Concrete Products

MAY 2017

Concrete Products covers the issues that attract producers of ready mixed and manufactured concrete focusing on equipment and material technology, market development and management topics.

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Page 33 of 67

32 • May 2017 Scottsdale, Ariz.-based Salt River Materials Group (SRMG) has added advanced blending capability to increase its stock of Class F fly ash, supplies of which have tightened due to weather and regulatory factors, plus changes in electric power generation. The producer landed an ash management contract in May 2016 for the Coronado Generating Station in St. John's, Ariz., where twin, 400-megawatt units run on low sulfur, Powder River Basin coal, and net up to 150,000 tons of Class C ash annually. Coronado joins contracts SRMG has acquired since 1973 covering Class F fly ash management at four Arizona and New Mexico generating stations; a contract involving a fifth such source, the Deseret Power Electric Cooperative station in Bonanza, Utah, just took effect (note page 34). Although widely adopted in manufactured concrete and stucco, Class C fly ash is restricted in key Southwest markets due to agency concerns with the material's limited role in combating alkali-sil- ica reactivity (ASR). To extend supply of Class F ash, synonymous with ASR factors and concrete mix economy, SRMG has engineered a system at its 19th Avenue Terminal, one of the company's five cemen- titious materials distribution facilities serving the Phoenix market. Twin Cyclonaire CB-150 Series Blend-Veyors have been deployed to blend and convey Class C and Class F ashes in semi-dense phase. Through precise weighing and robust blending, the CB-150s finish powder with calcium oxide content and other properties equivalent to a Class F ash per ASTM C618, Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete. The 19th Avenue Terminal has four conventional elevated silos, two 200-ton and two 400-ton capacity, plus a main, 5,000-ton slip formed concrete structure at grade. The Blend-Veyors rest at the base of the larger elevated silos, Class C forward, Class F aft. A series of air slides crisscrossing lower and mezzanine levels, and linking the four elevated vessels, will maximize the variety of Class C-F blends deliverable on short leads. The CB-150 Blend-Veyors consist of pods holding up to 4,500 lbs. of material and bearing on load cells, plus lower cone portions with 16 aeration points. A typical 90-second blending cycles equates to 25-30 tons/hour output. "We have blended Class C and Class F ashes by a more conventional, but less precise method: Blowing material simultaneously from two railcars into a dedicated silo," says SRMG Senior Vice President, Pozzolans Dale Diulus, P.E. "The new equipment supports a reproducible process, with much more verifiable blends of Class C and Class F ash feeds." FEATURE BY DON MARSH Better Blends Salt River Materials terminal leverages Class C feed to raise Class F ash output Continued on page 34 Class C (left) and Class F silos.

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