Individual microspheres are approximately the diameter of an average human hair. This photo shows one microsphere in concrete magnified 1500 times using a digital 3-D microscope.
In conventional air-entrained concrete, scaling or internal deterioration (shown in the photo) can be the result of an inadequate air void system caused by factors such as materials, production procedures, and construction practices.
These factors do not impact the freeze-thaw durability of concrete made with the microsphere-based admixture technology.
Microspheres are dispersed in a liquid admixture solution for ease of dispensing and mixing in concrete.
The Admixture Systems business of BASF's North American Construction Chemicals division today announced a breakthrough technology for freeze-thaw durability that eliminates the need for air-entrained concrete. This patent-pending, microsphere-based admixture and point-of-use manufacturing system is being developed to help concrete professionals overcome the challenges traditionally associated with the variability and uncertainty of producing air-entrained concrete.
Microspheres are extremely small, hollow spheres that have a highly resilient, tough, but flexible, polymeric shell. Similar to entrained air, they provide stress relief zones for the expansion of freezing water within concrete, enhancing its long-term durability.
However, unlike traditional air entrainment, microspheres are not susceptible to variations in ambient conditions, concreting materials, construction practices and other factors that often impact the air void system in concrete. In addition, the compressive strength of concrete treated with the microsphere-based admixture technology can be over 30 percent higher than an air-entrained concrete, because of the difference in air content. This results in opportunities to optimize concrete mixtures for performance and sustainability.
"Microspheres are manufactured at the producer’s plant to provide consistent, stable performance, every time,” said Paul Seiler, Technology Manager, Admixture Systems for BASF in North America. “They are dispensed and uniformly mixed into concrete at a fixed dosage and are the optimal size for freeze-thaw durability.”
Dry microspheres have been used successfully in Europe for many years in niche concrete applications. However, their widespread use has been limited due to the cost of delivery. The point-of-use manufacturing system BASF has developed makes it economically feasible to use this proven microsphere technology for freeze-thaw durability of concrete.
"Up until now, air entrainment has been the state-of-the-art technology for freeze thaw durability of concrete," said Juan Alfonso Garcia, Vice President, Admixture Systems, for BASF in 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 our customers more control so they can dose their concrete and be done with it.”
BASF plans to commercialize the microsphere-based admixture technology in 2015. For additional information, visit us on the web at www.master-builders-solutions.basf.us.