Concrete undergoes expansion due to high temperature when in a confined boundary which leads to cracks.
Expansion joint concrete block wall.
Expansion control joints to control the expansion and protect the wall structure from cracking under pressure masons install vertical control joints at specific locations.
Expansion joints are provided in slabs pavements buildings bridges sidewalks railway tracks piping systems ships and other structures.
The pre planned cracks will provide a better finish concrete product and will be formed in specific locations where those cracks could be monitored.
Thomas armstrong s technical guidance provides industry standard information on movement control on vertical and horizontal joints as well as concrete block wall ties in terms of spacing and positioning.
Change in wall height or thickness see figure 1 figure 2 change of loading see figure 3 abutments of walls and columns see figure 4 junctions of dissimiliar materials see figure 5.
Guidance for spacing and location of control joints can be found in the national concrete masonry association ncma tek note 10 02c control joints for concrete masonry walls empirical method 2010.
1 for more detailed information.
Standard specification for nonrigid vinyl chloride polymer and copolymer molding and extrusion compounds astm d2287 12.
These joints will absorb the pressure created by the expansion by giving the masonry wall flexible space to expand.
Aggregate concrete blocks position of movement joints consideration for the location of movement joints should be given at.
Details of this butt type con s t r uction joint are shown in figure 4.
Control joints are typically used in concrete masonry to reduce the occurrence of shrinkage related cracking.
If control joints are not provided a concrete masonry wall may crack as it shrinks over time.
This article emphases on need of expansion.
Other constru c tion joints coincide with or function as contraction or expansion joints.
Shrinkage cracks in concrete masonry are not a structural concern.
Control joints are typically required in exposed above grade concrete masonry walls where shrinkage cracking may detract from the appearance of the wall and to limit moisture or air infiltration.
This is unavoidable and perfectly natural for most construction products based on.
Joint sealants for concrete masonry walls tek 19 6a.
Concrete masonry banding details tek 5 2a ref.
Concrete joints are normally used to prevent cracks when the concrete shrinks by creating forming tooling sawing and placing joint formers.
National concrete masonry association 2009.
Concrete joints are used to compensate when concrete expands or shrinks with changes in temperature.
The simplest vertical constru c t i o n joint is formed using a bulkhead b o a r d.
It is a continuous vertical joint filled with mortar but with a bond breaker on one side so that tensile stress cannot develop across the joint.
Concrete blocks regardless of manufacturer will dry out and shrink slightly once the building is complete.
As mentioned in the expansion joints discussion the design of control joint spacing and location is the responsibility of the designer.
