Maximum joint spacing should be 24 to 36 times the thickness of the slab. Joints should be spaced about 10 feet and a maximum of 15 feet. When using joint groove for contraction joints, the joint should be a minimum depth of 1/4 thickness of the slab.
Generally speaking, expansion joints should be no farther apart than 2 to 3 times (in feet) the total width of the concrete (in inches).
Control Joints - Dimensions and Spacing
The spacing of Control Joints is related to the thickness of the concrete or mortar slab. It is generally 20 – 25 times the thickness of the slab. Ardex generally state that 4.5m is the maximum allowable spacing.
Joints shall not be less than 4mm and not greater than 10mm wide. Seal all movement joints with a suitable, expandable coloured silicone sealant to match your grout.
It is clear from above table that for rough interface the maximum spacing for expansion joint is 140 m.
As a general rule-of-thumb, joint spacing should be less than about 24 x slab thickness. Thus, a 230 mm slab (9 inches) should have joints spaced no more than about 5.5 m (18 ft.) apart. Also, as a general guide, the ratio of longer side slab length to the shorter side slab length should be kept less than about 1.25.
The distance between adjacent expansion joints and the dimensions of the individual joints must be such that any movements occurring do not exceed 16% or 20% of the joint width.
The minimum allowable width of an exterior movement accommodation joint is 3/8″ for joints 8′ on center and 1/2″ for joints 12′ on center. Minimum widths must be increased by 1/16″ for every 15 degree Fahrenheit temperature change over 100 degrees from summer high to winter low.
The imperial rule of thumb is as zestructural has stated, 3 times the slab thickness in inches gives you your maximum control joint spacing in feet. The metric version is even more simple: Divide your floor thickness by 0.028. Done. Units are consistent.
Standard Concrete Slab Thickness In Australia
In Australia, concrete slabs must be fixed in adherence with the Australian Standards AS 2870 and AS 3600. The most common slab thickness in Australia is between 85mm and 100 mm. The thickness of concrete slabs is usually stated in specification documents.
Any project involving concrete construction must include expansion joints. To reduce stresses, fractures or cracking, contractors utilise expansion joints to create a cushion between adjacent concrete sections. This cushion stops structural damage caused by movements brought on by weight, wind, or temperature changes.
For the most part, if the cracks are less than 1.5mm in width and the length is less than those specified in Australian Standards (generally ranging from 5mm to 15mm) then it can be assumed to be minor cracking that is acceptable.
The typical spacing in feet is 2 to 3 times the slab thickness in inches. So, for example, contraction joints in a 6-inch-thick slab would be 12 to 18 feet apart.
The gaps allow the slabs to move with normal expansion, contraction or settling that occurs due to temperature changes or moisture conditions. If no expansion joints are planned in large runs of concrete, there is a tendency to form significant cracks where the movement causes severe stress points in the concrete.
In order to help prevent problems like cracking, weeds, and settling from affecting your concrete, it's important to fill the expansion joints with a flexible non-sag and/or self-leveling caulk. This will provide protection against water and weeds while still allowing the concrete to move as it expands and contracts.
Historically, the maximum recommended distance or spacing in feet between joints has been two to three times the slab thickness in inches. For a 6 in. thick slab, this recommendation yields a maximum joint spacing between 12 and 18 ft.
In hot weather, concrete may crack if joints are not cut within 6 – 8 hours after finishing. The rule of thumb is to cut joints as soon as the concrete is hard enough that the edges don't ravel (dislodging the aggregates) by the saw blade.
Expansion joints are indispensable for large rooms
If a room is more than 8 m wide and/or 12 m long, additional expansion joints are required. If a room is over 25 meters long, several expansion joints will be necessary.
These are provided to allow the expansion of pavement due to a rise in temperature with respect to construction temperature. The maximum spacing between the expansion joint is 140 m. Generally, tie bars are provided at the longitudinal joints.
All construction joints should be located within the middle third of spans of slabs, beams, and girders. Vertical support members that are still plastic must not be used to support beams, girders, or slabs.
Normally these spacing will be as mentioned below : For beams, these distances are 300 mm, 180 mm and 150 mm for grades of main reinforcement of Fe 250, Fe 415 and Fe 500, respectively. (ii) The maximum spacing between two secondary parallel bars shall be 5dor 450 mm or whichever is less.
Minimum spacing between reinforcement bars
The minimum spacing between two reinforcement bars should be at least equal to the maximum coarse aggregate dimension plus a margin of 5 mm.
NZS 3101 Part 1 is used by structural engineers to design concrete structures. When read along with Verification Method B1/VM1, it provides a means of complying with the performance requirements of New Zealand Building Code clause B1 Structure.
In residential concrete, 4 inches is the minimum thickness for walkways and patios. Garage slabs and driveways should be 5 to 6 inches thick if any heavy truck traffic is anticipated, otherwise 4 inches is adequate.