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Besting Bubbles

BASF SET TO MASTER CONVENTIONAL AIR-ENTRAINING ALTERNATIVE

By Don Marsh

One of the more ambitious technologies in the long history of the Master Builders Solutions brand is on track for a commercial launch in the second half of 2015. After the 2014 ConExpo-Con/Agg preview of a polymeric, microsphere-based agent manufactured at the batch plant and aimed at replacing air-entraining agents, BASF Construction Chemicals’ Admixture Systems commenced market awareness and acceptance activities.

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Admixture Systems Manager, Product Management Tony Schlagbaum (left) and Product Manager Mark Bury open an Illinois Department of Transportation demonstration of the air-entraining alternative and production prototype. The event was staged at the agency’s Bloomington Maintenance Facility, nestled at the Interstate 55 & Interstate 70 junction, and drew 50 state, county and municipal engineers, including Chicago Department of Transportation staff.

Formally branded MasterSphere FT 300, the technology positions producers and their customers to improve slabs and structures’ freeze-thaw durability, and overcome void size and distribution variability challenges traditionally associated with air-entrained concrete mixes. That variability is especially owed to the effects on air voids of aggregate, cement and supplementary cementitious materials; air-entraining agent dosage; batch contaminants; mixing dynamics; temperatures during batch-to-placing window; and, mix slump changes.

MasterSphere FT 300 is dosed at 1 percent by volume of concrete, equating to upwards of 500 million microspheres per cubic yard, versus the 22 million air voids conventional air-entraining agents impart in the same quantity. BASF Admixture Systems’ on-site production process yields uniformly sized microspheres, primarily less than 100 microns in diameter.

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A late-summer Illinois Department of Transportation Bloomington Maintenance Garage workshop saw MicroSphere FT 300 production in a shipping container-housed prototype with polymer compound feed tank, conversion equipment and finished admixture storage vessel. A load of ready mixed dosed with the agent at 1 percent target was for test pavement sections, plus conventional cylinder and beam specimens. IDOT crews placed three slabs, where heavy truck traffic and deicing compound exposure are assured. The slabs will allow comparison of a conventional IDOT bridge deck mix and MasterSphere FT 300 concrete. Agency officials elected to have the control and microsphere mixes pumped, a delivery method that can challenge the effectiveness of air-entraining agents.

Low specified dosage rate for MasterSphere FT 300 enables producers to proportion new mix designs of optimized cement content, according to product developers. Using conventional air-entraining agents to achieve 5 percent to 8 percent air content, producers need to increase and tailor cementitious material content to meet compressive strength targets. By eliminating the need for air-entrained concrete and establishing a 1 percent MasterSphere FT 300 target volume, the new system invites fine and coarse aggregate optimization at the expense of higher cost binder.

“Up until now, air entrainment has been the state-of-the-art technology for freeze-thaw durability,” says Juan Alfonso Garcia, vice president, BASF Admixture Systems/North America. “But concrete professionals deserve a technology that is more stable and predictable no matter what the environmental conditions may be. Our global team has spent seven years developing this game-changing technology to give customers more control so they can dose their concrete and be done with it.”

“Microspheres are manufactured at the producer’s plant to provide consistent, stable performance, every time,” adds BASF Admixture Systems Technology Manager Paul Seiler. “They are dispensed and uniformly mixed into concrete at a fixed dosage and are the optimal size for freeze-thaw durability.”

FEATURE-BB-IDOTI-400The hollow MasterSphere FT 300 spheres have highly resilient, tough, but flexible, polymeric shells. Similar to entrained air, they provide stress relief zones for the expansion of freezing water within concrete, imparting long-term durability. The compressive strength of concrete treated with the microsphere-based admixture technology can be over 30 percent higher than an air-entrained concrete due to net air content difference.

PRODUCTION ECONOMY

Dry microspheres have been used successfully in Europe for years in niche concrete applications, notes BASF Admixture Systems, but the cost of delivery has hampered widespread adoption. With a footprint approximating a pickup truck bed, the company’s point-of-use MasterSphere FT 300 manufacturing and raw material feed make it economically feasible to use microsphere technology for freeze-thaw durability in lieu of conventional air-entrained concrete.

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BASF Admixture Systems Petrographer Jacki Atienza deploys a digital microscope with 3-D capability to illustrate a MasterSphere FT 300 concrete specimen; with the diameter approximately that of an average human hair, the microsphere shown in the close up view (below) is magnified 1,500 times. The product is dispersed in a liquid admixture solution (bottom) for ease of dispensing and mixing concrete.
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BASF Admixture Systems began aggressive freeze-thaw testing in early 2014 on concrete beams, cast with MasterSphere FT300-dosed mixes, along the Treat Island, Maine, shore—an environment where specimens are assured constant wetting and drying due to prolific Bay of Fundy tides. Additional testing has continued through concrete producers participating in beta phase microsphere manufacturing and specimen preparation, along with transportation agencies that have hosted BASF Admixtures Systems demonstrations in New York, Minnesota, Illinois, Utah and Alberta.

Anchoring market acceptance activities, the demonstrations have seen sample MasterSphere FT 300 production in a containerized lab, and preparation of test specimens affording freeze-thaw durability measurement against hosting agencies’ control samples—beams, cylinders and slabs cast with conventional air-entraining agents. BASF Admixture Systems is compiling performance data from the field and preparing to resume state and province demonstrations in the spring, leading to the MasterSphere FT 300 commercial debut later in the year. — www.master-builders-solutions.basf.us

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In conventional air-entrained concrete, scaling or internal deterioration can be the result of an inadequate air void system caused by factors such as materials, production procedures, and construction practices; none impact the freeze-thaw durability of MasterSphere FT 300 concrete.