New Materials Based on the Addition of Reactive Magnesia to Hydraulic Cements.

1. New Materials Based on the Addition of Reactive Magnesia to Hydraulic Cements. Hobart, Tasmania, Australia All I ask is that the industry think about what I am saying. John Harrison B.Sc. B.Ec. FCPA.

2. Materials - the Key to Sustainability The choice of materials controls emissions, lifetime and embodied energies, maintenance of utility, recyclability and the properties of wastes returned to the biosphere.

3. The Construction Industry • The built environment is our footprint on earth. • TecEco estimate that building materials comprise some 70% of materials flows. • Calcined minerals and their derivatives are the main materials used to construct the built environment. • Globally around 2 billion tonnes of calcined minerals (cement, lime and magnesia) are produced annually. • Portland cement is made by calcining limestone with clay and concrete made with it is the most widely used material on Earth. • Global Portland cement production is in the order of 1.7 billion tonnes. The largest producers of Portland cement are China at over 500 million tonnes followed by India at over 110 million tonnes. Globally this amounts to over 6 cubic kilometres of concrete per year. Downloaded from www.dbce.csiro.au/ind-serv/brochures/embodied/embodied.htm (last accessed 07 March 2000)

4. Embodied Energy of Building Materials Concrete has a relatively low embodied energy Downloaded from www.dbce.csiro.au/ind-serv/brochures/embodied/embodied.htm (last accessed 07 March 2000)

5. Embodied Energy in Buildings But because so much is used there is a huge opportunity for sustainability Downloaded from www.dbce.csiro.au/ind-serv/brochures/embodied/embodied.htm (last accessed 07 March 2000)

6. Sustainability is not just about reducing emissions. Other properties of concrete such as the amount of cement required for a given strength, durability, embodied energy, insulating capacity, weight etc. are also relevant. Concretes should not be thought of as just cement and aggregate. They will become a composite material with a range of tailored properties offering vastly improved overall performance as well as meeting specific performance criteria such as strength. As an ideal building material concrete should include other properties not usually provided such as insulating capacity and the ability to utilise wastes. All sorts of other materials such as industrial mineral wastes, sawdust, wood fibres, waste plastics etc. could be added for the properties they impart. More attention paid to the micro engineering of the material as well as the chemistry would result in improved properties. Concretes can cost affectively be everything we would like them to be! Sustainability = High Performance

7. Calcined mineral materials and their derivatives used in construction such as Portland cement, lime and magnesia are made from carbonates. The process of calcination involves driving off chemically bound CO2 with heat. MCO3 →MO + CO2 ∆ Heating requires energy. 98% of the world’s energy is derived from fossil fuels. Fuel oil, coal and natural gas are mainly directly or indirectly burned to produce the energy required for calcining of metal carbonates releasing CO2. Most of the embodied energy in the built environment is in concrete. The production of cement for concretes accounts for around 10% of global anthropogenic CO2. Emissions

8. The CO2 released by chemical reaction from the calcined materials in TecEco Eco-cement concretes can be captured during manufacture and reabsorbed on a widely distributed basis in eco-cements. A system using TecEco Eco-Cements to construct the built environment therefore offers enormous opportunities for sequestration, particularly if combined with mineral sequestration utilising magnesium silicates in a combined process. Other TecEco cements are also much more sustainable but for different reasons that include durability and the use of less cement to make more material. Opportunities for Sustainability

9. Issues with OPC Concrete • Talked about • Rheology • Workability, time for and method of placing and finishing • Shrinkage • Cracking, crack control • Durability and Performance • Permeability and Density • Sulphate and chloride resistance • Carbonation • Corrosion of steel and other reinforcing • Delayed reactions (eg alkali aggregateand delayed ettringite) • Bonding to brick and tiles • Efflorescence • Rarely discussed • Sustainability issues • Emissions and embodied energies Should the discussion be more about how we could fix the material, overcoming rather than tolerating and mitigating these problems?

10. Problems with Portland cement concretes are usually resolved by the “band aid” application of engineering fixes. They are rarely discussed in terms of the mineralogy. e.g. Use of calcium nitrite, silanes, cathodic protection or stainless steel to prevent corrosion. Use of coatings to prevent carbonation. Crack control joins to mitigate the affects of shrinkage cracking. Plasticisers to improve workability, glycols to improve finishing. Many of the problems with Portland cement are better fixed by fundamentally fixing the mineralogy! The flaw in the mineralogy of Portland cement concretes is the presence of Portlandite which is too soluble, mobile and reactive. The TecEco technology is not a “band aid”, it is a fundamental fix. Engineering Issues are Mineralogical Issues

11. TecEco Technology - Simple Yet Ingenious? The TecEco technology demonstrates that magnesia, provided it is reactive rather than “dead burned” (or high density, periclase type), can be beneficially added to cements in excess of the amount of 5 mass% generally considered as the maximum allowable by standards Reactive magnesia is essentially amorphous magnesia produced at low temperatures and finely ground. The important thing in science is not so much to obtain new facts as to discover new ways of thinking about them. -- Sir William Bragg

12. TecEco Concretes – A Blending System TecEco concretes are a system of blending reactive magnesia, Portland cement and usually a pozzolan with other materials.

13. Delayed hydration leads to dimensional distress. Magnesium was banned in Portland cements because when it goes through the high temperature process of making Portland cement it becomes periclase. It is “dead burned”, hydrates slowly and causes dimensional distress. Dead burned lime is much more expansive than dead burned magnesia(1), a problem largely forgotten by cement chemists. TecEco have demonstrated that highly amorphous reactive magnesia can beneficially be added to concrete formulations The reactivity of magnesia is a function of the state of disorder (lattice energy), specific surface area and glass forming impurities. The state of order or disorder is expressed in lattice energy and is dependent on the temperature of calcining. Specific surface area relates particle size. Make a particle small enough and it will react with just about anything. Glass forming impurities are formed when reactive magnesia reacts at high temperatures with impurities such as iron. A new TecEco kiln technology which combines calcining and grinding should make it possible to calcine at lower temperatures and produce more reactive magnesia with reduced problems due to impurities as well as capture CO2. (1) Ramachandran V. S., Concrete Science, Heydon & Son Ltd. 1981, p 358-360. Reactivity Overcomes Delayed Hydration Problems.

14. Why Replace Portlandite with Brucite? • Portlandite (Ca(OH)2) is not a suitable concrete matrix mineral. • Ca(OH)2 is reactive, carbonates readily and being soluble can act as an electrolyte. TecEco remove Portlandite in reactions with Pozzolans. • Brucite is much less soluble, mobile or reactive, does not act as an electrolyte or carbonate as readily. • The addition of magnesia which hydrates forming brucite improves the rheology, uses up bleed water as it hydrates, filling in the pores, increasing the density, reducing permeability, reducing shrinkage and providing long term pH control with many consequences including greater durability. • In porous eco-cements brucite carbonates forming stronger minerals. The consequences of removing Portlandite (lime) with the pozzolanic reaction and filling the voids between hydrating cement grains with brucite, an insoluble alkaline mineral, need to be considered.

15. Portlandite Compared to Brucite

16. TecEco Formulations • Three main formulation strategies so far: • Tec-cements (e.g. 10% MgO, 90% OPC.) • 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. Reactions with pozzolans are more affective. 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 without reaction problems. • Enviro-cements (e.g. 25-75% MgO, 25-75% OPC) • In non porous concretes brucite does not carbonate readily. • High proportions of magnesia are most suited to toxic and hazardous waste immobilisation and when durability is required. Strength is not developed quickly. • Eco-cements (egg 50-75% MgO, 50-25% OPC) • Contain more reactive magnesia than in tec-cements. • Brucite in porous materials carbonates • Forming stronger fibrous mineral carbonates. • Presenting huge opportunities for abatement.

17. TecEco Formulations (2)

18. Porosity and Magnesia Content Note that TecEco eco-cements require a porous environment.

19. Basic Chemical Reactions Notice the low solubility of brucite compared to Portlandite and that magnesite is stronger and adopts a more ideal habit than calcite & aragonite

20. Greater Strength • Tec-cements can be made with at least 25% less binder for the same strength. • Possible reasons for • Low binder/total solids ratio • More rapid strength development even with pozzolans • Reactive magnesia is an excellent plasticiser and results in: • Denser, less permeable concrete. • A significantly lower voids/paste ratio. • Higher early pH initiating more effective silicification reactions • The Ca(OH)2 normally lost in bleed water is used internally for reaction with pozzolans. • Super saturation caused by the removal of water by magnesia as it hydrates. Concrete technologists are obsessed by strength. They should be more interested in durability!

21. Rapid Water Reduction Water is required to plasticise concrete for placement, however once placed, the less water over the amount required for hydration the better. Magnesia rapidly removes water as it hydrates. Less water results in less shrinkage and cracking and improved durability. Concentration of alkalis and increased density result in greater strength.

22. Durability & Strength - Increased Density • Concretes have a high percentage of voids. • On hydration magnesia expands 116.9 % filling voids and surrounding hydrating cement grains. • Brucite is 44.65 mass% water. • Lower voids:paste ratios than water:binder ratios result in less bleed water and greater density. • Greater density results in greater strength, more durable concrete with a higher salt resistance and less corrosion of steel etc. • Self compaction of brucite may add to strength. • Compacted brucite is as strong as CSH (Ramachandran, Concrete Science p 358)

23. Hypothetical Tec-Cement pH Curves

24. Hypothetical Tec-Cement Concrete Strength Development Curve The possibility of high early strength gain with added pozzolans is of great economic importance.

25. Durability - A Lower More Stable Long Term pH In TecEco cements the long term pH is governed by the low solubility and carbonation rate of brucite and is much lower at around 10.5 -11, allowing a wider range of aggregates to be used, reducing problems such as AAR and etching. The pH is still high enough to keep Fe2O3 and Fe3O4 stable in reducing conditions. Eh-pH or Pourbaix Diagram The stability fields of hematite, magnetite and siderite in aqueous solution; total dissolved carbonate = 10-2M.

26. The passive coating on steel is iron oxide. According to the Pourbaix diagram it is magnesite but some authors such as Neville report the oxide is γFe3O(1). One of the problems associated with examining iron oxides is that they change rapidly from one form to another and are therefore difficult to characterise(2). The author would be interested in definitive information of any papers on this subject! The Passive Coating of Iron Oxide • (1) Neville, A. M. Properties of Concrete, 4th Ed. Pearson Prentice Hall, England, 2003, page 563.

27. A wide range of delayed reactions can occur in Portland cement based concretes Delayed alkali silica and alkali carbonate reactions The delayed formation of ettringite and thaumasite Delayed hydration of minerals such as dead burned lime and magnesia. Delayed reactions cause dimensional distress and possible failure. Durability – Reduced Delayed Reactions

28. Delayed reactions do no occur to the same extent in TecEco Cements. A lower long term pH results in reduced reactivity after the plastic stage. Potentially reactive ions are trapped in the structure of brucite. Ordinary Portland cement concretes can take years to dry out however Tec-cement concretes are dried out from the inside by the water demand of reactive magnesia as it hydrates. Durability – Reduced Delayed Reactions (2)

29. Carbonates are the stable phases of both calcium and magnesium. Carbonates lower the pH of concretes compromising the stability of the passive oxide coating on steel. The Portlandite in Portland cement concretes carbonates readily starting at the surface. Brucite in tec - cement concretes carbonates less readily (for the main kinetic pathway) because: The carbonation reaction has a less negative Gibbs free energy. Gor Brucite = -19.55 Gor Portlandite = -64.62 Carbon dioxide cannot enter the dense impermeable concrete matrix. The magnesium carbonates that form at the surface of tec – cement concretes expand, sealing off further carbonation. Eco-Cement Concretes Magnesite is formed deliberately and is stronger and more acid resistant than calcite or aragonite. Durability – Carbonation

30. Durability – Reduced Permeability • As bleed water exits ordinary Portland cement concretes it creates an interconnected pore structure that remains in concrete allowing the entry of aggressive agents such as SO4--, Cl- and CO2 • TecEco tec - cement concretes are a closed system. They do not bleed as excess water is consumed by the hydration of magnesia. • As a result TecEco tec - cement concretes dry from within, are denser and less permeable, and cement powder is not lost near the surfaces.

31. Reduced Shrinkage Dimensional change such as shrinkage results in cracking and reduced durability

32. Reduced Cracking in TecEco Cement Concretes Cracking, the symptomatic result of shrinkage, is undesirable for many reasons, but mainly because it allows entry of gases and ions reducing durability. Cracking can be avoided only if the stress induced by the free shrinkage strain, reduced by creep, is at all times less than the tensile strength of the concrete. Reduced in TecEco tec-cements because they do not shrink. After Richardson, Mark G. Fundamentals of Durable Reinforced Concrete Spon Press, 2002. page 212.

33. Corrosion in Portland Cement Concretes Both carbonation, which renders the passive iron oxide coating unstable or chloride attack (various theories) result in the formation of reaction products with a higher electrode potential resulting in anodes with the remaining passivated steel acting as a cathode. Passive Coating Fe3O4 intact Corrosion Anode: Fe → Fe+++ 2e-Cathode: ½ O2 + H2O +2e- → 2(OH)-Fe++ + 2(OH)- → Fe(OH)2 + O2 → Fe2O3 and Fe2O3.H2O (iron oxide and hydrated iron oxide or rust) The role of chloride in Corrosion Anode: Fe → Fe+++ 2e-Cathode: ½ O2 + H2O +2e- → 2(OH)-Fe++ +2Cl- → FeCl2FeCl2 + H2O + OH- → Fe(OH)2 + H+ + 2Cl-Fe(OH)2 + O2 → Fe2O3 and Fe2O3.H2O Iron hydroxides react with oxygen to form rust. Note that the chloride is “recycled” in the reaction and not used up.

34. Reduced Steel Corrosion • A pH of over 8.9 is maintained for much longer and steel remains passive due to a stable oxide coating. • Brucite does not react readily resulting in reduced carbonation rates and reactions with salts. • Concrete with brucite is denser and carbonation is expansive, sealing the surface preventing further access by moisture, CO2 and salts. • Brucite is less soluble and traps salts as it forms resulting in less ionic transport to complete a circuit for electrolysis and less corrosion. • Free chlorides and sulfates originally in cement and aggregates bound by magnesium • Magnesium oxychlorides or oxysulfates are formed. ( Compatible phases in hydraulic binders that are stable provided the concrete is dense and water kept out.)

35. Brucite has always played a protective role during salt attack. Putting it in the matrix of concretes in the first place makes sense. Brucite does not react with salts because of it’s low solubility (reactivity, mobility) and lower pH (reactivity) Ksp brucite = 1.8 X 10-11 Ksp Portlandite = 5.5 X 10-6 - 5 orders of magnitude Durability - Reduced Salt Attack

36. Improved Workability • Finely ground reactive magnesia acts as a plasticiser. • Improving rheology • Lower water cement ratio results in greater strength and reduced porosity. • The proportion and cost of binders and plasticisers can be reduced.

37. Reasons for Improved Workability There are also surface charge affects and water reducing agents are not required. Reactive Magnesia is a plasticiser as well.

38. Rheology • TecEco concretes are • very homogenous • very thixotropic and react well to energy input. • (Slump is therefore not a good measure of workability) • TecEco concretes with the same water/binder ratio have a lower slump but greater plasticity and workability.

39. Portland cement shrinks around .05%. Over the long term much more (>.1%). Mainly due to chemical shrinkage, plastic and drying shrinkage, as well as carbonation. Hydration: When magnesia hydrates it expands: MgO (s) + H2O (l) ↔ Mg(OH)2 (s) 40.31 + 18.0 ↔ 58.3 molar mass 11.2 + liquid ↔ 24.3 molar volumes Up to 116.96% solidus expansion depending on whether the water is coming from stoichiometric mix water, bleed water or from outside the system. In practice much less as the water comes from mix and bleed water. So far we have not observed shrinkage in TecEco tec - cement concretes (10% substitution OPC) also containing fly ash. The water lost by Portland cement as it shrinks is used by the reactive magnesia as it hydrates eliminating shrinkage. Dimensionally Neutral TecEco Tec - Cement Concretes During Curing?

40. Volume Changes on Carbonation • Carbonation: • Consider what happens when Portlandite carbonates: Ca(OH)2 + CO2 CaCO3 74.08 + 44.01 ↔ 100 molar mass 33.22 + gas ↔ 28.10 molar volumes • 18.22% shrinkage. Cracks appear allowing further carbonation. • Compared to brucite forming magnesite as it carbonates: Mg(OH)2 + CO2 MgCO3 58.31 + 44.01 ↔ 84.32 molar mass 24.29 + gas ↔ 28.10 molar volumes • 15.68% expansion and densification of the surface preventing further ingress of CO2 and carbonation. Self sealing? • Combined - Curing and Carbonation are close to Neutral. • At some ratio, thought to be around 10% reactive magnesia and 90% OPC volume changes cancel each other out. • More research is required for both tec - cements and eco-cements to accurately establish volume relationships. [1] The molar volume (L.mol-1)is equal to the molar mass (g.mol-1) divided by the density (g.L-1).

41. Tec - Cement Concretes - Potential for Neutral Cure

42. Most texts maintain the carbonation reaction is one between ions in solution yet carbonation is observable in very dry conditions. The transport of carbon dioxide is much more rapid in air than in water and adherence to Le Chatelier’s principal would also indicate dry conditions as the removal or water as a product would help the reaction Ca(OH)2 + CO2 CaCO3 + H2O (Gof - 64.62 kJ.mol-1) To proceed towards products (the right). The highly negative Gibbs free energy of the reaction indicates this should occur spontaneously. The author would be very interested in some definitive information on this as most of the texts seem to take a bet both ways! Are the Texts all Wrong About Carbonation? Please contact me if you know more about this than me!

43. The main phase in TecEco tec - cement concretes is brucite. The main phases in TecEco eco-cements are magnesite and hydromagnesite. Brucite, magnesite and hydromagnesite are excellent fire retardants and extinguishers. At relatively low temperatures Brucite releases water and reverts to magnesium oxide. Magnesite releases CO2 and converts to magnesium oxide. Hydromagnesite releases CO2 and water and converts to magnesium oxide. Fires are therefore not nearly as aggressive resulting in less damage to structures. Damage to structures results in more human losses that direct fire hazards. Safety – Reduced Fire Damage

44. The best thing to do with wastes is if at all possibleto use them. If they cannot directly be usedthen they have to be immobilised. Concretes represent a cost affective option: Chemically and physically enviro-cements are moresuited to toxic and hazardous waste immobilisationthan either lime, Portland cement or Portland cementlime mixes and they are more predicable than geopolymers. In a Portland cement brucite matrix OPC takes up lead, some zinc and germanium Brucite and hydrotalcite are both excellent hosts for toxic and hazardous wastes. Brucite has a layered structure and traps neutral compounds between the layers. Heavy metals not taken up in the structure of Portland cement minerals or trapped within the brucite layers end up as hydroxides. The pH which is controlled in the long term by brucite is around 10.52, and is an ideal long term value at which most heavy metal hydroxides are relatively insoluble. TecEco cements are also more durable, dense, impermeable and homogenous. They do not bleed water, are not attacked by salts in ground or sea water and dimensionally more stable with less cracking. TecEco Eco-Cements - Solving Waste Problems

45. Toxic and Hazardous Waste Immobilisation Brucite is an ideal mineral for trapping toxic and hazardous wastes. The brucite in TecEco cements has a structure comprising electronically neutral layers and is able to accommodate a wide variety of extraneous substances between the layers and cations of similar size substituting for magnesium within the layers and is known to be very suitable for toxic and hazardous waste immobilisation.

46. Lower Solubility of Metal Hydroxides

47. High Performance = Sustainability=Lower Cost Comprehensive high performance will include improvements in: Compressive and tensile strength/binder ratios Durability, insulating capacity, ability to host wastes Weight etc. etc. Increased durability will result in lower costs/energies/emissions due to less frequent replacement. Improvements in insulating capacity will mean lower lifetime as well as embodied energies in buildings. High Performance = Sustainability=Lower Cost

48. Lower water binder ratio means less binders (eg OPC) for same strength. Faster strength gain even with added pozzolans. Cheaper binders as less energy required and a higher proportion is water. Elimination of shrinkage reducing associated costs. Elimination of bleed water enables finishing of lower floors whilst upper floors still being poured. A high proportion of brucite compared to Portlandite is water and of magnesite compared to calcite is CO2. Every mass unit of TecEco cements therefore produces a greater volume of built environment than Portland and other calcium based cements. Less need therefore be used reducing costs/energy/emissions. TecEco Concretes - Lower Construction Costs

49. Homogenous, so no under plastic necessary. Because reactive magnesia is also an excellent plasticiser, other costly additives are not required for this purpose. Easier placement and better finishing. A wider range of aggregates can be utilised without problems reducing transport and other costs/energies/emissions. Greater durability reduces costs over time. Reduced or eliminated carbon taxes. Eco-cements can to a certain extent be recycled. TecEco cements utilise wastes many of which improve properties. TecEco Concretes - Lower Construction Costs (2)

50. Characteristics of TecEco Cements (1)