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Mix proportion and sample preparation

Concrete mix with 0.5 w/c ratio and 390 kg/m3
cement content was taken for design of M25 grade taking moderate environmental
condition. Table 1 represents details on materials used for compressive
strength and bond properties. Seven mix proportions of 0%, 5%, 10%, 15%, 20%,
30% and 40% were cast for compressive strength with 150 mm × 150 mm × 150 mm
cube. For each proportion the samples taken were OPC 43 grade cement, natural
sand, coarse aggregates of 20 mm and 10 mm with the proportion 60:40 and
potable water. Compressive strength of cubes was tested for 7 days and 28 days.

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The compressive strength was calculated y the
formula:

(1)

Where

is compressive strength (N/mm2),

is area of specimen (mm).

The optimum replacement of granite dust was then
compared with conventional concrete for bond strength. The bond strength was
determined by simple pull out test by inserting steel rod in concrete specimen
of 150 mm × 150 mm × 150 mm cube. Thermo mechanically treated (TMT) bars were
inserted up to the end eccentrically in the cubes. Total of 12 samples were
cast with 10 mm, 12 mm and 16 mm steels for control mix and optimum mix.

Sample preparation and test setup for pull-out test

To hold the bars in position eccentrically, special
precautions were taken. 2 samples for each casting were prepared. After 28 days
curing the samples were fixed in Universal testing machine (UTM) by fixing the
rod in upper jaw and the sample was kept below middle deck. First the machine
was adjusted by moving the middle deck such that 600 mm projected rod could be
fixed in the jaw present in upper deck. Load was applied and type of failure
was observed.

The average bond strength was calculated by the
formula:

(2)

Where

is
bond stress (N/mm2), F is applied load (N), d
the nominal bar diameter (mm), l  the embedment length (mm).