Warping joints

The function of warping joints is to stop the warping of slabs attributed to the differential temperature of the slab with respect to its depth. By no means are the warping joints created to withstand any slab expansion or contraction. Anchorage of the steel bars placed between the slabs is of vital importance. Because of the different functions of steel bars placed, they are called tie bars. 

The proper anchorage of the tie bars is achieved either by welding the tie bars on longitudinal supportive steel bars to be placed at a certain depth (or height) or by bending both ends. Suffice it to say that the tie bars are not covered with a corrosion-resistant coating at their full length, in contrast to the dowel bars in the expansion or contraction joints. 

As the tie bars are not designed to act as a load transfer mechanism, they have a smaller diameter and usually are longer than the dowel bars. 

In URCPs, usually every third contraction joint is replaced by a warping joint. 

In case of continuously reinforced pavements, the longitudinal construction joints are formed in a manner similar to the abovementioned ways. 

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In order to address the stresses described above, joints are provided, which are distinguished into three main categories (a) contraction joints, (b) expansion joints and (c) warping joints (see Figure 14.5). 

Figure 14.5 Contraction, expansion and warping joints, (a) Contraction joint (b) expansion joint and (c) warping joint.

For unreinforced and jointed reinforced type of concrete pavements, all types of joints are provided, while in the continuously reinforced pavements, only longitudinal (warping) joints are provided (see Figure 14.6). 

There are also joints that, because of the interruption of works or emergency joints (as will be explained later), do not constitute a separate joint type. The longitudinal construction joints are warping joints. 

A typical cross section of a warping joint for unreinforced pavements along the transverse direction is shown in Figure 14.9. 

Figure 14.9 Construction details of a typical warping joint in URCP, in the transverse direction. (Adapted from Highways Agency, The Manual of Contract Documents for Highway Works [MCDHW], Volume 3 Highway Construction Details, Department for Transport. London Highways Agency, 2006c [ Highways Agency].)...

Figure 2 is a detail of the sloped wood cap used in Figure 1. Note that the joints are taped (at the top of the cant) and caulked (between the lead flooring and wood cant) to keep manufacturing components and product out of joints. The tape material is 3 inch wide, 2 ply, 100 percent cotton, grade B fabric with a warp and fill of approximately 78 x 78 x 72 pounds breaking strength. It should be adhesive-applied using a water insoluble nitrile rubber/ resin solution. These are commonly referred to as "Airplane Fabric" and "Pliobond 20" adhesive. The Fiberfrax Paper is used below lead flooring as an insulation barrier with a low thermal conductivity to resist heat required for installation of lead conductive floor. Note also that nonsparking nails are required. These are usually aluminum or brass.

Observations demonstrated that bonding of concrete slabs with polymer PM reduces vertical and horizontal deformations of them of about 50%, allowing for safe work of airfield pavements. It should be noticed that contractions joints deform horizontally of about 5 mm between winter and summer and similar value was measured in cases of vertical deformation. An example of 24 hours measurements of vertical displacements of airfield slab is presented in Fig. 16 (for original slab with bituminous filling and slab bonded with polymer PM). Comparison of vertical displacement shows that the use of polymer joints in contradiction to bituminous mass reduces warping deformations of the comers about two times, what is very advantageous in aspect of airfield exploitation. 

Placing of the expansion, warping and longitudinal joints and slab reinforcement (if used) are carried out manually before concreting and after laying the separation membrane, in the case of jointed reinforced concrete. The contraction joints are formed soon after concreting. 

Corner cracking is caused by load repetitions combined with a loss of corner support (subbase or subgrade), poor load transfer across the joint, dowel bar restrain near the edge of the slab and ingress of solids into the joint. The loss of support may be created by pumping or warping stresses. 

Conventional standard weaving machines can create this type of shell three-dimensional woven fabric, if two layers are woven with areas of hollow and other areas of non-hoUow fabric. To avoid the potential danger of recoding fabric parts, a double-layer fabric should completed at the non-hollow zones with a long floating single-layer weave or with another double-layer weave having joints of warp ends or weft threads between the two layers. 

Temperature Compatibility. If pin-in-paste soldering is to be used, check that components are temperature-compatible with the oven reflow process. The high temperatures and long exposures associated with oven reflow soldering may cause unsuited molded component bodies to melt or warp. Connector contact normal force may be affected if the molded connector body softens or distorts. Solder joints or wire bonds internal to some devices may become disbanded, and some, such as electrolytic capacitors, may leak or even explode as a result of an oven reflow cycle. Check the component manufacturer s specification for thermal hmits and compatibihty with oven reflow soldering. 

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