Dealing with Concrete’s Shrinkage and Cracking Problem

Most material, including concrete, shrinks as it dries.  The Portland Cement Association (PCA) points out that the most common amount of shrinkage is about 1/16 of an inch in a 10-foot length of concrete.  To alleviate the problem, joints are placed in concrete pavement and floors “to allow the concrete to crack in a neat, straight line at the joint, where concrete cracks due to shrinkage are expected to occur.”   Likewise expansion joints are placed in bridges, concrete walls and other structures to allow for shrinkage and to control cracking.   

To help move and place concrete efficiently, concrete specialists add more water to the mix than what is strictly necessary to hydrate the cement materials.  Once the concrete is placed, the excess water begins to separate from the hardening concrete, which results in a loss of volume that causes the concrete to shrink.  As the concrete’s reinforcement or base friction works to restrain it, the tensile stresses in the slab cause the cracks.   

Since shrinking is one of the inherent properties of concrete, it is impossible to totally eliminate cracking but it can be controlled.  This is the job of concrete contractors and engineers who strive to understand and address the volume change that takes place in the concrete in order to reduce the amount of shrinkage.  

The PCA explains that, “The shortening of concrete slabs can be caused by temperature decreases or moisture loss. These two causes are also related to curling and warping of slabs, respectively. Curling is the deformation of the slab due to a difference in temperature between the surface and the bottom of the slab (temperature gradient).  Slab “warping” is the deformation of the slab surface profile due to a difference in moisture between the surface and bottom of the slab (moisture gradient),” 

To help solve the shrinkage problem, contractors take care to use the proper concrete mix design that will require the least amount of water as well as use the largest size of aggregate appropriate to the job.  Contractors especially watch for fluctuating temperatures during the first 24 hours after the concrete is placed.  

The Conco Companies are a leading supplier of concrete services for the Western U.S. and got our start in the Bay Area in 1959 by offering clients the best value on a wide range of concrete services and products.  Since that time, we have taken a leading role as one of the top concrete contractors in the region. Our offices serve California, Colorado, Oregon, Washington and Nevada.

Sources:

concretenetwork.com/concrete/concrete_cracks/preventing_concrete_cracks.htm

cement.org/cement-concrete-applications/cement-and-concrete-basics-faqs/lists/technical-information/concrete-cracking