to provide good bonding of the repair coating or to prevent any of the 

 normal types of coating failures. Coating failures may be identified by the 

 presence of blistering, undercutting, surfacing cracking, de lamination, 

 alligatoring, or chalking. Coating must have strength, adhesion, resistance 

 to the environment and, many times, a pleasing appearance to properly func- 

 tion. 



(31 Cathodic Protection . Cathodic protection is an electrical 

 process to protect metal structures in an electrolyte. The electrolyte may 

 vary from seawater to freshwater, saturated soil and even relatively dry 

 soils. Disolved ions of acids or alkali salts tend to promote metal deterior- 

 ation which can occur in localized areas or over large general areas of a 

 metal surface. Metal corrosion is a natural process involving electrochemical 

 reactions with a resulting flow of direct current from the anodic areas (the 

 corroding areas) to the cathodic areas of the structure through the surround- 

 ing electrolyte due to the electrical potential difference between the two 

 types of areas. Cathodic protection is the process of inducing an outside 

 electric current in the opposite direction and in this manner stopping the 

 normal corrosion process. 



The design and installation of a cathodic protection system is highly 

 technical. To ensure design of an effectively operating system, field 

 conditions of the structure must be examined to determine the total amount of 

 electrical current required to cathodically protect the structure and to 

 ensure proper current distribution. It must also be determined that there 

 will be no interference with other structures in the vicinity and that 

 potential differences within either the protected structure or of adjacent 

 structures are not impacted to ensure that no cathodic protection inter- 

 ference conditions exist. Cathodic protection requires periodic maintenance 

 and inspection to keep it in good working order. 



Generally good protective systems, both coatings and cathodic protection, 

 are economical, require maintenance, and will substantially extend the service 

 life of well-constructed structures. 



3. Some Present Investigations of Coastal Construction Materials . 



a. Stone. Stone is one of the most widely used materials in coastal 

 structures and shore protection works. There are two basic areas of research 

 on stone: the uses of stone in shore protection structures and the character- 

 istics of stone for use in coastal structures. 



Stone is used in revetments, jetties, groins, bulkheads, seawalls, and 

 other miscellaneous types of structures. Studies are being done on new types 

 of shore protection structures such as semisubmerged offshore structures, on 

 new structure configurations for jetties, on different distributions or 

 arrays of stone in armor units or layers, on the reliability of breakwater 

 model tests, and on the effect of breakwaters on waves. Programs have been 

 initiated to monitor and evaluate the performance of existing coastal struc- 

 tures in terms of their effectiveness, maintenance cost and life. This area 

 of research also deals with development of field techniques and criteria for 

 the functional and structural design of coastal structures. Work is also 

 continuing on the evaluation of parameters used for determining the effective 



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