Road Management & Engineering Journal
Road Management & Engineering Journal
June 1, 1998
TranSafety, Inc.
1-800-777-2338
(U.S. and Canada)
(360) 683-6276
Fax: (360) 335-6402
transafety@live.com

Questions and Answers:
Road Dust Control with Soapstock--A Soybean Oil By-Product

(The following information was reproduced, with permission, from a brochure created by Minnesota Soybean (360 Pierce Avenue, #110, North Mankato, MN 56003) and reprinted by the Rhode Island Department of Administration. Minnesota Soybean also provided the photograph.)

Q:

What is acidulated soybean oil soapstock?

A:

Acidulated Soybean Oil Soapstock is a by-product of the caustic refining process of soybean oil. It has traditionally been used by fatty acid producers, soap makers, foundries and animal feed manufacturers.

Q:

How did the use of soybean soapstock road oil come about?

A:

In 1988, the Minnesota State Legislature banned the use of waste petroleum oil as a dust suppressant on gravel roads. Since that time, a suitable replacement product has been sought that would not harm the environment.

Soybean oil soapstock is an environmentally friendly, biodegradable material. When used at suggested levels, this material does not migrate into the ground water nor harm agricultural crops.

Q:

How does it work?

A:

When soybean oil soapstock is applied to roads, it penetrates below the road's surface, "bonds" with the bed material of that surface, and forms a protective shield for the road. There is no dissolution, no toxic run-off.

Q:

Are there any negative effects on water quality?

A:

The environmental engineering unit of the MN/DOT has sampled test sections for water quality and found no water quality problems. These results were also reviewed by the Minnesota Pollution Control Agency.

Q:

What types of roads should soapstock be used on?

A:

Past experience has shown that soybean oil soapstock has worked very well on gravel-type roads which carry a wide variety of traffic loads. Dust on roads carrying continuous heavy-weight truck traffic, however, is very difficult to control, with soapstock as well as other products, because these road surfaces tend to be severely depressed by this type of traffic. Thus, if this type of heavy-weight truck traffic is expected, an application of soapstock may work well. However, do not expect it to perform any better than the road condition, itself, can support.

Q:

How long can we expect the dust control effect to last?

A:

When applied at the rate of .25 gal./sq. yd. dust control lasted all summer and into late fall before it was broken up by a grader. In fact, it was suggested that these application sites be broken up or graded before winter in order to avoid having to apply salt or sand products as one would with a bituminous road surface.

Q:

How is the product sold?

A:

When purchased from a soybean processor or oil distributor, soapstock is sold by the pound, with a gallon of product weighing approximately 7.5 to 7.6 lbs./gallon.

Q:

How much does the product cost?

A:

Although the price is driven by commodity prices, prices over the past years have ranged from $0.15 to $0.20 per pound or $1.12 to $1.50 per gallon. However, please check with a processor or distributor for current prices (see contact list). While this is somewhat more expensive than calcium chloride, soapstock will last the summer while calcium chloride must be applied more often. Additional research is being conducted on soapstock to lower the application rate in the future.

Q:

How should it be stored?

A:

Soapstock is a liquid oil at temperatures above 35 degrees. At temperatures lower than 35 degrees the viscosity increases in direct proportion to the temperature. It is recommended that soapstock be stored in stainless steel or black iron tanks. Fiberglass tanks have been used, but it is best to check with the tank manufacturer before doing so. Storing the product over one season is not recommended. If storage over winter is necessary, heat tapes are recommended.

Q:

Can it be mixed with water?

A:

Soapstock does not emulsify with water. Do not pre-mix water and soapstock.

Q:

How should it be handled?

A:

Soapstock can be handled much like the presently used #5 fuel oil with no additional pump requirements necessary. Check with soapstock suppliers for any additional questions regarding storage or handling of the product.

Q:

What road surface preparations are needed?

A:

In most cases the road surface need only be lightly graded prior to the application. This grading should leave at least 1" to 2" of loose material on the road surface and should cover any compacted traffic paths.

Also, it is recommended that the road surface be settled and not have major soft spots or frost boils as these tend to not support soapstock product and thereby reduce its effectiveness. For areas that are prone to have potholes, it is recommended that either these areas be graded deeper to eliminate the pothole or that a heavier application of soapstock be made to hold the loose road material in the potholes.

It is also recommended that the road surface be dry prior to application. Although rain or watering following the application of the soapstock may help with the penetration of the product, rain or watering within 24 hours prior to the application is not recommended.

Q:

Is oil temperature important?

A:

At application, oil temperatures should be at least 75 or elevated to a maximum of 110 if necessary. The warmer the oil, the faster the penetration.

Q:

How is it applied?

A:

Soapstock can be applied with existing bituminous applicator equipment, with no apparent compatibility problems to asphalt residues in the applicator. A spray-type application tends to work best. Spraying the product gives an even coverage at a consistent rate. As stated above, it has been applied with existing bituminous applicator equipment, but other equipment that could apply an oil product effectively would possibly work. Most county highway departments or local bituminous asphalt contractors have equipment available to apply the product.

Q:

What is the rate of application?

A:

Although rate applications are still being evaluated, the rate that has been used for first time applications is .25 gal/sq. yd. or 1 qt./sq. yd. At this rate, the product has been observed penetrating the road surface to approximately 1 inch in depth. This should be adequate to support normal traffic. However, if heavier traffic is anticipated, the application rate may need to be increased slightly to accommodate this heavier use. Also, according to observations over the past 2 years, applying the product at this rate produced a traffic bound mat that resembled a bituminous mat.

Q:

How long does it take for the soapstock to penetrate the road surface?

A:

This is a function of time and temperature. The warmer the oil, the faster the penetration. Similarly, the warmer the road surface, the faster the penetration. It generally takes 4-6 hours for the soapstock to penetrate. Application signs should be posted so that road traffic slows down during the initial 4-6 hour penetration stage to minimize the transfer of freshly-applied product to vehicles.

Q:

What about clean-up of freshly-applied product from vehicles or equipment?

A:

It is recommended that an industrial strength liquid soap be used followed by a power wash for best results. Should it be necessary to use something stronger, however, a solution made up of equal parts of mineral spirits and water may be used to remove the soapstock product. Note: If this method is used on a waxed surface, such as an automobile, it is recommended that the surface be rewaxed following this treatment.

Q:

What about applying it next year?

A:

It has been noted that when the product has been applied at the same rate over the same section of road the following year, the surface of the road appeared wetter than the first year's application. Since this may be an effect of some residual control, it has therefore been suggested that a reduced rate could possibly be used in subsequent years without a loss of dust control, even if the surface was broken up. This continues to be evaluated.



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