ASR leads to expansive products that can cause extensive cracking in concrete structures. The alkalies (potassium and sodium ions) in the cement paste react with reactive (amorphous) silica particles in fine or coarse aggregate and cause expansion and cracking..
To reduce the risk of ASR in new concrete structures, the quantity of sodium and potassium ions in the cement paste of fresh concrete should be reduced so as not to exceed the critical limit defined in standards, guidelines or particular project specifications.
The RAT measures the amount of sodium and potassium ions in fresh concrete or in its constituents and can also be used for testing powder samples of hardened concrete.
Rapid Alkali Content Test.