CoatingsPro Magazine

MAR 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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COATINGSPRO MARCH 2015 67 Library Floor Failure I had just completed working with a concrete supplier on some slab deformation studies, and while slab deformation was not new to me even before my participation in those studies, the studies did help prime my base of knowledge. Te library itself was fairly small: It's a single-story building with an imposing roof line and lots of windows. Natural light is great for library interi- ors because they tend to impart a more causal ambiance. Likewise, with all that light comes every opportunity to see any fooring irregularity. Te subfoor was a concrete slab on grade, and it was a little over 14 months old. I walked through the building, obser ving any and ever y space. W hat I saw was a grid of squares telegraphing, or showing, through to the surface of the finish f loor covering. The lines creating the grid were perfectly straight and, for the most part, contin- uously visible throughout the interior f loor space. Mi xed within the grid pattern were seemingly random lines that appeared to be cracks within the concrete. Those were also telegraphing through to the surface of the finish f loor covering. T he lines creating the g r id measured 10 feet (3 m) on center; each square was 10 feet by 10 feet (3 m x 3 m). T he g r id stayed conf ig ured in the 10 -foot (3 m) square patter n throughout the librar y, even when transiting f rom room to room or area to area. T he lines were actually a nar row bulge, pushing up from beneath the finish f loor cover ing and creating a r idge. It was this r idge that was mak ing the gr id v isible. T he bulge itself was hard to the touch; there was no def lection of the finish f loor cover- ing and no crack ing or fractur ing of the epox y. Te lines were familiar enough to me. Tey were control joints telegraph- ing through to the surface of the fnish foor covering. Control joints are a series of saw cuts placed into the surface of the concrete as soon as the concrete is frm enough to walk on (and always within 24 hours of placement). Control joints are placed as an aid in controlling the amount and location of cracking. Control joints are commonly placed at 24 to 30 times the concrete thickness. For example, the average 5-inch-thick (13 cm) slab would have control joints placed at a minimum of 10 feet (3 m) apart. Te control joints should extend down from the surface for a depth equal to a quarter of the thickness of the slab. To follow the 5-inch-thick (13 cm) slab example, that would be a minimum of 1ΒΌ inches (3 cm). After completing my visual inspection and taking some pictures and measurements, I asked if there was a conference room that we could use to discuss my obser vations. Settled around a large table, we chatted politely for a few minutes until my client inquired as to my thoughts about what we had just seen. It's Control joints are commonly placed at 24 to 30 times the concrete thickness. For example, the average 5-inch-thick (13 cm) slab would have control joints placed at a minimum of 10 feet (3 m) apart. Because fixing the control joints would have been expensive and time-consuming, the library decided to leave the condition and work with the district architect to design curl-resistant concrete slabs. Curling Slab Consequences

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