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Crack Development in Ternary Mix Concrete Utilizing Various Saw Depths (TR-587)

3 photos showing different saw cut depts

Joints with different sawing depths in the test sections

Researcher(s)

Principal investigators:

Student researchers:

Project status

Completed

Start date: 03/01/08
End date: 02/28/09

Publications

Report: Crack Development in Ternary Mix Concrete Utilizing Various Saw Depths (3.5 mb pdf) February 2009

Tech transfer summary: Effects of Early Entry Sawing on PCC Cracking (304 kb pdf) Feb 2009

Sponsor(s)/partner(s)

Sponsor(s):

About the research

Abstract:

Early entry sawing applies sawing earlier and more shallowly than conventional sawing and is believed to increase sawing productivity and reduce the cost of the joint sawing operations. However, some early entry sawing joints (transverse joints) in Iowa were found to experience delayed cracking, sometimes up to 30 days. A concern is whether early entry sawing can lead to late-age random cracking. The present study investigated the effects of different sawing methods on random cracking in portland cement concrete (PCC) pavements. The approach was to assess the cracking potential at sawing joints by measuring the strain development of the concrete at the joints using concrete embedment strain gages. Ten joints were made with the early entry sawing method to a depth of 1.5 in., and two strain gages were installed in each of the joints. Another ten joints were made with the conventional sawing method, five of which were sawed to a depth of one-third of the pavement thickness (3.3 in.), and the other five of which were sawed to a depth of one-quarter of the pavement thickness (2.5 in.). One strain gage was installed in each joint made using conventional sawing. In total, 30 strain gages were installed in 20 joints. The results from the present study indicate that all 30 joints cracked within 25 days after paving, though most joints made using early entry sawing cracked later than the joints made using conventional sawing. No random cracking was observed in the early entry sawing test sections two months after construction. Additionally, it was found that the strain gages used were capable of monitoring the deformations at the joints. The joint crack times (or crack initiation time) measured by the strain gages were generally consistent with the visual observations.