6. Maintenance and Preservation Requirements . 



These requirements and their annual costs are generally influenced by 

 comparison with the initial costs of construction. All materials require 

 some maintenance and preservation. The problem may be physical or chemical 

 maintenance and may vary not only between different materials but within 

 the same material . 



a. Stone. It is unusual, but possible, that stone will deteriorate 

 chemically^ The main problems are reduction in size through abrasion, 

 reduction in size through splitting or breaking, particularly of armor 

 stone, and loss of stone due to the power of waves or currents, or the 

 undermining of the structure. Preservation of stone as a material is not 

 generally feasible and maintenance is normally a matter of replacing damaged 

 or missing stones. Generally, damage to a breakwater, jetty, or groin does 

 not cause severe resultant damage immediately but mobilization costs to do 

 maintenance work are high. 



b. Earth. Little can be done to preserve an earth structure except to 

 protect it from erosion. Like stone, maintenance is a matter of replacing 

 lost material. Ease of access to the earth part of an installation will 

 determine the maintenance cost. 



c. Concrete . The quality and the life of concrete are largely con- 

 trolled by the methods of mixing and placing. Coatings are available which 

 improve the set period of the concrete and protect the surface from flaking 

 or dusting. In saltwater, and to a lesser extent freshwater, if the rein- 

 forcing steel is exposed to oxygen it will combine to produce corrosion. 

 The corroded surface of the steel expands greatly, resulting in cracks in 

 the concrete that admit more water and accelerate the process. The result, 

 is physical spalling, cracking, or splitting of the concrete resulting in 

 total failure. Such cracks must be kept sealed to slow this process. As 

 cement has a calcium base, it may be necessary to protect it from chemical 

 change by pollutants or biological attack. Like stone, the primary need 

 for maintenance or preservation is to prevent deterioration. This may be 

 from abrasion by harder and sharper substances, such as quartz sands, or 

 from the force of storm waves overstressing the structure. Impact by 

 rocks, barges, ships or debris may overload concrete, as in the case of 

 dock structures. Seismic damage may occur. Maintenance may consist of 

 sealing cracks, patching abraded or worn areas before the reinforcing steel 

 is exposed, or actually replacing individual concrete units within the 

 structure . 



d. Steel . In contrast to stone and concrete, the primary purpose of 

 maintenance or preservation of steel structures is to prevent chemical or 

 galvanic deterioration. Unless made of special and expensive alloys, 

 exposed steel is subject to rapid deterioration through oxidation or rust, 

 especially in the wet-dry tidal area and at the sandline. The latter can 

 be very severe in the surf zone where the corrosive process is accelerated 



by the abrasive action of the sand continually removing the rust and exposing 

 new steel. The application of paint or some of the new protective coatings 

 can greatly increase the life of such steel members. The galvanic process 

 can be greatly reduced or eliminated by the installation and maintenance of 

 "cathodic protection systems." 



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