1) Expansion, contraction and warping of concrete slabs resulting from temperature and moisture changes;
2) Facilitate a break in the construction at the end of day’s work or for any unexpected interruption to work progress; and
3) Construction of pavements in lanes of convenient width.
Quality Requirements for Joint Construction
1) All foreign material in the joints should be removed first. The manual cleaning of the joints is done with a raker followed by coir brushing. The fine particles are removed with the help of air compressor. After the joints have been cleaned, primer is used.
The primer has very low viscosity and penetrates in the pores of the concrete. This is followed by joint filler and finally sealing compound is used. The primer used earlier helps to improve bond between sealing compound and concrete
2) The joints should be sealed flush with the adjacent pavement surface on either side in summer and should be filled to a depth of 3-4 mm below the surface in winter so that they may become flush on expanding during hot weather.
3) Dowel bars are required for the transverse joints to
Transfer part load across the adjacent slab
Stresses becoming critical
Assist in the event of loss of sub grade support at the location of joint
4) Dowel bars are generally mild steel round bars embedded and bonded into concrete on one side of the joint and the other half length deliberately prevented from bonding with concrete on that side. A recess is provided at the sliding end for free movement of slab when used in the expansion joints.
5) The dowel bar should be supported on cradles/dowel chairs in pre-fabricated joint assemblies positioned prior to the construction of the slabs or mechanically inserted with vibration into the plastic concrete by method which ensures correct placement of the bars besides full re-compaction of the concrete around the dowel bars.
6) Dowel bars should be positioned at mid depth of the slab, and centered equally about intended lines of the joint. They should be aligned parallel to the finished surface of the slab and to the center line of the carriageway and to each other.
7) Dowel bars should be covered by a thin plastic sheath for at least two-thirds of the length from one end for dowel bars in contraction joints or half the length plus 50 mm for expansion joints. The sheath shall be tough, durable and of and average thickness not greater than 1.25 mm. The sheathed bar shall comply with the specified pullout tests.
8) For expansion joints, a closely fitting cap 100 mm long consisting of waterproofed cardboard or an approved synthetic material, like, PVC or GI pipe should be placed over the sheathed end of each dowel bar. An expansion space at least equal in length to the thickness of the joint filler board should be formed between the end of the cap and the end of the dowel bar by using compressible sponge to block the entry of cement slurry between dowel and cap. It may be taped.
9) Tie bars are provided to prevent adjacent slabs from separating, particularly on curves or at fills. The tie bars are not meant to add structural capacity of the slabs and are designed to withstand only tensile stresses.
10) Tie bars in longitudinal joints should be deformed steel bars of strength 415 Mpa complying with IS: 1786.
11) Tie bars projecting across the longitudinal joint shall be protected from corrosion for 75 mm on each side of the joint by a protective coating of bituminous paint.
12) Tie bars in longitudinal joints shall be made up into rigid assembles with adequate supports and fixings to remain firmly in position during the construction of the slab. Alternatively, tie bars at longitudinal joints may be mechanically or manually inserted into the plastic concrete from above by vibration using a method which ensures correct placement of the bars and re-compaction of the concrete around the tie bars.
13) Tie bars shall be positioned to remain within the middle third of the slab depth approximately parallel to the surface and perpendicular to the line of joint with a minimum cover of 30 mm below the joint groove.