Rigid pavements are often used for the construction of airport runways and major highways, including those in the highway system of the United States. They are also used for industrial applications such as harbor yard pavements, heavy vehicle parking locations and terminal pavements.
Function and Design
A rigid pavement is designed withstand all types of weather and is created to be long-lasting for high traffic. A rigid pavement functions as a load-bearing structural element that distributes vehicle loads across the base course and the sub-base in the most effective way possible.
The most commonly used material in the construction of rigid pavement surfaces is Portland cement concrete, or PCC. PCC is readily available and is an inexpensive option for paving. A properly-build rigid pavement can generally last up to 40 years, about twice the lifetime as that of a flexible pavement. Rigid pavements are designed to prevent fatigue failure from wheel load. The thermal loading if a roadway must also be taken into account. The thermal loads caused by the constant friction on the surface of the pavement can be equal to those created by the weight loads themselves. Because concrete has lower tensile strength than flexible pavements, the thermal stresses the road is expected to bear must be taken into account when determining the type of rigid pavement to put down.
Rigid Pavement Types
There are three main types of rigid pavement construction in use today: jointed plain concrete pavement (JPCP), jointed reinforced concrete pavement (JRCP) and continuously reinforced concrete pavement (CRCP).
- A jointed plain concrete pavement (JPCP) is designed with natural contraction joints designed to direct the spaces between the concrete slabs in such a way as to allow them a certain amount of give to bend and flex. A JPCP does not contain any reinforcing steel.
- Jointed reinforced concrete pavements (RCP) are designed with contraction joints along with steel reinforcements to limit and control the inevitable cracks within the slab. The steel rebar helps compensate for the high temperatures and excessive moisture that can lead to stress cracks by transferring the load across the entire slab of the JRCP. Dowel bars placed along transverse joints help provide additional structural support.
- Continuously reinforced concrete pavements (CRCP) are based on a framework of a steel reinforcement grid embedded in the concrete to strengthen the transverse joints between the paving slabs. To help take some of the strain off the road, pre-stressed pavements are sometimes used, but they are uncommon. A pre-stressed pavement permits a thinner slab to be used without as much need to compensate for thermal stresses.
Temperature changes can cause warping stresses, which in turn can lead to frictional stresses in the future. Expansion joints, contraction joints, dowel bars and tie bars help keep the load transfer even across the slabs. Dowel bars are bonded to the concrete on one side and left free on the other side, permitting the concrete to expand and contract as needed. Tie bars, on the other hand, are designed to connect two slabs tougher, rather than assist in transferring load. Tie bars are firmly anchored into the concrete at both ends and are smaller than dowel rods. Where dowel rods connect across transvers joints, tie bars connect across longitudinal joints.
The tendency of PCC to warp is greater during the day than at night. Because PCC is significantly stronger in compression than in tension, the amount of tensile stress a slab is able to withstand is a determining factor in the design and construction of a rigid pavement.