Highway Contractor: Sub-Bases
HighwayContractor
By John Latta
Base Breakthroughs
Researchers dig into sub-bases
A
quick look at some recent research into sub-bases presented at the American Society of Civil Engineers
(ASCE) GeoCongress 2012: State of the Art and Practice in Geotechnical Engineering, held this spring
in California, suggests that sub-base options are increasing rapidly. The full ASCE papers (below are abstracts) are available through the society’s website, www.asce.org
Reusing Glass
Triangle Power
The recycling industry continues to grow as a
means of utilizing waste materials in today’s
world and as such more markets must be urgently established for recycled products. Currently in
the state of Victoria, Australia, 186,000 tonnes
of recycled glass are stockpiled annually and
these stockpiles are growing. However, there is
little known reuse application for recycled glass
in pavement sub-base applications due to limited knowledge of its geotechnical properties.
The reuse of recycled glass in road pavement
applications will provide the opportunity not
only to get rid of the waste glass stockpiled and
minimize the use of virgin materials in pavement
applications but also to minimize the valuable
land being used for stockpiles. This paper presents a preliminary laboratory evaluation of select
geotechnical properties of recycled glass when
used in blends of up to 50 percent with recycled
crushed concrete in pavement sub base applications. Laboratory tests discussed in this paper include modified compaction, Los Angeles abrasion
loss, consolidated drained triaxial compression
test and California Bearing Ratio (CBR) test. The
findings of this laboratory evaluation indicate that
potentially up to 30 percent recycled crushed
glass of particle size less than 4.75 mm could be
safely added to Class 3 recycled crushed concrete
in pavement sub base applications.
A field study was performed to document the benefit of
a punched and drawn polypropylene triaxial geogrid. The
triaxial geogrids have triangular apertures and increased
rib thickness as compared to many geogrids with square
apertures. These fundamental changes to the geogrid structure, coupled with high junction efficiency, gives greatly
improved aggregate confinement and interaction, leading to
improved structural performance of the mechanically-stabilized layer (MSL). The project consisted of the widening of
La Media Road as part of the Highway 905 improvements.
La Media Road and Highway 905 typically experience heavy
truck traffic loads from the Mexico/U.S. border crossing.
The subgrade material beneath La Media Road is comprised
of clayey sand and clayey sand with gravel. Additionally,
cobbles ranging up to about 8 inches in diameter were observed on the surface of the subgrade. R-Values of 21 and
24 were determined for the subgrade material. Laboratory
testing included grain size analysis, Atterberg limits, maximum density, optimum moisture content and R-Value tests.
The field-testing consisted of 5-inchdiameter plate load tests
on the subgrade and at various levels of the pavement crosssection. Results of plate load testing indicate that the triaxial
geogrid increased the modulus of the mechanically stabilized section relative to the conventional unbound aggregate
pavement section. The measured improvement of the MSL
sections ranged between 27-percent and 52-percent greater
than the 30-percent thicker unbound aggregate conventional
design section.
Paper is entitled: Potential Use of Recycled Crushed Concrete-Recycled
Crushed Glass Blends in Pavement Subbase Applications
Paper is entitled: Performance Verification of a Geogrid Mechanically Stabilized Layer
Flexible Pavement Design as Part of the La Media Road Widening Project
Better Roads October 2012 7