Microcracking is a technique used to improve the performance of cement treated base. Cement treated base that is not microcracked has a tendency to form what is called block cracking. These large block cracks can be mitigated by microcracking after a short curing period by creating a network of finer cracks that will not become larger.
Typically an agency building a road with cement treated base will prescribe a 7-day unconfined strength (UCS) target to obtain the correct balance of resistance to cracking and strength. More cement will increase the strength of cement treated base but may not necessarily improve the performance of the pavement due to reflective cracking.
Implementation of microcracking will allow the roadway manager to direct larger UCS target strength target while not sacrificing performance. For cement treated base without microcracking typical 7-day UCS target strengths range from 200 to 350 psi. With microcracking 7-day UCS target strengths typically could range from 350 to 500 psi or higher.
The aim of microcracking is to create a network of finer cracks that relieves the stress on the the initial cracks formed during construction and mitigates the formation of larger cracks and reflective cracking.
What is microcracking?
24 to 72 hours after final grading and water curing, microcracking is typically performed making several passes by using the same 10 to 12 ton steel wheel vibratory roller that was used for to achieve compaction. Since cement treated base is sensitive to weather conditions the time range should be lengthened for cooler conditions and small end of the range time should be used for hotter conditions. The microcracking technique was developed by the the Texas Department of Transportation and the Texas A&M Transportation Institute and details are available in Technical Report 0-4502-1.
Tarrant County put microcracking to the test on Ottinger Road. Sections were selected to be microcracked and not microcracked. The difference is obvious.
No Microcracking
