7 Pavement Joints
Types of Joints
D-1 Contraction Joints Longitudinal Joints Transverse Construction Joints Terminal Joints Expansion Joints Retro-fitted Tie Bars
CHAPTER SEVEN: PAVEMENT JOINTS __________________________________________ Pavement joints are vital to control pavement cracking and pavement movement. Without joints, most concrete pavements would be riddled with cracks within one or two years after placement. Water, ice, salt and loads would eventually cause differential settlement and premature pavement failures. These same effects may be caused by incorrectly placed or poorly designed pavement joints. The Technician is responsible for inspecting all joints to avoid any of the problems associated with joint failure. Forethought should be given to the design and placement of the pavement joints so that the end result is a properly functioning pavement system. Special care is given at intersecting approaches, turn lanes and crossovers so that the joints required at these locations will complement the joints placed in the mainline pavement. Since the mainline pavement is typically placed prior to any auxiliary pavement, the location of all joints is required to be known in advance of the initial pours. If the initial joint placement is correct, the extension of the same joint lines throughout any adjacent pavements is done. "Dead ending" of joints in the middle of adjacent slabs is avoided whenever possible to prevent the risk of reflective cracking. An example of a well planned joint design is shown in Figure 7-1. The joints in this diagram are continuous from edge of pavement to edge of pavement. Also, the joints in the mainline pavement are aligned to serve the joints in the adjoining pavements. The following pavement joints and related materials are discussed: 1) D-1 contraction joints 2) Longitudinal joints 3) Transverse construction joints 4) Terminal joints 5) Expansion joints 6) Retrofitted tie bars ___________________________________________________________
Figure 7-1. Pavement Joint Design
TYPES OF JOINTS There are many types of joints used in the construction of concrete pavements but they all control the movement of the pavement and the associated cracking and/or differential settlement. Unless otherwise indicated, all joints are placed perpendicular to grade. Longitudinal joints are placed parallel to the center line, transverse joints are placed at right angles to the center line for the width of the pavement. Understanding the use and function of different types of joints is required in determining their placement. the and full the
D-1 CONTRACTION JOINTS
Typically, a contraction joint is a sawed transverse joint normally placed every 18 ft to control cracking due to pavement contraction caused by shrinkage and temperature fluctuations. The plans for the particular contract are required to be checked to verify the proper joint placement. The minimum/maximum joint spacing is reviewed with the Area Engineer or District Construction Engineer so that joints may be established in the initial pours that will complement adjacent pavements. A dowel bar assembly (Figure 7-2), commonly called a "basket", is placed on the subgrade before paving at the location of the contraction joint. The steel bars of this assembly are large and, once incorporated into the concrete pavement, transfer the vehicular load from one slab to another, eliminating differential settlement at the joint.
Figure 7-2. Dowel Bar Baskets The location of the center of the dowel bar assembly is marked outside of the form/slab line so that the dowel bar assembly may be established once the pavement is in place. These locations are maintained during the pouring operations because the markings may easily become disturbed during construction. The dowel bar assemblies are to be securely fixed to the subgrade by using metal pins to eliminate displacement by the plastic concrete (Figure 7-3)....
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