What is the purpose of a control joint?

The goal of the control joint is to allow the slab to crack, during expansion and contraction, in a known location and in a straight line. Expansion joints are put in place before the concrete is poured.

What are some of the reasons for using concrete joints?

To control tensile stresses due primarily to moisture change and thermal contraction of the slab, and thus to limit random cracking. For convenience during construction.

Where are control joints in concrete?

Control joints are generally placed into the concrete during the finishing process or within 24 hours of being poured….Control joints are commonly found in concrete:

1. Garage floors.
2. Driveways.
3. Sidewalks.
4. Patios.
5. Basement floors.
6. House slabs.

Do you need expansion joints in concrete slabs?

Expansion joints are virtually never needed with interior slabs, because the concrete doesn’t expand that much—it never gets that hot. Expansion joints in concrete pavement are also seldom needed, since the contraction joints open enough (from drying shrinkage) to account for temperature expansion.

What is concrete control joint?

Control joints are planned cracks which allow for movements caused by temperature changes and drying shrinkage. In other words, if the concrete does crack-you want to have an active role in deciding where it will crack and that it will crack in a straight line instead of randomly.

How often do you need control joints in concrete?

Usually, expansion joints should be no farther apart than 2 to 3 times (in feet) the total width of the concrete (in inches).

When should control joints be cut in concrete?

6 to 18 hours
Joints should be sawed as soon as the concrete can withstand the energy of sawing without raveling or dislodging aggregate particles. For most concrete work, cutting should take place within the first 6 to 18 hours and never beyond 24 hours.

What is the difference between control joint and expansion joint?

In building materials, a control joint is used to control cracking while an expansion joint is designed to handle structural movement. A control joint can be formed during placement of the building material or cut after the material is placed.

What is the difference between a control joint and a construction joint?

Both isolation and construction joints are formed before the concrete is poured; contraction joints (or control joints) are “placed” in the fresh concrete before it has a chance to create its own joints—also known as cracks.

What is control joint in concrete?

control joint (plural control joints) (construction) A groove which is formed, sawn, or tooled in a concrete or masonry structure to regulate the location and amount of cracking and separation resulting from the dimensional change of different parts of the structure, thereby avoiding the development of high stresses.

What is a slab control joint?

Contraction/Control Joints. Contraction/control joints are placed in concrete slabs to control random cracking. A fresh concrete mixture is a fluid, plastic mass that can be molded into virtually any shape, but as the material hardens there is a reduction in volume or shrinkage.

What are concrete control joints?

Concrete control joints are found in floor slabs, walls, foundations and sidewalks. As these structures dry, or cure, they experience significant shrinkage as water within the concrete evaporates. Over time, they continue to contract or expand due to changes in temperature, humidity and moisture levels.

Where should construction joint to be located in slab?

The ACI Code requires construction joints in elevated slabs to be located within the middle third of spans of slabs, beams, and girders. Joints must be located at least two beam widths away from beam-girder intersections.