Responding to the increasing use of blended cementitious materials in concrete, Cyclonaire Corp. has developed technology for terminal operators seeking to expedite batching and loading of portland cement, fly ash and ground granulated blast-furnace slag combinations.
| Central Plains uses the CB Series Conveyor for blending capability and to transfer products to various Omaha terminal silos. |
During the industry’s downturn, Omaha, Neb., terminal operator Central Plains Cement recognized the customer benefits of blending capability— starting with producers and contractors performing state work. Nebraska Department of Roads determined through rigorous tests and studies that Class F ash was well suited to mitigating alkali silica reactivity that had been observed in concrete around the state. The department adopted a specification requiring all cementitious materials in department projects have a fly ash factor up to 25 percent.
A business Dallas-based Eagle Materials rebranded in its 2012 assimilation of Lafarge North America’s Great Plains operations, Central Plains needed the flexibility of providing custom blends one tanker load at a time. The company enlisted York, Neb.-based Cyclonaire for a blending solution at the Omaha facility.
The CB Series Conveyor combines loading, blending and conveying functions into one high efficiency unit, eliminating multiple pieces of process equipment such as weigh feeders, ribbon mixers, and screw conveyors. The CB vacuum loads from multiple sources, blends, and then transfers the blended material to one or more destinations.
Free of vacuum pump or filter requirements, the system operates with a single, rugged rotary lobe pressure blower operating at 15 psi. Positive air from the single blower is used to drive a venturi generating the vacuum that loads two or more materials to a defined weight. Once the material has been batched into the CB, a pneumatic blend cycle ensues. At the conclusion of the blend cycle, the same positive air from the blower that was used to generate the vacuum now conveys the blended material to the next operation, typically to loadout or directly to a mixer.
The capability to vacuum load simplifies CB System installation because it does not require any costly pits or expensive structures. The Cyclonaire design allows customers to tap into existing silos without modifying current discharge equipment—allowing the blending and non-blended loadout to occur simultaneously. Flexibility in the routing of the vacuum lines, as well as the discharge convey line allows the CB Blender to be installed at a convenient location.
The Central Plains Omaha facility has four 5,000-ton silos. Once installed, the CB system allowed access to all five materials when producing blended products. To take full advantage of the new capability, two loadout silos were added in line with the existing vessels. All silos utilized the same loadout spout, truck scale, and controls, an arrangement enabling transfer high rate for portland cement or two custom
blended products.
Customers can call in their order in advance and the blender will batch the exact amount, allowing Central Plains to deliver the product without delaying tanker drivers. The entire system can be operated from the loadout control room, and does not require local supervision. An operator enters the ingredients, ratio, and amount to be blended and starts the system, which then operates automatically until it reaches the set point.
To save the operator time, combinations of portland cement and supplementary binding agents can be pre-programmed, saved and identified by a customer-designated product name or code. The operator is required only to enter the product ID, quantity to be blended, and the convey destination. Full logging and reporting of individual batches and total blended are available to meet quality requirements or state reporting regulations.
“We are able to easily stay within the NDOR’s specification of ±2 percent and also meet requirements of ASTM 595 for blended cements,” says Central Plains’ Joel Sedlacek. “We now not only [offer] the Class F ash blend, but can also produce many other blends that contain various percents of cement, slag and other ashes at any percent customers require.”