ITEM 407– CONCRETE STRUCTURES
407.1 Description
This Item shall consist of the general description of the materials,
equipment, workmanship and construction requirements of concrete structures
and the concrete portions of composite structures conforming to the
alignment, grades, design, dimensions and details shown on the Plans and in
accordance with the Specifications for piles, reinforcing steel, structural
steel, structural concrete and other items which constitute the completed
structure. The class of concrete to be used in the structure or part of the
structure shall be as specified in Item 405, Structural Concrete.
407.2 Material Requirements
1. Concrete and Concrete Ingredients
Concrete and concrete materials shall conform to the requirements in
Item 405, Structural Concrete. Unless otherwise shown on the Plans or
specified in Special Provisions, concrete shall be of Class A.
2. Reinforcing Steel
Reinforcing steel shall conform to the requirements in Item 404,
Reinforcing Steel.
3. Structural Steel
Structural steel shall conform to the requirements of corresponding
materials in Item 403, Metal Structures.
4. Bridge Bearing (Elastomeric Bearing Pad)
Elastomeric bearing pads shall conform to Item 412, Elastomeric Bearing
Pads.
5. Paints
Paints shall conform to the requirements in Item 411, Paint.
6. Waterproofing and Damp proofing Unless otherwise shown on the Plans or
indicated in Special Provisions, materials for waterproofing and
damp proofing shall conform to the requirements of the following
specifications:
a. AASHTO M 115 Asphalt for damp proofing and waterproofing.
b. AASHTO M 116 Primer for the use with Asphalt in damp proofing and
waterproofing.
c. AASHTO M 117 Woven cotton fabrics saturated with bituminous substances
for use in waterproofing.
d. AASHTO M 118 Coal-Tar pitch for roofing, damp proofing and
water-proofing.
e. AASHTO M 121 Creosote for priming coat with coal-tar pitch damp-proofing
and waterproofing.
f. AASHTO M 159 Woven burlap fabric saturated with bituminous substances
for use in waterproofing.
g. AASHTO M 166 Numbered cotton duck and array duck.
h. AASHTO M 239 Asphalt for use in waterproofing membrane construction.
7. Concrete Curing Compound
Curing compound shall conform to the requirements of AASHTO M 148 Liquid
membrane-forming compounds for curing concrete.
8. Joint Filler
Unless otherwise shown on the Plans or in Special Provisions, materials for
expansion joint filler shall conform to the requirements of the following
specifications:
a. AASHTO M 33 Preformed expansion joint filler for concrete.
b. AASHTO M 153 Preformed sponge rubber and cork expansion joint fillers
for concrete paving and structural construction.
c. AASHTO M 173 Concrete joint sealer hot poured elastic type.
d. AASHTO M 213 Preformed expansion joint filler for concrete paving and
structural construction-non-extruding and resilient bituminous types.
e. AASHTO M 220 Preformed elastomeric compression joint seals for concrete.
407.2.1 Proportioning and Strength of Structural Concrete
This shall be in accordance with Item 405, Structural Concrete.
407.2.2 Sampling and Testing
This shall be in accordance with Item 405, Structural Concrete.
407.3 Construction and Requirements
407.3.1 Handling and Placing Concrete: General
Concrete shall not be placed until forms and reinforcing steel have been
checked and approved by the Engineer.
If lean concrete is required in the Plan or as directed by the Engineer
prior to placing of reinforcing steel bar, the lean concrete should have a
minimum compressive strength of 13.8 MPa.
In preparation for the placing of concrete all sawdust, chips and other
construction debris and extraneous matter shall be removed from inside the
formwork, struts, stays and braces, serving temporarily to hold the forms
in correct shape and alignment, pending the placing of concrete at their
locations, shall be removed when the concrete placing has reached an
elevation rendering their service unnecessary. These temporary members
shall be entirely removed from the forms and not buried in the concrete.
No concrete shall be used which does not reach its final position in the
forms within the time stipulated under “Time of Hauling and Placing Mixed
Concrete”.
Concrete shall be placed so as to avoid segregation of the materials and
the displacement of the reinforcement. The use of long troughs, chutes, and
pipes for conveying concrete to the forms shall be permitted only on
written authorization of the Engineer. The Engineer shall reject the use of
the equipment for concrete transportation that will allow segregation, loss
of fine materials, or in any other way will have a deteriorating effect on
the concrete quality.
Open troughs and chutes shall be of metal lined; where steep slopes are
required, the chutes shall be equipped with baffles or be in short lengths
that reverse the direction of movement to avoid segregation.
All chutes, troughs and pipes shall be kept clean and free from coatings of
hardened concrete by thoroughly flushing with water after each run. Water
used for flushing shall be discharged clear of the structure.
When placing operations would involve dropping the concrete more than1.5 m,
concrete shall be conveyed through sheet metal or approved pipes. As far as
practicable, the pipes shall be kept full of concrete during placing and
their lower end shall be kept buried in the newly placed concrete. After
initial set of the concrete, the forms shall not be jarred and no strain
shall be placed on the ends of projecting reinforcement bars.
The concrete shall be placed as nearly as possible to its final position
and the use of vibrators for moving of the mass of fresh concrete shall not
be permitted.
407.3.1.1 Placing Concrete by Pneumatic Means
Pneumatic placing of concrete will be permitted only if specified in the
Special Provisions or authorized by the Engineer. The equipment shall be so
arranged that vibration will not damage freshly placed concrete.
Where concrete is conveyed and placed by pneumatic means, the equipment
shall be suitable in kind and adequate in capacity for the work. The
machine shall be located as close as practicable to the work. The discharge
lines shall be horizontal or inclined upwards from the machine. The
discharge end of the line shall not be more than 3 m from the point of
deposit.
At the conclusion of placing the concrete, the entire equipment shall be
thoroughly cleaned.
407.3.1.2 Placing of Concrete by Pumping
The placing of concrete by pumping will be permitted only if specified or
if authorized by the Engineer. The equipment shall be so arranged that
vibration will not damage freshly placed concrete.
Where concrete is conveyed and placed by mechanically applied pressure the
equipment shall be suitable in kind and adequate in capacity for the work.
The operation of the pump shall be such that a continuous stream of
concrete without air pockets is produced. When pumping is completed, the
concrete remaining in the pipeline, if it is to be used, shall be ejected
in such a manner that there will be no contamination of the concrete or
separation of the ingredients. After this operation, the entire equipment’s
shall be thoroughly cleaned.
407.3.1.3 Placing Concrete in Water
Concrete shall not be placed in water except with approval of the Engineer
and under his immediate supervision. In this case the method of placing
shall be hereinafter specified.
Concrete deposited in water shall be Class A concrete with a minimum cement
content of 400 kg/m3 of concrete. The slump of the concrete
shall be maintained between 10 and 20 cm. To prevent segregation, concrete
shall be carefully placed in a compact mass, in its final position, by
means of a tremie, a bottom-dump bucket, or other approved means, and shall
not be disturbed after being placed.
A tremie shall consist of a tube having a diameter of not less than 250 mm
constructed in sections having flanged couplings fitted with gaskets with a
hopper at the top. The tremie shall be supported so as to permit free
movement of the discharge and over the entire top surface of the work and
so as to permit rapid lowering when necessary to retard or stop the flow of
concrete. The discharge end shall be closed at the start of work so as to
prevent water entering the tube and shall be completely submerged in
concrete at all times; the tremie tube shall be kept full to the bottom of
the hopper. When a batch is dumped into the hopper, the flow of concrete
shall be induced by lightly raising the discharge end, but always keeping
it in the placed concrete. The flow shall be continuous until the work is
completed.
When the concrete is placed with a bottom-dump bucket, the top of the
bucket shall be open. The bottom doors shall open freely downward and out
ward when tripped. The buckets shall be completely filled and slowly
lowered to avoid backwash. It shall not be dumped until it rests on the
surface upon which the concrete is to be deposited and when discharged
shall be withdrawn slowly until well above the concrete.
407.3.2 Compaction of Concrete
Concrete during and immediately after placing shall be thoroughly
compacted. The concrete in walls, beams, columns and the like shall be
placed in horizontal layers not more than 30 cm thick except as hereinafter
provided. When less than a complete layer is placed in one operation, it
shall be terminated in a vertical bulkhead. Each layer shall be placed and
compacted before the preceding layer has taken initial set to prevent
injury to the green concrete and avoid surfaces of separation between the
layers. Each layer shall be compacted so as to avoid the formation of a
construction joint with a preceding layer.
The compaction shall be done by mechanical vibration. The concrete shall be
vibrated internally unless special authorization of other methods is given
by the Engineer or is provided herein. Vibrators shall be of a type,
design, and frequency approved by the Engineer. The intensity of vibration
shall be such as to visibly affect a mass of concrete with a 3 cm slump
over a radius of at least 50 cm. A sufficient number of vibrator shall be
provided to properly compact each batch immediately after it is placed in
the forms. Vibrators shall be manipulated so as to thoroughly work the
concrete around the reinforcement and embedded fixture sand into the
corners and angles of the forms and shall be applied at the point of
placing and in the area of freably placed concrete. The vibrators shall be
inserted into and withdrawn from the concrete slowly. The vibration shall
be of sufficient duration and intensity to compact the concrete thoroughly
but shall not be continued so as to cause segregation and at any one point
to the extent that localized areas of grout are formed. Application of
vibrators shall be at points uniformly spaced, and not farther apart than
twice the radius over which the vibration is visibly effective. Vibration
shall not be applied directly or thru the reinforcement to sections or
layers of concrete that have hardened to the degree that the concrete
ceases to be plastic under vibration. It shall not be used to make concrete
flow in the forms over distances so great as to cause segregation, and
vibrators shall not be used to transport concrete in the forms of troughs
or chutes.
407.3.3 Casting Sections and Construction Joints
The concrete in each form shall be placed continuously. Placing of concrete
in any such form shall not be allowed to commence unless sufficiently
inspected and approved materials for the concrete is at hand, and labor and
equipment are sufficient to complete the pour without interruption.
Joints in the concrete due to stopping work shall be avoided as much as
possible. Such joints, when necessary, shall be constructed to meet the
approval of the Engineer.
When the placing of concrete is temporarily discontinued, the concrete,
after becoming firm enough to retain its shape, shall be cleaned of
laitance and other objectionable material to a sufficient depth to expose
sound concrete. Where a “faster edge” might be produced at a construction
joint, as in the sloped top surface of a wingwall, an inset formwork shall
be used to produce an edge thickness of not less than 15 cm in the
succeeding layer. Work shall not be discontinued within 50 cm of the top of
any face, unless provision has been made for a coping less than 50 cm
thick, in which case if permitted by the Engineer, the construction joint
may be made at the underside of coping.
Immediately following the discontinuance of placing concrete, all
accumulations of mortar splashed upon the reinforcing steel and the
surfaces of forms shall be removed. Dried mortar chips and dust shall not
be puddled into the unset concrete. Care shall be exercised, during the
cleaning of the reinforcing steel, not to injure or break the
concrete-steel bond at and near the surface of the concrete.
407.3.4 Casting Box Culverts
In general, the base slab of box culverts shall be placed and allowed to
set before the remainder of the culvert is constructed. In the construction
of box culverts the side walls and top slab may be constructed as a
monolith.
If the concrete in the walls and top slab is placed in two separate
operations, special care shall be exercised in order to secure bonding in
the construction joint and appropriate keys shall be left in the sidewalls
for anchoring the top slab. Each wingwall shall be constructed, if
possible, as a monolith. Construction joints where unavoidable, shall be
horizontal and so located that no joints will be visible in the exposed
face of the wingwall above the ground line.
Vertical construction joints shall be at right angles to the axis of the
culverts.
407.3.5 Casting Columns, Slabs and Girders
Concrete in columns shall be placed in one continuous operation, unless
otherwise directed. The concrete shall be allowed to set for at least 20
hours before the caps are placed.
Unless otherwise permitted by the Engineer, no concrete shall be placed in
the superstructure until the column forms have been stripped sufficiently
to determine the condition of the concrete in the column. The load of the
super-structure shall not be allowed to come upon the bents until they have
been in place at least 14 days, unless otherwise permitted by the Engineer.
Concrete in slab spans shall be placed in one continuous operation for each
span unless otherwise provided.
Concrete in T-Beam or deck girder spans shall be placed in one continuous
operation unless otherwise directed. If it is permitted to place the
concrete in two separate operations, each of the operations, shall be
continuous: first, to the top of the girder stems, and second, to
completion. In the latter case, the bond between stem and slab shall be
secured by means of suitable shear keys which may be formed by the use of
timber blocks approximately 50 mm x 100 mm in cross-section having a length
of 100 mm less than the width of the girder stem. These key blocks shall be
placed along the girder stems as required, but the spacing shall not be
greater than 300 mm center to center. The blocks shall be beveled and oiled
in such a manner as to insure their ready removal, and they shall be
removed as soon as the concrete has set sufficiently to retain its shape.
If the contractor wishes to place the concrete in two separate operations,
he shall, with his request for permission to do so, submit plans and
proposals of the required changes to the reinforcement, which plans and
proposals shall be subject to the approval of the Engineer.
In box girders, the concrete in the bottom slab be poured first, as a
separate operation.
The concrete in the webs and the top slab shall be placed in one continuous
operation unless otherwise specified. If it is permitted to place the
concrete in more than one operation, the requirements for T-beam shall
apply.
407.3.6 Construction Joints
Construction joints shall be made only where shown on the Plans or called
for in the pouring schedule, unless otherwise approved by the Engineer.
Shear keys or reinforcement shall be used, unless otherwise specified, to
transmit shear or to bond the two sections together.
Before depositing new concrete on or against concrete which has hardened,
the forms shall be retightened. The surface of the hardened concrete shall
be roughened as required by the Engineer, in a manner that will not leave
loose particles of aggregate or damage concrete at the surface. It shall be
thoroughly cleaned of foreign matter and laitance. When directed by the
Engineer, the surface of the hardened concrete which will be in contact
with new concrete shall be washed with water to this satisfaction, and to
insure an excess of mortar at the juncture of the hardened and the newly
deposited concrete, the cleaned and saturated surfaces, including vertical
and inclined surfaces shall first be thoroughly covered with a coating of
mortar of the same proportion of sand and cement as the class of concrete
used against which the new concrete shall be placed before the grout or
mortar has attained its initial set.
The placing of concrete shall be carried continuously from joint to joint.
The face edges of all joints which are exposed to view shall be carefully
finished true to line and elevation.
407.3.7 Concrete Surface Finishing
Surface finishing shall be classified as follows:
Class 1, Ordinary Finish
Class 2, Rubbed Finish
Class 3, Floated Finish
All concrete shall be given Class 1, Ordinary Finish and additionally any
further finish as specified.
Unless otherwise specified, the following surfaces shall be given a Class
2, Rubbed Finish.
1. The exposed faces of piers, abutments, wingwalls, and retaining walls.
2. The outside faces of girders, T-beams, slabs, columns, brackets, curbs,
headwalls, railings, arch rings, spandrel walls and parapets.
Excluded, however, are the tops and bottoms of floor slabs and sidewalks,
bottoms of beams and girders, sides of interior beams and girders,
backwalls above bridge seats or the underside of copings. The surface
finish on piers and abutments shall include all exposed surfaces below the
bridge seats to 20 cm below low water elevation or 50 cm below finished
ground level when such ground level is above the water surface. Wingwalls
shall be finished from the top to 50cm below the finished slope lines on
the outside face and shall be finished on top and for a depth of 20 cm
below the top on the back sides.
Unless otherwise specified, the surface of the traveled way shall be
Class3, Floated Finish.
Class 1, Concrete Ordinary Finish
Immediately following the removal of forms, all fins and irregular
protection shall be removed from all surface except from those which are
not to be exposed or are not to be waterproofed. On all surfaces the
cavities produced by form ties and all other holes, honeycomb spots, broken
corners or edges and other defects shall be thoroughly cleaned, and after
having been kept saturated with water for a period of not less than three
hours shall be carefully pointed and made true with a mortar of cement and
fine aggregate mixed in the proportions used in the grade of the concrete
being finished. Mortar used in pointing shall not be more than one hour
old. The mortar patches shall be cured as specified under Subsection
407.3.8. All construction and expansion joints in the completed work shall
be left carefully tooled and free of all mortar and concrete. The joint
filler shall be left exposed for its full length with a clean and true
edges.
The resulting surface shall be true and uniform. All repaired surfaces, the
appearance of which is not satisfactory to the Engineer, shall be “rubbed”
as specified below.
Class 2, Concrete Rubbed Finish
After removal of forms, the rubbing of concrete shall be started as soon as
its condition will permit. Immediately before starting this work, the
concrete shall be kept thoroughly saturated with water for a minimum period
of three hours. Sufficient time shall have elapsed before the wetting down
to allow the mortar used in the pointing of road holes and defects to
thoroughly set. Surfaces to be finished shall be rubbed with a minimum
coarse carborundum stone using a small amount of mortar on each face. The
mortar shall be composed of cement and fine sand mixed in the proportions
used in the concrete being finished. Rubbing shall be continued until all
form marks, protections and irregularities have been removed, all voids
have been filled, and a uniform surface has been obtained. The face
produced by this rubbing shall be left in place at this time.
After all concrete above the surface being created has been cast, the final
finish shall be obtained by rubbing with a fine carborundum stone and
water. This rubbing shall be continued until the entire surface is of
smooth texture and uniform color.
After the final rubbing is completed and the surface has dried, it should
be rubbed with burlap to remove loose powder and shall be left free from
all unsound patches, paste, powder and objectionable marks.
Class 3, Concrete Floated Finish
After the concrete is compacted as specified in Subsection 407.3.2,
Compaction of Concrete, the surface shall be carefully struck off with a
strike board to conform to the cross-section and grade shown on the Plans.
Proper allowance shall be made for camber if required. The strike board may
be operated longitudinally or transversely and shall be moved forward with
a combined longitudinal and transverse motion, the manipulation being such
that neither is raised from the side forms during the process. A slight
excess of concrete shall be kept in front of the cutting edge at all times.
After striking off and consolidating as specified above, the surface shall
be made uniform by longitudinal or transverse floating or both.
Longitudinal floating will be required except in places where this method
is not feasible.
The longitudinal float, operated from foot bridges, shall be worked with a
sawing motion while held in a floating position parallel to the road
centerline and passing gradually from one side of the pavement to the
other. The float shall then be moved forward one-half of each length and
the above operation repeated. Machine floating which produces an equivalent
result may be substituted for the above manual method.
The transverse float shall be operated across the pavement by starting at
the edge and slowly moving to the center and back again to the edge. The
float shall then be moved forward one-half of each length and the above
operation repeated. Care shall be taken to preserve the crown and
cross-section of the pavement.
After the longitudinal floating has been completed and the excess water
removed, but while the concrete is still plastic, the slab surface shall be
tested for trueness with a straight-edge. For the purpose, the Contractor
shall furnish and use an accurate 3 m straight-edge swing handless 1 m
longer than one half the width of the slab.
The straight-edge shall be held in successive positions parallel to the
road centerline and in contact with the surface and the whole area gone
over from one side of the slab to the other as necessary advancement along
the deck shall be in successive stages of not more than one-half the length
of the straight-edge. Any depression found shall be immediately filled with
freshly mixed concrete, struck off, consolidated and refinished. The
straight-edge testing and refloating shall continue until the entire
surface is found to be free from observable departure from the
straight-edge and the slabs has the required grade and contour, until there
are no deviations of more than 3 mm under the 3 m straight-edge.
When the concrete has hardened sufficiently, the surface shall be given a
broom finish. The broom shall be an approved type. The strokes shall be
square across the slabs from edge to edge, with adjacent strokes slightly
overlapped, and shall be made by drawing the broom without tearing the
concrete, but so as to produce regular corrugations not over 3 mm in depth.
The surface as thus finished shall be free from porous spots,
irregularities, depressions and small pockets or rough spots such as may be
caused by accidental disturbing, during the final brooming of particles of
coarse aggregate embedded near the surface.
Concrete Surface Finish for Sidewalk.
After the concrete has been deposited in place, it shall be compacted and
the surface shall be struck off by means of strike board and floated with a
wooden or cork float. An edging tool shall be used on all edges and at all
expansion joints. The surface shall not vary more than 3 mm under a 3 m
straight-edge. The surface shall have a granular or matted texture which
will not slick when wet.
407.3.8 Curing Concrete
All newly placed concrete shall be cured in accordance with this
Specification, unless otherwise directed by the Engineer. The curing method
shall be one or more of the following:
1. Water Method
The concrete shall be kept continuously wet by the application of water for
a minimum period of 7 days after the concrete has been placed.
The entire surface of the concrete shall be kept dump by applying water
with an atomizing nozzle. Cotton mats, rugs, carpets, or earth or sand
blankets may be used to retain the moisture. At the expiration of the
curing period the concrete surface shall be cleared of the curing medium.
2. Curing Compound
Surfaces exposed to the air may be cured by the application of an
impervious membrane if approved by the Engineer.
The membrane forming compound used shall be practically colorless liquid.
The use of any membrane-forming compound that will alter the natural color
of the concrete or impart a slippery surface to any wearing surface shall
be prohibited. The compound shall be applied with a pressure spray in such
a manner as to cover the entire concrete surface with a uniform film and
shall be of such character that it will harden within 30 minutes after
application. The amount of compound applied shall be ample to seal the
surface of the concrete thoroughly. Power-operated spraying equipment shall
be equipped with an operational pressure gauge and means of controlling the
pressure.
The curing compound shall be applied to the concrete following the surface
finishing operation immediately after the moisture sheen begins to
disappear from the surface, but before any drying shrinkage or craze cracks
begin to appear. In the event of any delay, in the application of the
curing compound, which results in any drying or cracking of the surface,
application of water with an atomizing nozzle as specified under “Water
Method”, shall be started immediately and shall be continued until the
application of the compound is resumed or started, however, the compound
shall not be applied over any resulting freestanding water. Should the film
of compound be damaged from any cause before the expiration of 7 days after
the concrete is placed in the case of structures, the damaged portion shall
be repaired immediately with additional compound.
Curing compound shall not be diluted or altered in any manner after
manufacture. At the time of use, the compound shall be in a thoroughly
mixed condition. If the compound has not been used within 120 days after
the date of manufacture, the Engineer may require additional testing before
the use to determine compliance to requirements.
An anti-setting agent or a combination of anti-setting agents shall be
incorporated in the curing compound to prevent caking.
The curing compound shall be packaged in clean barrels or steel containers
or shall be supplied from a suitable storage tank located on the Site.
Storage tank shall have a permanent system designed to completely
redisperse any settled material without introducing air or any other
foreign substance. Containers shall be well-sealed with ring seals and lug
type crimp lids. The linings of the containers shall be of character that
will resist the solvent of the curing compound. Each container shall be
labeled with a manufacturer’s name, specification number, batch number,
capacity and date of manufacture, and shall have label warning concerning
flammability. The label shall also warn that the curing compound shall be
well-stirred before use. When the curing compound is shipped in tanks or
tank trunks, a shipping invoice shall accompany each load. The invoice
shall contain the same information as that required herein for container
labels.
Curing compound may be sampled by the Engineer at the source of supply and
on the Site.
3. Waterproof Membrane Method
The exposed finished surfaces of concrete shall be sprayed with water,
using a nozzle that so atomizes the flow that a mist and not as pray is
formed until the concrete has set, after which a curing membrane of
waterproof paper or plastic sheeting shall be placed. The curing membrane
shall remain in place for a period of not less than 72 hours.
Waterproof paper and plastic sheeting shall conform to the specification of
AASHTO M 171.
The waterproof paper or plastic sheeting shall be formed into sheets of
such width as to cover completely the entire concrete surface.
All joints in the sheets shall be securely cemented together in such a
manner as to provide a waterproof joint. The joint seams shall have a
minimum lap of 100 mm.
The sheets shall be securely weighed down by placing a bank of earth on the
edges of the sheets or by other means satisfactory to the Engineer.
Should any portion of the sheets be broken or damaged within 72hours after
being placed, the broken or damaged portions shall be immediately repaired
with new sheets properly cemented into place.
Sections of membrane which have lost their waterproof qualities or have
been damaged to such an extent as to render them unfit for curing, the
concrete shall not be used.
4. Forms-in-Place Method
Formed surfaces of concrete may be cured by retaining the form-in-place.
The forms shall remain in place for a minimum period of 7 days after the
concrete has been placed, except that for members over 50cm in least
dimensions, the forms shall remain in place for a minimum period of 5 days.
Wooden forms shall be kept wet by watering during the curing period.
5. Curing Cast-In-Situ Concrete
All newly placed concrete for cast-in-situ structures, other than highway
bridge deck, shall be cured by the water method, the forms-in-place method,
or as permitted herein, by the curing compound method, all in accordance
with the requirements of Subsection, 407.3.8 Curing Concrete.
The curing compound method may be used on concrete surfaces which are to be
buried under ground and surfaces where only Ordinary Surface Finish is to
be applied and on which a uniform color is not required and which will not
be visible from public view.
The top surface of highway bridge decks shall be cured by either the curing
compound method or the water method. The curing compound shall be applied
progressively during the deck finishing operations. The water cure shall be
applied not later than 4 hours after completion of the deck finishing.
When deemed necessary by the Engineer during periods of hot weather, water
shall be applied to concrete surface being cured by the curing compound
method or by the forms-in-place method until the Engineer determine that a
cooling effect is no longer required.
6. Curing Pre-Cast Concrete (except piles)
Pre-cast concrete members shall be cured for not less than 7 days by the
water method or by steam curing. Steam curing for pre-cast members shall
conform to the following provisions:
a. After placement of the concrete, members shall be held for a minimum
4-hour pre-steaming period.
b. To prevent moisture loss on exposed surfaces during the pre-steaming
period, members shall be covered immediately after casting or the exposed
surface shall be kept wet by fog spray or wet blankets.
c. Enclosures for steam curing shall allow free circulation of steam about
the member and shall be constructed to contain the live steam with a
minimum moisture loss. The use of tarpaulins or similar flexible covers
will be permitted, provided they are kept in good condition and secured in
such a manner to prevent the loss of steam and moisture.
d. Steam at jets shall be low pressure and in a saturated condition. Steam
jets shall not impinge directly on the concrete, test cylinders, or forms.
During application of the steam, the temperature rise within the enclosure
shall not exceed 200C per hour. The curing temperature
throughout the enclosure shall not exceed 650C and shall be
maintained at a constant level for a sufficient time necessary to develop
the required compressive strength. Control cylinders shall be covered to
prevent moisture loss and shall be placed in a location where temperature
of the enclosure will be the same as that of the concrete.
e. Temperature recording devices that will provide an accurate continuous
permanent record of the curing temperature shall be provided. A minimum of
one temperature recording device per 50 m of continuous bed length will be
required for checking temperature.
f. Curing of pre-cast concrete will be considered completed after the
termination of the steam curing cycle.
7. Curing Pre-cast Concrete Piles All newly placed concrete for pre-cast
concrete piles, conventionally reinforced or prestressed shall be cured by
the “Water Method” as described in Subsection 407.3.8, Curing Concrete,
except that the concrete shall be kept under moisture for at least 14 days.
At the option of the Contractor, stream curing may be used in which case
the steam curing provisions of Subsection 407.3.8 (6), Curing Pre-Cast
Concrete(except piles) shall apply except that the concrete shall be kept
wet for at least 7 days including the holding and steaming period.
407.3.9 Falsework Design and Drawings
Detailed working drawings and supporting calculations of the falsework
shall be furnished by the Contractor to the Engineer. No falsework
construction shall start until the Engineer has reviewed and approved the
design. The Contractor shall provide sufficient time for the Engineer to
complete this review. Such time shall be proportionate to the complexity of
the falsework design and in no case be less than two weeks.
The Contractor may review the falsework drawings at any time provided
sufficient time is allowed for the Engineer’s review before construction is
started on the revised portion.
Assumptions used in design of the falsework shall include but not be
limited to the following:
1. The entire superstructure cross-section, except for the railing, shall
be considered to be placed at one time, except when in the opinion of the
Engineer, a portion of the load is carried by members previously cast and
having attained a specified strength.
2. The loading used on timber piles shall not exceed the bearing value for
the pile and shall in no case exceed 20 tonne per pile.
3. Soil bearing values and soil condition (wet and dry) shall be designated
by the Contractor on the falsework drawings. Falsework footings shall be
designed to carry the loads imposed upon them without exceeding estimated
soil bearing values or allowable settlements.
4. The maximum loadings and deflections used on jacks, brackets, columns
and other manufactured devices shall not exceed the manufacture’s
recommendations. If requested by the Engineer, the Contractor shall furnish
catalogue or other data verifying these recommendations.
5. If the concrete is to be prestressed, the falsework shall be designed to
support any increased or readjusted loads caused by the prestressing
forces.
6. Joints supporting slabs and overhangs shall be considered as falsework
and designed as such.
For the construction of falsework over and adjacent to roadways where
falsework openings are required for maintaining traffic, the Contractor
shall provide any additional features for the work needed to insure that
the falsework will be stable if subjected to impact by vehicles.
The falsework design at the locations where said openings are required
shall include but not be limited to the following minimum provisions:
a. Each exterior stringer in a span shall be securely anchored to the
following cap or framing.
b. Adequate bracing shall be used during all stages of falsework
construction and removal over or adjacent to public traffic.
c. Falsework members shall be at least 300 mm clear of temporary protective
railing members.
The falsework drawings shall include a superstructure placing diagram
showing proposed concrete placing sequence and construction joint
locations, except that where a schedule for placing concrete is shown on
the Contract Plans, no deviation will be permitted there from unless
approved in writing by the Engineer.
The falsework drawings shall show pedestrian openings which are required
through the falsework.
Anticipated total settlements of falsework and forms shall be indicated by
the Contractor on the falsework drawings. These should include falsework
footing settlements over 20 mm will not be allowed unless otherwise
permitted by the Engineer. Deck slab forms between girders shall be
constructed with no allowance for settlement relative to the girders.
Detailed calculations by the Contractor showing the stresses deflections,
and camber necessary to compensate for said deflections in all load
supporting members shall be supplied.
After approving the Contractor’s falsework deflection camber, the Engineer
will furnish to the Contractor the amounts of camber necessary to
compensate for vertical alignment or anticipated structure deflection, if
these are not shown on the drawings. The total camber used in constructing
falsework shall be the sum of the aforementioned cambers.
407.3.10 Falsework Construction
The falsework shall be constructed to conform to the falsework drawings.
The materials used in the falsework construction shall be of the quantity
and quality necessary to withstand the stresses imposed. The workmanship
used in falsework shall be of such quality that the falsework will support
the loads imposed on it without excessive settlement or take-up beyond that
shown on the falsework drawings.
When falsework is supported on piles, the piles shall be driven to a
bearing value equal to the total calculated pile loading as shown on the
falsework drawings.
Suitable jacks or wedges shall be used in connection with falsework to set
the forms to their required grade and to take up any excessive settlement
in the falsework either before or during the placing of concrete.
The Contractor shall provide tell-tales attached to the soffit forms easily
readable and in enough systematically-placed locations to determine the
total settlement of the entire portion of the structure where concrete is
being placed.
Should unanticipated events occur, including settlements that deviate more
than ±20 mm from those indicated on the falsework drawings, which in the
opinion of the Engineer would prevent obtaining a structure conforming to
the requirement of the Specification, the placing of concrete shall be
discontinued until corrective measures satisfactory to the Engineer are
provided. In the event satisfactory measures are not provided prior to
initial set of the concrete in the affected area, the placing of concrete
shall be discontinued at a location determined by the Engineer. All
unacceptable concrete shall be removed.
407.3.11 Removing Falsework
Unless otherwise shown on the drawings, or permitted by the Engineer,
falsework supporting any span of a supported bridge shall not be released
before14 days after the last concrete, excluding concrete above the bridge
deck, has been placed. Falsework supporting any span of a continuous or
rigid frame bridge shall not be released before 14 days after the last
concrete excluding concrete above the bridge deck, has been placed in that
span and in the adjacent portions of each adjoining span for a length equal
to at least half the length of the span where falsework is to be released.
Falsework supporting deck overhangs and deck slabs between girders shall
not be released until 7 days after the deck concrete has been placed.
In addition to the above requirements, no falsework for bridges shall be
released until the supported concrete has attained a compressive strength
of at least 80% of the required 28-day strength. Falsework for cast-in
place prestressed portion of structure shall not be released until after
the prestressing steel has been tensioned.
All falsework materials shall be completely removed. Falsework piling shall
be removed at least 50 cm below the surface of the original ground or
stream bed. When falsework piling is driven within the limits of ditch or
channel excavation areas, the falsework piling within such areas shall be
removed to at least 50 cm below the bottom and side slopes of said
excavated areas.
All debris and refuse resulting from work shall be removed and the site
left in a neat and presentable condition.
407.3.12 Formwork Design and Drawings
The Contractor shall prepare drawings and materials data for the formwork
and shutters to be submitted to the Engineer for approval unless otherwise
directed.
The requirements for design of formwork are the same as described under
Section 407.3.9.
407.3.13 Formwork Construction
Concrete forms shall be mortar-tight, true to the dimensions, lines and
grades of the structure and with the sufficient strength, rigidity, shape
and surface smoothness as to leave the finished works true to the
dimensions shown on the Plans or required by the Engineer and with the
surface finish as specified.
Formwork and shutters are to be constructed in accordance with the approved
Plans.
The inside surfaces of forms shall be cleaned of all dirt, mortar and
foreign material. Forms which will later be removed shall be thoroughly
coated with form oil prior to use. The form oil shall be of commercial
quality form oil or other approved coating which will permit the ready
release of the forms and will not discolor the concrete.
Concrete shall not be deposited in the forms until all work in connection
with constructing the forms has been completed, all materials required for
the unit to be poured, and the Engineer has inspected and approved said
forms and materials. Such work shall include the removal of all dirt,
chips, sawdust and other foreign material from the forms.
The rate of depositing concrete in forms shall be such to prevent bulging
of the forms or form panels in excess of the deflections permitted by the
Specification.
Forms for all concrete surfaces which will not be completely enclosed or
hidden below the permanent ground surface shall conform to the requirements
herein for forms for exposed surfaces. Interior surfaces of underground
drainage structures shall be completely enclosed surfaces.
Formwork for concrete place under water shall be watertight. When lumber is
used, this shall be planed, tongued and grooved.
Forms for exposed concrete surface shall be designed and constructed so
that the formed surface of the concrete does not undulate excessively in
any direction between studs, joists, form stiffeners, form fasteners, or
wales. Undulations exceeding either 2 mm or 1/270 of the center to center
distance between studs, joists, form stiffeners, form fasteners, or wales
will be considered to be excessive. Should any form of forming system, even
though previously approved for use, produce a concrete surface with
excessive undulations, its use shall be discontinued until modifications
satisfactory to the Engineer have been made. Portions of concrete
structures with surface undulations in excess of the limits herein
specified may be rejected by the Engineer.
All exposed surfaces of similar portions of a concrete structure shall be
formed with the same forming material or with materials which produce
similar concrete surface textures, color and appearance.
Forms for exposed surfaces shall be made of form materials of even
thickness and width and with uniform texture. The materials shall have
sharp edges and be mortar-tight.
Forms for exposed surfaces shall be constructed with triangular fillets at
least 20 mm wide attached so as to prevent mortar runs and to produce
smooth straight chamfers at all sharp edges of the concrete.
Form fasteners consisting of form bolts, clamps or other devices shall be
used as necessary to prevent spreading of the forms during concrete
placement. The use of ties consisting of twisted wire loops to hold forms
in position will not be permitted.
Anchor devices may be cast into the concrete for later use in supporting
forms or for lifting precast members. The use of driven types of anchorage
for fastening forms of form supports to concrete will not be permitted.
407.3.14 Removal of Forms and Falsework
Forms and falsework shall not be removed without the consent of the
Engineer. The Engineer’s consent shall not relieve the Contractor of
responsibility for the safety of the work. Blocks and bracing shall be
removed at the time the forms are removed and in no case shall any portion
of the wood forms be left in the concrete.
Falsework removal for continuous or cantilevered structures shall be as
directed by the Engineer or shall be such that the structure is gradually
subjectedto its working stress.
When concrete strength tests are used for removal of forms and supports,
such removal should not begin until the concrete has attained the
percentage of the specified design strength shown in the table below.
Part of Structure
|
Minimum Time
|
Minimum Percentage Design Strength
|
| Centering under girders, beams frames or arches
Floor slabs Walls Columns Sides of beams and all other vertical surfaces |
14 days
14 days
1 day
2 days
1 day
|
80%
70%
70%
70%
70%
|
In continuous structures, falsework shall not be released in any span until
the first and second adjoining spans on each side have reached the strength
specified herein, or in the Special Specifications. When cast-in-place
posttensioned bridges are constructed, falsework shall remain in place
until all posttensioning has been accomplished.
Falsework under all spans of continuous structures shall be completely
released before concrete is placed in railings and parapets. In order to
determine the condition of column concrete, forms shall be removed from
columns before releasing supports from beneath beams and girders.
Forms and falsework shall not be released from under concrete without first
determining if the concrete has gained adequate strength without regard to
the time element. In the absence of strength determination, the forms and
falsework are to remain in place until removal is permitted by the
Engineer.
The forms for footings constructed within cofferdams or cribs may be left
in place when, in the opinion of the Engineer, their removal would endanger
the safety of the cofferdam or crib, and when the forms so left intact will
not be exposed to view in the finished structure. All other forms shall be
removed whether above or below the ground line or water level.
All forms shall be removed from the cells of concrete box girders in which
utilities are present and all formwork except that necessary to support the
deck slab shall be removed from the remaining cells of the box girder.
To facilitate finishing, forms used on ornamental work, railing, parapets
and exposed vertical surfaces shall be removed in not less than 12 nor more
than 48 hours, depending upon weather conditions. In order to determine the
condition of concrete in columns, forms shall always be removed from them
before the removal of shoring from beneath beams and girders.
Falsework and centering for spandrel-filled arches not be struck until
filling at the back of abutments has been placed up to the spring line.
Falsework supporting the deck of rigid frame structure shall not be removed
until fills have been placed back to the vertical legs.
407.4 Method of Measurement
The quantity of structural steel, structural concrete, reinforcing steel or
other Contract Pay Items shall constitute the completed and accepted
structure which shall be measured for payment in the manner prescribed in
the several items involved.
407.5 Basis of Payment
The quantities measured as provided in Section 407.4, Method of Measurement
shall be paid for at the contract price for the several pay items which
price and payment shall be full compensation for furnishing, preparing,
fabricating, placing, curing and for all labor, equipment, tools and
incidentals necessary to complete the Item. Such payment shall constitute
full payment for the completed structure ready for use.
Payment will be made under:
Pay Item Number
|
Description
|
Unit of Measurement
|
405 (1)
405 (2)
405 (3)
400
103
601
404
407 (1)
|
Concrete Class A, C & P
Concrete Post/Baluster Railings Parapet Walls Piling Structure Excavation Sidewalk Concrete Reinforcing Steel Bars Lean Concrete |
Cubic Meter
Each
Cubic Meter
Linear Meter
Cubic Meter
Square Meter or Cubic Meter
Kilogram
Cubic Meter
|
When more than one item is specified, means of identification shall be
inserted in parenthesis immediately after the Pay Item and letter suffixes
shall be included within the parenthesis of the Pay Item Number.
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