P N OJHA, BRIJESH SINGH, V V ARORA, PRAMOD NARAYAN, AMIT TRIVEDI & MANTU GUPTA


4. Chemical Analysis and Mineralogical Studies of Concrete


The data on cement (content, SO3 and Na2O equivalent) was not available. However, the SO3 content calculated from the chemical analysis of concrete core samples in the case of the gravity


dam varied from 0.12% to 0.34% per m3 of concrete, and the Na2O equivalent (water-soluble method) in the concrete of the gravity dam varied from 0.84 to 1.22 per m3 of concrete


(Table 2). The chloride, sulfate, pH and all other chemical parameters were within the permissible limit given in IS: 456-2000[7] for both concrete and water. No adverse chemical presence in the concrete and water samples, in general, was seen. From previous literature it is seen that the total mass of alkali in the concrete mix shall not exceed 3kg per m3 of concrete, and in the present investigation the values were also well below this limit.


Table 2. Test results of chemical analysis of concrete core samples


The detailed mineralogical investigation, such as petrographic studies of aggregate and concrete, presence of any reactive or abnormal products and Alkali Aggregate Reactivity (AAR) attack or sulfate attack is crucial for detecting the cause of distress, if any, in the aged concrete. Petrographic studies of the rock types present in the concrete cores extracted from the dam were carried out, and the details of this analysis are discussed next. The petrographic analysis of coarse aggregate indicates the major aggregate type as sedimentary (quartzite and sandstone). The modal compositions of the rock types are given in Table 3.


10 DAM ENGINEERING


Vol XXXII Issue 1


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