SECTION 06100 - CONCRETE AND CONCRETE STRUCTURES
This Specification section addresses requirements and procedures for concrete work which
shall include, but not be limited to, preparing concrete mixes of different classes,
transporting and placing on prepared surfaces or in pre-prepared forms, including supplying
and fixing of temporary and permanent formwork; vibrating, tamping and curing. This
Specification section shall be applicable to all concrete and concrete construction including
cast-in-place concrete elements, precast concrete members and pre-stressed concrete works....
DIVISION 6 CONCRETE AND CONCRETE STRUCTURES Concrete and Concrete StructuresSection 06100
SECTION 06100 - CONCRETE AND CONCRETE STRUCTURES
TABLE OF CONTENTS
1. DESCRIPTION .................................................................................................................................................1
2. STANDARDS AND CODES.............................................................................................................................1
3. MATERIALS .....................................................................................................................................................2
3.1 General 2
3.2 Cement 2
3.3 Aggregate 3
3.3.1 FINE AGGREGATES ..............................................................................................................................................4
3.3.2 COARSE AGGREGATE ..........................................................................................................................................5
3.4 Water for Concrete Mixing and Curing.............................................................................................................6
3.5 Admixtures.........................................................................................................................................................6
4. CONCRETE CLASSES.....................................................................................................................................7
4.1 General 7
4.2 Class Requirements ..........................................................................................................................................7
PREPARED BY N.D.TOAN
4.2.1 USES OF DIFFERING CLASSES OF CONCRETE ...........................................................................................................8
5. MIX DESIGNS ..................................................................................................................................................8
5.1 Samples 8
5.2 Mix Design .......................................................................................................................................................8
5.3 Adjustments During Progress of Work ............................................................................................................9
5.4 Contents of Chlorides and Sulphates..................................................................................................................9
6. WATER CEMENT RATIO..........................................................................................................................10
7. TESTING..........................................................................................................................................................10
7.1 Slumps 11
8. FORMWORK...................................................................................................................................................11
8.1 Design 11
8.2 Construction ...................................................................................................................................................12
8.3 General Requirements......................................................................................................................................12
9. CONCRETING.................................................................................................................................................13
9.1 General 13
9.2 Placing and Compacting...................................................................................................................................14
9.3 Weather Precautions .......................................................................................................................................15
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9.4 Continuity of Concrete Work...........................................................................................................................16
9.5 Batching 16
9.5.1 PORTLAND CEMENT ............................................................................................................................................16
9.5.2 WATER 17
9.5.3 AGGREGATES 17
9.5.4 BINS AND SCALES ..............................................................................................................................................17
9.6 Mixing and Delivery ......................................................................................................................................17
10. CONCRETE PLACEMENT ........................................................................................................................18
10.1 General 18
10.2 Chutes and Troughs .......................................................................................................................................18
10.3 Pumping .........................................................................................................................................................19
10.4 Vibrating ........................................................................................................................................................19
10.5 Concrete Consistency ....................................................................................................................................19
11. JOINTS............................................................................................................................................................19
11.1 General 19
11.2 Construction Joints .......................................................................................................................................20
11.3 Bonded Construction Joints ...........................................................................................................................20
11.4 Unbonded ......................................................................................................................................................21
PREPARED BY N.D.TOAN
11.5 Expansion Joints ...........................................................................................................................................22
12. CONCRETE FINISHING.............................................................................................................................22
12.1 Finishing Concrete Surfaces .........................................................................................................................22
12.1.1 CLASS F1 – FORMED SURFACE .........................................................................................................................22
12.1.2 CLASS F2 – FORMED SURFACE..........................................................................................................................22
12.1.3 CLASS F3 – FORMED SURFACE..........................................................................................................................23
12.1.4 CLASS F4 – FORMED SURFACE..........................................................................................................................23
12.1.5 CLASS U1 – UNFORMED SURFACE ....................................................................................................................23
12.1.6 CLASS U2 – UNFORMED SURFACE ....................................................................................................................23
12.1.7 CLASS U3 – UNFORMED SURFACE.....................................................................................................................23
12.2 Requirements for Formed Surfaces................................................................................................................24
12.3 Remedial Treatment of Finished Surfaces.....................................................................................................24
12.4 Fixing of Ironwork .......................................................................................................................................24
12.5 Reconstruction of Faulty Work ....................................................................................................................24
13. CURING..........................................................................................................................................................24
13.1 Supplying Additional Moisture ....................................................................................................................25
13.2 Preventing Moisture Loss .............................................................................................................................25
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13.3 Waterproof Paper ..........................................................................................................................................25
13.4 Plastic Sheets..................................................................................................................................................25
13.5 Curing Compounds.........................................................................................................................................25
13.6 Forms 26
14. PLACING OF CONCRETE IN OR UNDER WATER..............................................................................26
15. WATERSTOPS..............................................................................................................................................27
16. TOLERANCES...............................................................................................................................................28
16.1 General 28
16.2 Soffits 28
17. PRECAST CONCRETE ELEMENTS.........................................................................................................30
17.1 General 30
17.2 Materials 30
17.3 Fabrication......................................................................................................................................................31
18. MEASUREMENT AND PAYMENT...........................................................................................................31
18.1 General 31
18.1.1 MEASUREMENT ...............................................................................................................................................31
18.1.2 PAYMENT 32
PREPARED BY N.D.TOAN
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SECTION 06100 - CONCRETE AND CONCRETE STRUCTURES
1. DESCRIPTION
This Specification section addresses requirements and procedures for concrete work which
shall include, but not be limited to, preparing concrete mixes of different classes,
transporting and placing on prepared surfaces or in pre-prepared forms, including supplying
and fixing of temporary and permanent formwork; vibrating, tamping and curing. This
Specification section shall be applicable to all concrete and concrete construction including
cast-in-place concrete elements, precast concrete members and pre-stressed concrete works.
2. STANDARDS AND CODES
The following Standards and Codes in their latest edition shall be particularly applied to
Works covered by this Specification.
AASHTO M6 - Fine Aggregate for Portland Cement Concrete
♦
AASHTO M33 - Preformed Expansion Joint Filler for Concrete (Bituminous
♦
Type)
AASHTO M115 - Asphalt for Dampproofing and Waterproofing
♦
PREPARED BY N.D.TOAN
AASHTO M116 - Primer for Use With Asphalt in Dampproofing and
♦
Waterproofing
AASHTO M118 - Coal-Tar Pitch for Roofing, Dampproofing, and
♦
Waterproofing
AASHTO M148 - Liquid Membrane-Forming Compounds for Curing Concrete
♦
AASHTO M153 - Preformed Sponge Rubber and Cork Expansion Joint Fillers
♦
for Concrete Paving and Structural Construction
AASHTO M182 - Burlap Cloth made from Jute or Kenaf
♦
AASHTO T96 - Resistance to Abrasion of Small Size Coarse Aggregate by
♦
Use of the Los Angeles Machine
AASHTO T119 - Slump of Portland Cement Concrete
♦
AASHTO T134 - Moisture-Density Relations of Soil-Cement Mixtures
♦
AASHTO T224 - Correction for Coarse Particles in the Soil Compaction Test
♦
ASTM C33 - Concrete Aggregates
♦
ASTM C39 - Compressive Strength of Cylindrical Concrete Specimens
♦
ASTM C40 - Organic Impurities in Fine Aggregates for Concrete
♦
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ASTM C87 - Effect of Organic Impurities in Fine Aggregate on Strength of
♦
Mortar
ASTM C88 - Soundness of Aggregate by Use of Sodium Sulfate or Magnesium
♦
Sulfate
ASTM C91 - Masonry Cement
♦
ASTM C123 - Lightweight Pieces in Aggregate
♦
ASTM C136 - Sieve Analysis of Fine and Coarse Aggregates
♦
ASTM C143 - Slump of Portland Cement Concrete
♦
ASTM C144 - Aggregate for Masonry Mortar
♦
ASTM C150 - Portland Cement
♦
ASTM C227 - Potential Alkali Reactivity of Cement-Aggregate Combinations
♦
(Mortar-Bar Method)
ASTM C294 - Constituents of Natural Mineral Aggregates
♦
ASTM C494 - Chemical Admixtures for Concrete
♦
ASTM D1457 TFE-Fluorocarbon Resin Molding and Extrusion Materials
♦
3. MATERIALS
PREPARED BY N.D.TOAN
3.1 GENERAL
(a) All materials shall comply with all requirements as specified herein and other
applicable subsections of this Specification section.
(b) Materials shall be delivered, stored and handled so as to assure the preservation of
their quality and fitness for the Works. Materials, even though approved before
storage or handling, may again be inspected and tested prior to use in the Works.
Stored materials shall be located so as to facilitate their prompt inspection. All storage
sites shall be restored to their original condition at the Contractor’s expense prior to
acceptance of the Works.
(c) Materials that do not comply with the requirements of this Specification will be
rejected by the Engineer and removed immediately from the Site of the Works unless
otherwise instructed by the Engineer. No rejected materials shall be used in the
Works.
3.2 CEMENT
(a) The cement shall be portland cement Type I, complying in all respects with ASTM
C150 (AASHTO M85). All cement shall be manufacturer’s standard grey cement
unless otherwise specified on the Drawings. One brand of cement as approved by the
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Engineer shall be used for all concrete works throughout the project unless otherwise
authorized by the Engineer in writing.
(b) The source of supply of cement shall be subject to the Engineer’s approval and the
Contractor shall at all times furnish the manufacture’s test certificates and proof that
the specifications have been complied with, together with a note of the date of
manufacture, certified by an independent agency in the country of origin. The
Engineer shall have the power to reject a part or the whole of any consignment of
cement if he considers it to be unsuitable for use in the Works.
(c) Cement shall be delivered to the Site in sealed bags or water-tight barrels bearing the
manufacturer’s name, cement type and the date of manufacture. The bagged cement
shall be stored in piles not more than eight bags high. Storage areas shall be perfectly
dry waterproof sheds or other such temporary buildings approved by the Engineer.
The storage capacity shall correspond to the amount of concrete required for the
largest units to be cast. These buildings shall be used exclusively for the storage of
cement and shall be erected with the floors raised well above the ground at places on
or near the Site of the Works; and at the completion of the Works the buildings shall
remain the property of the Contractor and shall be dismantled and removed, the
foundations broken up and the site restored to its original condition by the Contractor.
(d) A free passage of at least one meter shall be left between the cement and the side
PREPARED BY N.D.TOAN
walls of the sheds. Access ways shall also be left between the stored containers of
cement such that every container is visible. Each consignment of cement shall be
stored apart form earlier consignments and consignments shall be used in the order in
which they are delivered. Any consignment which has become caked or otherwise
adversely affected shall be removed from the Site completely at the Contractor’s own
expense.
3.3 AGGREGATE
(a) Aggregates shall be free of substances that are deleteriously reactive with the alkalies
in the cement in an amount sufficient to cause excessive expansion of the concrete.
Aggregate acceptance shall be based on satisfactory evidence furnished by the
Contractor that the aggregate is free from such materials. This evidence shall include
service records of concrete of comparable properties under similar conditions of
exposure and/or certified records of tests by a testing laboratory that meets the
requirements of ASTM C 1077. Tests shall be made in accordance with ASTM C
227, ASTM C 295 and ASTM C 289.
(b) All aggregates shall consist of tough, hard, durable and uncoated particles. The
Contractor shall be responsible for satisfactorily processing this material to meet the
requirements of these Specifications. Thirty days before starting work, the Contractor
shall advise the Engineer of the sources of aggregates to be used to permit samples to
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be taken in the presence of a representative of the Engineer and the Contractor to test
before being brought to the Site. Approval of aggregate quality and/or gradation shall
not waive the responsibility of the Contractor to fabricate concrete of the strength
specified.
(c) Aggregates shall be stored in such a way as to prevent segregation and contamination.
The center of the storage area shall be free of excess moisture. Aggregate which has
become segregated or contaminated with foreign matter during storage or handling
will be rejected and shall be removed and reprocessed and/or replaced with material
of acceptable quality. Aggregates shall be stored in sufficient quantity to ensure that
there is no interruption of concreting work at any time.
(d) Both fine and coarse aggregates shall be tested in accordance with the following
standards:
ASTM C39 Compressive Strength
♦
ASTM C40 Organic Impurities
♦
ASTM C87 Mortar Strength
♦
ASTM C88 Soundness
♦
ASTM C123 Coal and Lignite
♦
ASTM C136 Sieve Analysis
♦
PREPARED BY N.D.TOAN
(e) Approval of aggregates will not prevent later rejection if results of subsequent tests do
not reflect compliance with the requirements of the specified standards.
3.3.1 FINE AGGREGATES
(a) Fine aggregate for portland cement concrete shall consist of natural sand or other
inert materials with similar characteristics, having hard, strong, durable particles. Fine
aggregate shall be clean and free from extraneous materials, clay balls, organic matter
or other detrimental material in accordance with AASHTO M6. The maximum
combined quantity of soluble chlorides and sulphates in the fine aggregate shall not
exceed 1000 ppm fine aggregate.
(b) The fine aggregates shall be reasonably graded and shall meet the grading
requirements contained in Table No. 1 below:
TABLE NO. 1
Grading Requirements of Fine Aggregate
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Sieve Size Percent Passing by weight
(mm)
9.5 100
4.75 95 100
2.36 80 100
1.18 50 85
0.600 25 60
0.300 5 30
0.150 2 10
(c) The fine aggregate shall be of such uniformity that the fineness modulus as defined in
AASHTO M6 shall not vary more than 0.20 either way from the fineness modulus of
the representative samples used in the mix designs.
(d) If required by the Engineer and in order to meet specification requirements, fine
aggregates for use in reinforced concrete shall be washed with fresh potable water.
3.3.2 COARSE AGGREGATE
PREPARED BY N.D.TOAN
(a) Coarse aggregate shall be crushed aggregate for reinforced concrete works and
unreinforced concrete works and shall be homogeneous, clean, free from extraneous
materials, clay lumps, organic matter alkaline and detrimental material. Coarse
aggregate for structural concrete shall meet the requirements of AASHTO M 80. The
Engineer may order that the coarse aggregate be washed if it is unclean, or may reject
any material that does not comply with this Specification.
(b) The quarry from which the coarse aggregate is to be obtained shall be approved by
the Engineer before material is delivered to the Site of the Works.
(c) Coarse aggregate shall meet the requirements of ASTM C33.
(d) The coarse aggregates shall be reasonably graded and shall meet the grading
requirements in Table No. 2 below.
TABLE NO. 2
Grading Requirements of Coarse Aggregates
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PERCENT PASSING BY WEIGHT
SIEVE SIZE
(mm) Concrete Concrete Concrete
Class A, B, C and D Class E and F Class G and P
37.5 100 100
25 100 90 100 95 100
19 90 100
12.5 30 70 25 60 25 60
No. 4 0 10 0 10 0 10
(e) The percentage of wear of the aggregate shall not be greater than 50 as determined by
AASHTO T96. The coarse aggregate shall withstand at least five cycles of immersion
and drying in both sodium sulphate and magnesium sulphate solutions, as prescribed
in the soundness test, and shall show an average weight loss of not more than 15
percent.
3.4 WATER FOR CONCRETE MIXING AND CURING
(a) Unless otherwise authorized in writing by the Engineer, only potable water free from
PREPARED BY N.D.TOAN
oil, salt, acid, sugar, vegetable matter or any other substance injurious to the concrete
may be used for mixing concrete and curing concrete and other products containing
cement.
(b) The Engineer may require additional compliance testing at any time, of any water
source.
3.5 ADMIXTURES
(a) To avoid cold joints the Contractor shall provide sufficiently large capacity in his
concrete producing plant and concrete transporting arrangements and use an
appropriate retarder when deemed necessary by the Engineer. The retarder shall be of
a type approved by the Engineer and shall comply with the requirements of Type D as
specified in ASTM C494. The Contractor shall be entirely responsible for the use of
any approved retarder in strict accordance with the manufacturer’s instructions.
(b) Retarders shall not be used together with other admixtures in the same mix unless
approved by the Engineer. The fluid content of admixtures shall be considered in the
determination of water/cement ratios.
(c) Preliminary tests of cylinder strength and any other tests shall be carried out for all
concrete with admixtures. When the Engineer approves changing the brand or type of
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cement, the Contractor will be required to carry out further tests and establish a
relative mix design.
(d) Water reducing and water reducing-retarding admixtures, in accordance with ASTM
C494 and plasticizing and retarding admixtures in accordance with ASTM C1017
may be used with the written permission of the Engineer in accordance with mix
designs and slump requirements as approved by the Engineer.
(e) Calcium chloride or admixtures containing calcium chloride will not be permitted.
(f) The Engineer shall approve the type of, amount of and place in which any or all
admixture shall be used.
4. CONCRETE CLASSES
4.1 GENERAL
Concrete to be used for this Contract shall have the following mix designations and strength
requirements except for those specifically mentioned elsewhere in this Specification.
4.2 CLASS REQUIREMENTS
(a) The approximate weights or volumes of the components for each class of concrete
PREPARED BY N.D.TOAN
and any other data given in any table of this Specification are an aid for suggested
trial mixes and may be of value to Contractors in determining the approximate
quantities of components required. However, the minimum crushing strength of the
Work Test cylinders at 7 days and 28 days must be strictly adhered to. Acceptance of
the work by the Engineer will be based on 28-day cylinder strength as determined in
accordance with requirements and procedures noted under this Specification section.
(b) Concrete to be used shall include the properties and strength requirements contained
in Table No. 3. Method for Testing Concrete, AASHTO T22 and T23 (ASTM C31
and C39) shall govern for the manufacture of compressive strength test cylinders for
all classes of concrete.
TABLE NO. 3
Composition and Strength of Concrete for Use in Structures
CLASS OF CONCRETE
REQUIREMENTS
A B C D E F G P
Maximum Size of
20 20 20 20 25 38 38 38
Course Aggregate
Minimum 45 40 35 30 25 20 15 Flexural
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CLASS OF CONCRETE
REQUIREMENTS
A B C D E F G P
Compressive Strength
Strength of 150 mm at 28 days
x 300 mm Concrete
5000 kPa
Cylinder at 28 days
(MPa)
Minimum Cement
450 420 380 350 330 280 220 350
Content (kg/m3)
Water Cement Ratio
0.375 0.40 0.45 0.475 0.50 0.60 0.76 0.40
(Max.)
Slump Range (mm) 50 50 50 50
2575 2575 2575 2550
100 100 100 100
4.2.1 USES OF DIFFERING CLASSES OF CONCRETE
The class of concrete to be used in each part of the Contract works shall be as called for on
the Drawings or as directed by the Engineer.
5. MIX DESIGNS
PREPARED BY N.D.TOAN
5.1 SAMPLES
Samples of all materials to be used in the mix shall be submitted to the Engineer and such
samples shall be tested in site laboratories as directed by the Engineer. No materials forming
any part of this mix shall be delivered to the Site before the Contractor receives the prior
written approval of the Engineer for such material.
5.2 MIX DESIGN
(a) After receiving written approval by the Engineer of the samples, the Contractor shall
submit in writing to the Engineer a proposed mix design proportioned by weight and
based on trial mixes conducted with the approved materials to be used for each
specified class of concrete for the project.
(b) No concrete works will be allowed to commence before the Contractor receives, in
writing from the Engineer, approval of the Contractor’s proposed mix design.
(c) The Contractor must make arrangements for all the foregoing as early as possible and
to allow the Engineer sufficient time to review the design(s) and if necessary conduct
and/or require additional strength testing.
(d) In the event of any changes in characteristics or source of supply of any of the
component parts, a new mix design must be submitted for approval by the Engineer as
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described. Any delay due to such changes will be entirely the responsibility of the
Contractor and no claims for delay or compensation will be considered. During the
currency of the Contract the Engineer can direct samples be taken of the work mix at
any time, in order to check their compliance with the approved mix design.
5.3 ADJUSTMENTS DURING PROGRESS OF WORK
After a mix design has been approved, as prescribed above, these proportions of the
constituents of the mix design shall not be changed during the progress of the work except
as follows:
(a) Adjustments for variations in workability:
If it is found impossible to obtain concrete of the desired workability with the
♦
proportions originally determined, the Engineer may allow changes in
aggregate weights as he may deem appropriate.
(b) Adjustment for variation in yield:
If the cement content of the concrete, determined by means of the yield test
♦
ASTM Designation C 138, varies more than two (2) percent from the
designated value, the proportions shall be adjusted so as to maintain a cement
content which does not vary more than two (2) percent from the designated
PREPARED BY N.D.TOAN
value.
(c) Adjustment for minimum strength:
If it is found impossible to produce concrete having the minimum allowable
♦
strength specified, the cement content shall be increased as directed by the
Engineer.
(d) Adjustment for new materials:
No change in the source or character of the materials shall be made without due
♦
notice to the Engineer.
No new materials shall be used until the Engineer has accepted such materials
♦
and new proportions based on the tests of trial mixes have been determined.
5.4 CONTENTS OF CHLORIDES AND SULPHATES
The amount of chlorides in the concrete mass shall not exceed 1,000 ppm when calculated
on the total concrete mass, or 6,000 ppm when calculated on the amount of cement in the
actual mix. The amount of sulphate in the concrete shall not exceed 800 ppm when
calculated on the total concrete mass, or 5,000 ppm when calculated on the amount of the
cement in the actual mix. For the above-mentioned calculations, the amounts of chlorides
and sulphates shall be determined by laboratory analyses of the cement, aggregates, water
and admixtures. The analyses shall be carried out by recognized methods.
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6. WATER - CEMENT RATIO
(a) The quantity of water used in mixing shall be approved by the Engineer on the basis
of preliminary tests and trial mixes and shall be the least amount that will produce a
workable homogeneous plastic mixture which can be worked into the forms and
around the reinforcement. In no circumstances shall the consistency of the concrete be
such as to permit a separation of the aggregate from the mortar during handling.
Excess water shall not be permitted and any batch containing such excess will be
rejected.
(b) In measuring water for each batch of concrete, allowance shall be made for the water
contained in the aggregates. The total water in the batch shall be deemed to consist of
the water carried by the aggregates plus the water added.
(c) Frequent tests including the slump test shall be carried out to ensure that a consistent
water content is maintained.
7. TESTING
(a) In addition to all previously mentioned tests, the following tests shall be carried out.
All tests must be carried out in a manner acceptable to the Engineer and shall be
conducted by the Contractors Independent Laboratory. The Contractor shall bear all
expenses involved in obtaining, cutting-out or sampling all specimens and/or
PREPARED BY N.D.TOAN
component parts for testing.
(b) Test cylinders shall be taken for each new grade of concrete or from each 100 cubic
meters of concrete when the same grade is being used continuously, or as directed by
the Engineer. Nine (9) test cylinders shall be taken at each time and each numbered
consecutively and marked with the date, the section of work from which it was taken
and any other information required and dispatched to the approved laboratory for
testing for compressive strength. Cylinders Numbers 1,5 and 9 shall be tested after 7
days.
(c) If the average of the three 7-day test cylinders is below 75 percent of the minimum 28
day requirement, the Contractor must immediately stop all concreting until checks are
made on the material and equipment and immediately rectify any defect which has
become apparent as the result of such checking. If the Contractor elects to remove and
replace the defective concrete without waiting for the results of the 28-day test,
concreting can then continue entirely at the responsibility of the Contractor. Cylinder
numbers 2 and 8, 3 and 7, and 4 and 6 will be considered three individual samples or
sets and after 28 days of curing shall be tested as specified above. If either of the
cylinders in any set shows definite evidence, other than low strength, of improper
sampling, molding, handling, curing or testing, it shall be discarded and the strength
of the remaining cylinder shall then be considered the test result of that set.
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(d) Final acceptance of the concrete works is based on 28 days’ testing on the three sets
of two cylinders each. The work is considered in compliance if the average of the
three sets of cylinders equals or exceeds the minimum specified for the class of
concrete being placed and if the average of the two cylinders in any one set does not
fall below the specified minimum strength by more than 35 kg/cm2. If the results of
the 28-day testing are unsatisfactory, the Contractor, in accordance with the
instructions of the Engineer, shall conduct tests in the suspect parts of the structure.
Should the tests prove that the concrete is unsatisfactory or below the standards
specified, the Engineer may order the concrete to be removed and replaced with
concrete of the specified quality or accepted at a reduced payment. All the above shall
be at the expense and responsibility of the Contractor.
7.1 SLUMPS
(a) Recommended limitations for slump are given in Table No. 3 above. The method of
making the slump test shall conform to ASTM C 143.
(b) One slump test, or more as directed by the Engineer, shall be carried out on every
batch of concrete produced, and the test shall not be deemed to have been carried out
unless witnessed by the Engineer or his representative.
(c) Mixes of the stiffest consistency that can be placed efficiently shall be used. Over wet
mixes will be rejected.
PREPARED BY N.D.TOAN
8. FORMWORK
8.1 DESIGN
(a) All formwork shall be the responsibility of the Contractor, who shall submit shop
drawings, calculations, materials and manufactured goods, to the Engineer for
approval at least 3 weeks before construction of the forms.
(b) The shop drawings shall show the proposed details of construction such as sizes of
members, spacing of bents, posts, studs, walers, stringers, collars, bolts, wedges,
bracing, rate of pour, and the manufacturer’s recommended safe working capacity of
all form ties and column clasps. All assumptions, dimensions, material properties and
other data used in making the structural analysis shall be noted on the shop drawings.
Upon request, the Contractor shall furnish copies of the design calculations to the
Engineer for examination as a condition for approval.
(c) When prefabricated formwork, shoring or scaffolding units are used, the
manufacturer’s recommendations for allowable loads may be followed if supported
by test reports or successful experience records. For materials which will experience
substantial reuse, reduced allowable load values may be required.
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(d) The design of the formwork shall be the sole responsibility of the Contractor and the
strutting and bracing of the formwork shall be such that there shall be no harmful
deformation of the forms under the weight of the plastic concrete, or due to methods
adopted for the placing and compacting thereof, or due to any incidental loading. No
accessory for supporting the formwork or stagings shall be built into the permanent
structure except with the Engineer’s approval.
(e) Formwork shall be designed for vertical loads and lateral pressures in accordance
with ACI 347. In addition, the formwork shall be constructed to provide completed
concrete surfaces complying with the tolerances specified therein.
8.2 CONSTRUCTION
(a) The formwork shall be constructed accurately to represent the shape of the concrete
as detailed on the Drawings. It shall be of suitable design and substantial construction
and be approved by the Engineer. The Contractor shall make any necessary
adjustments to allow for shrinkage, settlement or deflection which may occur during
construction so that the finished concrete sections conform accurately to the specified
dimensions true to line, level and camber.
(b) No concrete shall be deposited in the forms until all work connected with constructing
the forms and placing all reinforcing steel, ducts, anchorages, or prestressing steel has
been completed for the unit to be poured and the Engineer has given written approval
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of said forms, reinforcing steel, ducts, anchorages, or prestressing steel.
(c) Drainage holes and weep holes shall be constructed as detailed on the Drawings.
Forms for weep holes shall be as approved by the Engineer.
(d) The Contractor shall install in the formwork required inserts, anchors, expansion joint
elements, sleeves and other items specified under other Subsections of this
Specification and shall coordinate their installation with other trades in the proper
location of such items. Ends of piping and sleeves embedded in concrete shall be
closed with caps or plugs.
(e) To facilitate finishing, forms used for parapets, barriers, and exposed vertical surfaces
shall be removed in not less than 24 hours nor more than 48 hours, depending on
weather conditions.
8.3 GENERAL REQUIREMENTS
(a) The inside surfaces of forms shall, except for permanent formwork, or unless
otherwise agreed by the Engineer, be coated with a release agent approved by the
Engineer. Release agents shall be applied strictly in accordance with the
manufacturer’s instructions and shall not come into contact with the reinforcement or
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prestressing tendons and anchorages. Different release agents shall not be used in
formwork to concrete which will be visible in the finished Works.
(b) Immediately before concreting, all forms shall be thoroughly cleaned out.
9. CONCRETING
9.1 GENERAL
(a) All concrete shall be machine mixed. The location of the batching and mixing plant
shall be agreed with the Engineer and the Contractor must submit to the Engineer for
approval, before erection of any mixing plant, his proposed arrangements for the
storing of aggregates and the batching and mixing of the concrete. He must also
submit details of the type or types of mixers and machines to be used, and his
proposals for conveying the mixed concrete from the mixer to the points of deposit.
(b) All concrete shall be batched by weight unless otherwise directed by the Engineer.
The weight-batching machines used shall be of a type approved by the Engineer and
shall be kept accurate and in good condition while in use on the Works. Checks are to
be made as required by the Engineer to determine that the weighing devices are
registering correctly. Each mixer shall be fitted with a water measuring device having
an accuracy within one percent of the quantity of water required for the batch. The
measuring device shall be such that its accuracy is not affected by variations in the
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water supply pressure.
(c) In the event aggregate batching is by volume, the cement shall be batched by weight
and the water by weight or volume. Each size of aggregate shall be measured in a
metallic container, the depth of which is at least equal to its greatest width. The
containers shall be of such shape that their volume can be easily checked by
measurement.
(d) The approved type of mixer shall have a drum rotating about a horizontal or inclined
axis and must be kept in good condition at all times. The drum shall rotate at the
appropriate speed. Continuous mixers will not be permitted.
(e) The amount of concrete mixed in any one batch shall not exceed the rated capacity of
the mixer. The whole of the batch shall be removed before materials for a fresh batch
enter the drum. On cessation of work, including all stoppages exceeding 20 minutes,
the mixers and all handling plant shall be washed with clean water. Any deposits of
old concrete in the drum shall be cleaned out by rotating clean aggregate and water in
the drum before any fresh concrete is mixed.
(f) Concrete mixed as specified above shall not be modified by the addition of water or in
any other manner to facilitate handling or for any other reason.
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9.2 PLACING AND COMPACTING
(a) Immediately after mixing, the concrete shall be transported to the place of final
deposit by methods that will prevent the separation, loss or contamination of any of
the ingredients. Any method involving the use of pipes or chutes for transporting
concrete will not be permitted, except with the written approval of the Engineer.
(b) Transport of concrete from the mixers shall be as rapid as possible and the Contractor
shall always be responsible for the concrete being placed and compacted within such
a time from the addition of the water to the mixer that the previous lift of concrete has
not commenced setting.
(c) Before any concrete is placed, the formwork shall be thoroughly cleaned of all dirt,
shavings, loose stones and other debris.
(d) Forms shall be treated with a non-staining material or shall be saturated with water
immediately before the concrete is placed. For all exposed surfaces, the forms shall be
treated with a non-staining material, as approved by the Engineer, to prevent the
adherence to the concrete. The forms shall be free from any material that shall adhere
to or discolor the concrete.
(e) The concrete shall be placed gently in position and shall not have a free fall of more
than one meter.
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(f) Concrete shall be placed so as to prevent water from collecting at the ends, corners or
along the faces of the forms, and water shall not be placed in large quantities at a
given point and allowed to run or be worked over a long distance in the form.
(g) All concrete shall be placed and compacted in even layers with each batch adjoining
the previous one.
(h) The thickness of concrete layers shall be between 15 and 30 cm for reinforced
concrete and up to 45 cm for unreinforced concrete.
(i) The concrete shall be carefully and continually compacted and worked around the
reinforcement steel and into the corners of the formwork so that the concrete shall be
in close contact with the reinforcement steel and free from honeycombing.
(j) The concrete shall be compacted by a suitable mechanical or electromechanical poker
vibrators. Over-vibration of concrete in the formwork by means of vibrators will not
be permitted.
(k) The poker vibrators shall have a diameter compatible with the spacing of the
reinforcement, shall be of sufficiently high frequency, and shall be properly handled
by experienced personnel. They shall be immersed at regular intervals of
approximately 10 times the diameter of the vibrator and to such a depth that the fresh
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concrete will be worked into that previously placed. Care shall be taken not to
displace the reinforcement nor to disturb or affect partially set concrete. Vibrators
shall not be attached to the reinforcement in any circumstances. Each immersion shall
continue until shortly after air bubbles cease to appear on the surface of the concrete,
but shall not last more than 30 seconds. The vibrators shall be withdrawn gradually
and vertically to ensure that no air pockets are formed.
(l) The Contractor shall provide “stand-by” vibrators during all concrete pours.
(m) All vibration, compaction and finishing operations shall be completed immediately
after the placing of concrete in its final position.
(n) Workers shall not be permitted to walk over freshly placed concrete until it has
hardened sufficiently to carry their weight without distortion.
(o) Care shall be taken to ensure that reinforcement projecting from concrete recently
placed is not shaken or disturbed so as to destroy or damage the initial set of the
concrete in contact with it.
(p) Concreting in any one part or section of the work shall be carried out in one
continuous operation and no interruption of concerning work will be allowed.
(q) Freshly placed concrete shall be adequately protected from rain, dust storms,
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chemical attack and the harmful effects of sun, heat, wind, flowing water, vibrations
and shocks. It shall also be fenced off or otherwise protected to prevent persons from
walking thereon or articles being placed or thrown thereon. This protection shall
continue until the concrete is sufficiently set such that it can no longer be damaged by
these factors. The Engineer may determine when the protection is no longer required,
but in any case this shall not be less than 24 hours after the time of placing.
(r) The Contractor shall take all necessary precautions to prevent differential
temperatures across any concrete element exceeding 200 C during concrete placing
and curing.
9.3 WEATHER PRECAUTIONS
(a) During hot weather, steps shall be taken to reduce the concrete temperature and rate
of water evaporation by proper attention to the cooling of the mixing water before
use, production methods and the handling and curing.
(b) The concrete mixing plant shall be screened and covered as a protection from wind,
rain and sun and adequate similar precautions taken throughout the transit, placing
and curing of the concrete whenever conditions require them.
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(c) When the shade air temperature is 35 degrees C and rising, special precautions shall
be taken during all concrete operations so that the temperature of the concrete when
placed does not exceed 32 degrees C.
(d) Shading of aggregates and plant, the cooling of mixing water and other steps taken
shall be to the satisfaction of the Engineer.
(e) Fresh concrete placed at temperatures of 35 degrees or higher shall be shaded from
the direct rays of the sun to the satisfaction of the Engineer.
9.4 CONTINUITY OF CONCRETE WORK
(a) Whenever instructed by the Engineer, the Contractor shall carry out the work in such
a manner that the placing of the concrete in any particular section of the structure
shall be executed without any interruption whatsoever from the beginning to the end
of the operation. If interruptions are permitted, no fresh concrete shall be deposited on
or against the concrete placed before the interruption until the latter is sufficiently set
to resist injury.
(b) Particular care shall be taken to ensure that partially set concrete shall not be damaged
by shock or any other cause whatsoever.
(c) Casting of concrete shall not commence until a sufficient quantity of approved
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material is at hand to ensure continuity of operation.
(d) Concrete work shall not commence until there is sufficient equipment in reserve in
case of breakdown.
9.5 BATCHING
Measuring and batching of materials shall be done at a batching plant.
9.5.1 PORTLAND CEMENT
(a) Either sacked or bulk cement may be used. No fraction of a sack of cement shall be
used in a batch of concrete unless the cement is weighed.
(b) All bulk cement shall be weighed on an approved weighing device. The bulk cement
weighing hopper shall be properly sealed and vented to preclude dusting during
operation. The discharge chute shall not be suspended from the weighing hopper and
shall be so arranged that cement will not lodge in it nor leak from it.
(c) Accuracy of batching shall be within plus or minus 1 percent of the required weight.
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9.5.2 WATER
Water may be measured either by volume or by weight. The accuracy of measuring the
water shall be within plus or minus one percent of the required weight or volume.
9.5.3 AGGREGATES
(a) All aggregates produced or handled by hydraulic methods and washed aggregates
shall be stockpiled or binned for draining at least 12 hours before being batched. In
case the aggregates contain high or non-uniform moisture content, a storage or
stockpile period in excess of 12 hours may be required by the Engineer.
(b) The accuracy of measuring the aggregates shall be within plus or minus two percent
of the required weights.
9.5.4 BINS AND SCALES
(a) The batching plant shall include separate bins for the bulk cements, fine aggregate
and for each size of coarse aggregate, a weighing hopper, and scales capable of
determining accurately the weight of each component of the batch.
(b) Scales shall be accurate to one percent throughout the range of use.
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9.6 MIXING AND DELIVERY
(a) Concrete may be mixed at the site of construction, at a central point or by a
combination of central point and truck mixing or by a combination of central point
mixing and truck agitating.
(b) Mixing and delivery of concrete shall be in accordance with the appropriate
requirements of ASTM C-94 except as modified in the following paragraphs of this
Subsection for truck mixing or a combination of central point and truck mixing or
truck agitating. Delivery of concrete shall be so regulated that placing is at a
continuous rate unless delayed by the placing operations. The intervals between
delivery of batches shall not be so great as to allow the concrete in place to harden
partially, and in no case shall such an interval exceed 45 minutes.
(c) Additional mixing water and/or admixture may not be added on the Work Site unless
specifically authorized by the Engineer and if the water/cement ratio in the approved
job mix is not exceeded and the truck mixer is loaded to no more than 70 percent of
its rated capacity.
(d) The mixer shall be operated at the drum speed as indicated on the manufacturer’s
name plate on the mixer. Any concrete mixed less than the specified time shall be
discarded and disposed of by the Contractor.
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