been applied, or surfaces damaged by subsequent construction operations 

 within the curing period shall be immediately resprayed at the rate specified 

 above. Membrane curing compound shall not be used on surfaces that are to 

 receive any subsequent treatment that depends on adhesion or bonding to the 

 concrete. Membrane curing compound shall not be used on surfaces that are 

 maintained at curing temperatures with free steam. Where membrane- forming 

 curing compounds are permitted, permanently exposed surfaces shall be cured 

 by use of a nonpigmented membrane- forming curing compound containing a 

 fugitive dye. Where nonpigmented-type curing compounds are used, the 

 concrete surface shall be shaded from the direct rays of the sun for the 

 curing period. Surfaces coated with curing compound shall be kept free of 

 foot and vehicular traffic, and from other sources of abrasion and contamina- 

 tion during the curing period. 



(2) Special Conditions . There are some conditions of curing 

 concrete for coastal structures that frequently occur and require special 

 consideration. 



(a) Hot Weather Concreting . High temperatures impact on 

 concrete by more rapid hydration of cement, greater mixing water demand, 

 increased evaporation of mixing water, reduced strength, and a tendency to 

 crack either before or after hardening. Special precautions are necessary 

 such as cooling the aggregate, adding ice to the concrete mix, and covering 

 the curing concrete to keep it moist. Certain water-reducing retarders may 

 counteract the accelerating hardening of concrete at high temperatures and 

 reduce the need for additional mixing water. Curing concrete above 32.2 

 Celsius (90 Farenheit) is undesireable. 



(b) Cold Weather Concreting^ Fresh concrete should be 

 maintained at a minimum temperature of 10 Celsius (50 Farenheit) until 

 initial strength is attained. This requirement may require heating the 

 aggregate and mixing water, not adding admixtures until the mixing water 

 temperature is 32.2 Celsius or below, and protecting the concrete surface 

 from freezing temperatures until safe strength has developed in the concrete. 

 Most of the heat of hydration is developed in the first 3 days of hardening; 

 however, it may be necessary to provide housing or additional heat to 

 ensure adequate temperature and moisture for curing to obtain the strength 

 and durability intended of the concrete. 



(c) Underwater Concrete Curing . No special precautions are 

 usually feasible for curing concrete placed under water except for tempera- 

 ture control. Concrete will cure best in a temperature range of 10 to 



24 Celsius. Higher temperatures will accelerate curing while lower 

 temperatures will delay curing. 



(3) Preferred Curing Method . Where physical conditions permit and 

 to obtain a high durable concrete the following curing methods in order of 

 performances are: (1) continuously drenched with water; (2) burlap, blankets 

 or carpets continuously wet; (3) membrane- forming curing compounds; (4) 



sand or straw randomly dampened; and (5) air cured. 



6. Techniques to Enhance Durability . 



a. General . The designer and constructor-manufacturer share the re- 

 sponsibility to build concrete structures that remain essentially in their 



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