U.S. Concrete’s Polaris Materials business unit delivers premium aggregate to southern California practitioners pressed for lofty strength, modulus of elasticity targets
|Along with the washed sand and ½-in. grade from Orca Quarry (left), the 1-in. gravel has density, shape and surface texture characteristics yielding high performance structural concrete with lower portland cement and admixture requirements than mixes bearing sand & gravel typical of the southern California market. Eagle Rock Aggregates promotes the material for its early and ultimate high strength development, low drying shrinkage, in-place concrete thermal control and modulus of elasticity qualities.|
Prospects for high performance concrete in the Los Angeles Basin have been tempered by the average quality of sand & gravel deposits in southern California, and limited demand for higher than conventional design strength mixes due to past preeminence of structural steel in mid- to high-rise construction.
Raw-material logistics, market demands and enlightened engineering practices are turning the tide in HPC’s favor: A new source of premium sand & gravel, critical to attainment of compressive strength and modulus of elasticity (MOE) thresholds exceeding 8,000 psi and 4,000 ksi, supports a strong case for reinforced concrete in vertical and horizontal conditions subject to high seismic and wind loads. Developers responding to a downtown and west Los Angeles residential and commercial boom are pursuing tighter schedules on projects calling for leaner shear walls and columns or stiffened core walls with an eye to floor plates offering more usable square footage. And, engineers and agencies looking beyond compressive strength and MOE metrics are tapping the premium aggregates’ potential to raise concrete performance for non-building work.
Sand & gravel at the heart of the Los Angeles market’s HPC embrace is sourced from the Orca Quarry, a 130 million-ton glacial deposit developed by Vancouver, B.C.-based Polaris Materials Corp. Inordinately clean and dense, with natural micro surface texturing characteristics primed for strong matrix bonding, the material yields engineering properties matching or exceeding those of mixes in the leading HPC markets of Chicago and New York. In conjunction with synergistic-admixture dosing, portland cement and supplemental cementitious materials optimization, temperature control simplification on mass pours, plus elevated-slab, column and shear wall schedule reductions, Orca aggregates competes against local fine and coarse stock on mix design and in-place concrete cost criteria.
Polaris Materials’ U.S. subsidiary Eagle Rock Aggregates Inc. began supplying southern California concrete producers with three Orca grades in 2015, permitting a four-acre Port of Long Beach terminal for 1 million tons annually. Approvals from leading structural engineers and key agencies confirm how Orca washed sand and ½-in. or 1-in. gravel have already changed the Los Angeles County concrete market and justified pursuit of a second permit, awarded in fall 2018, increasing terminal throughput up to 2 million tons annually.
Against old methods and materials, Orca aggregate has rewritten the reinforced concrete value proposition around accelerated project schedules; simplified mix designs lighter on cement and admixture requirements; and, finished slabs or structures inviting characterizations like “smaller,” “thinner,” “stiffer,” “optimal,” “completed faster,” “of lower embodied carbon,” and “less prone to early and longer-term deflection.” In under three years, structural engineers and agencies have acknowledged Orca aggregate concrete advantages and specified or approved the premium sand & gravel for more than 30 high profile building or public works jobs. Eagle Rock continues market development with the help of Los Angeles ready mixed producers and mobile batch plant-equipped contractors.
“We target contracts in the eight-figure and above range,” says Director of Business Development Dick Williams. “We have been very fortunate to work on complex projects with leading structural designers who see the range of engineering properties that Orca aggregates impart in structural concrete. It requires a business, engineering and marketing-sales model to bring an optimum performance material like this into a major market and present clients and their customers with ‘cost-in-place’ proposals. When factoring all benefits related to project schedules, site labor and simplified mix designs, we can compete on a per cubic yard basis instead of accounting just for a price per ton of aggregate.”
Los Angeles is enjoying a high-rise building boom as developers reshape the downtown area around new apartment or condominium living projects abutting arts or entertainment districts and Staples Center, home to the NBA LA Lakers and LA Clippers teams, he adds. Facing high land values on points west of downtown, developers are also planning more mid-rise properties on sites that in the past might have topped out at three to five levels. Some high profile commercial work anticipates Los Angeles’ hosting of the 2028 Olympic Games. That event is likewise spurring higher transportation infrastructure investment, partly supported by receipts from 2017 state gas and diesel tax increases of 12 cents and 20 cents per gallon. Transportation and other public works projects are broadening Eagle Rock prospects, as Orca aggregate concretes exhibit low shrinkage characteristics and high flexural strength, alongside excellent compressive strength and MOE.
|The Long Beach Terminal is entering its fourth year of operation. It receives three grades from Polaris Materials’ Orca Quarry (opposite page), a pristine glacial deposit on northern Vancouver Island. One of three contract Polaris vessels, the dry bulk ship shown here is based on Canadian Steam Ship design, with self-unloading features and 76,000 metric ton capacity. A double bottom configuration sees material from a lower section collected on conveyors that converge in a vertical path for transfer to the terminal’s boom conveyor.|
Before setting its sights on southern California, Polaris Materials garnered an elite customer following in the San Francisco Bay Area, home to Eagle Rock’s premier facility, a Port of Richmond terminal permitted for 1 million tons annually. The Port of Long Beach terminal spawned a second Eagle Rock marketing and technical team charged with demonstrating Orca aggregates’ potential to advance HPC specifications and practice in the Los Angeles Basin. Team leader Dick Williams joined Polaris Materials and Eagle Rock after 40 years of industry service, including senior and executive management roles in multiple concrete industry segments. One of his later assignments was corporate vice president of Marketing and Sales (2000-2005) for U.S. Concrete Inc., which acquired Polaris Materials in 2017.
Through its San Jose-based Central Concrete Supply Co. business unit, U.S. Concrete had observed since 2007 the potential for Eagle Rock to disrupt San Francisco Bay Area construction and engineering. Management saw a similar story beginning to unfold in Los Angeles, where MOE thresholds rule the day in structural concrete.
“By having the superior quality of Orca materials, engineers don’t have to just talk about MOE. They can now produce high modulus of elasticity concrete designs in the 4,000-7,000 ksi ranges,” says Williams. “That was a discussion no one wanted to have when aggregates typical of the southern California market were yielding concrete with MOE in the 3,800 ksi area at best. Modulus of elasticity and other performance attributes have put our sand & gravel on the southern California map.”
A June 2017 memo, “Required Concrete Modulus of Elasticity Testing for High-Rise Concrete Buildings,” leaves no question where the City of Los Angeles Department of Building and Safety’s Permit & Engineering and Inspection Bureau Chiefs stand on structural concrete member stiffness:
|The Long Beach terminal launched with ships from Vancouver island delivering once a month, a frequency since increased as Orca aggregate demand and permitted output have climbed. The terminal boom has a 60-in. belt charging 48-in. main conveyor and stacker belts; target unloading rate for the premium sand & gravel is 2,500 mt/hour. Terminal staff create a small sand stockpile (above) for truck loading on ship days to eliminate interference with main and radial stacker conveyor operations.|
|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, Oceanwide 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. PHOTO: CallisonRTKL Inc.|
Concrete high-rise buildings are designed and constructed based on calculated modulus of elasticity (MOE) to confirm compliance with the building drift limits. MOE shall be part of the approval of the concrete mix design for all new concrete buildings with structural height of more than 160 feet. Notes on the structural plans shall specify the MOE for concrete used in the design of the seismic force resisting system, including beams, columns and shear walls … [and] indicate: ‘The mix design shall specify aggregate with a modulus of elasticity not less than that specified on the plans. This modulus of elasticity of the aggregate shall be consistent with modulus used in the trial mix designs for establishing the concrete f’c and MOE used in the building design’ … MOE of the trial mix design shall be verified through testing in accordance with ACI 318 R8.5.1, referencing ASTM C469 Standard Test Method for Static Modulus of Elasticity and Poisson’s Ratio of Concrete in Compression results.
The MOE–aggregate link in concrete specifications and structural member dimensions was astutely detailed months before the LA Building Department memo in a report from the industry’s foremost HPC producer, Chicago-based Prairie Material. In “The High E Trend Continues,” Lab Services Manager Nick Beristain cites a project analysis revealing that each 10 percent increase in MOE afforded a potential 10 percent decrease in concrete column sizing.
“Even though higher psi is generally indicative of higher modulus, we found that density of the stone has a greater impact on modulus values,” he observes. Prairie-branded High-E concrete mixes in structural conditions provide high compressive strength, reduced creep and higher stiffness than conventional mixes, he adds, while their “greater rigidity helps to control drift and motion in tall buildings.”
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 concrete 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 schedule 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 structural 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 CO2 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 elevated 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 producer and testing agency teams building structural concrete frames across the Los Angeles Basin.”