DETERIORATION OF CONCRETE STRUCTURES CAUSED BY INTERNAL DISTRESS MECHANISMS

Internal distress of concrete structures caused by chemical reactions between the cement and aggregates has been well documented since the early 1940s. Deterioration in the form of cracking due to the expansive forces of the gel produced from the alkali-silica reaction (ASR) was essentially a non-issue in Texas prior to the 1970s. Environmental restrictions placed on Texas portland cement plants led to increased alkali content in most cements. This increase in alkalis has been especially apparent during the last 25 years. Siliceous aggregate sources that have had a history of use for 50 to 60 years were identified as being potentially reactive with cement alkali. Numerous engineered structures constructed during the 1980s and early 1990s that incorporated potentially reactive aggregate and high content levels of cement alkalis have failed due to internal expansion cracking caused by ASR. Methods of mitigation include the use of mineral additives, such as fly ash, slag, and silica fume, if the option of using low alkali cements is not available.