Crack control joints vary in size from oneeighth inch to onequarter inch in width and half inch in depth. In fact, conventional concrete masonry crack control measures, such as those in tek 102b, control joints for concrete masonry wallsempirical method ref. Thus, for a 10foothigh wall, control joints should be. This guide identifies the various classes of floors based on use, construction design details, necessary site preparation, concrete type, and other related materials. Most of the time we saw the joints using an early entry soffcut saw. Executive summary the concrete, geotechnical, and structural laboratory group is often asked to assist in locating joints in various concrete structures. Properly placed control joints will allow concrete to shrink, expand, and contract, reducing the tendency for it to crack. These joints will crack all the way to the bottom of the concrete. Guidance for spacing and location of control joints can be found in the national concrete masonry association ncma tek note 1002c. Space joints in feet no more than 23 times the slab thickness in inches. Where to locate control joints in concrete youtube. On changing from a saturated to a dry condition, average concrete will contract approximately 23 of an inch per 100 linear feet. Crack and joint repairs on industrial concrete floors and other areas pdf slab curling is caused by drying and shrinkage, which is a separate issue, and this article explains it well.
The concrete will be relatively watertight as long as cracking is controlled. If uncontrolled cracking of concrete flatwork is to be avoided, contraction joints must be carefully designed and properly constructed. For better crack control keep the maximum distance between joints in. I typically see control joint placement across the slab with the cuts forming squares that are 10by10 or 15by15feet wide. Refer to the table below for the recommended joint spacing. The maximum joint spacing should be 24 to 36 times the thickness of the slab. See that code for specific crack control reinforcement, joint spacing and joint detailing. 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. Maximum joint spacing calculator american concrete pavement.
In this paper, causes of concrete cracking are discussed, including tensile strength of concrete, temperature, shrinkage and creep effects. Wellplaced joints in concrete help channel cracking. Concrete control joints and proper spacing, depth and timing. Follow these recommended practices when installing concrete contraction joints. Jun 16, 2019 maximum joint spacing should be 24 to 36 times the thickness of the slab. Design and construction of joints for concrete streets. Concrete control joints are used to minimize and possibly prevent random cracking in concrete slabs and floors. Crack control joints should be placed at all reentrant corners and slab penetrations, and evenly spaced throughout the rest of the slab. In general, characteristics of the concrete slab surface and joint. The maximum joint spacing should be 24 36 times the width of the slab.
How to evaluate cracks at control joints or expansion. Tips for placing control joints in concrete slabs including information about depth, proper. Why concrete cracks concrete crack solutions ardex ireland. Rules for designing contraction joints for construction pros. It is best to cut joints as early as possible either while finishing with a concrete groover or within 618 hours after finishing with a concrete saw. For an unreinforced slab, control joints should be spaced in feet 2 to 3 times the slab thickness in inches. Crack control for fiber reinforced concrete structural. Control joints are not intended to stop cracking but rather control cracking.
Oct 10, 2016 in todays video i want to share with the proper spacing for concrete control joints. It will lead you to greater reinforcing for crack control. In other words, if the concrete does crackyou want. Conventional concrete masonry crack control recommendations, such as those presented in tek 102c, control joints for concrete masonry wallsempirical method ref. Contraction joints in concrete slabs the concrete network.
Joints should be spaced about 10 feet and a maximum of 15 feet. Joints joints in concrete pavements fall into two basic categories. As i recall the joint spacing is not to exceed 20 feet for partial joints half the reinforcement discontinued, and 30 feet for full joints all reinforcement discontinued. See the full blog post about concrete control joints at. Sawcut joints should be done within 4 to 12 hours after the concrete has been finished. Another approach would be to place control joints 20 to 25 ft 6 8m apart on the two long walls with the short wall between them. Spacing control joints concrete construction magazine. A slab without expansion joints will crack where the joint should have been. For example, in a 4inch 100 mm thick slab the joint spacing should be about saw cut tooled wall or column expansion joint material. Concrete with a higher slump may be used providing the mixture is specifically designed to produce the required strength without excessive bleeding and or segregation. Maximum horizontal spacing of control joints in unreinforced concrete masonry walls should be approximately 32 feet, but a length spacing to height of wall ratio is a better measure. Proper application of crack control measures, including control joints when required, can help ensure satisfactory performance of the concrete masonry.
Joints may also be sawed into the hardened concrete surface. The joints help the cracking when it will occur, and it usually starts at the top because concrete dries out more quickly at the surface than at the bottom. For example, in a 4inch 100 mm thick slab the joint spacing should be about saw cut tooled wall or column. Reported by committee 302 american concrete institute. As such, the prescriptive crack control recommendations detailed in table 1 increase the area of horizontal reinforcement and decrease the maximum control joint spacing of half high unit assemblies compared to full height unit assemblies. It forms a break between the concrete and other parts of a structure to allow movement without causing stress, which can lead to cracking. The cuts should be made at a predetermined spacing and only after the concrete has obtained sufficient strength but before internal cracking begins. Ryan indicates that contraction joints in concrete slabs on metal decks are of little value and that cracking.
Some designers recommend reducing joint spacings by about 20% in walls with frequent openings, such as doors and windows. Control of random cracking in concrete residential pavements. Avoid retempering with water prior to placing concrete. These joints allow cracking in a controlled area as the slab settles over time. In other words, if the concrete does crackyou want to have an active role in deciding where it. A further type, construction joints, used when there is a break in.
Saw cuts are a used to create control joints in concrete, which help control where cracking occurs due to shrinkage. Aug 28, 20 this is from a company, and is a longer read, but has a lot of good information and good illustrations. The fine crack shown in the photo of a concrete slab control joint just above is normal this crack would have occurred in a random pattern instead of along the control joint if this floor slab the same floor shown at the top of this page had been poured without any control joints. How to evaluate cracks at control joints or expansion joints. See table 2b for horizontal reinforcement spacing translating to 0. For a six inch thick slab, the maximum joint spacing should be limited to 12 to 15 feet. Apr 03, 2018 i typically see control joint placement across the slab with the cuts forming squares that are 10by10 or 15by15feet wide. The reader is encouraged to refer to that tek for other pertinent information such as construction details and location of control joints. These cracks can be avoided by placing a control joint at the interior corner and a second control joint 20 ft. Concrete contraction joints how to minimize cracking in. If the spacing between these control joints is larger, even if the concrete follows the control joint pattern, you end up with extremely wide joints that become harder to fill and maintain. In a 4 thick slab the joint spacing should be 10 feet. Joint spacing in plain jointed concrete pavements, the joint is designed to provide a plane of weakness that will control the formation of transverse cracks.
Construction joints separate adjacent placements of concrete to make l a r ge pours manageable. When slabs are placed on problematic subbases with risks of nonuniform support or consist of moderate to high shrinkage concrete or joint spacings exceed 15 feet. Placing joints in concrete flatwork why, how, and when. When walking around town, inspect concrete slabs for cracking. Crack control measures for concrete masonry veneers are similar to those for other concrete masonry walls. In general, use concrete with a moderate slump up to 5 inches 125mm. Thats why theyre called control joints, because theyre controlling or at least trying to control where the cracking is going to happen.
Contraction joints wall contraction joints often are made by fastening projecting strips inside forms to create narro w g r ooves in the concrete figure 1. Joint spacing for concrete structures bureau of reclamation. How to reinforce concrete slab on ground to control cracking. Concrete is placed at a moderate slump up to about 5 inches 125 mm and excessive water is not added at the jobsite prior to placement. As previously indicated, establishing slab joint spacing, thickness, and. Two rules that will help when preplanning control joints. Joints in concrete slabs can be created by forming, tooling, sawing, and. An article published in concrete constructionaugust 1999 called let it crack, by j. With option 1, we tell the slab where to crack and widths of contraction joints or cracks in the joints are largely controlled by the joint spacing and concrete shrinkage. Online learning aci university on aci control joints.
The following recommended practices should be observed. It is important to provide sufficient control joints so that the movement occurs at the joint rather that midway between the control joints. Control joints contraction joints are formed, sawed, or tooled grooves which weaken the concrete so it cracks at the joint. Control joint spacings are based on the use of horizontal reinforcement having an equivalent area of no less than 0. Causes of cracking concrete can crack due to a number of causes.
Joints must be carefully designed and properly constructed if uncontrolled cracking of concrete flatwork is to be avoided. Installing joints can dictate where a crack occurs to help maintain the appearance of a concrete slab. Table 1 from ncma tek note 102c describing recommended control joint spacing for typical concrete block masonry assemblies. Concrete contractors will often say, there are two types of concrete. In other words, for a 4inch slab, space the joints 8 to 12 feet apart. Be active in deciding where control joints will be placed control joints are planned cracks. If the control joint is not deep enough, the concrete can crack near it instead of in it see figure 4. We typically use wwr for manholes barrels as the higher yield strength and closer wire spacing helps flexure and crack control. Joints are commonly spaced at distances equal to 24 to 30 times the slab thickness. Contraction joints in concrete slabs are placed to control cracking. Place vertical expansion joints 12 inch in width at max intervals of 90 feet throughout the length of retaining walls and fill with expansion joint material. Shrinkage control joints must be at a maximum of 6 m spacings to create bays.
Founded in 1904 and headquartered in farmington hills, michigan, usa, the american concrete institute is a leading authority and resource worldwide for the development, dissemination, and adoption of its consensusbased standards, technical resources, educational programs, and proven expertise for individuals and organizations involved in concrete design. A crack next to a tooshallow joint crack control joints should be placed at all reentrant corners and slab penetrations, and evenly spaced throughout the rest of the slab. Here you will learn how to properly install and where to place control joints in all types of concrete flatwork to reduce the chances of cracking. For straight solid walls, the spacing between control. Control joint layout design ideas for concrete patios. When using joint groove for contraction joints, the joint should be a minimum depth of. Cracking destroys the look of the concrete as well as reduces the life of the concrete slab. Control joints for concrete masonry walls empirical method 2010. Proper joint spacing and depth are essential to effective control of random cracking. What is the proper concrete control joint spacing youtube. This tool provides an estimate of the maximum allowable joint spacing based on the slab thickness and the subgradesubbase used, two of the variables with the most prominent effect on joint spacing requirements. Contraction joint spacing for unreinforced concrete linings used by. This tek supplements tek 102b control joints for concrete masonry walls empirical method ref. As mentioned in the expansion joints discussion, the design of control joint spacing and location is the responsibility of the designer.
Read more on lowshrinkage concrete mixes in the concrete mix design section. A guide to the minimum reinforcement used in slabs for different conditions is provided in as36002 sections relating to crack control for shrinkage and temperature effects. Ive installed thousands of lineal feet of control joints in my concrete floors. These joints accommodate the movement caused by temperature changes and drying shrinkage. Contraction control joints are placed in concrete slabs to control random cracking. By weakening the plane at the joint, it allows the concrete to crack into that joint, ralston adds. Apr 15, 2014 concrete slabs have a tendency to crack duration. Note that crack control considerations for concrete masonry veneers differ from the guidance presented below. Contraction joints may be tooled into the concrete surface at the time of placement. Joint spacing that is greater than 15 feet requires the use of load transfer devices.
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. Often times people dont put their cuts in the proper locations and rather decide to put them wherever looks. Concrete control joints proper spacing, depth and timing explained one thing that i was taught in my years as a concrete finisher is that there are two things in life that are certain, the first is of course death and the second is concrete is going to crack. Maximum spacing for control joints in concrete patio slabs design tips and. The spacing is highly dependent on the concrete mixs shrinkage potential. Constru c tion joints are commonly located to coincide with contraction or expansion joints. They do so by putting in control joints, sometimes referred to as. Recommended crack widths are presented along with design methods for sizing reinforcement to control crack widths. If joints are spaced to far apart uncontrolled cracks can occur between the control joints. These requirements on common slab formats are given in table 1.
Control joints, expansion joints and cold joints in concrete. The length to width ratio of bays between shrinkage control joints, or between shrinkage control joints and a free joint. Concrete control joints how to minimize cracking in. For standard reinforcing bar sizes, horizontal reinforcement spacings up to 48 in. The width of a concrete slab control joint is the same as the control joint insert 14 to 12 in width or of the veetrowel about 38 wide, or of the saw blade used to make the cut after the concrete has hardened typically about 18. When no joint reinforcing is used, national concrete masonry association ncma tek 53, design of concrete masonry for crack control, recommends spacing control joints in straight wall sections without openings no farther apart than twice the height of the wall, 40 feet maximum. Since it is a given that most concrete will crack, contractors like to control where it is going to crack. Longitudinal joint spacing on twolane and multilane concrete pavements typically is about 10 to ft 3. Ive been in the concrete floor business for over 30 years. A concrete expansion joint or control joint is a gap which allows the concrete to expand and contract aswhen the temperature changes. Control joints are planned cracks which allow for movements caused by temperature changes and drying shrinkage.
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