Uncontrolled shrinkage cracking refers to cracks in concrete’s structure due to tension failure caused by internal or external restraints during moisture reduction, carbonation, or both. Because concrete expands and contracts with moisture/temperature changes and because it also deflects depending on slab size, reinforcing, load, and support conditions. These factors can lead to uncontrolled cracking if the proper design & joint details are not addressed. The following jointing systems reduce uncontrolled cracks:
ISOLATION JOINTS: Joints that allow horizontal and vertical movement.
CONTRACTION JOINTS: Joints that allow horizontal movement of the slab and induce controlled cracking.
CONSTRUCTION JOINTS: Joints that are stopping points in the process of construction (also referred to as bulkheads).
Some causes for uncontrolled shrinkage cracking might be: An Improper jointing system, subgrade not properly prepped and compacted, jobsite addition of excessive amounts of water, improper finishing procedures, contraction joints not completed in a timely fashion, inadequate curing. Below are some ways to reduce the likelihood of such problems:
-Adequate subgrade preparation, keeping in mind loading conditions of the slab during its life. Includes appropriate thickness of sub base and proper compaction
-Utilize the proper mix design for the slab application
-Assure proper design: concrete thickness, joint spacing, joint depth, fiber reinforcement, structural reinforcement, appropriate timing of installing contraction joints.
-Implement curing as soon as possible to ensure performance properties fully develop