02751_en.pdf

Section 02751 1

SECTION 02751

CONCRETE PAVEMENT FOR AIRFIELDS AND OTHER HEAVY DUTY PAVEMENTS

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 the basic designation only.

AMERICAN CONCRETE INSTITUTE (ACI)

ACI 211.1 (1991) Selecting Proportions for Normal, Heavyweight, and Mass Concrete.

ACI 214 (1989) Evaluation of Strength Test Results of Concrete.

ACI 305R (1999) Hot Weather Concreting.

ACI 306R (1988) Cold Weather Concreting.

ACI 309R (1996) Consolidation of Concrete.

ACI 325.6R (1988) Texturing Concrete Pavements.

ACI 325.9R (1991) Guide for Construction of Concrete

Pavements and Concrete Bases.

AMERICAN SOCIETY FOR TESTING AND MATERIALS (ASTM)

ASTM C 31/C 31M (2000) Making and Curing Concrete Test

Specimens in the Field.

ASTM C 33 (1999ael) Concrete Aggregates.

ASTM C 42 (1994) Obtaining and Testing Drilled Cores and Sawed Beams of Concrete.

ASTM C 78 (1994) Flexural Strength of Concrete

(Using Simple Beam with Third-Point

Loading).

ASTM C 94/C 94M (2000) Ready-Mixed Concrete.

ASTM C 117 (1995) Materials Finer than 75-Micrometer

(No. 200) Sieve in Mineral Aggregates by

Washing.

ASTM C 123 (1998) Lightweight Pieces in Aggregate.

ASTM C 127 (2001) Specific Gravity and Absorption of

Coarse Aggregate.

2 Section 02751

ASTM C 131 (1996) Resistance to Degradation of Small-

Size Coarse Aggregate by Abrasion and

Impact in the Los Angeles Machine.

ASTM C 142 (1997) Clay Lumps and Friable Particles in

Aggregates.

ASTM C 143/C 143M (2000) Slump of Hydraulic Cement Concrete.

ASTM C 150 (2000) Portland Cement.

ASTM C 171 (1997a) Sheet Materials for Curing

Concrete.

ASTM C 172 (1999) Sampling Freshly Mixed Concrete.

ASTM C 173 (1994ael) Air Content of Freshly Mixed

Concrete by the Volumetric Method.

ASTM C 227 (1990) Potential alkali reactivity of cement-aggregate combination (mortar-bar method).

ASTM C 231 (1997el) Air Content of Freshly Mixed

Concrete by the Pressure Method.

ASTM C 260 (2000) Air-Entraining Admixtures for

Concrete.

ASTM C 309 (1998a) Liquid Membrane-Forming Compounds for Curing Concrete.

ASTM C 494/C 494M (1999a) Chemical Admixtures for Concrete.

ASTM C 535 (1996el) Resistance to Degradation of

Large-Size Coarse Aggregate by Abrasion and Impact in the Los Angeles Machine.

ASTM C 618 (2000) Coal Fly Ash and Raw or Calcined

Natural Pozzolan for Use as a Mineral

Admixture in Concrete.

ASTM C 989 (1999) Ground Granulated Blast-Furnace

Slag for Use in Concrete and Mortars.

ASTM D 75 (1997) Sampling Aggregates.

ASTM D 4791 (1999) Flat Particles, Elongated

Particles, or Flat and Elongated Particles in Coarse Aggregate

1.2 SUBMITTALS

Product Data:

Curing materials

Admixtures

Design Data:

Section 02751 3

Mix design

At least 30 days prior to the mixing and placing of concrete, submit mix design for approval. Furnish a complete list of materials including type, brand, source and amount of cement, fly ash, pozzolan, admixtures, aggregates, and applicable reference specifications. Obtain acknowledgement of approvals prior to concrete placement. Submit a new mix design for each material source change.

Test Reports:

Aggregate tests

Concrete slump tests

Air content tests

Pavement thickness tests

Flexural strength tests

Submit testing results as required in paragraph entitled "Field

Quality Control in Part 3 of this section."

Certificates:

Ready-mixed concrete plant identification

Batch ticket information

Cementitious Material

Aggregates

Admixtures

Curing materials

Closeout Submittals:

Control charts

Submit copies weekly.

1.3 DELIVERY, STORAGE, AND HANDLING

1.3.1 Cement and Fly Ash

Store immediately upon receipt. Store bagged material in a dry weathertight ventilated structure. Stack bags close together to reduce circulation of air but do not stack against outside walls. Transfer bulk material to weatherproof bins. Test cement stored longer than 6 months by standard mortar tests or loss on ignition tests to determine whether suitable for use. Do not use such cement without approval of the

Contracting Officer’s Technical Representative.

1.3.2 Aggregates

Sufficient aggregate shall be stored at the site at all times to permit continuous, uninterrupted operation of the mixing plant while concrete is being placed. Store aggregates in a manner to minimize segregation and prevent contamination. Store different sizes in separate piles. Stockpile coarse aggregates in thin, horizontal layers with no cone stockpiling permitted. Should coarse aggregates become segregated, remix stockpile to conform to the specified grading requirements.

1.3.3 Admixtures

Store admixture in undamaged containers which will prevent evaporation.

4 Section 02751

Retest air-entraining admixture stored longer than 6 months or which has been subject to freezing. Do not use admixtures stored longer than 15 months.

1.4 EQUIPMENT

Maintain all equipment in satisfactory working condition throughout the length of the contract.

1.4.1 Slipform and Fixed Form Pavers

Use equipment designed to spread, consolidate, screed, and float finish the freshly placed concrete in one pass requiring a minimum of hand finishing.

1.4.2 Curing Compound Spray Equipment

Self-propelled, with spraying nozzles and pressure that can be controlled and operated with a fine nozzle to completely and uniformly cover pavement surface with required amount of curing compound. Mechanically agitate curing compound throughout application. Small or irregular areas may be sprayed by hand methods.

1.5 QUALITY ASSURANCE

1.5.1 Required Data

Submit name and location of the ready-mixed concrete plant. Submit batch ticket information as specified in ASTM C 94.

PART 2 - PRODUCTS

2.1 MATERIALS

2.1.1.1 Cement

ASTM C 150 Type I, II or III. ASTM C 595M, Type IS or IP.

2.1.1.2 Fly Ash

ASTM C 618 Class F.

2.1.2 Water

ASTM C 94.

2.1.3 Aggregates

2.1.3.1 Alkali Reactivity Test

Fine and coarse aggregates to be used in all concrete shall be evaluated and tested by the Contractor for alkali-aggregate reactivity in accordance with ASTM C 1260. The coarse and fine aggregates shall be evaluated separately, in accordance with ASTM C 1260, and in combination, which match the Contractor's proposed mix design proportioning, utilizing the modified version of ASTM C 1260. Test results of the combination shall have a measured expansion of less than 0.08 percent at 16 days.

Should the test data indicate an expansion of greater than 0.08%, the

Section 02751 5 aggregate(s) shall be rejected and the Contractor shall submit new aggregate sources for retesting.

2.1.3.2 Fine Aggregates

ASTM C 33.

2.1.3.3 Coarse Aggregates

ASTM C 33, maximum size No. 57 or 25 mm except as otherwise modified herein.

a. Abrasion loss shall not exceed 40 percent for aggregates tested in accordance with ASTM C 131 or ASTM C 535.

b. Aggregates shall be gravel, crushed gravel, or crushed stone.

c. Specific gravity not less than 2.55, saturated-surface-dry (SSD).

Provide aggregate tests in conformance with ASTM C 127.

d. Furnish coarse aggregate in at least two separate sizes with separation at the 19 mm sieve when combined material graded from

4.75 mm to 37.5 mm nominal maximum size is specified. When the nominal maximum size of aggregate is 25 mm or less, such separation is not necessary.

e. Deleterious Substances: Requirements of Table 3 as given in ASTM C

33 apply, except deleterious substances in coarse aggregate shall not exceed the following percentages by weight:

(1) Clay Lumps and Friable Particles: 1.0 percent when tested in accordance with ASTM C 142.

(2) Lightweight Pieces: 1.0 percent when tested in accordance with

ASTM C 123, ASTM C 989. When blast furnace slag is used, unit weight shall control.

(3) Materials Finer than 75 micrometers No. 200 Sieve: 1.0 percent when tested in accordance with ASTM C 117.

(4) Flat and Elongated Particles: 5 to 1 ratio with a total of 15 percent when tested in accordance with ASTM D 4791.

2.1.3.4 Heat Resistant Concrete Aggregates

Both coarse and fine aggregates shall meet the above specifications but shall be a diabased, intrusive igneous rock or expanded shole lightweight aggregate.

2.1.4 Admixtures

Where not shown or specified, admixtures may be used subject to written approval of the Contracting Officer’s Technical Representative.

2.1.4.1 Air-Entraining Admixtures

ASTM C 260.

2.1.4.2 Retarding Admixtures

ASTM C 494/C 494M, Type B or D.

6 Section 02751

2.1.4.3 Water-Reducing Admixtures

ASTM C 494/C 494M, Type A, D, E, F or G.

2.1.4.4 Accelerating Admixtures

ASTM C 494/C 494M, Type C.

2.1.4.5 Fly Ash and pozzolans

ASTM C 618 Class N, F, or C except that the maximum allowable loss on ignition shall be 6 percent for Class N and F.

2.1.5 Curing Materials

2.1.5.1 Waterproof paper

ASTM C171, fiber reinforced, light colored, non-staining two ply kraft papers.

2.1.5.2 Polyethylene Sheeting

ASTM C171, white color with a minimum sheet thickness of 0.25 mm.

2.1.5.3 White-Burlap-Polyethylene Sheet

ASTM C 171, 0.10 mm thick white opaque polyethylene bonded to 0.31 kg per meter (1.0 m) wide burlap.

2.1.5.4 Liquid Membrane-Forming Compound

ASTM C 309, white-pigmented Type 2, Class B, or clear or translucent Type

1-D, Class B with white fugitive dye.

2.1.6 Joints, Reinforcement and Mooring Eyes

Provide as specified in Section 02762N, "Joints, Reinforcement, and

Mooring Eyes in Concrete Pavements."

2.2 CONCRETE MIX DESIGN

2.2.1 Contractor-Furnished Concrete Mix Design

Contractor-furnished mix design concrete shall be designed in accordance with ACI 211.1 except as modified herein, and the mix design shall be as specified herein under paragraph entitled "Submittals". The concrete shall have a minimum flexural strength of 4481 kPa at 28 days. The air content shall be 5.5 plus or minus 1.5 percent. Maximum size aggregate for slip forming shall be 38 mm. The minimum cement factor and slump shall be as follows:

Method of Finishing to be Used

Minimum Cement Factor, kg Per Cubic Meter

Aggregate Size

25 mm

Range in Slump (mm)

Machine finish with-out vibration

368 50 to 75 mm

Machine finish, with vibration (except

340 25 to 50 mm

Section 02751 7 slip form)

Hand tools 396 75 to 100 mm

Slip form 340 0 to 25 mm

The cement factors given in the foregoing table are minimum; if they are not sufficient to produce concrete of the flexural strength required, they shall be increased as necessary, without additional compensation under the contract. The cement factor shall be calculated using cementitious material, including pozzolan, fly ash and or slag. The slump will be determined by ASTM C 143/C 143M and shall be within the ranges given herein; the exact slump shall be as approved by the Contracting

Officer’s Technical Representative. Obtain acknowledgement of receipt prior to beginning any concrete work. Approved admixtures shall be used in proportions recommended by the manufacturer to obtain the optimum effect, with seasonal atmospheric and job conditions considered. If modifications to the mix are required, a new mix shall be submitted for approval. It will not be necessary to submit additional data regarding aggregate unless the source has changed.

2.3 FIXED FORMS

Use metal forms free from irregularities, bulges, warps, dents, and sags.

Top face of form shall not vary by more than 3 mm in 3 meters and lateral variation shall be less than 6 mm in 3 meters.

Use forms sufficiently strong to resist pressure of concrete and loads resulting from finishing operations without springing, settling, or losing their shape. Clean forms before reuse. Before placing concrete, coat contact surfaces of forms with a non-staining release agent.

PART 3 - EXECUTION

3.1 PREPARATION

Before placing concrete, bring base surface to finish grade and elevations as shown. Moisten underlying material in advance of placing concrete to ensure a firm, moist condition at time concrete is placed. Do not permit equipment other than concrete delivery or paving equipment on prepared underlying material. In cold weather protect underlying material from frost. Do not use chemicals to eliminate frost. Maintain drainage ditches, gutters and side drains to drain the base during construction.

3.1.1 Base for Fixed Form Construction

Finish to the design profile. Test prepared surfaces with a template. Do not vary surface of base material more than 12 mm from indicated elevations.

3.1.2 Base for Slipform Construction

Finish to the design profile. Do not vary surface of base material more than 12 mm from indicated elevations. Minimum width of sub-base shall be

600 mm greater on each side than the width of the paving to accommodate the slipform equipment tracks. Grade and elevation control of the slip form paver shall be by string line.

3.2 FIXED FORMS

8 Section 02751

Set forms for full bearing on foundation for entire length and width and in alignment with edge of finished pavement. Support forms during entire operation of placing, compaction, and finishing so that forms will not deviate vertically more than 3 mm from required grade and elevations indicated. Maximum vertical deviation of top of any side form, including joints, shall not exceed 3 mm from a 3 meters straightedge, nor shall inside face vary more than 6 mm from a 3 meters straightedge. Provide stake sockets and interlocking devices that will prevent movement of the form.

3.3 JOINTS, REINFORCEMENT AND MOORING EYES

Place joints, welded wire fabric and mooring eyes in accordance with

Section 02762, "Joints, Reinforcement, and Mooring Eyes in Concrete

Pavements."

3.4 MEASURING AND MIXING

3.4.1 Site Mixing

ACI 325.9R.

3.4.2 Ready-Mixed Concrete

ASTM C 94/C 94M, except as modified herein. Begin mixing within 30 minutes after cement has been added to aggregates. Additional water may be added to bring slump within required limits as specified in Section

11.7 of ASTM C 94/C 94M, provided that specified water-cement ratio is not exceeded.

3.5 CONVEYING AND PLACING CONCRETE

3.5.1 Placing

ACI 325.9R, except as modified herein. Place concrete continuously at a uniform rate, with a minimum amount of segregation, without damage to the grade and without unscheduled stops except for equipment failure or other emergencies. If an emergency stop does occur within 3 meters of a previously placed expansion joint, remove concrete back to joint, repair any damage to grade, install a construction joint and continue placing concrete only after cause of emergency stop has been corrected.

3.5.1.1 Cold Weather

ACI 306R. High-early-strength-concrete shall be maintained above freezing for a period greater than one-quarter of the period specified for

Portland cement concrete or a minimum of 48 hours.

3.5.1.2 Hot Weather

ACI 305R.

3.5.2 Consolidation

ACI 309R, Chapter 11.

3.5.3 Protection Against Rain

ACI 325.9R, Chapter 10.4.

Section 02751 9

3.6 FINISHING

Start finishing operations immediately after consolidation. Use finishing machine, except that hand finishing may be used in emergencies and for concrete slabs that are of shapes or locations that are not accessible with a finishing machine. Finishing operations shall not displace coarse aggregate from surface and shall produce a surface of uniform texture true to grade and design profile. Excessive operation over an area, which results in an excess of mortar and water being brought to the surface, will not be permitted. Finish pavement surface on both sides of a joint to the same grade. Finish transverse joints from a securely supported transverse bridge.

3.6.1 Fixed Form Finishing

Maintain travel of machine on forms without vertical movement which will affect precision of concrete finish. Keep form tops clean by a device attached to the machine. Finish concrete flush with top of forms.

3.6.2 Slip-Form Finishing

Remove concrete slurry from vertical edges of slip-formed concrete using stiff brushes or other approved scrapers. Do not use concrete slurry to build up edges of concrete to compensate for edge slump. In locations where sloughing occurs, attach temporary forms to underlying material in the proper location and correct defective edges. Such procedures are to be used sparingly. Should excessive sloughing occur, halt operations until proper corrective adjustments have been made.

3.6.2.1 Edge Slump

Determine slump of edges with a 3.66 meter straightedge. Before the concrete hardens, correct edge slump of pave exceeding 6 mm at edge of pavement. The area affected by the downward movement of the concrete along the pavement edge shall be limited to not more than 450 mm from the edge.

3.6.3 Hand Finishing and Floating

As soon as placed and consolidated, strike off and screed concrete to required cross section. If necessary, place and screed additional concrete and float until a satisfactory surface has been produced.

Advance floating operation not more than half the length of the float and then continue over new and previously floated surfaces. Hand finishing shall be limited to small irregular areas not accessible with finishing machine.

3.6.4 Surface Correction and Testing

After finishing is completed but while concrete is still plastic, use straightedges to eliminate minor irregularities and score marks. Use straightedges 3 meters in length and operated from sides of pavement and from bridges. Equip a straightedge operated from side of pavement with a handle 0.91 meters longer than one-half the width of pavement. Check surface for trueness with straightedge held in successive positions parallel and at right angles to center line of pavement, with whole area covered to detect variations. Advance straightedge along pavement in

10 Section 02751 successive stages of not more than one-half the length of the straightedge.

Immediately fill depressions with freshly mixed concrete, strike off, consolidate, and refinish. Strike off and refinish projections above required elevation. Continue straightedge testing and finishing until entire surface of concrete is free from observable departure from straightedge.

3.6.5 Texturing

ACI 325.6R. Before surface sheen has disappeared and before concrete becomes nonplastic, give the pavement surface a texture as specified in paragraph entitled "Surface Finish."

3.6.6 Surface Finish

3.6.6.1 Artificial Turf

Before concrete becomes non-plastic, finish surface by dragging a strip of clean, artificial turf 600 mm wider than pavement.

Select dimensions so that at least 600 mm of material in the direction of travel is in contact with pavement. Drag surface so as to produce a finished surface with a fine granular or sandy texture without leaving disfiguring marks.

3.6.7 Edging

At the time the concrete has attained a degree of hardness suitable for edging, carefully finish edges, including the edges at formed joints, with an edge having a maximum radius of 6 mm. Clean by removing loose fragments and soupy mortar from corners or edges of slabs which have crumbled and areas which lack sufficient mortar for proper finishing.

Refill voids solidly with a mixture of suitable proportions and consistency and refinish. Remove unnecessary tool marks and edges. After removal of forms, repair damaged and honeycombed areas with mortar composed of one part Portland cement to two parts sand.

3.7 CURING AND PROTECTION

Immediately after the finishing operations have been completed and the water film has evaporated from the surface or as soon as marring of the concrete will not occur, the entire surface of the newly placed concrete shall be covered and cured in accordance with ACI 325.9R using one of the following methods:

3.7.1 Liquid Membrane Curing

Uniformly coat the concrete surface with liquid membrane-forming compound with approved mechanical spray equipment at the rate of 2.7 liters per 10 square meters of surface or as recommended by the manufacturer. Irregular areas or sections of paving where the use of mechanical spraying equipment is not practicable may be sprayed with approved hand spraying equipment. Coat edges of paving within 60 minutes after the removal of forms. Protect concrete surfaces from foot and vehicular traffic and other sources of abrasion for a minimum of 72 hours.

Maintain continuity of applied liquid membrane-forming compound for the entire curing period. Prior to application of curing compound, fill open joints by inserting moistened paper or fiber rope, or cover joints with strips of waterproof material to prevent curing compound from entering

Section 02751 11 the joint. Seven days after application of curing compound, joints may be exposed and prepared to receive joint sealant materials.

3.7.2 White-Burlap-Polyethylene Sheet

Thoroughly wet the burlap and cover surface and edges of paving with the burlap face in contact with the concrete. Lap sheets to provide full coverage. Maintain the sheets fully wetted and in position for the entire curing period.

3.7.3 Polyethylene Sheeting

Apply white polyethylene to surface and edges of paving while concrete is still moist. If concrete surface appears dry, wet with a fine spray of clean water. Lap adjacent sheets 450 mm and weight to keep sheeting in contact with paving. Keep sheeting continuously in place for the entire curing period.

3.7.4 Waterproof Paper

Apply waterproof paper to surface and edges of paving while concrete is still moist. If concrete surface appears dry, wet with a fine spray of clean water. Lap adjacent sheets 300 mm and weight to keep sheeting in contact with paving for the entire curing period. Repair or replace paper that is damaged during the curing period. Moisten concrete surface prior to the replacement of damaged paper.

3.8 FIELD QUALITY CONTROL

Sampling and testing shall be conducted on site at the expense of the

Contractor, by a laboratory approved by the Contracting Officer’s

Technical Representative. Samples shall be supplied by the Contractor as specified at the expense of the Contractor.

3.8.1 Sampling

3.8.1.1 Aggregates

Sample fine and coarse aggregates at the batch plant. During concrete placement sample coarse aggregates for each 1360 cubic meters and fine aggregates for each 907 cubic meters or as specified in the delivery order. Sample in accordance with ASTM D 75. When test results indicate that fine aggregates consistently meet specified gradation requirements, the rate of sampling may be reduced if approved by the Contracting

Officer’s Technical Representative.

3.8.1.2 Concrete

Obtain samples of plastic concrete in accordance with ASTM C 172. Quality control samples may be taken at the concrete batch plant; however, samples for verification of concrete strength and slump for submittal to the Government shall be taken in accordance with ASTM C 172 at the job-site as concrete is delivered. From each sample mold the required number of beams and cylinders for each group of test specimens.

3.8.1.3 Sample Identification

Tag each for identification. Tag shall contain the following information:

Contract No. _____

12 Section 02751

Sample No. _____

Date of Sample _____

Sample _____

Source _____

Intended Use _____

For Testing _____

3.8.2 Testing

3.8.2.1 Aggregate Tests

Perform gradation tests on each sample. Make other aggregate tests on initial source samples, and repeat tests whenever there is a change of source. During progress of concrete placement perform gradation tests for fine and coarse aggregates. Include sieve analysis for each fractional size and gradation analysis of the combined material representing the aggregate part of the concrete mix.

3.8.2.2 Concrete Testing

a. Concrete Slump: Test consistency of concrete slump in accordance with ASTM C 143/C 143M. Determine consistency of concrete at the start of each day's concrete placement and for each group of test specimens.

b. Air Content: Determine air content at the start of concrete placement and for each group of test specimens. Record results with test specimens. Determine air content in accordance with ASTM C 173 or ASTM C 231.

c. Surface Tests: After curing, test pavement surface with a straightedge or device which will reveal irregularities in the concrete surface. Irregularities in the concrete surface shall not exceed 3 mm in 3 meters in the longitudinal direction and 6 mm in 3 meters in the transverse direction for primary roads, runways and taxiways and shall not exceed 6 mm in 3 meters in both the longitudinal and transverse direction for secondary roads. Where defective areas of pavement are removed or replaced, the portion of the slab which remains in the pavement abutting the replacement slab shall have length and width not less than 3 meters from the nearest edge or joint.

d. Test for Pavement Thickness: Obtain 100 mm diameter core samples to determine in-place thickness of concrete pavement.

Obtain cores in accordance with ASTM C 42/C 42M. Remove cores at varying intervals but in no case less than one core for each

800 square meters. Repair core holes with non-shrink grout. Measure cores in accordance with ASTM C 174/C 174M. A tolerance in pavement thickness of plus or minus 13 mm will be permitted for individual core; however, the average thickness of cores must be at least 300

mm. When determining the average, cores with a thickness of more than 13 mm greater than specified thickness shall be assigned a thickness of the specified thickness plus 13 mm. If measured pavement thickness is less than that shown by more than 13 mm, remove deficient areas and replace with pavement of the specified strength, quality and thickness. When a core indicates unsatisfactory thickness, limits of the pavement to be removed and replaced shall be determined as follows: Take one core for each slab of lane in question in both directions from unsatisfactory core

Section 02751 13 until satisfactory thickness is indicated; remove and replace pavement in each panel, for the full width of the lane, in which a core indicated unsatisfactory thickness. Include the following information in each of the reports of corings:

(1) Date concrete represented by core was placed

(2) Date core was taken

(3) Location of Core: Lane number, station number

(4) Thickness of core

(5) Condition of Core: Appearance, concrete texture, condition of bottom of core

(6) Disposition of Cores: In Contacting Officer’s Technical

Representative or Contractor possession.

e. Flexural Strength: During progress of work verify flexural strength by testing beams made from concrete taken from the delivery vehicle at intervals specified herein. Mold and cure beams in accordance with ASTM C 31/C 31M. Perform tests in accordance with ASTM C 78.

Mold at least eight beams each day from concrete placed that day.

Select one group of four beams near the beginning of the work and a second group of four beams from the final third of concrete to be placed that day. An approved laboratory shall furnish necessary labor, concrete and facilities for molding, handling, and storing the beams at the site of the work and testing beams. Perform tests at 7 days and 28 days. Concrete shall meet the following requirements:

(1) From each group of four beams, three beams tested at the end of

28 days shall have an average flexural strength equal to or greater than the specified strength.

(2) No individual beam of the three beams tested shall have a flexural strength less than 4.1 MPa. Discard defective beams.

(3) Test one beam of the group at 7 days. If the ratio of the 7-day strength test to the specified 28-day strength is less than expected make necessary adjustments for conformance.

(4) When a satisfactory relationship between 7-day and 28-day strengths has been established and approved by the Contracting

Officer’s Technical Representative, the 7-day test results may be used as an indication of the 28-day strengths. If test results of any concrete to be used in the project show that the concrete strength is below the specified limits and does not meet other requirements of this specification, the Contractor shall make necessary adjustments, as approved by the

Contracting Officer’s Technical Representative at the

Contractor's expense.

Concrete which at the end of 30 days does not meet the specified strength shall be removed or otherwise corrected at the Contractor's expense, with corrective methods subject to the approval of the Contracting Officer’s Technical

Representative.

f. Control Charts: Maintain control charts for concrete flexural strength in accordance with ACI 214, Appendix, except as otherwise modified herein. Post copies of charts at the job site. Indicate specified strength and average strength determined by the mix design. Each control chart shall consist of the following plots:

(1) Test Results: At the same location, plot each individual test strength (the beam tested at 7 days and the average results of three beams tested at 28 days).

14 Section 02751

(2) Moving Average for Strength: Moving average of five consecutive tests ACI 214.

3.9 PAVEMENT PROTECTION

Protect pavement against damage. Exclude traffic by erecting and maintaining barricades and signs until concrete is at least 14 days old.

When paving intermediate lanes between newly paved lanes, operation of hauling equipment will be permitted on pavement after curing for 7 days and the joints have been sealed or otherwise protected. Subgrade planer, concrete finishing machines, slipform pavers and similar equipment may be permitted to ride upon surface of previously constructed slabs when concrete has attained a minimum flexural strength of 3.1 MPa. For fill-in lanes, use equipment that will not damage or spall edges of joints of previously constructed pavement.

-- End of Section --