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 CO 2 e Material Per year A = % of a CO 2 e / yr B = % of b Reinforced 22 GT 56% 3.4 GT 9.1% Concrete 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. 2

2 0.6 5m beam 12m beam Steel 1.8 0.5 1.6 Steel EC f (beam) / kgCO 2 kN -1 m -2 EC f (beam) / kgCO 2 kN -1 m -2 1.4 0.4 1.2 HS Concrete 1 0.3 PFA Concrete 0.8 HS Concrete 0.2 0.6 0.4 0.1 Timber 0.2 Timber PFA Concrete 0 0 0 50 100 150 300 900 1500 2100 2700 Moment capacity / kN m Moment capacity / kN m 3

10% of CO 2 emissions >3,000,000,000,000 kg/year 40% energy: 60% CaCO 3  CaO + CO 2 4

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? ” 5

Non-carbonate feedstock Calcium minerals: Magnesium minerals: • Sense of scale: • Magnesite, dolomite: Limestone use >10GT reserves but carbonates for cement • Talc: 8 Mt ( 0.2% ) 5000 Mt p.a. • Carnalite, Brucite: <1 Mt ( <0.1% ) • Gypsum: • USGS: Resources from which Mg 263 Mt ( 5% ) compounds can be recovered range • Fluorite: from large to virtually unlimited [inc] 6 Mt ( 0.1% ) seawater – but the process requires Ca(OH) 2 derived from limestone! Source: USGS and BGS. Production figures. 6

Less concrete ~1800 0 Bending moment 0 2 4 6 8 10 ~1870 -50 / kNm -100 Ratio of skilled labour to -150 material prices (tonnes/year): Length, m 1830s: 8 0 Beam depth -0.1 D fixed D optimised 2010s: 150 D / m -0.2 27% less concrete -0.3 Sources for images used as basis for illustrations: -0.4 https://fet.uwe.ac.uk/conweb/commercial/armley2.jpg; https://www.gracesguide.co.uk/File:JD_Manchester_Bridges29. -0.5 jpg; http://www.archiexpo.com/prod/alfanar/product-89130- 7 1455923.html

Using wastes • PFA • GGBS – 0.7 Gt pa (17%) – 0.4 Gt pa (9%) – Coal use being phased – Move away from basic out: less ash oxygen furnaces to electric arc – Partial co-firing with furnaces/direct biomass and/or refuse- reduction of iron: less derived fuels (50% at slag, low quality slag Drax): low quality ash (low Si) (chlorides) – Importing slag: higher – Importing PFA: higher slag prices ash prices 8 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

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

Better existing concrete 0.007 Gravel, high slump M0-low M0-high 0.2 Crushed, low slump M1-low M1-high 0.006 0.18 Crushed, low slump EC f (beam) / kgCO 2 kN -1 m -2 M2-low M2-high + PFA 0.16 0.005 eCO 2 per MPa 0.14 0.004 0.12 0.003 0.1 0.002 0.08 0.06 0.001 0.04 0 0.02 0 50 100 150 l = 12m, h = 1.0m, b = 0.4m Target mean cube strength / MPa 0 0 20 40 60 80 100 Reducing slump and using SPs can have as large an effect as EC2 concrete grade (cylinder) / MPa using PFA. 10 Purnell et al - Adv Cem Res 25 (2013) 362; Cem Concr Res 42 (2012) 874

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; 11

Longevity B. Fletcher, A History of Architecture (17 th Ed) • Timespan: 300+ years – T. Fortuna Virilis 40BC – Therm. A. Wald, Diocletia 302 AD. 1943 • Alternate layers of rubble and mortars compressed [p168] • The important parts of the work were done by skilled craftsmen… • Survival bias: the logical error the purely mechanical tasks were of concentrating on things that performed by local slaves [p175] made it past some selection • Labour to price ratio = 0 process and overlooking those that did not. https://en.wikipedia.org/wiki/Survivorship_bias; https://pdfs.semanticscholar.org/5dcc/ab070b8f9c5d03e8a0d3a9e92327dbd31c44.pdf 12

Longevity • A product of Roman labour economics and statistics applied to prestige buildings made from a different material, not application of arcane knowledge. Characteristic strength of Roman concretes 14 12 10 8 MPa 6 4 2 0 Lamprecht Ferreti Giavarini Jackson* (EC2 Min) Investigator reported in Brune, 2010 P. Brune et al. pp38-45 in Fracture Mechanics of Concrete and Concrete Structures - Recent Advances in Fracture 13 Mechanics of Concrete - B. H. Oh, et al.(eds) ISBN 978-89-5708-180-8 *calculated from point tensile test results

Longevity 1970 1980 1990 2000 Google Ngram – “concrete cancer” Steel: 12% Mixed: 9% Timber: 22% Unknown: 8% 4% Steel Strike or overload 1 1 1 Concrete 42 Natural disaster 53 Mixed 9 Under construction Timber 6 Deterioration Masonry Fire Iron 5 23 Unknown 1 5 Unknown 9 11 Data: https://en.wikipedia.org/wiki/List_of_bridge_failures Bridge failures since 1950 14

Maintenance • “ 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 Source: https://www.brookings.edu/blog/up-front/2017/01/31/the-case-for-spending-more-on-infrastructure-maintenance/; 15

Maintenance Spend £Bn/year (2015/6-2020/1) 0.26% of asset valuation 0.3 0.75 1% of roads 99% of roads 2.5 New schemes (127) Resurfacing programme Normal maintenance Sources (including those of images used as basis for illustrations): Highways England Investment Plan 2015/16; 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;

Reuse 2000 • Recovery of function 1800 Lifetime CO 2 / kg m -2 and components not 1600 1400 resource and material 1200 1000 800 600 400 200 0 New Build Refurb Operational Embodied Power A, Energy Policy Volume 36, Issue 12, December 2008, Pages 4487-4501 Iacovidou & Purnell STOTEN 557-8 (2016) 791 17

Reuse Deconstruction • Cast-in-situ • Reclamation of components from existing structures concrete has no joints Adaptive reuse • Reuse of the basic structure and/or fabric of between the building members. • Section Design for deconstruction • Whole life-cycle consideration at planning capacity, stage component Design for reuse length and • Reuse of components mined from existing connection structures in new ones details Design for manufacture & usually assembly • Design and manufacture of construction bespoke. products off-site Iacovidou & Purnell STOTEN 557-8 (2016) 791 18

Information : identify value Market : distribute value Business models : exploit value and effect change Iacovidou, Purnell, Lim J Env Mgt (2017) in press; 19 https://upload.wikimedia.org/wikipedia/commons/thumb/b/ba/RFID_Chip_007.JPG/640px-RFID_Chip_007.JPG

Conclusions Reducing CO 2 Upper Optimistic Real? Potential bound (“expert” est.) +/- 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% • 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 20