Susceptibility of deformed granitic rocks of the Santa Rosa mylonite zone to the alkali-silica reaction in concrete.

摘要

The alkali-silica reaction in concrete has been a major concern since its discovery in the 1940's. Traditionally, most research focused on prevention and remediation techniques as applicable to the concrete industry. In this research, a new approach that integrates petrographic examination and expansion testing (current methods used in predicting the susceptibility of aggregates to the alkali-silica reaction) with transmission electron microscopy and the novel use of neutron diffraction Rietveld texture analysis with the software program MAUD (Material Analysis Using Neutron Diffraction).; Petrographic examination revealed that quartz grains were deformed, and as a result, mineral grain sizes were reduced with progressive deformation. Expansion testing documented that the susceptibility of rocks to the alkali-silica reaction increased as rocks are progressively deformed. Average ASTM C 1260 expansion values at 30 days for granite was 0.210%, mylonite was 0.424%, and phyllonite was 0.565%.; Transmission electron microscopy confirmed that the deformation process in quartz is caused by the creation and movement of dislocations. As these rocks become increasingly deformed, the dislocation density increases. The average dislocation density was 7.1 x 107 dislocations/cm 2 in granite, and 2.3 x 108 dislocations/cm 2 in mylonite. Phyllonite had a dislocation density of 2.0 x 108 in images where individual dislocations could be counted. However, the dislocation density for phyllonite ranged from areas of no dislocations to uncountable tangles. Dislocations cause an increase in the strain energy of quartz, leading to a higher susceptibility to the alkali-silica reaction.; Neutron diffraction texture analysis using MAUD was introduced as an alternative to the time consuming method of using transmission electron microscopy to assess the deformation state of a rock. The preferred orientation of biotite, a common accessory mineral in granite, shows a roughly linear relationship with the susceptibility of a rock to the alkali-silica reaction, with a (001) pole figure maximum of 4.50 m.r.d. occurring in PC 709, a highly deformed phyllonite.; The results of this study show that multiple techniques may be used with one another to provide an accurate assessment of the susceptibility of a rock to the alkali-silica reaction. This study demonstrates that geological and mineralogical methods of quantitative characterization can to contribute further the understanding of phenomenon in concrete research.