New zealand concrete masonry manual 6 3 control joints introduction where there is any conflict between linked concrete masonry walls whether they be walls forming part of a building structure retaining or garden walls often require control joints to be built in.
Control joints in poured concrete walls.
Cast in place concrete walls use three types of joints.
Construction joints in concrete walls construction joints shall be made and located so as not to detrimentally affect the strength of the wall.
2 wall height spacing 8 feet or less 3 times wall height.
Saw cutting cuts joints as soon as the concrete is hard enough that the edges abutting the cut don t chip from the saw blade.
When in a rectangle shape the rectangle ratio seldom exceeds a length to width ratio of 1 5 to 1.
Concrete masonry association inc.
Joints in poured walls by kim basham and bruce suprenant effective methods for controlling unsightly wall cracking f i g u r e 1.
Though concrete has a tendency to crack and does crack in most cases cracks can be controlled by joints or planned separations in concrete.
They are essentially vertical planes of weakness built into the wall to reduce restraint and permit longitudinal movement due to anticipated shrinkage and are located where stress concentrations may occur.
A 4 slab should have joints 8 12 feet apart.
Concrete at the interface of construction joints required to be roughened in order to create proper bond between previous and newly poured concrete.
Contraction joints are usually about 0 25 inches wide and about 1 2 to 3 4 inch deep and are provided at intervals of not exceeding 30 feet.
A 4 thick slab should have joints 1 deep.
Contraction joints are weakened planes built into walls to control the location of cracking caused by volume changes especially those related to shrinkage and temperature changes.
Space joints in feet no more than 2 3 times the slab thickness in inches.
Use projecting strips to reduce wall thickness by at least one fourth ref.
Recommended spacing of vertical contraction joints modified from ref.
These are vertical joints or grooves formed or cut into the wall that allows the concrete to shrink without noticeable harm.
Control joints in concrete slabs which are poured on grade on top of the ground are placed so that the concrete is in a square or rectangle pattern or shape.
Movement joints such as control joints are one method used to relieve horizontal tensile stresses due to shrinkage of the concrete masonry units mortar and when used grout.