Reinforced Concrete and Concrete Protection 



Before closing this discussion, some remarks re the use of concrete are 

 in order. 



Assuming a proper mix of concrete and adequate coverage of the steel, there 

 should be little deterioration of concrete below low tide level, A proper 

 mix of concrete based on requirements for the most severe exposure in the 

 tidal zone may be defined as one made tip to contain not. less than. 7 sacks 

 of cement per cubic yard of concrete with a maximum total water content 

 of 5 gallons ver sack of cement carefully measured as recommended by the 

 Portland Cement Association, 



In waters ivhere marine borers of the pholad types may be encountered, the 

 use of hard silica sand to form a concrete of high strength, e.g, 14,000 

 pound minimum test, will be required to resist penetration and deterioration 

 of the concrete by these borers. 



There is soine controversy as to the minimum thickness of coverage of con- 

 crete over the steel. The most conservative recommend a minimum of 3", 

 with It" at corners. Others believe that with the best grades of concrete 

 properly applied the coverage can be reduced to 2" . Apparently, there is 

 greater latitude with respect to coverar^e and grade of concrete for those 

 surfaces that are always under water. Requirements become more stringent 

 in tthe tidal and. splash zones \,'here the concrete is alternately wet and 

 dry. Here the chance of deterioration of the concrete and penetration of 

 water to corrode the steel is greatest. If any appreciable corrosion occurs, 

 the accumulated corrosion products will induce cracking and spalling of 

 the concrete and deterioration viill procead at an accelerated rate. Even 

 with good grades of concrete there are difficulties due to spalling and 

 cracking in northern climates ■'.''here the concrete is subject to T;ide fluctua- 

 tions in temperature, with freezing during the winter months. 



Attention is being given the application of cathodic protection to the 

 steel reinforced concrete, Hovrever, such protection is likely to be effec- 

 tive only belovic low tide where it apparently is least required. There is 

 a considerable question as to the benefits to be gained from cathodic pro- 

 tection of reinforced concrete in the most critical tidal and splash zones. 

 In addition, there have been reports of deterioration of the concrete virhen 

 the applied current or voltage have been too high. Several years ago, the 

 National Bureau of Standards observed vifeakening of the bond between the 

 concrete and the reinforcing steel when current was applied to the steel 

 as a cathode on specimens immersed in .Washington, D. C, tap water^. 



Protection of Steel Hardxvare and Fittings 



Steel in such forms as bolts, tie-rods and the like is used frequently in 

 the assembly of timber structures. It is d esirable to give such steel 



^E. B., M. licCollum, and 0. S. Peters, Technologic Paper ;rl8, "Electrolysis 

 in Concrete," National Bureau of Standards, 1919. 



E - 10 



