(3) cement containing high percentage of alkalis or 

 high C 3 A; 



(4) freeze-thaw cycles; 



(5) CO2 in air or surrounding water; 



(6) erosion and abrasion from cavitation, ice, surf, 

 moving sand; and 



(7) acids, sulphates, nitrates, or organic substances 



in mixing water or in surrounding water, as at discharge from 

 chemical plants or in sewage structures. 



(b) Those causing or accelerating corrosion of steel: 



(1) Salt or alkalis on aggregates; 



(2) chlorides in admixtures or water used for mixing 

 and curing; 



(3) chlorides in water surrounding concrete (salt- 

 water), salt spray, salt fog; 



(4) oxygen; 



(5) sulphides combined with moisture on stressed 

 tendons before encasement or protection; 



(6) stray electric currents; 



(7) alkalis in surrounding soils; 



(8) high temperature; 



(9) embedded metals other than steel, particularly 

 copper and aluminum; 



(10) inadequate thickness of concrete cover, or 

 permeability of cover; 



(11) cracks; 



(12) cement chemistry (e.g., too low C3A); and 



(13) deicing salts, acids, or other aggressive chemicals. 



c. Enhancement Techniques . Fortunately, the steps to be adopted to 

 overcome these many forms of attack are complementary to each other. Most 

 have been adopted as standard good practice. 



(1) Aggregates . Although aggregate is commonly considered to be 

 an inert filler in concrete, this is not always the case. Certain aggregates 

 can react with Portland cement, causing expansion and deterioration. 



104 



