g. Periodic Wetting and Drying . Periodic wetting and drying may 

 cause the formation on the concrete surface of "D cracks" (the progressive 

 formation of fine cracks, often in random pattern). Such cracks may 

 enlarge in time and if exposed to freezing and thawing can result in 

 concrete spalling. 



h. Wind Erosion . Concrete resistance to wind is usually not a serious 

 problem in coastal structures. Where strong winds may pick up sand parti- 

 cles, causing some etching of concrete surfaces similar to surf zone 

 abrasion (usually near the ground line), it would take many years of 

 exposure to structural grade concrete for wind erosion to become a problem. 



i. Effects of Burrowing Animals . Marine animals do not penetrate good 

 concrete as indicated in paragraph (f) above and the larger dryland animals 

 do not attack concrete. Concrete is one of the hardest materials in the 

 coastal environment and contains no food value for such animals. 



j . Effects of Flora . There are no reported effects of flora growth on 

 concrete. 



k. Fire. Concrete resistance to fire or extreme high temperatures is 

 stated in paragraph (e) above. 



1. Abrasion. Abrasion is defined as the ability of a surface to be 

 worn away by rubbing and friction. Wind- or water-borne particles can 

 abrade or etch concrete surfaces. If windborne particles cause abrasion, 

 some dusting problem could develop; however, the slow rate of the abrasion 

 process in the coastal zone is usually unnoticeable. Wear on concrete 

 structures exposed to high velocities and negative pressures is generally 

 known as cavitation erosion. Precise limits for abrasion resistance of 

 concrete are not possible. It is necessary to rely on relative values 

 based on weight or volume loss, depth of wear, or visual inspection. 



m. Seismic Effect . Severe seismic forces can cause failure of a 

 concrete structure directly or by altering the foundation on which the 

 structure rests such that subsequent settlement can result in structural 

 failure or deterioration. With proper design concrete can be made to 

 resist seismic effects. 



n. Human Activity . Human activity has very little impact on concrete 

 structures except where visual impact may be noticeable by graffiti or 

 other defacing actions. 



12. Use in Coastal Structures . 



a. General. Concrete is easily adapted to coastal construction in 

 that local aggregates are normally available at or near the site with the 

 only import materials being cement and steel reinforcing. It can be cast 

 in most any shape or size to fit site requirements and the structures can 

 be built in sections either by casting separate members and assembling in 

 place to create a large structure or as mass concrete placed a section at 

 a time to produce a large continuous structure. This characteristic 

 allows the design engineer a wide selection of type, size and configuration 

 of structure design. The excellent physical and strength properties of 



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