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TECHNICAL PAPER COLLECTOR’S EDITION

parent mix proportions were crushed, sieved and
stored separately. Four mixes of recycled concrete
were made with aggregates recycled from each of
the four parent mixes of concrete and tested for
28-day compressive strength.

RESULTS AND DISCUSSION
Properties of recycled aggregate

Particle size distribution
Fig 1 shows the result of sieve analysis carried Fig 1 Particle size distribution of fresh granite and
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out as per IS 2386 , for different types of crushed recycled aggregates
demolition aggregates. It is seen that the coarse
aggregate of concrete as well as brick rubble Bulk density and voids
are well graded, that is, the concrete and brick It is observed from Table 2 that though the rodded
masonry are reduced to various sizes during the bulk density of recycled concrete aggregate is
process of crushing. The amount of fine aggregate higher than that of fresh granite aggregate, its
in demolished concrete and brick masonry were loose bulk density is lower than that of the fresh
in the range of 5-10 percent and around 10-15 one. The mortar adhering to recycled concrete
percent, respectively. aggregate increases the size of aggregate and
have a better interlocking which in tum reduce the
Specific gravity and water absorption voids in rodded condition. The lower value of loose
The specific gravity (saturated surface dry bulk density of recycled concrete aggregate may
condition) of demolished concrete aggregate be attributed to its higher porosity than that of the
is lower than that of natural aggregate. Since fresh granite aggregate.
the aggregates from crushed concrete consist
of granite aggregate with old mortar adhering As expected, the bulk density of both types of
to it, the water absorption is relatively higher recycled brick masonry aggregates were observed
than that of the fresh granite aggregates, which to be lower than that of recycled concrete
corroborates the observation of Ravindrarajah and aggregate. As perASTMC 33O-1985 , the upper
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Tam . The specific gravity of both types of recycled limit for bulk density of light-weight coarse
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masonry aggregates (using table-moulded and aggregate is 880 kg/m . As the bulk density of both
wire-cut bricks) have been found to be lower than types of recycled brick masonry aggregates are
that of recycled concrete aggregate. Due to higher higher than this value, they do not fall under the
porosity of the country bricks, the water absorption category of light-weight aggregate.
is higher than that of the table moulded bricks. In
general, as the water absorption characteristics of It is interesting to note that the aggregate from
recycled aggregates are higher, it is advisable to masonry with wire-cut bricks had percentage
pre-soak the aggregates before using the same for voids almost similar to that of recycled concrete
concrete making. aggregate, while this value is higher for aggregate

78 The Indian Concrete Journal | November 2018