Handbook for Pavement Design, Construction and Management Pavement Types

2. PAVEMENT TYPES

IntroductionA roadway pavement is broadly defined as any hard-surfaced path upon which vehicles can travel from one place to another. Although the term “pavement” is sometimes taken to mean only the surface of the roadway, it is more commonly understood as being the set of structural layers—surface, base, and subbase courses—placed on a subgrade to support traffic loads and distribute those loads to the roadbed (Christopher et al. 2006). Figure 2-1 presents a typical pavement cross-section, including the key structural components and the underlying foundation.

Surface CourseBase Course

Subbase Course

Compacted/Natural Subgrade

Embankment/Natural Soil

Figure 2-1. Basic components of a typical pavement system.

The subgrade is the top surface of a roadbed upon which the pavement structure (and shoulders, typically) is constructed (Christopher et al. 2006). The purpose of the subgrade is to provide a platform for construction of the pavement structure and to support traffic loads without undue deflection that would impact the structure’s performance. For pavements constructed on-grade or in cuts, the subgrade is typically the natural soil at the site; although select borrow material may be brought in for poor soils or in particularly problematic areas. The upper layer of this natural soil may be compacted and/or stabilized (usually to a depth of 6 to 12 in.) to increase its strength, stiffness, and/or stability. For pavements constructed on embankment fills, the subgrade is typically a compacted borrow material.

The subbase course is a layer (or layers) of specified or select material placed on the subgrade to support the base course or to provide other functions (Christopher et al. 2006). The subbase is granular in nature and is usually of somewhat lower quality than the base course above it. In some cases, the subbase may be treated with portland cement, asphalt, lime, fly ash, or combinations of these admixtures to increase its strength and stiffness, and reduce moisture susceptibility. A subbase course is typically included when the subgrade soils are of very poor quality.

In addition to contributing to the structural capacity of the pavement systems, subbase layers have additional secondary functions (Christopher et al. 2006). These include preventing the intrusion of fine-grained subgrade soils into the base course, providing additional pavement thickness to combat frost-heave effects of susceptible subgrades, increasing the distance above a

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groundwater table, providing drainage for free water that may enter the pavement system, and providing a working platform for construction operations in cases where the subgrade soil is very weak and cannot provide the necessary support.

The base course is a layer (or layers) of specified or select material placed on a subbase or subgrade (when a subbase is not used) to provide a uniform and stable support for the surface course (Christopher et al. 2006). The base layer also serves the same secondary functions as the subbase, including a gradation requirement that retards subgrade migration into the base layer in the absence of a subbase layer.

Depending on the pavement structure type, the base course can provide a significant portion of the overall structural capacity or it can significantly improve the foundation stiffness (Christopher et al. 2006). Base course usually consists of high-quality aggregates, such as crushed stone, crushed slag, gravel and sand, or combinations of these materials. These higher quality aggregates are typically placed and compacted unbound, but are sometimes treated with stabilizing admixtures, such as portland cement, asphalt, lime, or fly ash, to increase the strength and stiffness and thus provide improved pavement performance. However, for concrete pavements, base layers that provide uniform support and are erosion-resistant are more important to performance than increasing the stiffness of a stabilized base (ARA 2004). High stiffness stabilized bases can results in higher curling stresses, which may lead to premature cracking. They may also cause reflection cracking in asphalt surfaced roadways. Curling stresses can be minimized by placing base materials that will yield during concrete slab expansion and contraction (Siddique, Hossain, and Devore 2004).

The surface course is comprised of one or more layers designed to accommodate the traffic load (Christopher et al. 2006). The surface course may consist of asphalt bound materials (e.g., hot mix asphalt [HMA], warm mix asphalt [WMA], open-graded friction course), portland cement concrete (PCC or concrete), bituminous or asphalt surface treatments (BST or AST), or, in the case of some low-volume roads, aggregate materials. In addition to providing a portion of the overall structural capacity of the pavement depending on the thickness of the surface course, the surface layer minimizes the infiltration of surface water, provides a smooth, uniform, and skid-resistant riding surface, and offers durability against traffic abrasion and climatic forces.

Depending on the specific type of pavement, other components of the pavement structure include drainage elements, geosynthetic paving materials, and embedded steel. Drainage elements may be in a variety of forms (e.g., drainable layers for surface and/or subsurface moisture, open-graded aggregate, transverse drain pipes, longitudinal edge drain collector systems) and are intended to quickly remove infiltrated water from the pavement structure. Geosynthetic materials may be used to retard or control reflection cracking, to provide separation between layers to prevent migration of fines into the base, or to provide additional structure or load-carrying capacity over soft subgrade soils. Embedded steel in concrete pavements may include dowel bars and tie bars. Smooth dowel bars are provided at transverse joints to provide load transfer at otherwise weakened points in the slab. Deformed tie bars are provided across longitudinal joints to hold adjacent slabs together and keep them in vertical alignment. Similarly, distributed steel reinforcement is provided in some jointed concrete pavements to keep any cracks held tightly together and to keep them from breaking down under traffic loadings. In

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continuously reinforced concrete pavement (CRCP) structures, longitudinal reinforcing steel is designed to create a pattern of closely spaced transverse cracks that can be effectively held together by the deformed bars.

Pavement TypesPavements can be categorized in many ways. The most common way of categorizing pavements is through a combination of structural type (i.e., rigidity or flexibility of the structure and how it behaves structurally when exposed to loading) and basic material type (i.e., basic type of paving materials that include asphalt, concrete, and/or aggregate, used to give structure to the pavement). Descriptions and illustrations of the four main pavement types given by this form of categorization are provided below, along with their basic functionality and application/use.

Asphalt Pavement—An asphalt pavement structure is one that maintains intimate contact with and distributes loads to the subgrade, and depends on aggregate interlock, particle friction, and cohesion for stability (Christopher et al. 2006). As illustrated in Figure 2-2, this type of pavement is surfaced with asphalt and is supported by stabilized and/or unstabilized base and subbase layers. The asphalt layer may include a variety of mixtures (e.g., hot mix asphalt, warm mix asphalt or surface treatment). The pavement structure undergoes more concentrated stresses under applied traffic loadings, causing it to “bend” or “deflect.”

Base Course

Subgrade

Asphalt

Figure 2-2. Asphalt pavement structure and load distribution.

Asphalt pavements comprise about 82 percent of U.S. paved roads (FHWA 2008a). They are used in a wide array of applications, from low-volume county roads and city streets to high-volume interstates and freeways.

Concrete Pavement—A concrete pavement structure is one that distributes loads to the subgrade through a concrete slab having relatively high-bending resistance (Christopher et al. 2006). As Figure 2-3 shows, the stiffness of the slab creates a wider distribution of

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stresses from applied traffic loadings to the underlying subgrade. The concrete layer may consist of various cement types, such as portland cement and hydraulic cement.

Base Course

Subgrade

Concrete

Figure 2-3. Concrete pavement structure and load distribution.

Concrete pavements comprise about 6 percent of U.S. paved roads (FHWA 2008a). They are also used in a variety of applications, but are commonly considered for use on high-volume roadways with heavy loads.

Composite Pavement—A composite pavement structure is one that combines the elements of both asphalt and concrete pavement systems and acts as one composite material (Christopher et al. 2006; Flintsch et al. 2008). While most composite pavements consist of an HMA surface placed over a concrete layer (either a new base or an existing concrete pavement surface) (see Figure 2-4), they may also consist of a concrete surface placed on an HMA layer (either a new base or an existing HMA pavement surface). The former structure takes advantage of the strong support provided by the rigid base and the latter structure benefits from a stronger, less erodible bound base (compared to an unbound base).

Asphalt Surface Course

Concrete Base Course (or existing layer)

Base (and subbase) Course

Embankment/Natural Soil

Asphalt Base Course (or existing layer)

Concrete Surface Course

Base (and subbase) Course

Embankment/Natural Soil

a. Asphalt over concrete b. Concrete over asphalt

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Figure 2-4. Composite pavements.

Composite pavements comprise approximately 12 percent of U.S. paved roads (FHWA 2008a), which includes HMA overlays of new and existing concrete pavements. Like asphalt and concrete pavements, they are used in a variety of applications, including low-volume city roads and streets and high-volume interstates and freeways.

Aggregate Surfaced: Aggregate surfaced roadways are used for low volume roadways, frequently with access to agricultural properties. They are not a major component of state agency systems.

Each of the four main pavement types (asphalt, concrete, composite, and aggregate-surfaced) is discussed in the sections below. Further breakdowns of each type, in terms of structural design (i.e., arrangement and degree of use of paving materials and other structural elements in the pavement system) are presented, along with other defining aspects, such as:

Surface Material Type: Specific type of paving material used at the surface of the pavement.

Construction Type: New construction, reconstruction, rehabilitation, or some forms of preservation.

Drainage Design: Type and degree of drainable features (subsurface and/or surface) included in the pavement system.

Design Longevity: Conventional or long-life (perpetual) design philosophy.

Asphalt Pavement

Asphalt pavements consist of an asphalt-bound surface course placed over a stabilized and/or unstabilized base and subbase layers. Drainage layers may also be provided to remove water quickly from the pavement structure and, in some cases, various geosynthetic materials (e.g., fabrics, geogrids) may be installed to prevent or delay the onset of reflection cracks in the surface, to provide separation, or to provide additional structural support over soft soils.

The asphalt-bound surface course in an asphalt pavement typically consists of a wearing course and a binder (or intermediate) course (Christopher et al. 2006). The wearing course is the topmost layer and normally contains the highest quality materials. Its primary objectives include waterproofing the pavement system and providing a smooth, quiet, rut-resistant, and skid-resistant surface for vehicular traffic. The wearing course usually consists of a dense-graded HMA, but it may also consist of an open-graded HMA (e.g., open-graded friction course [OGFC] or permeable friction course [PFC]), a gap-graded HMA (e.g., stone matrix asphalt [SMA] or thin bonded wearing surface), or a surface treatment (e.g., chip seal, slurry seal, microsurfacing).

Wearing courses are usually accompanied by a binder course. The purpose of the binder course is to distribute traffic loads so that stresses transmitted to the pavement foundation do not result in permanent deformation (i.e., rutting) of that layer (NAPA 2001). The binder course also facilitates the construction of the wearing course, helping ensure adequate compaction and

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smoothness of the wearing course. Binder courses may have a coarser aggregate gradation and lower liquid asphalt contents than wearing courses for economic and durability reasons.

The base and subbase courses in an asphalt pavement can consist of various types and qualities of aggregate, with or without treatment by different stabilizing admixtures, including cement, lime and/or flyash. Reclamation of existing flexible pavement may also provide the base. While the materials used in these layers are less stiff than the surface course materials, they are still important to pavement strength and provide protection from the damaging effects of moisture and frost. A separator layer of geotextile may be used to reduce fines migration into the base layer. They help define the seven most common asphalt pavement structural designs listed below and illustrated in Figure 2-5 (ARA 2004).

Conventional Asphalt. Long-Life Asphalt. Semi-Rigid. Porous Asphalt. Deep-Strength Asphalt. Full-Depth Asphalt. Surface-Treated.

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Conventional

Asphalt

Unbound Base

Unbound Subbase

Compacted Subgrade

Natural Subgrade

Deep-Strength

Asphalt

Unbound Base

Compacted Subgrade

Natural Subgrade

Long-LifeRut-Resistant Asphalt

Fatigue and Rut Resistance Asphalt

Fatigue Resistant Asphalt

Pavement Foundation

Full-DepthAsphalt

Asphalt Binder

Asphalt Base

Compacted Subgrade

Natural Subgrade

Semi-Rigid

Asphalt

Asphalt or Cement Treated Base

Unbound Subbase

Compacted Subgrade

Natural Subgrade

Figure 2-5. Common asphalt pavement structural designs (modified from ARA 2004) Used by permission ARA and AASHTO.

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Surface-TreatedSurface Treatment

Unbound Subbase

Natural Subgrade

Porous Asphalt

Crushed Stone

Recharge Bed

Uncompacted Subgrade

Non-Woven Geotextile

Porous

Figure 2-5. Common asphalt pavement structural designs (modified from ARA 2004) Used by permission ARA and AASHTO (continued).

Three other important components in an asphalt pavement structure are leveling courses, prime coats, and tack coats. A leveling course is a thin layer of HMA used in rehabilitation (prior to the placement of other layers, such as an HMA overlay) to correct minor variations in the longitudinal and transverse profile of the pavement (NAPA 2001). Prime coats and tack coats are thin liquid asphalt coatings that are applied to a surface (prime coat for an aggregate layer, tack coat for a stabilized layer) immediately before an HMA layer is placed, in order to promote bonding of the two layers. Layer bonding improves the layers’ response to loading by acting in unison.

Conventional Asphalt

Conventional asphalt pavements consist of an HMA surface course placed on a higher-quality dense-graded aggregate base and somewhat lower-quality dense-graded aggregate subbase (see Figure 2-5). In some instances, a surface treatment may be used for the wearing course. The thicknesses of the layers vary; depending on truck traffic volume, subgrade strength, climate, and how many times the pavement has been resurfaced (or received a preservation treatment). Typical thickness ranges for newly constructed or reconstructed pavements are 3 to 5 in. for the HMA surface, 6 to 12 in. for the base, and 8 to 16 in. for the subbase.

Conventional asphalt pavements are the most common type of asphalt pavement. They are used by all state highway agencies for mostly low- to moderate-volume roadways. The design service life of original conventional asphalt pavements is usually between 10 and 20 years. In some cases, they may include an open-graded aggregate base that either drains into an edge drain system or is daylighted to the roadside ditch.

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Deep-StrengthDeep-strength asphalt pavements consist of a thickened asphalt section over a granular base (see Figure 2-5). This type of pavement, as originally designed and constructed, includes the HMA surface course (typically, 2 in. or greater), an HMA base course (typically 4 in. or greater) placed in one or more lifts, and a high-quality aggregate base (typically, 6 to 12 in.).

Because of their added structure, deep-strength asphalt pavements are commonly used by highway agencies for moderate- to high-volume roads. While a surface treatment may be used for the wearing course, the higher traffic levels generally favor an HMA wearing course. The design service life of this type of pavement is typically 15 to 25 years, slightly longer than a conventional asphalt pavement, so as to minimize traffic disruptions due to future rehabilitation treatments.

Long-Life Asphalt PavementLong-life asphalt pavements often “are asphalt pavements that are designed and built to last longer than 50 years, without requiring major structural rehabilitation or reconstruction, and needing only periodic surface renewal in response to distresses confined to the top of the pavement (Newcomb et al. 2010).” Long-life asphalt pavements incorporate multiple layers of HMA material that are specially arranged so as to minimize bottom-up fatigue cracking and HMA and subgrade rutting, thereby producing a long-lasting road with only periodic renewal of the surface course. The term perpetual pavement has been used for these structures.

The concept of a long-life asphalt pavement is derived from the historical performance of many well-built, thick asphalt pavements that were categorized as either full-depth or deep-strength pavements that had been in service for decades with only minor periodic surface rehabilitation to remove defects and improve ride quality (Newcomb et al. 2010). The long-life pavement section consists of:

A renewable rut-resistant HMA surface layer. The surface layer is designed to not only resist rutting, but to also resist top-down cracking. Mix type selection of the surface layer is typically dependent on local experience and often includes either a stone mastic asphalt (SMA), an open-graded friction coarse (OGFC), or a dense-graded HMA layer. Typical thickness ranges from 1.0 to 3 in.

A fatigue and rut-resistant intermediate HMA layer that provides additional structural support. The intermediate layer must provide the pavement structure with both stability and durability, which can often be obtained using an aggregate structure that provides stone-on-stone contact and an asphalt binder that will resist rutting (i.e., a higher-temperature performance grade binder). Typical thickness of intermediate layer ranges from 4 to 7 in.

A HMA base layer that resists tensile strain due to traffic loadings (i.e., fatigue or bottom up cracking). The fatigue resistant base layer is obtained by increasing the layer thickness, increasing the asphalt content, or a combination of both to reduce the tensile strain at the bottom of the layer, typically to levels between 75 and 200 microstrains (Prowell et al. 2010). Typical thickness of base layer ranges from 3 to 4 in.

In addition, in order to resist rutting in the underlying unbound layers, the pavement foundation should provide support for the anticipated traffic loads and not be susceptible to volume changes

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(i.e., expansive soils) or freeze-thaw cycles (Newcomb et al. 2010). The pavement foundation may consist of compacted subgrade, chemically stabilized subgrade, stabilized granular material, and/or unstabilized granular material. A number of studies suggest a minimum subgrade CBR value of 5 percent, or a resilient modulus (MR) of roughly 7,500 psi for adequate foundation support (FMT 1989; LCPC 1992; Nunn et al. 1997a).

Studies conducted by Nunn (1997b), Mahoney (2001), and Newcomb (2002) have indicated that a minimum total HMA thickness of 6 to 8 in. for typical traffic loadings is recommended to reduce the potential for fatigue cracking originating at the bottom of the HMA layer.

As with any pavement structure, attention to construction techniques and practices is critical to achieving the maximum potential service from a long-life asphalt pavement. Specifically, this includes (Newcomb et al. 2010):

Obtaining adequate density to minimize cracking of the lower HMA layers and rutting in the upper HMA layers.

Minimizing moisture infiltration by eliminating the potential for aggregate segregation during production and temperature differentials during mix transport and paving (Willoughby et al. 2002).

Obtaining adequate density at longitudinal joints to minimize water infiltration. Obtaining adequate bond between each HMA lift. Maintaining quality control during mixture production and placement.

Semi-RigidSemi-rigid flexible pavements consist of an HMA surface course placed on an asphalt- or cement-treated base (ATB or CTB) (in some cases, a lime-fly ash-treated base), and a dense-graded aggregate subbase (see Figure 2-5). In some cases, a surface treatment may be used as the wearing course. The treated base provides increased strength/stiffness and durability, thereby improving pavement performance. Typical layer thicknesses for newly constructed or reconstructed semi-rigid flexible pavements are similar to those of conventional pavements, except that the base course is typically between 4 and 8 in. thick.

Although semi-rigid flexible pavements can be designed for low- to high-volume roadways, they are most prominent on moderate-volume roads. The design life of original semi-rigid flexible pavements is usually between 10 and 20 years, and some designs may incorporate subsurface drainage in the form of an asphalt- or cement-treated permeable base (ATPB or CTPB) connected to an edge drain system or daylighted to the roadside ditch.

Full-Depth AsphaltFull-depth asphalt pavements also consist of a thickened asphalt section. However, unlike deep-strength asphalt, HMA mixtures are employed for all courses above the compacted or improved subgrade (occasionally, granular material may be placed on the subgrade for construction purposes) (see Figure 2-5). The total thickness of the asphalt-bound layers is typically 6 in. or more.

The applications for full-depth asphalt pavement vary significantly, from low-volume local roads and streets to high-volume interstates and freeways. Correspondingly, the design service life of

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this pavement type can also vary significantly (10 to 25 years). The use of a surface treatment for the wearing course generally depends on the traffic loadings.

Surface-TreatedSurface-treated pavements are thin asphalt pavements consisting of one or more BST layers placed on a granular base (see Figure 2-5). Depending on whether the structure is new or has received subsequent BST, the total thickness of the asphalt-bound surface layer may range from 0.5 in. to as much as 3 in. or more. The granular base is generally of low to medium quality and often ranges between 4 and12 in. thick. Surface-treated pavements are used extensively on low-volume roads and streets.

Porous AsphaltPorous asphalt pavements are specially designed asphalt pavements that use porous HMA mixes to laterally or vertically drain storm water runoff (Iowa LTAP 2007). Porous HMA mixes have traditionally been used as surface courses on new asphalt pavement structures or as part of HMA overlays placed on existing pavements. Often referred to as open-graded surface or friction courses (OGSC or OGFC) and PFC, these surfaces are designed to facilitate storm water runoff and prevent the development of water films that decrease friction and increase splash/spray and hydroplaning potential. The high air voids of this mix also help to reduce pavement-tire noise. These noise reductions may not extend for the full service life, especially in areas where studded tires are used.

Porous HMA mixes have more recently been incorporated into full drainable pavement systems that substantially reduce runoff and promote natural infiltration of water into the soil. In this system, a somewhat thicker (2 to 4 in.) porous HMA layer is placed on top of a thin (1 to 2 in.) choke stone layer (0.5-in. chips) and thick (typically ≥10 to 12 in.) aggregate recharge bed/reservoir course (1.5 to 2-in. stone), lined with a geotextile filter fabric. The porous HMA layer could consist of an OGSC/OGFC/PFC layer and an ATPB layer containing even higher voids. Storm water flows through the porous HMA surface into the aggregate recharge bed where it is stored and allowed to infiltrate into the soil between rainfalls (FPO 2008).

Concrete Pavement

Concrete pavements generally consist of concrete slabs constructed on either a granular or treated base layer and a prepared subgrade, as depicted in Figure 2-6 (Christopher et al. 2006). The inclusion of a base layer provides a number of benefits, including the prevention of pumping of fine-grained soils at joints, cracks, and slab edges, the provision of additional load-carrying capacity, the provision of lateral drainage, the reduction of potential frost-heave effects, and the provision of a construction platform for the concrete slab.

The surface course in a concrete pavement is the concrete slab. In addition to providing the majority of strength to withstand traffic loadings, it must provide key functional characteristics (e.g., smoothness, friction, noise control) and serve as a waterproofing layer for the underlying system. Depending on the structural design, the concrete surface may require transverse joints located at specific intervals along the length of the roadway, and different types of embedded steel (at joints).

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Figure 2-6. Typical concrete pavement cross-section (modified from ARA 2004) Used by permission ARA and AASHTO.

A key component in all concrete pavements is joints. Joints are linear discontinuities formed into the concrete surface to serve various purposes. The types of joints and their purposes are summarized as follows (AASHTO 1993; ACPA 2010):

Contraction Joints—Sawed, formed, or tooled grooves that create a weakened vertical plane, thereby controlling the location of cracking caused by dimensional changes in the slab (see Figure 2-7a). Contraction joints are the most common joint type. They are installed both transversely (generally at regular, fixed intervals) and longitudinally (typically at 12 ft intervals to correspond with lane widths).

Construction Joints—Full-depth joints formed between slabs that are placed at different times (see Figure 2-7b). Construction joints can be longitudinal (between adjacent lanes or a lane and shoulder) or transverse (separation between the end of one day’s paving and the start of the next day’s paving) orientation.

Isolation Joints—Full-depth joints formed to separate the pavement from structures or objects (e.g., drainage features, bridges, sidewalks, curb) so to allow for the independent movement between the pavement and structure or object (see Figure 2-7c).

Concrete pavements can be divided into the following major categories: Jointed Plain Concrete. Jointed Reinforced Concrete. Continuously Reinforced Concrete. Prestressed Concrete. Long-Life Concrete. Pervious Concrete. Precast Concrete. Roller Compacted Concrete. Two-lift Concrete.

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Concrete Slab

Base Course

Compacted Subgrade

Natural Subgrade

Bedrock

Handbook for Pavement Design, Construction and Management Pavement Types

a. Contraction joints.

b. Construction joints.

c. Isolation joints.

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Figure 2-7. Concrete pavement joints (© ACPA 2010).

Brief descriptions of these concrete pavement designs are provided in the sections below.

Jointed Plain Concrete PavementsJointed plain concrete pavements (JPCP) are by far the most common concrete pavement type being constructed today (Hoerner et al. 2001). As illustrated in Figure 2-8, these pavements consist of nonreinforced concrete slabs that are typically 12 to 14 ft wide and 15 ft long (i.e., transverse joints spaced at regular intervals of 15 ft). Slab thickness typically ranges from 6 to 8 in. for low-volume roads to 10 to 13 in. for high-volume, heavily loaded routes. Transverse joints are typically sawed into JPCP to create a weakened plane to control the crack location within the slab. The contraction joints may either be left undoweled such that load transfer is provided solely through aggregate interlock or they may be fitted with a series of dowel bars (typically, 1 to 1.5 in. diameter and spaced at 12-in. intervals) to provide positive load transfer from one slab to the next. Undoweled JPCP pavements are usually most appropriate on low-volume roads, whereas doweled JPCP pavements are recommended for use on moderate- to high-volume roads. Typically no dowels are used when thickness is less than 8 in. Slabs in adjacent lanes or shoulders are normally tied together across longitudinal joints using tie bars. However, to minimize the potential of longitudinal cracking, industry guidance suggests that no more than 48 ft of concrete pavement width be tied together (ACPA 1997).

3.7 to 6.1 m (typ.)(12 to 20 ft)

Transverse Joints(with or without dowels)

Longitudinal Joint (with tiebars)

3.7 to 6.1 m (typ.)(12 to 20 ft)

3.7 to 6.1 m (typ.)(12 to 20 ft)

Transverse Joints(with or without dowels)

Longitudinal Joint (with tiebars)

3.7 to 6.1 m (typ.)(12 to 20 ft)12 to 20 ft (typ.) 12 to 20 ft (typ.)

Figure 2-8. Schematic of a JPCP pavement design (Hoerner et al. 2001).

Jointed Reinforced Concrete Pavements

Jointed reinforced concrete pavements (JRCP) were commonly constructed in the 1960s and 1970s (mostly in the midwestern states), but are no longer constructed due to long-term performance problems (Hoerner et al. 2001; ARA 2004). As Figure 2-9 illustrates, JRCP pavements employ both steel reinforcement (smooth or deformed welded wire fabric or deformed steel bars) and contraction joints to control slab cracking. Slab thickness typically ranged from 7 to 10 in. Steel reinforcement contents in JRCP are lower than in CRCP, typically

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around 0.2 to 0.3 percent of the cross-sectional area. Also, contraction joint spacings in JRCP are longer than those in JPCP, typically between 30 and 40 ft. Dowel bars are typically used at the transverse joints to assist in load transfer.

7.6 to 18.3 m (typ)(25 to 60 ft)

Transverse Joints(with dowels)

Welded WireFabric Reinforcing

Longitudinal Joint (with tiebars)

7.6 to 18.3 m (typ)(25 to 60 ft)

Transverse Joints(with dowels)

Welded WireFabric Reinforcing

Longitudinal Joint (with tiebars)

30 to 40 ft (typ.)

Figure 2-9. Schematic of a JRC pavement design (Hoerner et al. 2001).

Continuously Reinforced Concrete PavementsContinuously reinforced concrete pavements (CRCP) are routinely constructed by six state highway agencies, most notably on high-volume, urban roadways (Hoerner et al. 2001). As shown in Figure 2-, these pavements utilize continuous reinforcing steel bars (typically, #5 or #6 deformed bars) in the longitudinal direction to both induce the formation of closely spaced (3 to 8 ft) transverse cracks and to keep those cracks held tightly together. Although the steel provides some additional stiffness, it is not intended to contribute to the load-carrying capacity of the pavement. The longitudinal reinforcing bars are located near mid-depth to the upper third in the slab and typically constitute 0.6 to 0.8 percent of the cross-sectional area. As with JPCP pavements, tie bars are normally used across longitudinal lane-lane and lane-shoulder joints. Depending on the projected traffic loadings, slab thickness typically ranges between 9 and 14 in.

Longitudinal Joint (with tiebars)

Typical Crack Spacing(0.9 to 2.4 m)

(3 to 8 ft)

Continuous Longitudinal Reinforcement

(Deformed Bars)

Longitudinal Joint (with tiebars)

Typical Crack Spacing(0.9 to 2.4 m)

(3 to 8 ft)

Continuous Longitudinal Reinforcement

(Deformed Bars)

(3 to 8 ft)

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Figure 2-10. Schematic of a CRC pavement design (Hoerner et al. 2001).

Prestressed Concrete PavementsPrestressed concrete pavements (PSCP) are similar to CRCP pavements, except that the longitudinal reinforcement consists of continuous steel strands that are prestressed prior to placing the concrete (or post-tensioned after the concrete has hardened) (Christopher et al. 2006). The initial tensile stress in the reinforcement reduces the tensile stress in the concrete caused by traffic loads and thermal forces, thereby decreasing the required concrete thickness. Prestressed concrete pavements have not seen widespread use in highway pavements.

Long-Life Concrete PavementsA number of state highway agencies (e.g., Illinois, Minnesota, Texas, Washington State) have identified in-service concrete pavements (both JPCP and CRCP) that have exceeded their original design lives. Currently, many states are designing concrete pavements for service lives of 40 or more years (FHWA 2007). Tayabji and Lim (2006) have identified the following characteristics for a long-life concrete pavement:

Service life of 40 or more years. No premature construction or material-related distress. Reduced potential for cracking, faulting, and spalling. Maintain desirable ride and surface texture characteristics with minimal intervention

activities, for ride and texture, joint resealing, and minor repairs (when warranted).

The ability to achieve even longer-life concrete pavements does not require any new technology or materials and can be designed and constructed with currently available practices and procedures (FHWA 2007). The states that have demonstrated long-life concrete pavements have done so through proper design procedures, material selection, and quality construction practices. Procedures and practices for obtaining long-life concrete pavements include:

Materials and mix design – Include high-quality, durable aggregates, combined optimized aggregate gradation, hydraulic cement plus pozzolans or slag cement for durability, minimum cementitious content (e.g. 500 lb/yd3), effective air-void system for environment, and a maximum water-cementitious material ratio (w-c) of 0.45.

Structural design – Design a sufficient slab thickness to carry anticipated loading over the entire design period. Based on a summary of international and state highway practices, typical slab thickness for long-life concrete pavements range from 8 to 13 in. (Tayabji and Lim 2007; Hall et al. 2007) and for lower volume roads, a minimum thickness of 5 in. is recommended (ACPA 2006). For moderate to heavy truck traffic, in excess of 650 trucks per day in the design lane, the use of a lean concrete base (LCB), cement-treated base (CTB), or asphalt-treated base (ATB) should also be included.

Joint design – Using a short joint spacing of 15 ft or less has been shown to work well for most highway type pavements, although this does depend on slab thickness (e.g., thinner slabs may need to have shorter joint spacing). If joints are sealed, use a high quality sealant that will result in longer resealing cycles. When dowel bars are required (typically for slabs greater than 8 in.), use corrosion resistant dowel bars.

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Edge treatments – Construct a widened lane (slab paved 1 to 3 ft wider yet striped at 12-ft) to reduce critical edge and corner stresses and deflections. Incorporating a tied concrete shoulder is another method of reducing edge stresses and deflections while also reducing moisture infiltration at the lane-shoulder joint and also serving as an emergency or future traffic lane. The benefits of edge stress reduction is also obtained with tied concrete curb and gutter, typical of urban applications. Many agencies construct asphalt shoulders on concrete pavements. To reduction of edge stresses and deflections is realized.

Construction practices – Ensure uniform production, delivery, placement, and consolidation of the concrete mixture. Ensure embedded steel, if included, is effectively placed (properly aligned and adequately consolidated). Provide effective finishing, texturing, and curing that include minimal handwork. Conduct finishing and texturing that provides durable, low-noise surface texture characteristics. Provide timely and adequate curing and joint sawing. Strive to achieve high levels of initial surface smoothness.

Maintenance treatments – Over the life of the pavement provide timely maintenance treatments (as needed); this may include joint resealing, surface texturing to maintain rideability and frictional characteristics, and localized repairs.

Pervious Concrete PavementsPervious concrete pavements are open or closed pavement systems, whereby high-porosity (15 to 20 percent) concrete is used as a permeable surface layer that promotes the drainage of water into the underlying soil (open system) or into underlying storm pipes (closed system) for roadside discharge (Delatte et al. 2007) (see Figure 2-6). The concrete material contains the same material components as conventional concrete (i.e., cementitious binder, aggregate, water, and chemical admixtures), but through specific mixture proportioning maintains high porosity for water percolation (Schaefer et al. 2010). Currently, pervious concrete is primarily used in parking lots, shoulders, and facility access roads. However, investigations into its use on low-volume roads, streets, and main-line shoulders are on-going.

Pervious Concrete

Crushed Stone (optional)

Subgrade

Figure 2-6. Pervious concrete pavement cross-section.

Precast Concrete Systems

Precast concrete systems are a form of modular pavement technology, whereby pavement slabs are fabricated offsite, transported to the project site, and installed on a prepared foundation (FHWA 2008b; FHWA 2009). The precast slabs can be installed as intermittent panel replacements for existing damaged slabs or in a continuous application as part of a new

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construction project or long-length/large-area rehabilitation of badly deteriorated pavement (see Figure 2-7). The precast slabs come in the form of both conventional jointed systems and prestressed panels (fewer active joints) that are fitted with dowels and slots for panel connections and load transfer functionality.

Figure 2-7. Continuous application of precast concrete slabs (Buch 2007)

Two-Lift ConcreteBecause of diminishing sources of quality aggregate, and driven by increased knowledge in material use and behavior, advancements in construction equipment, and increased demands for pavement surfaces that are durable, safe, and result in lower tire-pavement noise characteristics, the use of two-lift concrete paving has gained increased use both nationally and internationally (Cable 2004). Two-lift concrete is an engineered system in which a thin (generally 3 in.) surface layer constructed with durable, higher quality aggregates is placed over a thicker (generally 9 in.) bottom layer constructed with locally available aggregates. The result is then a surface with strong durability and that exhibits improved friction and reduced noise characteristics, while the bottom layer possesses sufficient strength to meet fatigue design requirements. To produce monolithic behavior, the two layers are placed within a relatively short time period of each other, generally within 60 minutes, when the concrete of the two layers is still considered to be wet (also referred to as wet on wet).

There are a number of benefits to two-lift concrete pavements (Cable 2004):

Economically viable where the availability of high-quality aggregate is limited.

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Renewable surface layer. Wear resistant, durable, surface layer that can address noise and friction requirements.

Additional information on two-lift concrete can be found at the National Concrete Pavement Technology Center.

Roller Compacted ConcreteRoller compacted concrete (RCC) is a stiff, zero-slump concrete mixture that is placed with conventional or high-density asphalt paving equipment and then compacted with vibratory rollers. Its low water-cement ratio results in a drier mix than conventional concrete; a mix that can be placed quickly without forms, dowels, steel reinforcement, and finishing, and one that is capable of generating higher strengths than conventional concrete. The surface qualities of RCC, such as smoothness, surface texture and uniformity, and aesthetics, are lower than conventional concrete.

RCC was originally used in the construction of pavements for container ports and commercial facilities, but more recently has been used for base layers and shoulders. In addition, RCC is being used in new construction or mill-and-inlay for local roads and streets, and for fast-track construction for high-volume intersections.

Composite Pavements

HMA over concrete composite pavements take one of two forms—an HMA overlay placed on an existing concrete pavement or a newly constructed pavement consisting of an HMA surface placed on a concrete base (Flintsch et al., 2008). Each is described separately below.

Overlay Composite—although thin (1 to 1.5 in.) HMA overlays (and various asphalt surface treatments) have been placed on existing concrete, typically the HMA overlay is between 2 and 5 in. thick (thicker surfaces are possible with accumulated overlays). Dense-, open-, and gap-graded HMA mixtures are used to satisfy the structural and functional requirements.

All types of concrete pavement (JPCP, JRCP, and CRCP) can be overlaid with HMA mixtures. Overlay performance on jointed concrete pavements is generally governed by reflection cracking from underlying joints and cracks, whereas performance on CRCP is usually governed by the underlying CRCP support conditions. To combat reflection cracking, stress-absorbing interlayers or overlay reinforcement materials (e.g., paving fabrics, geogrids) are often installed with the overlay. Alternatively, the overlay may be saw cut at the known location of joints. Where drainage in the existing pavement is an issue, a longitudinal edge drain system is typically installed with the overlay. Pumping of the existing jointed concrete must be mitigated prior to placing a flexible overlay.

New Composite—historically, the placement of a new HMA or concrete layer over a new concrete pavement has been relatively rare. However, as part of SHRP 2 R21 Composite Pavement Systems, the design and construction of new composite pavements is being investigated. Specifically, this project is investigating two composite pavement systems an asphalt layer(s) over a concrete layer and a concrete surface over a concrete layer (wet on wet). The objective of the SHRP 2 R21 project is to determine the critical material and performance parameters, develop construction specifications and techniques, and develop and validate pavement performance models consistent with the MEPDG.

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Additionally, concrete overlays of asphalt are another major form of composite pavement. Bonded thin concrete overlays of existing flexible pavement may consist of 4 to 6 or more inches of concrete with joints cut at 4-6 feet both longitudinally and transversely.

Aggregate-Surfaced Roads

Aggregate-surfaced roads are typically designed and constructed to a depth of between 5 and 12 in., depending primarily on the projected traffic and subgrade characteristics. In weak soil situations, stabilization of the soil or use of a geosynthetic fabric can be done to reduce the granular layer thickness.

A variety of aggregates are available for use in aggregate-surfaced pavements, including gravels, crushed gravels, crushed stone, and asphalt cold millings (i.e., reclaimed asphalt pavement [RAP]). Requirements for these materials vary, but generally virgin aggregates are recommended to consist of a blend of well graded coarse aggregate (0.25 to 2 in. size), sand, and fine-grained soils. The blending allows material compaction to form a hard, durable surface crust to carry the load and minimize water infiltration.

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ReferencesAmerican Association of State Highway and Transportation Officials (AASHTO). 1993. AASHTO Guide for Design of Pavement Structures. American Association of State Highway and Transportation Officials, Washington, D.C.

American Concrete Pavement Association (ACPA). 2006. Design of Concrete Pavement for Streets and Roads. IS184.03P. American Concrete Pavement Association, Skokie, IL.

American Concrete Pavement Association (ACPA). 1997. Concrete Intersections, A Guide for Design and Construction. TB019P. American Concrete Pavement Association, Skokie, IL.

American Concrete Pavement Association. 2010. Joints. Available online at: http://www.pavement.com/Concrete_Pavement/Technical/Fundamentals/Joints.asp.

Applied Research Associates, Inc. (ARA). 2004. Guide for Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures. American Association of State Highway and Transportation Officials (AASHTO), Washington, DC. Used by permission ARA and AASHTO. Available online at: http://onlinepubs.trb.org/onlinepubs/archive/mepdg/guide.htm.

Buch, N. 2007. Precast Concrete Panel Systems for Full-Depth Pavement Repairs: Field Trials. FHWA-HIF-07-019. Federal Highway Administration, Washington DC. Available online at: http://www.fhwa.dot.gov/pavement/concrete/pubs/hif07019/07019.pdf.

Christopher, B. R., C. Schwartz, and R. Boudreau. 2006. Geotechnical Aspects of Pavements. Reference Manual for National Highway Institute (NHI) Course No. 132040. Federal Highway Administration, Washington, DC. Available online at: www.fhwa.dot.gov/engineering/geotech/pubs/05037.

Delatte, N., D. Miller, and A. Mrkajic. 2007. Portland Cement Pervious Concrete Pavement: Field Performance Investigation on Parking Lot and Roadway Pavements, Final Report. Ready Mixed Concrete (RMC) Research and Education Foundation, Silver Springs, MD. Available online at: www.rmc-foundation.org/images/Long%20Term%20Field%20Performance %20of%20Pervious%20Final%20Report.pdf.

Federal Highway Administration (FHWA). 2007. Long-Life Concrete Pavements: Best Practices and Directions from the States. FHWA-HIF-07-030. Federal Highway Administration, Washington DC. Available online at: http://www.fhwa.dot.gov/pavement/ concrete/pubs/07030/07030.pdf.

Federal Highway Administration (FHWA). 2008a. Highway Statistics 2008. Federal Highway Administration, Washington DC. Available online at www.fhwa.dot.gov/policyinformation /statistics/2008.

Federal Highway Administration (FHWA). 2008b. Precast Concrete Panels for Repair and Rehabilitation of Jointed Concrete Pavements. FHWA-IF-09-003. Federal Highway Administration, Washington DC. Available online at http://www.fhwa.dot.gov/pavement/ concrete/pubs/if09003/if09003.pdf.

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Federal Highway Administration (FHWA). 2009. Precast Prestressed Concrete Pavement for Reconstruction and Rehabilitation of Existing Pavements. FHWA-HIF-09-008. Federal Highway Administration, Washington DC.

Federal Ministry of Transportation (FMT). 1989. Guidelines for the Standardization of the Upper Structure of Traffic Bearing Surfaces. RS+O 86. Federal Ministry of Transportation, Bonn, Germany.

Flexible Pavements of Ohio (FPO). 2008. Porous Asphalt Pavement. Technical Bulletin. Flexible Pavements of Ohio, Dublin, OH.

Flintsch, G. W., B. K. Diefenderfer, and O. Nunez. 2008. Composite Pavement Systems: Synthesis of Design and Construction Practices. FHWA/VTRC 09-CR2. Virginia Department of Transportation, Blacksburg, VA. Available online at: http://www.virginiadot.org/vtrc/ main/online_reports/pdf/09-cr2.pdf.

Hall, K., D. Dawood, S. Vanikar, R. Tally, T. Cackler, A. Correa, P. Deem, J. Duit, G. Geary, A. Gisi, A. Hanna, S. Kosmatka, R. Rasmussen, S. Tayabji, and G. Voight. 2007. Long-Life Concrete Pavements in Europe and Canada. FHWA-PL-07-027. Federal Highway Administration, Washington, DC. Available online at: http://www.pavement.com/Downloads/ LLCP.pdf.

Hoerner, T. E., K. D. Smith, H. T. Yu, D. G. Peshkin, and M. J. Wade. 2001. PCC Pavement Evaluation and Rehabilitation. Reference Manual for National Highway Institute (NHI) Course No. 131062. Federal Highway Administration, Washington, DC.

Huang, Y. H. 1993. Pavement Analysis and Design. Prentice-Hall, Inc., Englewood Cliffs, NJ.

Iowa Local Technical Assistance Program (Iowa LTAP). 2007. “Popcorn Ball Pavement: Pervious Concrete and Porous Asphalt.” Technology News. January-February 2007. Iowa State University, Ames, IA. Available online at: http://www.intrans.iastate.edu/ltap/tech_news /2007/jan-feb/pervious_pavement.pdf.

Kannemeyer, L., B. D. Perrie, P. J. Strauss, and L. du Plessis. 2007. Ultra-Thin CRCP: Modelling, Testing under Accelerated Pavement Testing and Field Application for Roads. Council for Scientific and Industrial Research. Available online at: http://researchspace.csir.co.za/dspace/bitstream/10204/1320/1/Kannemeyer_2007.pdf.

Laboratoire Central de Ponts et Chasses and Service D’Etudes Techniques des Route et Antoroutes (LCPC). 1992. Realisation des Remblais et des Couches de Forme. Ministere de l’Equipment du Logement des Transports, Paris, France.

Mahoney, J. P. 2001. “Study of Long-Lasting Pavements in Washington State.” Transportation Research Circular 503: Perpetual Bituminous Pavements. Transportation Research Board, Washington, DC. Available online at: http://onlinepubs.trb.org/onlinepubs/circulars/ circular_503.pdf.

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National Asphalt Pavement Association (NAPA). 2001. HMA Pavement Mix Type Selection Guide. Information Series 128. NAPA (Lanham, MD) and Federal Highway Administration, Washington, DC. Available online at: http://isddc.dot.gov/OLPFiles/FHWA/010117.pdf.

National Asphalt Pavement Association (NAPA). 2008. Porous Asphalt Pavements for Stormwater Management. Information Series 131. National Asphalt Pavement Association, Lanham, MD.

Newcomb, D. E. 2002. APA 101: Perpetual Pavements: A Synthesis. Asphalt Pavement Alliance, Lanham, MD, 2002.

Newcomb, D. E., R. Willis, and D. H. Timm. 2010. Perpetual Asphalt Pavements: A Synthesis. Publication No. IM-40. Asphalt Pavement Alliance, Lanham, MD. Available online at: http://www.asphaltroads.org/documents/Perpetual_Pavement_Synthesis.pdf.

Nunn, M. 1997b. “Long-life Flexible Roads.” Proceedings, 8th International Conference on Asphalt Pavements, Vol. 1. University of Washington, Seattle, WA.

Nunn, M., A. Brown, D. Weston, and J. C. Nicholls. 1997a. Design of Long-Life Roads for Heavy Traffic. Report No. 250. Transportation Research Laboratory, Berkshire, United Kingdom.

Pavementinteractive.org. 2010. HMA Pavement. Pavement Interactive.

Prowell, B. D., E. R. Brown, R. M. Anderson, J. S. Daniel, A. K. Swamy, H. Von Quintus, S. Shen, S. H. Carpenter, S. Bhattacharjee, and S. Maghsoodloo. 2010. Validating the Fatigue Endurance Limit for Hot Mix Asphalt. NCHRP Report 646. Transportation Research Board, Washington, DC. Available online at: http://onlinepubs.trb.org/onlinepubs/nchrp/ nchrp_rpt_646.pdf.

Schaefer, V. R., J. T. Kevern, B. Izevbekhai, K. Wang, H. E. Cutler, and P. Wiegand. 2010. “Construction and Performance of the Pervious Concrete Overlay at MnROAD.” 89th Annual Meeting of the Transportation Research Board. Transportation Research Board, Washington, DC.

Siddique, Z., M. Hossain, and J. J. Devore. 2004. Investigation of the Effect of Curling on As-Constructed Smoothness and Ride Quality of KDOT Portland Cement Concrete (PCC) Pavements. K-TRAN: KSU-01-7. Kansas Department of Transportation, Topeka, KS. Available online at: http://ntl.bts.gov/lib/24000/24600/24688/KSU01-7.pdf.

Steyn, WJvdM, Strauss, P. J., Perrie, B. D., L. du Plessis. 2005. “Roodekrans Trial Sections: The Role of Structural Support under Very Thin Jointed CRC Pavements Subjected to Heavy Traffic.” 8th International Conference on Concrete Pavements. International Society for Concrete Pavements, Colorado Springs, CO. Available online at: http://researchspace.csir.co.za/dspace/bitstream/10204/1413/1/Steyn_2005.pdf.

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Tayabji, S. and S. Lim. 2006. Proceedings, International Conference on Long-Life Concrete Pavements. Chicago, IL, October 25-27, 2006. Federal Highway Administration, Washington DC.

Tayabji, S. and S. Lim. 2007. Long-Life Concrete Pavements: Best Practices and Directions from the States. Concrete Pavement Technology Program TechBrief, FHWA-HIF-07-030. Federal Highway Administration, Washington, DC.

Transportation Association of Canada (TAC). 1997. Pavement Design and Management Guide. Transportation Association of Canada, Ottawa, Canada.

Willoughby, K. A., J. P. Mahoney, L. M. Pierce, J. S. Uhlmeyer, and K. W. Anderson. 2002. “Temperature and Density Differentials in Asphalt Concrete Pavement.” Proceedings, 9th International Conference on Asphalt Pavements. International Society for Asphalt Pavements, Copenhagen, Denmark. CD-ROM.

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