Precast Inc. - March/April 2008 - (Page 14)

reduce shrinkage. The repair batch acts more Drypack material placed in layers like a dry-pack material that you force and Hammer used to hammer into place to compact drypack Hardwood material gain full compaction (see Figure 3). Another factor to consider is the size of the aggregate. The maximum size of aggregate should be as Restraining large as possible but formwork not greater than oneDrypack material half the minimum should be dry but dimension of the repair. cohesive enough to be formed into a ball. Consider using a materials supplier that specializes in concrete repair. These suppliers have the newest and best products available Figure 3 and can provide you with valuable intended purpose. If the customer is a information pertaining to your specific state DOT, always make certain that the application. The repair material’s strength, supplier uses materials that are state adhesion, shrinkage, color and appearance approved for all states in which you supply need to be compatible with the original products. concrete, and this is where concrete For most applications it is acceptable to suppliers can help. use the same ingredients from your A new product that precast concrete original mix, but proceed with caution. repair suppliers are now offering is called Concrete used in repairs should be “carvable” (shapeable) cement mortar. essentially the same as the original This product is used for structural and concrete, except that the repair concrete cosmetic repairs. Formerly these cement should contain less water. You should use mortars either set up too fast or too slow, less water if the repair area is not cut into or they were too light or too dark. Now a nice formed area, and typically it is not. they are offered in three different set Also, the reduction of water will help times of five, 15 and 30 minutes to meet the needs of a specific project. These mortars also come in different shades of gray to match the color of the existing concrete. They contain no gypsum cement and therefore will not swell when exposed to rain, snow and sleet. Many repair products can obtain high strengths, some at a very early age, which is often a selling point. Keep in mind that typically the higher the early strength gain, the lower the service life of the repair. This is because the ingredients used to obtain high early strengths (Type III cement, accelerators, water-reducing agents, etc.) can cause shrinkage cracking and can be more brittle than the concrete it is repairing. As a general rule use a material with the strength appropriate for the repair. After you have made all the corrections associated with concrete repair, how will you know whether it’s acceptable? Depending on the volume of material prepared, you could make and cure cylinders with the product just as you normally do. Most plants have a cylindrical impact hammer, which evaluates hardness by measuring rebound within the instrument. This can be used to compare the repair area with the base concrete. The bottom line is that concrete products can’t be perfect every time. But the manner in which these issues are handled will reflect on the integrity of your company and the industry as a whole. Evan Gurley is a staff engineer with NPCA. 14 MARCH/APRIL 2008 | PRECAST INC. http://www.eagleeyeproducts.com http://www.eagleeyeproducts.com

Table of Contents Feed for the Digital Edition of Precast Inc. - March/April 2008

Precast Inc. - March/April 2008 Contents Technically Speaking Concrete Repairs Return-to-Work Programs Marketing in a New World Building Confidence Risk Management Culture Bloquea La Energia – Es Tu Vida! Lock It Out – It’s Your Life! Fiber Optics in Countertops MCPX Wrap-Up Product Profile People & Products Advertisers Index NPCA Calendar

Precast Inc. - March/April 2008

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