Alkali silica reaction under the influence of chloride based deicers

Highways form the backbone of transportation in United States. As a result, issues related to distress in pavements and use of chemicals on pavement forms one of the major focus areas of highway agencies. One of the forms of distress in concrete pavements is Alkali silica reaction (ASR). The principal objective of this research study is to understand the role of chloride-based deicing chemical in causing or accelerating ASR distress. Sodium chloride or rock salt is one of the oldest forms of deicers. Several research studies have been done on ASR under the influence of sodium chloride and calcium chloride. However, limited information is available on effects of potassium chloride and magnesium chloride deicers. This research study is based on laboratory evaluation to assess effects of chloride deicers on alkali silica reactivity. Variations in exposure conditions, cement and aggregate are introduced to understand the effects of deicer solutions on a wider spectrum. Mortar bar tests based on ASTM C 1260 tests were conducted, in which reactive fused silica and non-reactive natural sand were used as aggregates and two Type I cement with different alkali contents (low and high) were used. Tests were carried out at two different storage temperatures, 38°C and 80°C.Findings from these tests show that 3% wt. solutions of sodium chloride and potassium chloride deicers can cause more expansion in mortar specimens containing fused silica, than even the standard 1 normal sodium hydroxide solution. Calcium chloride and magnesium chloride solutions have shown no effect on initiating or accelerating ASR in the same test specimens. Higher temperature accelerated the ASR distress, regardless of the source of alkali. The alkali content of cement itself did not have a major influence on mortar bar expansion, particularly in the presence of deicing solutions. However, this is due to the ample supply of alkalis from the deicer soak solution in the test method. Formation of chloroaluminates or Friedel's salt has been observed and is believed to be the principal mechanism through which the chlorides in the deicer solutions are chemically bound. With removal of chlorides from the solution, alkali hydroxides are formed, thus inducing the ASR distress and the accompanied expansions in the test specimens. Even though such chloroaluminates were observed in mortar specimens exposed to calcium and magnesium chloride solutions, no accompanying expansion was observed in those test specimens.