chapter 3 rigid pavement - DOT On-Line Publications - Department ...

sublect Examination of Cores from Kansas I-70
Ffm Chief, Pavement Division
Uashington, D.C. 20590
lo Mr. Thomas 3. Ptak,
Deputy Regional Federal Highway Administrator HEO-07
Kansas City, Missouri
Da’e AL 2 5 1969
Attached is Dr. Stephen Forster's report on the examination of the concrete
cores from Kansas I-70 east of Abilene (Kansas Project No. 70-21 K-2588-01).
Dr. Forster did not find any evidence of "D" cracking of the aggregate or
alkali-aggregate reactivity. The crack faces appear rough enough to provide
load transfer if the cracks remain tight. However, the cracks in these cores
have opened to the point where load transfer has been 1 ost and the cracks are
working.
We are observing a significant number of jointed reinforced concrete pavements
(JRCP) with working cracks. The two factors believed to be the primary cause
of working cracks in JRCP are corroded and locked up dowel bars and inadequate
reinforcement. The introduction of epoxy coated dowels has reduced the risk
of dowel bar corrosion. However, the procedures used to determine the amount
of reinforcement in JRCP are not adequate.
Reinforcement for JRCP is designed using the subgrade drag theory. The
procedure does not consider the crack aggregate interlock capability or the
repeated shear loads from traffic. Also, the subgrade drag theory does not
directly consider climatic effects. In the absence of a good design procedure
for the reinforcement in JRCP, we believe the following conclusion from an
ongoing research study "Performance/Rehabilitation of Rigid Pavements"
provides good guidance:
nT;:, amount of reinforcement appeared to have an effect in controlling
the amount of deteriorated transverse cracking. Although often
confounded by the presence of corrosion-resistance dowel bars, pavement
sections that contained more than 0.1 percent reinforcing steel
exhibited less deteriorated transverse cracking; sections with less than
that amount often displayed a significant amount of transverse cracking,
particularly in cold climates. A minimum of 0.1 percent reinforcing
steel is therefore reconmtended, wither amounts required for harsher
climates and longer slabs."
3.4.1