Concrete Products

JAN 2019

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 74 of 103 January 2019 • 69 FEATURE EAGLE ROCK/ORCA AGGREGATE FIRM VALUE Engineering behind Eagle Rock's largest southern California high-rise project to date, Oceanwide Plaza in downtown Los Angeles, aligns with the LA Building Department's view of MOE. The project topped out in mid-2018 and required more than 140,000 yd. of Orca aggregate mixes for one 53- and two 40-story reinforced concrete towers, fronted by a five-level podium of similar construction. The development leveraged a host of engineering properties attributable to Orca sand & gravel: A 14-ft. thick mat foundation saw placement of 26,000 yd. of con- crete designed to reach 6,000 psi at 56 days; the cement-optimized mix design with 25 percent fly ash met both strength development and thermal control requirements—the latter realized without the expense of embedded cooling pipes. Along with foundation pours, the Oceanwide Plaza concrete sched- ule had 5,000, 8,000 and 10,000 psi mixes for slabs, shear walls and columns with 3,500 to 6,000 ksi MOE targets. Suspended slab mixes, designed for 5,000 psi at 28 days, required minimum 3,000 psi strength development at three days or before stressing, and MOE of 3,122 ksi for primary shoring removal. Attainment of both struc- tural parameters at the earliest possible stages augmented schedule predictability and positioned concrete contractor Webcor Builders to accelerate floor-to-floor construction time frames. "We were able to optimize the cement content for all Oceanwide Plaza concrete," Williams observes. "Factoring all combinations of mixes on weighted averages, we reduced the portland cement requirement 140 lbs./yd. In terms of greenhouse gas emissions, the Orca aggregates' capacity to displace portland cement equated to a 19,600,000-pound reduction in carbon dioxide for the concrete schedule." The potential to lower net portland cement requirements enables Orca sand & gravel specs to bring additional value where project principals are calculating Materials & Resources credits related to CO 2 emissions reduction in LEED v4 or similar green building certification efforts. In that regard, Eagle Rock notes, Oceanwide Plaza sets a carbon benchmark that will inform schedules on forthcoming towers reshaping the Los Angeles skyline and proving the efficacy of tall reinforced concrete in high seismic/wind zones. "We are continually trying to push the compressive strength and MOE thresholds up; cut column and shear wall dimensions down to assist in lightening overall building weight; facilitate reduced ele- vated slab deflection; and, build rigidity in the frame," Williams affirms. "We have more than 20 projects in the pipeline over the next 24 months, a few in the 50- to 70-story range, and are working with ready mixed producers on approvals for 12,000 psi and 14,000 psi high performance concrete mixes. "We will continue to invest time and effort working with project stakeholders to exploit the potential of Orca sand & gravel and high performance concrete. We are committed to participating with the owner, structural engineer, architect, contractor, ready mixed pro- ducer and testing agency teams building structural concrete frames across the Los Angeles Basin." PHOTO: CallisonRTKL Inc. No project signals the arrival of all reinforced concrete, high-rise building designs in Los Angeles better than Oceanwide Plaza—Eagle Rock Aggregate's largest specification to date. With 40-story twin towers and a 53-story centerpiece, the project consumed 140,000 yd. of high performance concrete mixes bearing Orca washed sand and ½-in. and 1-in. gravel. Los Angeles Building Department, engineer and contractor observations on the successful Oceanwide Plaza concrete schedule will influence mat foundation, slab, shear wall and column construction for reinforced concrete high-rise buildings soon to break ground throughout downtown. Project principals: Developer, Ocean- wide Holdings; Architect, CallisonRTKL, Los Angeles; Engineer, Englekirk Structural Engineers, Los Angeles; General Contractor, Lendlease, Los Angeles; Concrete Contractor, Webcor Builders, Los Angeles; Ready Mixed Supplier, Catalina Pacific, Duarte Calif.

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