c. Portland Cement Concrete . 



(1) General . Concrete is used as unreinforced or mass concrete, as 

 steel reinforced concrete or as prestressed or posttensioned concrete. The 

 latter types are usually made in the form of precast structural elements. 

 Specific properties of concrete may be modified and improved by the addition 

 of admixtures for special purposes and to accommodate placing and installa- 

 tion requirements. The specific use of concrete in any structure will 

 determine the mix design and curing process necessary to obtain a satis- 

 factory result. Experience or consultation with experienced designers of 

 concrete structures is necessary to ensure a durable concrete appropriate to 

 the needs of the structure. 



Durability is generally a requirement in coastal structures and the 

 designer and constructor share the responsibility for creating structures 

 which will function as designed over the anticipated life of the structure. 

 Such structures have a high resistance to the disruptive attack of most 

 environments including saltwater, alkalis, most acids, corrosive atmospheres, 

 freeze-thaw cycles, and marine flora and fauna. Good concrete is also 

 highly resistant to abrasion. 



Failures of concrete structures have been studied and some of the more 

 common causes of failure and methods of prevention are discussed in Section 

 V. Determination of the cause of structural failure requires a careful 

 analysis of the site conditions, the concrete ingredients, and the original 

 design criteria by experienced professional engineers. Concrete failures 

 usually are the result of the selection of the wrong type of cement, unsound 

 aggregate, contaminated mixing water, improper admixtures or an inadequate 

 curing process. With all these possibilities for creating poor concrete 

 the design engineer must also have experience and good judgment in preparing 

 plans and specifications to ensure that concrete is used within its physical 

 capabilities. 



(2) Uses in Coastal Structures . Thousands of marine structures have 

 been satisfactorily designed and constructed of concrete with a long history 

 of excellent performance. Because the resources required to make good con- 

 crete are generally available in all regions of the world, concrete has wide 

 application for use in coastal and waterfront structures. Its successful use 

 in seawalls, bulkheads, revetments, groins, jetties, breakwaters, and a 

 variety of other structures over many years is evidence of its excellent 

 properties for coastal engineering use. 



d. Other Types of Concrete and Grout . 



(1) Asphalt . 



(a) General . Asphalt is a residue product from the refining of 

 petroleum. It can be used alone as a membrane or coating or it can be mixed 

 with other materials as a binder to produce mixes for a variety of purposes. 

 Asphalt can be combined with sand and graded aggregate to form a voidless and 

 impermeable asphalt concrete or with an open-graded aggregate to form a 

 stable porous mixture. A composite asphalt structure can easily be con- 

 structed of different asphalt mixes with each layer performing a particular 

 function. An example of this use might be an impermeable asphalt layer 



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