Why Concrete Shrinks and How it is Addressed

All concrete experiences some degree of shrinkage, which can result in cracks in the concrete.  Shrinkage may also affect the long-term strength and durability of the concrete.  Even though concrete contractors know that shrinkage is caused by a loss of volume that occurs in different stages of the process, it is still challenging to prevent or alleviate shrinkage, and thereby the cracking.  It is especially an important consideration when constructing industrial floors or pavement.

Since shrinking is one of the inherent properties of concrete, it is impossible to totally eliminate cracking but it can be controlled.  This is why contractors and engineers work to understand and address the volume change in concrete to reduce the amount of shrinkage.

According to the Portland Cement Association, “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 quickly move and place concrete, it is mixed with more water than is absolutely necessary for hydrating the cement materials.  Once the concrete is placed, the excess water separates from the hardening concrete, which results in a loss of volume that causes the concrete to shrink.  The concrete’s reinforcement or base friction works to restrain it, which in turn can create tensile stresses in the slab causing cracks. 

In an effort to prevent the shrinkage, one of the things that contractors watch out for is fluctuating temperatures during the first 24 hours after placement.  Also considerable care is taken to use the correct concrete mixture design so that the least amount of extra water is added and the largest size of aggregate is used.  All of this works toward reducing shrinkage.

*http://www.cement.org/for-concrete-books-learning/concrete-technology/focus-on-floors/concrete-shrinkage

 

Conco is one of the leading commercial concrete contractors in Sacramento and has been delivering first-rate services in the area since 1959.  We are experts at creating cost-effective solutions that take advantage of the most up-to-date techniques.  Our concrete services include commercial, educational, parking and other construction development as well as public works projects.