Alkali-silica reaction (ASR) is a chemical reaction between alkaline components in concrete structures and aggregate containing reactive silica. The result of this reaction is gel formation, which leads to expansions and cracks in the internal structure of concrete. The purpose of the ASR test is to evaluate the durability and longevity of the structure by detecting the potential presence and effects of this reaction in concrete building materials.
Principle of the Test
The alkali-silica reaction (ASR) is a chemical reaction between the alkaline components (sodium and potassium hydroxide) in concrete and amorphous or cryptocrystalline silica in aggregate in the presence of water. The result of this reaction is a gel-like substance. The ASR gel expands by absorbing the surrounding moisture and this expansion creates stresses in the internal structure of the concrete, causing cracks.
The principle of the experiment is based on expansion measurements to determine the effect of this chemical reaction on concrete specimens. The presence and severity of the alkali-silica reaction is directly related to the dimensional changes and structural deterioration of the specimens. The aim of the experiment is to detect the presence of this reaction at an early stage and to assess the long-term durability of the building material.
Conduct of the Experiment:
Sample Preparation: The cement mortar to be used in the test is prepared with aggregates containing reactive silica. The mortar is poured into prism or cube molds and left to cure.
Curing Process: The prepared specimens are cured in a water bath or in a humidity cabinet under certain temperature and humidity conditions for 14 days.
Expansion Measurement: After curing, the samples are measured at regular intervals (e.g. weekly) with a dilatometer to record the expansion rates.
Reaction Monitoring: The gel formation and cracks in the specimen caused by the alkali-silica reaction are observed. The amount of expansion indicates the presence and intensity of ASR in the sample.
Calculations
The expansion rate of the specimens is calculated as a percentage
Experimental Results and Interpretation
The expansion values obtained as a result of the test indicate the susceptibility of the specimen to ASR. If expansion occurs above a certain threshold value, this indicates that the concrete may be damaged by the alkali-silica reaction. In this case, additional precautions may be required in terms of building material.
Application Areas
Alkali-silica reaction testing is widely used to ensure the long-term durability of large-scale concrete structures such as bridges, dams and highway substructures. It is also important to choose non-reactive aggregates and use appropriate admixtures during the design of new concrete mixes to increase resistance to ASR.
Conclusion
According to the results of the alkali-silica reaction (ASR) test, the amount of expansion in the specimens and the observed structural distortions reveal the susceptibility of the concrete to ASR. If a certain expansion threshold is exceeded, this indicates that the specimen has been exposed to ASR and may suffer further damage over time.
If the expansion rates are low or negligible, it is concluded that the aggregate used is non-reactive and resistant to the alkali-silica reaction. This indicates that the concrete mix will be long-lasting. However, high expansion rates and crack formation indicate structural weaknesses and durability problems; in this case, the measures to be taken and the choice of materials should be reviewed.
The test results are critical to the safety of concrete structures and allow measures to be taken at the design stage, such as limiting the use of reactive aggregates or the addition of appropriate admixtures.
STANDARD CODE
ASTM C 1260