result of exposure to sulfates or acids. Natural-occurring sulfates of 

 sodium, potassium, calcium, or magnesium, which are sometimes in soil or 

 dissolved in ground water adjacent to concrete structures, can attack 

 concrete. 



There are two chemical reactions likely to be involved in sulfate 

 attack on concrete: (1] the combination of sulfate with free calcium 

 hydroxide liberated during the hydration of the cement to form calcium 

 sulfate (gypsum), and (2) the combination of gypsum and hydrated calcium 

 aluminate to form calcium sulfoaluminate. 



The effects of some of the more common chemicals on the deterioration 

 of concrete are indicated in Table 22. Many pollutants contain the chemicals 

 indicated in the table. 



b. Sunlight Exposure Effects . Sunlight has virtually no effect on the 

 deterioration of concrete. 



c. Water Penetration Effects. Pure water does not attack concrete, 

 but it can be the medium for dissolving most chemicals, which in solution 

 may cause concrete deterioration. Seawater has a high sulfate and chloride 

 content which may be only moderately aggressive to concrete; however, if 

 these chemicals can penetrate the concrete to the steel reinforcing then 

 rapid deterioration will occur. 



d. Wave and Current Effects . Waves and currents have no direct 

 effect on concrete or are not the direct cause of its deterioration. 

 Concrete destruction only occurs when the structure is not adequately 

 designed. Wear to concrete structures does occur because of cavitation 

 occurring as a result of the collapse of bubbles of water vapor. Concrete 

 wear by abrasion may also occur as a result of solid particle (such as 

 sand) transported by waves and currents impinging on a concrete surface. 



e. Effect of Severe Temperature and Ice . Resistance to severe tempera- 

 ture changes in concrete are more a function of proper mix design with good 

 aggregate and proper curing than any other factors. Generally, high 

 temperatures do not affect well-cured concrete. Building codes generally 

 require concrete to resist heat of S38 Celsius (1 000 Farenheit) for 5 

 minutes to more than 1 038 Celsius (1 900 Farenheit) for 3 hours, depending 

 on the thickness of concrete tested. Sustained high-ambient temperatures 

 (above 200 Celsius) will stop normal crystal growths in concrete and 

 normal strength gain with aging. 



To provide a high degree of resistance to the disruptive action of 

 freezing and thawing and of deicing chemicals air-entraining admixtures are 

 used. Unless low temperatures are very extreme, properly designed concrete 

 will not deteriorate or spall in freezing conditions. 



f . Marine Organisms . Marine organisms do not injure good concrete, 

 containing sound aggregate. For example, concrete which is composed of 

 siliceous aggregates is resistant to marine borer activity because the 

 material is extremely abrasive to the lime shells of boring organisms. 

 However, in tropical and semitropical water there have been instances of 

 borer damage in concretes where limestone or similar sand has been used. 



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