Precast Inc. - May/June 2008 - (Page 34) The particle size of the ultrafine fly ash has been optimized so that water can be removed from the mix and slump is still retained. This aspect allows for a lower water-cement ratio and stronger concrete. Less water in the mix also results in fewer bleed channels leading to lower permeability. Durable concrete is concrete that resists weathering, chemical attack, freeze-thaw abrasion, the ingress of salts and other service conditions. It is the salts that corrode the reinforcing steel. The rusting reinforcing steel expands and causes the concrete to crack. The longer you can keep the salts away from the THE I-10 BRIDGE OVER LAKE PONTCHARTRAIN IN NEW ORLEANS, SEVERELY DAMsteel, the longer the service time before cracks AGED BY HURRICANE KATRINA, WAS RECONSTRUCTED WITH PRECAST CONCRETE form and maintenance is required. USING ULTRAFINE FLY ASH THAT MITIGATES THE ADVERSE EFFECTS OF MARINE To meet the demands for durable concrete SALTS. without slowing production, Gulf Coast Pre-Stress along with the normal dosage of fly ash and will disperse chose to use ultrafine fly ash as a highly reactive pozzolan. The throughout the mix. required overnight strengths were met and the resulting low Typical dosages of ultrafine fly ash will range from 8 percent permeability was well below the required values. of total cementitious to as high as 12 percent depending on the particular performance desired. In a high-strength application, Kevin Foody is manager of the Technical Service Eastern the typical additional rate is 8 percent to 9 percent. If low Region, Boral Material Technologies Inc. Boral, based in permeabilities are required, then the dosage rate typically San Antonio, is a marketer of fly ash and all coal combusranges from 9 percent to 12 percent depending on how low tion products. Contact Boral at (800) 964-0951 or visit the permeability target is for the project. www.boralmti.com. BOOTH 1759 34 MAY/JUNE 2008 | PRECAST INC. http://www.boralmti.com http://www.hoistlift.com http://www.hoistlift.com
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