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1John Harrison Presentation AASMIC Conference TecEco Tec-Cement Concretes – Abatement, Strength, Durability and Waste Utilization in the Built EnvironmentAbatementStrengthDurabilityIf we can make materials that take less than half as much energy, last more than twice as long (are more durable) and have a use when they are retired then we are almost there in terms of sustainability.Our slides are deliberately verbose as most people download and view them from the net. Because of time constraints I will have to race over some slides John Harrison B.Sc. B.Ec. FCPA.
2John Harrison Presentation AASMIC Conference TecEco Binder SystemsSUSTAINABILITYPORTLANDPOZZOLANHydration of the various components of Portland cement for strength.Reaction of alkali with pozzolans (e.g. lime with fly ash.) for sustainability, durability and strength.TECECO CEMENTSDURABILITYSTRENGTHTecEco concretes are a system of blending reactive magnesia, Portland cement and usually a pozzolan with other materials and are a key factor for sustainability.REACTIVE MAGNESIAHydration of magnesia => brucite for strength, workability, dimensional stability and durability. In Eco-cements carbonation of brucite => nesquehonite, lansfordite and an amorphous phase for sustainability.
3The Magnesium Thermodynamic Cycle CalcinationCO2 Capture Non fossil fuel energyWe think this cycle is relatively independent of other constituents
4Strength with Blend & Porosity Tec-cement concretesEco-cement concretesHigh PorosityEnviro-cement concretesHigh OPCHigh MagnesiaSTRENGTH ON ARBITARY SCALE 1-100
5Many Engineering Issues are Actually Mineralogical Issues Problems with Portland cement concretes are usually resolved by the “band aid” engineering fixes. 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.Portlandite and water are the weakness of concreteTecEco remove Portlandite it and replacing it with magnesia which hydrates to Brucite.The hydration of magnesia consumes significant water
6John Harrison Presentation AASMIC Conference TecEco Binder TheoryPortlandite (Ca(OH)2) is too soluble, mobile and reactive.It carbonates, reacts with Cl- and SO4- and being soluble can act as an electrolyte.TecEco generally (but not always) remove Portlandite using the pozzolanic reaction andTecEco add reactive magnesiawhich hydrates, consuming significant water and concentrating alkalis forming Brucite which is another alkali, but much less soluble, mobile or reactive than Portlandite.In Eco-cements brucite carbonates
7Why Add Reactive Magnesia? John Harrison Presentation AASMIC ConferenceWhy Add Reactive Magnesia?To maintain the long term stability of CSH.Maintains alkalinity preventing the reduction in Ca/Si ratio.To remove water.Reactive magnesia consumes water as it hydrates to possibly hydrated forms of Brucite.To raise the early Ph.Increasing non hydraulic strength giving reactionsTo reduce shrinkage.The consequences of putting brucite through the matrix of a concrete in the first place need to be considered.To make concretes more durableBecause significant quantities of carbonates are produced in porous substrates which are affective binders.Reactive MgO is a new tool to be understood with profound affects on most properties
8John Harrison Presentation AASMIC Conference TecEco FormulationsTec-cements (5-15% MgO, 85-95% 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 many of which are potentially wastes without reaction problems.Eco-cements (15-95% MgO, 85-5% OPC)contain more reactive magnesia than in tec-cements. Brucite in porous materials carbonates forming stronger fibrous mineral carbonates and therefore presenting huge opportunities for waste utilisation and sequestration.Enviro-cements (5-15% MgO, 85-95% OPC)contain similar ratios of MgO and OPC to eco-cements but in non porous concretes brucite does not carbonate readily.Higher proportions of magnesia are most suited to toxic and hazardous waste immobilisation and when durability is required. Strength is not developed quickly nor to the same extent.
9Tec-Cement ReactionsMgO + H2O => Mg(OH)2.nH2O - water consumption resulting in greater density and higher alkalinity.Higher alkalinity => more reactions involving silica & alumina.Mg(OH)2.nH2O => Mg(OH)2 + H2O – slow release water for more complete hydration of PCMgO + Al + H2O => 3MgO.Al.6H2O ??? – equivalent to flash set??MgO + SO4-- => various Mg oxy sulfates ?? – yes but more likely ettringite reaction consumes SO4-- first.MgO + SiO2 => MSH ?? Yes but high alkalinity required. Strength??We think the reactions are relatively independent of PC reactions
10The Form of MgO Matters - Lattice Energy Destroys a Myth John Harrison Presentation AASMIC ConferenceThe Form of MgO Matters - Lattice Energy Destroys a MythMagnesia, provided it is reactive rather than “dead burned” (or high density, crystalline periclase type), can be beneficially added to cements in excess of the amount of 5 mass% generally considered as the maximum allowable by standards prevalent in concrete dogma.Reactive magnesia is essentially amorphous magnesia with low lattice energy.It is produced at low temperatures and finely ground, andwill completely hydrate in the same time order as the minerals contained in most hydraulic cements.Dead burned magnesia and lime have high lattice energiesCrystalline magnesium oxide or periclase has a calculated lattice energy of 3795 Kj mol-1 which must be overcome for it to go into solution or for reaction to occur.Dead burned magnesia is much less expansive than dead burned lime in a hydraulic binder (Ramachandran V. S., Concrete Science, Heydon & Son Ltd. 1981, p )
11More Rapid and Greater Strength Development Higher Strength Binder Ratio Concretes are more often than not made to strength.The use of tec-cement results in15-30% more strength or less binder for the same strength.more rapid early strength development even with added pozzolans.Straight line strength development for a long timeEarly strength gain with less cement and added pozzolans is of great economic and environmental importance as it will allow the use of more pozzolans.We have observed this sort of curve in over 300 cubic meters of concrete now
12Tec-Cement Strength Development Graphs above by Oxford Uni Student are for standard 1PC:3 aggregate mixes, w/c = .5BRE (United Kingdom)2.85PC/0.15MgO/3pfa(1 part) : 3 parts sand - Compressive strength of 69MPa at 90 days.Note that there was as much pfa as Portland cement plus magnesia. Strength development was consistently greater than the OPC control. TECECOWHITTLESEA SLAB (A modified 20 mpa mix)PC = 180 Kg / m3 MgO = 15 Kg / m3 Flyash = 65 Kg / m3Rate of strength development is of great interest to engineers and constructors
13Calorimetric Evidence of Faster Strength Gain Faster Strength DevelopmentEvolution of Less HeatEnergy associated with complexing?
14Reasons for Compressive Strength Development in Tec-Cements. Reactive magnesia requires considerable water to hydrate resulting in:Denser, less permeable concrete. Self compaction?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 of alkalis caused by the removal of water?Micro-structural strength due to particle packing (Magnesia particles at 4-5 micron are a little over ½ the size of cement grains.)Formation of MgAl hydrates? Similar to flash set in concrete but slower??Formation of MSH??Slow release of water from hydrated Mg(OH)2.nH2O supplying H2O for more complete hydration of C2S and C3S?Brucite gains weight in excess of the theoretical increase due to MgO conversion to Mg(OH)2 in samples cured at 98% RH.Dr Luc Vandepierre, Cambridge University, 20 September, 2005.
15Greater Tensile Strength ++++++++Cement++MgO+Sand+++++++++Mutual RepulsionPh 12 ?=>Mutual Repulsion+++-+-+++Cement+-MgO-Sand+--+++-++Mutual AttractionMgO Changes Surface Charge as the Ph Rises. This could be one of the reasons for the greater tensile strength displayed during the early plastic phase of tec-cement concretes. The affect of additives is not yet known
16DurabilityConcretes are said to be less durable when they are physically or chemically compromised.Physical factors can result in chemical reactions reducing durabilityE.g. Cracking due to shrinkage can allow reactive gases and liquids to enter the concreteChemical factors can result in physical outcomes reducing durabilityE.g. Alkali silica reaction opening up cracks allowing other agents such as sulfate and chloride in seawater to enter.This presentation will describe benchmark improvements in durability as a result of using the new TecEco magnesia cement technologies
17Crack CollageAlkali aggregate ReactionEvaporative Crazing ShrinkageDrying ShrinkageThermalSettlement ShrinkageFreeze Thaw D CracksStructuralPlastic ShrinkagePhotos from PCA and US Dept. Ag WebsitesCorrosion RelatedAutogenous or self-desiccation shrinkage (usually related to stoichiometric or chemical shrinkage)TecEco technology can reduce if not solve problems of cracking:Related to (shrinkage) through open system loss of water.As a result of volume change caused by delayed reactionsAs a result of corrosion.Related to autogenous shrinkage
18Causes of Cracking in Concrete Cracking commonly occurs when the induced stress exceeds the maximum tensile stress capacity of concrete and can be caused by many factors including restraint, extrinsic loads, lack of support, poor design, volume changes over time, temperature dependent volume change, corrosion or delayed reactions.Causes of induced stresses include:Restrained thermal, plastic, drying and stoichiometric shrinkage, corrosion and delayed reaction strains.Slab curling.Loading on concrete structures.Cracking is undesirable for many reasonsVisible cracking is unsightlyCracking compromises durability because it allows entry of gases and ions that react with Portlandite.Cracking can compromise structural integrity, particularly if it accelerates corrosion.
19Graphic Illustration of Cracking Autogenous shrinkage has been used to refer to hydration shrinkage and is thus stoichiometricAfter Tony Thomas (Boral Ltd.) (Thomas 2005)
20Cracking due to Loss of Water Brucite gains weight in excess of the theoretical increase due to MgO conversion to Mg(OH)2 in samples cured at 98% RH.Dr Luc Vandepierre, Cambridge University, 20 September, 2005.Drying ShrinkageFoolPlastic ShrinkageEvaporative Crazing ShrinkageBucket of WaterSettlement ShrinkagePicture from:We may not be able to prevent too much water being added to concrete by fools. TecEco approach the problem in a different way by providing for the internal removal/storage of water that can provide for more complete hydration of PC.
21Solving Cracking due to Shrinkage from Loss of Water In the system water plus Portland cement powder plus aggregates shrinkage is in the order of .05 – 1.5 %.Shrinkage causes crackingThere are two main causes of Portland cements shrinking over time.Stoichiometric (chemical) shrinkage andShrinkage through loss of water.The solution is to:Add minerals that compensate by stoichiometrically expanding and/or toUse less water, internally hold water or prevent water loss.TecEco tec-cements internally hold water and prevent water loss.MgO (s) + H2O (l) ↔ Mg(OH)2.nH2O (s)
22Preventing Shrinkage through Loss of Water When magnesia hydrates it consumes 18 litres of water per mole of magnesia probably more depending on the value of n in the reaction below:MgO (s) + H2O (l) ↔ Mg(OH)2.nH2O (s)The dimensional change in the system MgO + PC depends on:The ratio of MgO to PCWhether water required for hydration of PC and MgO is coming from stoichiometric mix water (i.e. the amount calculated as required), excess water (bleed or evaporative) or from outside the system.In practice tec-cement systems are more closed and thus dimensional change is more a function of the ratio of MgO to PCAs a result of preventing the loss of water by closing the system together with expansive stoichiometry of MgO reactions (see below).↔ molar mass (at least!)liquid ↔ molar volumes (at least!)It is possible to significantly reduce if not prevent (drying, plastic, evaporative and some settlement) shrinkage as a result of water losses from the system.The molar volume (L.mol-1)is equal to the molar mass (g.mol-1) divided by the density (g.L-1).
23Preventing Shrinkage through Loss of Water Portland cements stoichiometrically require around % water for hydration yet we add approximately 45 to 60% at cement batching plants to fluidise the mix sufficiently for placement.If it were not for the enormous consumption of water by tri calcium aluminate as it hydrates forming ettringite in the presence of gypsum, concrete would remain as a weak mush and probably never set.26 moles of water are consumed per mole of tri calcium aluminate to from a mole of solid ettringite. When the ettringite later reacts with remaining tri calcium aluminate to form monosulfoaluminate hydrate a further 4 moles of water are consumed.The addition of reactive MgO achieves water removal internally in a closed system in a similar way.MgO (s) + H2O (l) ↔ Mg(OH)2.nH2O (s)
24Stop Press – Confirmation of Brucite Hydrates UK Student 17/10/05 to John HarrisonBrucite indeed gains more weight when cured at 98% RH forming probably a Mg(OH)2.nH2O phase. Further research is under way to establish the stability and nature of this phase (what is n number and whether it desiccates). So far, thermo gravimetric analysis showed that the weight loss of Mg(OH)2.nH2O --> MgO is between 39% and 42%, significantly more than the expected 30.8% (Mg(OH)2 --> MgO).
25Other Benefits of Preventing Shrinkage through Loss of Water Internal water consumption also results in:Greater strengthMore complete hydration of PC .Reduced in situ voids:paste ratioGreater densityIncreased durabilityHigher short term alkalinityMore effective pozzolanic reactions.Small substitutions of PC by MgO result in water being trapped inside concrete as Brucite and Brucite hydrates which can later self desiccate delivering water to hydration reactions of calcium silicates (Preventing so called “Autogenous” shrinkage).
26Bleeding is a Bad Thing Better to keep concretes as closed systems Bleeding is caused by:Lack of finesToo much waterBleeding can be fixed by:Reducing water or adding finesAir entrainment or grading adjustmentsBleeding causes:Reduced pumpabilityLoss of cement near the surface of concretesDelays in finishingPoor bond between layers of concreteInterconnected pore structures that allow aggressive agents to enter laterSlump and plastic cracking due to loss of volume from the systemLoss of alkali that should remain in the system for better pozzolanic reactionsLoss of pollutants such as heavy metals if wastes are being incorporated.Concrete is better as a closed systemBetter to keep concretes as closed systems
27Dimensional Control in Tec-Cement Concretes over Time By adding MgO volume changes are minimised to close to neutral.So far we have observed significantly less shrinkage in TecEco tec - cement concretes with about (8-10% substitution OPC) with or without fly ash.At some ratio, thought to be around % reactive magnesia and 90 – 95% OPC volume changes cancel each other out.The water lost by concrete as it shrinks is used by the reactive magnesia as it hydrates eliminating shrinkage.Note that brucite is > mass% water and it makes sense to make binders out of water!More research is required to accurately establish volume relationships.
29Long Term pH controlTecEco add reactive magnesia which hydrates forming brucite which is another alkali, but much less soluble, mobile or reactive than Portlandite.Brucite provides long term pH control.A pH in the range 10.5 – 11.2 is ideal in a concrete
30Reducing Cracking as a Result of Volume Change caused by Delayed Reactions An Alkali Aggregate Reaction Cracked Bridge ElementPhoto Courtesy Ahmad Shayan ARRB
31Types of Delayed Reactions There are several types of delayed reactions that cause volume changes (generally expansion) and cracking.Alkali silica reactionsAlkali carbonate reactionsDelayed ettringite formationDelayed thaumasite formationDelayed hydration or dead burned lime or periclase.Delayed reactions cause dimensional distress, cracking and possibly even failure.
32Reducing Delayed Reactions Delayed reactions do not appear to 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 the reactive magnesia in Tec-cement concretes consumes unbound water from the pores inside concrete.Magnesia dries concrete out from the inside. Reactions do not occur without water.
33Reduced Steel Corrosion Related Cracking Rusting Causes Dimensional DistressSteel remains protected with a passive oxide coating of Fe3O4 above pH 8.9.A pH of over 8.9 is maintained by the equilibrium Mg(OH)2 ↔ Mg++ + 2OH- for much longer than the pH maintained by Ca(OH)2 because:Brucite does not react as readily as Portlandite resulting in reduced carbonation rates and reactions with salts.Concrete with brucite in it is denser and carbonation is expansive, sealing the surface preventing further access by moisture, CO2 and salts.
34Reduced Steel Corrosion 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 are bound by magnesiumMagnesium oxychlorides or oxysulfates are formed. ( Compatible phases in hydraulic binders that are stable provided the concrete is dense and water kept out.)As a result of the above the rusting of reinforcement does not proceed to the same extent.Cracking or spalling due to rust does not occur
35Steel Corrosion is Influenced by 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 , allowing a wider range of aggregates to be used, reducing problems such as AAR and etching. The pH is still high enough to keep Fe3O4 stable in reducing conditions.Eh-pH or Pourbaix Diagram The stability fields of hematite, magnetite and sideritein aqueous solution; total dissolved carbonate = 10-2M.Steel corrodes below 8.9Equilibrium pH of Brucite and of lime
36Reducing Cracking Related to Autogenous Shrinkage Autogenous shrinkage tends to occur in high performance concretes in which dense microstructures develop quickly preventing the entry of additional water required to complete hydration.First defined by Lynam in 1934 (Lynam CG. Growth and movement in Portland cement concrete. London: Oxford University Press; p )The autogenous deformation of concrete is defined as the unrestrained, bulk deformation that occurs when concrete is kept sealed and at a constant temperature.
37Reducing Cracking Related to Autogenous Shrinkage Main cause is stoichiometric or chemical shrinkage as observed by Le Chatelier.whereby the reaction products formed during the hydration of cement occupy less space than the corresponding reactants.A dense cement paste hydrating under sealed conditions will therefore self-desiccate creating empty pores within developing structure. If external water is not available to fill these “empty” pores, considerable shrinkage can result.Le Chatelier H. Sur les changements de volume qui accompagnent Ie durcissement des ciments. Bulletin de la Societe d'Encouragement pour I'Industrie Nationale 1900:54-7.
38Reducing Cracking Related to Autogenous Shrinkage Autogenous shrinkage does not occur in high strength tec-cement concretes because:The brucite hydrates that form desiccate back to brucite delivering water in situ for more complete hydration of Portland cement.Mg(OH)2.nH2O (s) ↔ MgO (s) + H2O (l)As brucite is a relatively weak mineral is compressed and densifies the microstructure.The stoichiometric shrinkage of Portland cement (first observed by Le Chatelier) is compensated for by the stoichiometric expansion of magnesium oxide on hydration.MgO (s) + H2O (l) ↔ Mg(OH)2.nH2O (s)↔ molar mass (at least!)liquid ↔ molar volumes (at least 116% expansion, probably more initially before desiccation as above!)
39Improved Durability Reasons for Improved Durability: Materials that last longer need replacing less often saving on energy and resources.Reasons for Improved Durability:Greater Density = Lower PermeabilityPhysical Weaknesses => Chemical AttackRemoval of Portlandite with the Pozzolanic Reaction.Removal or reactive componentsSubstitution by Brucite => Long Term pH controlReducing corrosion
40Reduced PermeabilityAs 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 CO2TecEco 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 therefore stronger more durable and less permeable. Cement powder is not lost near the surfaces. Tec-cements have a higher salt resistance and less corrosion of steel etc.
41Greater Density – Lower Permeability Concretes have a high percentage (around 18% – 22%) of voids.On hydration magnesia expands >=116.9 % filling voids and surrounding hydrating cement grains => denser concrete.On carbonation to nesquehonite brucite expands 307% sealing the surface.Lower voids:paste ratios than water:binder ratios result in little or no bleed water, lower permeability and greater density.
42Densification During the Plastic Phase Water is required to plasticise concrete for placement, however once placed, the less water over the amount required for hydration the better. Magnesia consumes water as it hydrates producing solid material.Less water results in increased density and concentration of alkalis - less shrinkage and cracking and improved strength and durability.
43Durability - Reduced Salt & Acid Attack 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 it is a least 5 orders of magnitude less soluble, mobile or reactive.Ksp brucite = 1.8 X 10-11Ksp Portlandite = 5.5 X 10-6TecEco cements are more acid resistant than Portland cementThis is because of the relatively high acid resistance (?) of Lansfordite and nesquehonite compared to calcite or aragonite
44Less Freeze - Thaw Problems Denser concretes do not let water in.Brucite will to a certain extent take up internal stressesWhen magnesia hydrates it expands into the pores left around hydrating cement grains:MgO (s) + H2O (l) ↔ Mg(OH)2 (s)↔ molar mass↔ molar volumes↔ molar volumesAt least 38% air voids are created in space that was occupied by magnesia and water!Air entrainment can also be used as in conventional concretesTecEco concretes are not attacked by the salts used on roads
45Rosendale Concretes – Proof of Durability Rosendale cements contained 14 – 30% MgOA major structure built with Rosendale cements commenced in 1846 was Fort Jefferson near key west in Florida.Rosendale cements were recognized for their exceptional durability, even under severe exposure. At Fort Jefferson much of the 150 year-old Rosendale cement mortar remains in excellent condition, in spite of the severe ocean exposure and over 100 years of neglect. Fort Jefferson is nearly a half mile in circumference and has a total lack of expansion joints, yet shows no signs of cracking or stress. The first phase of a major restoration is currently in progress.More information from
46Using Wastes and Non-Traditional Aggregates to Make TecEco Cement Concretes As the price of fuel rises, the use of on site low embodied energy materials rather than carted aggregates will have to be considered.No longer an option?Recent natural disasters such as the recent tsunami and Pakistani earthquake mean we urgently need to commercialize TecEco technologies because they provide benign environments allowing the use of many local materials and wastes without delayed reactions
47Using Wastes and Non-Traditional Aggregates to Make TecEco Cement Concretes Many wastes and local materials can contribute physical property values.Plastics for example are collectively light in weight, have tensile strength and low conductance.Tec, eco and enviro-cements will allow a wide range of wastes and non-traditional aggregates such as local materials to be used.Tec, enviro and eco-cements are benign binders that are:low alkali reducing reaction problems with organic materials.stick well to most included wastesTec, enviro and eco-cements can utilize wastes including carbon to increase sequestration preventing their conversion to methaneThere are huge volumes of concrete produced annually (>2 tonnes per person per year)
48Solving Waste & Logistics Problems TecEco cementitious composites represent a cost affective option forusing non traditional aggregates from on site reducing transports costs and emissionsuse and immobilisation of waste.Because they havelower reactivityless waterlower pHReduced solubility of heavy metalsless mobile saltsgreater durability.denser.impermeable (tec-cements).dimensionally more stable with less shrinkage and cracking.homogenous.no bleed water.TecEco Technology - Converting Waste to Resource
49Role of Brucite in Immobilization In a Portland cement Brucite matrixPC derive CSH takes up lead, some zinc and germaniumPozzolanic CSH can take up mobile cationsBrucite and hydrotalcite are both excellent hosts for toxic and hazardous wastes.Heavy metals not taken up in the structure of Portland cement minerals or trapped within the brucite layers end up as hydroxides with minimal solubility.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.Layers of electronically neutral brucite suitable for trapping balanced cations and anions as well as other substances.Salts and other substances trapped between the layers.Van de waals bonding holding the layers together.
50Lower Solubility of Metal Hydroxides There is a 104 differenceAll waste streams will contain heavy metals and a strategy for long term pH control is therefore essential
51Easier to Finish Concretes Easier to pump and finish Concretes are likely to have less water added to them resulting in less cracking
52Non Newtonian Rheology The strongly positively charged small Mg++ atoms attract water (which is polar) in deep layers introduce a shear thinning property affecting the rheological properties and making concretes less “sticky” with added pozzolanIt is not known how deep these layers getEtc.Etc.Ca++ = 114, Mg++ = 86 picometres
53Bingham Plastic Rheology TecEco concretes and mortars are:Very homogenous and do not segregate easily. They exhibit good adhesion and have a shear thinning property.Exhibit Bingham plastic qualities and react well to energy input.Have good workability.TecEco concretes with the same water/binder ratio have a lower slump but greater plasticity and workability.TecEco tec-cements are potentially suitable for mortars, renders, patch cements, colour coatings, pumpable and self compacting concretes.A range of pumpable composites with Bingham plastic properties will be required in the future as buildings will be “printed.”
54Problems with Portland Cement Fixed StrengthFaster & greater strength development even with added pozzolansWater removal by magnesia as it hydrates in tec-cements results in a higher short term pH and therefore more affective pozzolanic reactions.Brucite hydrate fills pore spaces taking up mix and bleed water as it hydrates reducing voids and shrinkage (brucite hydrate is > mass% water!). Greater density (lower voids:paste ratio) and lower permeability results in greater strength.Possible formation of Mg Al hydrates.Strength from self compaction
55Problems with Portland Cement Fixed (1) Durability and PerformancePermeability and DensitySulphate and chloride resistanceCarbonationCorrosion of steel and other reinforcingTecEco tec - cements areDenser and much less permeableDue mainly to the removal of water by magnesia and associated volume increasesProtected by bruciteWhich is 5 times less reactive than PortlanditeNot attacked by salts,Do not carbonate readilyProtective of steel reinforcing which does not corrodedue to maintenance of long term pH.
56Problems with Portland Cement Fixed (2) Durability and PerformanceIdeal lower long term pHDelayed reactions (eg alkali aggregate and delayed ettringite)As Portlandite is removedThe pH becomes governed by the pH of CSH and Brucite andIs much lower at aroundStabilising many heavy metals andAllowing a wider range of aggregates to be used without AAR problems.Reactions such as carbonation are slower andThe pH remains high enough to keep Fe3O4 stable for much longer.Internal delayed reactions are preventedDry from the inside out andHave a lower long term pH
57Problems with Portland Cement Fixed (3) ShrinkageCracking, crack controlNet shrinkage is reduced due to:Stoichiometric expansion of magnesium minerals, andReduced water loss.RheologyWorkability, time for and method of placing and finishingThe Mg++ ion adds a shear thinning making TecEco cements very workable.Hydration of magnesia rapidly adds early strength for finishing.
58Problems with Portland Cement Fixed (4) Improved PropertiesTecEco cementsCan have insulating propertiesHigh thermal mass andLow embodied energy.Many formulations can be reprocessed and reused.Brucite bonds well and reduces efflorescence.Properties (contd.)Fire RetardationBrucite, hydrated magnesium carbonates are fire retardantsTecEco cement products put out fires by releasing CO2 or water at relatively low temperatures.CostNo new plant and equipment are required. With economies of scale TecEco cements should be cheaper
59Problems with Portland Cement Fixed (5) Sustainability issuesEmissions and embodied energiesTec, eco and enviro-cementsLess binder is required for the same strengthUse a high proportion of recycled materialsImmobilise toxic and hazardous wastesCan use a wider range of aggregates reducing transport emissions andHave superior durability.Tec-cementsUse less cement for the same strengthEco-cements reabsorb chemically released CO2.