Page 11 - Open-Access-Sep-2019

6.00
2%
3%
3%
5.00
5.00
5.00
5.00
5.00
5.00
Tensile strength (Mpa)
4.00
4.00
4.00
4.00
13%
4.00
4.00
3.00
3.00
Concrete
2.00
2.00
3.00
3.00
Bricks
Bricks
3.00
3.00
28d
28d
28d
28d
1.00
1.00
Asphalt
Asphalt
28d
28d
56d
56d
56d
56d
2.00
2.00
0.00
0.00
2.00
2.00
Tiles
Tiles
56d
56d
91d
91d
91d
91d
Others
Others
1.00
1.00
79%
79%
1.00
1.00
0.00
0.00
0.00
0.00
50RCA2NS 50RCA10UFFA
50RCA2NS 50RCA10UFFA
Control
50RCA50FA50RCA50Slag
Control
50RCA
50RCA50FA50RCA50Slag
Mix types 7d Tensile strength (Mpa) 6.00 Mix types 7d Tensile strength (Mpa) 6.00 13% 3% 3% 2% 50RCA Mix types Concrete 7d Tensile strength (Mpa) 6.00 Control 50RCA Mix types 7d Tensile strength (Mpa) 6.00 Mix types 7d Tensile strength (Mpa) 6.00 Control 50RCA Mix types 7d
TECHNICAL PAPER
70 2% 6.00 seen in the table that the CO 2 emission of RCA is slightly higher
70
70
Compressive strength (Mpa)
450
70
6.00
60 70 70 3% 3% 60 than the NCA and can be attributed to the additional energy 6.00 450
Tensile strength (Mpa)
60
60
60
60
400
400
Compressive strength (Mpa) 40 7d Compressive strength (Mpa) 40 7d Compressive strength (Mpa) 40 13% Concrete 7d Tensile strength (Mpa) CO2 emission (Kg CO2e) 5.00 7d 6 shows the total CO 2 emission of control concrete and the 7d 7d Tensile strength (Mpa) Compressive strength (Mpa) 4.00 7d CO2 emission (Kg CO2e) 300
Compressive strength (Mpa)
5.00
required for crushing, grinding, separation and cleaning. Figure
5.00
50
50
50
50
50
50
350
350
4.00
4.00
40
40
300
3.00
40
recycled aggregates concretes containing SCMs and nano silica.
7d
30
30
30
30
2.00
250
7d
3.00
250
Due to unavailability of emission data for UFFA the concrete
3.00
20
Bricks
28d
20
28d
28d
28d
20
20
28d
30
30
28d
1.00
28d
Asphalt
200
200
28d
10
56d
containing UFFA is not considered in the analysis. However, its
56d
28d
10
10
56d
10
56d
56d
56d
2.00
0.00
2.00
Tiles
91d
91d
20
20
56d
56d
150
56d
150
0
0
0
0
91d
91d
Others
1.00
79%
to energy required for additional grinding. It can be seen in
100
10
10
Figure 6a that the addition of 50% RCA as partial replacement
50
50 91d CO 2 emission value will be much higher than the fly ash due 91d 1.00 100
0.00
0 0.00 0 of NCA did not increase the CO 2 emission value above the Control 50RCA 50RCA2NS 50RCA10UFFA
50RCA
50RCA50FA50RCA50Slag
Control
Control 50RCA 50RCA50FA50RCA50Slag Mix types 0 Control 50RCA 50RCA50FA50RCA50Slag Mix types 0
Mix types
Mix types Control 50 RCA 50 RCA+50 Slag 50 RCA+50 Fly ash control concrete containing 100% NCA. However, significant Mix types Control 50 RCA 50 RCA+50 Slag 50 RCA+50 Fly ash
Mix types
Mix types
Mix types Mix types Types of mixes
Types of mixes
reduction of about 38% and 48% CO 2 emission is observed
(a) when 50% slag and 50% fly ash are used to partially replace the
OPC. The effects of addition of various SF contents in the above
500 two fly ash and slag concretes are shown in Figure 6b, where it
500
450 450 70 70 450 can be seen that slight reduction in CO 2 emission of recycled 450
450
CO2 emission (Kg CO2e) 350 CO2 emission (Kg CO2e) 350 Compressive strength (Mpa) 50 7d Compressive strength (Mpa) CO2 emission (Kg CO2e) 50 350 7d addition of SF. However, the scenario is different in the case of CO2 emission (Kg CO2e) 400
70
Compressive strength (Mpa)
400
400
60
aggregate concrete containing 50% slag and 50% fly ash due to
400
400
60
CO2 emission (Kg CO2e)
60
350
50
300
300
350
recycled aggregate concrete containing 2% NS shown in Figure
40
40
250
250
300
300
300
40
6c, where about 15% increase in CO 2 emission is observed
200
30
200
30
250
250
7d
250
150
20
200
28d
100
10
100
56d
the significantly higher CO 2 emission of NS listed in Table 7 due
56d
10
150
150
20
91d
50 200 30 28d 20 0 150 28d compared to concrete containing 50% RCA. This can be due to 200
50
56d
150
0
to its energy intensive manufacturing technique. However, if the
91d
100
0 100 0 nano silica is used together with higher volume fraction of slag 100
50 50 50 50 50 50 50 50 50 50 10 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 RCA RCA+50 RCA+50 RCA+50 RCA+50 RCA+50 RCA+50 RCA+50 RCA+50 or fly ash this negative impact in carbon footprint in concrete 50
Slag Slag+5 SF Slag+10 Slag+15 Fly ash Fly ash+5 Fly ash Fly ash 0 0 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 SF SF SF +10 SF +15 SF can be avoided as very small quantity of nano silica is actually 0
Control 50 RCA 50 RCA+2 NS Control 50RCA 50RCA50FA50RCA50Slag Mix types Control 50 RCA 50 RCA+2 NS
Types of mixes Types of mixes Mix types Control 50 RCA 50 RCA+50 Slag 50 RCA+50 Fly ash
Types of mixes
Types of mixes required to improve the properties of concrete.
Mix types Types of mixes
(b)
This analysis shows that the use of recycled aggregates in
concrete alone is not environmentally beneficial as far as CO 2
500 emission is concern, but this will help divert this material from
450 450 landfilling which might cause other environmental issues.
CO2 emission (Kg CO2e) 350 CO2 emission (Kg CO2e) 350 partial replacement of natural aggregates and OPC in concrete
400
However, if recycled aggregates are used together with SCMs as
400
300
the overall CO 2 emission of concrete can be significantly
250
300
reduced while maintaining comparable properties and in some
200
250
instances better to the control concrete.
150
100
150
50 200 8. coNclUsIoNs
0 100
50 50 50 50 50 50 50 50 50 50 This study presents the results on effects of SCMs and nano- and
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 ultrafine materials on properties and CO 2 emission of recycled
SF SF SF +10 SF +15 SF Control 50 RCA 50 RCA+2 NS aggregates concretes. The following conclusions can be made
Types of mixes
Types of mixes
based on this study:
(c)
1. The addition of high volume slag and fly ash at 50%
Figure 6: CO2 emission analysis of concretes. reduced the compressive strength of recycled aggregate
table 6: co 2 emission values of various ingredients of concrete
oPc fly Ash slAg ns UffA sf ncA rcA sAnD
Emission (kg CO 2e) 0.971 0.0189 0.214 8.3 N/A 0.00315 0.00477 0.00563 0.00310
62 The IndIan ConCreTe Journal | SepTember 2019