Structural Factors of Jointed Plain and Concrete Pavements: SPS-2 - Initial Evaluation and Analysis

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APPENDIX A. SUMMARY OF SPS-2 PROJECT NOMINATION AND CONSTRUCTION GUIDELINES

To ensure proper selection of the SPS-2 sites and to maximize the uniformity of the design and construction details at all SPS-2 sites and sections, the following two documents were prepared for the SPS-2 experiment:

• Specific Pavement Studies Guidelines for Nomination and Evaluation of Candidate Projects for Experiment SPS-2 Strategic Study of Structural Factors for Rigid Pavements⁽¹¹⁾
• Specific Pavement Studies Construction Guidelines for Experiment SPS-2 Strategic Study of Structural Factors for Rigid Pavements ⁽¹²⁾

These guidelines were developed to control the quality and integrity of the SPS-2 experiment results and findings. A summary of the documents is provided in this appendix.

Project Selection Criteria

The following criteria are to be used to evaluate candidate projects for inclusion in the SPS-2 experiment:

• The project must include new construction of all pavement lanes for a new route, realignment, reconstruction, or construction of an experimental parallel roadway. Projects in which the experimental sections are constructed as additional lanes or as a partial reconstruction (removal and replacement on surface layers only) are not acceptable.
• The construction project must be of sufficient length to accommodate all of the experimental test sections. Transition zones are required between test sections, and the length of these zones depends on site conditions such as location of cut and fills and drainage provisions. A minimum transition length of approximately 54.9 m should be provided between test sections.
• All test sections at one site must be constructed on soils classified as either fine-grained or coarse-grained. Further, it is desired that all of the test sections be located on subgrade soils of similar characteristics and classification. Variation in soil characteristics at each site should be minimized as much as possible.
• Test sections should be located on portions of the project that are relatively straight and have a uniform vertical grade. Horizontal curves greater than 3 degrees, and vertical grades greater than 4 percent, should be avoided. Left-hand horizontal curves in which superelevation forces surface water to flow toward the inside shoulder should be avoided. All test sections of a project must have the same transverse cross section profile of the pavement surface to obtain the same surface drainage conditions.
• Ideally, all test sections should be located on shallow fills. However, the entire length of each test section should be located completely on either a cut or a fill. Cut-fill transitions and side hill fills should be avoided.
• It is highly desirable that the portion of the project that includes the proposed test sections be opened to traffic at the same time.
• Culverts, pipes, and other structures beneath the pavement should be avoided within the limits of each test section. It is recommended that subsurface structures, if required, be located in the transition zones between test sections.
• It is desired that the project be located on a route with an expected traffic loading level in the study lane in excess of 200,000 ESALs per year. However, projects on the primary system with high traffic relative to the region, but less than the desired rate, will be considered.
• Traffic flow over all the test sections of a project should be uniform. All sections should carry the same traffic stream. Intersections, rest stops, on-off ramps, weaving areas, quarry entrances, and so on must be avoided on and between test sections on a project.

These criteria and considerations will help identify projects in which the relative performance of the test sections is due to the design parameters used and not to external factors (e.g., changes in the subgrade or traffic patterns). They also serve to identify projects at different locations with relatively similar details so that differences in performance from one location to another are primarily due to differences in climatic conditions and subgrade types.

It is recognized that "perfect" projects containing all of the desirable characteristics are rare. Each proposed site will be evaluated individually and compared to other candidates in order to select the best set of projects to satisfy experimental considerations. Some deviation from the desired project characteristics may be necessary to obtain sufficient projects for the experiment. For example, projects will be considered where it is not possible to locate all of the test sections completely in cuts or on fills. In this case, it may be necessary to locate some test sections in cuts and others in fills.

Preparation and Compaction of Subgrade

Ideally, the test sections shall be located in shallow fills. However, if the test section cannot be placed in a fill, the entire length of the section shall be located completely in a cut section. Cut-fill transitions or side hill fills should not be located within a test section. In addition, rock cut sections should be avoided unless all test sections are located within the cut.

Subgrade soils shall be prepared according to the following requirements:

• The subgrade soil shall be tested according to AASHTO T99, method D, to determine the moisture-density relationship.
• Fill material shall be compacted to a minimum of 95 percent of AASHTO T99 density for the top 305 mm. Expansive soils shall be compacted to a minimum of 90 percent of AASHTO T99 for the top 305 mm.
• Moisture content of the compacted subgrade soil should be in the range of 85 percent to 120 percent of the optimum moisture content.
• Sections built as part of a reconstruction project shall have the upper 305 mm of subgrade compacted to the appropriate specification.
• Subgrade shall be compacted for the width of the travel lanes plus the width of the inside and outside shoulders, except where sections are built as part of reconstruction of an existing pavement. In this case, reconstruction must extend a minimum of 914 mm outside the edge of the travel lanes to allow proper preparation of the subgrade and base course.
• Where sections are constructed on newly placed fill material, the thickness of the fill should be as uniform as possible along the test section. Geotextile reinforcement shall not be used to stabilize the subgrade.
• Proof rolling should be performed to verify the uniformity of support and to identify unstable areas that might require remedial construction (undercutting and replacement).
• Surface irregularities shall not exceed 6 mm between two points longitudinally or transversely using a 3.05-m straightedge.
• Final subgrade elevations shall not vary from design more than 12 mm, based on rod and level survey readings taken at a minimum of five locations (edge, outer wheel path, midlane, inner wheel path, and inside edge of lane) at longitudinal intervals no greater than 15.25 m.
• Modifiers, lime, portland cement, and the like can be added to provide a stable working platform to facilitate construction. The use of modifiers shall be limited to materials and quantities that will alter the index properties of the subgrade (e.g., reduce the plasticity index) without unduly increasing the strength of the subgrade in the pavement structure. Working platforms consisting of thin asphalt concrete layers placed directly on subgrade are not permitted.

Note: The working platform is considered a pavement layer; therefore, sampling and testing, in addition to that required for the subgrade, must be planned and performed.

Base Layers

The discussion of construction guidelines for base materials is divided into two categories: undrained and drained base structures. The drained and undrained designations do not refer to external pavement drainage features such as cross-slope and ditches. Undrained base structures refer to relatively impermeable dense graded base layers consisting of DGAB or lean concrete LCB. The drained base structures refer to a system that consists of PATB drainage layer and edge drains.

Undrained Base Layers

Sections 1 through 8 and 13 through 20 of the primary experiment (25 through 28, 31 through 34, 37 through 40, and 45 through 48 of the supplemental experiments) are constructed with undrained base layers that incorporate DGAB or LCB. Drainage layers and longitudinal edge drains shall not be used on these sections.

Dense-Graded Aggregate Base

DGAB is an untreated, crushed material. Requirements and construction guidelines for this material are presented in the following sections.

Aggregate Requirements

The quality and gradation criteria for selection of the aggregate required in the construction in the DGAB shall be as follows:

• The base material must consist of a high quality crushed stone, crushed gravel, or crushed slag.
• The base aggregate shall consist of a minimum of 50 percent of material retained on the No. 4 sieve. Of the particles retained on the 8-mm (3/8-in) sieve, at least 75 percent shall have two or more fracture faces.
• A 38-mm top size aggregate is preferred; however, the maximum top size normally specified by the State agency, if less than 38 mm, may be used.
• The final aggregate mixture must be dense graded.
• The fraction passing the No. 200 sieve shall be less than 60 percent of the fraction passing the No. 30 sieve and not more than 10 percent of the total sample.
• The fraction passing the No. 40 sieve shall have a liquid limit not greater than 25 and plasticity index not greater than 4.

• Aggregate tested with L.A. Abrasion^TM, which shows loss of more than 50 percent at 500 revolutions, shall not be used.
• No additives, other than water, are allowed in the DGAB.

Construction Requirements

The base course shall be prepared to grade according to the participating agency's practice and the following requirements:

• No segregation or degradation of materials should occur during laydown and compaction. Areas of excessive segregation shall be removed and replaced with proper aggregate.
• Maximum lift thickness shall be 152 mm compacted.
• Maximum dry density and optimum moisture content shall be determined by AASHTO T180, method D.
• DGAB course must be compacted to an average of not less than 95 percent of AASHTO T180 density.
• The DGAB shall be compacted for the width of the travel lanes plus the width of the inside and outside shoulders, except in cases where sections are built as part of reconstruction of an existing pavement. In this case, reconstruction must extend a minimum of 914 mm outside the edge of the travel lanes to allow proper preparation of the subgrade and base course.
• For those sections incorporating a PATB layer, a DGAB base course will be constructed over the subgrade prior to placement of the PATB. Low-viscosity asphalt shall be used to prime the surface of the DGAB before placing the PATB. Application and curing will be according to the participating agency's practice.
• In-place density for purposes of construction quality control shall be measured and recorded prior to application of an asphalt cement prime coat (in drained sections), if used.
• Prior to the placement of the PCC surface layer, the DGAB shall be kept uniformly moist; however, the method of moistening shall not be such as to form mud or pools of water.
• Surface irregularities shall not exceed 6 mm between two points longitudinally or transversely using a 3.05-m straightedge.
• Final DGAB elevations shall not vary from design more than 12 mm, based on a rod and level survey conducted taking readings at a minimum of five locations (edge, outer wheel path, midlane, inner wheel path, and inside edge of lane) at longitudinal intervals no greater than 15.25 m.

Lean Concrete Base

The LCB shall consist of a mixture of aggregate, hydraulic cement, water, and admixtures. The variability in specifications used by the different highway agencies makes it impractical to specify the same materials or mix design for all test locations. Therefore, the participating agency's procedures and specifications shall be used to produce and place an LCB with a target average compressive strength, slump, and air content as follows:

• Compressive strength-3.4 MPa (5.2 MPa maximum) at 7 days.
• Slump (slip-formed paving) -25 to 76 mm.
• Air content-4 to 9 percent.

Material Properties

Cement and aggregate used in producing the LCB shall meet the following requirements:

• Only Type I or Type II portland cement shall be used and shall meet the requirements of AASHTO specification M85.
• Coarse aggregate (retained on the No. 8 sieve) shall consist of crushed gravel or crushed stone particles meeting the requirements of AASHTO M80. It is recommended that the coarse aggregate meet the gradation requirements of AASHTO 57 gradation. The following specific requirements shall be met by the coarse aggregate:
  • Abrasion loss, maximum-50 percent.
  • Magnesium sulfate ssoundness, maximum-12 percent.
  • Crushed particles, minimum-55 percent.

It is important that the coarse aggregate meet the highest standard of durability specified by the agency. Coarse aggregate must be reasonably free from deleterious substances such as chert, gypsum, iron sulfide, amorphous silica, and hydrated iron oxide, and must be obtained from a source approved by the agency. Coarse aggregate for use in LCB that will be subject to wetting or extended exposure to moist ground shall not contain any materials that are deleteriously reactive with alkalies in the cement in an amount sufficient to cause excessive expansion of mortar or concrete. The potential reactivity should be determined in accordance with the procedure given in AASHTO M80.

Construction Requirements

Construction requirements for the LCB include the following:

• LCB shall be 152 mm thick.
• For new construction, the LCB layer will be constructed the full width of the travel lanes plus the width of the inside and outside shoulders. For sections built as part of reconstruction (inlay), the LCB will be placed to a width not less than 914 mm outside the edges of the travel lanes.
• Wax-base curing compound (AASHTO description: M 148, Type 2) shall be used at a rate of 4 liters per 10 m². A second coat of curing compound shall be applied within 24 hours before concrete placement at a rate of 4 liters per 15 square meters.
• The LCB surface shall not be textured and shall be finished to a smooth surface, free from mortar ridges and other projections, before the curing compound is applied.
• Final LCB elevations shall not vary from design more than 12 mm based on a rod and level survey. Readings shall be taken at a minimum of five locations (edge, outer wheel path, midlane, inner wheel path, and inside edge of lane) at longitudinal intervals no greater than 15.25 m.
• Surface irregularities shall not exceed 6 mm between two points longitudinally or transversely using a 3.05-m straightedge.
• LCB constructed in widths greater than 7.92 m shall be constructed with a longitudinal joint offset not more than 914 mm from the centerline of the width being constructed.
• A longitudinal joint in the LCB shall not be within 0.305 m of the planned longitudinal joint in the concrete pavement.
• Procedures normally used for placing concrete pavements shall be used for placing LCB. The use of slip-form paving is recommended.
• Traffic will not be allowed on the LCB surface for 7 days or until the compressive strength of the LCB has reached a minimum of 3.4 MPa. No traffic should be allowed onto the LCB after the second application of curing compound.

Drained Base Structures

Sections 9 through 12 and 21 through 24 of the primary experiment (and sections 29, 30, 35, 36, 41 through 44, and 49 through 52 of the supplementary experiments) are constructed with drained base structures that incorporate a PATB and edge drains. The PATB is constructed in combination with the DGAB materials previously described.

Permeable Asphalt-Treated Base

The PATB serves as a drainage layer in the pavement structure. Material and construction requirements for the PATB are presented below.

• PATB shall be an open graded, hot laid, central plant mixed, asphalt base material.
• The use of asphalt cement emulsion in the mix is prohibited.
• An AASHTO No. 57 size stone, or such other gradation used by an agency as a highly permeable drainage material in pavement structures, shall be used. It is required that this gradation has no more than 2 percent passing the No. 200 sieve. The aggregate shall consist of crushed material having more than 90 percent with at least one fractured face.
• The mix shall be designed with an asphalt cement content of 2 to 2.5 percent.
• Additives or modifiers may be used to reduce stripping of asphalt if such use represents the participating agency's practice. Experimental additives or modifiers shall not be used in the sections.
• Asphalt grade and type may vary according to agency practice. Experience on early SPS-2 projects indicated good placement experience when using AC-30 for the PATB mix.
• No recycled asphalt concrete shall be permitted in the PATB.

Table 53. Gradation table

Sieve	Percent Passing
38 mm	100
25 mm	95-100
13 mm	25-60
No. 4	0-10
No. 8	0-5
No. 200	0-2

Construction Requirements

Construction requirements for the PATB include the following:

• A static steel wheel roller shall be used to compact the permeable base, applying 14.6 kN to 29.1 kN per meter of roller width.
• No portion of the PATB layer shall be daylighted.
• Appreciable amounts of distortion shall be avoided on the permeable base.

• A roller may be used immediately in front of the paver to dress up the permeable base, if required.
• A track-mounted paver is strongly recommended for operation on the permeable base. It has been the experience on early projects in this experiment that the PATB may be sufficiently stable, after cooling or with the use of stiffer asphalt grades or modifiers, to allow wheeled pavers and construction trucks to operate on the PATB surface. However, sharp turning movements do cause significant distortion and should be avoided.
• Other than the paver and roller, no other equipment or vehicles should be allowed to operate or park on the travel lane or outside shoulder portion of the permeable base. Limited operation of equipment on the inside lane may be permitted. The use of side-dump delivery for layers constructed on the PATB should be encouraged to minimize damage to the PATB layer. Limited construction traffic (with reduced loads) may be allowed if the contractor is cautioned that excessive shoving and tearing of the PATB surface will be cause for prohibiting traffic. This requirement is intended to prevent damage to the PATB layer, which would affect layer thicknesses in subsequent layers, and also to prevent damage to the drainage properties of the finished PATB layer.
• Transverse interceptor drains shall be installed on the down slope end of the permeable base layers. They shall be placed in the transition zone between drained and undrained base structure test sections. They should be placed at least 30.5 m past the end of the 152.5-m monitoring section, or in the center of transitions, which are shorter than 30.5 m. The interceptor drains shall be placed along the midlength of a slab panel and will not be placed along a transverse joint.

Filter Fabrics

Filter fabric (or geotextiles) shall be used to prevent the clogging of the permeable material in the edge drains and transverse interceptor drains due to the migration of fine aggregates from untreated layers, the shoulder, and the subgrade. The requirements for the filter fabrics used in the edge drains are given below.

Material Requirements

Nonwoven or woven geotextile materials, which conform to recommendations for Class B drainage applications where installation stresses are low, will be used in edge drains. Fabric for the transverse interceptor drains shall meet Class A requirements. The following physical requirements on an average per roll basis sampled in accordance with ASTM D4354 shall be met.

Table 54. Geotextile material properties.

Property	Minimum Value		Test Method
	Class A	Class B
Grab strength, N	800 (180)	355 (80)	ASTM D 4632
Puncture strength, N	355 (80)	111 (25)	ASTM D 3787
Trapezoid Teartear, N	222 (50)	111 (25)	ASTM D 4533
Burst strength, kPa	2000 (290)	896 (130)	ASTM D 3786
Permeability	kfabric > ksoil		ASTM D 4491
Apparent opening size 1. Soil with £ 50% passing No. 200 sieve. 2.Soil with > 50% passing No. 200 sieve.	AOS < 0.6 mm > #30 U.S. std. sieve AOS < 0.3 mm > #50 U.S. std. sieve		ASTM D 4751

Construction Requirements

Construction requirements include the following:

• Filter fabrics shall extend around each of the edge drains. The filter fabric must extend around each edge drain and wrap around the outer edge of the PATB layer, but does not need to extend under the full width of the pavement. The fabric must wrap around the edges of the PATB layer, extending over the top of the PATB and under the pavement a minimum of 610 mm beyond the shoulder joint.
• Filter fabrics must be installed according to manufacturer's specifications and as shown in the typical drawings.
• Exposure of geotextiles to the elements between laydown and cover shall not exceed 14 days or manufacturer's manufacturer's specifications, whichever is less.
• Any filter fabric that is ripped or torn during the construction process shall be replaced or repaired with a patch that extends 914 mm beyond the perimeter of the tear or damage.
• Any filter fabric that is ripped or torn during the construction process shall be replaced or repaired with a patch which extends 914 mm beyond the perimeter of the tear or damage.
• Geotextile shall be overlapped a minimum of 610 mm at all longitudinal and transverse geotextile joints. Joints may be sewn if required by agency practice.

Edge Drains

Edge drains shall be used in the shoulders of the pavement sections with PATB to collect the water from the permeable base. The following requirements must also be met:

• Both inside and outside edge drains shall be constructed for crowned pavement cross-sections. For pavements with cross-slope, only one edge drain will be required.
• The edge drains should be located a minimum of 914 mm outside the edge of the mainline pavement.
• The edge drains shall run continuously throughout each of the 183-m minimum length permeable base test sections.
• The PATB is recommended as backfill in the edge drain trench; however, other approved open-graded material may be used.
• Collector pipes shall be a minimum 76-mm-diameter slotted plastic pipe and outlet pipes shall be a minimum 76-mm-diameter unslotted rigid plastic pipe. Pipes must be capable of withstanding the temperature of the PATB without damage if PATB is used as backfill.
• Transverse collector subdrains shall be located in transition zones between drained and undrained sections where a longitudinal slope exists. The drain should be installed at an acute angle relative to the downslope direction.
• Drainage pipes should be sized for the expected flows determined as part of design. Discharge outlet pipes should be located at maximum intervals of 76.2 m and rodent protected. Outlets must be at least 152 mm above the expected 10-year flow elevation of the collector ditches to prevent backflow into the drainage system.

Shoulders

For the SPS-2 experiment, participating agency practice shall be used to provide asphalt concrete or PCC shoulders. PCC shoulders shall not be tied to the mainline pavement. Also, if the concrete shoulder is placed monolithically with the traffic lanes, then the shoulder joint shall be sawed to full depth. Tied PCC shoulders may be constructed in additional supplemental test sections. The longitudinal joint between the mainline concrete pavement and the shoulder shall be sealed.

Portland Cement Concrete Mix Design

The quality of concrete as delivered, as placed, and the subsequent strength development in concrete are critical factors in concrete pavement performance. Although only the strength property (flexural strength) is normally considered in evaluating the structural behavior of concrete pavements, durability-related properties (entrained air content, aggregate type, degree of consolidation) are also important in evaluating long-term performance.

The test sections in the SPS-2 experiment will be constructed for two levels of flexural strength (3.8 and 6.2 MPa) as determined from third-point loading tests at 14 days. The concrete mixture should be designed according to the procedures and specifications followed by the participating agency. It is recommended that a slip-form method be used for placement of the concrete. In such a case, slump of the as-delivered concrete shall not exceed 64 mm.

Concrete with an average 14-day flexural strength of 3.8 MPa is considered standard and readily available. However, some agencies have reported difficulty in achieving this strength level while maintaining sufficient cement content for acceptable durability. In such cases, an average strength level of 4.1 MPa is considered acceptable for the lower strength level criterion. For the higher strength concrete, well-planned laboratory testing may be required to design a mixture capable of achieving an average flexural strength of 6.2 MPa at 14 days. The higher strength should be achievable by using a higher cement content (cement factor). Laboratory mix design will be in accordance with participating agency practice, except for the determination of the strength level.

The following is a summary of the requirements for the portland cement concrete PCC:

• Flexural strength-3.8 or 6.2 MPa average at 14 days.
• Slump (slip-form paving)-25 to 64 mm.
• Air content-6.5 ± 1.5 percent for freeze-thaw areas.

Materials

Material requirements for the concrete should be based on the normal practice of the participating highway agency. Many agencies have specific requirements for coarse and fine aggregates based on durability concerns and local availability of quality aggregates. However, it is necessary to maintain a high degree of uniformity and consistency in the construction of the test sections to achieve the objectives of a coordinated national experiment. Therefore, concrete materials must conform to certain minimum requirements to ensure consistency in the concrete quality at the different sites.

Portland Cement

Only Type I or Type II portland cement shall be used and shall meet the requirements of AASHTO specification M85.

Fly Ash

Fly ash may be used as substitute for a portion of the portland cement. The amount of substitution shall not exceed 15 percent by weight of cement. The fly ash replacement amount shall be determined through laboratory trial mix investigations using the specific materials proposed for the project. Use of Class F fly ash meeting the specific requirements of the agency is permitted. The use of Type C fly ash is not permitted. Participating agency practice concerning the use of fly ash in concrete in certain months of the year should be observed.

Fine Aggregate

Fine aggregate (passing the No. 8 sieve) shall consist of natural sand, manufactured sand, stone screenings, slag screenings, or a combination thereof, and meet the quality requirement of AASHTO M29. The fineness modulus of the fine aggregate shall not be less than 2.3 and shall not be greater than 3.1.

Coarse Aggregate

Coarse aggregate (retained on the No. 8 sieve) shall consist of crushed gravel or crushed stone particles meeting the requirements of AASHTO M80. It is recommended that the coarse aggregate conform to AASHTO 57 gradation as follows:

Table 55. Gradation table.

Sieve Size	Percent Passing
38 mm	100
25 mm	95-100
13 mm	25-60
No. 4	0-10
No. 8	0-5
No. 200	0-2

Coarse aggregate with a 25.4-mm maximum size aggregate may be used if such use represents the common practice of the participating agency.

The coarse aggregate shall conform to the following specific requirements:

Table 56. Course aggregate requirements.

Course Aggregate	Value
1. Abrasion loss, maximum %	50
2. Magnesium sulfate soundness, maximum %	12
3. Thin and elongated pieces, maximum %	15
4. Crushed particles, minimum %	55
5. Total of deleterious materials including chert, shale, and friable particles, maximum %	3

It is important that the coarse aggregate meet the highest standard of durability specified by the participating agency. Coarse aggregate must be obtained from a source approved by the agency and must be reasonably free from deleterious substances such as chert, gypsum, iron sulfide, amorphous silica, and hydrated iron oxide.

Coarse aggregate for use in concrete that will be subject to wetting, extended exposure to humid conditions, or contact with moist ground shall not contain any materials that are deleteriously reactive with alkalies in the cement in an amount sufficient to cause excessive expansion of mortar or concrete. However, if such materials are present in injurious amounts, the coarse aggregate may be used with a cement containing less than 0.6 percent alkalies calculated as sodium oxide equivalent or with the addition of a material that has been shown to prevent harmful expansion due to the alkali-aggregate reaction. The potential reactivity should be determined in accordance with the procedure given in AASHTO M80.

Other Items

Other items used in the production of concrete, such as water and admixtures, shall conform to the requirements normally specified by the agency for interstate concrete pavement construction. Use of microsilica (silica fume) as an additive is not permitted. Also, the use of additives to accelerate the strength gain of the concrete is not permitted for the SPS-2 experiment.

Concrete Pavement Requirements

Concrete pavement requirements for SPS-2 are summarized in the following sections.

The primary experiment SPS-2 addresses doweled JPCPs. The concrete pavement design for this experiment stipulates the following details:

• Slab thickness-203 and 279 mm.
• Joint spacing-4.57 -m uniform spacing.
• Lane width-3.66 and 4.27 m. A solid white line shall be painted to delineate the 3.66-m-wide travel portion of the widened lane.
• Joint load transfer-Doweled perpendicular transverse joints, with 32-mm dowel bars for the 203-mm-thick pavement and 38-mm dowel bars for the 279-mm-thick pavement. Dowels are to be epoxy coated, 457 mm long, spaced at 305 mm, and conforming to the requirements of AASHTO M254. Dowels are to be placed middepth using basket assemblies or dowel bar inserters with each bar aligned parallel to the longitudinal direction (with a tolerance of 1 mm per 50 mm of length) and located such that the bars will be centrally located (longitudinally) at the joint. Dowels shall be placed no closer than 152 mm from the longitudinal joints.
• Longitudinal joints-Between lanes should be sawcut, preferably using up to an 8-mm-wide blade, to a depth of D/3 (where D = slab thickness). The sealant reservoir may be formed later using a second sawcut to provide an 8-mm-wide by 25-mm-deep cut. The use of plastic inserts to form longitudinal joints is not permitted. The longitudinal joint between lanes will be tied using epoxy-coated deformed steel bars, No. 5 grade 40 steel, spaced at 762 mm center to center and 762 long. The tie bars shall be placed perpendicular to the longitudinal joint at a target depth of D/2.

Concrete Pavement Construction Operations

The concrete pavement for the SPS-2 test sections shall be constructed in accordance with the practices and specifications that have proven successful for the participating highway agencies. It is strongly recommended that slip-form-paving procedures be used for concrete placement, and that the test lane and adjacent lane be slip-formed in one operation. The key items related to construction are outlined below.

Concrete Placement and Finishing

The test sections at each site incorporate several variables pertaining to the concrete slabs, including pavement thickness, concrete strength, and lane width. Therefore, it is recommended that special consideration be given to arranging the test sections at the site in a manner that will facilitate construction operations. Concrete placement for each test section should be done in a single continuous operation.

When dowel baskets are used at transverse joints, concrete placement using side-dump procedures will facilitate placement of dowel bars ahead of concrete placement. Therefore, this procedure shall be used for placement of concrete.

Use of slip-form equipment is recommended. The equipment shall spread, consolidate, screed, and float-finish the concrete so that a minimum of hand finishing will be necessary and a well-consolidated and homogeneous pavement is produced. The machine shall vibrate the concrete for the full width and depth of the concrete. Internal spud-type vibrators shall be used at a spacing of no more than 610 mm.

Jointing

Transverse contraction joints with dowel bars shall be provided at a spacing of 4.57 m and 9.14 m, respectively. These joints shall be sawed perpendicular to the longitudinal direction of the pavement. At these joints, dowel bars shall be provided using basket assemblies or dowel bar inserters. Dowels should be properly aligned and the dowel baskets, if used, should be securely anchored to the base layer and placed at pavement middepth. Dowels should be lightly coated with grease or other suitable lubricant over their entire length to prevent bonding of the dowel to the concrete.

All joints shall be sawed. For transverse contraction joints, an initial sawcut of D/3 is required, preferably made using up to an 8-mm-wide blade. A second sawcut should be made later, if necessary, to provide the required shape factor for the sealant material. Longitudinal joints between lanes should be sawed initially, preferably using up to an 8-mm-wide blade, to a depth of D/3. A second sawcut should be made later to provide for an 8-mm-wide by 25.4-mm-deep sealant reservoir.

The use of plastic inserts to form longitudinal joints is not permitted. The longitudinal joint will be tied using epoxy-coated deformed steel bars, No. 5 grade 40 steel, spaced at 762 mm center to center and 762 mm long. The tie bars shall be placed perpendicular to the longitudinal joint at a target depth of D/2.

If a concrete shoulder is used along the test sections, then the longitudinal joint between the outside shoulder and the travel lanes shall not be tied. The joint will be formed by placing the shoulder separately or by sawcutting to full depth if the concrete is placed at the same time as the travel lanes.

Timing of initial sawing of both transverse and longitudinal joints is critical. Therefore, sawing should begin as soon as the concrete is strong enough to both support the sawing equipment and prevent excessive raveling of the concrete surface. Longitudinal sawing shall be initiated at the same time as the transverse sawing. All sawing shall be completed within 24 hours of placement.

Curing

Only liquid curing compound is permitted for curing the concrete pavement. Curing compound shall be applied to the concrete surface within 15 minutes after the surface texturing operation and no later than 45 minutes after concrete placement. Participating agency practice shall be followed for surface texturing and in specification of the type of curing compound and application rate.

Joint Sealing

Joint sealing shall be accomplished using only silicone sealants. The sealant shall be either self-leveling or a tooled, no-slump material proven by the agency to work satisfactorily. Neither new or experimental sealants nor field poured liquid sealants shall be used for test sections. All pavement joints shall be sealed before opening to traffic.

Thickness Tolerance

It is necessary that every effort be made to obtain slab thickness as close to the target values of 203 and 279 mm as possible. Neither a deficiency nor an excessive thickness is desired. Final pavement thickness should be within 6 mm of the target values, as determined from cores and rod and level survey elevation changes. Elevation measurements are to be taken at intervals of 15.25 m or less within the test sections, both before and after concrete placement.

Pavement Smoothness

The surface of the finished pavement shall be tested with a California-type profilograph. Profiles shall be made in both wheel paths parallel to each edge of the pavement. The pavement shall have a prorated profile index of less than 158 mm per 1,000 m, as evaluated using California test 526. The contractor shall remove high pavement areas with vertical deviations greater than 11 mm in 8 m using diamond grinding devices or multiple-saw devices as approved by the agency. Only localized grinding is permitted; wholesale grinding of the finished pavement surface is not permitted.

Opening to Traffic

The test section pavements shall not be opened to traffic before 7 days after concrete placement, or before concrete flexural strength has reached 3.8 MPa. Joint sealing must be completed before opening to traffic. No construction traffic will be allowed on the test section until that time.

Repair of Defective Slabs

Pavement slab panels exhibiting cracking before the test sections are opened to traffic shall not be repaired. In cases where slab panels are damaged to the extent that structural repairs are necessary, the FHWA Pavement Performance Division shall be consulted prior to performing any repair activity.

Construction Operations

Construction operations shall be performed in compliance with the guidelines and specifications established by the participating agency for road and bridge construction. The agency's high- quality construction practice should be enforced for the experiment. Adequate attention shall be given to details and control of the mix plant, hauling, placement, and consolidation operations to prevent construction practices that result in poor pavement performance. In addition, care should be taken to ensure that the test sections are constructed in a manner consistent with normal highway construction.

Transitions

The 183 m overall length of each test section includes 152.5 m for monitoring and 15.25 m before and after the section for materials sampling. The distance between these 183-m sections must be sufficient to allow changes in materials and thicknesses during construction. This distance is required to accommodate changes in concrete mix and slab thickness in a manner that will reduce the effect on the properties of the finished pavement. A minimum transition length of 36.6 m is recommended between the test sections to provide sufficient production in order to develop consistency after changes in materials, thicknesses, or lane widths.

Section Stationing

The test site shall be surveyed to the extent that the limits of each test section location will be known to an accuracy of 0.305 m. The first test section occurring in the direction of traffic at a site will have the project station 0+00 at the beginning of the monitoring section. Subsequent test sections will have a test section station 0+00 at the beginning of each monitoring section. Site and individual test section beginning stations will be located 3.05 m before the first joint of the monitoring section. The ending stations will be 3.05 m beyond the last joint in the monitoring section.

Deviations from Guidelines

An agency that wants to participate in the SPS-2 experiment, but finds it necessary to deviate from some of the guidelines described in the report, should review these deviations with the LTPP Regional Office or LTPP Division. These authorities will assess the implications of these deviations on the study objectives. If the implications of the noncompliance appear minimal, the deviations will be accepted; otherwise, LTPP will suggest alternatives for consideration by the participating agency.

 

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