Classifications

• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
  • C04B28/30—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing magnesium cements or similar cements
  • C04B28/32—Magnesium oxychloride cements, e.g. Sorel cement
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
  • C04B28/02—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing hydraulic cements other than calcium sulfates
  • C04B28/04—Portland cements
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
  • C04B28/02—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing hydraulic cements other than calcium sulfates
  • C04B28/06—Aluminous cements
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
  • C04B28/02—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing hydraulic cements other than calcium sulfates
  • C04B28/10—Lime cements or magnesium oxide cements
  • C04B28/105—Magnesium oxide or magnesium carbonate cements
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
  • C04B2111/20—Resistance against chemical, physical or biological attack
  • C04B2111/23—Acid resistance, e.g. against acid air or rain
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
  • C04B2111/20—Resistance against chemical, physical or biological attack
  • C04B2111/24—Sea water resistance
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
  • Y02W30/00—Technologies for solid waste management
  • Y02W30/50—Reuse, recycling or recovery technologies
  • Y02W30/91—Use of waste materials as fillers for mortars or concrete

Definitions

• This invention relates to magnesium cements and in particular to cements containing magnesium oxide (magnesia). Background to the Invention
• Magnesium oxychlorides were first discovered and prepared by Sorel in 1867. Magnesium oxysulphates were discovered by Olmer and Delyon in 1934 . Magnesium oxychlorides and oxysulphates are commonly referred to as Sorel cements.
• a number of compounds are formed when magnesia reacts with magnesium chloride to form oxychlorides.
• the main bonding phases so far found in hardened cement pastes are Mg(OH) 2 , (Mg(OH) 2 )3 .MgCl 2 .8H 0 and (Mg(OH) 2 )5.MgCl 2 .8H 2 0.
• soluble silicates such as sodium silicate has been described as a means of improving the water resistance of Sorel type cements. These cements are of little practical use however because of the high cost of soluble silicates.
• Magnesia reacts with soluble phosphates to precipitate almost totally insoluble magnesium phosphate.
• a range of magnesium phosphate cements has been used including magnesium ammonium phosphate which is thought to be formed by an acid- base reaction between magnesia and di hydrogen ammonium phosphate. This results in an initial gel formation followed by the crystallisation into an insoluble phosphate, mainly magnesium ammonium phosphate hexahydrate, [NH 4 M P ⁇ 4 .6H 2 0].
• the magnesium oxide used in this system is produced by calcining at higher temperatures and is referred to in the industry as being "dead burned" and is not as reactive as magnesia made at lower temperatures.
• a set retarder typically either borax or boric acid is also used to give a workable set time.
• High-lime magnesiochrome cement finds use in refractories.
• the cement is based upon magnesia plus calcium chromate - chromite, a complex mineral produced by the combination of lime with chrome oxide (Cr 2 0 3 ) in an oxidising environment. Hydration is normally performed with a 30% aqueous solution of magnesium chloride hexahydrate (MgCl 2 .6H 2 0) solution at 8 per cent by weight of the cement.
• the products are complex. As well as hydrates they also consist of carbonates, which are formed by the effects of carbonation. Typical products formed can include brucite [Mg(OH) 2 ], various magnesium oxychlorides
• cementitious magnesia compounds include hydroxychlorides and sulphates such as Mg(OH) 2 .MgCl 2 .8H 2 0, hydroxy carbonates [Mg 5 (OH) 2 (C0 3 ) 4 .4H 2 0] and hydroxy chloro carbonates [e.g.
• the invention provides in one form a cement composition that includes reactive magnesium oxide at a level of at least 5% w/w of hydraulic cementitious components.
• the magnesium oxide is prepared by low temperature calcination and fine grinding.
• cementitous components can include any hydraulic cement including Portland type cements, calcium aluminate cements, alinite cements, belinite cements, belite cements, hydrogarnet cements and ferrari cements as well as other magnesium cements such as Sorel cements.
• Portland type cements calcium aluminate cements
• alinite cements alinite cements
• belinite cements belite cements
• hydrogarnet cements hydrogarnet cements and ferrari cements
• other magnesium cements such as Sorel cements.
• Sorel cements include water in their composition and are therefore considered as hydraulic cements.
• the composition further includes at least 10% of a pozzolan.
• the hydraulic cement composition includes ground Portland cement clinker type minerals.
• the present invention provides cement compositions containing substantial proportions of reactive magnesia that hydrates to form brucite which is a useful cementitious component. They generally but not always contain a high proportion of pozzolans, many of which are wastes such as fly ash.
• the compositions include the blending of reactive magnesia with hydraulic cements, preferably Portland cements but also other cements including other magnesium cements and/or the use of various accelerators as a means of improving the setting and hardening times and early strength. Both blending with other cements and the use of accelerators as formulation strategies can be used independently, or sometimes combined to advantage rendering brucite useful as a binder in a cement matrix.
• magnesia When other commercially useful cements are blended with reactive magnesia in the formulations provided for in this invention ultimate strength is also improved.
• the magnesia in turn provides a virtually insoluble matrix of high pH in which most other cements are stable and affords a degree of protection in normally aggressive solutions such as sulphates.
• MgO reactive magnesia
• the magnesium oxide and ground Portland clinker weight ratio may vary depending on the rate of strength gain and ultimate strength required or desired sustainability.
• the ratio of reactive magnesia to ground Portland clinker is in the range 1:3 to 2:1.
• Higher proportions of the magnesia - Portland component result in more rapid setting times, particularly when the ratio of Portland cement to reactive magnesia is also higher.
• the addition of pozzolans is not necessary as a strong cement is produced by merely blending Portland cement clinker minerals and reactive magnesia.
• accelerators are both an additional and alternative technique to improve early setting and hardening times. If accelerators such as ferrous sulphate are used whether with blends of reactive magnesia and pozzolans alone (an alternative technique) or also with other cementitious components (an additional technique) they are added in small proportion only (less than 20% of the MgO proportion).
• a particular embodiment of the strategy of blending magnesia with Portland clinker minerals was made with the following proportions that achieved high strengths in the order of 12-20 mpa after pre curing for 48 hours followed by steaming at 55°C for 48 hours and then further curing for a period of three weeks.
• the composition was made by mixing as dry powders 600 g (94% by weight) fly ash from the Gladstone power station in Australia, 30 g (4.67 % by weight) reactive magnesia ground to 95% passing 45 micron and 100% passing 125 micron (branded as XLM and from Causmag in Australia) and 12 g (1.87 % by weight) ground Portland cement clinker ground to 100% less than 125 micron from Australian Cement in Railton Switzerland. Water was added to make a stiff paste and this was then vibrated into moulds. After approximately six weeks the sample reached a strength approaching 20 mpa and was resistant to sulphates and other solutions aggressive to Portland cement.
• Portland cements containing magnesium oxide are currently termed “unsound” and the use of limestones containing magnesium for making Portland cements is avoided.
• the reason why is because when magnesite or dolomite, present as an "impurity" contained in limestone, is slaked at high temperatures during the manufacture of Portland cement, a highly unreactive oxide termed “dead burned magnesia” is produced which hydrates long after other cementitious components when water is added.
• Magnesite begins decomposing to the oxide at a substantially lower temperatures and pressure than limestone (CaC0 3 ) This is true of mixtures of limestone and magnesite as well as for the distinguishable mineral dolomite which contains both magnesium and calcium as carbonates.
• Portland cement is typically made between 1450°C and 1500°C. At these temperatures any magnesium carbonate content becomes unreactive due to the formation of larger more defined crystals with less surface area and lower porosity than at lower temperatures.
• Magnesia produced in this manner referred to as 'dead burned', is unreactive and hydrates very slowly - usually long after the other components in a cement such as Portland cement have hydrated. As a result stresses are introduced resulting in what is often termed unsound cement. Because of this magnesium oxides have been condemned for many years in Portland cement. Unreactive magnesia is also unsuitable for use in the present invention.
• magnesia and other cements and in particular Portland type cements The key for the successful blending of magnesia and other cements and in particular Portland type cements is that the hydration rates of all components in the cement must be matched.
• magnesia component In order to achieve this the magnesia component must be separately calcined at lower temperatures and in conditions that are suitable for the manufacture of reactive magnesia, ground to a fine size depending on the reactivity required and only then blended with other cementitious components, pozzolans or both.
• Suitable magnesia should be calcined at low temperatures (less than
• a test for reactivity is the citric acid test and low temperature calcined magnesia ground to 95% passing 45 micron tests at about 10 seconds using this method which uses .5g sodium benzoate, 28g citric acid monhydrate and .lg phenolphthaleim dissolved in water and diluted to 1 litre. If the above small amounts of sodium benzoate and phenophthaleim do not dissolve, a small amount of methylated spirits should be used as well.
• the prepared solution is stored in a water bath at 30°C ⁇ 0.2 C.
• the test method is to first weigh a 2.00g sample of magnesia on a watch glass. Then Pipette 100ml of the prepared solution in to a dry 250ml tall form beaker. Add the 2.00g powder sample previously weighed and stir (preferably with a magnetic stirrer) immediately. Record the time in seconds for the stirred solution to turn pink.
• the reactivity and hydration rates of hydraulic cements, and in particular Portland clinker products, magnesia and lime are affected by the temperature and conditions of calcining as well as the particle porosity, texture and size and the porosity, texture and size of interspersed components such as pozzolans including fly ash and can therefore be engineered to match mainly by varying slaking temperatures and grind sizes.
• volume changes are approximately neutral to prevent structural defects occurring during setting and volume changes are related to reactivity.
• brucite As the magnesia component of the cements provided for in this invention hydrates, brucite is formed which is highly insoluble (Ksp 1.8 x 10 " ⁇ , equivalent to .018g/litre) and it blocks off access to water for further hydration.
• the addition of pozzolans such as fly ash tends to reduce the amount of brucite that needs to form for strength to develop and negates the blocking off affect of the advancing brucite reaction front as well as taking up minute volume changes (if any) and acting as a microaggregate at a microscopic level.
• Pozzolans including natural pozzolans and artificial pozzolans such as fly ash and other wastes also react with the free lime component included in Portland cement clinker products and formed as a result of the hydration of calcium silicates to produce more calcium silicates that also hydrate and further bond the components of the cement together. Inter particle surface interaction also results in chemical as well as physical bonding between fine grains of pozzolan and other cementitious components and between the pozzolan grains themselves.
• the grains of pozzolan also provide nucleation sites for the hydration of other components of the cement.
• pozzolan is used to described materials containing silicon and aluminium that react with or are activated by an alkali, and in the presence of water form stable silicon and aluminium compounds.
• Wastes which are pozzolans and which contribute to strength given the longer term or shorter periods if accelerated by accelerators also described or by heating preferably in a moist environment are wastes produced by the agriculture and mining industry in increasing amounts such as reactive fly ash, flue wastes, iron ore slag, and other wastes from the metal production industry as well as silica fume, ground brick, and sewerage sludge ash.
• Passive wastes take no chemical part in the formation of a cement and include, sawdust, unburnt rice husks, some mine tailings, mineral extraction wastes etc. and virtually all may be used as fillers. A high proportion can be added without loss in strength and add to abrasion resistance (and in many cases workability). If fine enough they act as micro aggregates and often result in greater strength.
• fly ash is economically the most important and has been found to make a slightly better cement when combined with magnesia than ground vitrified iron ore slag and the reasons for this could be that the heat treatment has been more appropriate and the silicon alumina ratio is closer to ideal proportions.
• Ground bauxite or brick has been found to increase strength when added to mixtures of magnesia and fly ash. As mixtures of magnesia and silica fume hardly show any strength but mixtures of magnesia silica fume and bauxite do the increased reactivity due to the inclusion of bauxite is probably a function of the addition of alumina, but this has not been proven as it may also be due to a concentration affect. It has also been found possible to include large amounts of waste containing alumina such as "red mud" which is a waste form the aluminium industry.
• red mud contains soluble sodium compounds, particularly sodium carbonate, sodium sulphate is produced and could be effectively recovered.
• the carbonates remain as siderite, or alternatively combine with the magnesium forming magnesite and hydromagnesite.
• Bauxite may also be used as a source of alumina depending on the alumina content of the primary waste and is available in large quantities at low cost.
• Bauxite consists mainly of gibbsite (A1 2 0 3 .3H 2 0), boehmite (A1 2 0 3 .H 2 0), and diaspore, which has the same composition as boehmite but is denser and harder.
• Sewerage sludge ash besides being a source of reactive silica and alumina and therefore a pozzolan, is a rich source of soluble phosphates.
• the phosphates react readily with magnesia forming mostly stable insoluble phosphates which have good binding properties.
• the residue from burning organic wastes such as rice husks is also reactive and may contain ideal quantities of silica and alumina.
• gypsum limestone and other additives normally used in Portland cement is usually unnecessary.
• gypsum does not appear to be deleterious and may even have a small advantage as a set regulator for the Portland cement component, accelerator for the magnesium oxide component and flocculation agent, commercial Portland cement containing a small percentage of ground gypsum may be used as an alternative to pure ground Portland clinker materials in virtually any ratio.
• calcareous magnesite and dolomite can be of economic advantage, particularly if fluxes such as sodium chloride or fluoride are added. Both calcareous magnesite and dolomite can be slaked at temperatures insufficient to break down the calcium carbonate to make a mix of magnesia and calcium carbonate suitable for the manufacture of cements described in this invention
• Reactive magnesia added during the final stages of manufacture of other cements such as calcium aluminate cements, slag cements, Sorel cements and geopolymeric cements etc. can also be an advantage.
• accelerants There are three main classes of accelerants that can be used in the composition of the present invention: 1. Alkaline chemicals which mobilise silica and alumina.
• Alkaline chemicals that accelerate the setting of Portland cement include chemicals such as alkali and alkali earth hydroxides, carbonates, formates, aluminates and silicates.
• alkaline accelerants work with the composition of the present invention. If Portland cement is included in the blend they aid the formation not only of calcium aluminates but also of calcium silicates by mobilising silica and alumina, both of which are much more soluble in an alkaline environment.
• alkaline accelerants Some of the alkaline accelerants that have been tested are listed below in order of effectiveness.
• sodium silicate and sodium aluminate The most affective in this group are sodium silicate and sodium aluminate, and of these sodium silicate is known to be an accelerator of geopolymeric reactions.
• accelerants are acids and in particular soluble salts of acids and generally both the cation and anion contribute to the overall affect facilitating the dissolution of magnesia and lime. Although early setting is accelerated long term strength is generally reduced.
• accelerators that are salts of acids such as ferrous sulphate, it is important to note that initial setting may be accelerated, but the addition of too much does not contribute to longer term hardening and can be deleterious.
• triethanolamine works by combining with aluminium dissolving tricalcium aluminate prior to formation of tricalcium aluminate hydrate. Too much causes retardation of tricalcium silicate hydrate.
• Iron salts including sulphates and chlorides and in particular ferrous sulphate are the most recommended accelerants because of cost and environmental benefits as many of them are wastes.
• reactive magnesia can be blended with a range of hydraulic and chemical cements and iron salts can also be used in many such blends including the commercially more important blends with ground Portland clinker minerals discussed.
• the quantity added should be kept as low as possible to achieve the required initial set. Iron salts do not appear to contribute to final strength, and if too much is added this may even be reduced.
• Ferrous sulphate is recommended in most instances because it is less aggressive than ferric sulphate or ferrous or ferric chloride for instance and also cheaper.
• a small percentage (.5 - 20 % of the MgO content) of ferrous sulphate is effective in accelerating the initial setting of cements made using a proportion of added reactive magnesium oxide and in particular with blends of such cements with pozzolans including pozzolanic wastes such as fly ash. The amount added depends on a number of factors including the reactivity of the magnesia and other components of the cement.
• iron salts The specific role of iron salts is to speed up initial setting. Small quantities do not appear to affect final strength and hardness however if too much is added reactions are too rapid and cracking and increased susceptibility to weathering result. It is believed that initially an acid base reaction takes place with the sulphate (or chloride) forming magnesium sulphate (or chloride) and in the presence of calcium, calcium sulphate (or chloride). This acid base reaction serves to mobilise the magnesium which ends up mostly as magnesium hydroxide (brucite). The iron initially forms a hydroxide but generally ends up in iron minerals such as haematite and magnetite. Iron is also bound into ferro brucite and amakinite and a number of other compounds.
• magnesium sulphate or chlorides formed then react with magnesium hydroxide resulting in compounds such as magnesium oxysulphates or oxychlorides that also act to bind the cement.
• magnesium hydroxide resulting in compounds such as magnesium oxysulphates or oxychlorides that also act to bind the cement.
• the continued hydration of brucite takes over as the principle setting mechanism depending on the proportions.
• ferrous sulphate is also not anywhere near as hygroscopic as either magnesium sulphate or magnesium chloride used in the manufacture of Sorel cements and in a dry atmosphere it can be ground to a fine size enabling the economical production of "all in the bag" mixes.
• cements containing a high proportion of reactive magnesia small quantities (.5 to 20% of the MgO content) of ferrous sulphate reduces setting times considerably and it is possible to cause such cements to set with sufficient moulding strength (.5-5 mpa) within just a few hours.
• Some other sulphate or chloride salts of elements with a similar ionic radius to iron and of similar charge have a similar affect but are not cost effective, e.g salts of manganese.
• Ferric sulphate reacts with magnesia more aggressively than ferrous sulphate and therefore whether ferrous or ferric sulphate is used depends on the reactivity of the magnesia (which in turn depends on slaking temperature, particle size and age) and other materials added. The same applies to ferrous and ferric chloride, but costs and comparative lack of strength do not favour then- use except when stronger magnesium oxy-chloride cements are to be modified by the inclusion of iron. It is recommended that the amount and type of iron salt added is determined by trial and error as the reactions in the case of pure magnesia depend on the reactivity of the magnesia, particle size etc. and if pozzolans including wastes such as fly ash are also added, are heavily masked.
• blended wastes may also have a masking affect and more or less quantity or more or less aggressive iron salts may need to be used depending on the nature of the waste, be it fly ash, sewerage ash, rice husks etc all of which vary in reactivity.
• iron salts As the reaction of magnesia with iron salts is exothermic, and can get too warm if too much iron salt is added, care needs to be taken.
• steam or autoclaving is also used needs to be considered as reaction rates roughly double with every 10 deg. rise in temperature, whereas increases in pressure do not have quite such a marked affect.
• the graph below shows strength on the vertical axis determined on an apparatus for measuring comparative compressive and shear strength on an arbitrary linear scale. (The scale is arbitrary in that it has not been equated to standard test units. The results produced by the apparatus are however very consistent and thus can be used for comparison purposes.)
• the horizontal axis is time.
• the cementitious minerals forming in the above example include brucite, ferro brucite, amakinite, iron oxysulphate, magnesium (iron) oxysulphate (see below) haematite and magnetite and near the surface, where access to C02 is possible, hydromagnesite and magnesite and a magnesium hydroxy sulpho carbonate. Ultimately silicates and aluminates, and their hydrates form very slowly.
• Brucite is the main cementing phase and the structure consists of layers of hydroxyls with magnesium in between. Fe " " " " substitutes for Mg* " in brucite forming a mineral known as akmanite and this may even be slightly stronger than brucite.
• a fine dispersion of magnetite also often occurs in the structure, possibly also adding to strength. It has been found that the addition of iron salts is compatible with Sorel cements as well as Portland and many other hydraulic cements. Ferrous sulphate or ferric sulphate are most compatible with magnesium sulphate forming a magnesium oxysulphate cement that contains haematite. Iron may also be present as an oxysulphate and may substitute for magnesium in magnesium oxysulphates.
• iron chlorides blend best with magnesium chloride and iron sulphates with magnesium sulphate, however, as in the case of Sorel cements where the addition of magnesium sulphate and magnesium chloride can be mixed, mixtures of both iron sulphate and magnesium chloride or iron chloride and magnesium sulphate set effectively, and can be an advantage if calcium is also present as the calcium hydroxide formed reacts with the sulphate forming calcium sulphate which in turn reacts with magnesium hydroxide producing more Sorel cement.
• a pozzolan such as fly ash or an alternative source of reactive silica and alumina is added to cements containing reactive magnesia (with or without added iron salts or salts used for making Sorel cements) the pozzolan reacts in a number of ways previously discussed including reacting with any free lime producing more calcium silicate hydrates if free lime is present such as caused by the addition of Portland clinker as well as surface hydrolysis and geopolymeric reactions occurring. Other reactions also occur very slowly involving Mg ++ and Fe "1-1" as a suitable environment is formed in which the very slow formation of magnesium (iron) silicates and aluminates occurs. Some minerals formed are not of great strength and are almost gel like such as sepiolite, others are weak such as hydrotalcite and talc but others such as enstatite and forsterite are strong minerals.
• Soluble silicates and aluminates can also be added to advantage encouraging the formation of silicate and aluminate minerals but cost will generally rule out the use of these materials.
• compositions of the present invention are that they able to accommodate a wide variety of extraneous cations and anions. Many of these extraneous cations and anions are thought to find their way into the open layered structure of brucite, where if the are toxic, they are rendered inert as long as the brucite does not dissolve.
• compositions of the present invention are generally not attacked by soft waters. Surface protection by carbonates ensues with most acid rains.
• the high reactive magnesia cement compositions described are also very resistant to sea and ground water attack and this is thought to be because brucite, the main component, is virtually insoluble at the pH of sea water (8.2) and in most ground waters and does not suffer ion replacement or decomposition in the same manner as the calcium silicate hydrate found in Portland cement as portlandite is replaced or leached out. Tests have confirmed resistance to agents such as glaubers salts, epsom salts, sodium chloride, ammonium nitrate and week organic acids.
• Neosyn EA is a sodium salt of naphthalene sulphonic acid polymer with formaldehyde. These appear to work in a manner similar to Portland cement affecting surface charge however in most situations they do not seem to be needed.

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