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Growing With Power

Down in Milltown, Ind., a family operation is steadily producing more than 700,000 tons per year of high-quality limestone. Robertson Crushed Stone has


Down in Milltown, Ind., a family operation is steadily producing more than 700,000 tons per year of high-quality limestone. Robertson Crushed Stone has been hard at work for 29 years, and reserves are projected to last another 60 years at current production rates.

There's not much else in this small town, maybe a thousand people and the scenic Blue River. It's located about 30 minutes northwest of Louisville, probably too far for a competitive advantage in the construction materials market. Still, the Robertsons have been able to maintain a solid operation and a good life selling material to coal-fired power plants.

The ledges of the quarry face at Robertson Crushed Stone yield a limestone that is rich in calcium carbonate and low in magnesium. This chemical composition is ideal for scrubber stone used to remove sulfur dioxide from power plant emissions. President Charlie Robertson says the company's two biggest customers are Duke Energy's Gibson Station in Princeton, Ind., and Indianapolis Power & Light in Petersburg, Ind.


The competition among aggregate operations producing this stone is tremendous, explains Vice President of Sales Katie Robertson. She says Duke Energy's Gibson Station alone is projected to consume up to 1 million tons of scrubber stone this year. This demand keeps the Robertsons busy with potential for growth.

Charlie says demand for scrubber stone increased in the early 1980s and really took off in the early 2000s as environmental regulations became more stringent. Acid rain, which is largely caused by sulfur dioxide, was a growing concern. Before the regulations went into effect, a power plant would only consume an average of 50,000 tons per year. The power plants operate in accordance with the law, Charlie says.

ìThe federal mandates made our markets grow because they would not have installed the scrubbers otherwise,î Charlie says. ìThey are very expensive to build and very expensive to operate.î


The process is called wet scrubbing. The stone that the plant receives is ground by ball mills to a 200 mesh or finer. It is mixed with water to create a slurry, which will absorb the sulfur dioxide from the coal emissions. As the material dries from the heat, it falls to the bottom of the scrubber as a cake. Often it is just disposed of in the landfills, but it also can be transformed into a synthetic gypsum and sold to the wallboard industry, Charlie says.

Most aggregate operations that focus on the construction materials market are concerned by the level of fines entering their product. This is less of an issue for the scrubber stone market because the end product is a fine dust. Charlie says the company avoids filling the stockpiles with too many fines because that becomes a handling issue. The stone the power plants receive is no larger than æ inch.


The most important consideration is the chemical composition of the product. The power plants supplied by Robertson Crushed Stone are looking for a stone that has high levels of calcium carbonate and very low levels of magnesium.

ìLast year we invested in a testing machine so that we could test our own stone,î says Vice President of Operations Will Robertson. ìThat helps us as much as it does the customer because we know exactly what we are dealing with and what we have to do to get our numbers where they need to be.î

Samples now can be analyzed in hours versus weeks. So if there is a problem, it can be corrected immediately. Historical data on the chemical compositions also is available on each ledge, dating back 50 years. Will and Katie often joke about their dad who saves everything, but it apparently pays off because they know the calcium content of each quarry ledge. If excavations lead to a seam with high magnesium content, that material will likely be used in agricultural lime and driveways or parking lots. Charlie says blending product is an option, but the company prefers to maintain the highest quality for its customers. Also, those seams are few and far between.


The production process at Robertson Crushed Stone is typical of any aggregates operation that produces a DOT stone, explains Quarry Manager Bud Bischoff. The overburden runs an average of 50 feet deep. On average Robertson Crushed Stone invests four months removing topsoil, clay, sandstone and a small layer of poor limestone. It is all landfilled on site with the exception of some topsoil that is sold. However, Charlie points out that there is a small market for dirt in this rural setting.

As useable material is exposed, the company turns to Impact Drilling & Blasting, an independent blasting company. Charlie says Robertson has been purchasing explosives from the company for more than 30 years. Three years ago, they contracted for its drilling and blasting services, as an in-house driller and blaster retired.

Impact Drilling & Blasting uses electric caps; a typical pattern is 12 ◊ 14 feet. Charlie says secondary breaking at the muck pile rarely is needed. Recently, however, the company has been experimenting with various ledges, which has left a few boulders behind. In this case, a hydraulic hammer would be used for secondary breaking.

The shot rock is loaded onto two Euclid R35 haul trucks by a Volvo 330C wheel loader. Each truck makes a round trip in about 10 minutes, moving about 400 tons per hour. The material is dumped into the hopper of a vibratory feeder with a grizzly. The scalped material, which is larger than 5 inches, falls into a 34- ◊ 44-inch Nordberg jaw crusher. The throughs bypass the crusher and are blended with crushed material on the primary conveyor.

This material is conveyed up to a 6- ◊ 16-foot Seco screen. It is a triple-deck, but only two screens are utilized for the scrubber stone, a æ-inch- to 0-sized material. Robertson, however, does have the ability to produce up to seven products at once with the help of a flop-gate system. The screen also is equipped with spray bars and nozzles to provide dust control. The screen also is enclosed for additional dust suppression and noise control.

The oversize of this screen is transferred to the secondary crusher; a Stedman 54- ◊ 60-inch impact crusher. Crushed material that falls through the finishing screen meets a second stacker and falls off as finished product. Everything else is transferred to a 54 El Jay cone crusher, which is on a closed circuit and discharges oversize back onto the primary conveyor until it is sized to leave.


Loadouts are a seamless process at Robertson Crushed Stone. A Volvo 220D, the primary loader, and a Volvo 150C wheel loader work the stockpiles. Charlie intends to replace the 150C with a larger loader as it retires. Each Volvo is equipped with Evergreen bucket scales. They are calibrated and set in accordance to Robertson's Thurman loadout scale.

Charlie says these scales help load trucks within a couple hundred pounds of the legal limits. The scales are particularly helpful while handling the scrubber stone because size varies from æ inch to 0. Volume is not necessarily an indicator of weight, Charlie says. One bucket may be dense with fines, but the next might be loose with coarse material.

The regular drivers carry truck-identification cards with magnetic strips that they present to a JWS automatic card reader while weighing in. The computer records the empty weight and uses that to calculate the weight of the load when the truck is ready to leave. When the calculation is complete, the driver is given the green light to creep forward for his printed ticket. Charlie says there are often 50 trucks lined up in the morning waiting for product, and they are usually gone within an hour.

ìThe card reader is tremendous,î Charlie says. The drivers do not have to waste time by coming into the office to retrieve tickets.î


Will says that the average haul for a truck is a four- to five-hour round trip. This lengthy voyage can drive up the cost of the end product. Unfortunately there are no alternatives. Will says there are no navigable waters near the power plants to support barge traffic.

Diesel costs are a primary concern because it is such a great distance to the power plant. With such volatility in the market, Robertson and most other scrubber stone producers now are including fuel formulas into their contract pricing. So if fuel prices go up, the cost per ton follows. ìIt is past the point where you can look into a crystal ball and say, ëHere is our price. We are going to be OK,íî Charlie says. And contracts with power plants usually are for multiple years.

Even with a fuel formula as a safeguard, everyone still suffers when the price of fuel skyrockets. This will be a key criterion for the operation to consider when it comes time to upgrade the facilities. Charlie says the company is running some older equipment, and the operation will be tailored for efficiency as it retires.

Robertson Crushed Stone owns 10 trucks and employs eight drivers. And its new International trucks do yield certain savings, Charlie says. They meet higher standards set by the Environmental Protection Agency and are built light. For example, newer trucks can haul up to 1Ω tons more because they are built lighter. And fewer hauls to power plants equal a lower rate of fuel consumption.


ìWhen certain contracts come to beî and it is time to upgrade, the Robertsons will likely turn to Process Machinery Inc. ìThey have done a tremendous amount of work for us,î Charlie says. ìI can say nothing but good about them.î

It was through Process Machinery that the Robertsons bought their cone and jaw crushers, as well as the stackers and conveyors. Charlie says he will likely work with the company to install two tandem cone crushers, a larger secondary screen and other equipment when the time comes.

Another key player in the history and future of Robertson Crushed Stone is Skelly & Loy, a consulting firm that provides environmental, engineering, geologic and other resource services. Charlie says they have worked with Skelly & Loy on and off for more than 15 years. The firm has provided guidance on engineering, quarry development and cost management. Also, Skelly & Loy will have a role in any upcoming development at Robertson Crushed Stone.

Relationships such as these, whether they are with consultant or contract blaster, are what make an operation successful. And let's not forget about those under the company umbrella. Robertson Crushed Stone employs 20 people. There are generally four people operating and maintaining the crushers and two in the scale house. Then, of course, there are loader operators, haul truck operators and office employees.

Bud, the quarry manager, has been working for the Robertson's since 1986. He started as a subcontractor, stripping. Since then he has been involved in every aspect of the quarry. Also, Charlie is particularly indebted to Jean Ann Birkle, the office and scale house manager who joined the company in 1995 after retiring from life on the road with some traveling musicians.


Despite the terms of a contract or the length of an employee's stay, nothing is more binding than blood. And now that Charlie's children (Will and Katie) are back from Indiana University, the company will have a new perspective on the industry. Will is bringing a management degree in public affairs, and Katie has a master's in business communication.

ìThe new blood does help bring in a fresher set of eyes,î Charlie says. ìThey show me at times that I am still a stick in the mud.î

One example is the company Web site, which is indefinitely under construction. Charlie says it is not critical to business, as about 90% of the product is sold to only two customers. Will, on the other hand, argues that a Web site will be an invaluable communication channel for the future because slowly but surely single-family homes are creeping up on their operation.

The future of the company's Web site may be up for debate, but one thing is definite: Even though the Robertsons are not producing a DOT stone, they have certainly paved the way to a solid future in the aggregates industry.

ìOur business here is steady and that's how you want to approach it,î Charlie says. ìIt is not something that you get really rich doing, but you will make a nice living for your family.î