Page 80 - ICJ Jan 2023

TECHNICAL PAPER COLLECTOR’S EDITION

(i) Even when the recycled concrete is of (iii) When the recycled concrete of richer mix
same mix as that of parent concrete (example, 1:2:4) is made with aggregate
(example 1:1½:3), the strength of recycled taken from leaner parent concrete mix
aggregate concrete is relatively lower. In (e.g. 1:4:7), the bond is between recycled
the case of parent concrete the bond is aggregate coated with leaner mortar
between the fresh granite aggregate and (1:4) and the richer mortar of the recycled
mortar, whereas in the case of recycled concrete (1:2).
concrete the bond is between mortar
adhering to the aggregate and the mortar The above bond characteristics between recycled
of the recycled concrete (different age
though of same mix, that is, 1:1½). aggregates and mortar of recycled concrete
contribute to the relatively lower strength of
(ii) When the recycled concrete of leaner recycled aggregate concrete. These difference
mix (e.g. 1:4:7) is made with aggregate in bond characteristics require further in-depth
taken from richer parent concrete mix study.
(e.g., 1:2:4), the bond is between recycled
aggregate coated with richer mortar (1:2)
and the leaner mortar of the recycled The results presented in this paper pertain only
concrete (1:4). to one workability (that is, a low-workability
with a compacting factor of around 0.85) chosen
specifically to study the relative behaviour of
Table 4: Strength or original and recycled
aggregate concrete. different types of recycled aggregates with various
mix proportions, and hence it should be noted
Original mix Recycled mix Compressive
proportion* proportion strength, that the variations in water content will affect the
2
N/mm at 28 days strength of recycled aggregate concrete.
1:1½:3 original mix 49.80
1:l½:3 40.00
1:2:4 36.35 CONCLUSIONS
1:3:5 32.20
1:4:7 25.70 1. Recycled aggregates possess relatively lower
1:2:4 original mix 41.50 bulk density and higher water absorption as
1:l½:3 32.16
1:2:4 25.00 compared to those of fresh granite aggregates.
1:3:5 22.70 This is mainly due to the porous mortar
1:4:7 18.60
1:3:5 original mix 32.70 adhering to the recycled concrete aggregate
1:l½:3 24.20 and the relatively higher porosity of bricks.
1:2:4 20.90
1:3:5 15.40 2. Though the impact value of recycled concrete
1:4:7 13.10 aggregate and both impact and crushing
1:4:7 original mix 22.00 values of two types of recycled brick masonry
1:l½:3 15.80
1:2:4 10.60 aggregates are exceeding the BIS specified
1:3:5 9.40 limits, it has been shown, through the range of
1:4:7 7.30
compressive strengths obtained, that recycled
*Original mix indicates the concrete made using fresh concrete of different mixes made with recycled
granite aggregate (from which recycled aggregate has aggregates obtained from i) demolished brick
been made) masonry can be used for manufacture of load
bearing masonry units and PCC works, and ii)
#
Recycled mix indicates the mix of the new concrete
using recycled aggregate from original mix. demolished concrete aggregates can be used
for both PCC and RC construction.

The Indian Concrete Journal | November 2018 81