There is a need to make modifications to existing patch size selection, construction requirements and specifications to extend repair life while maintaining good ride quality.
Findings: In early November, 1999, the panel met to consider this research problem statement and decided that, for a change, no research was needed. The panel determined that the problems occurring on Concrete Pavement Restoration (CRP) projects on I-29 in the southeastern corner of the state were probably best addressed by a problem solving approach, as a literature search prior to the November meeting indicated that most states and the FHWA recommend a minimum patch width of 6 feet for joint rehabilitation using dowels. The bulk of the joint repairs carried out on the 48 and 61.5 foot panels on I-29 were only 4 feet wide, well below the recommended minimum.
The issue of what to do with respect to the poor performance of the I-29 joint repairs is complicated by at least two additional factors:
1) Failure to provide sufficient epoxy to completely fill the drill hole adjacent to the dowel resulting in poor anchorage.
2) An incorrect specification for epoxy due to a change in ASTM designation.
Both these issues have been addressed by appropriate changes to the plans and specifications. Although these have definitely contributed to the poor performance to some extent, the overall results of a survey of joint repair performance conducted in the spring of 2000, excluding rocking slabs which may have resulted from either of the above factors, argues strongly in favor of specifying a minimum repair width of 6 feet.
Of the 18 sections looked at, dating from the early 1990’s to the present, all but one had transverse cracking visible. Considering the driving lane and passing lane as separate joints, the average number of cracks per section was 8.7 out of 20 panels. Some of the repairs had widths of 5-10 feet although the vast majority were 4 feet. None of the repairs 6 feet or greater had transverse cracks and most of the 5’ repairs were not cracked. Unfortunately, there were only 15 joints with widths 5’ or greater which represents only 8% of the sample. Even so, the difference in performance of the wider patches, no matter what problems may have been occurring in a section, was marked.
Assuming the difference in cost going from a 4 foot patch to a 6 foot patch resides solely in the increased quantity of concrete needed for the patch, a 10" thick slab would require an additional 0.75 yd3 of concrete which would increase the cost by approximately $37.50 per joint at a concrete cost of $50/ yd3. The table below shows the additional cost for three typical joint spacings.
Joint Spacing Increased Cost per Lane-mile
Increasing the minimum width requirement for joint repairs will also provide additional benefits to the quality of joint rehabilitation performance by improving access to the repair areas. Dowel installation and any needed repair to the subbase or subgrade will be facilitated by the greater work area which should improve dowel insertion and provide more uniform support to the joint repairs.