P N OJHA, BRIJESH SINGH, V V ARORA, PRAMOD NARAYAN, AMIT TRIVEDI & MANTU GUPTA
The results from the 14 day accelerated mortar bar test (carried out as per ASTM C-1260 (2014) standards[1]) for coarse aggregate taken from concrete cores, and measured using mortar bars of 25mm × 25mm × 285mm, indicated that the net expansion in the coarse aggregate sample was 0.08%. The results from this test indicated net expansion of 0.04%. As the residual net expansion of the concrete samples was less than 0.1% the aggregates were not under the potentially reactive category and therefore there was no potential ASR in the concrete. The concrete core specimens from both wet and dry portions of the dam were selected for residual expansion testing in a similar line to the procedure in ASTM C 1293 (2018)[2] in order to determine the susceptibility of the concrete to alkali-silica reaction. The concrete core was tested with a deviation of temperature from 38ºC to 60ºC. This range in temperature was used because it was seen from past studies carried out by NCB that the slow reactive aggregate gives expansion at 60ºC. The higher temperature was also recommended in Indian Standard codes IS: 2386 Part VII[5] and IS: 383-2016[8]. The average residual expansion of concrete cores in the case of the gravity dam varied from 0.0231% to 0.0271% (see Figure 7). 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 thus indicates no potential of alkali-silica reaction.
Figure 7. Residual expansion of concrete cores by ASTM C1293 (2018) method
The in situ properties of concrete obtained from the investigation were used in the advanced FEM modelling of the dam, wherein the basic objectives were to obtain reliable model output regarding the realistic deformations, stresses, inclination, etc. to study the unusual deflection of dams conducted under the ongoing Dam Rehabilitation & Improvement Project (DRIP).
16 DAM ENGINEERING Vol XXXII Issue 1
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