Concrete construction contractors in Michigan need to overcome three key challenges to successfully use concrete in a commercial building project — cracks from shrinkage, the curling of slab edges, and delamination of the concrete surface.
Shrinkage is one of the most common issues faced by concrete construction contractors. Concrete is made of water, cement, and sand and shrinks as it cures.
If it was allowed to shrink freely, it wouldn’t crack. However, it is often restrained by additional forces like steel reinforcements or subgrade friction. As the concrete cures, it shrinks until its tensile strength is equal to that of whatever is restraining it. Shrinkage cracks develop wherever the tension occurs.
Shrinkage-compensating concrete addresses this problem by incorporating an expansion mechanism that counteracts the force of shrinkage. Concrete construction contractors can formulate a concrete mix that builds in an expansion capability slightly greater than the shrinkage force, which usually solves the problem and prevents the development of shrinkage cracks.
A concrete slab contains water to allow the convenient placement and finishing of the slab. Excess water may rise to the surface of the slab and evaporate. Alternatively, the force of gravity might cause it to descend to the subgrade.
Concrete floor slabs are typically placed on a vapor barrier, trapping water under the slab. The water on the top surface of the slab usually dries at a faster rate than the water underneath. As a result, the slab edges may begin to curl upward.
There are a couple of approaches used by concrete construction contractors to eliminate this problem. One is to use special shrinkage-compensating concrete, which balances the contraction of the top portion with the expansion of the lower surface.
Another solution is to try and reduce or eliminate joins between the concrete slabs, essentially creating a design with as few edges as possible. By its very nature, reducing the number of edges reduces the prevalence of edge curling.
When a concrete slab is laid, the cement and aggregate solids begin to settle. Excess water and air trapped in the concrete mix are displaced and rise to the surface. As the concrete hardens, the air and water create gaps in its structure. These weak spots can detach from the concrete surface with minimal pressure.
To prevent delamination, a contractor must wait to finish the concrete until any water in the slab has bled off. However, timing this can be more of an art than a science.
The stickiness of the concrete mix, the thickness of the slab, the nature and quality of the subgrade, and differences in temperature of the concrete and its surroundings can all affect how quickly the water bleeds off and when the finishing can begin.
Fixing delamination may require the concrete construction contractor to break the slab down until the concrete is structurally sound again, before relaying and refinishing.
Merlo Construction has been working on commercial construction projects in the Michigan area for over 25 years. If you would like professional guidance on how to work with concrete, please contact us.