CPR smooths ride on Kansas road The section of Ip;70 extending nine
miles east of Abilene is now a smoother ride thanks to concrete pavement
restoration (for a closer look at CPR, see Georgia Boasts Smoothest Roads,
4/96). The first of its kind in Kansas, this $2.2 million project consisted
of patching, dowel bar retrofitting, diamond grinding and sealing of joints
and cracks. The project was conceived by KDOT engineers after a visit to
an open house showcasing a similar project in Washington State.
With doweled joints spaced at 30 ft, the Kansas pavement had developed faulting
of mid-panel cracks, thus the need for dowel bar retrofitting. Dowel bar
retrofit is an operation in which slots are cut into the concrete across
the joints and cracks and dowels are placed in the slots to restore load
transfer and increase structural capacity.
The contractor, Highway Services, Inc. of Rogers, Minn., developed special
equipment which made saw cuts for six dowel slots simultaneously leaving
three concrete fins. Conventional jack hammers removed the fins to complete
the slots. The slots were then sand-blasted and cleaned with compressed
air. The usual slot pattern was specified-three slots, spaced 12 in. apart,
per wheel path.
Prefabricated chairs were used to hold the 11¦2 ¥ 18 in. dowel
bars at the proper position while the slots were backfilled with a proprietary
rapid set grout material. Designed to reach a compressive strength of 5,000
psi in 24 hours, the non-shrink grout was mixed by a mobile mixer on site.
The next step after patching and dowel retrofitting was diamond grinding
of the entire surface of the four driving lanes-243,000 sq yd. With one
lane, at a time, closed to traffic, the contractor's profiling machine made
three passes with its 4 ft grinding head. The States Profile Index specification
of 30 in./mile was easily met with an average value of 20 for the project,
which represents a very smooth ride. With smoothness incentives kicking
in at a value of 18 in./mile or less, the contractor received bonus for
31% of the work.
Formerly, wide spread use of retrofit dowels was hampered by slow completion
rates, quality control problems and high costs. Recent improvements in equipment
and techniques now makes CPR operations much faster and less expensive than
replacing the pavement or overlaying it.
This project was a co-winner of ACPA's 1995 Award for Excellence in Concrete
Pavement in the CPR category.
Packard is director of engineering-design for the American Concrete Pavement
Association. You may write him in care of the editor.