1 Introduction
1.1 Sustainable concrete production
1.2 Concrete mix design
1.3 Considerations and limiting factors of concrete mix
1.4 Recent LCA approach and methods
2 Methods
2.1 Background of the underlying approach
2.2 The LCA approach of three concrete mixed designs
-
Compile and quantify the inputs and outputs throughout the life cycle of each concrete mix design.
-
Feed data into the software for each mix design. This should include all materials and processes that have been outlined in the system boundary.
-
Calculate tabulated numerical values showing inputs and outputs with respect to the environment for various processes. Inventory tables are extensive and can contain thousands of items.
2.3 Preparing test cases
2.4 System boundary of the concrete production
2.5 Assumptions
2.6 Concrete mix designs
Material | Mix 1: CEM I (kg/m3) | Mix 2: CEM II/B-V (kg/m3) | Mix 3: CEM III/B (kg/m3) |
---|---|---|---|
PC
| 380 | 247 | 114 |
GGBS
| 0 | 0 | 266 |
FA
| 0 | 133 | 0 |
10/20-mm limestone Aggregate
| 615 | 606 | 610 |
4/10-mm limestone
Aggregate
| 413 | 407 | 410 |
0–4-mm Fine aggregate
| 806 | 794 | 800 |
Plasticiser
| 2 | 2 | 2 |
Water
| 190 | 190 | 190 |
TOTAL:
|
2406
|
2379
|
2392
|
3 Life cycle assessment results
Impact category | Unit | CEM I concrete | CEM II/B-V concrete | CEM III/B concrete |
---|---|---|---|---|
Global warming (GWP100)
|
kg CO
2
eq.
| 339 | 227 | 127 |
Ozone layer depletion (ODP)
|
kg CFC-11 eq.
| 1.04E − 05 | 8.10E − 06 | 6.76E − 06 |
Photochemical oxidation
|
kg C
2
H
4
eq.
| 0.1113 | 0.0893 | 0.0774 |
Acidification
|
kg SO
2
eq.
| 0.5437 | 0.4134 | 0.3191 |
Eutrophication
|
kg PO
4
- eq.
| 0.1377 | 0.1064 | 0.0846 |
Non renewable, fossil
|
MJ eq.
| 1761 | 1328 | 1003 |
Impact category | Unit | CEM I concrete | CEM II/B-V concrete | CEM III/B concrete |
---|---|---|---|---|
NOx
|
g
| 645 | 510 | 430 |
SOx
|
g SO2 eq.
| 198 | 141 | 91 |
NMVOC
|
g
| 98 | 80 | 72 |
NH3
|
g
| 16 | 12 | 9 |
Dust PM10
|
g
| 116 | 101 | 91 |
CO2
|
g CO2 eq.
| 334,148 | 227,600 | 127,635 |
Ozone layer
|
g CFC-11
| 0.0115 | 0.0090 | 0.0075 |
Pb (air)
|
g
| 0.0609 | 0.0437 | 0.0288 |
Cd (air)
|
g
| 0.0054 | 0.0038 | 0.0024 |
Zn (air)
|
g
| 0.0982 | 0.0779 | 0.0658 |
Hg (air)
|
g
| 0.0131 | 0.0089 | 0.0050 |
COD
|
g
| 276 | 243 | 250 |
P
|
g
| 0.0119 | 0.0108 | 0.0112 |
N
|
g
| 0.4868 | 0.3788 | 0.2978 |
Cr (water)
|
g
| 0.2913 | 0.2448 | 0.2308 |
Zn (water)
|
g
| 3.66 | 2.92 | 2.52 |
Cu (water)
|
g
| 0.5801 | 0.4416 | 0.3261 |
Cd (water)
|
g
| 0.0429 | 0.0320 | 0.0229 |
Hg (water)
|
g
| 0.0039 | 0.0029 | 0.0020 |
Pb (water)
|
g
| 0.1029 | 0.0766 | 0.0543 |
Ni (water)
|
g
| 1.38 | 1.03 | 0.73 |
AOX (water)
|
g Cl-
| 0.0008 | 0.0007 | 0.0007 |
Nitrate (soil)
|
g
| 0.4584 | 0.3620 | 0.3003 |
Metals (soil)
|
g Cd eq.
| 0.0007 | 0.0007 | 0.0008 |
Pesticide soil
|
g act.subst.
| 0.0033 | 0.0031 | 0.0033 |
Waste
|
g
| 21,724 | 20,933 | 20,859 |
Waste (special)
|
g
| 0.9267 | 0.7798 | 0.7276 |
LMRAD
|
cm3
| 1.11 | 0.78 | 0.47 |
HRAD
|
cm3
| 0.2435 | 0.1711 | 0.1038 |
Energy
|
MJ LHV
| 1826 | 1372 | 1028 |
Impact category | Unit | CEM I concrete | CEM II/B-V concrete | CEM III/B concrete |
---|---|---|---|---|
Total
|
kPt
| 173 | 130 | 94 |
NOx
|
kPt
| 43 | 34 | 29 |
SOx
|
kPt
| 10.49 | 7.48 | 4.84 |
NMVOC
|
kPt
| 3.15 | 2.57 | 2.31 |
NH3
|
kPt
| 0.9999 | 0.7665 | 0.5455 |
Dust PM10
|
kPt
| 13 | 11 | 10 |
CO2
|
kPt
| 67 | 46 | 26 |
Ozone layer
|
kPt
| 0.0230 | 0.0181 | 0.0151 |
Pb (air)
|
kPt
| 0.1765 | 0.1268 | 0.0835 |
Cd (air)
|
kPt
| 0.6469 | 0.4599 | 0.2928 |
Zn (air)
|
kPt
| 0.0511 | 0.0405 | 0.0342 |
Hg (air)
|
kPt
| 1.57 | 1.07 | 0.60 |
COD
|
kPt
| 1.63 | 1.43 | 1.48 |
P
|
kPt
| 0.0237 | 0.0215 | 0.0224 |
N
|
kPt
| 0.0336 | 0.0261 | 0.0205 |
Cr (water)
|
kPt
| 0.1923 | 0.1615 | 0.1523 |
Zn (water)
|
kPt
| 0.7695 | 0.6141 | 0.5295 |
Cu (water)
|
kPt
| 0.6961 | 0.5300 | 0.3913 |
Cd (water)
|
kPt
| 0.4720 | 0.3517 | 0.2518 |
Hg (water)
|
kPt
| 0.9461 | 0.6938 | 0.4785 |
Pb (water)
|
kPt
| 0.0154 | 0.0115 | 0.0081 |
Ni (water)
|
kPt
| 0.2627 | 0.1951 | 0.1386 |
AOX (water)
|
kPt
| 0.0003 | 0.0002 | 0.0002 |
Nitrate (soil)
|
kPt
| 0.0124 | 0.0098 | 0.0081 |
Metals (soil)
|
kPt
| 0.0823 | 0.0810 | 0.1007 |
Pesticide soil
|
kPt
| 0.0027 | 0.0025 | 0.0027 |
Waste
|
kPt
| 11 | 10 | 10 |
Waste (special)
|
kPt
| 0.0222 | 0.0187 | 0.0175 |
LMRAD
|
kPt
| 3.68 | 2.58 | 1.55 |
HRAD
|
kPt
| 11.20 | 7.87 | 4.78 |
Energy
|
kPt
| 1.83 | 1.37 | 1.03 |
4 Discussion
4.1 Mix 1 (CEM I concrete) option
-
CEM I concrete can be recycled for use in aggregate applications. This has an official designation as recycled Portland cement concrete (RPCC).
-
PC is more readily available than FA/GGBS. PC is manufactured specifically for the purpose of concrete production, so it is made to satisfy demand.
-
PC has shorter transportation distances to the concrete plant than SCMs, which implicates reduced environmental impacts and CO2 emissions for transportation of materials in this mix design.
-
This mix presented the highest CO2 emissions; kilogram CO2 equivalent values are greater than both Mix 2 and Mix 3 by both 107 and 207, respectively. Thus, Mix 1 is 32 % higher than Mix 2 and 62 % more than Mix 3.
-
This mix has the highest total single scores in both the Eco-indicator 99 and Ecopoints 97 methods with values of 13.9 and 173 kPt, respectively.
4.2 Mix 2 (CEM II/B-V concrete) option
-
Mix 2 does demonstrate considerable CO2 reductions when compared with Mix 1. According to this study, a 32 % decrease in kilogram CO2 equivalent would result from using a CEMII/B-V as opposed to a CEM I mix.
-
A single score totals from the Eco-indicator 99 and Ecopoints 97 methods, Mix 2 exhibited 3.1 Pt (− 23 %) and 43 kPt (−25 %) reductions when compared with Mix 1, respectively.
-
Transport distances for FA to the concrete plant are estimated to be 314 km on average in the UK. This is 123 km less than the value for GGBS.
-
CEMII/B-V mixes can only contain a maximum of 55 % FA addition, but in the UK, this figure rarely rises above a 30 % replacement level. This is not as high when compared with replacement levels of other concrete classifications.
-
Many coal power stations do not operate constantly, and some are even closing down completely. This affects the availability of FA.
4.3 Mix 3 (CEM III/B concrete) option
-
CEM III/B mixes can contain up to 80 % GGBS addition. This high PC replacement level offers a larger scope for sustainability than other concrete classifications.
-
The results from the LCA show that Mix 3 has the lowest CO2 emissions with a value of 127 kg CO2 eq. This is lower than the values of Mix 1 and Mix 2 by a massive 207 and 100 kg CO2 eq., 62 and 32 % respectively.
-
Single score totals from the LCA results are much lower for Mix 3 than for the other two mixes. The single scores from Eco-indicator 99 and Ecopoints 97 are only 8.52 Pt (40 and 27 % lower than Mix 1 and Mix 2) and 94.5 kPt (45 and 27 % lower than Mix 1 and Mix 2), respectively. The EPD 2008 method also indicates that Mix 3 has the smallest value across all of the impact categories.
-
GGBS used within the CEMIII/B mix tends to have the largest transport distance compared to other cementitious materials; this is due to a select amount of locations that still operate blast furnaces in the UK. Some iron slag is even imported from mainland Europe to maintain the supply.