Precast Inc. - March/April 2008 - (Page 12)

Avoid use when reinforcing steel is encountered. See enlarged view for potential problems. reinforcement are cosmetic in nature and can be fixed by filling in the cracks with dry cement. The moisture in the concrete and in the air will hydrate the cement and fill the cracks. • Honeycombing – Small honeycomb areas can be cleared of any unsecured stone by chipping or sawing down to solid concrete, blowing or brushing the area clean, and filling in with standard repair materials (see Figure 2). Saw cutting the existing concrete is more effective than chipping it out, because the cut lines create a well-defined retaining boundary in which the repair material can easily be compacted and consolidated. This standard repair material is what you list on your standard repair procedure. It can be the same blend of materials used in the product, or it may be your favorite proprietary repair material. • Chipping and Spalling – Chips and spalls are handled in the same routine manner. Spalled corners or edges from rough stripping or handling are common problems. Spalling is normally a minor defect, but it should serve as a signal that additional training and instruction on product handling may be necessary. When repairing spalling, like the repair of honeycombing, the broken area must be properly prepared before applying repair material. The nature of these defects most often involves angular breaks, which have outer edges tapering to thin edges. Since a repair material can’t be tapered to a thin edge (it will shrink away or flake off), it is better to saw cut at the edge of the break, then cut out a minimum thickness of material to allow the repair to have some substance. Surface defects, whether honeycombing, sand streaking, form joint offsets or spalling, are among the easiest and most common repairs to make. Even 12 MARCH/APRIL 2008 | PRECAST INC. Joint Between Layers Specially formulated, “non-sag” repair material is pressed into the substrate with the use of a trowel or similar tool. Caution: Use only dimensionally stable materials. Materials with high shrinkage may crack and debond. Enlarged View of Void Formed Behind Reinforcing Steel Substrate Void Figure 2 Reinforcing Steel Repair Material though these are minor defects, they must be competently applied and finished. This includes proper preparation of the defective area, placing the repair material, adequately curing the repair and acceptably finishing the exposed surface. Unless you are using a proprietary material that does not call for it, the area to be repaired must be thoroughly dampened to keep it from pulling moisture from the freshly applied material. Placing a damp burlap sheet or cover with a larger sheet of plastic on top and taping the edges to keep in the moisture should suffice. The bond strength of new concrete to old concrete develops much more slowly, and the tendency to shrink and loosen is reduced by a long, moist curing period. Applying heat to the repaired areas may also be necessary to ensure hardening and strength gain. After the repair has cured, evaluate the finished surface for appearance. Appearance holds more significance than it should; even if the repair is structurally sound, it won’t be looked upon as a quality product if the repair doesn’t look flush and similar in appearance as the rest of the product. Repair of Major Defects. Repairs for major defects require the same preparation, material selection, workmanship and curing as for minor defects. However, according to the NPCA QC Manual, major repairs must be analyzed by a qualified person; they require the repair procedure to be established and written out; they often require approval by an outside agency before work begins; and they must be inspected (witnessed) and documented. This is another reason to have a standard repair procedure in place. Repair materials Many different repair products are on the market, and in fact several businesses are making repair materials specifically for the precast industry. Consider several material properties when selecting a particular repair product. These include permeability, strength, adhesion, corrosion resistance and application method. Base your selection of a repair material on its

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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