Laboratory and finite element evaluation of joint lockup

Transverse joints are introduced in portland cement concrete pavements to allow for expansion and contraction due to temperature and moisture variation in the concrete layer. With the use of dowels, the ability of the concrete to expand and contract at the joint may be restrained. This action leads to joint lockup, the severe restriction in the ability of the joint to open and close. Joint lockup had been attributed to rotational misalignments of dowels. The results of this study indicate that other factors may have a greater effect on joint opening behavior. It was demonstrated in the laboratory that dowel misalignment did not significantly increase pullout force for properly greased dowels. It was also found from laboratory testing that a lack of proper greasing significantly increased the dowel pullout force. Dowel-concrete friction was identified as an important parameter that controlled the joint behavior according to the finite element model. High friction may induce damage in concrete and thus cause distresses traditionally attributed to rotational misalignment of dowels; this suggests that designers and contractors should ensure proper bond breaking between dowel and concrete.