Since the days of the Roman gladiators, road builders and
other inventive construction contractors have devised numerous methods for
stabilizing soils. The materials introduced varied anywhere from seashells and
wood chips to today's more popular and successful lime, fly ash and cement.
Unstable soils are generally characterized as those unable
to support a load, including those with excess moisture content and those with
aggregate having minimal angularity--in other words, the stone is too smooth,
preventing it from interlocking.
So the materials used to stabilize these soils have to
offset the problem. They have to be locally available and in a bid situation,
and they have to be cheap. The path to today's material markets must meet these
parameters to be acceptable.
In order to be useful, these materials have to be processed,
moved from the processing plant to the jobsite, then placed where they will do
the most good. The recipe for a successful soil stabilization project includes
just enough lime to stabilize the soil. Too little additive won't work and too
much wastes money.
To fine-tune this end of the process, Stoltzfus Spreaders,
Morgantown, Pa., developed a line of soil cement spreaders that can accurately
place lime, fly ash and other materials. Stoltzfus is located in the heart of
farm country in central Pennsylvania. They have over 58 years of experience in
solving the spreading problems of the agricultural industry.
Stoltzfus engineers had little problem adapting the concepts
employed in the agricultural arena to meet the needs of their new-found
construction materials market.
Heads in the clouds
Soil stabilization technologies may have been around for
centuries, but until recently no one really paid much attention to the content
of the materials or the dust they created. yes">
Concerns about the health effects of airborne respirable
dusts have led to regulations that have established exposure standards for
particulate matter that can cause
lung diseases. In addition, spreading operations can produce a cloud of
emissions that obscure visibility. These dust clouds create a safety hazard to
workers as well as drivers that may be passing through the construction zone. style="mso-spacerun: yes">
The public no longer looks the other way when it sees dust
blowing around a jobsite, and regulators are straining to levy fines for air
quality violations to fund empty state coffers. The bottom line was Stoltzfus
had to come up with a solution for the fugitive dust.
Mist is a must
NESCO, Mendham, N.J., specializes in the design and
development of spray systems to control dust from material handling operations.
Carmeuse Lime Co., Pittsburgh, brought NESCO's Dr. Mark Kestner together with
Gary Lake of Stoltzfus Spreaders. Kestner is the country's leading expert on
dust control from mining and material handling. He's been in the business for
so long he's known as "Dr. Dust." With North American headquarters in
Pittsburgh, Carmeuse is a major supplier of lime products. Its concern about
the environmental impact of its products provided the impetus for the research
and development of an effective and affordable dust control system out in the
Carmeuse supplies much of the lime products for road and
land development stabilization projects east of the Mississippi. According to
Joel Beeghly, technical specialist for Carmeuse, the commonwealth of
Pennsylvania is a good example of things to come in the industry.
"With this Pennsylvania example of in-situ lime
subgrade stabilization, the cost of a good pavement soil subgrade was reduced
from $28 per sq meter for undercutting poor soil to $4 per sq meter for in-situ
soil stabilization. But in order to gain the cost benefits of spreading lime,
we had to find a way to reduce fugitive dust," stated Beeghly.
A case in point was PennDOT, which now includes lime
stabilization and dust control in some of its road construction specs. With
lime stabilization the key to many projects, and control of dust critical to
meeting specs, Carmeuse met with NESCO and Stoltzfus to discuss possible
solutions and the system that would work.
First of all, the spray system had to be mobile. Secondly,
spray treatment had to knock down the dust without wetting the aggregate. The
system had to be cost-effective, too. Mobile baghouse operations exist, but are
very costly. And last but not least, the system had to use as little water as
According to Kestner, "We knew that just dumping water
on the problem was not going to cut it. First, adding water to a site with a
stabilization problem would be pouring gas on the fire. And secondly, this is a
mobile application that realistically can't tow water in a trailer or stop for
NESCO recommended its MicroMist spray system, which is
custom-modified for OEM applications. It was modified to meet Stoltzfus' needs
and was installed at the output of their spreader. As the name MicroMist
implies, water consumption is minimal and depends largely on the size of the
application and number of nozzles required.
Information provided by NESCO, Mendham, N.J.