Material: Recycled
Glass
Issue: The production of glass aggregate requires crushing, which
inevitably creates fine particles of glass.
When the aggregate is moved around construction sites, these
particles can become airborne as dust, which may present a nuisance
to workers in the vicinity. In
order to maintain a safe working environment and reduce the environmental
impact on and around the site, procedures for worker protection and
dust control should be implemented on the construction site.
Best Practice: Studies
have been conducted on glass dust to determine the presence of crystalline
silica, a known carcinogen. These
studies show that cullet aggregate typically contains less than one-
percent crystalline silica by weight and is therefore not considered
hazardous by federal standards. This places cullet in the category
of nuisance dust with a Permissible Exposure Limit of 10 mg/m3.
Glass cullet dust can be a
skin and eye irritant. Because
cullet particles are abrasive due to their high angularity in particle
shape, they appear to be more irritating than dust from natural aggregate
or soil. However, experience gained on construction
sites has indicated that cullet dust, and the irritations associated
with cullet dust, can be easily suppressed using simple measures.
As with any aggregate, the need for cullet dust control
is most obvious during periods of dry weather. Since glass has a specific gravity less than
that of a natural aggregate, the fines from cullet aggregate may be
more prone to becoming airborne. On construction sites, the dust is typically generated when the
material is imported and end-dumped from trucks. When the material is dry, the surface tension at the particle interface
is minimal. As such, the apparent
cohesion may become inadequate to keep the fine particles adhered
to the mass. The dumping of
dry material with more than 5% to 10% fines can generate a dust cloud,
which can be transported by wind a great distance.
The handling and transporting of cullet aggregate onsite can
also create a dust cloud or dust plume.
Handling procedures may of necessity include the use of a loader,
backhoe, bobcat, or a hopper, all of which can stir up dust clouds.
In windy conditions, the dust at a stockpile surface can also
become airborne and be transported by wind.
Wet suppression using a garden
hose is the most common and effective procedure for dust control on
construction sites. This procedure
is sometimes not recommended for fill soils and some natural aggregate,
because adding moisture can change the engineering characteristics
of the materials. However,
because glass aggregate is generally free-draining and has compaction
characteristics that are not moisture sensitive, the application of
water to cullet stockpiles or filled areas will not negatively impact
the use of the material. However, if the glass aggregate contains more
than 10% fines (particles smaller than No. 200 sieve in size) the
material may become moisture-sensitive.
Qualified geotechnical engineering personnel should handle
this situation.
Water can be applied to the cullet aggregate in the
truck bed before dumping. To
avoid ponding of surface water, the stockpile should be built at locations
with positive drainage away from the stockpile area. During the dry summer months, the stockpile can be sprinkled with
water whenever the surface is dry and fine particles can become airborne
and transported by wind.
Implementation: For every construction project,
the use of cullet aggregate should be discussed among the owner, engineers,
general contractor, contractor’s earthwork sub-contractor, labor foremen
and laborers. The discussion
should include but not be limited to the following items:
1.
The advantages
and disadvantage of using cullet as a construction aggregate and the
merit of glass fill. The awareness
of the rationale for using such new construction material at all levels
of construction crew tends to mitigate the concern for a new material,
and to facilitate the cost-effective use of such material.
2.
The proper
procedures for handling, placing, and compacting glass. Discussion of this topic allows project team
members and workers to realize that cullet aggregate will behave similarly
to a natural aggregate; and that the cullet aggregate has a good workability
in terms of handling and compaction.
3.
The potential
hazards and preventive measures, such as wet suppression, to be implemented.
Construction personnel should be made aware of the potential
inhalation hazard and skin and eye irritation.
All personnel should have knowledge of preventive measures,
but the responsibility of such measures should be clearly assigned.
4.
The required
safety gear when working with cullet aggregate. All personnel should know that direct skin
contact with the glass cullet should be avoided. Also, heavy gloves, long-sleeved shirts, heavy boots, hard hats,
and ear and eye protection are required when working with cullet aggregate.
Benefits:
Understanding the hazards
of cullet aggregate dust, and the associated preventative measures
will help create a safe worksite environment and less environmental
impact on site vicinity.
Application
Sites: Construction
sites.
Contact: For more information about this Best Practice, contact
CWC, mailto:info@cwc.org.
References: Case Studies for the Use of Post Consumer
Glass as a Construction Aggregate, CWC, 1997. Best Practice Analysis of Glass Dusts Issue Date / Update: November 1996
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