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from masonry with table-moulded bricks. Such a masonry) were determined at the age of 7, 14 and
behaviour may be attributed to the fact that table- 28-days and are reported in Tables 3(a) to 3 (d).
moulded brick aggregate have a tendency to crush
and re-adjust during packing. Table 2 : Physical and mechanical properties
of coarse aggregates from demolition waste

Elongation and flakiness Indices Property of Type of aggregate used
aggregate
Fresh Demolished Demolished Demolished
The elongation and flakiness indices of recycled granite concrete masonry masonry
aggregate
concrete aggregate were closer to that of fresh aggregate aggregate aggregate (with table
(with wire-
granite aggregate. Recycled brick masonry cut brick) mounted
brick)
aggregates are observed to have relatively higher
Specific 2.62 2.38 1.78 1.64
elongation and flakiness indices than those of gravity
crushed concrete aggregate. Water percent 3.5 8.3 9.67 14.2
absorption
Bulk roded 1430 1584 1193 1000
Crushing and Impact values density,
kg/m 3 loose 1310 1194 980 910
The recycled concrete aggregate is relatively Voids rodded, 45.4 33.44 33.0 39.0
weaker than the fresh granite aggregate against loose, 50.0 49.83 46.0 44.5
12
mechanical actions. As per 15:2386 (Part_IV) , the percent
Flakiness percent 33.0 30.0 43.0 46.0
crushing and impact values for concrete wearing index
surfaces should not exceed 30 percent and for other Elongation percent 26.0 28.0 40.0 46.0
index
concrete works these values should not exceed 45
Crushing percent 29.5 38.0 72.0 85.0
percent and 50 percent, respectively. While the value
crushing value of recycled concrete aggregate Impact percent 16.0 58.0 64.0 66.0
value
satisfies crushing value specification for concreting
works other than wearing surfaces, the impact
Table 3(a) Compressive strength of concrete
value is higher. The crushing and impact values with fresh granite aggregate
of recycled brick masonry aggregates are much Mix w/c Compacting Mean compressive strength,
2
higher than those of recycled concrete aggregate proportions ratio factor N/mm at
7-day 14-day 28-day
and also do not satisfy the specifications. Such a
1:1½:3 0.50 0.87 33.14 43.13 49.80
failure to meet the specifications need not be a
1:2:4 0.52 0.83 22.80 32.20 41.50
constraint for using these aggregates in making 1:3:5 0.60 0.83 15.00 25.40 32.70
low and medium strength concrete, which has 1:4:7 1.00 0.85 14.40 18.20 22.00
been shown later through compressive strength
Table 3(b) Compressive strength of concrete
results of different mixes of recycled aggregate
with recycled concrete aggregate (from
concrete. concrete of unknown strength)
Mix w/c Compacting Mean compressive
2
Compressive strength proportions ratio factor strength, N/mm at
7-day 14-day 28-day
The mean compressive strengths (of 6 cubes each) 1:1½:3 0.50 0.87 20.13 33.74 40.00
of 150 mm concrete cubes cast using different 1:2:4 0.60 0.84 17.95 26.40 35.30
aggregates (viz., fresh granite, recycled concrete, 1:3:5 0.80 0.85 12.80 18.20 22.70
1:4:7 1.10 0.85 8.46 10.20 12.76
wire-cut brick masonry and table moulded brick

The Indian Concrete Journal | November 2018 79