Use of Microcracking to Reduce Shrinkage Cracking in Cement-Treated Bases (05-0805)**
Stephen Sebesta, Texas A&M Transportation Institute
Shrinkage cracking occurs in cement-treated bases due to desiccation and cement hydration; eventually these cracks start to reflect through the pavement surfacing. While initially considered cosmetic in nature, these cracks open the pavement to water infiltration and increase the likelihood of accelerated pavement distress. Although numerous options exist for minimizing the amount of reflective cracks that appear, this paper focuses on the performance of controlled test sections utilizing a promising approach termed “microcracking.” The microcracking concept can be defined as the application of several vibratory roller passes to the cement treated base at a short curing stage, typically after one to three days, to create a fine network of thin cracks. In addition to the microcracked test sites, the contractor constructed moist cured, dry cured, and asphalt curing membrane sites for comparison. Researchers used falling weight deflectometer (FWD) tests to control the microcracking process, periodic crack surveys to monitor crack performance, and FWD tests through time to track base moduli. Microcracking proved quite effective at reducing shrinkage cracking problems in the base; applying the procedure with three passes of the roller after two to three days curing resulted in the best performance. Additionally, researchers observed that without microcracking, excessively high cement contents result in problematic cracking in the base even if cured according to good construction practice. Microcracking did not result in pavement damage or diminished in-service modulus; thus, microcracking should be considered a viable and inexpensive option to incorporate shrinkage crack control into construction of cement-treated bases.