types of Portland cercent, n\m±ns. Canent and superfine Portland cement were 

 used in varying proportions from 3 bags per cubic yard to 9"| bags per cubic 

 yard. 



From the long; time tests, at Portsmouth plus observations made on concrete 

 Naval structures located in many parts of the v/orld the folloviring con- 

 clusions have been drawn: The concrete appears to fail through disinte- 

 gration of the cement which progressively loses its bond and cementing 

 power. This disintegration occiurs more rapidly in some Portland cements 

 than in others . of the same type. Alumina cement has not demonstrated a 

 superiority o"^er Portland ce?-;ent. The admixtures virhich were used did 

 not appreciably retard deterioration of the concrete nor did the use of 

 silica sand inprove the density of the concrete by chemical action with 

 the cement. Improved density can be achieved by the use of well graded 

 aggx-e gates, 



Siurface density is an important factor in the life of concrete piling. 

 It can be improved by the use of very smooth surface foi'mwork, plus form 

 vibration. No appreciable advantage is gained by the use of corrosion 

 resistant reinforcing. Increased clear cover over reinforcing is a more 

 economical solution, 



Comiiaratively rich mixes of concrete are required to prevent the deterio- 

 ration of concrete in the tide zone. It is interesting to note that the 

 most perfect concrete pile specimen hung at Portsmouth contains a mixture 

 of cements from four different producers. The concrete contains 6^ bags 

 of cement per cubic yard. Ti'o other specimens in excellent condition after 

 27 years contain 9 bags of cement per cubic yard of concrete. The water- 

 cement ratio has a marked influence on the durability of concrete. This 

 is evidenced by the fact that the less the slump the more resistant the 

 nile specimens have been to deterioration. The selection of both fine 

 and coarse aggregates that are kna-m to be chemically stable with cement, 

 in the presence of salt water, is esvsential. 



Steel Construction: 



Although the process of sneltin:-' iron has been knovm for thousands of 

 years, it was I8U0 before tiie principal support of a v/aterfront structure 

 was formed of cast iron. Solid wrought iron piles were installed about 

 10 years later, while steel shapes viere not used until about I87O, 



Although service records indicate that cast iron, in the form of cylinders 

 or piles, is the most durable material currently available for use in 

 waterfront structures, it has received little consideration during the 

 last 35 years because of its lack of taiisile . strength and comparatively 

 high first cost. Reports on solid v/rought iron piles indicate a service 

 life comparable to those of hollow cast iron, Hovj-ever, the wrought iron 

 or steel bracing members required in connection virith either w-ought or 

 cast iron piles and cylinders have required rather frequent replacement. 

 This replacement cost, rather than the high first cost of cast or wrought 



/ -^j , -^ V\ «** \ 



G - 3 / / n^TgVi \ (Si\ 



\^{ LISRARY ^. 



