Page 10 - Open-Access-Sep-2019

TECHNICAL PAPER

strength of control recycled aggregate concrete containing 50%
6.00
3% 2% RCA and 100% OPC. However, the scenario is quite different in
3% 6.00 6.00
Tensile strength (Mpa)
5.00 the case of combined use of slag and SF in recycled aggregate 5.00
5.00
4.00
13% 4.00 concretes. It can be seen in the same figure (Figure 5b) that 4.00
the addition of SF improved the tensile strength of recycled
3.00
Concrete 7d aggregate concrete containing 50% slag at all ages except in 7d
2.00
Bricks Tensile strength (Mpa) 3.00 28d Tensile strength (Mpa) 3.00 7d
1.00
Asphalt few cases with the highest improvement of about 4-19% at SF 28d 28d
0.00
Tiles 2.00 56d content of 10%. The trend is quite consistent to that observed 56d 2.00 56d
Others 91d in compressive strength, however, at later ages e.g. 28-91 days 91d
79% 1.00 1.00
the tensile strength of recycled aggregate concrete containing
0.00 50% slag and 10% SF exceeded the tensile strength of control 0.00 Control 50RCA 50RCA2NS 50RCA10UFFA
Control 50RCA 50RCA50FA50RCA50Slag recycled aggregate concrete, which happened only at 91 days
Mix types
Mix types in the case of compressive strength. This indicates that the Mix types
environmental friendliness of recycled aggregate concrete can
(a)
be significantly improved by partially replacing 60% OPC by slag
6.00
2% and SF.
3%
3% 70 6.00 6.00
5.00 70 The effects of addition of small amount of nano silica (2 wt%) 450
70
5.00
Compressive strength (Mpa)
Tensile strength (Mpa)
60
60
13% 4.00 Tensile strength (Mpa) 4.00 and 10% UFFA as partial replacement of OPC in recycled 400
60
4.00
3.00
50
50
Concrete 50 7d 2.00 7d aggregate concrete are shown in Figure 5c, where it can be 350
Bricks Tensile strength (Mpa) 3.00 28d Compressive strength (Mpa) 5.00 seen significant improvement in tensile strength of recycled 7d
40
3.00
40
Asphalt 40 7d 1.00 28d aggregate concrete by about 16-35% due to addition of 2% 28d 300
30
30
7d
56d
2.00
Tiles Compressive strength (Mpa) 2.00 28d 0.00 56d NS with highest improvement in tensile strength observed at 7d CO2 emission (Kg CO2e) 250
20
28d
20
56d
Others 30 91d 91d
1.00
10
79% 1.00 56d 10 0 56d 7 days by about 35%. On the other hand improvement is also 28d 200
91d
20
56d
150
0
observed in tensile strength of recycled aggregate concrete
91d
0.00
0.00
10
50RCA2NS 50RCA10UFFA
50RCA
Control
Control 50RCA 50RCA50FA50RCA50Slag due to addition of 10% UFFA, however, by moderate amount 100
Mix types Mix types 50
0 Mix types of about 10-17% with highest improvement at 7 days by about
Control 50RCA 50RCA50FA50RCA50Slag Mix types 17%. The trend is quite consistent to that observed in the 0 Control 50 RCA 50 RCA+50 Slag 50 RCA+50 Fly ash
(b)
Mix types
Mix types compression test. However, environmental friendliness of these Types of mixes
6.00
2% recycled aggregate concretes is not comparable to that where
3%
3% 6.00 6.00 60% OPC is replaced by slag and SF. More research need to be
5.00 5.00 5.00 done to evaluate whether the use of these nano- and ultrafine
70
450
70
500
13% 4.00 Tensile strength (Mpa) 70 4.00 4.00 size SCM can be used to improve the environmental friendliness
60
60 3.00
450
400
Concrete 7d 50 2.00 7d 60 450 of recycled aggregate concrete by further reducing the OPC
CO2 emission (Kg CO2e)
50
350
Bricks Tensile strength (Mpa) 3.00 28d 400 Tensile strength (Mpa) 50 400 7d beyond 60% and increasing the RCA content above 50% due to
350
Asphalt 40 Compressive strength (Mpa) 40 1.00 28d Compressive strength (Mpa) 40 28d 300
350
300
30
Tiles 2.00 7d 56d 30 0.00 56d 2.00 56d their faster pozzolanic reaction kinetics and the nano- and micro-
7d
250
91d
Others Compressive strength (Mpa) 28d CO2 emission (Kg CO2e) 20 250 91d 20 300 7d pore filling abilities due to their extremely small particle sizes.
28d
30
1.00
79% 1.00 56d 10 200 56d CO2 emission (Kg CO2e) 3.00 28d 7. cARboN FootPRINt ANAlysIs
200
10
250
20
91d
150
56d
0.00
150
0
0
0.00
50RCA2NS 50RCA10UFFA
100
50RCA50FA50RCA50Slag
Control
50RCA
10
150
50
Mix types 91d 100 Mix types 200 Control 50RCA Mix types The recent climate change policy provides a set target to every
50
0 0 100 (c) country to reduce the CO 2 emission into atmosphere. Concrete
0
Control 50RCA 50RCA50FA50RCA50Slag 50 50 50 50 50 50 50 50 50 50 industries around the world are in forefront in the reduction
Mix types
RCA RCA+50 RCA+50 RCA+50 RCA+50 RCA+50 RCA+50 RCA+50 RCA+50 Mix types Control 50 RCA 50 RCA+50 Slag 50 RCA+50 Fly ash
0
Mix types Slag Slag+5 SF Slag+10 Slag+15 Fly ash Fly ash+5 Fly ash Fly ash Figure 5: Indirect tensile strength development of concretes. of carbon footprint of concrete and cementitious construction
Types of mixes
SF SF SF +10 SF +15 SF Control 50 RCA 50 RCA+2 NS
Types of mixes Types of mixes materials to address this issue by partially replacing OPC
70 The effects of addition of different SF contents in recycled by various SCMs. While the main contributor for the carbon
450
60 70 70 aggregate concretes containing 50% fly ash and 50% slag are footprint of concrete is the OPC, the use of C&D wastes as
60
500
60
400
recycled aggregates in concrete will also impact its carbon
shown in Figure 5b. It can be seen in the figure that the tensile
Compressive strength (Mpa) 40 7d Compressive strength (Mpa) CO2 emission (Kg CO2e) 50 7d Compressive strength (Mpa) CO2 emission (Kg CO2e) 40 7d ash is increased at all ages due to addition of SF with highest analyses the CO 2 emission of recycled aggregates concretes and
450
CO2 emission (Kg CO2e)
50
50
450
strength of recycled aggregates concrete containing 50% fly
350
footprint and divert the C&D wastes from landfilling. This paper
400
40
400
300
350
30
30
the impact of use of SCMs and nano silica on carbon footprint
350
improvement observed in the case of SF content of 5% where
300
250
28d
20
20
28d
30
300
of concrete. The CO 2 emission values for various materials
250
about 10-25% improvement is observed. Nevertheless, this
200
28d
56d
10
10
56d
200
of concrete in this study are obtained from life cycle analysis
250
91d
20
improvement does not help the recycled aggregates concrete
0
150
56d
0
91d
150
100
10
100
150
50
50 200 containing 50% fly ash and 5% SF to achieve the same tensile software SimaPro and the values are listed in Table 6. It can be
0 0 100
Control 50RCA 50RCA50FA50RCA50Slag 50 50 50 50 50 50 50 50 50 Mix types 0 Control 50 RCA 50 RCA+50 Slag 50 RCA+50 Fly ash The IndIan ConCreTe Journal | SepTember 2019 61
Mix types
Mix types RCA RCA+50 RCA+50 RCA+50 RCA+50 RCA+50 RCA+50 RCA+50 RCA+50 50 Types of mixes
Slag Slag+5 SF Slag+10 Slag+15 Fly ash Fly ash+5 Fly ash Fly ash 0
SF SF SF +10 SF +15 SF Control 50 RCA 50 RCA+2 NS
Types of mixes
Types of mixes
500
450 450
CO2 emission (Kg CO2e) 350 CO2 emission (Kg CO2e) 350
400
400
300
250
300
200
250
150
100
150
50 200
0 100
50 50 50 50 50 50 50 50 50 50
RCA RCA+50 RCA+50 RCA+50 RCA+50 RCA+50 RCA+50 RCA+50 RCA+50
Slag Slag+5 SF Slag+10 Slag+15 Fly ash Fly ash+5 Fly ash Fly ash 0
SF SF SF +10 SF +15 SF
Control 50 RCA 50 RCA+2 NS
Types of mixes
Types of mixes