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.

The compressive strength was calculated y the

formula:

(1)

Where

is compressive strength (N/mm2),

is load (N),

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).