In order to prevent concrete structures from damage caused by plastic shrinkage, thermal shrinkage, settlement, movement…, concrete joints are required. There are 3 common types of concrete joints as outlined bellows.
1. Contraction (Control) Joints
Contraction Joints are purposely installed joints designed to regulate cracking that might otherwise occur due to the unavoidable, often unpredictable, contraction of concrete. These joints are often called control joints because they are intended to control crack locations. The necessary plane of weakness may be formed by reducing the concrete cross-section by tooling or saw cutting a joint within 24 hours of placing. Contraction joint movement is supposed to be small.
2. Construction Joints
Construction Joints are made before and after interruptions in the placement of concrete or through the positioning of precast units. Locations are usually predetermined so as to limit the work that can be done at one time to a convenient size, with least impairment of the finished structure, though they may also be necessitated by unforeseen interruptions in concreting operations. Depending on the structural design, they may be required to function later as expansion or contraction joints, or they may be required to be soundly bonded to the first so as to maintain complete structural integrity. Construction joints may run horizontally or vertically depending on the placing sequence prescribed by the design of the structure.
3. Expansion Joints
Expansion Joints are designed to prevent the crushing and distortion of the abutting concrete structural units that might otherwise occur due to the transmission of compressive forces that may be developed by expansion, applied loads, or differential movements arising from the configuration of the structure or its settlement. Expansion joints are made by providing a space over the entire cross section between abutting structural units. Expansion joint movement may be high (up to 30 % of joint width).
Sealant for above joints are needed for any concrete structures. Concrete joint sealant will be discussed on next coming articles.