|Major Topics on this Page|
|6.1||Jointed Plain Concrete Pavement|
|6.2||Jointed Reinforced Concrete Pavement|
|6.3||Continuously Reinforced Concrete Pavement|
Almost all rigid pavement is made with PCC, thus this Guide only discusses PCC pavement. Rigid pavements are differentiated into three major categories by their means of crack control:
- Jointed plain concrete pavement (JPCP). This is the most common type of rigid pavement. JPCP controls cracks by dividing the pavement up into individual slabs separated by contraction joints. Slabs are typically one lane wide and between 3.7 m (12 ft.) and 6.1 m (20 ft.) long. JPCP does not use any reinforcing steel but does use dowel bars and tie bars.
- Jointed reinforced concrete pavement (JRCP). As with JPCP, JRCP controls cracks by dividing the pavement up into individual slabs separated by contraction joints. However, these slabs are much longer (as long as 15 m (50 ft.)) than JPCP slabs, so JRCP uses reinforcing steel within each slab to control within-slab cracking. This pavement type is no longer constructed in the U.S. due to some long-term performance problems.
- Continuously reinforced concrete pavement (CRCP). This type of rigid pavement uses reinforcing steel rather than contraction joints for crack control. Cracks typically appear ever 1.1 - 2.4 m (3.5 - 8 ft.) are held tightly together by the underlying reinforcing steel.
Jointed plain concrete pavement (JPCP, see Figure 2.39) uses contraction joints to control cracking and does not use any reinforcing steel. Transverse joint spacing is selected such that temperature and moisture stresses do not produce intermediate cracking between joints. This typically results in a spacing no longer than about 6.1 m (20 ft.). Dowel bars are typically used at transverse joints to assist in load transfer. Tie bars are typically used at longitudinal joints.
|Crack Control:||Contraction joints, both transverse and longitudinal|
|Joint Spacing:||Typically between 3.7 m (12 ft.) and 6.1 m (20 ft.). Due to the nature of concrete, slabs longer than about 6.1 m (20 ft.) will usually crack in the middle. Depending upon environment and materials slabs shorter than this may also crack in the middle.|
|Load Transfer:||Aggregate interlock and dowel bars. For low-volume roads aggregate interlock is often adequate. However, high-volume roads generally require dowel bars in each transverse joint to prevent excessive faulting.|
|Other Info:||A majority of U.S. State DOTs build JPCP because of its simplicity and proven performance.|
Washington State JPCP Information
WSDOT builds only JPCP. Links to further WSDOT JPCP design practices are listed below:
Jointed reinforced concrete pavement (JRCP, see Figure 2.40) uses contraction joints and reinforcing steel to control cracking. Transverse joint spacing is longer than that for JPCP and typically ranges from about 7.6 m (25 ft.) to 15.2 m (50 ft.). Temperature and moisture stresses are expected to cause cracking between joints, hence reinforcing steel or a steel mesh is used to hold these cracks tightly together. Dowel bars are typically used at transverse joints to assist in load transfer while the reinforcing steel/wire mesh assists in load transfer across cracks.
|Crack Control:||Contraction joints as well as reinforcing steel.|
|Joint Spacing:||Longer than JPCP and up to a maximum of about 15 m (50 ft.). Due to the nature of concrete, the longer slabs associated with JRCP will crack.|
|Reinforcing Steel:||A minimal amount is included mid-slab to hold cracks tightly together. This can be in the form of deformed reinforcing bars or a thick wire mesh.|
|Load Transfer:||Dowel bars and reinforcing steel. Dowel bars assist in load transfer across transverse joints while reinforcing steel assists in load transfer across mid-panel cracks.|
During construction of the
interstate system, most agencies in the Eastern and Midwestern U.S. built
JRCP. Today only a handful of agencies employ this design (ACPA, 2001).
In general, JRCP has fallen out of favor because of inferior performance when compared to JPCP and CRCP.
Continuously reinforced concrete pavement (CRCP, see Figure 2.41) does not require any contraction joints. Transverse cracks are allowed to form but are held tightly together with continuous reinforcing steel. Research has shown that the maximum allowable design crack width is about 0.5 mm (0.02 inches) to protect against spalling and water penetration (CRSI, 1996). Cracks typically form at intervals of 1.1 - 2.4 m (3.5 - 8 ft.). Reinforcing steel usually constitutes about 0.6 - 0.7 percent of the cross-sectional pavement area and is located near mid-depth in the slab. Typically, No. 5 and No. 6 deformed reinforcing bars are used.
During the 1970's and early 1980's, CRCP design thickness was typically about 80 percent of the thickness of JPCP. However, a substantial number of these thinner pavements developed distress sooner than anticipated and as a consequence, the current trend is to make CRCP the same thickness as JPCP (FHWA, June 1990). The reinforcing steel is assumed to only handle nonload-related stresses and any structural contribution to resisting loads is ignored.
|Crack Control:||Reinforcing steel|
|Joint Spacing:||Not applicable. No transverse contraction joints are used.|
|Reinforcing Steel:||Typically about 0.6 - 0.7 percent by cross-sectional area (ACPA, 2001).|
|Load Transfer:||Reinforcing steel, typically No. 5 or 6 bars, grade 60.|
|Other Info:||CRCP generally costs more than JPCP or JRCP initially due to increased quantities of steel. Further, it is generally less forgiving of construction errors and provides fewer and more difficult rehabilitation options. However, CRCP may demonstrate superior long-term performance and cost-effectiveness. Some agencies choose to use CRCP designs in their heavy urban traffic corridors (ACPA, 2001).|
WSDOT Rigid Pavement Intersections
In 1995, WSDOT began replacing flexible pavement with rigid pavement at selected intersections. These intersections were severely rutted and distressed due to loads from slow moving vehicles and warm temperatures. Statewide, ruts of 50 mm (2 inches) or more occasionally have occurred and resurfacing to restore the intersection to an acceptable level recurred at intervals of eight years or less. Though WSDOT has numerous rigid pavement intersections, the unique feature with these particular intersections was the replacement of existing flexible with rigid pavement only at intersections.
A major advantage with rigid pavement replacement is that once the rigid pavement is placed rehabilitation should not be necessary for 40 years. The major disadvantage with rigid pavement intersections is the initial construction cost; however, these costs appear to be coming down, particularly as contractors become familiar with this type of construction. Rigid pavement intersections in the Tri-Cities area completed in 2000 showed that an entire intersection can be paved in a single weekend closure.
The following WSDOT report discusses rigid pavement intersection design and construction in detail:
The following is a overview of some considerations for rigid pavement intersection design: