joints
Transverse joints shall be
contraction and expansion joints, cut with mechanical saw, could start as early
as 6-8 hours, i.e. initial hardening of concrete, after paving. The contraction
joints shall consist of mechanical sawn joint groove, 3 to 5mm wide and 1/4 to
1/3 depth of the slab. The expansion joints shall consist of a joint filler
board positioned vertically with the prefabricated assemblies along the line of
joint.
The dowel bars shall mild
steel with details and dimensions as indicated in the drawings. Unless
otherwise shown in the drawings the dowel bars shall be positioned at the mid
depths of the slab with suitable tools/means within +/-20mm tolerances. The
dowel bars shall be covered with plastic sheath for at least 2/3rd from one end
for contraction joint, and ½ length +50mm for expansion joint. For expansion
joints, a closely fitting cap of 100mm long shall be provided at the sheath
end. To block the entry of cement slurry between dowel and cap a compressible
sponge may be used.
The dowel bars shall be
supported on cradles / chairs in pre-fabricated joint assemblies positioned
prior to the construction of slab or mechanically inserted with vibration into
the plastic concrete by a method which ensures correct placement of the bars
besides full re-compaction of the concrete around the dowel bars.
Longitudinal Joints:
The longitudinal joints
shall be saw cut as shown in the drawings. A groove of 1/3rd the depth of the
slab may be cut after the final set of the concrete. The tie bars shall be
deformed steel bars of 415 Mpa complying to IS 1786. Tie bars shall be painted
with bituminous paint for 75mm at the both ends and positioned with suitable
tools/means. Tie bars shall be placed
within the middle third of the slab depth.
Tie bars in the
longitudinal joints shall be made up into rigid assemblies with adequate
supports to remain firmly in position during the construction of slab.
Construction Joints:
Transverse construction
joints shall be place whenever concreting is completed for the day’s work on is
suspended for more than 30 minutes. These shall be provided at regular location
of contraction joints using dowel bars as stated above.
Using sealants, not before
14days after construction of slab shall seal all transverse and longitudinal
joints, but prior to allowing the traffic ply on the new construction.
Separation membrane:
A separation membrane of
impermeable plastic sheeting 125 microns thick shall lay between the concrete
slab and the sub base by nailing with concrete nails to the lower layer.
Wherever overlap is necessary, the same shall be laid by at least 300mm. Before
placing the separation membrane the sub-base shall be swept clean of all
extraneous materials using high pressure water jetting or compressed air.
Construction
by fixed form:
This shall consist of straight side forms
made of steel of thickness not less than 5mm and of minimum 3000mm length.
These shall have a depth equal to the prescribed thickness of the pavement.
These forms shall be straight and free from bends and warps. Side forms shall
be of sufficient rigidity in the form and in the interlocking connection with
adjoining form such that springing will not occur under the weight of the sub
grade and paving equipment or from pressure of concrete.
The vibrators for
concreting shall be either surface pan type or internal type with immersed tube
or multiple spuds. The surface vibrators shall a frequency not less than 3500
impulse per minute and the internal type vibrators shall have frequency more
than 5000 impulse per minute.
Curing:
Curing shall be done manually
by sprinkling water on PQC surface. Wet Jute bags shall be used to cover whole
surface. Curing shall be start day after concreting and shall be done everyday
up to 14th day.
8. Trial
length:
A trial length of 60m shall
be made for the full width of the pavement and rolled, by involving at least
one transverse construction joint involving hardened concrete and freshly lay
concrete.
After the side forms are
removed, edges of slabs shall be corrected wherever irregularities have
occurred by using fine concrete consisting 1:3 ratio of cement to fine chips
and aggregate.
After the final regulation
of the slab and before the application of curing membrane, the surface of the
concrete shall be brush-textured at right angles to the longitudinal axis. The
wire brush used for this purpose shall be made of 32 gauge type wired grouped
together in tufts at 10mm centers and of width not less than 450mm.
The total time taken from
addition of water to the mix, until the completion of surface finishing and texturing
shall not exceed 120minutes when the concrete temperature is less than 250C and
90minutes when the temperature of concrete is between 250C-300C.
Immediately after the
surface texturing, the surface and sides shall be cured by application of curing
compound, which hardens in to impervious film with the help of mechanical
sprayer. The curing compound shall have a water retention efficiency of 90%.
After 3hours, the pavement shall be covered with moist Hessian cloth or pond
with water for at least a period of 14 days.
Joints sealing:
When saw cuts joints are adopted in construction, they are not made to provide
the minimum width specified in the drawings, they shall be widened subsequently
by sawing before sealing, and the width and depth are controlled by gauges.
When sealants are applied, an appropriate primer shall also be used, if
recommended by the manufacturer and it shall be applied in accordance with
their requirements. The sealant shall be applied within the minimum and maximum
drying time of the primer recommended by the manufacturer. Before sealing, the
temporary seal provided for blocking the ingress of dirt, soil, etc. should be
removed. A highly compressible heat resistant paper-backed de-bonding strip as
shown in drawing shall be inserted in the groove to serve the purpose of
breaking the bond between sealant and the bottom of the groove and to plug the
joint groove, so that the sealant may not leak through the cracks.
The road may be opened for
regular traffic after completion of curing period and after sealing of joints.
Sand Patch Test (for
measuring the texture depth)
The surface to be tested
shall be dried; any extraneous mortar and loose material shall be removed and
swept clean, using a wire brush at right angles and parallel to the
carriageway. A cylindrical container of 25ml capacity shall be filled with sand
passing 300microns sieve and retained on 150microns sieve, compacted by tapping
the base and excess sand stroked off to level with the top of cylinder. Then
the sand shall be poured on the surface to be tested into a heap and spread
with the help of flat wooden disc of 64mm diameter of 1.5mm thick, with its
face kept flat, in a circular motion, so that the sand is spread into a
circular patch, with the surface depressions filled with sand to the level of
peaks.
The diameter of the patch
shall be measured to the nearest 5mm. The texture depth of concrete shall be
calculated as follows:
Texture depth in mm =
31000/ D2
Where D is the mean
diameter of the patch.
Five such texture depth
tests shall be taken along the diagonal line across the lane width at least 2m
apart, between 50m points along the road. No measurement shall be taken within
the 300mm of longitudinal edges of the slab constructed in one pass.
The requirements of texture
depth as per MORT&H table 600-2 are as follows:
Time of test
|
No. Of measurements
|
Required texture depth
(mm)
|
|
Specified value
|
Tolerances
|
||
Between 24hrs. and 7days after the
construction of the slab
|
Average of 5 measurements
|
1.00
|
±0.25
|
Not later than 6 weeks, before the road
is opened to traffic
|
Average of 5 measurements
|
1.00
|
+0.25
-0.35
|
9. Safety
Requirements :
a. All concrete transit millers shall be provided with
reverse horns.
b. Flagman shall be provided at all exit points of the
trucks / tippers.
c. The speed of vehicles plying in the work area shall be
restricted to 40kmph maximum.
d. If night work is to be carried out the area shall be
sufficiently provided with lighting.
e. Check for the working condition of safety valves of
air compressors, if compressed air is being used for cleaning.
f. Check for the working condition of safety valves of
air compressors, if compressed air is being used for cleaning.
g. The 1000mm work area on the both sides of the paving
area shall be kept clear of any unauthorized person / workmen.
h. All the exposed moving parts of the joint saw cutters
shall be provided with guards.
i. Hand gloves shall be used while application of joint
sealants.
j. PQC shall be done in half width so that traffic
interruption will be minimum. 150 mm compacted layer of GSB shall be laid on
rest of half width in order to make smooth flow of traffic. After setting
of PQC layer, work shall be executed in rest half width.
10. Manpower
Requirement :
1. Section Engineer
2. Site In charge
3. Site Supervisor
4. Surveyor team
5. Concreting team
11. Machinery Requirement:
Batching plant, Transit
Miller, Water Tanker, Vibrator, Shovels, Broom, Wire brush, Straight edge.
Setting out will be done prior to work demarking the area of execution.
Any other
points the contractor likes to mention:
a)
The manpower
& machinery proposed is indicative only. The requisite qty. of resources
may vary based upon site condition.
b)
Any modification
in execution of activity shall be done with prior information with consultant.
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