ASSESSMENT OF MATERIAL PROPERTIES OF CONCRETE GRAVITY DAMS – AN INDIAN CASE STUDY


of crystalline ettringite in mass concrete of the upstream, gallery and downstream samples varied from 0.01% to 0.03%. Ettringite formation of such a small magnitude was unlikely to cause any expansion, and it has also been reported in the past that the ettringite found in this benign state as large needle-like crystals, should not be interpreted as causing the expansion of deteriorating concrete[13]. However, it was recommended to conduct periodic inspections on selected samples after five years to understand the growth rate of ettringite formation in the future.


The X-Ray Diffraction (XRD) analysis of the samples collected from the upstream, galleries and downstream concrete core samples showed minor peaks of ettringite, portlandite, akermanite and larnite. The intensity of ettringite peaks in all these samples was low, which indicated that these concrete samples had a low concentration of ettringite crystals. A minor percentage of unconsumed larnite was still present in the concrete at higher elevations, which may hydrate in the later stage. Portlandite and akermanite peaks indicate the hydration products of the cement used. It is seen that there is no significant unhydrated part left in the samples, and no extraordinary phases are identified. Minor ettringite formation is also detected. From the XRD results, no symptoms of alkali-silica reaction were observed.


Figure 4 Scanning Electron Microscope images of ettringite in air void of concrete sample


Vol XXXII Issue 1


DAM ENGINEERING


13


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