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• Highway Concrete Technology Development and Testing Volume IV:Field Evaluation of SHRP C-206 Test Sites (Early Opening of Full-Depth Pavement Repairs)

Highway Concrete Technology Development and Testing Volume IV:Field Evaluation of SHRP C-206 Test Sites (Early Opening of Full-Depth Pavement Repairs)

CHAPTER 4. CONCLUSIONS AND RECOMMENDATIONS

The full-depth repairs made with HES materials placed under SHRP C-206 gave variable long-term performance. All sections in Georgia provided excellent performance; however, the performance of the Ohio sections was plagued by the longitudinal cracking that developed in a majority of the repairs within few weeks after the repairs were opened to traffic. An analysis conducted under this study showed that the most likely cause of the longitudinal cracking in the Ohio sections is the excessive difference between the PCC temperature during curing and the nighttime low temperatures. Two of the Ohio sections (VES and FS) also started to develop map cracking by 1997. These two sections developed extremely high temperatures during curing (excess of 70 °C); DEF is the suspect cause of the map cracking.

The following conclusions can be made based on the performance of the full-depth repairs at the two SHRP C-206 test sites:

• Full-depth repairs made with HES PCC can provide good long-term performance; however, adverse temperature conditions during installation can cause premature failures.
• A large difference in the average PCC temperature during curing and overnight low temperatures should be avoided. If this difference in temperature is large, longitudinal cracking is possible, because the thermal contraction in the transverse direction is restrained by dowels.
• The temperature data from the Ohio site suggest that the risk of longitudinal cracking is high if the difference in average curing temperature and nighttime low temperatures exceeds about 10 °C (50 °F). The use of HIPERPAV is recommended in adverse conditions to avoid premature failures.
• Extremely high PCC temperatures during curing should be avoided. If the PCC temperature during curing exceed 70 °C, DEF is possible. Two of the Ohio sections (VES and FS) showed map cracking characteristic of DEF, and core testing confirmed DEF in those sections.
• All sections except the RSC 1 section in Ohio showed excellent faulting performance. Average faulting was less than 1 mm and remained unchanged throughout the monitoring period.
• The fatigue damage due to early opening is negligible, especially for repairs 3.7 m (12 ft) or shorter. The repairs in each experimental section had a range of strength at the time of opening to traffic; however, within the range of strength evaluated, the strength at opening could not be correlated to performance. The minimum compressive strength at opening was 6.9 megapascals (MPa) for all sections.

The results of this evaluation showed that in terms of fatigue damage or faulting performance, the repairs could be opened to traffic at much lower strengths than those typically recommended. However, opening at strengths much less than those recommended in various manuals of practice (ACPA 1995; Yu et al., 1994; Snyder et al., 1989) is not advisable because of the risk of random failures caused by a single heavy load at an early age. Therefore, the following opening criteria suggested in the SHRP C-206 manual of practice are still recommended:

• PCC modulus of rupture of 2.0 MPa by third-point testing.
• Compressive strength of 13.8 MPa.

No change is recommended to the minimum repair size, but further research is recommended into the effects of repair size on potential for longitudinal cracking. The Ohio site where the longitudinal cracking was a problem only had 1.8-m repairs. Therefore, the effects of repair size could not be determined. Although the temperature conditions during construction appear to be the dominant factor affecting the risk of longitudinal cracking, it is possible for repair dimension to be a factor.

FHWA-RD-02-085