03300 Cast in Place Concrete.doc

Base Pavements IDIQ

JCGU 09-1700

DIVISION 03 - CONCRETE

SECTION 03300 - CAST-IN-PLACE CONCRETE

PART 1 – GENERAL:

1.1 REFERENCES: The publications listed below form a part of this specification to the extent referenced. The publications are referred to in the text by basic designation only. All publications shall be the latest version/edition/revision of the documents listed below, in effect on the date of this solicitation, except where a date is given.

AMERICAN CONCRETE INSTITUTE (ACI)

ACI 211.1 Selecting Proportions for Normal, Heavyweight and Mass

Concrete

ACI 318/318R

Building Code Requirements for Structural Concrete and Commentary

AMERICAN SOCIETY FOR TESTING AND MATERIALS (ASTM)

ASTM A615/615M

Deformed Billet-Steel Bars for Concrete Reinforcement

ASTM A706/706M

Low-Alloy Steel Deformed Bars for Concrete Reinforcement

ASTM C 33

Concrete Aggregates

ASTM C 39

Compressive Strength of Cylindrical Concrete Specimens

ASTM C 94

Ready-Mixed Concrete

ASTM C136

Fine Aggregates

ASTM C 150

Portland Cement

ASTM C 171

Sheet Materials for Curing Concrete

ASTM C 172

Sampling Freshly Mixed Concrete

ASTM C 192

Making and Curing Concrete Test Specimens in the Laboratory

ASTM C 260

Air-Entraining Admixtures for Concrete

ASTM C 309

Liquid Membrane-Forming Compounds for Curing Concrete

ASTM C 494

Chemical Admixtures for Concrete

ASTM C 618

Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Portland Cement Concrete

ASTM D 98

Calcium Chloride

ASTM D 1751

Preformed Expansion Joint Fillers for Concrete Paving and Structural Construction

ASTM D 1752

Preformed Sponge Rubber and Cork Expansion Joint Filler for Concrete Paving and Structural Construction

ASTM E 96

Water Vapor Transmission of Materials

FEDERAL SPECIFICATIONS (Fed. Specs.)

FS CCC-C-467

Cloth, Burlap, Jute (or Kenaf)

FS SS-S-1401C

Sealant, Joint, Non-Jet-Fuel-Resistant, Hot-Applied, for Portland Cement and Asphalt Concrete Pavements

National Ready-Mixed Concrete Association (NRMCA)

NRMCA-01-84

Certification or Ready-Mixed Concrete Production Facilities

NRMCA TMMB 100

Truck Mixer and Agitator Standards

NRMCA CPMB 100

Concrete Plant Standards

NRMCA QC 3

Quality Control Manual

1.2 SUBMITTALS:

The following shall be submitted in accordance with Specification SECTION 01010:

Mix Designs:

The Contractor shall submit the results of trial mix along with a statement giving the maximum nominal coarse aggregate size and the proportions of all ingredients that will be used in the manufacture of each strength of concrete. Aggregate weights shall be based on the saturated surface dry condition. The statement shall be accompanied by test results from an independent commercial testing laboratory, attesting that the proportions selected will produce concrete of the qualities indicated. No substitutions shall be made in the materials used in the work without additional tests to show that the quality of the concrete is satisfactory.

Test Reports:

Certified copies of laboratory test reports, including all test data, shall be submitted for aggregate, admixtures, and curing compound. These tests shall be made by an approved commercial laboratory or by a laboratory maintained by the manufacturers of the materials.

Certificates of Compliance:

Cement, pozzolan, and ground iron blast-furnace slag will be accepted on the basis of manufacturer's certification of compliance, accompanied by mill test reports attesting that the materials meet the requirements of the specification under which it is furnished. No cement, pozzolan, or slag shall be used until notice of acceptance has been given by the Contracting Officer. Cement, pozzolan, and slag may be subjected to check testing by the Government from samples obtained at the mill, at transfer points, or at the project site.

1.3 GENERAL REQUIREMENTS:

1.3.1 Strength Requirements: Structural concrete for all work shall have a 28-day compressive strength of 4000 pounds per square inch. Concrete slabs on-grade shall have a 28-day flexural strength of 600 pounds per square inch. Concrete made with high-early strength cement shall have a 7-day strength equal to the specified 28-day strength for concrete made with Type I or II Portland cement.

1.3.2 Air Entrainment: Concrete shall contain from 3 to 5 percent total air.

1.3.3 Special Properties: Concrete may contain other-admixtures, such as water reducers, superplasticizers, or set retarding agents to provide special properties to the concrete, if approved.

1.3.4 Slump: Slump shall be 3 inch minimum and 4 ½ inch maximum. Where use of superplasticizers are approved to produce flowing concrete these slump requirements do not apply.

1.4 PROPORTIONS OF MIX:

1.4.1 Mixture Proportioning, Normal Weight Concrete: Trial batches shall contain materials proposed to be used in the project. Trial mixtures having proportions, consistencies and air content suitable for the work shall be made based on methodology described in ACI 211.1, using at least three different water-cement ratios Trial mixes shall be proportioned to produce concrete strengths specified. In the case where ground iron blast-furnace slag is used, the weight of the slag will be substituted in the equations for the term P which is used to denote the weight of pozzolan. Trial mixtures shall be designed for maximum permitted slump and air content. The temperature of concrete in each trial batch shall be reported. For each water-cement ratio at least three test cylinders for each test age shall be made and cured in accordance with ASTM C 192. They shall be tested at 7 and 28 days in accordance with ASTM C 39. From these test results a curve shall be plotted showing the relationship between water-cement ratio and strength.

1.4.2 General Portland Cement Concrete Requirements: Concrete (PCC) shall contain five (5) sacks of cement per cubic yard of mix. Concrete shall contain Pozzolith 30-N or equal at a rate of five (5) ounces per 100 pounds of cement in mix. Use of accelerating mixtures in cold weather or self retarding admixtures in hot weather must be approved by the Contracting Officer.

1.4.3 Average Strength: In meeting the strength requirements specified, the selected mixture proportion shall produce an average compressive strength exceeding the specified strength by the amount indicated below. Where a concrete production facility has test records, a standard deviation shall be established. Test records from which a standard deviation is calculated shall represent materials, quality control procedures, and conditions similar to those expected; shall represent concrete produced to meet a specified strength or strengths within 1000 psi of that specified for proposed work; and shall consist of at least 30 consecutive tests. A strength test shall be the average of the strengths of two cylinders made from the same sample of concrete and tested at 28 days or at other test age designated for determination of the specified strength.

1.5 STORAGE OF MATERIALS:

Cement and pozzolan shall be stored in weathertight buildings, bins, or silos which will exclude moisture and contaminants. Aggregate stockpiles shall be arranged and used in a manner to avoid excessive segregation and to prevent contamination with other materials or with other sizes of aggregates. Reinforcing bars and accessories shall be stored above the ground on platforms, skids or other supports. Other materials shall be stored in such a manner as to avoid contamination and deterioration. Admixtures which have been in storage at the project site for longer than 6 months or which have been subjected to freezing shall not be used unless retested and proven to meet the specified requirements.

PART 2 – PRODUCTS:

2.1 ADMIXTURES:

Admixtures shall conform to the following:

2.1.1 Accelerating Admixture: Calcium chloride conforming to ASTM D 98, Type 1 or 2.

2.1.2 Air-Entraining Admixture: ASTM C 260.

2.1.3 Hater-Reducing or Retarding Admixture: ASTM C 494, Type A, B, or D.

2.2 CEMENTITIOUS MATERIALS:

Cementitious materials shall each be of one type and from one source when used in concrete which will have surfaces exposed in the finished structure. Cementitious materials shall conform to one of the following:

2.2.1 Cement: ASTM C 150, Type I or II. The alkali content shall not exceed 0.6 percent.

2.2.2 Pozzolan: ASTM C 618.

2.3 AGGREGATES:

Aggregates shall conform ASTM C 33. Coarse aggregate shall be well graded from fine to coarse within prescribed limits. Maximum nominal coarse aggregate size shall be 3/4 inches. Fine aggregate shall comply with ASTM C 136.

2.4 CURING MATERIALS: After placement a minimum 7 day time period shall be allowed for concrete curing.

2.4.1 Burlap: Shall conform to FS CCC-C-467.

2.4.2 Impervious Sheets: Shall conform to ASTM C 171, type optional, except that polyethylene film, if used, shall be white opaque.

2.4.3 Membrane-Forming Compounds: White pigmented membrane-forming curing compound shall conform to ASTM C 309, Type 2, Class A or B.

2.4.4 Vapor barrier shall be polyethylene sheeting with a minimum of 6 mils or other equivalent material having a vapor permeance rating not exceeding 0.5 perms as determined in accordance with ASTM E 96.

2.5 EMBEDDED ITEMS:

Embedded items shall be of the size and type indicated or as needed for the application.

2.6 JOINT FILLER STRIPS: Reference Specification SECTION 02511 for Sidewalks, Troopwalks, and Curb and Gutter.

2.6.1 Contraction Joint Filler: Shall consist of hard-pressed fiberboard, unless otherwise noted.

2.6.2 Expansion-Joint Filler: Shall be pre-molded, conforming to ASTM D 1751 or ASTM D 1752, 3/8-inch thick, unless otherwise noted.

2.7 JOINT SEALANTS:

Hot-Poured sealant shall conform to Fed Spec SS-S-1401.

2.8 REINFORCEMENT:

Shall be deformed bars conforming to ASTM A 615 or ASTM A 706 Grades and sizes as indicated.

2.9 WATER:

Water shall be potable. The strength comparison shall be made on mortars, identical except for mixing water, prepared and tested in accordance with ASTM C 109. Water for curing shall not contain any substance injurious to concrete, or which causes staining.

PART 3 – EXECUTION:

3.1 PREPARATION OF SURFACES:

3.1.1 Surfaces to receive concrete shall be clean and free from frost, ice, mud, and water.

3.1.2 Preparation of Previously Placed Concrete: Concrete surfaces to which other concrete is to be bonded shall be roughened in an approved manner that will expose sound aggregate uniformly without damaging the concrete. Laitance and loose particles shall be removed. Surfaces shall be moist but without free water when concrete is placed.

3.2 INSTALLATION OF EMBEDDED ITEMS:

Embedded items shall be free from oil, loose scale or rust, and paint. Embedded items shall be installed at the locations indicated and required to serve the intended purpose. Voids in sleeves, slots and inserts shall be filled with readily removable material to prevent the entry of concrete.

3.3 BATCHING, MIXING AND TRANSPORTING CONCRETE:

3.3.1 Ready-mixed concrete shall be batched, mixed and transported in accordance with ASTM C 94, except as otherwise specified. Truck mixers, agitators, and nonagitating units shall comply with NRMCA TMMB. Ready-mix plant equipment and facilities shall be certified in accordance with NRMCA. Site-mixed concrete shall be mixed in accordance with ACI 318.

3.3.2 Admixtures: Admixtures shall be batched within an accuracy of 3 percent. Where two or more admixtures are used in the same batch, they shall be batched separately and must be compatible.

3.3.3 Control of Mixing Water: No water from the truck system or elsewhere shall be added after the initial introduction of mixing water for the batch except when on arrival at the job site, the slump of the concrete is less than that specified. Water added to bring the slump within the specified range shall not change the total water in the concrete to a point that the approved water-cement ratio is exceeded. The drum shall be turned an additional 30 revolutions, or more, if necessary, until the added water is uniformly mixed into the concrete. Water shall not be added to the batch at any later time.

3.4 SAMPLING AND TESTING:

Sampling and Testing is the responsibility of the Contractor and shall be performed by an approved testing agency.

3.4.1 Aggregates: Aggregates for normal weight concrete shall be sampled and tested in accordance with ASTM C 33. Gradation tests shall be performed on the first day and every other day thereafter during concrete construction.

3.4.2 Sampling of Concrete: Samples of concrete for air, slump, unit weight, and strength tests shall be taken in accordance with ASTM C 172.

3.4.2.1 Air Content: A minimum of 2 test per day shall be conducted.

3.4.2.2 Slump: At least 2 slump tests shall be made on randomly selected batches of each mixture of concrete during each day's concrete placement.

3.4.2.3 Unit Weight: Tests shall be conducted on each batch sampled for strength tests and on random samples taken for each 75 cubic yards of concrete placed. The unit weight of fresh concrete shall not vary more than 2 pounds per cubic foot from the corresponding unit weight of the approved proportions.

3.4.3 Evaluation and Acceptance of Concrete:

3.4.3.1 Frequency of Testing: Samples for strength tests of each class of concrete placed each day shall be taken not less than once a day, nor less than once for each 8 cubic yards of concrete, nor less than once for each 150 square feet of surface area for slabs. If this sampling frequency results in less than 5 strength tests for a given class of concrete, tests shall be made from at least 5 randomly selected trucks or from each truck if fewer than 5 truck loads are used. Field cured specimens for determining form removal time or when a structure may be put in service shall be made in numbers directed to check the adequacy of curing and protection of concrete in the structure. The specimens shall be removed from the molds at the age of 24 hours and shall be cured and protected, insofar as practicable, in the same manner as that given to the portion of the structure the samples represent.

3.4.3.2 Testing Procedures: Cylinders and beams for acceptance tests shall be molded and cured in accordance with ASTM C 31. Cylinders shall be tested in accordance with ASTM C 39 and beams shall be tested in accordance with ASTM C 78. A strength test shall be the average of the strengths of two cylinders made from the same sample of concrete and tested at 28 days or at another specified test age.

3.4.3.3 Evaluation of Results: Concrete specified on the basis of compressive strength will be considered satisfactory if the averages of all sets of three consecutive strength test results equal or exceed the specified strength and no individual strength test result falls below the required strength by more than 500 pounds per square inch.

3.4.4 Investigation of Low-Strength Test Results: When any strength test of standard-cured test cylinder falls below the specified strength requirement by more than 500 pounds per square inch, or if tests of field-cured cylinders indicate deficiencies in protection and curing, steps shall be taken to assure that load-carrying capacity of the structure is not jeopardized. When strength of concrete in place is considered potentially deficient, cores shall be obtained and tested in accordance with ASTM C 42. At least three representative cores shall be taken from each member or area of concrete in place that is considered potentially deficient. The location of cores shall be determined by the Contracting Officer to least impair the strength of the structure. If the concrete in the structure will be dry under service conditions, the cores shall be air dried (temperature 60 to 80 degrees F, relative humidity less than 60 percent) for seven days before testing and shall be tested dry. If the concrete in the structure will be more than superficially wet under service conditions, the cores shall be tested after moisture conditioning in accordance with ASTM C 42. Concrete in the area represented by the core testing will be considered adequate if the average strength of the cores is equal to or at least 85 percent of the specified strength requirement and if no single core is less than 75 percent of the specified strength requirement. If the core tests are inconclusive or impractical to obtain, or 1f structural analysis does not confirm the safety of the structure, load tests may be directed by the Contracting Officer in accordance with the requirements of ACI 318. Concrete work evaluated by structural analysis or by results of a load test and found deficient shall corrected in a manner satisfactory to the Contracting Officer. All investigations, testing, load tests, and correction of deficiencies shall performed, and approved by the Contracting Officer, at the expense of the Contractor.

3.5 CONVEYING CONCRETE:

Concrete shall be conveyed from mixer to forms as rapidly as possible and within the time interval specified in paragraph "CONCRETE PLACEMENT" by methods which will prevent segregation or loss of ingredients.

3.5.1 Chutes: When concrete can be placed directly from a truck mixer or other transporting equipment, chutes attached to this equipment may be used. Separate chutes will not be permitted except when specifically approved.

3.5.2 Buckets: Bucket design shall be such that concrete of the required slump can be readily discharged. Bucket gates shall be essentially grout tight when closed. The bucket shall provide means for positive regulations of the amount and rate of deposit of concrete in each dumping position.

3.5.3 Pumps: Concrete may be conveyed by positive displacement pumps when approved. Pump shall be the piston or squeeze pressure type. Pipeline shall be steel pipe or heavy duty flexible hose. Inside diameter of the pipe shall be at least three times the maximum size of the coarse aggregate. Distance to be pumped shall not exceed the limits recommended by the pump manufacturer. Concrete shall be supplied to the pump continuously. When pumping is completed, the concrete remaining in the pipeline shall be ejected without contaminating the concrete in place. After each use, the equipment shall be thoroughly cleaned. Flushing water shall be wasted outside the forms.

3.6 REINFORCEMENT:

Reinforcement shall be fabricated to the shapes and dimensions shown, and shall be placed where indicated. Reinforcing steel shall not be bent or straightened in a manner injurious to steel or to the concrete. Bars with kinks or bends not shown on the drawings shall not be placed. The use of heat to bend or straighten reinforcing steel shall be permitted only if the entire operation is approved. Bars shall be moved as necessary to avoid interference with other reinforcing steel, conduits, or embedded items. If bars are moved more than one bar diameter, the resulting arrangement of bars shall be approved before concrete is placed. Reinforcing steel shall not be spliced at points of maximum stress. Laps or splices shall conform to ACI 318. Tack welding to, or of reinforcement is prohibited. Reinforcement shall be free from loose or flaky rust and mill scale, except tight mill scale, or any other coating which might reduce the bond to the concrete. After any substantial delay in the work previously placed, reinforcing steel left for future bonding shall be inspected and cleaned.

3.6.1 Wire-Mesh Reinforcement: Shall not be used.

3.6.2 Dowels: Dowels in slabs on grade shall be installed at right angles to construction and expansion joints. They shall be accurately aligned parallel to the finished surface, and shall be rigidly supported during the placing of concrete. One end of the dowels shall be oiled or greased.

3.7 CONCRETE PLACEMENT:

Mixed concrete which is transported in truck mixers or agitators or concrete which is truck mixed, shall be discharged within 1-1/2 hours or before the 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. These limitations may be waived by the Government if the concrete is of such slump after the 1-1/2 hour time or 300 revolution limit has been reached that it can be placed, without the addition of water to the batch. When the concrete temperature exceeds 85 degrees F, the time shall be reduced to 45 minutes. Concrete shall be placed within 15 minutes after it has been discharged from the truck.

3.7.1 Placing Operation: Concrete shall be handled from mixer to forms in a continuous manner until the approved unit of operation is completed. Adequate scaffolding, ramps and walkways shall be provided so that personnel and equipment are not supported by in-place reinforcement. Placing will not be permitted when the sun, heat, wind, or limitations of facilities furnished by the Contractor prevent proper consolidation, finishing and curing. Concrete shall be deposited as close as possible to its final position in the forms, and there shall be no vertical drop greater than 8 feet except where suitable equipment is provided to prevent segregation and where specifically authorized. Depositing of the concrete shall be so regulated that it will be effectively consolidated in horizontal layers not more than 12 inches thick, except that all slabs shall be placed in a single layer. Concrete to receive other construction shall be screeded to the proper level to avoid excessive shimming or grouting.

3.7.2 Consolidation: Immediately after placing, each layer of concrete shall be consolidated by internal vibrators, except for slabs 4 inches or less. The vibrators shall at all times be adequate in effectiveness and number to properly consolidate the concrete; a spare vibrator shall be kept at the job site during all concrete placing operations. The vibrators shall have a frequency of not less than 8000 vibrations per minute, and the head diameter and amplitude shall be appropriate for the concrete mixture being placed. Vibrators shall be inserted vertically at uniform spacing over the area of placement. The distance between insertions shall be approximately 1.5 times the radius of action of the vibrator so that the area being vibrated will overlap the adjacent just-vibrated area by a few inches. The vibrator shall penetrate rapidly to the bottom of the layer and at least 6 inches into the preceding layer if there is such. Vibrator shall be held stationary until the concrete is consolidated and then withdrawn slowly. The use of form vibrators must be specifically approved. Vibrators shall not be used to transport concrete within the forms. Slabs 4 inches and less in thickness shall be consolidated by properly designed vibrating screeds or other approved technique. Excessive vibration of lightweight concrete resulting in segregation and flotation of coarse aggregate shall be avoided.

3.7.3 Cold Weather Requirements: Special protection measures, approved by the Contracting Officer, shall be used if freezing temperatures are anticipated before the expiration of the specified curing period. The ambient temperature of the air where concrete is to be placed and the temperature of surfaces to receive concrete shall be not less than 40 degrees F. The temperature of the concrete when placed shall be not less than 50 degrees F nor more than 75 degrees F. Heating of the mixing water or aggregates will be required to regulate the concrete placing temperature. Materials entering the mixer shall be free from ice, snow, or frozen lumps. Salt, chemicals or other materials shall not be incorporated in the concrete to prevent freezing. Upon written approval, calcium chloride or chemical admixture conforming to ASTM C 494 Type C or E may be used. The amount of calcium chloride shall not exceed 2 percent by weight of the cement, and it shall be batched in solution form. Calcium chloride shall not be used where concrete will be in contact with aluminum or zinc-coated items, or where sulfate resistant or prestressed concrete is specified.

3.7.4 Warm Weather Requirements: The temperature of the concrete placed during warm weather shall not exceed 95 degrees F except where an approved retarder is used. The mixing water and/or aggregates shall be cooled, if necessary, to maintain a satisfactory placing temperature. In no case shall the placing temperature exceed 95 degrees F.

3.7.5 Prevention of Plastic Shrinkage Cracking

During hot weather with low humidity, and particularly with appreciable wind, as well as interior placements when space heaters produce low humidity, the Contractor shall be alert to the tendency for plastic shrinkage cracks to develop and shall institute measures to prevent this. Particular care shall be taken if plastic shrinkage cracking is potentially imminent and especially if it has developed during a previous placement. Periods of high potential for plastic shrinkage cracking can be anticipated by use of Fig. 2.1.5 of ACI 305R. In addition the concrete placement shall be further protected by erecting shades and windbreaks and by applying fog sprays of water, sprinkling, ponding or wet covering. Plastic shrinkage cracks that occur shall be filled by injection of epoxy resin as directed, after the concrete hardens. Plastic shrinkage cracks shall never be troweled over or filled with slurry.

3.7.6 Placing Concrete in Congested Areas

Special care shall be used to ensure complete filling of the forms, elimination of all voids, and complete consolidation of the concrete when placing concrete in areas congested with reinforcing bars, embedded items, waterstops and other tight spacing. An appropriate concrete mixture shall be used, and the nominal maximum size of aggregate (NMSA) shall meet the specified criteria when evaluated for the congested area. Vibrators with heads of a size appropriate for the clearances available shall be used, and the consolidation operation shall be closely supervised to ensure complete and thorough consolidation at all points. Where necessary, splices of reinforcing bars shall be alternated to reduce congestion. Where two mats of closely spaced reinforcing are required, the bars in each mat shall be placed in matching alignment to reduce congestion.

3.8 CONSTRUCTION JOINTS: : Reference Specification SECTION 02511 for Sidewalks, Troopwalks, and Curb and Gutter.

3.8.1 Reinforcement or other fixed metal items shall not be continuous through expansion joints, or through construction or contraction joints in slabs on grade. Reinforcement shall be 2 inches clear from each joint.

3.8.2 Pre-molded Expansion Joint Filler: Strips shall be used in slabs as required. The filler shall extend the full slab depth unless otherwise indicated. The edges of the joint shall be neatly finished with a finishing tool of l/8-inch radius. Where the joint is to receive a sealant, the filler strips shall be installed at the proper level below the floor with a slightly tapered, dressed-and-oiled wood strip temporarily secured to the top there of to form a recess 3/4-inch deep to be filled with sealant. The wood strip shall be removed after the concrete has set.

3.9 FINISHING CONCRETE:

3.9.1 Formed Surfaces: Surface defects shall be repaired within 24 hours after the removal of forms. Honeycombed and other defective areas shall be cut back to solid concrete or to a depth of not less than 1 inch, whichever is greater. Edges shall be cut perpendicular to the surface of the concrete. The prepared areas shall be dampened and brush-coated with neat cement grout. The repair shall be made using mortar consisting of not more than 1 part cement to 2.5 parts sand. The mixed mortar shall be allowed to stand to stiffen (approximately 45 minutes), during which time the mortar shall be intermittently remixed without the addition of water. After the mortar has attained the stiffest consistency that will permit placing, the patching mix shall be thoroughly tamped into place by means approved by the Contracting Officer and finished slightly higher than the surrounding surface. For Class B finished surfaces the cement used in the patching mortar shall be a blend of job cement and white cement proportioned to produce a finished repair surface matching, after curing, the color of adjacent surfaces. Holes left after the removal of form ties shall be cleaned and filled with patching mortar. Holes left by the removal of tie rods shall be reamed and filled by dry-packing. Repaired surfaces shall be cured as required for adjacent surfaces. The temperature of concrete, mortar patching material, and ambient air shall be above 50 degrees F while making repairs and during the curing period. Concrete with defects which affect the strength of the member or with excessive honeycombs will be rejected, or the defects shall be corrected as directed. Any concrete surface that exhibits significant cracking, discoloration, form marks, or tool marks shall be removed and replaced. The finished surface of the completed work shall be uniform in color and free of blemishes. During finishing operations, surfaces shall be checked with a 10 foot straightedge applied in both directions at regular intervals while the concrete is still plastic, to detect high or low areas.

3.9.1.2 Class B Finish: Where a Class B finish is indicated in the Task Order, fins shall be removed. Concrete surface shall be smooth with a texture at least equal to that obtained through the use of Grade B-B plywood forms.

3.9.2 Unformed Surfaces:

3.9.2.1 Rough-Slab Finish: Slabs to receive fill or mortar setting beds shall be screeded with straightedges immediately after consolidation to bring the surface to the required finish level with no coarse aggregate visible.

3.9.2.2 Float Finish: Slabs to receive a steel trowel finish and slabs shall be given a float finish. Screeding shall be followed immediately by darbying or bull floating before bleeding water is present, to bring the surface to a true, even plane. After the concrete has stiffened to permit the operation and the water sheen has disappeared, it shall be wood floated. Lightweight concrete or concrete that portrays stickiness shall be finished with a magnesium float in lieu of a wood float, and left free of ridges and other projections.

END OF SECTION

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