Cold Joints and Expansion Joints in Concrete

by Awais
(Pakistan)

Q: What is the difference between concrete cold joints and concrete expansion joints?

Are joints in concrete work desirable, especially roof slabs, water tank side walls?

Hi Awais,

I'm happy to answer your questions.

A cold joint occurs the meeting point of adjacent concrete pours done at different times (i.e. one pour is setting up and a new pour is made that meets. Cold joints are a result of different pours - they do nothing to control cracking in a concrete slab

Concrete expansion joints account for volume changes in concrete at preselected points. Concrete both expands and contracts when moisture and temperature change. Strategically placed expansion joints can control the concentration of forces that cause cracking.

If they are made properly, they eliminate random surface cracks by distributing stresses that come from moisture and temperature changes. To be effective, concrete expansion joints must be both located and made correctly.

Are they desirable? They are not only desirable, Awais, they are essential. Without concrete expansion joints, any restraint with concentrated drying stress forces may cause cracks in a restrained concrete member.

Here is further reading on all types of concrete joints

MMC.com

johnbridge.com


Best regards,

Alan
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