Petrography of fine aggregates from Kaligandaki River, western Nepal: implication for assessment of deleterious constituents

Seven fine aggregate samples from test pits driven at the river banks of the Kaligandaki River and banks of the contributing streams around Kokethanti-Chhyo Bagar area were petrographically analysed as these will be used for concrete aggregates. The aggregates had median grains size of 0.45-1.00 mm and were well graded. They were dominantly composed of carbonate rock fragments and the total QFL modes being Q14.81–28.87F0.63–4.58L66.55–84.15. All the samples were classified as medium-grained calc-lithic sands. Quartz grains were dominantly megaquartz. Some chert grains and few quartz grains occurring in siliceous limestones were of microquartz. Considering deletereous constituents, the sample T1 had chert fragments. The sample T2 had high amount of micas suggesting its low workability. Silt/clay-grade size fraction was the deletereous material to all the samples and this fraction should be removed during processing. The samples T2, T6 and T7 showed greater preferability among the samples as these had lower amount of unsound rock fragments such as carbonaceous schists/phyllite, and other deletereous materials