Joints in concrete

1
Joints in concrete

• Construction joints
• made such that new concrete is bonded with
  hardened concrete and concrete appears to be
  monolithic and homogenous across the joint.
• Usually located where shear forces are a minimum.
  In beams and slabs this is usually in the middle
  third of the span.
• Whenever possible positioned at locations of
  movement joints or where a plane of weakness is
  required.
• Joint surface needs to be prepared before new
  concrete is placed.
• wire brushing and removal of loose material
• scabbling with high pressure water or sand
  blasting to expose the coarse aggregate.
• In liquid retaining structures, water stops are
  usually used to seal a vertical construction
  joint.

2
Joints in concrete

• Contraction joints
• Incorporated to relieve the tensile stresses
  resulting from the shrinkage of concrete.

3
Joints in concrete

• Expansion joints
• Creates a gap between two mating concrete
  surfaces to allow for expansion. The gap is
  usually filled with a compressible filler such as
  rubber, plastic, mastic or cork.

4
Joints in Concrete

• Some rules
• Need isolation joints around columns
• Diamond shape corners to match up with the slab
  joints
• Avoid re-entrant angles
• Joint spacing 30x thickness (4.5 m max)
• Rectangular panels
• max length 1½ x short side

5
Types of joints
6
Dowelled joint

7
Expansion joint
8
Contraction joint
9
Crack control joints
10
Crack control joints