Section 6: Terminal Anchor Joint Selection for Concrete PavementAnchor: #i1008032
6.1 Terminal Joint Design Recommendation
Concrete experiences volume changes due to temperature and moisture variations. Normally, concrete pavement is abutted to bridge structures via approach slabs. To prevent damage to the bridge structures, some form of system is installed at the bridge and pavement interface. There were three systems in use at the department: expansion joint system, wide-flange system, and anchor lug system.
The basic premise of the expansion joint system is that the expansion joint width will be able to absorb any concrete pavement expansion without transmitting the compression forces to the bridge structure.
The wide-flange system is similar to the expansion system, except that the expansion joints exist under the wide flange and are not seen from the pavement surface. One advantage is that, since the joint is not exposed to the pavement surface, joint maintenance is minimized.
An anchor lug system tries to contain the concrete movement at the interface between bridge and pavement by providing five anchor lugs.
The department has investigated the movements of CRCP near bridges and the effectiveness of these three terminal systems in Research project 0-6326, “Rational Use of Terminal Anchorages in Portland Cement Concrete Pavements.”
The research data has shown that the anchor lug system is not effective. The stresses generated in soil due to slab expansion at lug walls are large enough to result in permanent deformations in soils. The soil does not retract with the lug when the pavement contracts. The permanent deformations result in voids between soil and lug walls.
Field measurements have indicated that the base friction restrains slab movements effectively. Using coarse-textured base such as HMA might be the most effective tool to control slab movements. Simple expansion joint systems or wide-flange systems are effective in accommodating slab movements. Expansion joint systems should cost less than wide-flange systems and attain comparable performance.
The use of anchor lug systems is no longer allowed, and the standard TA(CP)-99 has been deleted. The transverse expansion joint details at bridge approaches are shown in the concrete pavement standards.
Districts may develop a Special Specification to use the wide-flange system.