What Are Joints? Although concrete expands and contracts with
changes in moisture and temperature the general overall tendency
is to shrink and, therefore, crack. Irregular cracks are
unsightly and difficult to maintain. Joints are simply pre-
planned cracks. Some forms of joints are: - Control
(contraction) joint – These joints are constructed to create
planes of weakness so that cracks will occur at the desired
location. - Isolation (expansion) joints – They separate or
isolate slabs from other parts of the structure such as walls,
footings, or columns, and driveways and patios from sidewalks,
garage slabs, stairs, light poles and other obstructions. They
permit movement of the slab and help minimize cracking caused
when such movements are restrained. - Construction joints –
These are joints that are placed at the end of a day’s work. In
slabs they may be designed to permit movement and/or to transfer
load. Often in reinforced concrete a conscious effort is made to
clean the joint and bond the next day’s wor