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  Chloride Testing

There are two major types of Chloride tests, Acid-Soluble and Water-Soluble. Acid-Soluble (ASTM C-1152, FM 5-516) is theoretically a total extraction method, whereas Water-Soluble (ASTM C-1218) run results that are generally twenty to twenty-five percent less. Also the Water-Soluble, due to differences in the method, take an extra day in the turn-around time. Chloride testing is the number one defense against corrosion.
A high number in chlorides will result in the weakening of structures and dramatic shortening of their life expectancy. Some of the reasons Chloride testing is very important are listed in the information below.

  AASHTO T 277
This test method is used to determine how conductible a sample of concrete is, which will indicate how resistant the concrete will be to penetration of chloride ions. In this test a 4x8” cylinder is a sliced into a 2” piece. After the sample is prepared it is placed between two plastic molds, one containing sodium chloride(-) and one containing sodium hydroxide(+). An electrical current is then applied and readings are taken over a six hour period.
   
  ASTM C 1202
This test method is used to determine how conductible a sample of concrete is, which will indicate how resistant the concrete will be to penetration of chloride ions. In this test a 4x8” cylinder is a sliced into a 2” piece. After the sample is prepared it is placed between two plastic molds, one containing sodium chloride(-) and one containing sodium hydroxide(+). An electrical current is then applied and readings are taken over a six hour period.
   
  AASHTO T 260
This Method covers procedures for the determination of the total chloride ion content or the water-soluble chloride ion content of aggregates, portland cement, mortar or concrete. This method is limited to materials that do not contain sulfides. The water-soluble version of this test is known as Procedure A. The acid-soluble version, or total chloride version, is known as Procedure B.
   
  ASTM C 1524
This test method is a way to test aggregate for chlorides in a different water-soluble procedure. It is normally used when an aggregate has tested particularly high. It is a method in which aggregate is boiled in a soxhlet flask for twenty-four hours, in order to extract chlorides in a water matrix. Then the extracted water is tested in accordance with ASTM C 114.


Corrosion

The corrosion of metals, especially steel, in concrete has received a lot of attention because of its widespread occurrence in certain types of structures and because of the high cost of repairs it causes. The consequent extensive research on factors contributing to steel corrosion has increased our understanding of corrosion, especially concerning the role of chloride ions. Chloride ions are common in nature and small amounts are usually unintentionally contained in the mix ingredients of concrete. That is why research has pointed to the need for quality concrete with careful testing and reasonable limits on the amount of chloride in concrete as well as in the concrete components used to create the mix.
Chloride ions are considered to be the major cause of corrosion of steel reinforcement. However, corrosion can occur in the absence of chloride ions. For example, carbonation of concrete results in reduction of its alkalinity, thereby permitting corrosion of embedded steel. Carbonation is a usually a slow process in concrete which has a low water-cement ratio and carbonation-induced corrosion is not as common as corrosion induced by chloride ions. The rate of corrosion of steel reinforcement embedded in concrete is strongly influenced by environmental factors. Both oxygen and moisture must be present if electrochemical corrosion is to occur. Dissolved chloride ions also may penetrate unprotected hardened concrete in structures exposed to marine environments or to deicing salts. Reinforced concrete with significant chloride ion content is vulnerable to macrocell corrosion, especially if subjected to cycles of wetting and drying. Deterioration of concrete due to corrosions results because the products of corrosion, which is rust, occupy greater volume than the steel and in turn exert substantial stresses on the surrounding concrete. The outward effects of the corrosion include staining, cracking, and spalling of the concrete. The research on corrosion to date has not produced a steel or other type of reinforcement which will not corrode when used in concrete and which is both economical and technically feasible. Other measures which are being investigated include the use of corrosion inhibitors, protective coatings on the steel, and cathodic protection. There has been some success in each of these areas though problems resulting from corrosion of embedded metals were far from eliminated.
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