Table 6. Permissible chloride ions. 

 Type of Concrete Maximum (pet) 



Prestressed concrete 



0.06 



Conventionally reinforced concrete 





in a moist environment and exposed 





to chloride 



0.10 



Aboveground building construction 





where concrete will stay dry (does 





not include locations where concrete 





will be occasionally wetted such as 





waterfront structures). 



No limit for corrosion 



r a ) no impurities that will cause a change in time of set 

 greater than 2.5 percent nor a reduction in 14-day strength 

 greater than 5 percent as compared with distilled water; 



(b) less than 650 parts per million of chloride ion (some 

 authorities permit up to 1 000 parts per million); 



(c) less than 1 300 parts per million of sulfate ion (some 

 authorities limit this to 1 000 parts per million); and 



(d) no oil. 



Seawater may be used, if no other is available, and no steel reinforce- 

 ment is present. The early strength of seawater concrete will be somewhat 

 stronger than that made with freshwater but after about a month the strength 

 of the freshwater concrete will be stronger. At the Port of Los Angeles, 

 thousands of specimens were made for long-time testing using seawater for 

 gaging and tapwater for control specimens. Storage environments were as 

 follows: fog room for controls, air, freshwater and seawater. Compression 

 tests were made at increments of 1 day, 7 days, 28 days, 6 months, 1 year, 

 and thereafter each 5 years through 35 years. 



The results showed that in the early phases of the program (within the 

 first year) strength gains for the seawater-gaged concrete (compressive 

 strength, modulus of rupture, and modulus of elasticity) slightly exceeded 

 those of the tapwater controls. However, beginning at about 1 year, the 

 tapwater control increased above that of the seawater specimens. At the 

 end of the 35-year period the tapwater series were roughly 15 percent stronger 

 then the seawater series. All concrete mixes were of excellent quality, 

 structural grade concrete and, of course, no form of reinforcement was 

 used. Table 7 compares tapwater to seawater for total dissolved solids. 



Seawater containing up to 35 000 parts per million of dissolved salts 

 is generally suitable as mixing water for unreinforced concrete. The 

 strength reduction can be compensated for by reducing the water-cement 

 ratio. Quality concrete can he made with seawater if the mix is properly 

 adjusted. 



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