2. The use of various non-air-entraining admixtures did not 

 appear to be of material "benefit in increasing the dura- 

 bility of plain concrete but were not harmful in that they 

 did not appear to decrease the durability of air-entrained 

 concrete. 



3. The use of air entrainment does not protect concrete which 

 contains unsound aggregate. 



k. The blending of natural cement with plain portland cement 

 greatly improves the durability of concrete if by so doing 

 the proper amount of entrained air is produced in the 

 concrete. 



5. No definite trends in the effect of curing conditions on 

 durability have been revealed. 



6. Aluminous cement produced highly durable concrete. 



T. The use of absorptive form-lining improves the durability 

 of concrete surfaces. 



8. The quality of horizontal construction joints appears to 

 be governed primarily by the quality of the concrete at 

 the top of the lower lift. 



9. The use of cement with a tricalcium aluminate content in 

 excess of 12 percent has resulted in concrete that is non- 

 durable in warm seawater. The use of Type II cement with 

 a tricalcium aluminate content less than 8 percent appears 

 warranted for such exposure. 



Although the above conclusions were not based on tests of concrete jackets 

 on steel piles, they should be considered when designing concrete jackets. 



The literature surveyed did not indicate a life expectancy for steel 

 piling with concrete jackets in the critical corrosion areas. Ayers and 

 Stokes (1961) reported that concrete jacketing of steel piling has proven 

 very effective when it extends from the top of the piling, above high 

 tide to well below mean low water. They also concluded that concrete 

 jackets in the tide range and cathodic protection below low tide was the 

 most complete system for protecting steel piling. One publication reported 

 that a reinforced concrete sheet pile wall at Neptune Beach, Florida, was 

 still in good condition except for storm damage after I6 years of service, 

 also that service records indicate that good concrete can endure for 50 

 years or more without excessive maintenance (Mather, 1957)- 



39 



