P N OJHA, BRIJESH SINGH, V V ARORA, PRAMOD NARAYAN, AMIT TRIVEDI & MANTU GUPTA
where K represents permeability in milli darcy (MD) and Φ (%) is porosity. The coefficient of permeability values obtained for the left and right bank rock samples were 1.59 x 10-5 and 1.66 x 10-5, respectively.
6. Conclusions
The field studies indicate that there is no carbonation and corrosion activity taking place inside the concrete structure of the dam. The overall quality of the concrete is sound and the experimental test results of compressive strength, modulus of elasticity, Poisson’s Ratio and split tensile strength are in a similar range to the designed values for those parameters considered in the design. The test results of the resistivity test and humidity meter indicate that moisture content in the upstream side is higher than the downstream side.
Petrographic analysis of the coarse aggregate indicates it is non-reactive to alkali-aggregate reaction, and major aggregate type is sedimentary (quartzite and sandstone). The sulfate, in the form of pyrite, was found in the aggregates from petrographic, SEM and XRD studies and this is the reason for crystalline ettringite formation. Ettringite percentage in open-air voids is maximum on the upstream side (3-4% of open-air voids) and minimum in the gallery and downstream (1-2% of open-air voids). The percentage of crystalline ettringite present in open-air voids is about 2% of open-air voids in mass concrete. The percentage of crystalline ettringite in the mass concrete of the upstream, gallery and downstream samples varied from 0.01% to 0.03%. The ettringite formation of such a small magnitude in large voids does not cause any expansion. The results of an accelerated mortar bar test conducted on concrete cores along similar lines to standard code ASTM C-1260[1] for determining residual expansion indicated net expansion of 0.04%.
The average residual expansion of cores similar to the procedure of ASTM C-1293[2] varied from 0.0231% to 0.0271%. This average residual expansion after more than 50 years is not significant keeping in view that the limit is 0.04% at the age of one year and therefore indicates no alkali-silica reaction. However, it was recommended that periodic inspections were conducted on selected concrete every five years in order to understand the growth rate of ettringite formation in the future. The results of the petrography studies, SEM studies, colour test and accelerated test on the cores indicated there was no alkali-silica reaction in the concrete.
The ultrasonic pulse velocity (P wave only) values for the rock cores extracted from the left and right bank on the downstream side of the dam varied from 2.93km/sec to 3.41km/sec. The overall average values of compressive strength, Poisson’s Ratio, modulus of elasticity and coefficient of permeability were 64.60N/mm2, 0.186, 14,944N/mm2, 1.59 × 10-5 (for the left bank) and 1.66 × 10-5 (for the right bank), respectively. One of the reasons for lower pulse velocity and modulus of elasticity, as indicated from the petrographic studies,
18 DAM ENGINEERING Vol XXXII Issue 1
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