PLAIN AND REINFORCED CONCRETE
SCOPE OF WORK
This item shall consist of furnishing, placing, and finishing concrete in buildings and related
structures, flood control and drainage, and water supply structures in accordance with these
specifications and conforming to the lines, grades, and dimensions shown on the plans.
3-1 GENERAL REQUIREMENTS
1. Acronyms
The following acronyms for applicable standards/publications are referred to in this specification:
● ASTM – American Society for Testing Materials
● ACI – American Concrete Institute
● PCI – Pre-Stressed Concrete Institute
● AWS – American Welding Society
● AISC – American Institute of Steel Construction
2. Standard Specifications and Codes
The work covered by this section, unless otherwise specified or detailed, shall be governed by
the Building Code Requirements for Reinforced Concrete (ACI 318) and the Standard Code for
Arc and Gas Welding Society. The latest edition of all standard specifications or codes will be
used.
SPECIFICATIONS AND CONTRACT
3. Coordination
The concrete work shall be coordinated with the work of other trades to allow reasonable time to
set sleeves, inserts, and other accessories, which must be in position before concrete bases
and pads of mechanical equipment are placed to comply with approved shop drawings for the
equipment.
4. Workmanship
The contractor shall be responsible for any additional cost that may result from concrete
surfaces that are not finished to the required profile or elevation.
5. Samples
The contractor shall submit samples of cement and aggregates proposed for use in the concrete
work for approval, enumerating names, sources, and descriptions of materials.
3-2 MATERIAL REQUIREMENTS
1. Portland Cement
● Portland cement shall conform to the requirements of ASTM C-150:
○ Type I for normal Portland cement
○ Type III for high early strength Portland cement
● Cement shall be any standard commercial brand in 40-kilogram bags, such as
Filipinas, Union, Republic, Apo, or other locally available equivalents.
2. Fine Aggregates
● Sand shall be clean, hard, coarse river sand or crushed sand, free from injurious
amounts of clay, loam, and vegetable matter.
● It shall conform to ASTM C-33 or C-330 standards.
PLASTICIZING ADMIXTURE
Concrete admixture shall be free from chlorides and shall conform to ASTM C-494-651. The
admixtures shall be used in all concrete mixtures in accordance with the manufacturer's
specifications.
Calcium Chloride
Calcium chloride shall not be used under any circumstances.
3-5 PROPORTIONING OF CONCRETE
1. Mix Design and Testing
The contractor shall employ, at his own expense, an approved testing laboratory to design the
mix for each type of concrete required by the specifications and drawings. The mix shall be
designed to obtain a strength at least 15% higher than required, as determined by test
cylinders.
2. Strength Requirements
Strength requirements shall be as noted on the drawings. The adequacy of the mix design shall
be verified by testing a minimum of six (6) cylinders, as follows:
● Three (3) cylinders tested at 7 days
● Three (3) cylinders tested at 28 days
Testing shall be conducted in accordance with ASTM C-192 and C-39, with slump tests
performed per ASTM C-143.
3. Submission of Test Results
The testing laboratory shall submit five (5) copies of the mix design and test results to the
Owner or his authorized representative for approval before any concrete is placed.
4. Modifications to Mix Design
If at any time during construction the concrete from the approved mix design proves to be
unsatisfactory due to:
● Excessive water content
● Lack of sufficient plasticity (leading to segregation or honeycombing)
● Insufficient strength
The Contractor shall immediately notify the testing laboratory and the supervising engineer.
The laboratory shall modify the mix design, subject to approval by the supervising architect or
engineer, until a satisfactory concrete mix is obtained.
SPECIFICATIONS AND CONTRACT
Stone Concrete
The minimum compressive cylinder strength of concrete (fc') at 28 days shall be as follows:
● fc' = 27.58 MPa for suspended beams, slabs, and columns.
● fc' = 20.68 MPa for footings and walls.
The water content shall not exceed 28 liters per 40-kilogram bag of cement, and the slump
test shall not exceed 10 cm in all cases unless otherwise modified by the supervising architect
or engineer.
Lean Concrete
The lean concrete mix shall be designed to produce concrete with a 28-day strength of 13.79
MPa. The slump and aggregate size shall be subject to approval depending on where it is
mixed.
3-6 DETERMINING CONCRETE
PROPORTIONS
The determination of the proportions of cement, aggregate, and water to attain the required
strengths shall be made using one of the following methods. However, lower water-cement
ratios may be required to ensure the quality of the concrete.
Method 1 – Without Preliminary Test
1. When preliminary test data on the materials to be used in the concrete have not been
obtained, the water-cement ratio for a given concrete strength shall not exceed the
values shown in Table 3-1.
2. When strengths exceeding 28.1 MPa (4000 psi) are required, or when lightweight
aggregates or air-entraining admixtures are used, the required water-cement ratio
shall be determined in accordance with Method 2.
METHOD 2 – FOR COMBINATION OF MATERIALS PREVIOUSLY
EVALUATED OR ESTABLISHED BY TRIAL MIXTURES
The water-cement ratio for strengths greater than those shown in Table 3-1 (Maximum
Permissible Water-Cement Ratio) may be used if the relationship between strength and
water-cement ratio has been previously established by reliable test data, and the resulting
concrete meets the required quality standards.
TRIAL MIXTURES (WHEN PREVIOUS DATA IS UNAVAILABLE)
If previous data is not available, trial mixtures shall be prepared with proportions and
consistency suitable for the work. The trials shall:
● Use at least three different water-cement ratios (or cement content, in the case of
lightweight aggregates).
● Produce a range of strengths encompassing those required for the work.
● For each water-cement ratio (or cement content), at least three specimens per test age
shall be made, cured, and tested for strength in accordance with ASTM C-39 and
C-192.
● Strength tests shall be conducted at 7, 14, and 28 days, or as specified in the plans.
ESTABLISHING THE STRENGTH RELATIONSHIP
A curve shall be developed to show the relationship between the water-cement ratio and
compressive strength. The maximum permissible water-cement ratio for the concrete used
in the structure shall be:
● The ratio that produces an average strength meeting the strength test
requirements.
● No greater than the permissible ratio for concrete quality, especially when the
concrete is subjected to freezing temperatures.
SPECIFICATIONS AND CONTRACT
The water-cement ratio shall not exceed 6 gallons per bag, and the concrete mix shall contain
entrained water.
Where different materials are used for different portions of the work, each combination shall be
evaluated separately.
TABLE 3-1: MAXIMUM PERMISSIBLE WATER-CEMENT
RATIOS FOR CONCRETE (METHOD 1)
Compressive Strength Non Air-Entrained Concrete Air-Entrained Concrete
at 28 Days (psi)
2500 7-1/4 gal per 42.6 kg bag 6-1/4 gal per 42.6 kg bag
(0.642 absolute ratio by weight) (0.554 absolute ratio by weight)
3000 6-1/2 gal per 42.6 kg bag 5-1/4 gal per 42.6 kg bag
(0.576 absolute ratio by weight) (0.465 absolute ratio by weight)
3500 5-3/4 gal per 42.6 kg bag 4-1/2 gal per 42.6 kg bag
(0.510 absolute ratio by weight) (0.399 absolute ratio by weight)
4000 5 gal per 42.6 kg bag (0.443 4 gal per 42.6 kg bag (0.354
absolute ratio by weight) absolute ratio by weight)
3-7 CONCRETE PROPORTIONS AND CONSISTENCY
1. The proportions of aggregate to cement for any concrete mix shall be such that it:
○ Produces a workable mixture that readily fills corners and angles of the form.
○ Properly surrounds the reinforcement without segregation of materials.
○ Prevents the accumulation of excess free water on the surface.
2. The methods of measuring concrete materials shall:
○ Ensure that proportions are accurately controlled.
○ Be easily checked at any time during the work.
Here is your revised and well-structured paragraph:
PLAIN AND REINFORCED CONCRETE
3-8 CONCRETE TEST
A. Testing Laboratory
1. The Contractor shall, at their own expense, employ an approved Testing Laboratory
to conduct compression and slump tests. The laboratory shall immediately submit 5
copies of the test reports to the supervising Architect or Engineer.
2. Ready-mixed concrete companies may use their own laboratories, provided that the
testing is done under the supervision of the Owner or their authorized representatives.
B. Compression and Slump Test
● Compression and slump tests shall be performed for every 50 cubic meters of
concrete or fraction thereof.
● At least one set of tests shall be made for each batch of concrete. All tests must be
conducted from the same batch.
C. Compression Tests
● Prepare 3 standard 15 cm x 30 cm cylinders and test in accordance with ASTM C-31
and C-39.
● Test one (1) cylinder at the age of 28 days, and keep one (1) cylinder in reserve for a
56-day test.
● If the 28-day test does not meet the requirements, additional cylinders shall be made as
required to check the strength of concrete in the construction.
● These cylinders must be cured in the field in the same manner as the concrete in the
construction.
SPECIFICATIONS AND CONTRACT
E. Test Report
The testing laboratory shall submit 4 copies of its test cylinder reports. These reports must
include, as applicable, the following information:
● Location of the structure where the concrete is used.
● Design number, concrete design strength, type, and manufacturer of Portland cement.
● Amount of any admixtures used, slump tests, date of sampling, cylinder application
number, days cured in the field, and days cured in the laboratory.
● Age at the time of testing, crushing stress, type of failure, who made the cylinders, who
shipped the cylinders to the laboratory, and whether concrete strength meets the
specifications.
F. Inspection of Batch Plant Operation
Inspection shall be conducted on a "Spot Check" basis as required to ensure that concrete
delivery to the job complies with the Specifications and the design mix. The testing
laboratory shall provide this service as directed by the Owner's supervising Engineer.
G. Additional Tests
If, in the opinion of the supervising Engineer, concrete of poor quality has been placed due to
cylinder strengths below specification requirements or visual defects, additional tests shall be
performed as directed by the Owner at the expense of the Contractor.
Tests may include:
● Compression Tests on core cylinders per ASTM C-42.
● Lead Tests as outlined in ACI 318, Section 202, or as specified.
MIXING CONCRETE
The mixing and measuring equipment shall be approved by the supervising Architect or
Engineer. Unless otherwise authorized, concrete shall be machine mixed at the site or by
ready-mixed concrete.
A. Site Mixed Concrete
Provide a batch mixer equipped with accurate timing and measuring devices. The mixer shall
be operated in accordance with the manufacturer's recommendations.
B. Mixing Time
1. For each batch, after all solid materials are placed inside the mixing drum and water is
introduced, the mixing time shall not be less than 1 minute for mixers having a capacity
of one (1) cubic meter or a fraction thereof for additional concrete.
2. The concrete mixer shall revolve at no less than 14 revolutions per minute and no
more than 20 revolutions per minute.
● Speed greater than 20 revolutions per minute and less than 14 revolutions per
minute are usually found to be unsatisfactory.
3-10 READY MIXED CONCRETE
1. All ready-mixed concrete shall conform to the requirements of ASTM C-94, and shall
be placed in forms within one hour after adding water, or within a maximum of two
hours if a retarder is used. It shall be kept constantly agitated during the transit.
2. Pouring of concrete should not begin until after the forms and reinforcement for the
entire unit are properly laid, installed, cleaned, inspected, and approved.
3-11 HANDLING AND PLACING CONCRETE
1. Immediately after the concrete is mixed, it shall be conveyed by an approved push cart
or buggies to designated locations. The concrete should be carefully deposited in such
a manner as to prevent the separation of ingredients or displacement of the
reinforcements.
2. Temporary runways shall be built in such a manner that the runway supports do not bear
upon the reinforcement of fresh concrete.
3. Conveying or hauling of concrete by the use of long inclined chutes or pipes shall not be
permitted.
4. Dumping concrete into carts or buggies with a free fall of more than one (1) meter will
not be permitted.
5. Hardened splashes or accumulation of concrete on forms or reinforcements shall be
removed before continuing the work.
6. When placing operations involve dropping the concrete from a height of more than 1.50
meters, it shall be deposited through a sheet metal or other approved conveyors.
7. For practicality, the conveyors shall be kept full of concrete during the placing, and their
lower ends shall be kept buried in the newly placed concrete.
8. After the initial set of the concrete, the forms shall not be jarred, and no strain shall be
placed on the ends of the projecting reinforcing bars.
9. The foundation shall be free from water during concreting, and the construction joints
shall be determined by the supervising Architect or Engineer.
3-12 RE-TAMPERING
The Contractor shall mix only such quantities of concrete as are required for immediate use.
Mixture that has developed initial setting shall not be used. Concrete that has partially hardened
shall not be re-tampered for use.
3-13 CURING AND PROTECTION
1. All concrete work shall be protected from drying out after removal of forms. This can be
achieved by covering the concrete with waterproof paper, polyethylene sheeting, or
burlap, with a coating of an approved membrane curing compound that ensures moisture
retention of at least 90%, based on ASTM C-309 and C-156. The compound shall be
applied in accordance with the manufacturer's instructions.
2. Membrane curing compound shall not be used where floor hardeners, waterproofing,
damp-proofing, resilient floor tiles, or other floor or wall coverings set in adhesive,
concrete fill, or setting beds, paint, plaster, or other applied finishing or surface
treatments are to be subsequently applied.
3. Wet burlap shall be used as often as required to keep concrete wet throughout each day
for a period of at least 7 days where normal Portland cement is used, and 3 days where
high-early-strength cement is used.
3-14 METAL REINFORCEMENT
Concrete in columns shall be placed in one continuous pouring operation and allowed to set for
12 hours before caps are placed. Similarly, concrete in beams and slabs in superstructures shall
be poured in one operation.
L. Steel Bars
1. Reinforcing bars shall conform to ASTM Specifications A-615. All mild steel for columns,
shear walls, footings, and footing beams shall be high-grade deformed bars with Fy =
413.7 MPa.
2. For 10 mm and smaller bars, use intermediate grade deformed bars with Fy = 275.8
MPa.
3. If reinforcing bars are to be welded, these specifications shall be supplemented by
additional requirements to ensure satisfactory weldability.
4. Bar and rod mats for concrete reinforcement shall conform to ASTM Specifications
A-184. Wires for concrete reinforcement shall conform to ASTM A-82.
5. Welded wire fabric for concrete reinforcement shall conform to ASTM A-185, with the
additional requirement that the weld shear strength specifications include a wire size
differential up to and including six gauges.
6. Wire and strand shall conform to ASTM A-416. Structural steel shall conform to ASTM
A-26. Steel pipe for composite columns shall conform to ASTM Specification A-377.
2. Provide Accessories
Bar supports and other accessories necessary to hold reinforcing bars in the proper positions
while concrete is being placed shall be provided. Bar supports that come in contact with forms
for concrete exposed to view in the finished structure shall be galvanized or made of stainless
steel, subject to approval.
Testing and Certification
1. The Contractor shall furnish 2 copies of the manufacturer's certificate of mill tests for all
reinforcing steel.
2. The Contractor shall employ, at his own expense, an approved testing laboratory to
conduct testing of all reinforcement sizes for each bulk under the supervision of the
supervising Architect or Engineer.
4. Shop Drawings
1. Each reinforcing steel detail and placement drawing shall be submitted for approval.
2. Any material fabricated before the final approval of the shop drawings will be done at the
Contractor's risk. However, no material shall be installed until the final approval of the
shop drawings.
3. All shop drawings shall be in accordance with the Manual Standard Practice for Detailing
Reinforced Concrete Structures ACT-315.
5. Bars Labeling
1. Bars shall be properly labeled with weatherproof tags to facilitate identification.
3-15 Placing of Reinforcement
1. All reinforcement shall be placed according to the approved drawings. The Contractor
shall provide sufficient bar supports, ties, anchors, and other accessories to hold all bars
securely in place.
2. Unless detailed on the drawings, all stirrups shall be held in place by bar spacers.
Reinforcing steel shall be...
Reinforcement and Welding
1. Bars shall be free from oil, grease, scale, rust, or other coatings that will impair the bond.
2. All bars shall be bent cold.
3. All welded splices shall be done by certified welders having a welder's certificate. This
certificate shall be submitted and approved by the supervising Architect or Engineer
before any welding work begins.
4. The welding of bars shall conform to AWS D-12.1 Recommended Practices for Welding
Reinforcing Steel.
3-16 Storage of Materials
1. Reinforcing steel bars shall be stored on supports above ground level and properly
covered with a roof or plastic materials for protection from direct moisture exposure and
considerable delay in use.
3-17 Forms
General Conditions
1. Forms shall conform to the shape, lines, and dimensions shown on the drawings. They
must be substantial and designed to resist the pressure and weight of the concrete.
2. Forms shall be properly tied, braced, or shored to maintain their position and shape.
3. Forms shall be sufficiently tight and strong to prevent leakage of mortar.
4. Where required by the Owner, shop drawings of the formwork shall be submitted for
approval before fabrication and erection of such formwork.
Plain and Reinforced Concrete
1. Provide temporary openings where necessary to facilitate cleaning and inspection before
depositing concrete.
2. Before construction, all form materials are subject to approval.
3. The type of form used shall be in accordance with the finish requirements as specified or
as shown on the detailed drawings.
4. Forming shall start at the first-floor level with new materials.
5. Forms for exposed concrete may be reused only if the surface has not absorbed
moisture and has not splintered, warped, or peeled, subject to the approval of the
supervising Architect or Engineer.
6. Forms shall be coated with non-staining form oil before setting reinforcement. The form
oil shall not contain chemicals that will impair the strength of the concrete.
7. Side forms of footings may be omitted, and concrete placed against the next excavation
only when approved by the supervising Architect or Engineer.
8. All exposed corners shall be square.
9. Extra care shall be exercised while stripping the forms. Corners shall be protected
against chipping or other damage that may be caused by the workforce.
10.Removal of forms or shoring is subject to approval by the supervising Architect or
Engineer, and under no circumstances shall bottom forms and shoring be removed until
after the members have acquired sufficient strength to support their weight and the load
thereon.
11.Forms shall remain in place for a minimum time as follows:
● Columns, shear, and bearing walls: 3 days
● Stairs (bottom forms): 21 days
38.
Gradation of Aggregates
1. Fine and coarse aggregates used in concrete shall be tested in accordance with the
requirements of the "Standard Specifications for Concrete Aggregates" ASTM 033-67m,
with a minimum frequency of one (1) set of 6 and one (1) set of 7 tests per 1,000 cubic
meters of the source, as follows:
2. At least one sample of fine and coarse aggregates used in concrete shall be tested in
accordance with the requirements of the "Standard Specifications for Concrete
Aggregates" ASTM 033-67, grading as follows:
○ Coarse Aggregates:
■ Material finer than No. 200 sieve
■ Absorption
■ Specific Gravity
■ Abrasion
■ Soundness
■ Grading
○ Fine Aggregates:
■ Grading
■ Absorption
■ Soundness
■ Organic Impurities
■ Material finer than No. 200 sieve
■ Mortar strength, 7 days
■ Specific Gravity
Plain and Reinforced Concrete
● Coarse Aggregates:
○ 38 mm sieve: 100%
○ 25 mm sieve: 95-100%
○ 13 mm sieve: 25-50%
○ No. 4 sieve: 0-10%
○ No. 8 sieve: 0-5%
● Fine Aggregates:
○ 9 mm sieve: 100%
○ No. 1 sieve: 90-100%
○ No. 8 sieve: 80-95%
○ No. 16 sieve: 50-85%
○ No. 30 sieve: 30-70%
○ No. 50 sieve: 10-45%
○ No. 100 sieve: 0-10%
Gradation of Aggregates
1. Fine and coarse aggregates used in concrete shall be tested in accordance with the
requirements of the "Standard Specifications for Concrete Aggregates" ASTM 033-67m,
with a minimum frequency of one (1) set of 6 tests and one (1) set of 7 tests per 1,000
cubic meter source, as follows:
2. At least one sample of fine and coarse aggregates used in concrete shall be tested in
accordance with the "Standard Specifications for Concrete Aggregates" ASTM 033-67
grading as follows:
Coarse Aggregates:
● Material finer than No. 200 sieve
● Specific Gravity
● Absorption
● Abrasion
● Soundness
Fine Aggregates:
● Soundness
● Grading
● Organic Impurities
● Material finer than No. 200 sieve
● Mortar strength (7 days)
● Specific gravity
lain and Reinforced Concrete
● Coarse Aggregate Gradation:
○ 38 mm sieve: 100%
○ 25 mm sieve: 95-100%
○ 13 mm sieve: 25-50%
○ No. 4 sieve: 0-10%
○ No. 8 sieve: 0-5%
● Fine Aggregate Gradation (percent passing):
○ 9 mm sieve: 100%
○ No. 1 sieve: 90-100%
○ No. 8 sieve: 80-95%
○ No. 16 sieve: 50-85%
○ No. 30 sieve: 30-70%
○ No. 50 sieve: 10-45%
○ No. 100 sieve: 0-10%
● Aggregate Usage:
○ Aggregates failing to meet these specifications, but which have been shown by
approved laboratory tests to produce concrete of the required quality, may be
used where authorized by the Architect or Engineer.
○ Aggregates shall be quarried or washed in fresh water and shall contain no more
than one twentieth (1%) of salt by weight.
Cement Storage and Handling
● Bags of Cement:
○ Bags shall have a guaranteed constant cement content and shall be properly
labeled with the number of the consignment and the date of site delivery.
○ Bags shall be stacked close together to reduce the circulation of air but should
not be stacked against outside walls. They should be arranged in such a way that
they are easily accessible for inspection and testing, and used in the order of
their delivery.
○ Cement that has been in storage longer than six months will be tested by
standard mortar tests or other tests as deemed necessary by the Owner to
determine its suitability. Such cement shall not be used without the express
approval of the Owner.
○ Bags shall not be stored to a height greater than two (2) meters. All cement must
be free from lumps or any signs of deterioration.
● Bulk Cement:
○ Cement delivered in bulk shall be stored in properly designated, elevated,
airtight, and waterproofed silos or bins, provided at the Contractor's expense.
○ The silos shall be adequate in size to ensure continuity of work at all times, and
the site shall be kept perfectly dry.
○ Bagged cement shall be transported closed and effectively protected from
weather by adequate coverings.
○ Bulk cement shall be transported in closed containers.
Aggregates Storage
● Storage Conditions:
○ All aggregates shall be stored in bunkers provided with proper floors or tightly laid
wood planks, sheet metals, or other hard and clean surfaces.
○ Fine and coarse aggregates of different sizes shall be stored separately.
Plain and Reinforced Concrete
● Stockpiles of Coarse Aggregate:
○ Stockpiles of coarse aggregate shall be built in horizontal layers not exceeding
1.20 meters in depth to minimize segregation.
○ To prevent contamination, the stockpiles shall be arranged in such a manner as
to avoid aggregation, inclusion, and contamination by dirt and other injurious
foreign materials.
○ Should the coarse aggregate become segregated, it should be re-mixed to
conform to the grading requirements as specified.
Reinforcing Steel Bars
● Transport and Storage:
○ Reinforcing steel bars shall be transported and stored at the site in such a way as
to prevent damage or deterioration of the steel by rust or coating with grease, oil,
dirt, and other objectionable materials.
○ The storage of steel bars shall be in separate piles or racks to avoid confusion or
loss of identification after the bundles are broken.
Rebar Spacing and Cover
1. Reinforcing Bars:
○ Reinforcing bars shall be fixed one to the other by means of adequate steel wire
ties to form rigid reinforcement cages or nets.
○ The reinforcement shall be fixed in the form by approved concrete distance
blocks, spacer bars, links, and stirrups, all provided at the Contractor's expense.
○ Reinforcing bars shall be spaced according to the approved working drawings,
and the distance between bars shall not be less than those recommended in
ACI-318.
2. Concrete Cover:
○ The concrete cover to the gutter reinforcing bars shall meet the requirements
recommended in ACI-318, unless otherwise specifically indicated on the
drawings.
41
SPECIFICATIONS AND CONTRACT
3. Anchorage Length.
Plain bars shall be provided with end hook unless otherwise specified.
The lengths of the anchorage of reinforcing bars shall be at least
those recommended in ACI 318.
4. Splices
Splices in bars shall be avoided as far as possible and shall be
staggered in any one structural member. They shall conform to the
recommendations in ACI 318. In no case shall splices be made at
critical points of maximum stress.
3-29 PATCHING
1.Immediately after the forms have been removed and work has
been examined by the Owner, and his permission given, all loose
materials shall be removed.
2.All holes, stone pockets and other surfaces which were in
contact with forms treated with cement retarding materials shall
be removed with wire brush or other approved method until a
rough bonding surface of exposed aggregate is obtained.
3.Any surface considered by the supervising Engineer to be
insufficiently roughened shall be further roughened by an
approved mechanical means. Surfaces shall be thoroughly
washed down with water.
4.Honey combed and other defective areas must be chipped out to
solid concrete, the edge cut as straight as possible and at right
angles to the surface of slightly undercut to provide a key at the
edge of the patch.
5.Shallow patches may be filled with mortar similar to that used in
the concrete. This should be placed in layers not more than 12
mm thick and each layer given a scratch finish to improve bond
with the succeeding layer.
3-30 CONSTRUCTION JOINTS
1.Once started, concreting shall be continued without interruption
and shall only be stopped at properly indicated and prepared
construction joints.
2.The position of construction joints shall be decided in advance so
that the amount of concrete required to be placed at any one
time does not exceed the capacity of the mixing plant.
3.In all cases where the positions of construction joints have not
been indicated on the drawings, they must be approved by the
Architect or Engineer.
4.Except where inclined joints are specified, all joints shall be
formed to vertical or horizontal planes. Vertical joints shall be
formed against a properly constructed stop-board.
5.As a general rule, joints in columns shall be made as near as
possible to a beam haunching and joint in beams and slabs shall
be made at positions shown on the drawings.
6.Construction joints shall be wire-brushed while the concrete is
still green, roughened or hacked to expose the aggregate across
the whole area of the joint.
7.Before fresh concrete is placed, the roughened surface shall be
swept clean of all loose materials, thoroughly wetted and
covered with a 12 mm thick layer of mortar composed of cement
and sand in the same ratio as the cement and sand in the
concrete mix.
8.Special care shall be taken to ensure that the first layer of fresh
concrete is thoroughly rammed against the existing layer.
