Material: Recycled
Glass
Issue: Visual inspection is a common procedure for the initial assessment of
the acceptability of construction aggregate.
The inspection is usually performed at storage sites prior
to any laboratory testing of the material.
Sometimes, visual inspection is performed as a field screening
procedure. In some cases,
the acceptability of the material for a particular application may
be based solely on the results of the field visual inspection.
Recycled glass is a relatively new construction aggregate material, so
there is little background for standardized visual inspection procedures. Such procedures will allow effective information
exchange and ultimately increase the use of recycled glass in construction.
The inspection should be simple, easy to perform, and provide
an initial classification of debris content and material gradation.
Best
Practice: Debris Content: A simple method has been
used to obtain a percentage level of debris content of a glass cullet
sample. The debris includes
metal caps, plastic, paper, and any other non-glass materials. The
method is based on the Percent Composition Charts developed by American Geological Institute
(Comparison Chart for Estimating Percentage Composition, AGI Data
Sheets 23.1 and 23.2). These
charts show the estimated percentage of composition of debris in a
sample from 1 to 50%.
The method uses a test pan of eight to ten inches in
diameter and one to two inches in depth.
One to three pounds of glass cullet is placed and leveled in
the test pan. The test pan is then placed next to the standard charts
and an estimated percentage is selected based on the comparison of
the composition shown on the charts and the debris present on the
test pan. It is important to disregard the aggregate and compare only the
contaminants with the charts. The
results can be recorded quantitatively using percentages, or qualitatively
using terms such as low for
1 to 3%, medium for 3 to 15%, and high for over 15%. Inter-medium terms such as low to medium, and medium to high can also be considered.
The visual inspection and classification test should
be used for sub-samples retrieved from various portions of the glass
storage. The number of tests
should be based on the quantity and homogeneity of the bulk material. In general, at least one test should be conducted
for every 50 cubic yards of material. The test results for all sub-samples should be reported.
The visual inspection is based on the two-dimensional
view of debris. Since the
debris in recycled glass is typically platy, the visual inspection
method will generally produce results higher than the debris content
measured by physical tests such as the measurement of percent debris
by weight or volume. A comparison
of the visual inspection and the physical test results can be found
in Reference 1 listed at the end of this document.
Maximum Particle
Size The tendency of particle breakdown increases
as the maximum particle size of glass aggregate increases. For example, there will be more breakdown during
placement of 3/4” aggregate than during placement of 3/8” aggregate. Therefore, limits on maximum particle size
are usually specified for recycled glass used as aggregate. Such requirements can be easily checked using
a measuring ruler. In addition,
an estimate on the percentage of over-sized particles should be obtained
using the same visual inspection procedure presented above.
Implementation: Reproduce the Percent Composition
Charts and distribute to contractors, suppliers, test agents, and
consultants. Seminars or discussions
with the permitting offices of the city, county, and state should
be held so that the inspection method becomes part of the permitted
use of recycled glass. Information should also be disseminated among
designers and engineers.
Benefits:
This
best practice presents a simple field screening method for initial
characterization of recycled glass.
The method is simple, easy to perform, and can provide characteristics
that are critical to the acceptability of the material.
For some construction applications, this method may be the
only procedure in assessing the material acceptability. The implementation of such practical methods can greatly increase
the efficiency in initial material characterizations and ultimately
increase the potential use of the material.
Application
Sites: Recycled
glass storage and processing facilities, construction sites, and testing laboratories.
Contact: For more information about this Best Practice, contact
the CWC, info@cwc.org.
References: Glass Feedstock Evaluation Project: Engineering suitability Evaluation, Report
#GL-93-5, Clean Washington Center, 1994. Available only in hardcopy – contact CWC. Glass Feedstock Evaluation Project: Environmental suitability Evaluation, Report
#GL-93-3, , Clean Washington Center, 1994. Available only in hardcopy
– contact CWC Case Studies for the Use of Post Consumer
Glass as a Construction Aggregate, CWC, 1997. Shin, C. J., S&EE, Inc., Bellevue, WA Issue
Date / Update: January
1997 |
