Page 100 - ICJ Jan 2023

TECHNICAL PAPER COLLECTOR’S EDITION

Stone dust was used as procured from the crusher. RESULTS AND DISCUSSION
The fine aggregates used were 100 percent river The effect of superplasticiser and partial
sand, a mix of 80 percent river sand and 20 percent replacement of stone dust on workability,
crushed stone dust and 60 percent river sand compressive strength, modulus of rupture and
and 40 percent crushed stone dust. The sieve splitting tensile strength are illustrated in Figs
analysis results on random samples for these fine 1 to 4. It is clear from the figures that there is a
aggregates are indicated in Table 1. significant increase in workability, compressive
strength, modulus of rupture and split tensile
Two basic concrete mixes designated as A (1 : 1.44 strength. Fig 1 shows the variation of compacting
: 3.28; w/c = 0.50) and B (1 : 1.23 : 2.93; w/c = 0.45) factor with dosages of superplasticiser. It was
were chosen for study. The mix proportions were noticed that addition of stone dust decreases the
obtained using IS code method of mix design to workability of concrete mixes significantly. This is
achieve M 20 and M 30 grade of concrete, with due to the reason that, stone dust is used as it is
granite aggregate and 100 percent river sand as procured from the crusher and contains a larger
fine aggregate (referred to here as conventional portion of fine particles, which is evident from the
concrete). The superplasticiser dosages used were sieve analysis result also. The workability of mixes
0.5, 1, 2 and 3 percent by weight of cement. made by using stone dust can be increased by
addition of superplasticiser. From Fig 1 it can be
PREPARATION OF SPECIMENS observed that the workability level of 100 percent
sand without superplasticiser can be obtained
The exact amounts of cement, sand, stone dust and by using 40 percent stone dust and 2 percent
coarse aggregate were weighed and then placed superplasticiser. Figs 2 (a), (b) and (c) show the
in a laboratory concrete mixer. The water was variation of compressive strength with percentage
then added in required amount and workability of superplasticiser after 7 days, 28 days and three
of fresh concrete was measured by compacting months curing, for mix A. It can be seen from the
factor method immediately after mixing. The test graphs that replacement of sand by stone dust does
specimens were cast in steel moulds and compacted not affect the strength. Addition of superplasticiser
on a vibrating table. They were demoulded a day increases the strength of concrete mixes.
after casting. The specimens were cured in water
until the test date.

TESTS

For each batch of concrete, six 150-mm cubes were
tested to determine the compressive strength,
three at the age of 7 days and the remaining three
at the age of 28 days. Three 100 mm x 100 mm x 400
mm size prisms were tested in flexure under three
point loading to determine modulus of rupture,
and three 150 mm x 300 mm cylinders were tested Fig 1 Variation of compacting factor with superplasticiser
for splitting tensile strength both at 28 days. content for mix A and mix B

The Indian Concrete Journal | November 2018 101