Freer Finds Recycling Failed
Pavements Profitable
 Edited
by Jeff Hawk
 City
of Freer officials have opted to take a new approach toward rehabilitating
the city's failed pavements.
The
city recently completed the reconstruction of two miles of city
streets using a method that recycles the existing base and deteriorated
asphalt surface course with portland cement.
"Many
of our streets here in Freer are very old now and are failing badly,"
said Freer Mayor Arnold Cantu. "We tried to rehabilitate some
of our streets with another product three years ago, but they are
just not holding up."
The
city's consultant, Daniel Rios, regional manager for S&B Infrastructure
Ltd. in McAllen, proposed the alternative of recycling failed flexible
pavements with cement. According to Rios, a project evaluation indicated
that city maintenance crews trying to keep up with the repairs were
devoting a high percentage of their time to Longview Avenue and
other three streets - Tipton, Rosita and White.
S&B
investigated various options for rehabilitating the streets, including
recycling with cement or lime or placing a thick HMAC overlay. The
company found that cement stabilization reduced construction time
and lowered its cost, extending the budget to rehabilitate more
streets. Cement would bind the granular materials and decrease the
plasticity of "clayey" soils, as well. In addition, cement
offered higher strength for an equivalent amount of stabilizer.
One potential disadvantage was the lack of inspection experience
with the process.
Inspectors
did have some experience with lime stabilization but the higher
cost of the process reduced miles of work. The lime stabilization
process also required a longer construction time and a detailed
traffic control plan.
A
third option, overlaying the streets with hot mix asphalt concrete
(HMAC), also offered the advantage of inspection experience but
also provided the most expensive option. Placing the overlay required
repairing the failed base, thus extending construction time. The
asphalt would also need periodic seal coats and future overlays.
Rehabilitating
the failed pavements with cement seemed to offer the most economical
solution for the longest life. The existing base materials and asphalt
mat could be reused, eliminating the cost of hauling in new base
material.
 The
project was specified in accordance with Texas Department of Transportation
(TxDOT) Specification Item 275, "Portland Cement Treated Materials
(Road Mixed)." Standard compaction requirements were used.
The typical section consisted of treating 6 in. of existing material
with 3 percent cement (by weight of dry material), a prime coat,
a one-course surface treatment, and a 1-in. HMAC surface. A concrete
valley and curb and gutter at the intersections completed the project.
King-Isles
Construction Inc. and its subcontractor, LM Asphalt Maintenance,
both out of Corpus Christi, achieved the recycling process in one
day. Crews scarified and pulverized the existing roadbed to proper
gradation. Processed material was required to pass the 2-in. sieve
before being pre-wetted and shaped to the lines and grades of the
typical section. After workers spread portland cement over a designated
area and mixed it thoroughly with the pulverized materials, water
was added to reach optimum moisture.
Crews
compacted and graded the mixture to finish grade. The surface was
then cured with water spray for three days prior to applying the
chip seal and the HMAC surfacing. The process allowed the city to
avoid excavating, removing and discarding the old pavements and
allowed crews to use the salvaged material.
Ultimately,
the completed $258,787 project returned 2.077 mi. of city streets
to a high level of serviceability, said Rios, which translated to
$124,597 per mi. or $3.53 per sq. yd. for the entire recycling and
surfacing process.
Note:
Jeff Hawk edited this article originally submitted by Daniel 0.
Rios, a transportation engineer for S&B Infrastructure Ltd.,
McAllen. A registered engineer in Texas, Rios spent ten years in
TxDOT's Corpus Christi District in various positions.
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