Diamonds in the Rough

By Mike Crummy, Technical Writer, The Promersberger Company | September 28, 2010

Few people would relate the everyday work performed by a diamond cutter to that of an operator running a hydraulic breaker in a quarry. While each makes a living working with rock or stone, the similarity between the two occupations seemingly ends there.

Certainly the skill of transforming a rough piece of rock into a dazzling diamond for a lucky lady's engagement ring is more of a science than busting up limestone or granite. But rock breaking also requires precision, particularly for those in the business of producing custom varieties of riprap — a coarse, angular-shaped rock primarily used in anti-erosion applications along shorelines. Given its successful history filling the riprap niche, Gulf Coast Limestone, Inc. is one company that fully appreciates the art of producing this natural rock product.

Based in Seabrook, Texas, Gulf Coast Limestone provides a number of services for various entities in north, central and southeast Texas. From specialty rail car unloading to providing crushed granite and concrete base materials, the company has earned a strong reputation for filling specific customer needs. While versatility is certainly a notable strength for Gulf Coast Limestone, its expertise in the production of riprap has become the company's calling card.

Gulf Coast Limestone didn't start out with an aim to become a big time riprap producer. The company got off the ground in 1962 when its founder, G.W. Robinson, served as a board member for a school district that needed a new parking lot. After placing an order for a railcar of limestone and hiring someone to haul and unload it, Robinson decided to go into the aggregate business, essentially as a limestone dealer. The venture was financially successful from the get-go and quickly expanded.

In the early days, the company was just a rock broker, acquiring crushed stone from quarries before hauling and selling it to customers. In some ways, little has changed. Gulf Coast Limestone still doesn't operate its own quarries and relies on other producers for rock to sell. The business has also stayed within the family. The founder's three children — Bob Robinson, Suzy Mayfield and Glenda Walker — co-own the company, while grandson Bobby Walker is the operations manager.

The most significant adjustment in company history came after a decision by several big producers to get out of the riprap game. "The specifications are so tight," said Walker, who began working with his family's company in 1977. "Several different entities and agencies need riprap, and each has their own strict set of requirements. It's very labor intensive and time consuming to meet the different specifications. Ultimately, many of the large quarry operations just didn't find it feasible to continue making riprap."

While Gulf Coast Limestone's established customer base still required and demanded riprap, the company's supply lines had seemingly been cut off. "At that point we were basically forced to produce riprap ourselves," said Walker. "Fortunately we became pretty good at it."

The company now works with three different quarries, each providing a separate work area for Gulf Coast Limestone's operation. The arrangements have been mutually beneficial for both sides. Typically, any oversized boulders produced during a blast must be set aside in a stockpile. It can sometimes be a long wait before they are broken down and eventually crushed. With Gulf Coast Limestone on-site, the boulders can be processed immediately, freeing up space for the quarry and keeping business flowing for its riprap-producing partner. "It's far more efficient for them," said Walker. "They bring us the oversize rock and we turn it into a sellable product."

Rather than simply producing a large reserve of standard riprap that sits until purchased, Gulf Coast Limestone fulfills special orders from a number of customers. Clients include the Natural Resource Conservation Service and Lower Colorado River Authority, both of which utilize riprap for water erosion control; the Texas Department of Transportation, which applies rock as part of bridge and road embankment construction; and the U.S. Army Corps of Engineers, which uses riprap for breakwater structures and flood control projects. The company also offers riprap for private jobs and smaller day-to-day orders.

A typical riprap order for Gulf Coast Limestone comes about through a bidding process for a job with specific gradation requirements. "Once we have the specs for the job, we start by reducing the oversize boulders with our hydraulic breakers," said Walker.

The company currently runs four Atlas Copco breakers, with each handling breaking duties at different locations. Two HB 2200 models, both mounted on Cat 325 excavators, are stationed at quarries near Dallas and Austin. An MB 1200 works in a quarry north of San Antonio and an MB 800 produces concrete riprap at ready-mix yards in the Houston area. The breakers were all purchased within the past two years.

"We produce some granite product at one location, so we have a larger unit there," said Walker. "The smaller breakers won't break granite, but they're perfect for other applications. The MB 1200 is being used exclusively on limestone. And since concrete is easier to break than the natural stone riprap, we use the smallest unit for our concrete riprap product."

The breakers' dependability is aided by the ContiLube II automatic lubrication system. Mounted directly onto the breaker, ContiLube II takes the chore of greasing the breaker out of the operator's hands. Walker also cited the AutoControl monitoring system, another standard feature on the three largest breakers, as a benefit that further contributes to equipment reliability and more efficient performance.

AutoControl allows the breaker to adapt its frequency and power output to match actual operating conditions. The system begins by firing the piston at half power until the working tool is hitting against a solid surface, at which point energy output is increased to full power. "The breakers hit hard when they need to," said Walker. "And when full power isn't needed, they hit fast. It's a constant, automatic adjustment that really allows our operators to turn out a lot of product in a short time."

In addition to impressing with their performance, Gulf Coast Limestone's Atlas Copco breakers have also defied a common misperception that productive breakers must be noisy breakers. Each unit is equipped with the VibroSilenced system, a standard feature that uses an arrangement of elastic damping elements to isolate and contain sound produced by the breaker's percussion mechanism.

"The breakers are remarkably quiet," said Walker. "One day we were about to break some rock near an engineer's trailer, and he came out to tell the operator not to work so close. But once the breaker started up, he realized it wasn't a problem and went back inside. With all the noise being generated out in a quarry, I think it's pretty beneficial for our crews to be able to work with a quiet piece of equipment."

Gulf Coast Limestone has 42 employees, 10 of whom are the company's "diamond cutters," the specialists who construct the weighted gradations of riprap. While certainly there is technical expertise involved in assembling and testing a custom riprap order, much of the actual process involves a purely intuitive assessment. "The top size of rock is sized visually," said Walker.

When training a new crew or operator, Gulf Coast Limestone runs through a drill where everyone guesses the weight of various stones as they're placed on a platform scale. This practice helps operators become proficient at knowing the approximate size and weight of stones just by looking at them, a skill that saves invaluable hours while building a stockpile.

"Not everyone can look at a set of numbers on a piece of paper and visualize what a pile of rock should look like," said Walker. "Not everyone has an eye for it."

Once enough broken rock is compiled, operators build a stockpile model based on the specified gradation requirements for a given order. Stones are visually sorted by size and then dry-screened on a grizzly bar screen to remove any lingering chips or fines. The next step is a weighted gradation, where every stone is weighed individually. Each piece of riprap is charted to make sure the overall pile fits the customer's needs.

In the example gradation chart shown here, there are five sizes of riprap, from 6-inch to 30-inch, and the stockpile's total weight is 20,000 pounds. An actual gradation would list the specific weight of each of the 157 stones. In this case, 75 stones are 6 inches or smaller. The smaller stones might weigh just 1 pound, while the heaviest in this bunch weighs 25 pounds. Collectively, the 6-inch stones weigh 500 pounds, accounting for 2.5-percent of the stockpile's weight. This falls within the customer's requirements of 0 to 20 percent for that stone size.

Fifty additional stones weighing 3,500 pounds collectively come in between 6 inches and 12 inches, the heaviest rock weighing 125 pounds. Together with the 6-inch stones, the 4,000 pounds of rock make up 20 percent of the stockpile, again falling within the specifications for the order. Rocks fitting within the 18-inch and 24-inch sizes bring the weight totals to 9,000 poundsand 16,500 pounds, respectively. The percentages fit within the job requirements. The gradation concludes with two 30-inch pieces of riprap, with one weighing 1,500 pounds and the other 2,000 pounds.

Even the most precise operators may have to make slight adjustments after the weighted gradation process. Once the order is ready, Gulf Coast Limestone contacts the customer for approval.

"We require the customer to approve the product before it's shipped, and we strongly encourage them to physically come to the site to do so," said Walker. "It's not uncommon for an inspector to make a few changes like adding some smaller rock, and we can do that easily enough in the quarry. But once that order hits the job site, it's too late."

Trucks carrying a maximum load of 25 tons are used to haul most of the finished product to its destination. "We also occasionally use 100-ton railway gondolas to transport product," said Walker. "We used to do a lot more by rail delivery, but some changes in railroad procedure have made trucking more practical."

While Gulf Coast Limestone doesn't heavily utilize railroads for its own purposes any longer, the company is still very much involved in offering its expertise in rail car unloading, a specialty that accounts for $4 million of annual income. "We've always been very proficient at unloading," said Walker. "And since we have special equipment and the expertise, it only makes sense to keep that aspect of the business going strong."

Business has been good all-around for Gulf Coast Limestone. The company's annual production includes 350,000 tons of crushed limestone, 50,000 tons of concrete riprap and 75,000 tons of limestone riprap. The numbers are impressive for an operation that doesn't even run its own quarry. "We're unique," said Walker. "Obviously there are thousands of producers, but nobody else runs their business quite like we do."

Given the company's aptitude for providing niche services, "rock producer" doesn't feel like the proper term to describe Gulf Coast Limestone. Instead, "rock specialist" or "diamond cutter" may be more appropriate monikers. And sure, though Gulf Coast Limestone will never be asked to make a solitaire cut on a 2,000-pound stone, the precision the company offers is matched by few — and just as valuable to its customers.