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  Module 4: Pavement Design
Lecture 29 Rigid pavement design
  

Contraction joints

The purpose of the contraction joint is to allow the contraction of the slab due to fall in slab temperature below the construction temperature. The design considerations are:
  • The movement is restricted by the sub-grade friction
  • Design involves the length of the slab given by:
    \begin{displaymath} L_c=\frac{2\times10^4S_c}{W.f} \end{displaymath} (1)

    where, $S_c$ is the allowable stress in tension in cement concrete and is taken as 0.8 kg/cm$^2$, $W$ is the unit weight of the concrete which can be taken as 2400 kg/cm$^3$ and $f$ is the coefficient of sub-grade friction which can be taken as 1.5.
  • Steel reinforcements can be use, however with a maximum spacing of 4.5 m as per IRC.
Figure 1: Contraction joint
\begin{figure}\centerline{\epsfig{file=../../../figeps/p27-rigid-pavement-contraction-joint,width=7cm}}\end{figure}

Dowel bars

The purpose of the dowel bar is to effectively transfer the load between two concrete slabs and to keep the two slabs in same height. The dowel bars are provided in the direction of the traffic (longitudinal). The design considerations are:
  • Mild steel rounded bars,
  • bonded on one side and free on other side