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|Title:||Quartz bearing aggregates and their role in the alkali-silica reaction in concrete prism tests|
|Authors:||Smith, Andrew Simon.|
|Presented at:||University of Leicester|
|Abstract:||Undulatory extinction in quartz is a wide spread feature found in many different rock types. The degree of undulosity exhibited is a function of the processes of rock formation and deformation. As undulosity suggests a level of instability of the quartz, the degree of undulosity has been used, for some time, to indicate the potential reactivity of the quartz in the alkali-silica reaction. The method of routine measurement of the degree of undulosity, on investigation, has been found to be inaccurate. A new method for this routine measurement is proposed, utilising the universal stage assembly fixed to a petrological microscope. Instability of quartz grains can also be gauged by the assessment of grain textures, grain and crystallite sizes. Analysis of 70 quartz-bearing rock types from different parts of UK has been carried out. The results indicate that if all these features are investigated and quantified then it is possible to classify the stability of the quartz, and therefore assess the potential for reaction in the alkali-silica reaction.;Three aggregate types, containing quartz with undulose extinction, have been identified as being either reactive or potentially reactive: Dry Rigg Siltstone, Horrocksford (Siliceous) Limestone and the Coedana Granite. Two of these aggregates, the siltstone and the limestone, have been shown to be reactive when used in concrete road and bridge structures. The third, the granite, has been identified as having quartz with a very high degree of undulose extinction, and other deformation features, which indicate this as being potentially reactive. Concrete test prisms have been made with alkali levels of 7.0kg/m3 to investigate if the aggregate type has any affect on the composition of the reaction product, the gel, being produced when stored at 38oC and 100% RH. The three aggregate types do produce gels of different composition, though this is not conclusively attributed to the aggregate type. It is concluded that there may well be a relation between the composition of the gel produced and the type of aggregate reacting, but this may well be overprinted by reactions that have taken place between the time of the expansion measurement ending and the time of chemical analysis by EPMA.|
|Rights:||Copyright © the author. All rights reserved.|
|Appears in Collections:||Theses, Dept. of Geology|
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