Diagnosis and Control of Alkali-Aggregate Reactions in Concrete
Aggregates containing certain constituents can react with alkali hydroxides in concrete. The reactivity is potentially harmful only when it produces significant expansion.(1)** This alkali-aggregate reactivity (AAR) has two forms—alkali-silica reaction (ASR) and alkali-carbonate reaction (ACR, sometimes called alkali-carbonate rock reaction, or ACRR). ASR is of more concern than ACR because the occurrence of aggregates containing reactive silica minerals is more common. Alkali-reactive carbonate aggregates have a specific composition that is not very common. Alkali-silica reactivity has been recognized as a potential source of distress in concrete since the late 1930s.(2,3) Even though potentially reactive aggregates exist throughout North America, ASR distress in structural concrete is not common. There are a number of reasons for this:
Investigation of Concrete from I-20 Near Monroe, Louisiana
Abstract : This report covers an investigation conducted in l994-1995 to determine the probable cause of concrete pavement deterioration in certain lanes of I-20 east and west of Monroe, LA. The investigation was conducted by the U.S. Army Corps of Engineers Waterways Experiment Station at the request of the Louisiana Department of Transportation. Cores taken from distressed and non-distressed areas from different sections of the roadway were evaluated to determine the following: (a) the role of alkali-carbonate-rock reaction: (b)the role of alkali-silica reaction; (c) the contribution of freezing-and-thawing action to the deterioration; and (d) the contribution of fresh concrete properties and construction practices to the deterioration. The report includes the results of these analyses as well as conclusions and recommendations.
THE STRUCTURAL STATUS OF CLAY SYSTEMS
Illite and montmorillonite have been compressed into cores under a pressure of 1200 atm. The structural status of these clays has been examined by means of detailed nitrogen adsorption-desorption isotherms and by means of electron micrographs of fracture surfaces of the clay cores. The subsequent swelling behavior of sodium and calcium clay cores has been analyzed in terms of the model derived from these measurements and the specific surface area of the clay. A generalized theory for the condensation of plate-shaped particles into domains has been proposed.