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.
Spreadable
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.
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.
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 field.
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 possible.
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 frequent refills."
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.
