CoatingsPro Magazine

MAY 2015

CoatingsPro offers an in-depth look at coatings based on case studies, successful business operation, new products, industry news, and the safe and profitable use of coatings and equipment.

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Page 38 of 92

38 MAY 2015 COATINGSPROMAG.COM (ASR), spalding, crazing, or delami- nation, need to be identified. Surface contamination from oils, lubricants, silicones, chemicals, cleaners, process water, and food products need to be checked. Evaluating the depth of the contamination into the concrete is important. Some contaminants w ill penetrate well below the surface, making them ver y difficult to remove. Joints Tere are four common types of joints in concrete foors: isolation joints, expansion joints, construction joints, and contraction joints. Isolation joints are used around columns, foundations, walls, pipes, equipment, pads, etc. Te purpose of these joints is to allow for movement from concrete curing and shrinkage or to reduce noise vibrations. Quite often, these joints will have a closed-cell foam or fberboard in them. Expansion joints are used in larger buildings when movement needs to be allowed. Tese are commonly an engineered joint. Tey come in a variety of diferent shapes and styles. Most are extruded and designed to cover a one- to two-inch-wide (2.5–5 cm) gap. Tese joints may be mechanically fastened or set in a construction grout. Epoxies do not adhere well to some construction grouts. If these joints are not sealed properly, epoxy could run under them and compromise the joint. Construction joints are start and stop points for concrete pours. T hey are also the joint by default whenever a concrete f loor is cut and patched. Because they are start/stop points from different pours unevenness, curling or different heights can occur. A four-foot (1.2 m) level is an excellent tool for checking the transition of these ty pes of joints. Contraction joints are the most common t y pe of joint on most concrete f loors. T hese are a lso commonly referred to as sawcuts or control joints. T he sole pur pose of these joints is to control the crack ing of freshly placed concrete. Technica lly they are engineered cracks in concrete. T he depth of properly cut contraction joints w ill be 25 percent of the thickness of the concrete slab. Contraction joints can tell you a lot about the condition of the concrete. Some of the things to look for here are excessive gap, excessive curl, and broken edges. T hese are a ll indicators of weak concrete. T he sawcuts rarely extend r ight to the edge of a slab at the wall and column junctions. T here is seldom traffic or damage at these locations, and the amount of shr ink- age is easy to identif y. Cracks Tere are two types of cracks found in concrete foors: static and dynamic. Static cracks do not move. Static cracks, for the most part, are smaller, thinner, irregular-shaped lines. Dynamic cracks can have movement for a variety of reasons. Heav y forklift trafc, poor compaction, and sudden temperature change are a few of the ways concrete foors move. T he t y pe of crack and what caused it needs to be identified so that proper Inspector's Corner

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