WO2009156740A1 - Binder composition - Google Patents

Binder composition Download PDF

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Publication number
WO2009156740A1
WO2009156740A1 PCT/GB2009/001610 GB2009001610W WO2009156740A1 WO 2009156740 A1 WO2009156740 A1 WO 2009156740A1 GB 2009001610 W GB2009001610 W GB 2009001610W WO 2009156740 A1 WO2009156740 A1 WO 2009156740A1
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WO
WIPO (PCT)
Prior art keywords
mgo
magnesium
composition
magnesium carbonate
binder
Prior art date
Application number
PCT/GB2009/001610
Other languages
French (fr)
Inventor
Nikolaos Vlasopoulos
Christopher Robert Cheeseman
Original Assignee
Novacem Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Family has litigation
First worldwide family litigation filed litigation Critical https://patents.darts-ip.com/?family=39989881&utm_source=google_patent&utm_medium=platform_link&utm_campaign=public_patent_search&patent=WO2009156740(A1) "Global patent litigation dataset” by Darts-ip is licensed under a Creative Commons Attribution 4.0 International License.
Priority to EA201100036A priority Critical patent/EA201100036A1/en
Priority to US12/736,928 priority patent/US8496751B2/en
Priority to JP2011515595A priority patent/JP2011525885A/en
Priority to EP09769581.1A priority patent/EP2297062B1/en
Priority to BRPI0914763-2A priority patent/BRPI0914763B1/en
Application filed by Novacem Limited filed Critical Novacem Limited
Priority to CN200980125190.7A priority patent/CN102083764B/en
Priority to MX2010013764A priority patent/MX2010013764A/en
Priority to CA2727072A priority patent/CA2727072C/en
Priority to AU2009263979A priority patent/AU2009263979B2/en
Publication of WO2009156740A1 publication Critical patent/WO2009156740A1/en
Priority to IL209547A priority patent/IL209547A0/en
Priority to ZA2010/08761A priority patent/ZA201008761B/en

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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
    • C04B28/02—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
    • C04B9/00—Magnesium cements or similar 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
    • C04B14/00—Use of inorganic materials as fillers, e.g. pigments, for mortars, concrete or artificial stone; Treatment of inorganic materials specially adapted to enhance their filling properties in mortars, concrete or artificial stone
    • C04B14/02—Granular materials, e.g. microballoons
    • 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
    • C04B22/00—Use of inorganic materials as active ingredients for mortars, concrete or artificial stone, e.g. accelerators, shrinkage compensating agents
    • C04B22/06—Oxides, Hydroxides
    • C04B22/066—Magnesia; Magnesium hydroxide
    • 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
    • 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
    • C04B9/00—Magnesium cements or similar cements
    • C04B9/02—Magnesium cements containing chlorides, e.g. Sorel cement

Definitions

  • This invention relates to a cement binder composition, i.e. a composition that is settable to a solid, and to the use of the binder composition in construction products.
  • Portland cement is the most common type of cement in general use at this time. It is an essential element of concrete, mortar and non-speciality grouts. Portland cement consists of over 90% Portland cement clinker, up to 5% gypsum and up to 5% other minor constituents. Portland cement clinker is a hydraulic material consisting mainly of dicalcium silicate (2CaCSiO 2 ), tricalcium silicate (3CaO-SiO 2 ), tricalcium aluminate (3CaO-AI 2 O 3 ) and calcium aluminoferrite (4CaO-AI 2 O 3 Fe 2 O 3 ) phases.
  • dicalcium silicate (2CaCSiO 2 ) tricalcium silicate
  • 3CaO-SiO 2 tricalcium silicate
  • 3CaO-AI 2 O 3 tricalcium aluminate
  • 4CaO-AI 2 O 3 Fe 2 O 3 calcium aluminoferrite
  • Magnesium oxide (MgO) can also be present in Portland cement, although its amount must not exceed 5% by mass' as its delayed hydration is believed to give rise to unsoundness in concrete.
  • Gypsum CaSO 4 .2H 2 O
  • the constituents of the cement hydrate forming a solid complex calcium silicate hydrate gel and other phases.
  • the manufacture of Portland cement is a highly energy intensive process that involves heating high volumes of raw materials to around 145O 0 C.
  • the basic raw material used in making Portland cement is calcium carbonate (limestone, CaCO 3 ), and this decomposes during processing to CaO, releasing additional geologically sequestered CO 2 .
  • the manufacture of Portland cement emits approximately 1 tonne CO 2 for every tonne of cement produced and is responsible for approximately 5% of all anthropogenic CO 2 emissions.
  • Binders based on systems other than calcium oxide and silicates are known.
  • Sorel cement (magnesium oxychloride cement or magnesia cement) is a hydraulic cement that is a mixture of magnesium oxide (burnt magnesia, MgO) and magnesium chloride together with filler materials like sand or crushed stone. It sets to a very hard abrasive-resistant material and so is used for grindstones, tiles, artificial stone (cast stone) and cast floors, in which application it has a high wear resistance.
  • MgO magnesium oxide
  • MgO magnesium oxide
  • MgO magnesium oxide
  • magnesium chloride magnesium chloride
  • magnesium based cements include magnesium oxysulfate cement and magnesium phosphate cements but both these have drawbacks, the former having a poor water resistance and the latter sets very fast so that it is difficult to work with.
  • GB-1160029 discloses cements based on mixing magnesium oxide (MgO), sodium chloride (NaCI) or sodium nitrate (NaNO 3 ) and calcium carbonate (CaCO 3 ).
  • CaCO 3 is used as a "moderating substance" to enable the salt and the MgO to perform the chemical reactions necessary to set, which are similar to those of the other Sorel cements.
  • These cements require the use of hard-burnt MgO 1 which is generally produced by high-temperature treatment ( ⁇ 1000°C) of magnesite (MgCO 3 ), which causes CO 2 emissions not only from the calcining of magnesite but also from the burning of fossil fuel.
  • US-5897703 discloses binder compositions based on mixing MgO with a hardening agent, propylene carbonate.
  • the magnesium oxide used can be any mixture of soft- burnt and hard-burnt MgO. It is known that in the presence of water, propylene carbonate decomposes to carbon dioxide and propylene glycol and so the addition of the propylene carbonate provides a source of CO 2 to carbonate the magnesium oxide.
  • US-6200381 discloses a dry powdered cement composition derived from dolomite (a magnesium and calcium carbonate mineral; MgCO 3 CaCO 3 ).
  • dolomite a magnesium and calcium carbonate mineral
  • MgCO 3 CaCO 3 a magnesium and calcium carbonate mineral
  • the dolomite is heated to decarbonate the MgCO 3 so that the composition contains CaCO 3 and a partially decarbonated MgCO 3, i.e. a mixture of MgCO 3 and MgO
  • Certain additives may be included in the composition (e.g. aluminium sulphate (AI 2 (SO 4 ) 3 ), citric acid, sulphuric acid (H 2 SO 4 ), NaCI, etc.), which assist the composition to set on addition of water; the water may be contaminated water, e.g. sea water.
  • the CaCO 3 component of the cement composition reacts with several of the specified additives that are used. For example, the addition of H 2 SO 4 will react with CaCO 3 yielding hydrated CaSO 4 (e.g. CaSO 4 .2H 2 O) and CO 2 . The CO 2 released assists the carbonation of MgO and Mg(OH) 2 .
  • NaCI may be added before the thermal treatment of dolomite to decrease the decarbonation temperature of MgCO 3 , and in the binder composition as an additive, where it appears to assist in achieving an early strength to the composition, which is probably due to reactions with MgO (Sorel cement type reactions).
  • CaCO 3 acts as a "moderating substance" to enable NaCI and the MgO to perform the necessary chemical reactions (see GB 1160029 above).
  • US-1867180 describes a cement composition based on slaked lime (Ca(OH) 2 ) that contains less than 1% MgO and NaCI.
  • US1561473 discloses that, when a wet mixture of aggregates and magnesium oxide is treated with gaseous or dissolved CO 2 , its tensile strength is improved. The composition must be exposed to CO 2 when wet and the patent discloses the exposure of the wet mixture to a special atmosphere of moist CO 2 .
  • WO 01/55049 discloses a dry powdered cement composition containing MgO, a hydraulic cement, such as Portland cement, Sorel cements or calcium aluminate cements, and optionally pozzolanic materials.
  • the cement composition can also contain various additives such as ferrous sulphate (FeSO 4 ), sodium or potassium silicates or aluminates, phosphoric acid (HPO 3 ) or phosphoric acid salts, copper sulphate (CuSO 4 ), and various other organic polymers and resins, such as polyvinyl acetate (PVA), vinylacetate-ethylene, styrene-butyl acrylate, butyl acrylate- methylacrylate, and styrene-butadiene.
  • PVA polyvinyl acetate
  • the magnesium oxide is obtained by low temperature calcining.
  • GB-529128 discloses the use of magnesium carbonate as an insulating material; it is made from concentrated sea water containing magnesium salts by precipitating the salts with alkali metal carbonates, which forms needle-like crystals that can set. A slurry of such crystals, when paced in a mould, will set to provide a slab or block that is useful as insulation. If there are any bicarbonate ions in the alkali metal carbonate, magnesium bicarbonate will form in the above reaction, which slows down the setting reaction. In order to counteract this, 1-5% magnesium oxide may be added, which will precipitate the bicarbonate as magnesium carbonate.
  • US-5927288 discloses that a mixture of hydromagnesite and magnesium hydroxide, when incorporated into a cigarette paper, reduces sidestream smoke.
  • the hydromagnesite/magnesium hydroxide compositions have a rosette morphology and the hydromagnesite/magnesium hydroxide mixture is precipitated from a solution of magnesium bicarbonate and possible other soluble magnesium salts by adding a strong base, e.g. potassium hydroxide.
  • EP-0393813 and WO 01/51554 relate to flame retardants for plastics.
  • EP-0393813 discloses that a mixture of a double salt of calcium and magnesium carbonate (e.g. dolomite), hydromagnesite, and magnesium hydroxide can provide flame resistance to thermoplastics, e.g. a sheath of an electric wire.
  • WO01/51554 teaches the addition of various magnesium salts, including hydromagnesite and magnesium hydroxide, to polymers.
  • US2009/0020044 discloses the capture of carbon dioxide by sea water to precipitate carbonates, which can be used in hydraulic cements; up to 10% of a pH regulating material, including magnesium oxide or hydroxide, can be added to the cement to regulate the pH.
  • a pH regulating material including magnesium oxide or hydroxide
  • JP2006 076825 is concerned with reducing the amount of CO 2 emitted from power stations and by the steel industry. It proposes capturing the CO 2 by reaction with ammonium hydroxide to form ammonium carbonate: 2NH 4 OH + CO 2 ⁇ (NH 4 ) 2 CO 3 +H 2 O
  • magnesium chloride is made by reacting magnesium oxide and hydrochloric acid
  • the magnesium chloride is reacted with the ammonium carbonate, which precipitates magnesium carbonate leaving a liquor containing dissolved ammonium chloride: (NH 4 ) 2 CO 3 + MgCI 2 ⁇ 2(NH 4 )CI + MgCO 3
  • the precipitated magnesium carbonate is filtered out and used as a cement component while the ammonium chloride liquor is treated to regenerate ammonium hydroxide and hydrochoric acid.
  • binders could be 'carbon neutral' if they are able to counteract or balance the release of CO 2 in the process of their production by absorbing CO 2 during a hardening stage following hydration; or 'carbon negative' if they are able to absorb and store more CO 2 than was released during their production.
  • This invention provides a cement binder composition based on MgO plus special magnesium carbonates (see Formula I below).
  • the magnesium oxide used can be soft-burnt MgO, hard-burnt MgO, or any mixture of soft-burnt and hard-burnt MgO.
  • a key ingredient of the cement composition is the special magnesium carbonate (either hydrated or unhydrated) in the form x MgCO 3 ⁇ y Mg(OH) 2 • z H 2 O Formula I where x is a number greater than 1 , and at least one of y or z is a number greater than O; the carbonate may be non-stoichiometric; x, y and z may be (but need not be) integers.
  • the composition may also comprise a hydroscopic material, such as NaCI.
  • the above formula I excludes the use of magnesite (MgCO 3 ) and dolomite (MgCO 3 CaCO 3 ) as the principal source of magnesium carbonate.
  • the composition can contain minor amounts of these minerals, e.g. up to 25% of the total magnesium carbonate content of the composition. It is preferred that substantially all the magnesium carbonate content of the composition is in accordance with Formula
  • the carbonate of the general formula I is hydromagnesite, which has the general formula 4MgCO 3 .
  • Mg(OH) 2 .4H 2 O although some degree of non-stoichiometry can be tolerated, e.g. x in the above formula I can be 3.5 - 4.5, y can be 0.5 - 1.5 and z can be 3.5.- 5.5. In addition, x, y and z may all be greater than 0.
  • the composition is preferably in the form of a dry powder that can be mixed with water, optionally together with other ingredients such as sand, gravel or other fillers (e.g. fly ash), to form a slurry of varying consistency that will set, i.e. the composition of the present invention is a hydraulic binder/cement.
  • the wet composition can be made plastic and workable by the addition of plasticisers.
  • the composition may include Mg(OH) 2 in place of some or all of the MgO.
  • the Mg(OH) 2 used should preferably have the low crystallinity, high surface area and the rosette-like morphology described below.
  • Such Mg(OH) 2 may be produced by pre-hydrating MgO in the presence of the special magnesium carbonates of the general formula I.
  • a minor part of any Mg(OH) 2 in the composition e.g. below 50% of the total Mg(OH) 2 content, may have a platelet morphology shown in Figure 2.
  • the Mg(OH) 2 morphology formed in accordance with the present invention has a higher surface area per unit weight than Mg(OH) 2 having a platelet morphology; the latter will normally have a surface area of less than 45 m 2 /g whereas the former has a surface area of at least 45 m 2 /g, generally higher than 70 m 2 /g (surface area values were measured according to the Brunauer-Emmett-Teller (BET) method).
  • BET Brunauer-Emmett-Teller
  • Mg(OH) 2 in the binder composition in place of MgO reduces the green strength and the set strength of the hydrated binder because most of the strength of the binder of the present invention results from MgO hydration, but this is acceptable in certain applications, e.g. in mortars or plasters; an excessively strong mortar for bonding together blocks and bricks in the construction of walls can cause the development of hairline cracks from shrinkage or from minor structural movement.
  • Mg(OH) 2 also extends the time before a mortar will set, which is useful in plaster and mortar.
  • the binder composition of the present invention sets and hardens when mixed with water and this is believed to take place in two stages:
  • the addition of the special magnesium carbonates of Formula I to MgO alters its hydration mechanism, and leads to the formation of the Mg(OH) 2 crystals with the different physical and microstructural properties as described above. The effect of the special magnesium carbonate of Formula I to MgO hydration will be described in further detail later.
  • the rosette morphology of the Mg(OH) 2 crystals has Mg(OH) 2 plates that are connected to each other but are angled with respect to each other, thereby forming spaces between the plates.
  • Mg(OH) 2 crystals produced are contained within and, at the outer edges of, the rosette folds of the originally included hydromagnesite crystals.
  • the hydrated material absorbs CO 2 from the atmosphere to form one or more magnesium carbonate phases, such as hydromagnesite (4MgCO 3 .
  • Mg(OH) 2 .4H 2 O dypingite (4MgCO 3 .Mg(OH) 2 .5H 2 O), nesquehonite (MgCO 3 .3H 2 O) and lansfordite (MgCO 3 -5H 2 O), which further increases sample strength.
  • the addition of the special magnesium carbonates of Formula I to MgO significantly increases the carbonation rate of the Mg(OH) 2 crystals produced during MgO hydration . This is explained in further detail later.
  • this MgO-based binder composition has the potential to absorb up to 1.09 tonne of CO 2 for every tonne of MgO included in its composition when hardening.
  • the amount of the chloride salt may be up to 10%, e.g. up to 5%, such as up to 3%, based on the combined weight of (a) magnesium oxide, (b) magnesium carbonate of the general formula I and (c) the chloride salt.
  • the chloride salt is optional but, when present may form at least 1 %, e.g. at least 2%, such as at least 3%, of the combined weight of (a) to (c).
  • the components may be mixed in situ and so the present invention provides a combination of (a) a quantity of magnesium oxide, (b) a quantity of magnesium carbonate of the general formula I and optionally (c) a quantity of the chloride salt.
  • the combination may also include instructions to combine the components in the quantities discussed in the present specification in connection with the ready-mixed composition.
  • Figure 1 shows the x-ray diffraction spectra of hydrated (a) 100% MgO, (b) 80% MgO - 20% MgCO 3 and (c) 80% MgO - 20% hydromagnesite samples.
  • Figure 2 shows a scanning electron micrograph of a hydrated 100% MgO sample.
  • Figure 3 shows a scanning electron micrograph of a hydrated 80% MgO - 20% hydromagnesite sample.
  • Figure 4 compares the heat rate profile from conduction calorimetry of (a) 100% MgO, (b) 80% MgO - 20% MgCO 3 and (c) 80% MgO - 20% hydromagnesite samples.
  • hydromagnesite (4MgCO 3 .Mg(OH) 2 .4H 2 O), a man-made magnesium carbonate, is used as an example to describe the invention.
  • any material having the formula I: x MgCO 3 ⁇ y Mg(OH) 2 ⁇ z H 2 O, wherein x is at least 1 and at least one of y or z is greater than 0 may be used instead or in addition to hydromagnesite.
  • x may be 1 , 2, 3, 4, or 5
  • y and z may for example each independently be 0, 1 , 2, 3, 4, or 5, providing that at least one of y or z is greater than 0, e.g.
  • Materials of the general formula I are known but do not occur naturally. Methods of manufacturing these compounds are well-known, but generally they can be made by exposure of magnesium compounds, e.g. MgO or Mg(OH) 2 (or mixtures of thereof) to CO 2 under a variety of conditions.
  • magnesium compounds e.g. MgO or Mg(OH) 2 (or mixtures of thereof)
  • Stage 1 Water adsorbs at the MgO surface and diffuses inside porous MgO particles; Stage 2: MgO dissolution occurs within the particles, changing particle porosity with time; Stage 3: Creation of supersaturation, and occurrence of nucleation and growth of
  • the rate of MgO hydration is believed to be controlled by the extent of MgO dissolution.
  • the Mg(OH) 2 produced during MgO hydration is deposited in the pores of the MgO particles, creating a Mg(OH) 2 film that imposes an increasing resistance to the hydration process .
  • the above hydration mechanism is altered when a magnesium carbonate of the formula I, e.g. hydromagnesite, is added to the MgO.
  • a magnesium carbonate of the formula I e.g. hydromagnesite
  • hydromagnesite is believed to reduce the formation of the Mg(OH) 2 film on the MgO surface so that the MgO hydration can proceed unimpeded.
  • the different MgO hydration mechanism achieved due to the addition of the special magnesium carbonates of Formula I to MgO leads to the formation of the Mg(OH) 2 crystals with the different set of physical and microstructural properties as described above.
  • Figure 1 shows the x-ray diffraction spectra of (a) hydrated 100% MgO sample, (b) hydrated 80% MgO - 20% MgCO 3 sample and (c) hydrated 80% MgO - 20% hydromagnesite sample.
  • the Mg(OH) 2 diffraction peaks of samples (a) 100% MgO, and (b) 80% MgO - 20% MgCO 3 (i.e. not in accordance with the invention) are narrow with high intensity, indicating high crystallinity.
  • the Mg(OH) 2 diffraction peaks in the 80% MgO - 20% hydromagnesite sample are significantly broader with low intensity, thus denoting the presence of semi-crystalline crystals.
  • Figure 2 shows a scanning electron micrograph (SEM) of a hydrated 100% MgO sample.
  • the Mg(OH) 2 forms 'platelet-type' aggregates.
  • the platelets lie on top of each other and the upper platelets occlude the lower platelets.
  • Figure 3 shows a 'rosette-type' crystal structure formed when MgO is hydrated in the presence of hydromagnesite.
  • Figure 4 shows the heat rate profiles upon hydration of (a) 100% MgO sample, (b) 80% MgO - 20% MgCO 3 sample and (c) 80% MgO - 20% hydromagnesite samples.
  • magnesium carbonate of the formula I (x MgCO 3 • y Mg(OH) 2 • z H 2 O, wherein x is at least 1 and one of y or z is greater than 0, for example hydromagnesite), is included in the composition, it significantly accelerates the carbonation rate of Mg(OH) 2 , which is believed to be due to the following reasons:
  • Mg(OH) 2 crystals with a rosette-like morphology increases the surface area exposed to carbonation and provides space for the carbonate products formed.
  • a hydroscopic material such as NaCI or other chlorides
  • these salts should only be included in compositions which will not be in contact with metals, such as steel-reinforcements in concrete structures.
  • the high CO 2 absorption ability of MgO offers the unique potential to develop "carbon negative" concrete and concrete products, namely products that absorb carbon overall (taking into account both its production and its use) and may have a net absorption of as much as 0.59 tonnes of CO 2 per tonne of MgO, which is the main constituent of the binder.
  • compositions of the binder of the present invention represent example compositions of the binder of the present invention; in all these compositions the addition of a chloride salt is optional and a substantial proportion of any Mg(OH) 2 added has the rosette morphology, high surface area and low crystallinity discussed above.
  • composition of the present invention comprises, by weight: (a) 10% to 95%, e.g. 10% to 85%, for example 30% to 80%, such as 40% to 70% magnesium oxide (MgO) and/or magnesium hydroxide (Mg(OH) 2 );
  • the amount of MgO and/or (Mg(OH) 2 may be greater than 10%, e.g. 15% or more.
  • Typical sub-ranges of the cement composition are (by weight) for different applications:
  • magnesium oxide MgO
  • magnesium hydroxide MgO
  • magnesium oxide or (a) 10% to 60% magnesium oxide (MgO);
  • compositions with higher percentages of MgO and Mg(OH) 2 (and lower percentages of magnesium carbonate of Formula I) tend to have a higher strength under compression but require a greater CO 2 output to make the MgO and Mg(OH) 2 while the compositions with lower percentages of MgO and Mg(OH) 2 (and higher percentages of magnesium carbonate of Formula I) tend to have a lower strength under compression but require less CO 2 output to make.
  • the preferred particle size of the magnesium carbonates is between 0.01-800 ⁇ m in diameter, and preferably between 0.01 and 600 ⁇ m in diameter, in order to achieve a good reaction rate.
  • the particle size of the MgO/Mg(OH) 2 may be between 0.01-800 ⁇ m in diameter, and preferably between 0.01 and 100 ⁇ m in diameter, in order to achieve a good reaction rate.
  • the composition comprising Mg(OH) 2 is produced by mixing water with MgO, magnesium carbonate of Formula I and optionally NaCI and plasticisers, i.e. the MgO composition of the present invention.
  • the composition may be allowed to set to form a dry solid mass.
  • the Mg(OH) 2 will precipitate and the the precipitate can be collected together with the magnesium carbonate.
  • the composition containing Mg(OH) 2 can then be ground to a specific particle size distribution. These compositions can then be further blended with additional MgO and magnesium carbonates of Formula I if desired.
  • the hydroscopic material for example NaCI
  • the binder composition can be present in the binder composition, it can be added in the water used to wet the composition and accordingly it is possible to use, at least in part, seawater to make up a wet cement with the composition of the present invention.
  • the amount of water added to the composition can be freely chosen, depending on the mix plasticity required and the final intended use. Based on the total weight of the binder components, the amount of water can for example be 5-120%, e.g. 5-80%, depending on the expected use.
  • Additives may be mixed with the binder of the present invention either when in powder or in the course of making a cement slurry.
  • the binder composition has a pH of about 10.2 (although it can vary within a range depending on the presence of other oxides or hydroxides impurities in the composition); this is generally lower than Portland cement.
  • This low pH makes it possible to use a wide range of aggregates, including waste aggregates, such as glass aggregates, and other fillers when the binder is used to make construction products, whilst minimising the chance of disruptive reactions, e.g. alkali silica reactions.
  • Other fillers or extenders can be used, e.g. siliceous materials such as fly ash.
  • Suitable aggregates are for example gravel, sand, glass, and other waste products.
  • the amount (w/w) of waste aggregates and other fillers and additives can be e.g. 0-99% of the total dry weight of the composition, depending on the expected use.
  • the exact amount of aggregates and fillers in the binder composition will depend on the desired application. Generally, in concrete and mortars and other compositions containing aggregates, the weight of the binder components (the magnesium oxide/hydroxide and the magnesium carbonate of the formula I, optionally together with the chloride salt) will be 1 - 70%, e.g. 5 - 60%, for example 10 - 40%, including 15 - 30%, of the total dry weight of the composition, i.e. the combined weight of the binder components and of the aggregates/binders.
  • the binder composition of the present invention may consist substantially of: (a) 10% to 95 % MgO , and
  • An aggregate-containing composition (e.g. concrete and mortar) of the present invention may consist substantially of: up to 99% aggregates and other fillers and additives, with the balance being:
  • the workability of a binder-water system can be improved by the addition of super- plasticisers, such as lignosulfonates, sulfonated naphthalene, sulfonated melamine formaldehyde, polyacrylates and polycarboxylate ethers.
  • super- plasticisers such as lignosulfonates, sulfonated naphthalene, sulfonated melamine formaldehyde, polyacrylates and polycarboxylate ethers.
  • superplasticisers are particularly useful when a low amount of water is added to the composition in order to obtain a stronger hardened binder product. The low addition of water will result in a stiff composition which is difficult to work with.
  • the inclusion of a superplasticiser enables the water-binder system to retain good workability and eases its use and placement.
  • the binder composition of the present invention could be mixed with other binders, e.g. Portland cement and/or lime, but the advantages of the present invention, especially in reducing overall carbon dioxide emissions, are reduced by doing so.
  • other hydraulic binders in the compositions of the present invention should preferably not be added but if they are added the amount of such other binders should be kept low, e.g. less than the overall weight of components (a) to (c) of the present invention, such as less than 50% (including amounts less than 25%) of the overall dry weight of the binder components (a) to (c).
  • the binder can be used in many different types of construction product, but usually it is used in porous or semi-porous products, for example dense or lightweight blocks, porous breeze block type products, bricks, tiles, concrete roof tiles, and mortar. However, the binder can also be used in a wide range of other applications where Portland cement is used, e.g. to form screed floors.
  • the binder has a white colour, which is retained even once the material has become hydrated and carbonated. This feature allows the binder composition to be used for premium construction products, where a white colour is required. Alternatively, a pigment may be added to form coloured products and the white base colour of the binder produces a better base for coloured products than grey Portland cement.
  • soft-burnt MgO with a mean particle size of 10 ⁇ m was used.
  • Magnesium carbonates used included hydromagne- site with a mean particle size of 16 ⁇ m, and MgCO 3 with a particle size of 17 ⁇ m.
  • fine sand with a mean particle size of 250 ⁇ m was also used.
  • the MgO and magnesium carbonates were initially dry mixed to homogenise. When aggregates were added to the mix, they were first dry mixed with the cementitious binder before adding the water. NaCI and the superplasticiser were added in the cement or cement-aggregates systems with the mixing water.
  • Example 1 2Og of soft-burnt MgO and 5g of hydromagnesite were mixed with 229g of glass sand. 1.3g of NaCI was dissolved in 31 g of water and the solution was mixed with the dry solids for 5min. The final mass was pressed using a hydraulic press to form a 50mm cubic sample. The sample was stored at ambient conditions (40%-60% relative humidity) and achieved compressive strength of 4.5 MPa after 28 days.
  • the compressive strength of composite materials made using the binder of the present invention tend to be lower than composite materials made using Portland cement but there are applications where Portland cement is used that do not require high compressive strength, e.g. in mortar and breeze blocks, and the present invention provides adequate strength for such applications while requiring a lower net CO 2 output (such output may even be negative).
  • the binders of the present invention are stable in the presence of water.

Abstract

This invention relates to a cement binder composition and to the use of the binder composition in construction products. The cement binder composition is based on MgO that absorbs CO2 when hardening. The binder composition of the present invention also comprises at least one magnesium carbonate (either hydrated or unhydrated) having the formula xMgCO3- yMg(OH)2- zH2O, wherein x is at least 1, and at least one of y or z is greater than 0. The binder composition may optionally comprise a hydroscopic material, for example NaCI. The MgO when mixed with water in the presence of the magnesium carbonate produces magnesium hydroxide that has a rosette-like morphology (as shown).

Description

BINDER COMPOSITION
Technical Field
This invention relates to a cement binder composition, i.e. a composition that is settable to a solid, and to the use of the binder composition in construction products.
Background Art Emissions of 'greenhouse gases', and predominantly carbon dioxide (CO2), are thought to contribute to an increase in the atmospheric and surface temperatures of the Earth - a phenomenon commonly referred to as 'global warming'. Such temperature increases are predicted to have serious environmental consequences. The main contributor to this increase in man-made CO2 is the burning of fossil fuels such as coal and petroleum.
Portland cement is the most common type of cement in general use at this time. It is an essential element of concrete, mortar and non-speciality grouts. Portland cement consists of over 90% Portland cement clinker, up to 5% gypsum and up to 5% other minor constituents. Portland cement clinker is a hydraulic material consisting mainly of dicalcium silicate (2CaCSiO2), tricalcium silicate (3CaO-SiO2), tricalcium aluminate (3CaO-AI2O3) and calcium aluminoferrite (4CaO-AI2O3 Fe2O3) phases. Magnesium oxide (MgO), can also be present in Portland cement, although its amount must not exceed 5% by mass' as its delayed hydration is believed to give rise to unsoundness in concrete. Gypsum (CaSO4.2H2O) is added to Portland cement clinker to control its setting time, and the mixture is ground to give a fine powder. On reaction with water, the constituents of the cement hydrate forming a solid complex calcium silicate hydrate gel and other phases.
The manufacture of Portland cement (PC) is a highly energy intensive process that involves heating high volumes of raw materials to around 145O0C. In addition to the CO2 generated from burning fossil fuels to reach these temperatures, the basic raw material used in making Portland cement is calcium carbonate (limestone, CaCO3), and this decomposes during processing to CaO, releasing additional geologically sequestered CO2. As a result, the manufacture of Portland cement emits approximately 1 tonne CO2 for every tonne of cement produced and is responsible for approximately 5% of all anthropogenic CO2 emissions. Binders based on systems other than calcium oxide and silicates are known. For example Sorel cement (magnesium oxychloride cement or magnesia cement) is a hydraulic cement that is a mixture of magnesium oxide (burnt magnesia, MgO) and magnesium chloride together with filler materials like sand or crushed stone. It sets to a very hard abrasive-resistant material and so is used for grindstones, tiles, artificial stone (cast stone) and cast floors, in which application it has a high wear resistance. However its chief drawback is its poor resistance to water, making it unsuitable for external construction applications.
Other magnesium based cements include magnesium oxysulfate cement and magnesium phosphate cements but both these have drawbacks, the former having a poor water resistance and the latter sets very fast so that it is difficult to work with.
GB-1160029 discloses cements based on mixing magnesium oxide (MgO), sodium chloride (NaCI) or sodium nitrate (NaNO3) and calcium carbonate (CaCO3). CaCO3 is used as a "moderating substance" to enable the salt and the MgO to perform the chemical reactions necessary to set, which are similar to those of the other Sorel cements. These cements require the use of hard-burnt MgO1 which is generally produced by high-temperature treatment (~1000°C) of magnesite (MgCO3), which causes CO2 emissions not only from the calcining of magnesite but also from the burning of fossil fuel.
US-5897703 discloses binder compositions based on mixing MgO with a hardening agent, propylene carbonate. The magnesium oxide used can be any mixture of soft- burnt and hard-burnt MgO. It is known that in the presence of water, propylene carbonate decomposes to carbon dioxide and propylene glycol and so the addition of the propylene carbonate provides a source of CO2 to carbonate the magnesium oxide.
US-6200381 discloses a dry powdered cement composition derived from dolomite (a magnesium and calcium carbonate mineral; MgCO3 CaCO3). The dolomite is heated to decarbonate the MgCO3 so that the composition contains CaCO3 and a partially decarbonated MgCO3, i.e. a mixture of MgCO3 and MgO Certain additives may be included in the composition (e.g. aluminium sulphate (AI2(SO4)3), citric acid, sulphuric acid (H2SO4), NaCI, etc.), which assist the composition to set on addition of water; the water may be contaminated water, e.g. sea water. The CaCO3 component of the cement composition reacts with several of the specified additives that are used. For example, the addition of H2SO4 will react with CaCO3 yielding hydrated CaSO4 (e.g. CaSO4.2H2O) and CO2. The CO2 released assists the carbonation of MgO and Mg(OH)2. NaCI may be added before the thermal treatment of dolomite to decrease the decarbonation temperature of MgCO3, and in the binder composition as an additive, where it appears to assist in achieving an early strength to the composition, which is probably due to reactions with MgO (Sorel cement type reactions). CaCO3 acts as a "moderating substance" to enable NaCI and the MgO to perform the necessary chemical reactions (see GB 1160029 above).
US-1867180 describes a cement composition based on slaked lime (Ca(OH)2) that contains less than 1% MgO and NaCI.
US1561473 discloses that, when a wet mixture of aggregates and magnesium oxide is treated with gaseous or dissolved CO2, its tensile strength is improved. The composition must be exposed to CO2 when wet and the patent discloses the exposure of the wet mixture to a special atmosphere of moist CO2.
WO 01/55049 discloses a dry powdered cement composition containing MgO, a hydraulic cement, such as Portland cement, Sorel cements or calcium aluminate cements, and optionally pozzolanic materials. The cement composition can also contain various additives such as ferrous sulphate (FeSO4), sodium or potassium silicates or aluminates, phosphoric acid (HPO3) or phosphoric acid salts, copper sulphate (CuSO4), and various other organic polymers and resins, such as polyvinyl acetate (PVA), vinylacetate-ethylene, styrene-butyl acrylate, butyl acrylate- methylacrylate, and styrene-butadiene. The magnesium oxide is obtained by low temperature calcining.
GB-529128 discloses the use of magnesium carbonate as an insulating material; it is made from concentrated sea water containing magnesium salts by precipitating the salts with alkali metal carbonates, which forms needle-like crystals that can set. A slurry of such crystals, when paced in a mould, will set to provide a slab or block that is useful as insulation. If there are any bicarbonate ions in the alkali metal carbonate, magnesium bicarbonate will form in the above reaction, which slows down the setting reaction. In order to counteract this, 1-5% magnesium oxide may be added, which will precipitate the bicarbonate as magnesium carbonate.
US-1819893 and US-1971909 disclose the use of magnesium hydroxide or a mixture of magnesium hydroxide and calcium carbonate as an insulating material since such magnesium hydroxide is light and highly flocculated.
US-5927288 discloses that a mixture of hydromagnesite and magnesium hydroxide, when incorporated into a cigarette paper, reduces sidestream smoke. The hydromagnesite/magnesium hydroxide compositions have a rosette morphology and the hydromagnesite/magnesium hydroxide mixture is precipitated from a solution of magnesium bicarbonate and possible other soluble magnesium salts by adding a strong base, e.g. potassium hydroxide.
EP-0393813 and WO 01/51554 relate to flame retardants for plastics. EP-0393813 discloses that a mixture of a double salt of calcium and magnesium carbonate (e.g. dolomite), hydromagnesite, and magnesium hydroxide can provide flame resistance to thermoplastics, e.g. a sheath of an electric wire. WO01/51554 teaches the addition of various magnesium salts, including hydromagnesite and magnesium hydroxide, to polymers.
US2009/0020044 discloses the capture of carbon dioxide by sea water to precipitate carbonates, which can be used in hydraulic cements; up to 10% of a pH regulating material, including magnesium oxide or hydroxide, can be added to the cement to regulate the pH.
JP2006 076825 is concerned with reducing the amount of CO2 emitted from power stations and by the steel industry. It proposes capturing the CO2 by reaction with ammonium hydroxide to form ammonium carbonate: 2NH4OH + CO2 → (NH4)2CO3 +H2O
Meanwhile magnesium chloride is made by reacting magnesium oxide and hydrochloric acid
MgO + 2HCI → MgCI2 + H2O
The magnesium chloride is reacted with the ammonium carbonate, which precipitates magnesium carbonate leaving a liquor containing dissolved ammonium chloride: (NH4)2CO3 + MgCI2 → 2(NH4)CI + MgCO3
The precipitated magnesium carbonate is filtered out and used as a cement component while the ammonium chloride liquor is treated to regenerate ammonium hydroxide and hydrochoric acid.
Apart from the intrinsic benefit of reducing CO2 emissions, it is likely that CO2 emissions by the cement industry will be regulated in an attempt to reduce environmental damage. Therefore, there is a real need to develop a new range of cementitious binders that are associated with minimal or even negative CO2 emissions. Such binders could be 'carbon neutral' if they are able to counteract or balance the release of CO2 in the process of their production by absorbing CO2 during a hardening stage following hydration; or 'carbon negative' if they are able to absorb and store more CO2 than was released during their production.
Disclosure of the Invention
The invention is set out in the claims.
This invention provides a cement binder composition based on MgO plus special magnesium carbonates (see Formula I below). The magnesium oxide used can be soft-burnt MgO, hard-burnt MgO, or any mixture of soft-burnt and hard-burnt MgO. A key ingredient of the cement composition is the special magnesium carbonate (either hydrated or unhydrated) in the form x MgCO3 ■ y Mg(OH)2 • z H2O Formula I where x is a number greater than 1 , and at least one of y or z is a number greater than O; the carbonate may be non-stoichiometric; x, y and z may be (but need not be) integers. The composition may also comprise a hydroscopic material, such as NaCI.
The above formula I excludes the use of magnesite (MgCO3) and dolomite (MgCO3 CaCO3) as the principal source of magnesium carbonate. However, the composition can contain minor amounts of these minerals, e.g. up to 25% of the total magnesium carbonate content of the composition. It is preferred that substantially all the magnesium carbonate content of the composition is in accordance with Formula
I. In one embodiment, the carbonate of the general formula I is hydromagnesite, which has the general formula 4MgCO3. Mg(OH)2.4H2O, although some degree of non-stoichiometry can be tolerated, e.g. x in the above formula I can be 3.5 - 4.5, y can be 0.5 - 1.5 and z can be 3.5.- 5.5. In addition, x, y and z may all be greater than 0.
The composition is preferably in the form of a dry powder that can be mixed with water, optionally together with other ingredients such as sand, gravel or other fillers (e.g. fly ash), to form a slurry of varying consistency that will set, i.e. the composition of the present invention is a hydraulic binder/cement. The wet composition can be made plastic and workable by the addition of plasticisers.
In accordance with a further embodiment, the composition may include Mg(OH)2 in place of some or all of the MgO. The Mg(OH)2 used should preferably have the low crystallinity, high surface area and the rosette-like morphology described below. Such Mg(OH)2 may be produced by pre-hydrating MgO in the presence of the special magnesium carbonates of the general formula I. However, a minor part of any Mg(OH)2 in the composition, e.g. below 50% of the total Mg(OH)2 content, may have a platelet morphology shown in Figure 2. The Mg(OH)2 morphology formed in accordance with the present invention has a higher surface area per unit weight than Mg(OH)2 having a platelet morphology; the latter will normally have a surface area of less than 45 m2/g whereas the former has a surface area of at least 45 m2/g, generally higher than 70 m2/g (surface area values were measured according to the Brunauer-Emmett-Teller (BET) method).
The presence of Mg(OH)2 in the binder composition in place of MgO reduces the green strength and the set strength of the hydrated binder because most of the strength of the binder of the present invention results from MgO hydration, but this is acceptable in certain applications, e.g. in mortars or plasters; an excessively strong mortar for bonding together blocks and bricks in the construction of walls can cause the development of hairline cracks from shrinkage or from minor structural movement. The use of such Mg(OH)2 also extends the time before a mortar will set, which is useful in plaster and mortar.
The binder composition of the present invention sets and hardens when mixed with water and this is believed to take place in two stages:
Firstly when the composition is initially mixed with water, the MgO hydrates in the presence of the special magnesium carbonates forming Mg(OH)2 crystals that are significantly less crystalline, have higher surface area and a rosette-like morphology, which increases the green strength of the cement sample. The term 'green strength' refers to the initial strength of the cement sample over a period of 6 hours. The addition of the special magnesium carbonates of Formula I to MgO alters its hydration mechanism, and leads to the formation of the Mg(OH)2 crystals with the different physical and microstructural properties as described above. The effect of the special magnesium carbonate of Formula I to MgO hydration will be described in further detail later. The rosette morphology of the Mg(OH)2 crystals has Mg(OH)2 plates that are connected to each other but are angled with respect to each other, thereby forming spaces between the plates. However, it is possible that some of the Mg(OH)2 crystals produced are contained within and, at the outer edges of, the rosette folds of the originally included hydromagnesite crystals.
Secondly, the hydrated material, over time, absorbs CO2 from the atmosphere to form one or more magnesium carbonate phases, such as hydromagnesite (4MgCO3.
Mg(OH)2.4H2O), dypingite (4MgCO3.Mg(OH)2.5H2O), nesquehonite (MgCO3.3H2O) and lansfordite (MgCO3-5H2O), which further increases sample strength. The addition of the special magnesium carbonates of Formula I to MgO significantly increases the carbonation rate of the Mg(OH)2 crystals produced during MgO hydration . This is explained in further detail later.
The addition of a hygroscopic material such as NaCI or other chlorides further increases the carbonation rate of the Mg(OH)2 crystals by providing the necessary humidity for the carbonation reactions. Therefore, this MgO-based binder composition has the potential to absorb up to 1.09 tonne of CO2 for every tonne of MgO included in its composition when hardening. The amount of the chloride salt may be up to 10%, e.g. up to 5%, such as up to 3%, based on the combined weight of (a) magnesium oxide, (b) magnesium carbonate of the general formula I and (c) the chloride salt. The chloride salt is optional but, when present may form at least 1 %, e.g. at least 2%, such as at least 3%, of the combined weight of (a) to (c).
The components may be mixed in situ and so the present invention provides a combination of (a) a quantity of magnesium oxide, (b) a quantity of magnesium carbonate of the general formula I and optionally (c) a quantity of the chloride salt. The combination may also include instructions to combine the components in the quantities discussed in the present specification in connection with the ready-mixed composition.
Brief Description of the Figures
Figure 1 shows the x-ray diffraction spectra of hydrated (a) 100% MgO, (b) 80% MgO - 20% MgCO3 and (c) 80% MgO - 20% hydromagnesite samples. Figure 2 shows a scanning electron micrograph of a hydrated 100% MgO sample. Figure 3 shows a scanning electron micrograph of a hydrated 80% MgO - 20% hydromagnesite sample.
Figure 4 compares the heat rate profile from conduction calorimetry of (a) 100% MgO, (b) 80% MgO - 20% MgCO3 and (c) 80% MgO - 20% hydromagnesite samples.
Detailed Description and Best mode for carrying out the invention
In the description below, hydromagnesite (4MgCO3.Mg(OH)2.4H2O), a man-made magnesium carbonate, is used as an example to describe the invention. However, any material having the formula I: x MgCO3 ■ y Mg(OH)2 ■ z H2O, wherein x is at least 1 and at least one of y or z is greater than 0 may be used instead or in addition to hydromagnesite. For example, x may be 1 , 2, 3, 4, or 5, and y and z may for example each independently be 0, 1 , 2, 3, 4, or 5, providing that at least one of y or z is greater than 0, e.g. dypingite (4MgCO3.Mg(OH)2.5H2O), nesquehonite (MgCO3.3H2O) and lansfordite (MgCO3 SH2O). Many of the carbonates of the formula I are metastable and will transform over time to hydromagnesite.
Materials of the general formula I are known but do not occur naturally. Methods of manufacturing these compounds are well-known, but generally they can be made by exposure of magnesium compounds, e.g. MgO or Mg(OH)2 (or mixtures of thereof) to CO2 under a variety of conditions.
It is believed that the usual hydration mechanism of MgO proceeds as follows Stage 1 : Water adsorbs at the MgO surface and diffuses inside porous MgO particles; Stage 2: MgO dissolution occurs within the particles, changing particle porosity with time; Stage 3: Creation of supersaturation, and occurrence of nucleation and growth of
Mg(OH)2 at the oxide surface.
The rate of MgO hydration is believed to be controlled by the extent of MgO dissolution. The Mg(OH)2 produced during MgO hydration is deposited in the pores of the MgO particles, creating a Mg(OH)2 film that imposes an increasing resistance to the hydration process .
The above hydration mechanism is altered when a magnesium carbonate of the formula I, e.g. hydromagnesite, is added to the MgO. Without wishing to be bound by theory, the addition of for example hydromagnesite is believed to reduce the formation of the Mg(OH)2 film on the MgO surface so that the MgO hydration can proceed unimpeded. The different MgO hydration mechanism achieved due to the addition of the special magnesium carbonates of Formula I to MgO leads to the formation of the Mg(OH)2 crystals with the different set of physical and microstructural properties as described above.
Figure 1 shows the x-ray diffraction spectra of (a) hydrated 100% MgO sample, (b) hydrated 80% MgO - 20% MgCO3 sample and (c) hydrated 80% MgO - 20% hydromagnesite sample. The Mg(OH)2 diffraction peaks of samples (a) 100% MgO, and (b) 80% MgO - 20% MgCO3 (i.e. not in accordance with the invention) are narrow with high intensity, indicating high crystallinity. In contrast, the Mg(OH)2 diffraction peaks in the 80% MgO - 20% hydromagnesite sample are significantly broader with low intensity, thus denoting the presence of semi-crystalline crystals.
Figure 2 shows a scanning electron micrograph (SEM) of a hydrated 100% MgO sample. The Mg(OH)2 forms 'platelet-type' aggregates. The platelets lie on top of each other and the upper platelets occlude the lower platelets. In contrast, Figure 3 shows a 'rosette-type' crystal structure formed when MgO is hydrated in the presence of hydromagnesite.
Figure 4 shows the heat rate profiles upon hydration of (a) 100% MgO sample, (b) 80% MgO - 20% MgCO3 sample and (c) 80% MgO - 20% hydromagnesite samples.
The replacement of some of the MgO by magnesite (MgCO3) (sample b) does not change the hydration behaviour of MgO (sample a) as depicted by the similar maximum heat rate and time to maximum heat rate. However, when hydromagnesite (4MgCO3. Mg(OH)2.4H2O) is added to MgO (sample c), it significantly accelerates MgO hydration increasing the maximum heat rate by -150% and decreasing the time to maximum heat rate by -70%. The naturally-occurring magnesite (MgCO3) does not alter the MgO hydration as discussed above and should not be used as the principal magnesium carbonate source.
When the magnesium carbonate of the formula I (x MgCO3 • y Mg(OH)2 • z H2O, wherein x is at least 1 and one of y or z is greater than 0, for example hydromagnesite), is included in the composition, it significantly accelerates the carbonation rate of Mg(OH)2, which is believed to be due to the following reasons:
1. The addition of special magnesium carbonates, for example hydromagnesite, provides nucleation sites for accelerated carbonate formation.
2. The formation of Mg(OH)2 crystals with a rosette-like morphology increases the surface area exposed to carbonation and provides space for the carbonate products formed.
These factors speed up the rate of the carbonation reaction and allows the binder composition to reach its final strength more quickly. During natural carbonation of hydrated 100% MgO and 80% MgO - 20% hydromagnesite powder samples, the following results are achieved:
■ 90% carbonation of the 80% MgO - 20% hydromagnesite sample in less than 9 days versus over 50 days for the 100% MgO sample (conditions: 98% relative humidity/ 0.03% CO2 level)
■ 70% carbonation of the 80% MgO - 20% hydromagnesite sample in less than 28 days versus over 45 days for the 100% MgO sample (conditions: 65% relative humidity/ 0.03% CO2 level)
The optional addition of a hydroscopic material, such as NaCI or other chlorides, to the composition may be useful in low humidity conditions to assist in the absorption of moisture from the environment. However, due to the risk of corrosion, these salts should only be included in compositions which will not be in contact with metals, such as steel-reinforcements in concrete structures. The high CO2 absorption ability of MgO (up to 1.09 tonne of CO2/tonne MgO) offers the unique potential to develop "carbon negative" concrete and concrete products, namely products that absorb carbon overall (taking into account both its production and its use) and may have a net absorption of as much as 0.59 tonnes of CO2 per tonne of MgO, which is the main constituent of the binder. Of course the exact net absorption of the binder will depend on the method used to manufacturing the MgO that is used. In contrast, the production of Portland cement releases 1 tonne CO2/tonne cement and as a binder, Portland cement is only able to absorb 0.12-0.51 tonne of CO2/tonne binder, producing a net emission of 0.49 to 0.88 tonnes of CO2 per tonne of binder. These figures for CO2 production include the emissions due to the burning of fossil fuel in the production processes
The following embodiments represent example compositions of the binder of the present invention; in all these compositions the addition of a chloride salt is optional and a substantial proportion of any Mg(OH)2 added has the rosette morphology, high surface area and low crystallinity discussed above.
The composition of the present invention comprises, by weight: (a) 10% to 95%, e.g. 10% to 85%, for example 30% to 80%, such as 40% to 70% magnesium oxide (MgO) and/or magnesium hydroxide (Mg(OH)2);
(b) 5% to 80%, e.g. 10% to 60%, for example 20% to 40%, such as 20% to 30% of one or more magnesium carbonate of Formula I; and
(c) 0% to 10% chloride salt based on the total weight of components (a) to (c).
The amount of MgO and/or (Mg(OH)2 may be greater than 10%, e.g. 15% or more.
Typical sub-ranges of the cement composition are (by weight) for different applications:
a) 70% to 95% magnesium oxide (MgO) and/or magnesium hydroxide
(Mg(OH)2);
(b) 5% to 20% of one or more magnesium carbonate of Formula I, and (c) 0% to 10% chloride salt based on the total weight of components (a) to (c). or
(a) 30% to 80% magnesium oxide (MgO) and/or magnesium hydroxide
(Mg(OH)2); (b) 20% to 60% of one or more magnesium carbonate of Formula I; and (c) 0% to 10% chloride salt based on the total weight of components (a) to (c).
or
(a) 10% to 40% magnesium oxide (MgO) and/or magnesium hydroxide
(Mg(OH)2);
(b) 60% to 80% of one or more magnesium carbonate of Formula I; and
(c) 0% to 10% chloride salt based on the total weight of components (a) to (c). or
(a) 40% to 85 % magnesium oxide (MgO); (b) 5% to 30% magnesium hydroxide (Mg(OH)2);
(c) 10% to 20% of one or more magnesium carbonate of Formula I; and
(d) 0% to 10% chloride salt based on the total weight of components (a) to (d).
or
(a) 20% to 75 % magnesium oxide (MgO);
(b) 5% to 30% magnesium hydroxide (Mg(OH)2);
(c) 20% to 40% of one or more magnesium carbonate of Formula I; and (d) 0% to 10% chloride salt based on the total weight of components (a) to (d).
or (a) 10% to 60% magnesium oxide (MgO);
(b) 30% to 50% magnesium hydroxide (Mg(OH)2);
(c) 10% to 30% of one or more magnesium carbonate of Formula I; and
(d) 0% to 10% chloride salt based on the total weight of components (a) to (d). or
(a) 30% to 90% magnesium hydroxide (Mg(OH)2); (b) 10% to 60% of one or more magnesium carbonate of Formula I; and (c) 0% to 10% chloride salt based on the total weight of components (a) to (c).
or
(a) 75% to 90% magnesium oxide (MgO)
(b) 10% to 20% of one or more magnesium carbonate of Formula I; and (C) 0% to 5% chloride salt based on the total weight of components (a) to (c).
or
(a) 65% to 80% magnesium oxide (MgO)
(b) 20% to 30% of one or more magnesium carbonate of Formula I; and (c) 0% to 5% chloride salt based on the total weight of components (a) to (c).
or
(a) 55% to 70% magnesium oxide (MgO)
(b) 30% to 40% of one or more magnesium carbonate of Formula I; and
(c) 0% to 5% chloride salt based on the total weight of components (a) to (c).
or
(a) 45% to 60% magnesium oxide (MgO)
(b) 40% to 50% of one or more magnesium carbonate of Formula I; and
(c) 0% to 5% chloride salt based on the total weight of components (a) to (c). or.
(a) 35% to 50% magnesium oxide (MgO)
(b) 50% to 60% of one or more magnesium carbonate of Formula I; and (c) 0% to 5% chloride salt based on the total weight of components (a) to (c).
or
(a) 25% to 40% magnesium oxide (MgO)
(b) 60% to 70% of one or more magnesium carbonate of Formula I; and
(c) 0% to 5% chloride salt based on the total weight of components (a) to (c).
In the above compositions all the Mg(OH)2 is made by hydrating MgO in the presence of one or more magnesium carbonate of Formula I. In the above compositions, compositions with higher percentages of MgO and Mg(OH)2 (and lower percentages of magnesium carbonate of Formula I) tend to have a higher strength under compression but require a greater CO2 output to make the MgO and Mg(OH)2 while the compositions with lower percentages of MgO and Mg(OH)2 (and higher percentages of magnesium carbonate of Formula I) tend to have a lower strength under compression but require less CO2 output to make.
The preferred particle size of the magnesium carbonates is between 0.01-800 μm in diameter, and preferably between 0.01 and 600 μm in diameter, in order to achieve a good reaction rate.
The particle size of the MgO/Mg(OH)2 may be between 0.01-800 μm in diameter, and preferably between 0.01 and 100 μm in diameter, in order to achieve a good reaction rate.
As mentioned above, the composition comprising Mg(OH)2 is produced by mixing water with MgO, magnesium carbonate of Formula I and optionally NaCI and plasticisers, i.e. the MgO composition of the present invention. The composition may be allowed to set to form a dry solid mass. Alternatively, if a large amount of water is added, the Mg(OH)2 will precipitate and the the precipitate can be collected together with the magnesium carbonate. In either case, the composition containing Mg(OH)2 can then be ground to a specific particle size distribution. These compositions can then be further blended with additional MgO and magnesium carbonates of Formula I if desired.
Although the hydroscopic material, for example NaCI, can be present in the binder composition, it can be added in the water used to wet the composition and accordingly it is possible to use, at least in part, seawater to make up a wet cement with the composition of the present invention.
The amount of water added to the composition can be freely chosen, depending on the mix plasticity required and the final intended use. Based on the total weight of the binder components, the amount of water can for example be 5-120%, e.g. 5-80%, depending on the expected use.
Additives may be mixed with the binder of the present invention either when in powder or in the course of making a cement slurry. The binder composition has a pH of about 10.2 (although it can vary within a range depending on the presence of other oxides or hydroxides impurities in the composition); this is generally lower than Portland cement. This low pH makes it possible to use a wide range of aggregates, including waste aggregates, such as glass aggregates, and other fillers when the binder is used to make construction products, whilst minimising the chance of disruptive reactions, e.g. alkali silica reactions. Other fillers or extenders can be used, e.g. siliceous materials such as fly ash. Suitable aggregates are for example gravel, sand, glass, and other waste products. The amount (w/w) of waste aggregates and other fillers and additives can be e.g. 0-99% of the total dry weight of the composition, depending on the expected use. The exact amount of aggregates and fillers in the binder composition will depend on the desired application. Generally, in concrete and mortars and other compositions containing aggregates, the weight of the binder components (the magnesium oxide/hydroxide and the magnesium carbonate of the formula I, optionally together with the chloride salt) will be 1 - 70%, e.g. 5 - 60%, for example 10 - 40%, including 15 - 30%, of the total dry weight of the composition, i.e. the combined weight of the binder components and of the aggregates/binders.
The binder composition of the present invention may consist substantially of: (a) 10% to 95 % MgO, and
(b) 5% to 80% magnesium carbonate of the above formula I;
(c) 0% to 10% chloride salt and other additives.
An aggregate-containing composition (e.g. concrete and mortar) of the present invention may consist substantially of: up to 99% aggregates and other fillers and additives, with the balance being:
(a) 10% to 95 % MgO, and
(b) 5% to 80% magnesium carbonate of the above formula I; (c) 0% to 10% chloride salt.
The workability of a binder-water system can be improved by the addition of super- plasticisers, such as lignosulfonates, sulfonated naphthalene, sulfonated melamine formaldehyde, polyacrylates and polycarboxylate ethers. Superplasticisers are particularly useful when a low amount of water is added to the composition in order to obtain a stronger hardened binder product. The low addition of water will result in a stiff composition which is difficult to work with. However, the inclusion of a superplasticiser enables the water-binder system to retain good workability and eases its use and placement. Between 0 and 5%, for example between 0.5 and 2.5% of superplasticiser by dry weight of the binder composition (combined weight of MgO, Mg(OH)2 and magnesium carbonate of Formula I) may be added. Other additives usual in binders, cements, concretes, mortars and plasters in amounts up to 10% by dry weight of the binder composition (combined weight of MgO, Mg(OH)2 and magnesium carbonate of Formula I) may be added for example between 0 and 5%, e.g. between 0.5 and 2.5%.
The binder composition of the present invention could be mixed with other binders, e.g. Portland cement and/or lime, but the advantages of the present invention, especially in reducing overall carbon dioxide emissions, are reduced by doing so. For this reason other hydraulic binders in the compositions of the present invention should preferably not be added but if they are added the amount of such other binders should be kept low, e.g. less than the overall weight of components (a) to (c) of the present invention, such as less than 50% (including amounts less than 25%) of the overall dry weight of the binder components (a) to (c). The binder can be used in many different types of construction product, but usually it is used in porous or semi-porous products, for example dense or lightweight blocks, porous breeze block type products, bricks, tiles, concrete roof tiles, and mortar. However, the binder can also be used in a wide range of other applications where Portland cement is used, e.g. to form screed floors.
All the reactions occurring in the manufacture and setting of these construction products are reversible. For example partly carbonated construction products can be crushed and the recovered binder containing magnesium carbonates recycled to MgO by calcining (heating). Alternatively, the partly carbonated construction products can be crushed, optionally further carbonated, and then mixed with additional MgO to make new products that are of the same high value, unlike Portland cement, which is only recyclable to low value products. Relatively low loss of strength is observed when the products of the present invention are recycled and again made into construction products.
The binder has a white colour, which is retained even once the material has become hydrated and carbonated. This feature allows the binder composition to be used for premium construction products, where a white colour is required. Alternatively, a pigment may be added to form coloured products and the white base colour of the binder produces a better base for coloured products than grey Portland cement.
The present invention is now described with reference to the following non-limiting examples:
In practising preferred forms of the present invention, soft-burnt MgO with a mean particle size of 10 μm was used. Magnesium carbonates used included hydromagne- site with a mean particle size of 16 μm, and MgCO3 with a particle size of 17 μm. In addition, fine sand with a mean particle size of 250 μm was also used. The MgO and magnesium carbonates were initially dry mixed to homogenise. When aggregates were added to the mix, they were first dry mixed with the cementitious binder before adding the water. NaCI and the superplasticiser were added in the cement or cement-aggregates systems with the mixing water.
Example 1. 2Og of soft-burnt MgO and 5g of hydromagnesite were mixed with 229g of glass sand. 1.3g of NaCI was dissolved in 31 g of water and the solution was mixed with the dry solids for 5min. The final mass was pressed using a hydraulic press to form a 50mm cubic sample. The sample was stored at ambient conditions (40%-60% relative humidity) and achieved compressive strength of 4.5 MPa after 28 days.
Example 2.
15g of soft-burnt MgO, 5g of hydromagnesite, and 5g of MgCO3 were mixed with 229g of glass sand. 0.6g of NaCI was dissolved in 28g of water and the solution was mixed with the dry solids for 5min. The final mass was pressed using a hydraulic press to form a 50mm cubic sample. The sample was stored at ambient conditions (40%-60% relative humidity) and achieved compressive strength of 4.2 MPa after 28 days.
Example 3.
8Og of soft-burnt MgO and 2Og of hydromagnesite were mixed with 40Og of glass sand. 0.6g of NaCI was dissolved in 12Og of water and the solution was mixed with the dry solids for 5min. The final mass was poured and vibrated to form 50mm cubic samples. The samples were stored at ambient conditions (40% relative humidity) and achieved compressive strength of 2.6 MPa after 1 day.
Example 4.
8Og of soft-burnt MgO and 2Og of hydromagnesite were mixed with 12Og of water for 5min. The final mass was poured and vibrated to form 50mm cubic samples. The samples were stored at 5% CO2 and 90%RH and achieved compressive strength of 10 MPa after 5 days.
Example 5.
8Og of soft-burnt MgO, 2Og of hydromagnesite and 10Og of fine sand were mixed with 9Og of water and 20ml of a sulfonated naphthalene plasticiser for 5min. The final mass was poured and vibrated to form 50mm cubic samples. The samples were stored at ambient conditions (40% relative humidity, 0.03% CO2) and achieved compressive strength of 25 MPa after 28 days.
The compressive strength of composite materials made using the binder of the present invention tend to be lower than composite materials made using Portland cement but there are applications where Portland cement is used that do not require high compressive strength, e.g. in mortar and breeze blocks, and the present invention provides adequate strength for such applications while requiring a lower net CO2 output (such output may even be negative).
In contrast to Sorel cements, the binders of the present invention are stable in the presence of water.

Claims

CLAIMS:
1. A binder composition comprising: (a) 10% to 95 % MgO; and (b) 5% to 80% magnesium carbonate;
(c) 0% to 10% chloride salt based on the total weight of components (a) to (c) wherein the magnesium carbonate is in the form x MgCO3 • y Mg(OH)2 ■ z H2O wherein x is a number that is at least 1 , and at least one of y or z is a number that is greater than 0.
2. A settable binder composition comprising:
(a) 10% to 95 % Mg(OH)2 and optionally MgO; (b) 5% to 80% magnesium carbonate;
(c) 0% to 10% chloride salt based on the total weight of components (a) to (c) wherein: the magnesium carbonate is in the form x MgCO3 • y Mg(OH)2 ■ z H2O wherein x is a number that is at least 1 , and at least one of y or z is a number that is greater than 0 and the magnesium hydroxide is selected from the group consisting of: magnesium hydroxide formed by hydrating MgO in the presence of a magnesium carbonate of the above form; magnesium hydroxide having a surface area of than 60 m2/g (measured according to the Brunauer-Emmett-
Teller (BET) method); and magnesium hydroxide having a rosette-like morphology.
3. A binder composition as claimed in claim 1 or claim 2, wherein in the formula x MgCO3 • y Mg(OH)2 • z H2O1 x is a number in the range of 3.5 - 4.5, y is a number in the range of 0.5 - 1.5, and z is a number in the range of 3.5 - 5.5.
4. A binder composition as claimed in claim 1 or claim 2, wherein in the formula x MgCO3 • y Mg(OH)2 • z H2O, x is 4, y is 1 , and z is 4 or 5.
5. A binder composition as claimed in claim 1 or claim 2, wherein the magnesium carbonate is in the form x MgCO3 • z H2O wherein x is at least 1 , and z is greater than O.
6. A binder composition as claimed in claim 1 or claim 2, wherein in the formula x MgCO3 ■ y Mg(OH)2 ■ z H2O: x, y , z are all greater than O.
7. A binder composition as claimed in any preceding claim, wherein the magnesium carbonate is hydromagnesite.
8. A binder composition as claimed in any preceding claim , wherein the chloride salt is NaCI.
9. A binder composition as claimed in any preceding claim , comprising MgO and/or Mg(OH)2, magnesium carbonate and optionally chloride salt in an amount selected from one of the following ranges:
i)
(a) 70% to 95% magnesium oxide (MgO); (b) 5% to 20% of one or more magnesium carbonate; and
(c) 0% to 10% chloride salt based on the total weight of components (a) to (c);
ϋ) (a) 30% to 80% magnesium oxide (MgO);
(b) 20% to 60% of one or more magnesium carbonate; and (C) 0% to 10% chloride salt based on the total weight of components (a) to (c);
iii) (a) 10% to 40% magnesium oxide (MgO) and / or magnesium hydroxide
(Mg(OH)2);
(b) 60% to 80% of one or more magnesium carbonate; and
(c) 0% to 10% chloride salt based on the total weight of components (a) to (c);
iv)
(a) 40% to 85 % magnesium oxide (MgO);
(b) 5% to 30% magnesium hydroxide (Mg(OH)2);
(c) 10% to 20% of one or more magnesium carbonate; (d) 0% to 10% chloride salt based on the total weight of components (a) to (d);
v)
(a) 20% to 75% magnesium oxide (MgO); (b) 5% to 30% magnesium hydroxide (Mg(OH)2);
(c) 20% to 40% of one or more magnesium carbonate; and
(d) 0% to 10% chloride salt based on the total weight of components (a) to (d); vi)
(a) 10% to 60 % magnesium oxide (MgO);
(b) 30% to 50% magnesium hydroxide (Mg(OH)2);
(c) 10% to 30% of one or more magnesium carbonate; and
(d) 0% to 10% chloride salt based on the total weight of components (a) to (d);
vii)
(a) 30% to 90% magnesium hydroxide (Mg(OH)2);
(b) 10% to 60% of one or more magnesium carbonate; and (c) 0% to 10% chloride salt based on the total weight of components (a) to (c);
10. A binder composition as claimed in any preceding claim, wherein the average particle diameter of the MgO / Mg(OH)2 particles is approximately 0.01 to 800μm, for example approximately 0.01 to 600μm; and / or wherein the average particle diameter of the magnesium carbonate particles is approximately 0.01 to 800μm, for example approximately 0.01 to 600μm.
11. A binder composition as claimed in claim 2, wherein the magnesium hydroxide in the composition has a surface area of at least 60 m2/g.
12. A binder composition as claimed in claim 2 or claim 11, wherein at least 50% of any magnesium hydroxide in the composition has a rosette-like morphology.
13. A binder composition as claimed in claim 12, wherein substantially all of the magnesium hydroxide in the composition has a rosette morphology.
14. A composition comprising a binder as claimed in any preceding claim in dry powder form.
15.. A composition comprising a binder as claimed in any preceding claim and a filler, e.g. a siliceous material or an aggregate.
16. Use of a composition of any preceding claim as a binder in concrete, mortars, cements or other building construction products.
17. A construction product comprising the composition claimed in any one of claims 1 to 15 that has set; for example a dense building block, a lightweight building block, a tile, a roof tile, a brick, or mortar.
18. A method of forming a construction material comprising mixing together the binder of any one of claims 1 to 15 with:
(e) water and (f) optionally an additive or filler, e.g. a siliceous material or an aggregate and allowing the mixture to set;
19. A method as claimed in claim 18 wherein the amounts of components (e) to (f) are, in weight % based on the total weight of components (a) to (f):
(e) up to 5-80% water; and (T) up to 99% filler and other additives.
20. A method of making a composition as claimed in any of claims 2, 11 or 12, wherein the Mg(OH)2 is produced by hydrating MgO in the presence of a magnesium carbonate of the general formula I, drying the composition and optionally grinding the composition.
21. A kit comprising
(a) a quantity of magnesium oxide and/or a quantity of magnesium hydroxide selected from the group consisting of: magnesium hydroxide formed by hydrating MgO in the presence of a magnesium carbonate of the formula I; magnesium hydroxide having a surface area of than 60 m2/g (measured according to the Brunauer-Emmett-Teller (BET) method); and magnesium hydroxide having a rosette-like morphology,
(b) a quantity of magnesium carbonate of the general formula I as defined in claim 1 and optionally (c) a quantity of the chloride salt, together with instructions to combine the components in the quantities set out in any of claims 1 , 2 or 9.
PCT/GB2009/001610 2008-06-26 2009-06-26 Binder composition WO2009156740A1 (en)

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AU2009263979A AU2009263979B2 (en) 2008-06-26 2009-06-26 Binder composition
US12/736,928 US8496751B2 (en) 2008-06-26 2009-06-26 Binder composition
JP2011515595A JP2011525885A (en) 2008-06-26 2009-06-26 Binder composition
EP09769581.1A EP2297062B1 (en) 2008-06-26 2009-06-26 Binder composition
BRPI0914763-2A BRPI0914763B1 (en) 2008-06-26 2009-06-26 HYDRAULIC BINDING COMPOSITION, USE OF SUCH COMPOSITIONS, CONSTRUCTION PRODUCT, METHOD OF FORMING A CONSTRUCTION MATERIAL AND KIT
EA201100036A EA201100036A1 (en) 2008-06-26 2009-06-26 COMPOSITION OF THE CONNECTOR
CN200980125190.7A CN102083764B (en) 2008-06-26 2009-06-26 Adhesive composition
MX2010013764A MX2010013764A (en) 2008-06-26 2009-06-26 Binder composition.
CA2727072A CA2727072C (en) 2008-06-26 2009-06-26 Binder composition
IL209547A IL209547A0 (en) 2008-06-26 2010-11-24 Binder composition
ZA2010/08761A ZA201008761B (en) 2008-06-26 2010-12-06 Binder composition

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AU2009263979A2 (en) 2011-01-20
CO6321196A2 (en) 2011-09-20
EP2297062B1 (en) 2020-01-15
CL2010001549A1 (en) 2011-03-11
CN102083764B (en) 2016-11-09
AU2009263979A1 (en) 2009-12-30
US8496751B2 (en) 2013-07-30
EA201100036A1 (en) 2011-08-30
KR20110053926A (en) 2011-05-24
BRPI0914763B1 (en) 2020-09-15
US20110290155A1 (en) 2011-12-01
CN102083764A (en) 2011-06-01
MX2010013764A (en) 2011-05-03
JP2011525885A (en) 2011-09-29
IL209547A0 (en) 2011-01-31
AU2009263979B2 (en) 2015-10-29
BRPI0914763A2 (en) 2016-09-06
CA2727072A1 (en) 2009-12-30
CA2727072C (en) 2019-06-11
ZA201008761B (en) 2011-08-31

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