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Bus Parking Lot Finds Stability through Full-Depth
Reclamation with Cement
Spotsylvania County, located halfway between
Richmond, Va. and Washington, DC, is considered in the top 100 of
fastest growing counties in the nation. Since the year 2000 the
population has increased by 33 percent.
Due to this tremendous growth, a transportation
facility was constructed with a 45,000 square yard bus
parking lot to accommodate the entire fleet for the county schools.
The 140-bus fleet would make two trips in and two trips out per
day for the 200-day school year. This equates to more than 100,000
bus passes.
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| Rutting and pumping of fines in failing parking
lot. |
Within 6 months of completion of the parking lot, the pavement began
to experience severe deterioration and within a year 35 percent of
the parking lot was distressed with rutting and cracking. The pavement
structure consisted of 1.0 to 1.25 inches of prime and double asphalt
seal surface on top of 4.5 to 16.0 inches of aggregate base course.
Subgrade soils were plastic in nature and had California Bearing Ratio
(CBR) values ranging from 1.5 to 10.0. Subsequent testing revealed
the aggregate base course did not meet Virginia Department of Transportation
specifications (VDOT 21A).
Rehabilitation was necessary to restore the
lot to its expected structural capacity. Removal and replacement
of the aggregate base would have been extremely expensive, and with
bearing capacity an issue, the use of an asphalt overlay would not
solve the pavement base and subbase problems. The perfect solution
was full-depth reclamation (FDR) with cement since it would restore
bearing capacity to the parking lot and provide a cost-effective,
durable base.
FDR is also an environmentally friendly repair
option because it uses in-situ materials, and thereby the process
conserves natural resources and energy. Portland cement was the
obvious stabilizer choice for the varying thickness and changing
nature of underlying materials due to its ability to adequately
stabilize clay-rich (cohesive) and granular (unbound) materials.
Spotsylvania County Schools released the project for formal proposals
on March 1, 2009. Selection of the successful bidder was based on:
1. Proposed Methodology of Pavement Repair Including
Equipment, Mix Design, and Full-Depth Reclamation.................. |
35% |
| 2. Experience / Qualifications / Ability to Perform....................... |
20% |
| 3. Proposed Cost(s)................................................................. |
35% |
| 4. Favorable References.......................................................... |
10% |
As can be seen, the “Proposed Methodology” ranked very
important in the decision of awarding the project along with the
cost. When the proposals were evaluated, Ruston Paving Company,
Inc. of Manassas, Virginia was awarded the bid. Ruston Paving completed
the FDR with cement as well as the required asphalt paving.
 |
| Ruston Paving pulverizing existing parking
lot to 12 inches |
The 20-year pavement design life incorporated a 12-inch FDR with
cement base section and 3 inches of asphalt surfacing. The FDR with
cement mixture design specified approximately 70 lbs/yd2 (6 percent
by dry weight of roadway materials) for the 12-inch depth with a
98 percent dry density using standard Proctor testing. Proof-rolling
would be used to assure the stability of the reclaimed section.
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| Portland cement and water incorporated prior
to compaction of reclaimed material |
Ruston Paving work began in late June and all reclamation was completed
in about 15 days with 1,600 tons of portland cement being used. Proof-rolling
revealed less than one percent of the reclaimed section deficient
and asphalt paving began the next week.
Now the Spotsylvania County Fleet Transportation Facility has a
parking lot that is worthy of the facility and county it serves.
FDR with cement provided a cost effective, durable and eco-friendly
pavement solution.
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| Reclaimed section ready for surfacing |
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