Silica Fume Alternative
- Published: Wednesday, 01 July 2009 08:00
- Written by CP Staff
Under a new partnership with Calgary-based Whitemud Resources Inc., Cemstone Products Co., Mendota Heights, Minn., has begun using WhitemudMK high-reactivity metakaolin (HRM) as a supplementary cementitious material in concrete mix designs for heavy/civil work, including bridges, structural slabs and parking structures. The premier WhitemudMK source in the U.S., Cemstone will promote the material at its 50-plus ready mixed plants in Minnesota, western Wisconsin and northern Iowa. The company will also distribute the MK agent through its standard and supersack bagging operations.
Whitemud Resources is dispatching its branded HRM by rail to Cemstone's Twin Cities base from a new Saskatchewan mill, built specifically to supply concrete and energy (oil well capping) markets. The operation draws from a large deposit of white kaolin (or China clay), batches of which undergo calcining and kiln processes similar to those for portland cement. The finished WhitemudMK is an ASTM C618 aluminosilicate pozzolan that can be dosed as an SCM at rates up to 20 percent.
With particle sizing finer than cement and fly ash, it imparts higher strength and improved durability when used as a supplementary binder, owing to reactivity with calcium hydroxide in the mixture. In strength activity and permeability tests, Whitemud Resources found an 80/20 portland cement plus MK mix specimen exhibited 21 percent higher strength and 28-day coulomb rating (just over 1,000) nearly one-third that of a 100 percent portland cement control specimen. WhitemudMK has exhibited favorable performance compared with slightly coarser GGBF slag. Blends of the two SCM with portland cement have performed well in curtailing or eliminating potential alkali silica reactivity.
Compared to the finer silica fume, concrete-grade HRM has been recognized as yielding better mix workability, while offering similar strength and lower permeability benefits. A consistent buff-colored (WhitemudMK) or white (Southeastern U.S.) powder, depending on the clay, concrete-grade metakaolin is also specified for architectural applications, or wherever designers or owners seek lighter slabs or structures Û especially compared to finished silica fume concretes. HRM has likewise been used for shotcrete and packaged mixes for concrete countertops, where fabricators and artisans place a high premium on color uniformity.
Cemstone Products figures to be a primary Upper Midwest user of HRM. Prior to Whitemud Resources' emergence, the material has seen limited field applications and promotion, and little, if any, support from admixture suppliers, fly ash marketers or cement companies. Other HRM suppliers have included (pre-BASF) Englehard Corp. and Burgess Pigment, milling kaolin from Southeast U.S deposits. Outside their main metakaolin markets of paper and paint, the companies have established some presence with ready mixed, precast and packaged dry mix producers, but not on the scale of a user and distributor like Cemstone.
Whitemud Resources credits Cemstone as a company with a tremendous reputation for innovation. The producer most recently underscored that renown with a 70,000-yd. contract, combining conventional and high performance mixes (cement, fly ash, silica fume blend; cement and slag at 50 percent-plus) for the stellar Interstate 35W St. Anthony Falls Bridge, reconnecting Minneapolis and St. Paul. Our ingredient is ideal for high-performance concrete, notes Whitemud CEO Kelly Babichuk, and that's an area where Cemstone excels.
In addition to performance merits, WhitemudMK has environmental benefits green building-conscious ready mixed producers like Cemstone are factoring into promotion efforts and LEED rating point audits. Whitemud Resources notes that MK processing generates 55 percent of the carbon dioxide emissions of portland cement. A mix design with an 80/20 portland cement and WhitemudMK blend, for example, would have a potential carbon footprint reduction of at least 10 percent against a comparable portland cement-only mix design.