1. Re Entrant Corner Crack Filler
2. Reentrant Corner Check
3. Reentrant Corner Irregularity Example
4. Reentrant Corner Crack
5. Reentrant Corner Definition

The first crack of all the above beams was always initiated from the re-entrant corner. Even though using different concrete types, the DEB-19 and DEB-18 exhibited similar crack patterns and failure modes. The DR had the ability to resist the diagonal crack from the re-entrant corner, but then the crack. Re-entrant corners are corners that point into a slab. For example, if one were to pour concrete around a square column, you would create four re-entrant corners. Because the concrete cannot shrink around a corner, the stress will cause the concrete to crack from the point of that corner (See Figure 1). May 18, 2017 Re-entrant corner cracks are especially prevalent in concrete slabs that are relatively thin in comparison to their plan size. In this article, I will focus on re-entrant corners in slabs-on-grade. Why Cracks Form in Concrete Structures. Concrete provides structures with strength, rigidity,. At re-entrant or internal corners, two strips, minimum 2 m in length, of 3–L8TM or one strip of 3–L11TM (or 3-N12 bars) must be placed diagonally across the corner in accordance with Open link in same page Figure 3.2.5.1.

What Causes Concrete to Crack?

Posted By:Dynamic Concrete Pumping , Date: May 22, 2019

Concrete is a miraculous substance. Extremely hard and durable, it is an ideal material for construction, whether you are building the foundation of an apartment building or an outdoor pool. One drawback of concrete is that it has a tendency to crack. But why does concrete crack — and what can you do about it?

There are actually several common causes of concrete cracking. Here is a list of some of the basic types of concrete cracks, what causes concrete to crack in these ways, and what you can do about it.

Types of Concrete Cracks

• Shrinkage: The most common type of cracking in concrete, especially early on, is shrinkage. Concrete is a mix of cement and water. As the concrete hardens, which is caused by the cement and water forming bonds, some of that water escapes through evaporation. This reduces the size of the concrete slab, and since concrete is a very hard, tightly bound substance, this loss of material creates stress. This stress can lead to cracks in the concrete. Solutions to shrinkage cracks include reducing the amount of water in your concrete mix and cutting control joints in the slab so that if it does crack, it cracks along predetermined lines that do not significantly affect the integrity of the concrete.
  
• Re-Entrant Corner Cracks: Re-entrant corner cracks are a special kind of shrinkage that occurs when concrete is poured around a column with corners. They can also happen when the concrete is poured around a rounded object, like a manhole. When shrinkage takes place, the concrete cannot shrink evenly around the object. Instead, long cracks can result, radiating from said object. Properly cut control joints are the generally accepted method for warding off this issue.
  
• Expansion Cracks: In hot weather, bonds within the concrete can weaken and the concrete can expand, creating stress. If the concrete does not have room to expand, it will crack. You can prevent this by adding an expansion joint made of a compressible material, like tar-impregnated cellulose fiber, to allow some “give” in the concrete.
  
• Heaving Cracks: In very cold weather, the freeze and thaw cycle may cause the concrete to lift and heave, resulting in cracks. Avoid this by paving over soil that drains away moisture and will “give” with the slab, rather than tightly packed, unyielding soil, and by not pouring too close to large tree roots.
  
• Settlement Cracks: These usually occur if the concrete has been poured over ground that is not well-suited to hold it. Examples include soil where a nearby tree has just been removed and the roots are decomposing, or where a utility trench has been refilled but not properly compacted.
  
• Excessive Weight Cracks: Concrete, like anything else, has load limits, although they can be very high. If the weight you put on concrete exceeds this limit, expect cracks to form. This is rarely a problem in residential situations, but if you are working with very heavy equipment or other items, you may wish to verify that your concrete can bear it.
  

For more valuable tips on pouring concrete effectively, contact Dynamic Concrete Pumping today.

DIY Concrete Guide: There are two guarantees when it comes to a concrete driveway or slab. Spellforce 2 gameplay. It will get hard and it will crack. Concrete shrinks as it dries out and when it cools during temperature changes. When control joints are not provided or cut into the slab, uncontrolled shrinkage cracks occur at fairly predictable intervals. Because these cracks are predictable, they can be controlled with pre-planned joints. Preventing cracks with proper jointing and good construction practices, and adequate reinforcing is far less expensive than making repairs later. There are three different types of joints used in slab on grade construction: Contraction or “Control Joints”, Isolation or “expansion Joints”, and “Construction Joints”.

Control Joints (Contraction Joints)
Control Joints (Contraction Joints) are formed, sawed, or tooled grooves which weaken the concrete so it cracks at the joint. These joints accommodate the movement caused by temperature changes and drying shrinkage.

Joint Spacing is Critical – As shown in the drawing above an un-jointed slab will usually develop a similar pattern of uncontrolled cracking cause by shrinkage. The patterns will change depending on the dimensions of the slab, (including depth), the psi of the concrete, curing, and the temperature extremes the slab is exposed to especially during the first few hours and days after the pour. If joints are spaced to far apart uncontrolled cracks can occur between the Control Joints.

Re Entrant Corner Crack Filler

Two rules that will help when pre-planning control joints.

Reentrant Corner Check

• Rule #1 – Keep joints as square as possible.
• Rule #2 – In order to prevent intermediate cracking, space joints (in feet) no more than 2 – 3 times the slab thickness (in inches). Refer to the table below for the recommended joint spacing. The thicker the slab the farther apart these joints can be place without violating Rule #1.

Example:
A sidewalk that is 4” thick but only 3’ wide using only the chart below you would cut joints 8’ – 12’ apart, however if you did this it would develop uncontrolled cracks approximately every 3’ – 4’. So Rule #1 (Keep Joints as square as possible) first then if it applies rule number 2.

Reentrant Corner Irregularity Example

Joint Depth is Critical – It is extremely important for the joints to be cut at least ¼ of the slab depth. This will weaken the slab along this joint line and let the slab crack at this controlled point. If the depth is not deep enough the crack may not follow the desired path along the joint. Refer to the table below for the recommended joint depth.

DIY Concrete Guide: Cut Joints A.S.A.P.
Waiting to long to cut joints is a rookie mistake. Waiting until the next day is normally to long in the Florida Climate. In hot weather, concrete may crack if joints are not cut within 6 – 8 hours after finishing. The ruler of thumb is, cut joints as soon as the concrete is hard enough that the edges don’t ravel (dislodging the aggregates) by the saw blade. With conventional wet saws, you can usually start to cut joints 4 – 8 hours after finishing. Using a long-handle lightweight dry-cut saw will allow joints to be cut almost immediately after finishing. The saw is designed to let the operator cut up to 30’ without walking on the slab.

Reentrant Corner Crack

Re-entrant Corners Should be Avoided
Re-entrant corners will usually cause cracking. Proper planning of the joint pattern to eliminate re-entrant corners will correct this problem. Even though you isolate the column box as shown here the slab will still develop uncontrolled cracks. In most cases, as shown here, the simplest way to avoid the re-entrant corner may be to rearrange the joint pattern.

DIY Concrete Guide: Isolation Joints
Install Isolation joint material anywhere concrete will come into contact with existing slabs, steps or buildings. The Isolation joint should reach the bottom of the slab, this ensures the new slab will be separated from existing structures. If there is no isolation joint as the new slab cures it will shrink slightly, if the existing slab which is not moving is not isolated the new slab will crack as it pulls away from the existing slab. When installing use a chalk line to mark the top of the isolation joint. Secure the isolation joint to the existing slab prior to the pour, or use a chalk line to mark the wall, then as you start the pour, shovel some concrete up against the isolation joint to hold it in place.

Reentrant Corner Definition

DIY Concrete Guide: Construction Joints
Keyed Construction Joints provides for the transition from one days pour to the next. When concrete placement is stop at the end of the day, a construction joint must be formed. Keyed Construction joints are also used when pouring adjacent paving lanes and load transfer is important, such as with heavy forklifts. If the ends of the slab are not supported by the keyed construction joint, cracking may occur 1’ – 2’ from the joint. It is critical that the key measure ¼ of the slab thickness. A beveled wood strip which attaches to the side of the form can be used for the key (See example Below). Butt joints (Smooth Face) are satisfactory if no load transfer is required.