How to cut control joints in concrete slab?
Tips for Making Control Joints
- Do not twist the saw blade.
- Do not let the blade spin in the cut as this will increase wear on the bond.
- When cutting concrete with heavy rebar, use blades with soft metal segment bonds.
- Always use the required PPE (personal protection equipment).
What are the different types of concrete joints?
Types of Joints in Concrete Slabs
- The Purpose of Joints in Concrete Slabs. As concrete moves, if it is tied to another structure or even to itself, we get what's called restraint, which causes tensile forces ...
- Decorative Joints. A cleanly sawed joint detracts very little from the appearance of a stamped slab. ...
- Jointless Slabs. ...
- Load Transfer
Can joint compound be used on concrete walls?
Simply so, can joint compound be used on concrete walls? Apply joint compound to the concrete seams, sanding between coats as necessary, to achieve a feathered out surface, flush with the concrete surface, free of ridges, tool marks and sanding grooves. Apply a final thin coat of compound to the entire concrete surface.
What are concrete joints used for?
Concrete joints are used to compensate when concrete expands or shrinks with changes in temperature. Concrete joints are normally used to prevent cracks when the concrete shrinks by creating forming, tooling, sawing, and placing joint formers.
What is the difference between a control joint and an expansion joint?
In building materials, a control joint is used to control cracking while an expansion joint is designed to handle structural movement.
Do you need control joints in concrete?
Concrete expands and contracts with changes in temperature and moisture. If not properly controlled, cracks can begin to appear. Placement of concrete control joints and expansion joints are crucial when designing and pouring concrete slabs and sidewalks.
What is the difference between a construction joint and a control 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 a control joint construction?
A control joint is a continuous vertical joint filled with mortar, but with a bond breaker on one side so that tensile stress cannot develop across the joint. If control joints are not provided, a concrete masonry wall may crack as it shrinks over time.
How big can a concrete slab be without control joints?
Usually, expansion joints should be no farther apart than 2 to 3 times (in feet) the total width of the concrete (in inches). So for a 4 inch thick concrete slab, expansion joints should be no more than 8 to 12 feet apart.
What happens if you don't put expansion joints in concrete?
Concrete expansion joints give the slabs just enough room to move which helps prevent cracks & buckling. Without these joints, even a little movement creates pressure and stress on the concrete. Eventually weak spots can crack or buckle.
Where do you cut control joints in concrete?
Cut joints 25% of the depth of the slab. A 4" thick slab should have joints 1" deep. Groover tools cut joints in fresh concrete. Saw cutting cuts joints as soon as the concrete is hard enough that the edges abutting the cut don't chip from the saw blade.
What is a control joint in masonry?
Control joints in masonry are vertical weak planes intentionally built or cut into masonry to control where cracking occurs. Control joints should be installed in any masonry assembly that expected to experience net shrinkage over time. Usually, we think of control joints in concrete masonry (CMU).
What are the joints in concrete called?
In slabs, there are three types of joints: Isolation joints (also sometimes functioning as expansion joints) Construction joints (which can also function as contraction joints) Contraction joints (also sometimes called control joints)
How do you fill a concrete control joint?
1:135:31How to fill a crack or joint in an indoors concrete floor - YouTubeYouTubeStart of suggested clipEnd of suggested clipA pancake mix type density. That allows it to flow into the cracks. And the joints in that area byMoreA pancake mix type density. That allows it to flow into the cracks. And the joints in that area by the way you can also use this material to fill in cracks.
What happens if you don't cut concrete?
Late sawing can result in random concrete cracks. Shallow cracks aren't sufficient to prevent uncontrolled cracking while deep cuts are excessively labor intensive and undermine the aggregate interlock in the concrete.
Where would you find a control joint?
Control joints are provided in concrete pavements, slabs, walls, floors, dams, canal linings, bridge, retaining walls etc. When concrete is placed, due to shrinkage, creep and thermal movement concrete tends to reduce in size due to which small cracks are formed in the concrete at weak zone.
Do concrete driveways need expansion joints?
Concrete expansion joints are important for your sidewalk or driveway. Keeping your joints watertight will prevent moisture from seeping under concrete pads and causing them to heave or sink.
Do you need expansion joints in concrete sidewalk?
A.: According to several industry sources, expansion joints, even at 50-foot intervals, are not necessary for the sidewalk project. Long stretches of concrete do not require intermediate expansion joints.
Why joints are necessary in concrete structures?
Joints allow one concrete element to move independently of other parts of the building or structure. Joints also let concrete shrink as it dries—preventing what's called internal restraint. Internal restraint is created when one part of a slab shrinks more than another, or shrinks in a different direction.
Do I need expansion joints in concrete garage floor?
Many people understand that wood shrinks and expands as temperature and humidity ebb and flow through the year. But the same thing happens with concrete. That's why it is necessary to include expansion joints along the edges of the concrete garage floor as well as around posts or other protrusions in the slab.
Why do concrete joints crack?
Often times people think that concrete joints are put in to prevent it from cracking but truth be told, they are simply to create a weak point so the concrete can crack in a more controlled manner. As concrete goes through it’s curing process it shrinks as much as 1/2″ over 100′ which of course will cause it to pull apart resulting in hairline cracks. It is also important to know that the more water used in the placing process, the more likely it is to shrink and crack.
What angle should I use for control joints?
Another very important part about figuring out where your control joints are going to is and outside 45 degree angle (or any sharp angles for that matter). Often times this is going to be the very first point that you will run into concrete starting to crack. It is very important to get your cuts put on your 45’s either while finishing or as soon as you possibly can afterwards. Often times I have even returned early when saw cutting my joints just to cut my corners and then came back a little later to do the rest.
How soon after a concrete saw can you cut off a joint?
Here is a quick recap of what you need to know. It is best to cut joints as early as possible either while finishing with a concrete groover or within 6-18 hours after finishing with a concrete saw. Always cut off of your corners as soon as possible because this is usually the first place cracking starts.
What happens if you don't cut your concrete?
If this step is not done properly then you are essentially wasting your time. You will find that your concrete is still going to crack wild in an uncontrolled manner. To plan out where you are going to puts your cuts it is going to be important to know the depth of your concrete slab.
What happens if you cut concrete too early?
If you cut to early though you can cause your concrete to ravel on the edge of the cuts but if you cut to late you will end up with uncontrolled cracking. There are many different factors that come in to play when it comes to timing of administering cuts such as. Tools used to cut concrete. Blade type. Saw speed.
Do you need to score concrete in between cuts?
If you plan to put in decorative concrete cuts the you simply just need to score the surface in between all of your regular cuts.
Can you cut concrete with a saw?
When you are cutting your floor with a concrete saw it is very important to make sure that you are not moving your saw as faster than the blade can cut. So always be sure to keep it in the back of your mind to check your blade depth regularly, if you can’t see it from standing behind it then either have someone watch it or continuously glance around at it.
What is the purpose of different joints in concrete?
Different joints in concrete slabs all have the same bottom-line purpose of preventing cracks.
Why do we use joints in concrete?
Joints in concrete can serve both to prevent cracking and as a decorative element. Concrete is not a ductile material—it doesn't stretch or bend without breaking. That's both its greatest strength and greatest weakness. Its hardness and high compressive strength is why we use so much of it in construction. But concrete does move—it shrinks, it ...
What are the different types of joints in concrete?
Different joints in concrete slabs all have the same bottom-line purpose of preventing cracks. In slabs, there are three types of joints: Isolation joints ( also sometimes functioning as expansion joints) Construction joints (which can also function as contraction joints) Contraction joints (also sometimes called control ...
What causes concrete to crack?
As concrete moves, if it is tied to another structure or even to itself, we get what's called restraint , which causes tensile forces and invariably leads to cracking. Restraint simply means that the concrete element (whether it's a slab or a wall or a foundation) is not being allowed to freely shrink as it dries or to expand and contract with temperature changes or to settle a bit into the subgrade (see Subgrades and Subbases ).
What is joint free slab?
A recently introduced product from Australia, the Joint Free Slab, induces narrow cracks on a 1-meter-square grid by positioning crack inducer tubes on the subbase before placing the concrete .
How does aggregate interlock work?
Aggregate interlock is created within an activated contraction joint. The broken edge below the joint is irregular enough that the aggregate that projects locks into the other side. If the joints are spaced close together (or the concrete doesn't shrink much), so that they don't open too much, aggregate interlock can be effective. For heavier loads, though, use a mechanical shear-transfer method.
What is a K concrete?
Shrinkage compensating concrete (Type K), with an experienced contractor and designer, can allow a reduction or elimination of joints. Reinforcement (rebar or steel fibers) is placed and the concrete actually expands as it cures, resulting in tensioning of the steel. Eventually, the concrete shrinks back and behaves similar to a post-tensioned slab. Shrinkage compensating concrete has, however, resulted in some problems when improperly used. It requires knowledge of how much expansive cement to use and other factors. One company that has seen a lot of success with this is CTS Cement.
What is control joint filler?
Control joint fillers are flowable and easy to apply with consistency. SpecChem Concrete control joint fillers have quite a history. Joint filling products have evolved closely with the evolution of the warehousing and distribution industries, forklift and machinery technologies, and the technology behind the products and materials used to fill joints.
How much does it cost to fill a control joint?
On average, filling control joints costs approximately $2.00 per linear foot. Instead of comparing this to not filling the joints at all, consider the repair costs involved with not filling the joints initially. The repair costs involved with repairing damaged or spalled control joints can range from $5.00 to $10.00 per linear foot.
What is polyurea control?
Polyureas have a higher elongation, which helps resist tearing due to shrinkage and movement of the slab. They are also generally found in one-to-one ratio, easy-to-use options, often in cartridges for manual application or pumped with a dual component pump. Semi-rigid, polyurea control joint fillers, however, have several unique advantages ...
What is the best durometer for a control joint?
Durometer, or hardness, has become one of the key parameters in considering a proper control joint filler. A Shore A durometer of 80-85 offers the optimal hardness for transferring wheel loads across the joint while maintaining the flexibility that prevents the slabs from being welded together.
How long does concrete shrink?
And while most shrinkage occurs within the first year, a concrete slab can continue to shrink and move for years. Any interior concrete, anything from residential slabs to decorative applications to commercial and industrial floors will utilize control joints.
How long does it take for a control joint to open?
The key to a successful, long-term control joint application in today’s warehousing/distribution center floors is to give the slab enough time – generally 60-90-120 days – to maximize shrinkage, allowing joints to open, which minimizes the long-term potential for tearing.
What happens if the joint movement exceeds the capability of the joint filler?
Another key physical property is that if the joint movement exceeds the capability of the joint filler, the product, not the concrete, will tear cohesively or adhesively rather than delaminating the concrete itself. This tear is by design and does not constitute a failure of the joint filler.
What is concrete mixture?
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 . When shrinkage is restrained by contact with supporting soils, granular fill, adjoining structures, or reinforcement within the concrete, tensile stresses develop within ...
How many times should a contraction joint be spaced?
Joints are commonly spaced at distances equal to 24 to 30 times the slab thickness.
How long does it take to saw concrete?
For most concrete mixtures, this means sawing should be completed within the first six to 18 hours and never delayed more than 24 hours.
How deep should a concrete slab be for cracking?
Contraction/control joints must be established to a depth of ¼ the slab thickness (Figure 2). Proper joint spacing and depth are essential to effective control of random cracking.
Is concrete a compressive or tensile material?
While concrete is very strong in compression the tensile strength is only 8 to 12 percent of the compressive strength. In effect, tensile stresses act against the weakest property of the concrete material. The result is cracking of the concrete.
Is concrete cracked or uncracked?
The concrete has still cracked which is normal behavior, but the absence of random cracks at the concrete surface gives the appearance of an un-cracked section. Concrete slabs-on-ground have consistently performed very well when the following considerations are addressed.
Can steel reinforcement be used on concrete?
It is important to recognize that using steel reinforcement in a concrete slab actually increases the potential for the occurrence of random hair line cracks in the exposed surface of the concrete. The most widely used method to control random cracking in concrete slabs is to place contraction/control joints in the concrete surface ...
What are the details of a control joint?
Common control joint details are illustrated in Figure 3. The joints permit free longitudinal movement, and some also allow the transfer of lateral or out-of-plane shear loads. Although the details in Figure 3 show vertical reinforcement on each side of the control joint, walls that do not otherwise require vertical reinforcement will not require reinforcement at the control joints.
Where should control joints be located?
When required, control joints should be located where volume changes in the masonry due to drying shrinkage, carbonation, or temperature changes are likely to create tension in the masonry that will exceed its tensile capacity. In practice, this can be difficult to determine since some movements are reversible, quick or gradual, but several methods are presented in the following sections to provide guidance in locating control joints.
What is a movement joint?
Movement joints such as control joints are one method used to relieve horizontal tensile stresses due to shrinkage of the concrete masonry units, mortar, and when used, grout. They are essentially vertical planes of weakness built into the wall to reduce restraint and permit longitudinal movement due to anticipated shrinkage, and are located where stress concentrations may occur. A bond break is accomplished by replacing all or part of a vertical mortar joint with a minimum of a backer rod and sealant. This keeps the joint weather tight while accommodating small movements. Joint reinforcement and other horizontal reinforcement should be discontinued at control joints unless it is required for structural purposes, as it will act to restrain horizontal movement.
What is vertical reinforcement?
In walls containing vertical reinforcement, the cell adjacent to the opening is usually grouted and reinforced to provide solid support and additional strength for jambs. Using the same type of detail as for the unreinforced wall would require the control joint to cross the vertical reinforcement, thereby preventing movement and defeating the purpose of the control joint. However, if the opening is completely surrounded by reinforcement as shown in Figure 2c and 2d, the area around the opening is strengthened and control joints can be placed away from the opening.
How far past the vertical reinforcement is a lintel?
As an alternative to extending the lintel reinforcement a minimum of 12 in. (305 mm) past the vertical reinforcement adjacent to the opening (Figure 2c), joint reinforcement may be placed in the first two mortar joints above the opening and extended to the control joint on each side, or a horizontal bond beam could be used, as shown in Figure 2d.
What is the width of a crack in a concrete wall?
An engineered method is presented in TEK 10-3 Control Joints for Concrete Masonry Walls—Alternative Engineered Method, which is based on limiting crack width to 0.02 in. (0.51 mm), since water repellent coatings can effectively resist water penetration for cracks of this size. The engineered method is generally used only when unusual conditions are encountered such as dark-colored units in climates with large temperature changes.
What is a TEK in concrete?
This TEK focuses on non-structural cracking resulting from internal volume change of the concrete masonry. Potential cracking resulting from externally applied design loads due to wind, soil pressure, seismic forces, or differential settlement of foundations is controlled by structural design considerations not addressed here. Where external loads are an issue in combination with internal volume change, the design should consider the combined effects of these influences on cracking.
What is control joint?
Generally these joints are pre-defined in the drawings given by designer or architect. If not defined, they will be in a regular pattern or be an integral part of the architectural features. Control joints form a convenient point at which to stop concrete work at the end of the day. Control joints should never be formed in the middle of a bay.
Where is the control joint placed?
Control joint is placed at the location of highest concentration of tensile stresses resulting from shrinkage are expected:
Why are expansion joints needed in concrete?
Expansion joints are placed in concrete to prevent expansive cracks formed due to temperature change. Concrete undergoes expansion due to high temperature when in a confined boundary which leads to cracks. Expansion joints are provided in slabs, pavements, buildings, bridges, sidewalks, railway tracks, piping systems, ships, and other structures.
What are the characteristics of expansion joints?
Characteristics of Expansion Joints 1 Expansion joints permits thermal contraction and expansion without inducing stresses into the elements. 2 An expansion joint is designed to absorb safely the expansion and contraction of several construction materials, absorb vibrations, and permit soil movements due to earthquakes or ground settlement. 3 The expansion joints are normally located between sections of bridges, paving slabs, railway tracks, and piping systems. 4 The expansion joints are incorporated to endure the stresses. 5 An expansion joint is simply a disconnection between segments of the same materials. 6 In the concrete block construction, the expansion joints are expressed as control joints.
What is an expansion joint?
An expansion joint is designed to absorb safely the expansion and contraction of several construction materials, absorb vibrations, and permit soil movements due to earthquakes or ground settlement. The expansion joints are normally located between sections of bridges, paving slabs, railway tracks, and piping systems.
Why are expansion joints incorporated?
The expansion joints are incorporated to endure the stresses.
Why does concrete shrink?
When concrete is placed, due to shrinkage, creep and thermal movement concrete tends to reduce in size due to which small cracks are formed in the concrete at weak zone.