A.
Description.
(1)
The work of this article includes but is not limited to:
(3)
CONCRETE
EXPOSED CONSTRUCTION
f'c
Definitions. As used in this article, the following terms shall have
the meanings indicated:
Normal weight concrete for which density is not a controlling
attribute, made with aggregates of the types covered by ASTM C33,
and having unit weights in the range of 135 to 160 pounds per cubic
foot.
Permanently exposed to view.
The design compressive strength of the hardened concrete
at an age of 28 days.
(4)
Applicable Standard Details: none.
B.
Quality assurance.
(1)
Reference standards.
(a)
American Concrete Institute (ACI).
(b)
American Society for Testing and Materials (ASTM):
[1]
A185, Specification for Steel Welded Wire Fabric, Plain, for
Concrete Reinforcement.
[2]
A615, Specification for Deformed and Plain Billet-Steel Bars
for Concrete Reinforcement.
[3]
C31, Practice for Making and Curing Concrete Test Specimens
in the Field.
[4]
C33, Specification for Concrete Aggregates.
[5]
C39, Test Method for Compressive Strength of Cylindrical Concrete
Specimens.
[6]
C42, Test Method of Obtaining and Testing Drilled Cores and
Sawed Beams of Concrete.
[7]
C94, Specification for Ready-Mixed Concrete.
[8]
C138, Test Method for Unit Weight, Yield, and Air Content (Gravimetric)
of Concrete.
[9]
C143, Test Method for Slump of Hydraulic Cement Concrete.
[10]
C150, Specification for Portland Cement.
[11]
C171, Specification for Sheet Materials for Curing Concrete.
[12]
C172, Practice for Sampling Freshly Mixed Concrete.
[13]
C173, Test Method for Air Content of Freshly Mixed Concrete
by the Volumetric Method.
[14]
C192, Practice for Making and Curing Concrete Test Specimens
in the Laboratory.
[15]
C231, Test Method for Air Content of Freshly Mixed Concrete
by the Pressure Method.
[16]
C260, Specification for Air-Entraining Admixtures for Concrete.
[17]
C309, Specification for Liquid Membrane-Forming Compounds for
Curing Concrete.
[18]
C494, Specification for Chemical Admixtures for Concrete.
[19]
D698, Test Method for Laboratory Compaction Characteristics
of Soil Using Standard Effort (12,400 ft-lb/ft3).
[20]
D994, Specification for Preformed Expansion Joint Filler for
Concrete (Bituminous Type).
[21]
D1751, Specification for Preformed Expansion Joint Filler for
Concrete Paving and Structural Construction (Nonextruding and Resilient
Bituminous Types).
[22]
D1752, Specification for Preformed Sponge Rubber and Cork Expansion
Joint Fillers for Concrete Paving and Structural Construction.
[23]
E329, Specification for Agencies Engaged in the Testing and/or
Inspection of Materials used in Construction.
(c)
National Ready-Mixed Concrete Association, 900 Spring Street,
Silver Spring, MD 20910: Checklist for certification of ready-mixed
concrete production facilities.
(2)
Testing agencies. Testing services shall be performed by an independent
testing agency acceptable to the municipality at the contractor's
expense. All testing agencies shall meet the requirements of ASTM
E329.
C.
Submittals.
(1)
Submit manufacturer's or supplier's certification for the
following materials verifying compliance with these specifications:
(2)
Submit concrete mix designs, including strength test records, for
review and approval.
(3)
Submit certified results of compressive strength cylinder tests.
(4)
Submit copies of concrete batch slips.
A.
Concrete.
(1)
Cement. Unless otherwise specified, Portland cement shall be Type
I cement conforming to ASTM C150.
(2)
Aggregates. Aggregates for normal-weight concrete shall meet the
requirements of ASTM C33.
(3)
Water. Mixing water for concrete shall be clean, potable water meeting
the requirements of ASTM C94.
B.
Reinforcement.
(1)
Reinforcing bars. All reinforcing bars shall be deformed, except
spirals, which may be plain bars. Reinforcing bars shall be Grade
60, billet-steel conforming to the requirements of ASTM A615, including
supplementary requirement on the drawings.
(2)
Welded wire fabric. Welded wire fabric shall be fabricated from smooth
or deformed wire of the size and spacing required on the drawings
and shall conform to the requirements of ASTM A185, except welded
intersections shall be spaced not farther apart than 12 inches in
the direction of the principal reinforcement.
A.
Proportioning.
(1)
General. Concrete for all parts of the work shall be of the specified
quality and capable of being placed without excessive segregation.
When hardened, concrete shall develop all characteristics required
by these specifications.
(2)
Strength. Unless otherwise specified, the minimum twenty-eight-day
compressive strength of the concrete, f'c, shall be 3,000 psi.
(3)
Durability. All concrete which will be subjected to potentially destructive
exposure, including freezing and thawing, weather, and/or deicer chemicals,
shall be air-entrained and shall conform to the air content limits
in ACI 301 moderate exposure.
C.
Embedded items.
(1)
All sleeves, inserts, anchors, and embedded items required for adjoining
work or for its support shall be placed prior to concreting.
(2)
All contractors whose work is related to the concrete or must be
supported by it shall be given ample notice and opportunity to introduce
and/or furnish embedded items before the concrete is placed.
(3)
Placing embedded items. Expansion joint material, waterstops, and
other embedded items shall be positioned accurately and supported
against displacement. Voids in sleeves, inserts, and anchor slots
shall be filled temporarily with readily removable material to prevent
the entry of concrete into the voids.
D.
Production of concrete.
(1)
Production method. All concrete shall be ready-mixed concrete batched,
mixed and transported in accordance with ASTM C94. Plant equipment
and facilities shall conform to Certification of Ready-Mixed Concrete
Production Facilities (Checklist with Instructions) of the National
Ready-Mixed Concrete Association.
(2)
When concrete arrives at the project with slump below that suitable
for placing, as indicated by the specifications, water may be added
only if neither the maximum permissible water-cement ratio nor the
maximum slump is exceeded. The water shall be incorporated by additional
mixing equal to at least half of the total mixing required. Discharge
of the concrete shall be completed within 1 1/2 hours, or before
the truck drum has revolved 300 revolutions, whichever comes first,
after the introduction of the mixing water to the cement and aggregates
or the introduction of the cement to the aggregates. Truck batch slips
must include time of batching, total drum revolutions upon arrival
at site, and quantity of water (in gallons) per cubic yard available
to be added to attain the maximum design water-cement ratio.
E.
Placing.
(1)
Preparation before placing.
(a)
Hardened concrete and foreign materials shall be removed from
the inner surfaces of the conveying equipment.
(b)
Formwork shall be completed; snow, ice and water shall be removed;
reinforcement shall be secured in place; expansion joint material,
anchors, and other embedded items shall be positioned; and the entire
preparation shall be accepted.
(c)
Concrete shall not be placed on frozen ground.
(2)
Conveying.
(a)
Concrete shall be handled from the mixer to the place of final
deposit as rapidly as practicable by methods which will prevent segregation
or loss of ingredients and in a manner which will assure that the
required quality of the concrete is maintained.
(b)
Conveying equipment shall be of a size and design such that
detectable setting of concrete shall not occur before adjacent concrete
is placed. Conveying equipment shall be cleaned at the end of each
operation or work day.
[1]
Truck mixers, agitators and nonagitating units and their manner
of operation shall conform to the applicable requirements of ASTM
C94.
[2]
Belt conveyors shall be horizontal or at a slope which will
not cause excessive segregation or loss of ingredients. Concrete shall
be protected against undue drying or rise in temperature. An acceptable
arrangement shall be used at the discharge end to prevent segregation.
Mortar shall not be allowed to adhere to the return length of the
belt. Long runs shall be discharged into a hopper or through a baffle.
[3]
Chutes shall be metal or metal-lined and shall have a slope
not exceeding one vertical to two horizontal and not less than one
vertical to three horizontal. Chutes more than 20 feet long and chutes
not meeting the slope requirements may be used provided they discharge
into a hopper before distribution.
[4]
Pumping or pneumatic conveying equipment shall be capable of
pumping the specified mix with adequate pumping capacity. Pneumatic
placement shall be controlled so that segregation is not apparent
in the discharged concrete. The loss of slump in pumping or pneumatic
conveying equipment shall not exceed two inches. Concrete shall not
be conveyed through pipe made of aluminum or aluminum alloy.
(3)
Depositing.
(a)
General. Concrete shall be deposited continuously, or in layers
of such thickness that no concrete will be deposited on concrete which
has hardened sufficiently to cause the formation of seams or planes
of weakness within the section. If a section cannot be placed continuously,
construction joints shall be located as indicated on the drawings.
Placing shall be carried on at such a rate that the concrete which
is being integrated with fresh concrete is still plastic. Concrete
which has partially hardened or has been contaminated by foreign materials
shall not be deposited.
(b)
Segregation. Concrete shall be deposited as nearly as practicable
in its final position to avoid segregation due to rehandling or flowing.
Concrete shall not be subjected to any procedure which will cause
segregation.
(c)
Consolidation. All concrete shall be consolidated by vibration,
spading, rodding or forking so that the concrete is thoroughly worked
around the reinforcement, around embedded items, and into corners
of forms, eliminating all air or stone pockets which may cause honeycombing,
pitting, or planes of weakness. Internal vibrators used shall be the
largest size and the most powerful that can be properly used in the
work. They shall be operated by competent workmen. Use of vibrators
to transport concrete within forms shall not be allowed. Vibrators
shall be inserted and withdrawn at points approximately 18 inches
apart. At each insertion, the duration shall be sufficient to consolidate
the concrete but not sufficient to cause segregation, generally from
five to 15 seconds. A spare vibrator shall be kept on the job site
during all concrete placing operations. Where the concrete is to have
an as-cast finish, a full surface of mortar shall be brought against
the form by the vibration process, supplemented if necessary by spading
to work the coarse aggregate back from the formed surface.
(4)
Protection.
(a)
Unless adequate protection is provided, concrete shall not be
placed during rain, sleet or snow.
(b)
Rainwater shall not be allowed to increase the mixing water
nor to damage the surface finish.
(c)
The temperature of the concrete as placed shall not be so high
as to cause difficulty from loss of slump, flash set, or cold joints
and should not exceed 90° F. When the temperature of the steel
is greater that 120° F., steel forms and reinforcement shall be
sprayed with water just prior to placing the concrete.
F.
Finishing of formed surfaces. If the finish is not designated on
the drawings, the following finishes shall be used as applicable:
(1)
Rough form finish for all concrete surfaces not permanently exposed.
Tie holes and defects shall be patched and fins over 1/4 inches in
heights rubbed off.
(2)
Smooth rubbed finish for all concrete surfaces permanently exposed.
Apply on newly hardened concrete within one day following form removal.
Surfaces shall be wetted and rubbed until uniform color and texture
are produced.
G.
Slabs.
(2)
Preparation of subgrade for slabs on ground.
(a)
The subgrade shall be well drained and of adequate and uniform
load-bearing capacity. The minimum in-place density of the subgrade
soils shall be not less than 95% of its maximum dry-weight density
at its optimum moisture content, plus or minus 2%, as determined by
ASTM D698.
(b)
The subgrade shall be free of frost before concrete placing
begins. If the temperature inside a building where concrete is to
be placed is below freezing it shall be raised and maintained above
50° F. long enough to remove all frost from the subgrade.
(c)
The subgrade shall be moist at the time of concreting. If necessary,
it shall be dampened with water in advance of concreting, but there
shall not be standing water on the subgrade nor any muddy or soft
spots when the concrete is placed.
(3)
Finishes.
(a)
Floated finish. After the concrete has been placed, consolidated,
struck off, and leveled, the concrete shall not be worked further
until ready for floating. Floating with a hand float or with a bladed
power trowel equipped with float shoes, or with a powered disc float,
shall begin when the water sheen has disappeared and when the surface
has stiffened sufficiently to permit the operation. During or after
the first floating, planeness of surface shall be checked with a ten-foot
straightedge applied at not less than two different angles. All high
spots shall be cut down and all low spots filled and the slab shall
then be refloated immediately to a uniform sandy texture.
(b)
Broom or belt finish. Immediately after the concrete has received
a float finish, it shall be given a coarse transverse scored texture
by drawing a broom or burlap belt across the surface.
(c)
Unspecified finish. When type of finish is not specified on
the drawings, use broom finish.
H.
Curing and protection.
(1)
General. Beginning immediately after placement, concrete shall be
protected from premature drying, excessively hot or cold temperatures,
and mechanical injury, and shall be maintained with minimal moisture
loss at a relatively constant temperature for the period necessary
for hydration of the cement and hardening of the concrete.
(2)
Preservation of moisture.
(a)
For concrete surfaces not in contact with forms, one of the
following procedures shall be applied immediately after completion
of placement and finishing:
[1]
Application of acceptable moisture-retaining covering as approved
by the municipality.
[2]
Application of a curing compound conforming to ASTM C309. The
compound shall be applied in accordance with the recommendations of
the manufacturer immediately after any water sheen which may develop
after finishing has disappeared from the concrete surface. It shall
not be used on any surface against which additional concrete or other
material is to be bonded unless it is proven that the curing compound
will not prevent bond, or unless positive measures are taken to remove
it completely from areas to receive bonded applications.
(b)
Moisture loss from surfaces placed against wooden forms or metal
forms exposed to heating by the sun shall be minimized by keeping
the forms wet until they can be safely removed. After form removal
the concrete shall be cured.
(c)
Curing shall be continued for at least seven days. Alternatively,
if tests are made of cylinders kept adjacent to the structure and
cured by the same methods, moisture-retention measures may be terminated
when the average compressive strength has reached 70% of the strength,
f'c. Moisture-retention measures may also be terminated when
the temperature of the concrete is maintained at least at 50°
F. for the same length of time that laboratory-cured cylinders, representative
of the concrete in-place, require to achieve 85% of f'c.
(3)
Temperature, wind, and humidity.
(a)
Cold weather. When the mean daily outdoor temperature is less
than 40° F., the temperature of the concrete shall be maintained
between 50° and 70° F. for the required curing period. When
necessary, arrangements for heating, covering, insulating, or housing
the concrete work shall be made in advance of placement and shall
be adequate to maintain the required temperature without injury due
to concentration of heat. Combustion heaters shall not be used during
the first 24 hours unless precautions are taken to prevent exposure
of the concrete to exhaust gases which contain carbon dioxide.
(b)
Hot weather. When necessary, provision for windbreaks, shading,
fog spraying, sprinkling, ponding, or wet covering with a light colored
material shall be made in advance of placement, and such protective
measures shall be taken as quickly as concrete hardening and finishing
operations will allow.
(c)
Rate of temperature change. Changes in temperature of the air
immediately adjacent to the concrete during and immediately following
the curing period shall be kept as uniform as possible and shall not
exceed 5° F. in any one-hour or 50° F. in any twenty-four-hour
period.
(4)
Protection from mechanical injury. During the curing period, the
concrete shall be protected from damage due to mechanical disturbances,
such as load stresses, heavy shock, and excessive vibration. All finished
concrete surfaces shall be protected from damage by construction equipment,
materials or methods, by application of curing procedures, and by
rain or running water.
I.
Testing.
(1)
General. Concrete materials and operations will be tested and inspected
as the work progresses. Failure to detect any defective work or material
shall not in any way prevent later rejection when such defect is discovered
nor shall it obligate the municipality for final acceptance.
(2)
Testing services. The following testing services shall be performed
by the designated testing agency.
(a)
Conduct strength tests of the concrete during construction in
accordance with the following procedures:
[1]
Secure composite samples in accordance with ASTM C172. Each
sample shall be obtained from a different batch of concrete on a random
basis, avoiding any selection of the test batch other than by a number
selected at random before commencement of concrete placement.
[2]
Mold and cure four specimens from each sample in accordance
with ASTM C31. Any deviations from the requirements of this standard
shall be recorded in the test report.
[3]
Test the specimens in accordance with ASTM C39. Two specimens
shall be tested at 28 days for acceptance and two shall be tested
at seven days for information. The acceptance test results shall be
the average of the strengths of the two specimens tested at 28 days.
If one specimen in a test manifests evidence of improper sampling,
molding or testing, it shall be discarded and the strength of the
remaining cylinder shall be considered the test result. Should both
specimens in a test show any of the above defects, the entire test
shall be discarded.
[4]
Make at least one strength test for each 50 cubic yard, or fraction
thereof, of each mixture design of concrete placed in any one day.
(b)
Determine slump of the concrete sample for each strength test
and whenever consistency of concrete appears to vary, using ASTM C
143.
(c)
Determine air content of the concrete sample for each strength
test in accordance with either ASTM C231, ASTM C173, or ASTM C138.
(d)
Determine temperature of the concrete sample for each strength
test.
(3)
Additional services when required. The following services shall be
performed by the testing agency when required by the municipality
at the contractor's expense:
(a)
Inspect concrete batching, mixing and delivery operations to
the extent deemed necessary by the municipality.
(b)
Sample concrete at point of placement and perform required tests.
(c)
Review the manufacturer's report for each shipment of cement
and reinforcing steel and conduct laboratory tests or spot checks
of the materials as received for compliance with specifications.
(d)
Mold four specimens from each sample (in addition to those required
above) in accordance with ASTM C31 and field cure in or on the structure
providing the same method of cure for the specimens as that which
the structure receives.
(4)
Other services as needed. The following services shall be performed
by the testing agency at the contractor's expense:
(5)
Duties and authorities of designated testing agency.
(a)
Representatives of the agency shall inspect, sample and test
the materials and the production of concrete as required by the municipality.
When it appears that any material furnished or work performed by the
contractor fails to fulfill specification requirements, the testing
agency shall report such deficiency to the municipality and the contractor.
(b)
The agency shall report all test and inspection results to the
municipality and contractor immediately after they are performed.
All test reports shall include the exact location in the work at which
the batch represented by a test was deposited. Reports of strength
tests shall include detailed information on storage and curing of
specimens prior to testing.
(c)
The testing agency and its representatives are not authorized
to revoke, alter, relax, enlarge or release any requirement of the
specifications, nor to approve or accept any portion of the work.
(6)
Responsibilities and duties of contractor.
(b)
The use of testing services shall in no way relieve the contractor
of the responsibility to furnish materials and construction in full
compliance with the contract documents.
(c)
The contractor shall submit to the municipality the concrete
materials and the concrete mix designs proposed for use with a written
request for acceptance. This submittal shall include the results of
all testing performed to qualify the materials and to establish the
mix designs. No concrete shall be placed in the work until the contractor
has received such acceptance in writing.
(d)
To facilitate testing and inspection, the contractor shall:
[1]
Furnish any necessary labor to assist the testing agency in
obtaining and handling samples at the project or other sources of
materials.
[2]
Advise the testing agency sufficiently in advance of operations
to allow for completion of quality tests and for the assignment of
personnel.
[3]
Provide and maintain for the sole use of the testing agency
adequate facilities for safe storage and proper curing of concrete
test specimens on the project site for the first 24 hours as required
by ASTM C31.
