ALKALI-AGGREGATE REACTIVITY EVALUATION OF AGGREGATES FOR APPLICATION IN INDIAN CONCRETE DAMS


The major mineral constituent was quartz. Accessory minerals were muscovite and iron oxide. Subhedral to anhedral quartz grains with sharp grain margins were well-graded and homogeneously distributed in the sample. Grain size variation in quartz was too large. Grain size of quartz varied from 8μm to 651μm, with an average of 235μm. However, the majority of quartz grains were in the size range 180μm to 250μm. The strained quartz percentage was about 17%, and their undulatory extinction angle (UEA) varied from 14º to 16º. Lath-shaped muscovite grains were randomly distributed throughout the rock. Anhedral to subhedral iron oxide grains with corroded margins were randomly distributed in the rock.


(a) (b) Figure 1. Micrographs showing distribution of mineral grains in CA-1 sample 4.2.2 Coarse Aggregate, CA-2


The petrographic studies conducted on coarse aggregate CA-2 (Figures 2a and 2b) indicated that the sample was fine to medium grained textured partially weathered. The modal composition is given in Table 4.


Table 4. Modal composition of coarse aggregate CA-2 (results in %) Vol XXXI Issue 3 DAM ENGINEERING 173


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