Making gravel is a lot like making cookies from scratch: it starts with a recipe.
In this article, you’ll learn about how we create our product recipes, the basics of crushing rock, and the ways we’re changing the system.
Specifications: The First Step in Creating a Recipe
Some people like chocolate chip cookies; some like peanut butter or sugar cookies. Just like different people like different flavors of cookies, different clients need “flavors,” or specifications, of rock products.
Specifications tell rock producers like Washington Rock exactly what a rock product should look like. They give us information such as the size, durability, and gradation* of a rock product. They also tell us how the rock should be used, like whether it will be used as a road base or as a fill around pipes. (*Gradation refers to the percentage of product that fits into certain screen sizes.)
Specifications are often created by state and federal agencies. They set these standards to tell rock producers like Washington Rock which recipes to use.
State and federal agencies often write their specs based on standards set by organizations like the American Railway Engineering and Maintenance-of-Way Association (AREMA), ASTM International (formerly the American Society of Testing and Materials), and the American Association of State Highway Transportation Officials (AASHTO).
Even organizations like the United States Golf Association (USGA) and the National Football League (NFL) have their own specs.
The specifications used depend on the project, and some projects use specs from multiple sources. so Washington Rock makes products based on project requirements.
Trial and Error: Creating Product Recipes
The process of making the right product requires a “recipe,” explains Ryan Hogg, quality control manager for Washington Rock. A recipe tells crew members which order of crushers, screens, and wash cycles to use to make a product while creating the least amount of waste. Waste means lost time and money.
A recipe might contain other instructions, like how fast the material should be processed, how much water should be used, etc. A recipe might also explain how to create more than one product from the same batch of material and whether “leftovers” can be recycled back into the system to be processed all over again.
The end results of the recipe are sent to the Quality Control Lab (QC Lab) to be tested and inspected for compliance with project requirements. The video below shows how the QC lab’s efforts result in usable products.
“We measure the qualitative value of each recipe at each variable,” Hogg said. The QC Lab then reports back to plant operators and supervisors to let them know the results of the test. If the recipe doesn’t meet product specs, the QC Lab will work with team members to figure out ways to adjust the recipe.
For example, if a gravel product is too coarse, the team might adjust the crusher so that it crushes more finely. If the product is too dirty, spray nozzles might be adjusted to increase water pressure and volume. In tough cases, one product might be mixed with another product to get the right result.
The Basics of Rock Production
At Kapowsin Quarry in Orting, Washington, it takes many pieces of equipment configured in just the right way to make just one type of rock product.
In a hard rock quarry, it starts with using dynamite to blast a rock face, which breaks a solid mass of rock into manageable chunks. Some big pieces from the blast are set aside for projects like rock walls, shorelines, and seawalls. But most of the rock has to be crushed into smaller pieces to create rock products like gravel or quarry spalls*. (Quarry spalls are rocks that range from 2″-8″ in diameter. They are used for projects like gabion baskets.)
Let’s follow the journey of making 5/8” minus, otherwise known as Crushed Surfacing Top Course (CSTC) or driveway gravel.
An excavator drops large pieces of rock into the mouth of a machine called a jaw crusher. Like a jaw, it uses ridged teeth that move up and down to smash rock against manganese chrome plates and break it into smaller pieces.
The smaller pieces ride a conveyor belt to the main plant, which has a series of crushers, screens, and washing equipment. At the main plant, the crushed rock is sent through a secondary crusher, then a screening plant. The screening plant separates the rock into different sizes by shaking it through large metal screens with different hole sizes.
Conveyors carry each size of product to different stockpiles where the material is deposited. Sometimes one material is combined with another, or it can be used as is.
Upgrading the System
Recently, Washington Rock added a new processing unit to the production system: a Kodiak K400+ cone crusher, which uses a cone-shaped piece of manganese to crush rock against the sides of a manganese liner.
Gary Hamilton, manager at Kapowsin Quarry, said that the new crusher will make products more efficiently and quickly, reducing overhead and increasing production. “The team saw that there was a bottleneck—the existing crusher couldn’t keep up with what we were demanding from that position,” Hamilton said. “That was the main strategy: to get something to keep up with the plant production we were throwing at it.”
The crew can configure output from the crusher so that materials can easily be sent back to earlier points in the system, eliminating some of the time required to mix and recycle products.
Adding a new piece to the system was not a simple process. Head mechanic Jim Nehrbas led the installation of the crusher, including taking measurements, drawing up plans, and assembling the new component. Plant mechanics Joey Shockley, Travis Petersohn, and Travis Garcia assisted in disassembling the old crusher. Nevada-based Goodfellow Brothers provided the cone crusher and manufactured a custom stand to incorporate the new crusher into the existing system. Welders Henry Goble and Tyler Luepke worked on integrating the new stand into the system.
Understanding exactly what the crusher can do and how recipes might change is an ongoing adventure, Hamilton explained. But it’s evident that it will improve the production process.
“Simply put, it’s bigger, better, more efficient, and easier to record cone settings as well as easier to adjust,” Hogg said.