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Integrated Paving Solutions Case Study - Port
of Houston, Texas
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Texas
Building it Right the First Time
By: Matthew W. Singel, PE, Cement Council of Texas
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| RCC placement at the Port of Houston |
The Port of Houston is a complex of shipping and cargo-handling facilities
that spans 25 miles along the Houston Ship Channel. In 2009, the Port
ranked first in U.S. import tonnage and second in export tonnage,
with 220 million tons of cargo serviced. It has traditionally been
a bulk carrier facility, but in recent years has significantly expanded
its container-handling capacity. This growth will continue and even
accelerate, because of the anticipated 2014 completion of the Panama
Canal expansion.
Solving Problems
At the Bayport Terminal, integrated concrete and cement pavement
options are solving some difficult problems faced at many ports:
poor soils, high water tables, no locally available aggregates,
huge loading requirements, and a need for fast construction. Low
maintenance is also essential, as pavement closures reduce handling
capacity and profitability.
When the first phase of the Terminal was in final design, Jim McQueen,
the Port of Houston Authority’s (PHA) chief construction manager,
learned of roller-compacted concrete (RCC) as a cost-effective pavement
option. He allowed RCC bid alternates for the two container yard
expansions. In addition, he specified cement/lime stabilization
of the subgrade, and cement-treated base (CTB), to reduce cost and
ensure 30-year durability.
The Savings
Bids on the most recent project, Bayport Phase 1, Stage 2 Container
Yard, provided nearly a 15% savings compared to the non-RCC alternate,
for a final bid price of $34.7 million. The unit costs were $38.89/square
yard and $48.46 /square yard for the 14- and 18-inch thick RCC pavements,
respectively. The RCC alternate was awarded to McCarthy Building
Companies, with Interstate Highway Construction (IHC) being the
RCC subcontractor.
Heavy-Duty Designs
Intermodal container pavements have to withstand heavy loads, including
gantry cranes carrying shipping containers, which are then stacked
five-high. Three loading environments were considered for the most
recent expansion: Grounded container storage, wheeled container
storage, and the circulation roads. The designer, Klotz Associates
of Houston, developed multiple pavement options for a 30-year design
life. The RCC pavement sections consisted of 1) cement/lime stabilized
subgrade, 2) a geotextile fabric, 3) an open-graded drainage layer,
4) cement-treated recycled concrete aggregate subbase, and 5) an
RCC surface layer (Fig. 1).
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| Figure 1- Pavement sections: (a) Grounded
container storage; (b) Wheeled container storage; and (c) Circulation
roads |
RCC Pavement
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| General view of pavement layers |
RCC production/placement rates are very high, making this an ideal
concrete paving material for large, thick industrial pavements.
Additionally, no steel (neither dowels nor reinforcing) is needed,
further speeding placement and reducing cost. Wide allowable joint
spacing and thin saw cut joints keep long-term maintenance to a
minimum. The pavement thicknesses required two-lift placements to
allow full compaction, but this is quickly and easily achieved with
RCC.
The RCC mixture was an optimized blend of Type I/II portland cement,
washed concrete sand, manufactured sand/crusher screenings, and
coarse aggregate. The specified strength of the RCC was 550 psi
at seven days. In addition, project specifications dictated quality
control testing for density and compressive strength. The required
minimum average density was 98%, with no test falling below 95%
of maximum wet density as determined by the modified Proctor method
(ASTM C1557).
RABA Kistner Consultants (Houston) performed the RCC testing. IHC
constructed a test section prior to production placement. Results
of the test and production RCC are summarized in Table 1.
| Table 1 – Summary of RCC test results |
Test |
Test Section |
Production |
| Average flexural Strength at 7 days, psi |
570 |
--- |
| Average compressive strength of cylinders at 7 days, psi |
4,030 |
5,050 |
| Average compressive strength of cores at 7 days, psi |
3,430 |
4,440 |
"Green" Cement-Treated Base
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| Compacted CTB ready to receive RCC surface |
The subbase for the RCC needed to be uniform and resillient, even
under saturated conditions. It also had to be non-pumping under
heavy, repeated loads. The designer chose CTB, as it fulfilled all
these requirements at an economical cost.
Houston is an aggregate-poor locale, so the CTB supplier, Southern
Crushed Concrete, suggested the use of recycled crushed concrete
to serve as the CTB aggregate. This saved trucking aggregate from
over 100 miles away, and the cement treatment helped improve the
durability of this marginal material. The CTB also served as an
all-weather work platform that provided a stiff surface for effective
RCC compaction.
The CTB was produced using a pugmill plant. Southern Crushed Concrete
utilized its existing plant, four miles away, eliminating plant
mobilization costs. Jim Miller of Southern states, "CTB is
a great product at an affordable price. In the Houston market, you
commonly realize a 20 to 25 percent material cost savings using
recycled concrete over virgin aggregate."
Subgrade Treatments
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| Surface appearance of RCC placed adjacent
to conventional concrete |
A stable and durable subgrade is another key to long-term pavement
performance. Due to the complex, poor quality soils encountered (mostly
dredged fill material), the geotechnical consultant called for 5%
lime to modify soil characteristics, followed by 5% cement to ensure
long-term strength and reduced moisture susceptibility. The cement/lime
treatment eliminated the need to remove and replace thousands of tons
of subgrade with select fill. This work was performed by Laguna Construction
Company of Laguna Pueblo, New Mexico.
Impressive Results
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| Extracted RCC Core for quality control observations
and testing |
By using RCC pavement, the Port estimated that it reduced the project
construction schedule by four months while keeping maintenance to
a minimum. The ability to open for business earlier, while minimizing
maintenance "down-time," continues to reinforce the Port's
decision to select RCC for the Port of Houston pavements.
Since 2007, nearly 100 acres have been paved with RCC (along with
CTB subbase, and cement/lime subgrade treatment). Additional expansions
at Bayport are planned to continue until the 1,043 acre complex
reaches completion. The RCC paving in Stage 1, Phase 2, the most
recent section, encompassed 44 acres. IHC began the RCC placement
in January 2010, and paving was finished by early May, less than
5 months later.
Customer Satisfaction
PHA's Jim McQueen is convinced that RCC, combined with the CTB and
cement/lime stabilized subgrade, was the right solution for the
Port. "I have been very pleased with the excellent job performed
by the McCarthy/IHC team and the professional nature in which they
both operate. The Port of Houston is hoping that the success of
these projects will inspire future RCC projects across Texas.”
Credits
Owner: Port of Houston Authority, Houston, Texas
General Contractor: McCarthy Construction Company,
Houston, Texas
RCC Contractor: Interstate Highway Construction,
Mansfield, Texas
Civil Engineer: Klotz Associates, Houston, Texas
Materials & Testing: Raba Kistner Consultants,
Houston, Texas
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