ASSESSMENT OF MATERIAL PROPERTIES OF CONCRETE GRAVITY DAMS – AN INDIAN CASE STUDY
Table 3. Modal composition of coarse aggregates (results in %)
Petrography analysis of the concrete samples indicated that there was no alkali-silica reaction in the concrete. From this analysis, five different major rock types and one minor rock type (granite) were found. For estimating the percentages of different types of coarse aggregates, samples were taken from concrete cores representing different locations. The total weight of the coarse aggregates in the overall concrete separated, based on the petrographic examination, was approximately 90kg. In the petrographic analysis various rock types, i.e. quartzite, feldspathic sandstone, calcareous sandstone, micaceous sandstone, and ranite were observed. The percentage distribution of these different rock types in the total weight of the coarse aggregate was calculated, and the percentage of the rocks were as follows: quartzite - 25.33%, feldspathic sandstone - 23.32%, sandstone - 23.13%, calcareous sandstone - 12.48%, micaceous sandstone - 11.13%, and granite rocks - 4.59%. A similar exercise was repeated for calculating the percentage distribution of various rock types in the coarse aggregates of rich concrete and mass concrete. The percent distribution of various rock types present in rich concrete (A and C) were analysed. In the petrographic analysis various rock types, namely quartzite, feldspathic sandstone, calcareous sandstone and granite were observed. The percentage distribution of these different rock types in the total weight of the coarse aggregate was calculated, and the percentage of rocks was as follows: quartzite - 30.99%, feldspathic sandstone - 13.2%, calcareous sandstone - 30.6% and granite - 25.10%. The distribution of aggregate types in mass concrete (B) was analysed and various rock types, i.e. quartzite, feldspathic sandstone, sandstone, calcareous sandstone, micaceous sandstone and granite were observed. The percentage distribution of different rock types in the total weight of the coarse aggregate was calculated and the results were as follows: quartzite - 30.2%, feldspathic sandstone - 13.5%, sandstone - 28.9%, calcareous sandstone - 14.4%, micaceous sandstone - 8.60% and granite - 4.1%. However, the overall percentage of the rocks in this category may also vary when the total mass of the rocks used in the mass concrete of the dam are considered.
The petrographic analysis results indicated the presence of pyrite (FeS2) in a variable percentage (1-4%).
The concrete core samples were also tested for a Scanning Electron Microscope (SEM) study. The concrete core samples were divided into three categories, i.e. upstream, gallery and downstream. The numerous open-air voids of various shapes and sizes with smooth margins were uniformly distributed in the concrete. The growth of perfect ettringite crystal, mostly in
Vol XXXII Issue 1 DAM ENGINEERING 11
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