Published on February 11, 2008
Greening Concrete: Greening Concrete Why Green Concrete? Huge impact on sustainability Most widely used material on Earth 30% of all materials flows on the planet 70% of all materials flows in the built environment. > 2.1 billion tonnes per annum. >15 billion tonnes poured each year. Over 2 tonnes per person per annum The fine print which is there for people to read if they download the presentation from the web site Roadmap to Greening Concrete: Roadmap to Greening Concrete Background Emissions, contribution and production Options for Greening Concrete Scale down production. Untenable, especially to developing nations unless population growth also attenuated Use waste for fuels OK in some circumstances, others questionable. Capture and convert CO2 emissions to fuel and other materials Very promising technology. Reduce net emissions from manufacture Increase manufacturing efficiency Waste stream sequestration using MgO and CaO E.g. Carbonating the Portlandite in waste concrete Given the current price of carbon in Europe this could be viable Greening Concrete: Greening Concrete Increase the proportion of waste materials that are pozzolanic Using waste pozzolanic materials such as fly ash and slags has the advantage of not only extending cement reducing the embodied energy and net emissions but also of utilizing waste. We could run out of fly ash as coal is phasing out. (e.g. Canada) TecEco technology will encourage the use of pozzolans Improve particle packing for binder minimisation and carbonation Probably the lowest cost alternative for making a big difference. Greening Concrete: Greening Concrete Innovative New Concrete Products Including aggregates that improve or introduce new properties reducing lifetime energies E.g. Including wood fibre or Hemp hurd reduces weight and conductance Phase change minerals to improve specific heat capacity Use aggregates with lower embodied energy and that result in less emissions or are themselves carbon sinks materials that be used to make concrete have lower embodied energies. Local low impact waste aggregates Local “dirt” Recycled aggregates from building rubble Glass cullet Materials that are non fossil carbon are carbon sinks in concrete Plastics, wood etc. Using aggregates that extend concrete Aluminium use questionable Foamed Concretes Use for slabs to improve insulation Innovative products the reduce emissions and other impacts TecEco Eco-Cement Porous Pavement Greening Concrete: Greening Concrete Replace or partially replace Portland cement with viable alternatives There are a number of products with similar properties to Portland cement Carbonating Binders Lime mixes, Eco-Cements. Non-carbonating binders Tec-Cements, geopolymers etc. The research and development of these binders needs to be accelerated Conclusion There is plenty of scope! Portland Cement & Global Warming: Portland Cement & Global Warming Third largest contributor to CO2 emissions after the energy and transportation sectors. Portland cement production will reach 3.5 billion tonnes by 2020 - a three fold increase on 1990 levels. To achieve Kyoto targets the industry will have to emit less than 1/3 of current emissions per tonne of concrete. Carbon taxes and other legislative changes will provide legislative incentive to change. There is already strong evidence of market incentive to change Hansen, J et. al. Climate Change and Trace Gases Emissions from Cement Production: Emissions from Cement Production Chemical Release (approx 50%) The process of calcination involves driving off chemically bound CO2 with heat. CaCO3 →CaO + ↑CO2 Process Energy (approx 50%) Most energy is derived from fossil fuels. Fuel oil, coal and natural gas are directly or indirectly burned to produce the energy required releasing CO2. The production of cement for concretes accounts for around 10% of global anthropogenic CO2. Pearce, F., "The Concrete Jungle Overheats", New Scientist, 19 July, No 2097, 1997 (page 14). CO2 The Carbon Cycle and Emissions: The Carbon Cycle and Emissions Source: David Schimel and Lisa Dilling, National Centre for Atmospheric Research 2003 Emissions from fossil fuels and cement production are the cause of the global warming problem Cement Production ~= Carbon Dioxide Emissions: Cement Production ~= Carbon Dioxide Emissions Embodied Energy of Building Materials: Embodied Energy of Building Materials Downloaded from www.dbce.csiro.au/ind-serv/brochures/embodied/embodied.htm (last accessed 07 March 2000) Concrete is relatively environmentally friendly and has a relatively low embodied energy Average Embodied Energy in Buildings: Average Embodied Energy in Buildings Downloaded from www.dbce.csiro.au/ind-serv/brochures/embodied/embodied.htm (last accessed 07 March 2000) Because so much concrete is used there is a huge opportunity for sustainability by reducing the embodied energy, reducing the carbon debt (net emissions) and improving properties that reduce lifetime energies. Most of the embodied energy in the built environment is in concrete. Concrete Industry Objectives: Concrete Industry Objectives PCA (USA) Improved energy efficiency of fuels and raw materials Formulation improvements that: Reduce the energy of production and minimize the use of natural resources. Use of crushed limestone and industrial by-products such as fly ash and blast furnace slag. WBCSD Fuels and raw materials efficiencies Emissions reduction during manufacture 1. Scale Down Production?: 1. Scale Down Production? Currently growing at around 5% a year globally. Mainly China and India. GDP growth = concrete poured Can the Asian economic boom continue? What is Africa and South America also catch up to the western world? Zero population growth? Is really the amount of concrete we pour a measure of the welfare or wellbeing of a society? Buildings and infrastructure are only being designed to last 50 not hundreds of years. Will there be a shift to quality not quantity If so when? 2. Use Waste for Fuels: 2. Use Waste for Fuels Expanded use of alternative fuels is viewed by the industry as the most significant opportunity to enhance sustainability and reduce consumption of fossil fuels Cement kilns are being integrated into the recycling hierarchy for some common wastes Biomass, tires, used oils and used solvents. Questionable emissions implications? Do some organics have more value than as fuel? Tyres? Solvents that can be recycled Oils that can be recycled 3. Capture and Convert CO2 Emissions to Fuel: 3. Capture and Convert CO2 Emissions to Fuel ACC Emissions to Fuel Project: ACC Emissions to Fuel Project ACC, formerly Associated Cement Companies and now part of the Holcim group have initiated a project to Sequester CO2 generated by cement kilns Produce high energy algal biomass Reused as fuel in its cement kilns. Cellulose contents could be converted to alcohols Protein residue could be use for animal feed The project involves The screening of appropriate high yielding algae cultures The development of a bioreactor on a lab bench scale Scaling up the technology to a pilot plant and then Demonstrating the commercial viability. This will require A multi disciplinary approach and Involve microbiologists, algae experts, bio-technologists, engineers and other professionals Cost around $ 3m over a period of 3 years. 4. Reduce Net Emissions from Manufacture: 4. Reduce Net Emissions from Manufacture Increase manufacturing efficiency Has the industry reached the point of diminishing returns? Wet to dry process, heat exchangers etc Combining calcination with size reduction using a new type of kiln TecEco are developing may reduce energy consumption by 20-30% Reason - Only about 98% of the energy of grinding actually goes into cleaving minerals Around 30% of the energy used to make cement is used for grinding CO2 capture Calcination in an oxygen atmosphere to capture pure CO2 Suggested to me by a director of ACC a few weeks ago Would make capture of CO2 more worthwhile but cost money Use of CO2 for carbonation of concrete seems pointless Better to have use e.g. algal bioreactor on site (See 3) 5. Increasing the Proportion of Waste Materials that are Pozzolanic: 5. Increasing the Proportion of Waste Materials that are Pozzolanic Advantages Lower costs More durable greener concrete Disadvantages Rate of strength development retarded Resolved by TecEco technology Potential long term durability issue due to leaching of Ca from CSH. Glasser and others have observed leaching of Ca from CSH and this will eventually cause long term unpredictable behavior of CSH. Resolved by TecEco technology Higher water demand due to fineness. Finishing is not as easy Supported by WBCSD and virtually all industry associations Driven by legislation and sentiment Impact of TecEco Tec-Cement Technology on the use of Pozzolans: Impact of TecEco Tec-Cement Technology on the use of Pozzolans In TecEco tec-cements Portlandite is generally consumed by the pozzolanic reaction and replaced with brucite Increase in rate of strength development particularly in the first 3-4 days. concrete gells more quickly and finishers can go home! Kosmotrophic property of the magnesium ion Change in surface charge on MgO Improved durability as brucite is much less soluble or reactive Potential long term durability issue due to leaching of Ca from CSH resolved. Easier to finish fly ash concretes - Mg++ contributes a strong shear thinning property 6. Improve Particle Packing for Binder Minimisation and Carbonation: 6. Improve Particle Packing for Binder Minimisation and Carbonation In the past, concrete proportioning was based on experience and estimates only. TecSoft Pty. Ltd. are developing batching software, using theory from the world’s best experts (F. de Larrard and Ken Day), to optimize mix design and particularly particle packing. Satterfield, S. G. (2001). Visualization aggregate in high performance concrete, National institute of standard and technology.(NIST) Scientific knowledge of the concrete behaviour coupled with the use of optimization software will allow concrete technologists to: Design more sustainable concrete Less cement of same strength More durable Use secondary aggregate and mining wastes (poor size distribution) Dramatically reduce the number of experiment needed to design a concrete for a special application Scientific Approach to Concrete Design: Scientific Approach to Concrete Design Optimization of particle packing will improve The strength/cost ratio and Concrete sustainability Less cement for the same strength Improving packing (other parameters being equal) leads to an increase of: The compressive and tensile strength The workability The durability And a decrease of: The porosity The risk of segregation The yield stresses (easier to compact) Could help improve the skill level in the industry An expert in the box 7. Innovative New Concrete Products: 7. Innovative New Concrete Products Room for innovation in the concrete industry Demand for more sustainable materials Need to take a more holistic view Cementitious composites not cement Barriers to innovation are Low skill level For innovation to occur the skill level will have to improve dramatically This could be a government initiative – i.e require people in the industry to do an apprenticeship (as for other industries) As part of the course work alternatives would be examined. Formula rather than performance based standards entrench mediocrity and dogma Better connections between market demand and production and supply Technologies that Introduce New Properties: Technologies that Introduce New Properties Introduce new components that improve performance. Reducing lifetime energies in use e.g. That reduce conductance (e.g. wood fibre or hemp hurd ) That increase specific heat capacity (e.g. phase change materials) Reduce weight/strength ratio Organic fibres and fillers Many of the above components can be wastes Improve durability Remove lime by adding pozzolans or as in Tec-Cement concretes Reduce Embodied Energy: Reduce Embodied Energy Local low impact waste aggregates Local “dirt” On site excavation materials Recycled aggregates from building rubble Tec and Eco-Cements do not have problems associated with high gypsum content Glass cullet fly ash, ggbfs and other industrial wastes Reduce transport embodied energies by using local materials such as low impact wastes and earth Mud bricks and adobe. TecEco research in the UK and with mud bricks in Australia indicate that eco-cement formulations seem to work much better than PC for this Lower Net Emissions: Lower Net Emissions Making Concretes that are carbon sinks Eco-Cements - Addition of magnesium oxide which re-carbonates with carbon capture technology Materials that are non fossil carbon are carbon sinks in concrete Plastics, wood etc. Eco-Cements bond well to sawdust and other carbon based aggregates. Many of the above components can be wastes paper and plastic have in common reasonable tensile strength, low mass and low conductance and can be used to make cementitious composites that assume these properties Extending Cement: Extending Cement Air used in foamed concrete is a cheap low embodied energy aggregate and has the advantage of reducing the conductance of concrete. Concrete, depending on aggregates weighs in the order of 2350 Kg/m3 Concretes of over 10 mp as light as 1000 Kg/m3 can be achieved. At 1500 Kg/m3 25 mpa easily achieved. From our experiments so far with Build-lite Cellular Concrete PL Tec-Cement formulations increase strength performance by around 5-10% for the same mass. Claimed use of aluminium and autoclaving to make more sustainable blocks questionable? Concrete Porous Pavements?: Concrete Porous Pavements? Perhaps the greenest concrete product in the world is a new porous low fines concrete that is being made using recycled aggregate and with Eco-Cements that set by absorbing CO2 8. Replace Portland Cement with Viable Alternatives: 8. Replace Portland Cement with Viable Alternatives The concrete industry are in the business of selling binders Need to get away from the “all that is grey is great, all we make goes out the gate” philosophy The industry can also make money learning about and selling alternatives Sell knowledge as well as product Many alternatives just as suitable The problem is in implementation Could be difficult given the low level of skill in the industry We will consider two main groups of alternative cements Carbonating alternatives Potentially carbon neutral of carbon sinks Non carbonating alternatives Some have much lower embodied energies Replacement of PC by Calcium Based Carbonating Binders: Replacement of PC by Calcium Based Carbonating Binders Lime The most used material next to Portland cement in binders. Generally used on a 1:3 (PC:Sand) paste basis since Roman times Non-hydraulic limes set by carbonation and are therefore close to carbon neutral once set. CaO + H2O => Ca(OH)2 Ca(OH)2 + CO2 => CaCO3 33.22 + gas ↔ 36.93 molar volumes Very slight expansion, but shrinkage from loss of water. Carbonates not generally fibrous so do not add as much microstructural strength as Mg cements Do not stick to other materials as well as Mg cements. Low long term pH = low reactivity with wastes included Replacement of PC with Magnesium Based Carbonating Binders: Replacement of PC with Magnesium Based Carbonating Binders Eco-Cement (TecEco) Have high proportions of reactive magnesium oxide Carbonate like lime Generally used in a 1:2:18 (PC:MgO:Sand) paste basis because much more carbonate “binder” is produced than with lime. Like lime are carbon neutral but take up more weight of CO2 due to low weight of Mg MgO + H2O <=> Mg(OH)2 Mg(OH)2 + CO2 + H2O <=> MgCO3.3H2O 58.31 + 44.01 <=> 138.32 molar mass (at least!) 24.29 + gas <=> 74.77 molar volumes (at least!) 307 % expansion (less water volume reduction) producing much more binder per mole of MgO than lime (around 8 times) and les shrinkage Carbonates tend to be fibrous adding significant micro structural strength compared to lime Can include a wider range of wastes Stick well due to hydrogen bonding Low long term pH = low reactivity Mostly CO2 and water Replacement with Non Carbonating Binders: Replacement with Non Carbonating Binders There are a number of other novel cements with intrinsically lower energy requirements and CO2 emissions than conventional Portland cements that have been developed High belite cements Being research by Aberdeen and other universities Calcium sulfoaluminate cements Used by the Chinese for some time Magnesium phosphate cements Proponents argue that a lot stronger than Portland cement therefore much less is required. Main disadvantage is that phosphate is a limited resource Sorel Type Cements Stronger and more convenient to place and use (with the appropriate know how. Tend to break down in water PC – Magnesia blends (Tec-Cements) Geopolymers More research needed. I will only have time to mention geopolymers and Tec-Cements Geopolymers: Geopolymers “Geopolymers” consists of SiO4 and AlO4 tetrahedra linked alternately by sharing all the oxygens. Positive ions (Na+, K+, Li+, Ca++, Ba++, NH4+, H3O+) must be present in the framework cavities to balance the negative charge of Al3+ in IV fold coordination. Theoretically very sustainable Unlikely to be used for pre-mix concrete or waste in the near future because of. process problems Requiring a degree of skill for implementation Skill level problem in the industry needs to be addressed nano porosity Causing problems with aggregates in aggressive environments no pH control strategy for heavy metals in waste streams Tec - Cements: Tec - Cements Tec-Cements (Low MgO) contain more Portland cement than reactive magnesia. Reactive magnesia hydrates in the same rate order as Portland cement forming Brucite which uses up water reducing the voids:paste ratio, increasing density and possibly raising the short term pH. More pozzolans can be used. After all the Portlandite has been consumed Brucite controls the long term pH which is lower and due to it’s low solubility, mobility and reactivity results in greater durability. Other benefits include improvements in density, strength and rheology, reduced permeability and shrinkage and the use of a wider range of aggregates many of which are potentially wastes without reaction problems.