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IS120 - Construction Specification Guideline for Ultra-Thin Whitetopping

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Ultra-thin whitetopping (UTW) is a process where a thin layer of concrete [50 to 100 mm (2 to 4 in.)], usually with fibers and often of high strength, is placed over a pre­pared surface of distressed asphalt pavement. In addi­tion to the thinness of the concrete overlay, other factors differentiate UTW from conventional concrete overlays of existing asphalt pavement (conventional whitetopping). These are: (1) a substantial degree of bond between the concrete overlay and the prepared asphalt surface, and (2) much closer joint spacing.

UTW Applications

Ultra-thin whitetopping provides a durable wearing sur­face for pavements. Since the first experimental project when a landfill access road near Louisville Kentucky was overlaid with UTW in 1991, about 200 UTW projects have been built through 1998. The predominant use has been to rehabilitate distressed asphalt pavement at intersec­tions where rutting and washboarding was a recurring problem. Other uses include: city streets, general avia­tion airfields, automobile parking lots, bus lanes, and rural highways.

For More Information

For more information about UTW, including applications, history and use, material requirements, project selection criteria, load-carrying capacity, research and performance, joint design, construction procedures and repair, obtain these publications from the American Concrete Pavement Association:

  • Ultra-thin Whitetopping (IS100P)
  • Whitetopping - State of the Practice (EB210P)


© American Concrete Pavement Association 1999

Foreword to Guideline

This document provides guideline specifications useful for developing concrete project specifications for ultra-thin whitetopping pavement. These guidelines should not be used as a specification by reference in contract docu­ments. A contracting agency must modify these guide­lines for local conditions, preferences and construction practices.

Project specifications denote specific requirements for construction. They are not intended to provide general or educational information about material, equipment or con­struction procedures. Therefore, the language in these guidelines is generally imperative and terse as would be used in project specifications.

A contracting agency must specify items designated in the "Mandatory Specification Checklist" portion of this document. The contracting agency may also choose from the provisions in the "Optional Specification Checklist" portion of this document. Checklists are to assist in prop­erly choosing and specifying requirements for the project specifications. These checklists should not be part of the final project specifications.

This document references appropriate material stan­dards, test methods and specifications of the American Society of Testing and Materials (ASTM), American Asso­ciation of State Highway and Transportation Officials (AASHTO), and Canadian Standards Association (CSA). These references assume that the contractor and the en­gineer will use the applicable standards or methods that are in effect when bids are solicited for the project or at the time of construction. It also assumes that the specifi­cation writer will choose the standard or test most suitable for their agency and project. These guidelines are written in the three-part section format of the Construction Speci­fications Institute.

Mandatory Specification Checklist

Section/Part/Article Action Required by Engineer
Section 1 - General
1.7.2 Testing and Inspection Review for compliance with Project Specifications. Designate the Contracting Agency representatives for "Testing and Inspection."
Section 2 - Products
2.1.2 Concrete air content Specify expected exposure condition (mild, moderate, or severe).
2.1.4 Fibers Specify type and amount, when used.
Section 3 - Execution
3.1.1 Asphalt surface preparation Specify depth of milling on Project Drawings.
3.4.6, 3.5.4 Overlay thickness Specify Ultra-thin Whitetopping thickness on Project Drawings.
3.12 Jointing Specify joint locations, depths, and dimensions on Project Drawings [3.12.1], or review and accept drawings from the Contractor describing jointing requirements [3.12.2].

Optional Specification Checklist

Section/Part/Article Action Required by Engineer
Section 1 - General
1.7.5 Testing Specify other than ASTM C 94 (AASHTO M I57, CSA A23.1) for concrete testing, inspection and remedy for concrete failing to meet strength requirements, when permitted.
Section 2 - Products
2.1 Concrete Specify cement specifications and type when other than ASTM C 150, C 595, or C 1157 (AASHTO M 85 or M 240, CSA A5 or A 362)
2.1.1 Concrete strength Specify strength when other than 31.0 MPa (4500 psi) compressive strength at 28 days is required.
2.1.2 Concrete air content Specify total required air content when other than those listed in Table 2.1.2 is required.
2.1.5 Slump Specify slump other than required in Section 2.1.5, when permitted.
Section 3 - Execution
3.7 Final surface texture Specify the final surface finish (broom, burlap-drag, turf drag or tined) if a particular texture is desired. (Otherwise the final surface finish will be the Contractor's option for roadways designed for vehicle speeds less than 80 km/h (50 mph). Tining will be required for higher speed roadways.)
3.9 Curing Specify curing method other than membrane-forming curing compound, when permitted.
3.14 Opening to traffic Specify other than 20.7 MPa (3000 psi) compressive strength, when permitted.

Submital Specification Checklist

Section/Part/Article Notes to Engineer
Section 2 - Products
2.1.6 Concrete mix proportions Required
Section 3 - Execution
3.10 Hot weather construction When required.
3.11 Cold weather construction When required
3.12.2 Jointing When required

Section 1 - General

Scope

This Specification covers the requirements for the construc­tion of Ultra-thin Whitetopping of existing asphalt pavement.

Definitions

These definitions are to assist in interpreting the provisions of this specification.

Accepted - Accepted by or acceptable to Engineer.

Cold Weather - A period when for more than 3 succes­sive days the average daily outdoor temperature drops be­low 4° C (40° F.) The average daily temperature is the aver­age of the highest and lowest temperature during the pe­riod from midnight to midnight. When temperatures above 10° C (50° F) occur during more than half of any 24-hr dura­tion, the period shall no longer be regarded as Cold Weather.

Contractor - The person, firm, or corporation with whom the Contracting Agency enters into an agreement for con­struction of the Work.

Contract Documents - Documents including Project Drawings and Project Specifications covering the required Work.

Contracting Agency - The corporation, association, partnership, individual, or public body or authority with whom the Contractor enters into an agreement, and for whom the Work is accomplished.

Engineer - The engineer or engineering firm issuing Project Drawings and Project Specifications, or adminis­tering the Work under the Contract Documents.

Hot Weather - Any combination of the following condi­tions that tend to impair the quality of freshly mixed or hard­ened concrete by accelerating the rate of moisture loss and rate of cement hydration or causing concrete crack­ing at locations other than joints:

a. High ambient temperature.
b. High concrete temperature.
c. Low relative humidity.
d. Wind velocity
e. Solar radiation.

Isolation Joint - A full-depth joint which isolates or sepa­rates the pavement from fixed objects within or abutting the newly paved area.

Moderate Exposure Condition - Exposure in a cli­mate where freezing is expected but where the concrete will not be continually exposed to moisture or free water for long periods prior to freezing and will not be exposed to deicing agents or other aggressive chemicals.

Panel - A section of concrete pavement between joints.

Project Drawings - The drawings which, along with the Projects Specifications, complete the descriptive in­formation for constructing the Work required or referred to in the Contract Documents.

Permitted - Permitted by the Engineer.

Project Specifications - The written documents which specify requirements for a project in accordance with ser­vice parameters and other specific criteria established by the Contracting Agency.

Reference Standards - Standards of a technical so­ciety, organization, or association, including the building codes of local or state authorities, which are referenced in the Contract Documents.

Severe Exposure Condition - Exposure to deicing chemicals or other aggressive agents or where the con­crete may become highly saturated by continued contact with moisture or free water prior to freezing.

Submitted - Submitted to the Engineer for review.

Ultra-thin Whitetopping - A concrete overlay, 50-mm to 100-mm (2 in. to 4 in.) thick with closely spaced joints bonded to an existing asphalt pavement.

Work - The entire construction of separately identifiable parts thereof which are required to be furnished under the Contract Documents. Work is the result of performing services, furnishing labor, and furnishing and incorporat­ing materials and equipment into the construction, all as required by the Contract Documents.

Reference organizations

AASHTO - American Association of State Highway and Transportation Officials 444 N. Capitol Street, NW, Suite 249 Washington D. C. 20001

ACI - American Concrete Institute P. 0. Box 9094 Farmington Hills, Ml 48333

ASTM - American Society for Testing and Materials 100 Barr Harbor Drive West Conshohocken, PA 19428-2959

CSA - Canadian Standards Association 178 Rexdale Boulevard Etobicoke (Toronto), ON, Canada M9W1R3

Reference standards

ACI standards:

117. Standard Specifications for Tolerances for Con­crete, Construction and Materials

306.1. Standard Specification for Cold Weather Concreting

ASTM standards:

C 94. Standard Specification for Ready-Mixed Con­crete

C 150. Standard Specification for Portland Cement

C 309. Standard Specification for Liquid Membrane Forming Compounds

C 595M. Standard Specification for Blended Hy­draulic Cement

C 1116. Standard Specification for Fiber-Reinforced Concrete and Shotcrete

C 1157M. Standard Performance Specification for Blended Hydraulic Cement

C1399. Test Method for Obtaining Average Residual Strength of Fiber-Reinforced Concrete

D 1751. Standard Specification for Preformed Expansion Joint Filler for Concrete Paving Structural Construction (Nonextruding and Resilient Bituminous Types)

D 1752. Specification for Preformed Sponge Rub­ber and Cork Expansion Joint Fillers for Concrete Pav­ing and Structural Construction

AASHTO standards

M 85. Standard Specification for Portland Cement

M 148. Standard Specification for Liquid Membrane-Forming Compounds for Curing Concrete

M 153. Standard Specification for Preformed Sponge Rubber and Cork Expansion Joint Fillers for Concrete Paving and Structural Construction

M 157. Standard Specification for Ready-Mixed Concrete

M 213. Standard Specification for Preformed Expansion Joint Fillers for Concrete Paving and Structural Construction

M 240. Standard Specification for Blended Hydrau­lic Cements

CSA standards

A 5. Portland Cement

A 23.1. Concrete Materials and Methods of Con­crete Construction

A 362. Blended Hydraulic Cement

Submittals

  • Submit drawings and documentation as required in this specification.
  • Obtain written acceptance of submittals before using the material or methods requiring acceptance.

Storage and handling

Store construction material in a clean, dry location.

Testing and Inspection

  • Tests required to document submittals, certify product compliance with this specification prior to construction, establish concrete mixture proportions, provide acceptability of changes requested by the Contractor, or appeal rejection of material found defective by Contracting Agency test, shall be performed by accepted laboratories.
  • The Work in progress will be inspected and mate­rials, equipment, and procedures will be evaluated for quality and acceptability by representatives of the Contracting Agency or as designated in the Contract Documents.
  • Permit and facilitate access of the Contracting Agency's representatives to the construction sites for the performance for all inspection and testing.
  • Failure to detect defective work or material shall not prevent later rejection when the defect is discovered nor shall it obligate the Contracting Agency for final acceptance.
  • Test concrete in accordance with ASTM C 94 or C 1116 (AASHTO M 157, CSA A23.1). Concrete failing to meet strength requirements shall be remedied in accor­dance with ASTM C 94 or C 1116 (AASHTO M 157, CSA A23.1), unless otherwise specified.

SECTION 2 - PRODUCTS

Concrete

Comply with ASTM C 94 or C 1116 (AASHTO M 157, CSA A 23.1) and the following requirements:

Strength.

Use concrete with a compressive strength of 31.0 MPa (4500 psi) at 28 days unless other­wise specified.

Total air content.

Comply with Table 2.1.2 unless otherwise specified.

Aggregates

Use a maximum aggregate size of one-third of the pavement thickness.

Fibers

If fiber-reinforced concrete is specified, use fibers of the type and in the amount shown in the Con­tract Documents, and comply with ASTM C 1116. When fibers are used, use fibers providing a residual strength of at least 0.6 MPa (80 psi) as measured by ASTM C 1399, unless otherwise specified.

Slump

Use concrete with a maximum slump of 100 mm (4 in.) for pavements placed by other than slipform equipment or 25 mm (1 in.) for concrete placed with slipform equipment. Concrete with different slumps may be used when accepted.

Submittal

Submit documentation describing concrete mixture proportions in accordance with Section 1.5-Submittals.


Table 2.1.2 - Required total air content

Nominal maximum aggregate size, mm (in.) Total air content, percent
Mild exposure Moderate exposure Severe exposure
9.5 (3/8) 4.5 6.0 7.5
13 (1/2) 4.0 5.5 7.0
19 (3/4) 3.5 5.0 6.0
25 (1) 3.0 4.5 6.0

Membrane-forming curing compounds

Comply with ASTM C 309 (AASHTO M 148), Type 2, Class A.

Isolation joint material

Comply with ASTM D 1751 or ASTM D 1752 (AASHTO M213orM 153).

Forms

Use forms made of steel or wood or other material ca­pable of supporting mechanical concrete placing equip­ment without settling vertically, bowing inward or outward, or crushing. Use forms, with sufficient rigidity to maintain specified tolerances, that are clean and free of dirt, rust, and hardened concrete.


Section 3 - EXECUTION

Asphalt surface preparation

  • Mill existing asphalt surface to the depth indicated on the Project Drawings using self-propelled milling equip­ment having an effective means for preventing dust from escaping into the air. All removed material becomes the property of the Contractor unless otherwise designated in the Contract Documents.
  • Remove all loose foreign material from asphalt sur­face with compressed air, by brooming or other methods immediately prior to placing concrete.

Setting forms

  • Set, align, and brace forms so that pavement will meet the tolerances specified in Section 3.8 - Tolerances.
  • Apply form release agent to inside face of forms prior to placement of concrete. The vertical edge of previously placed concrete may be used as a form. Do not apply form release agent to previously placed concrete. Do not apply form release agent to prepared asphalt surface.
  • Comply with ASTM C 94 or C 1116 (AASHTO M 157).

Placing fixed-form pavement

  • Deposit concrete directly from the transporting equipment onto the prepared dry asphalt surface. Other methods of conveying the concrete may be used when accepted by the Engineer.
  • Do not place concrete when the asphalt surface temperature is less than 0° C (32° F).
  • Deposit concrete between the forms to a uniform height.
  • Vibrate concrete to remove voids and air pockets. Do not move concrete horizontally with vibrator.
  • Strike off concrete between forms using a form-riding paving machine or vibrating screed. Vibrate the surface of the concrete at a frequency of no less than 3500 vibrations/minute. Other strikeoff devices may be used when accepted.
  • Construct concrete overlay to the thickness shown on Project Drawings within tolerances required in Section 3.8-Tolerances.

=Placing slipform pavement

  • When accepted, slipform equipment may be used. Furnish machines capable of spreading, consolidating, screeding and finishing concrete in one pass.
  • Deposit concrete in accordance with Sections 3.4.1 and 3.4.2.
  • Produce a dense and homogeneous concrete over­lay requiring minimal hand finishing by vibrating the sur­face of the concrete with a pan vibrator operating at a frequency of no less than 3500 vibrations/minute.
  • Construct concrete overlay to the thickness shown on Project Drawings within tolerances required in Section 3.8-Tolerances.

Surface finishing

  • Check the surface of the fresh concrete with a long-handled straightedge that is 3 m (10 ft) or longer. Remove high areas indicated by the straightedge. Over­lap each successive pass of the straightedge by about 1.5 m (5 ft).
  • Hand-float the surface only as needed to produce a uniform surface and sharp corners. Do not use excess mortar to build up slab edges or round the slab corners.
  • Edge each side of transverse Isolation Joints, formed joints, transverse construction joints, and fixed forms to produce a 6-mm (1/4-in.) continuous radius and a smooth, dense mortar finish.

Final surface texture

  • After surface finishing, texture all concrete sur­faces that will be used by traffic. Use either hand-oper­ated or mechanical tools to produce a uniform texture.
  • For roadways designed for vehicle speeds of less than 80 km/h (50 mph), texture the surface with a burlap drag, turf drag or broom.

For a burlap-drag texture, drag two layers of moist­ened burlap along the pavement in the direction of pav­ing. The burlap must be sufficiently long and wide enough to cover the entire pavement width and produce a uniform texture with corrugations about 1.5 mm (1/16 in.) deep. Clean the burlap periodically to remove encrusted mortar or replace with new burlap.

For a turf-drag texture, drag plastic turf along the pavement in the direction of paving. The plastic turf must be sufficiently long and wide enough to cover the entire pavement width and produce a uniform texture with cor­rugations about 1.5 mm (1/16 in.) deep. Use turf with a blade density of 77500 blades/m2 (7200 blades/ft2) with blades at least 20 mm (0.75 in.) long.

For a broom texture, use a stiff-bristled broom, drawing it from the pavement center to the edges. Over­lap strokes slightly to produce a uniform texture with cor­rugations about 1.5 mm (1/16 in.) deep.

  • For roadways designed for vehicle speeds greater than 80 km/h (50 mph), tine the surface in the trans­verse or longitudinal direction to a depth of 3 to 6 mm (1/8 to 1/4 in.) and individual tine width of 2.5 to 3.5 mm (0.10 to 0.14 in.)

When tining transversely, space tines randomly at a minimum spacing of 13 mm (1/2 in.) apart, a maximum spacing of 38 mm (1-1/2 in.) apart, with no more than 50% of the tines apart by more than 25 mm (1 in.).

When tining longitudinally, texture parallel to the pavement centerline with tines spaced uniformly at 18 mm (3/4 in.).

Tolerances

Construct pavement within the following tolerances:

Concrete overlay thickness
13mm; - 6 mm (+ 1/2 in.; - 1/4 in.)
Asphalt surface after milling
13 mm; - 6 mm (+ 1/2 in.; - 1/4 in.)
Joint spacing
75 mm (± 3 in.)
Contraction joint depth
6 mm; - 0 mm (+ 1/4 in., - 0 in.)
Joint width
3 mm (± 1/8 in.)

Surface: In the principal direction of vehicle travel, the gap below a 3 m (10 ft) straightedge resting on highspots shall not exceed....3 mm (1/8 in.).

Exceptions: Areas within 3 m (10 ft) of fixtures such as manholes, drainage inlets and catch basins and in areas where the UTW meets existing curb and gutter, cross­roads, side-roads and driveways.

Curing

Apply membrane-forming curing compound to all exposed surfaces at a maximum coverage rate of 2m2/ liter (100 ft2/gal). Apply curing compound immediately after final surface texture has been obtained and water sheen has disappeared. Apply curing compound to pavement edges after forms have been removed. Alternate curing methods may be used when specified or accepted.

Hot weather construction

In Hot Weather, protect finished concrete with windbreaks, shading, fog spraying, ponding, or wet covering to prevent cracking at locations other than contraction joints. If required, submit detailed procedures for the produc­tion, transportation, placement, protection, curing, and temperature monitoring of concrete during Hot Weather.

Cold weather construction

In Cold Weather, comply with ACI 306.1, Standard Speci­fication for Cold Weather Concreting. This defines the con­ditions for which concrete shall be protected from freez­ing, and describes the operations of placement and pro­tection of concrete during Cold Weather. If required, sub­mit detailed Cold Weather procedures for the production, transportation, placement, protection, curing, and tem­perature monitoring of concrete.


Jointing

  • Construct joints at the locations, depths, and with dimensions indicated on the Project Drawings or ac­cepted drawings submitted by the Contractor.
  • If Project Drawings do not indicate jointing re­quirements or if submittals are required, submit drawings describing jointing requirements in accordance with Sec­tion 1.5 - Submittals, and the following requirements:
  • Indicate locations of all contraction joints, con­struction joints, and Isolation Joints. Locate joints at spac­ings shown in Table 3.12.2.1.

Table 3.12.2.1 - Spacing between joints

Pavement thickness, mm (in.) Approximate spacing, m (ft)
50 (2) 0.6-1.0 (2-3)
63 (2.5) 0.75-1.1 (2.5-3.5)
75 (3) 0.9-1.2 (3-4)
88 (3.5) 1.1-1.5 (3.5-5)
100 (4) 1.2-1.8 (4-6)
  • The larger dimension of any Panel shall not exceed 125 percent of the small dimension.
  • The minimum angle between any two inter­secting joints shall be 80 degrees.
  • Joints shall intersect pavement free edges at a 90-deg angle and shall extend straight for a minimum of 0.3 m (1 ft) from the pavement edge.
  • Align joints of adjacent Panels.
  • Describe joint depths and widths.
  • Minimum contraction joint depth shall be one-fourth of the UTW thickness.
  • Use Isolation Joints only where pavement abuts buildings, existing curbs, manholes, and other fixed objects.
  • Construct contraction joints by one of the follow­ing methods:
  • Tool contraction joints in fresh concrete after concrete has set sufficiently to maintain the formed joint to the specified depth and width.
  • Saw-cut concrete after concrete has hardened sufficiently to prevent excessive aggregate being dis­lodged and soon enough to control pavement cracking. If contraction joint sawing causes a crack, discontinue sawing that contraction joint and continue sawing other contraction joints.

Protection

Protect pavement from damage.

Opening to traffic

Open the pavement to vehicular traffic after the concrete compressive strength exceeds 20.7 MPa (3000 psi) or when accepted for opening to traffic.

Method of Measurement

  • Asphalt Surface Preparation. The area of asphalt surface preparation, will be computed by the En­gineer in square meters (square yards) from measurements of the locations.
  • Concrete, Furnish Only. The amount of con­crete will be measured by the Engineer in cubic meters (cubic yards).
  • Concrete, Placement Only. The area of concrete overlay placement will be computed by the En­gineer in square meters (square yards) from measurements of the locations.

Basis of payment

  • Asphalt Surface Preparation. Payment will be made at the contract price per square meter (square yard) for asphalt surface preparation. This will include full compensation for removal and disposal of material.
  • Concrete, Furnish Only. For the concrete incorporated, payment will be made at the contract price per cubic meter (cubic yard) of concrete. This will be full compensation for furnishing all materials, and for propor­tioning, mixing and delivery of concrete to the paving site.
  • Concrete, Placement Only. For the con­crete overlay constructed (placement only), payment will be made at the contract price per square meter (square yard). This will be full compensation for furnishing all la­bor, equipment and materials to place, finish, texture, cure the concrete, and to saw or form the joints, in accordance with the Contract Documents.


This publication is intended SOLELY for use by PROFESSIONAL PERSONNEL who are competent to evaluate the significance and limitations of the information provided herein, and who will accept total responsibility for the application of this information. The American Concrete Pavement Association DISCLAIMS any and all RESPONSIBILITY and LIABILITY for the accuracy of and the application of the information contained in this publication to the full extent permitted by law. American Concrete Pavement Association 5420 Old Orchard Road, Suite A100, Skokie, Illinois 60077-1083 (847) 966-2272, FAX (847) 966-9970, www.pavement.com

A national organization with the mission to increase the use of concrete pavement in construction and rehabilitation of transportation facilities in North America, by continually providing a quality product that is safe, cost effective and environmentally sound.

IS120P