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thirty (30) minutes. A second application of curing compound <br /> shall be made one (1) hour after the initial application. <br /> 11.2 MINIMUM CURING PERIODS <br /> Basic Tyne of Cement 50OF - 70OF 70OF - 100OF <br /> Normal or Sulphate Resistant 7 days 5 days <br /> 11.3 PROTECTION <br /> 11.3.1 COLD WEATHER <br /> When the mean daily temperature of the atmosphere is less than <br /> forty degrees Fahrenheit (400F), the temperature of the concrete <br /> shall be maintained between fifty degrees Fahrenheit (50°F) and <br /> seventy degrees Fahrenheit (70°F) for the required curing period. <br /> When necessary, arrangements for heating,covering,insulating or <br /> housing shall be made in advance of placement and shall be <br /> adequate to maintain the required temperature and moisture <br /> conditions without injury due to the concentration of heat. <br /> Detailed recommendations are given in "Recommended Practice <br /> of Cold Weather Concreting" (ACI 306). <br /> 11.3.2 HOT WEATHER <br /> When the air temperature is expected to exceed ninety degrees <br /> Fahrenheit (90°F) within forty-eight (48) hours after placement, <br /> all surfaces shall be protected from direct sunlight and maintained <br /> in a moist condition for a minimum period of forty-eight (48) <br /> hours. Detailed recommendations are given in "Recommended <br /> Practice for Hot Weather Concreting" (ACI 305). <br /> 11.3.3 EXCESSIVE TEMPERATURE CHANGES <br /> Changes in temperature of the concrete shall be as uniform as <br /> possible and shall not exceed five degrees Fahrenheit (5OF) in any <br /> one (1) hour or twenty degrees Fahrenheit (20°F) in any twenty- <br /> four (24) hour period. <br /> SPEC.B- CONCRETE <br /> PAGE 18 <br />