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Nozzleman Knowledge Fig. 5: Recommended concrete temperatures—ACI 306R-10, Table 5.1 Fig. 6: Graphical determination of safe differential temperature for walls (Mustard and Gosh 1979) concrete as placed; and weather conditions, such as calm, windy, clear or cloudy; and • Record maximum and minimum temperature reading at the concrete surface and ambient conditions in each 24-hour period. Table 5.1 in ACI 306R-10 lists the recommended concrete temperatures at various ambient temperatures during and after the protection period (Fig. 5). Oftentimes a crew will remove protection immediately after the 7-day curing and protection period, not knowing the concrete should be exposed gradually over a 24-hour period to the ambient temperature. If a crack occurs, it’s almost always overlooked or is blamed on the live traffic on the highway bridge, railroad bridge, or even attributed to cold joints/cracks in the structure that run through and behind the repair. Using the material compression strength test results from the preconstruction testing (3-, 7-, and 28-day) will help with the decision regarding when the protection and formwork should be removed. The colder the ambient temperature, the longer the protection stays on. Proper preparation before placement in cold weather often requires a temperature increase of Shotcrete • Spring 2016 53


2016SpringShotcreteEMag
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