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| FHWA > Engineering > Pavements > Research > Concrete > FHWA-RD-02-083 > Chapter 4 |
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Highway Concrete Pavement Technology Development and Testing Volume II:Field Evaluation of Strategic Highway Research Program (SHRP) C-203 Test Sites (Freeze-Thaw Resistance)CHAPTER 4. CONCLUSIONS AND RECOMMENDATIONSField test sections were constructed during 1992 as part of the SHRP program investigating the frost resistance of concrete. The test sections had three general purposes:
FREEZE-THAW RESULTSThe Minnesota sections contained concrete slabs having fresh air contents ranging from 1.4 to 5.6 percent (hardened entrained air ranged from 0.7 to 4.4 percent). Other than minor surface scaling, none of the Minnesota freeze-thaw sections shows any evidence of significant deterioration after six Minnesota winters. This is contrary to expectations based on the lack of "adequate" entrained air in most of the sections (Snyder and Janssen, 1994). However, these results must be tempered with the fact that no de-icing salts were used on these sections since they were not trafficked. Also, the monitoring only covered a period of six winter exposures. Additional exposure may be necessary to produce measurable damage. A recent survey conducted in May 2001 showed some additional scaling and popouts on the sections with a lower entrained air content (<2.5 percent), but the other sections did not show significant further deterioration. With de-icing salts, the deterioration is expected to be much greater for the lower air content concrete (Janssen and Snyder, 1994). Concrete specimens prepared from cores taken from the Minnesota sections after six winters did deteriorate in laboratory freeze-thaw testing. These results are in contrast to the results of tests conducted when the sections were placed. Table 6 shows that section MN1, with close to the recommended maximum spacing factor of 0.20 mm, performed well in the more recent tests, while sections MN2 and MN3 performed much more poorly. The spacing factors for MN2 and MN3 were much worse than the recommended 0.20 mm; however, all three sections performed well in freeze-thaw tests conducted on concrete that had not received any "real" winter exposure. This difference in test results may be due to shortcomings in the AASHTO T161 test procedure (El-Korchi et al., 1995). No significant evidence of frost-related deterioration was identified in the diamond-ground Ohio early-strength sections, and these were regularly subjected to de-icing salts. The fresh mix air contents ranged from 1.8 to 4.5 percent, and hardened from 1.8 to 3.3. Some of these sections are cracking, but the cause does not appear to be frost-related. Surface scaling is the most likely form of freeze-thaw deterioration in a concrete pavement. The diamond grinding of the Ohio sections prevented the detection of scaling in those early-strength patches. Light scaling was seen in the Minnesota sections, but the severity was too low to describe it as significant deterioration. Because the Minnesota sections did not receive any de-icing salt, it is recommended that portions of these sections receive de-icing salt for the next 5 years to determine whether the de-icing salt causes significant deterioration. D-CRACKING MITIGATIONThe D-cracking mitigation study indicated that in many cases the D-cracking returned after 6 years, independent of the mitigation technique tried. Whether this is because the edge treatments were not effective in preventing the ingress of moisture through the vertical faces is not known. Cores should be taken at the treated edges and investigated to determine the effectiveness of the aged sealers. Additional testing would be required with other materials and existing D-cracked concrete to further evaluate the specific mitigation approaches.
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This page last modified on 09/25/06 |
