Requires the provision of joints:
1) expansion, contraction and warping of concrete slabs as a result of changes in temperature and moisture;
2) to facilitate breaks in construction at the end of the day’s work or for any unforeseen interruption in work progress; And
3) Construction of footpaths in streets of convenient width.
Quality requirements for joint construction
1) All foreign material in the joints must be removed first. The joints are manually cleaned with a raker followed by coir brushing. Fine particles are removed with the help of air compressor. After cleaning the joints, primer is used.
The primer has a very low viscosity and penetrates the pores of the concrete. This is followed by the use of joint filler and finally sealing compound. The primer used previously helps to improve the bond between the ceiling compound and the concrete
2) Joints should be flush with the adjacent pavement surface on either side in summer and filled to a depth of 3-4 mm below the surface in winter so that they are flush when expanded during hot weather.
3) Dowel bars are required for transverse joints
- Transfer part load to adjacent slab
- increasing tension
- To assist in the event of loss of sub grade support in place of a joint
4) Dowel bars are typically mild steel round bars that are embedded and bonded into the concrete on one side of the joint and the other half the length deliberately prevented from bonding with the concrete on that side. A recess is provided at the sliding end for free movement of the slab when used in expansion joints.
5) Dowel bars should be supported on cradles/dowel chairs in pre-fabricated joint assemblies positioned prior to slab fabrication or mechanically inserted with vibration into the plastic concrete ensuring correct placement of the bars. Concrete around the dowel bar.
6) The dowel bar should be positioned at the middle depth of the slab, and centered evenly across the intended lines of the joint. They should be aligned to the prepared surface of the slab and the center line of the carriageway and parallel to each other.
7) The dowel bar should be covered by a thin plastic sheath from one end at least two-thirds the length for dowel bars in contraction joints or half the length plus 50 mm for expansion joints. The sheath should be tough, durable and of average thickness not exceeding 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 waterproof cardboard or approved synthetic material, e.g., PVC or GI pipe, shall be fitted to the sheath end of each dowel bar. An expansion space equal to the thickness of the joint filler board should be created between the end of the cap and the end of the dowel bar by using a compressible damper to prevent penetration of cement slurry between the dowel and the cap. It can be taped.
9) Tie bars are provided to prevent separation of adjacent slabs, especially on curves or fills. Tie bars are not meant to add to the structural capability of the slab and are designed to withstand tensile stresses only.
10) In longitudinal joints the tie bar should be deformed steel bar with a strength of 415 MPa IS: 1786,
1 1) Tie bars projected into the longitudinal joint shall be protected from corrosion by a protective coating of bituminous paint up to 75 mm on each side of the joint.
12) Tie bars in longitudinal joints should be made in rigid combinations with sufficient support and fixings to remain firmly in position during the construction of the slab. Alternatively, tie bars at longitudinal joints can be mechanically or manually inserted from above into the plastic concrete by vibrating which ensures the correct placement of the bars and re-compacting of the concrete around the tie bar. Is.
13) The tie bar should be placed approximately parallel to the surface to remain within the middle third of the depth of the slab and perpendicular to the line of the joint with a minimum cover of 30 mm below the joint groove.