Building Industry Magazine - August 2011 - (Page 48)

BY JUDITH SHINSATO “Concrete is one of the most widely used construction materials in the world,” states Wayne Kawano, president of the Cement and Concrete Products Industry of Hawaii (CCPI). “The key reason for its widespread use is the durability characteristics of concrete. When properly designed, proportioned, placed, finished, tested, inspected, and cured, concrete is capable of providing decades of service with little or no maintenance.” That being said, the concrete industry continues to develop new methods and mixtures to further enhance the life of concrete structures and pavements. Here are a few of the latest advances affecting local builders. All Mixed Up Kawano says today’s concrete is not just a simple mixture of cement, water and aggregates but a more complex recipe that frequently includes mineral components, synthetic fibers, corrosion inhibitors, shrinkage reducers and other chemical admixtures. He also points to the emergence of nanocement and nanoconcrete, a “smart” building material with inherent sensor and structural health monitoring capabilities. “In the packaged concrete industry we are regularly investigating improved additives,” adds Jeff Deer, president of Bonded Materials Co. “Apart from the standard cement and aggregate components, we review, test and sometimes update our products with additives such as new polymers, corrosive inhibitors and specialty fibers. Corrosive inhibiting additives, especially, are becoming much more prevalent in both concrete and cementitious repair products. The various additives help prevent corrosion of the reinforcing steel, which can contribute to concrete failures. When steel reinforcement rusts, it changes volume and creates extraordinary internal forces within the concrete that can cause cracks, spalling and delamination. Most corrosion inhibiting admixtures are based on calcium nitrite; they are liquid and added to ready mix concrete. They have also been around for more than a decade so they are not that new. However, concerns for inhibiting the corrosion of the reinforcing steel within concrete have elevated the admixtures consideration and use under many circumstances, such as with marine construction.” According to Kawano, the University of Hawaii College of Civil and Environmental Engineering is in the process of concluding a 10-plus year concrete durability study on various concrete mixes used locally, with results expected to be announced soon. Filling a Void Recent developments have been made in the use of fly ash, specifically Type F fly ash, to increase the strength and durability of concrete, according to George Stewart, cement sales manager of concrete manufacturer Hawaiian Cement. Explaining the science behind it, Stewart adds, “The small spherical fly ash particles fill the spaces between the cement, sand and aggregate to produce a denser concrete matrix thus improving cementitious efficiency. (It also) has a lower specific gravity than the cement it replaces; occupying greater volume per pound. Fly ash improves the durability of concrete by converting the weak, slightly water soluble calcium hydroxide into the stronger, non-water soluble, durable calcium silicate hydrate. This conversion increases the chemical resistance of the concrete to sulfate and acid attack. This is further enhanced by the reduced permeability for the These concrete blocks, using different concrete “recipes,” are being tested by UH for durability. 48 | BUILDING INDUSTRY | AUGUST 2011

Table of Contents for the Digital Edition of Building Industry Magazine - August 2011

Building Industry Magazine - August 2011
Catepillar Showcase
Seminars Augment PBT Expo
BIA Dedicates New Hawaiian Home
NAVFAC Awards New Contracts
Living Museum Getting $38 Million Makeover
Pearl City Street Dedicated
Contracts Awarded
Spotlight on Success: New Target Store in Hilo
Architects Corner
Best Practices
Low Bids
Concept to Completion: Grand Hyatt Kauai Resort Renovation
The House Built for Hope
News Makers
New Products

Building Industry Magazine - August 2011