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Concrete Dec 2017

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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30 CONCRETE COVERED 2017 COATINGSPROMAG.COM Photos Courtesy of BASF Construction Chemicals By Fred Goodwin, EB Construction Chemicals Global Corrosion Competency Center Head for BASF Construction Chemicals Concrete and Water: Secrets to Success Concrete Covered C oncrete is claimed to be the second most common manmade material after potable water. As a construction material, more concrete is used than all of the wood, steel, plastic, glass, and alumi- num combined each year. Concrete uses the largest quantity of recycled material, mostly consisting of industrial byprod- ucts, such as fly ash, blast furnace slag cement, silica fume, and other pozzolans. It can also be very durable as shown by its use in ancient structures, such as the Pantheon, which is approaching 2,000 years old. Our most critical structures today are constructed with concrete, such as our tallest buildings, largest dams, and longest bridges, not to mention more mundane projects, such as our roads, hospitals, schools, and homes. Yet when we look at most concrete, we see cracks, falling pieces, and other forms of deterioration. As much as 80 percent of concrete's deterioration has a root cause in latent construction defects caused by failures in design, workmanship, or materials not apparent or readily detectable (even with the exercise of reasonable care) until many years after completion of the construction. W hat can we do to mitigate these faults? Latent Construction Defects Water is required for concrete production: It is essential for the hydration of the hydraulic cement, which is the glue holding the aggregate together. Water makes placing and finishing the concrete easier and is simple to add; however, the more water that is added to concrete, the lower the strength and durability of the hardened material. Water that is needed for complete hydration of the hydraulic cement has a ratio of only about 0.2 for the mass of the cement binder (known as the water to cementitious material ratio, or W/CM), yet typical W/CM for concrete ranges from 0.35 to 0.6 for placement of the concrete, as low W/CMs are difficult or impossible to consolidate. e addition of extra water is commonly done during construction, and detection of it after its addition is difficult to estimate. Extra water is the first latent construction defect responsible for concrete's poor performance. Concrete must have proper consolidation to minimize voids. Admixtures can be used to improve durability and placement of the concrete, but these increase cost and Most concrete shows cracks, falling pieces, and other forms of deterioration. Water alone can be the reason for several different latent construction defects. Water, aggregate, and cement are required for concrete production. Because concrete is strong in compression and weak in tension, reinforcement via steel rebar may be used. Corrosion, though, is a concern. Water is required for concrete produc tion: It is essential for the hydration of the hydraulic cement, which is the glue holding the aggregate together.

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