Between a rock and a hard place : options for reducing the carbon - - PowerPoint PPT Presentation

Between a rock and a hard place: options for reducing the carbon emissions associated with the use of cement and concrete

• Prof. Phil Purnell, University of Leeds

@PhilPurnell

Global figures (2010 estimate)

• (a) 40 GT of products

(b) 37 GT of CO2e

Material Per year A = % of a CO2e / yr B = % of b Reinforced Concrete 22 GT 56% 3.4 GT 9.1% Steel* 0.95 GT 2.4% 3.0 GT 8.1% Timber 2.2 GT 5.6% 5.1 GT** 14%**

(a) Resource consumption minus: major wastes (agricultural waste, mine tailings); grazed crops; fossil fuels – Krausmann et al Ecol Econ 68 (2009) 2696. (b) Estimate derived from various sources. *Virgin steel not including rebar. **IPCC estimate of emissions owing to forestry operations & thus upper

• bound. Full details of calculations based on 2005 figures in Purnell Adv Cem Res 25 (2013) 362 &

update estimated by scaling using growth data from Krausmann et al PNAS 114 (2017) 1880.

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0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 50 100 150 ECf (beam) / kgCO2 kN-1 m-2 Moment capacity / kN m

5m beam

Steel Timber HS Concrete PFA Concrete

0.1 0.2 0.3 0.4 0.5 0.6 300 900 1500 2100 2700 ECf (beam) / kgCO2 kN-1 m-2 Moment capacity / kN m

Steel Timber HS Concrete PFA Concrete

12m beam

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10% of CO2 emissions >3,000,000,000,000 kg/year

40% energy: 60% CaCO3  CaO + CO2

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Options

• Use non-carbonate feedstocks
• Use less concrete for the same function
• Use wastes to replace cement
• Improve processing energy efficiency
• Use existing concrete better
• Keep what we have already made in service

longer: longevity*, maintenance and reuse

– *A (brief) rant: “what have the Romans ever done for us?”

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Non-carbonate feedstock

Calcium minerals:

• Sense of scale:

Limestone use for cement 5000 Mt p.a.

• Gypsum:

263 Mt (5%)

• Fluorite:

6 Mt (0.1%) Magnesium minerals:

• Magnesite, dolomite:

>10GT reserves but carbonates

• Talc: 8 Mt (0.2%)
• Carnalite, Brucite: <1 Mt (<0.1%)
• USGS: Resources from which Mg

compounds can be recovered range from large to virtually unlimited [inc] seawater – but the process requires Ca(OH)2 derived from limestone!

Source: USGS and BGS. Production figures.

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Less concrete

Sources for images used as basis for illustrations: https://fet.uwe.ac.uk/conweb/commercial/armley2.jpg; https://www.gracesguide.co.uk/File:JD_Manchester_Bridges29. jpg; http://www.archiexpo.com/prod/alfanar/product-89130- 1455923.html

~1800 ~1870

Ratio of skilled labour to material prices (tonnes/year):

1830s: 8 2010s: 150

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• 150
• 100
• 50

2 4 6 8 10 Bending moment / kNm Length, m

• 0.5
• 0.4
• 0.3
• 0.2
• 0.1

Beam depth D / m D fixed D optimised

27% less concrete

Using wastes

• PFA

– 0.7 Gt pa (17%) – Coal use being phased

• ut: less ash

– Partial co-firing with biomass and/or refuse- derived fuels (50% at Drax): low quality ash (chlorides) – Importing PFA: higher ash prices

• GGBS

– 0.4 Gt pa (9%) – Move away from basic

• xygen furnaces to

electric arc furnaces/direct reduction of iron: less slag, low quality slag (low Si) – Importing slag: higher slag prices

Khatib (ed), Sustainability of Construction Materials 2016; Rashad et al Int J Sust Built Env 6 (2017) 91; http://www.globalslag.com/news/itemlist/tag/GGBS

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Improving process energy

• Average: ≈5 GJ/t
• Theory: ≈2 GJ/t
• Best practice: ≈3 GJ/t
• Much closer than

aluminium, steel

• Limited scope

– Waste heat recovery for urban home heating? – Using wastes/biomass for fuel?

See Allwood, Sustainable Materials: with both eyes open - http://www.withbotheyesopen.com/

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Better existing concrete

0.001 0.002 0.003 0.004 0.005 0.006 0.007 50 100 150 eCO2 per MPa Target mean cube strength / MPa

Reducing slump and using SPs can have as large an effect as using PFA.

Purnell et al - Adv Cem Res 25 (2013) 362; Cem Concr Res 42 (2012) 874

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0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 20 40 60 80 100 ECf (beam) / kgCO2 kN-1 m-2 EC2 concrete grade (cylinder) / MPa

M0-low M0-high M1-low M1-high M2-low M2-high l = 12m, h = 1.0m, b = 0.4m

Gravel, high slump Crushed, low slump Crushed, low slump + PFA

Longevity

Sources of images used as basis for illustrations: https://www.theguardian.com/science/2017/jul/04/why-roman-concrete-still-stands-strong-while-modern-version- decays; https://www.nature.com/news/seawater-is-the-secret-to-long-lasting-roman-concrete-1.22231;

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Longevity

• Survival bias: the logical error
• f concentrating on things that

made it past some selection process and overlooking those that did not.

https://en.wikipedia.org/wiki/Survivorship_bias; https://pdfs.semanticscholar.org/5dcc/ab070b8f9c5d03e8a0d3a9e92327dbd31c44.pdf

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• A. Wald,

1943

• B. Fletcher, A History of Architecture

(17th Ed)

• Timespan: 300+ years

–

• T. Fortuna Virilis 40BC – Therm.

Diocletia 302 AD.

• Alternate layers of rubble and

mortars compressed [p168]

• The important parts of the work

were done by skilled craftsmen… the purely mechanical tasks were performed by local slaves [p175]

• Labour to price ratio = 0

Longevity

• A product of Roman labour

economics and statistics applied to prestige buildings made from a different material, not application of arcane knowledge.

2 4 6 8 10 12 14 Lamprecht Ferreti Giavarini Jackson* (EC2 Min) MPa Investigator reported in Brune, 2010

Characteristic strength of Roman concretes

• P. Brune et al. pp38-45 in Fracture Mechanics of Concrete and Concrete Structures - Recent Advances in Fracture

Mechanics of Concrete - B. H. Oh, et al.(eds) ISBN 978-89-5708-180-8 *calculated from point tensile test results

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Longevity

1970 1980 1990 2000 Google Ngram – “concrete cancer”

42 23 11 9 5 1 53 Steel Concrete Mixed Timber Masonry Iron Unknown 9 5 6 1 1 1 Strike or overload Natural disaster Under construction Deterioration Fire Unknown Data: https://en.wikipedia.org/wiki/List_of_bridge_failures

Bridge failures since 1950

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Steel: 12% Mixed: 9% Timber: 22% Unknown: 8% 4%

Maintenance

Source: https://www.brookings.edu/blog/up-front/2017/01/31/the-case-for-spending-more-on-infrastructure-maintenance/;

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• “Prevention is cheaper than cure. Waiting for the

bridge to collapse is much more expensive than buttressing before it collapses. Deferred maintenance is a debt burden on the next generation.” L. Summers (Harvard)

• “You get a lot of new press for a new project. You

don’t get a lot of press for maintaining the HVAC system in the school.” E Glaeser (Harvard)

• The Tyranny of the ribbon

Maintenance

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99% of roads 1% of roads

2.5 0.75 0.3

Spend £Bn/year (2015/6-2020/1)

New schemes (127) Resurfacing programme Normal maintenance

Sources (including those of images used as basis for illustrations): Highways England Investment Plan 2015/16; http://www.citylab.com/cityfixer/2015/02/americas-infrastructure-crisis-is-really-a-maintenance-crisis/385452/; http://www.constructors.com.au/wp- content/uploads/2015/09/Major-Infrastructure-Projects-Costs-and-Productivity-Issues-7-March-2014.pdf;

0.26% of asset valuation

Reuse

• Recovery of function

and components not resource and material

Iacovidou & Purnell STOTEN 557-8 (2016) 791

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200 400 600 800 1000 1200 1400 1600 1800 2000 New Build Refurb

Lifetime CO2 / kg m-2

Operational Embodied

Power A, Energy Policy Volume 36, Issue 12, December 2008, Pages 4487-4501

Reuse

• Cast-in-situ

concrete has no joints between members.

• Section

capacity, component length and connection details usually bespoke.

Iacovidou & Purnell STOTEN 557-8 (2016) 791

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• Reclamation of components from existing

structures Deconstruction

• Reuse of the basic structure and/or fabric of

the building Adaptive reuse

• Whole life-cycle consideration at planning

stage Design for deconstruction

• Reuse of components mined from existing

structures in new ones Design for reuse

• Design and manufacture of construction

products off-site Design for manufacture & assembly

Iacovidou, Purnell, Lim J Env Mgt (2017) in press; https://upload.wikimedia.org/wikipedia/commons/thumb/b/ba/RFID_Chip_007.JPG/640px-RFID_Chip_007.JPG

Information: identify value Market: distribute value Business models: exploit value and effect change

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Conclusions

Reducing CO2 Upper bound Optimistic Real? (“expert” est.) Potential +/- Non-carbonate Ca sources 6% 2% ↑ Structural (shape) optimisation 13% 5% ↑ Use of pozzolanic wastes 23% 10% ↓ Energy efficiency (cement manufacture) 24% 16% ~ Strength (material) optimisation 36% 18% ↑ Lifespan extension/reuse 90% 50% ↑ Total (allowing for interactions) 97% 71%

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• There is no silver bullet – we must advance on all fronts – but design

interventions are more powerful than materials interventions

• Think about how technical factors interact with economic and cultural

factors