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
  • C04B20/00—Use of materials as fillers for mortars, concrete or artificial stone according to more than one of groups C04B14/00 - C04B18/00 and characterised by shape or grain distribution; Treatment of materials according to more than one of the groups C04B14/00 - C04B18/00 specially adapted to enhance their filling properties in mortars, concrete or artificial stone; Expanding or defibrillating materials
  • C04B20/10—Coating or impregnating
• • 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
  • C04B28/34—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 cold phosphate binders
• • 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

• Various aspects of this disclosure may relate to a cementitious composition.
• Various aspects of this disclosure may relate to a cement-based structure.
• Various embodiments may relate to methods of forming the cementitious composition and/or the cement-based structure.
• SHCC Strain hardening cementitious composites
• SHCC can normally achieve at least 1% tensile strain capacity, which is about a hundred times that of conventional concrete.
• the extraordinary tensile properties are achieved by the addition of a small portion of fibers, which helps the formation of multiple microcracks with tight crack width, instead of few large cracks seen in conventional concrete.
• the superior tensile ductility, together with tight crack width result in stronger corrosion resistance, and improve potential of self-healing of cracks in SHCC -based structures. While a wide range of fibers, such as metallic fibers, polymeric fibers, and natural fibers, have been used to manufacture SHCC, the selection of materials for matrix composition has been rather limited.
• SHCC normally requires a high Portland cement (PC) content. Accordingly, the production of SHCC -based structures would consume large amount of energy, and would result in a high amount of carbon dioxide (CO2).
• PC Portland cement
• Various embodiments may provide a cementitious composition.
• the cementitious composition may include a mixture including a binder component including reactive magnesium oxide cement (RMC).
• the mixture may further include water.
• the cementitious composition may also include one or more fibers dispersed in the mixture.
• Various embodiments may provide a cement-based structure.
• the cement-based structure may include a matrix including one or more hydrated magnesium carbonates.
• the cement-based structure may include one or more fibers embedded in the matrix.
• Various embodiments may provide a method of forming a cementitious composition.
• the method may include forming a mixture.
• the mixture may include a binder component including reactive magnesium oxide cement.
• the mixture may also include water.
• the method may include dispersing one or more fibers in the mixture.
• Various embodiments may provide a method of forming a cement-based structure.
• the method may include forming a matrix including one or more hydrated magnesium carbonates.
• One or more fibers may be embedded in the matrix.
• FIG. 1 shows a general illustration of a cementitious composition according to various embodiments.
• FIG. 2 shows a general illustration of a cement-based structure according to various embodiments.
• FIG. 3 is a schematic showing a method of forming a cementitious composition according to various embodiments.
• FIG. 4 is a schematic showing a method of forming a cement-based structure according to various embodiments.
• FIG. 5A is a plot of weight percentage (in percent or %) /heat flow (in milli- Watts or mW) as a function of temperature (in degrees Celsius or °C) showing the thermogravimetric analysis (TGA) and differential thermal analysis (DGA) results of samples formed from Mix 1 and Mix 2 according to various embodiments.
• TGA thermogravimetric analysis
• DGA differential thermal analysis
• FIG. 5B is a plot of tensile stress (in mega-Pascals or MPa) as a function of tensile strain (in percent or %) showing the uniaxial tensile stress-strain curves of samples formed from Mix 1 according to various embodiments.
• FIG. 5C is a plot of tensile stress (in mega-Pascals or MPa) as a function of tensile strain (in percent or %) showing the uniaxial tensile stress-strain curves of samples formed from Mix 2 according to various embodiments.
• FIG. 6 is a plot of fiber-bridging stress ( ⁇ ) as a function of crack opening displacement ( ⁇ ) showing the tensile stress-crack opening displacement curve and strain-hardening criteria, illustrating the fiber-bridging constitutive law.
• FIG. 7 is a plot of cumulative fraction (in percent or %) as a function of particle diameter (in micrometers or ⁇ ) showing particle size distribution of reactive magnesium oxide cement (RMC) and fly ash (FA) used in compositions according to various embodiments.
• RMC reactive magnesium oxide cement
• FA fly ash
• FIG. 8A shows the rheometer used to measure the samples according to various embodiments.
• FIG. 8B shows the test setup used to measure the samples according to various embodiments.
• FIG. 9A shows the top view and side view of a dog-bone shaped mold according to various embodiments.
• FIG. 9B shows the test setup for conducting the uniaxial tensile test for the samples according to various embodiments.
• FIG. 10A is a plot of torque ⁇ (in Pascals or Pa) as a function of shear rate N (per second or 1/s) showing the torque-shear rate ( ⁇ - N) of sample FA60-0.53 at 6 minutes (mins), 12 minutes (mins), and 18 minutes (mins) according to various embodiments.
• FIG. 10B is a plot of torque ⁇ (in Pascals or Pa) as a function of shear rate N (per second or 1/s) showing the magnified plot of the box outlined in FIG. 10A according to various embodiments.
• FIG. 11A shows a plot of plastic viscosity (in Pascals second or Pa s) as a function of fly ash / binder ratio (FA/b) (in percent or %) illustrating the effects of the water and fly ash contents on the plastic viscosity of the mixture according to various embodiments.
• FIG. 10B is a plot of torque ⁇ (in Pascals or Pa) as a function of shear rate N (per second or 1/s) showing the magnified plot of the box outlined in FIG. 10A according to various embodiments.
• FIG. 11A shows a plot of plastic viscosity (in Pascals second or Pa s) as a function of fly ash / binder ratio (FA/b) (in percent or %) illustrating the effects of the water and fly
• IB shows a plot of yield stress (in Pascals or Pa) as a function of fly ash / binder ratio (FA/b) (in percent or %) illustrating the effects of the water and fly ash contents on the yield stress of the mixture according to various embodiments.
• FIG. 12A is a plot of tensile stress (in mega Pascals or MPa) as a function of tensile strain (in percent or %) illustrating tensile stress-strain curves of the samples NC- 12-0.41 after curing for 7 days according to various embodiments.
• FIG. 12B is a plot of tensile stress (in mega Pascals or MPa) as a function of tensile strain (in percent or %) illustrating tensile stress-strain curves of the samples NC- 12-0.41 after curing for 28 days according to various embodiments.
• FIG. 12C is a plot of tensile stress (in mega Pascals or MPa) as a function of tensile strain (in percent or %) illustrating tensile stress-strain curves of the samples OC- 12-0.41 after curing for 7 days according to various embodiments.
• FIG. 12D is a plot of tensile stress (in mega Pascals or MPa) as a function of tensile strain (in percent or %) illustrating tensile stress-strain curves of the samples OC-12-0.53 after curing for 7 days according to various embodiments.
• FIG. 12E is a plot of tensile stress (in mega Pascals or MPa) as a function of tensile strain (in percent or %) illustrating tensile stress-strain curves of the samples OC-8-0.53 after curing for 7 days according to various embodiments.
• FIG. 13 is an image showing the typical crack distribution of a failed specimen (NC- 12-0.41 with 7 days of curing) after unloading according to various embodiments.
• FIG. 14A is an image showing the fracture surface of the specimen shown in FIG. 13 according to various embodiments.
• FIG. 14B is a field emission scanning electron microscopy (FESEM) image of a pulled-out fiber shown in FIG. 14A according to various embodiments.
• FESEM field emission scanning electron microscopy
• FIG. 14C is a field emission scanning electron microscopy (FESEM) image of a left-over tunnel in the matrix after the fiber shown in FIG. 14B is pulled out according to various embodiments.
• FIG. 15 is a plot of mass (in percent or %) / heat flow (in milli-Watts or mW) as a function of temperature (in degree Celsius or °C) showing the thermogravimetric analysis (TGA) curve and the differential scanning calorimetry (DSC) curve of a sample of OC-12-0.53 according to various embodiments.
• TGA thermogravimetric analysis
• DSC differential scanning calorimetry
• Embodiments described in the context of one of the methods, compositions or structures are analogously valid for the other methods, compositions, or structures. Similarly, embodiments described in the context of a method are analogously valid for a composition and/or structure, and vice versa.
• the word “over” used with regards to a deposited material formed “over” a side or surface may be used herein to mean that the deposited material may be formed “directly on”, e.g. in direct contact with, the implied side or surface.
• the word “over” used with regards to a deposited material formed “over” a side or surface may also be used herein to mean that the deposited material may be formed "indirectly on” the implied side or surface with one or more additional layers being arranged between the implied side or surface and the deposited material.
• a first layer "over" a second layer may refer to the first layer directly on the second layer, or that the first layer and the second layer are separated by one or more intervening layers.
• the articles “a”, “an” and “the” as used with regard to a feature or element include a reference to one or more of the features or elements.
• the term “about” or “approximately” as applied to a numeric value encompasses the exact value and a reasonable variance.
• Reactive magnesium oxide (MgO) cement i.e. RMC
• RMC reactive MgO cement
• brucite Mg(OH) 2
• C0 2 carbon dioxide
• reactive MgO cement (RMC) is first mixed and reacts with water to form brucite.
• the brucite is subsequently carbonated by the ambient CO2 in air, or elevated CO2 conditions in a controlled environment, to set into a hardened matrix including different hydrated magnesium carbonates (HMCs).
• the hydrated magnesium carbonates may have the formula of xMg(CO) 3 -yMg(OH)2-zH20.
• the hardened dense carbonate network may reduce sample porosity, and may provide binding strength within RMC based samples.
• Reactive MgO cement may be a good sustainable alternative to Portland cement in the preparation of strain hardening cementitious composites (SHCC.)
• reactive MgO based matrix is brittle and cannot be reinforced with traditional steel reinforcing bar due to the high risk of rebar corrosion.
• the relatively low pH (i.e. -10) of carbonated RMC formulations may present a challenge in the use of steel reinforcement, which can face a risk of corrosion due to the loss of the passivated surface at such relatively low alkalinities, thereby potentially creating structural safety issues.
• the carbonation of MgO binder reduces pH of matrix, which causes depassivation of steel reinforcement and subsequent corrosion.
• SHMC strain hardening reactive MgO composites
• RMC -based concrete is still considered as a brittle material, which could highly benefit from the use of reinforcement in the development of structural members.
• ECC engineered cementitious composites
• the fibers may occupy a fraction of volume, typically about 2%.
• ECC demonstrates strain-hardening behavior as their tensile stress continues to increase even in the presence of cracks.
• ECC samples can achieve tensile ductilities of about 1 % to about 5%, enabled by the formation of multiple fine cracks ( ⁇ 100 ⁇ ) with very small spacing (about 1 mm to about 5 mm).
• the tensile properties of ECC may be further tailored with micromechanics to achieve multiple attributes such as high impact resistance and fatigue resistance. Therefore, to increase the use of RMC without relying on steel reinforcements, it may be desirable to engage similar tensile strain-hardening behavior and high ductility within RMC -based formulations via the addition of short fibers, such as polymeric fibers.
• Various embodiments may relate to a CO2 sequestrating strain hardening brittle matrix structure or composite formed using reactive magnesium oxide cement as the binder.
• cementitious composition may relate to a cement-based structure.
• the cement-based structure may refer to a cement-based composite.
• cement-based structure may be used to refer to the microstructure of the composite, i.e. the internal structure of the composite.
• the cementitious composition may be used to form a cement-based structure or composite.
• cementitious composition may refer to the mix composition of the composite (before hardening).
• FIG. 1 shows a general illustration of a cementitious composition 100 according to various embodiments.
• the cementitious composition 100 may include a mixture 102 including a binder component 104 including reactive magnesium oxide cement (RMC).
• the mixture may further include water 106.
• the cementitious composition 100 may also include one or more fibers 108 dispersed in the mixture 102.
• various embodiments may relate to a cement-based composition 100 including a binder component 104 and water 106, which may form a mixture 102.
• the composition 100 may also include fiber(s) 108 mixed into the mixture 102.
• FIG. 1 serves purely for illustrating various possible constituents of the composition 100 according to various embodiments, and may not denote, for instance, the arrangement of the different constituents in the composition 100.
• the composition 100 may be referred to as a cement.
• the reactive magnesium oxide cement may include predominantly magnesium oxide (MgO).
• the reactive magnesium oxide cement may include a small amount of other materials such as calcium oxide (CaO), silicon oxide (S1O2), iron oxide (Fe 2 03), and/or aluminum oxide (AI2O3).
• the reactive magnesium oxide cement may include more than about 50% magnesium oxide, e.g. more than about 80% magnesium oxide, e.g. more than 90% about magnesium oxide, e.g. more than about 95% magnesium oxide, e.g. more than about 96% magnesium oxide, e.g. more than about 97% magnesium oxide, e.g. more than about 98% magnesium oxide, e.g. more than about 99% magnesium oxide, e.g. about 100% magnesium oxide by mass.
• SHCC is a superior construction material, but may not be environment-friendly due to the high Portland cement usage.
• Reactive MgO cement RMC
• RMC Reactive MgO cement
• Various embodiments may integrate reactive MgO cement into SHCC, resulting in a sustainable construction material. Compared with traditional Portland cement-based SHCC, various embodiments may reduce carbon dioxide emissions, from raw material manufacturing to SHCC field applications, by at least about 40% to about 60%.
• the binder component 104 may further include any one or more binders selected from a group consisting of hydraulic cement, coal fly ash, silica fume, and ground granulated blast furnace slag.
• binders selected from a group consisting of hydraulic cement, coal fly ash, silica fume, and ground granulated blast furnace slag.
• the addition of such binders may greatly reduce the cost of production, and may contribute to mechanical performance through cementitious and pozzolanic reactions.
• Such binders may be obtained from industrial wastes.
• the binder component 104 may include reactive magnesium oxide cement (RMC), and coal fly ash (alternatively referred to as fly ash (FA)).
• RMC reactive magnesium oxide cement
• FA coal fly ash
• FA may increase fluidity and may improve the rheological properties of the composition due to its spherical shape, which decreases inter-particle friction.
• fly ash may occupy any value from about 0% to about 60%, e.g. from about 0% to about 30%, of the binder component 104 by mass.
• Fly ash may include predominantly silicon oxide (S1O2) and aluminum oxide (AI2O3). Silicon oxide (S1O2) and aluminum oxide (AI2O3) may occupy more than 50%, e.g.
• fly ash may also include a small amount of other materials such as magnesium oxide (MgO), calcium oxide (CaO), iron oxide (Fe203), potassium oxide (K2O), titanium oxide (Ti02) etc.
• MgO magnesium oxide
• CaO calcium oxide
• Fe203 iron oxide
• K2O potassium oxide
• Ti02 titanium oxide
• the binder component 104 may consist of only reactive magnesium oxide cement.
• a percentage of reactive magnesium oxide cement in the binder component 104 by mass may be any one percentage value selected from a range from about 40 % to about 100%.
• a mass ratio of water to binder component may be any one ratio selected from a range from about 0.4 (i.e. 0.4 : 1) to about 0.8 (i.e. 0.8 : 1), e.g. from about 0.4 (i.e. 0.4 : 1) to about 0.6 (i.e. 0.6: 1).
• a low w/b ratio may lead to higher viscosity for better fiber dispersion.
• a low w/b ratio may also be associated with high compressive strength of the resultant composite. However, reduction of w/b, e.g. from 0.53 to 0.41, may enhance first cracking and ultimate tensile strength, as well as lead to better ductility.
• the mixture 102 may further include a water reducing agent.
• the water reducing agent may be sodium hexametaphosphate solution (Na(P0 3 ) 6 ).
• a percentage of the water reducing agent relative to the binder component by mass may be any one percentage value selected from about 2% to about 4%.
• the mixture 102 may also include a viscosity controlling agent.
• the viscosity controlling agent may be hydroxypropyl methylcellulose (HPMC).
• HPMC hydroxypropyl methylcellulose
• a percentage of the viscosity controlling agent relative to the binder component by mass may be any one percentage value selected from a range from about 0.05% to about 0.5%.
• the water 106 may be present in the mixture 102 in conjunction with the water reducing and/or the viscosity control agent to achieve adequate rheological properties.
• the mixture 102 in the fresh stage may be a Bingham liquid.
• the one or more fibers 108 may be one or more types of fibers selected from a group consisting of metallic fibers, polymeric fibers, and natural fibers.
• the one or more fibers 108 or polymeric fibers may be any one type of fibers selected from a group consisting of polyvinyl alcohol (PVA) fibers, ethyl vinyl acetate (EVOH) fibers, (PE) polyethylene fibers, acrylic fibers, polypropylene (PP) fibers, and acrylamide fibers.
• PVA polyvinyl alcohol
• EVOH ethyl vinyl acetate
• PE polyethylene fibers
• acrylic fibers acrylic fibers
• PP polypropylene
• acrylamide fibers acrylamide fibers
• a percentage of the one or more fibers 108 in the cementitious composition by volume may be any one percentage value selected from a range from about 0.5% to about 10%, from about 1% to about 3%, e.g. from about 1% to about 2%.
• the one or more fibers 108 may have an average tensile strain capacity of about 1% to about 10%, e.g. of about 3% to about 7%.
• the one or more fibers 108 may have an average diameter selected from a range from about 10 ⁇ to about 60 ⁇ , e.g. from about 25 ⁇ to about 50 ⁇ , e.g. from about 35 ⁇ to about 45 ⁇ .
• the one or more fibers 108 may have an average length selected from a range from about 5 mm to about 30 mm, e.g. from about 6 mm to about 25 mm, e.g. from about 6 mm to about 18 mm, e.g. from about 8 mm to about 12 mm.
• an increase in fiber aspect ratio may lead to improvements in tensile strength and/or ductility.
• each of the one or more fibers 108 may include a coating of an oiling agent (may alternatively be referred to as oil).
• the oiling agent may be poly- oxymethylene. Any other suitable oiling agents may also be used.
• the one or more fibers 108 may be hydrophilic fibers.
• the hydrophilicity of certain types of fibers 108 may introduce strong interfacial bonds between fibers and the surrounding matrix when the composition 100 is cured.
• the oiling agent may be applied to prevent over-enhancement of the interfacial bonds.
• the oiling agent may help improve tensile ductility.
• each of the one or more fibers 108 may not include, i.e. may be devoid of, a coating of an oiling agent.
• Various embodiments may involve using fibers 108 to reinforce brittle matrix including reactive MgO cement.
• the resulting strain hardening reactive MgO composites (SHMC) or structures may have a density of any value in the range from about 1,500 kg/m 3 to about 2,500 kg/m 3 , and may have a tensile ductility of at least about 1%.
• Various embodiments may sequestrate carbon dioxide (C0 2 ) of up to 1 ton during the curing process before it reaches its designed compressive strength.
• composition 100 formed by any suitable method as described herein.
• Various embodiments may relate to a composition including reactive MgO cement (RMC), water, and fibers in different proportions.
• RMC reactive MgO cement
• Other optional constituents such as water reducing agents and viscosity controlling agents, may be needed to adjust thixotropic rheology and viscosity characteristics to achieve adequate workability and to disperse the fibers uniformly.
• Reactive MgO cement may be obtained from the calcination of magnesium carbonate or magnesium hydroxide at temperatures lower than 1000°C.
• Other binders like hydraulic cement, coal fly ash, silica fume, and ground granulated blastfurnace slag may be added as optional supplements.
• the addition of such binders from industrial wastes may greatly reduce the cost of MgO, and may contribute to mechanical performance through cementitious and pozzolanic reactions.
• the fraction of reactive MgO cement in the binder component may be of any percentage selected from a range from about 40% to about 100%.
• the binders may set in the presence of water and may gain strength under exposure to carbon dioxide.
• Water may be present in the fresh mixture in conjunction with a water reducing and viscosity controlling or modifying agent to achieve adequate rheological properties.
• a water-to- binder ratio of any value selected from a range from about 0.4 to about 0.8 may be used to achieve the desired strength.
• a water reducing agent may be used to adjust the desired workability level after the water content in the composite is determined. The quantity of water reducing agent needed may vary with the water-to-binder ratio, composition of binder, and/or type of water reducing agent.
• An illustrative water reducing agent may be sodium hexametaphosphate (NaHMP) (Na(P03) 6 ) solution.
• the amount of (Na(P03) 6 ) may be of any percentage selected from a range from about 2% to about 4% of the binder by mass.
• An illustrative viscosity controlling agent is hydroxypropyl methylcellulose (HPMC).
• HPMC hydroxypropyl methylcellulose
• the typical amount of HPMC may be of any percentage selected from a range from about 0.05% to about 0.5% of the binder by mass.
• the fibers may be one or more of any suitable types of discontinuous fibers, and may be provided in a bundled form.
• suitable fibers may include, but may not be limited to polyvinyl alcohol (PVA) fibers, ethyl vinyl acetate (EVOH) fibers, polyethylene (PE) fibers, acrylic fibers, polypropylene (PP) fibers and acrylamide fibers.
• the amount of fibers, the nature of the fibers, and/or the size of the fibers in the composition may vary.
• the amount of fibers required may be so that it is sufficiently high enough for the provision of the required ductility to the composition, but may be of a low level enough to allow self-compaction
• the tensile strain capacity of the composition may be of any percentage selected from a range from about 1% to about 10%, e.g. from about 3% to about 7%.
• compaction may be difficult without vibration if the fiber content exceeds 2.5%.
• Fibers included in SHMC may be of any percentage selected from a range of about 0.5% to 10% by volume, e.g. from about 1% to about 3% by volume, e.g. from about 1% to about 2% by volume.
• the fibers may have diameters of from about 10 ⁇ to about 60 ⁇ , e.g. from about 10 ⁇ to about 20 ⁇ , or from about 25 ⁇ to about 50 ⁇ , e.g. from about 35 ⁇ to about 45 ⁇ , and lengths from about 5 mm to about 30 mm, e.g. from about 6 mm to about 25 mm, e.g. from about 6 mm to about 18 mm, e.g. from about 8 mm to about 12 mm.
• the fibers may be PVA fibers.
• the surface of PVA fibers may be coated with oiling agent (such as poly-oxymethylene) by up to about 1.5% by the weight of the fibers, e.g. of any value selected from a range from about 0.8% to about 1.2% by weight relative to the fibers.
• the fibers may be coated with the oiling agent by any conventional manner, such as by dip-coating or spraying the fibers. Other oiling agents may be used.as well.
• the hydrophilicity of PVA fibers may introduce strong interfacial bonds between fibers and surrounding matrix. The oiling agent may be applied to prevent over-enhancement of the interfacial bonds.
• Various embodiments may relate to a cement-based structure.
• the cement-based structure may be a composite structure.
• the cement-based structure may be formed from the cementitious composition.
• FIG. 2 shows a general illustration of cement-based structure according to various embodiments.
• the cement-based structure 200 may include a matrix 202 including one or more hydrated magnesium carbonates.
• the cement-based structure 200 may include one or more fibers 204 embedded in the matrix 202.
• various embodiments may provide a structure having fibers 204 within a matrix 202 including one or more hydrated magnesium carbonates.
• the structure 200 may be a composite structure, and may be referred to as a composite.
• the structure 200 may be formed by hardening of the cementitious composition. In various embodiments, the structure 200 may be formed by curing of the cementitious composition.
• FIG. 2 serves purely for illustrating various possible constituents of the cement-based structure 200 according to various embodiments, and may not denote, for instance, the arrangement of the various constituents within the structure 200.
• the one or more hydrated magnesium carbonates may be selected from a group consisting of nesquehonite (MgC0 3 -3H20), hydromagnesite (4MgC0 Mg(OH) 2 -4H20), dypingite (4MgC0 Mg(OH)2-5H 2 0), and artinite (MgC0 3 Mg(OH) 2 -3H 2 0).
• the one or more fibers 204 may be bonded to the matrix 202. There may be interfacial bonds between the matrix 202 and the one or more fibers 204.
• the one or more fibers 204 may extend or may be uniformly dispersed throughout the structure 200.
• the cement-based structure 200 may be concrete. In various other embodiments, the cement-based structure 200 may be mortar.
• Various embodiments may relate to a structure 200 formed by any suitable method described herein.
• FIG. 3 is a schematic showing a method of forming a cementitious composition according to various embodiments.
• the method may include, in 302, forming a mixture.
• the mixture may include a binder component including reactive magnesium oxide cement.
• the mixture may also include water.
• the method may include, in 304, dispersing one or more fibers in the mixture.
• various embodiments may relate to forming a cement.
• the cement may include a binder including reactive magnesium oxide cement.
• the cement may also include water.
• the cement may also include one or more fibers.
• the binder component may further include any one or more binders selected from a group consisting of hydraulic cement, coal fly ash, silica fume, and ground granulated blast furnace slag.
• a percentage of reactive magnesium oxide cement in the binder component by mass may be any one percentage value selected from a range from 40 % to 100%.
• a mass ratio of water to binder component may be any one ratio selected from a range from 0.4 to 0.8.
• the mixture may further include a water reducing agent, such as sodium hexametaphosphate (Na(P0 3 ) 6 ) solution.
• a water reducing agent such as sodium hexametaphosphate (Na(P0 3 ) 6 ) solution.
• a percentage of the water reducing agent relative to the binder component by mass may be any one percentage value selected from 2% to 4%.
• the mixture may further include a viscosity controlling agent, such as hydroxypropyl methylcellulose.
• a viscosity controlling agent such as hydroxypropyl methylcellulose.
• a percentage of the viscosity controlling agent relative to the binder component by mass may be any one percentage value selected from a range from 0.05% to 0.5%.
• the one or more fibers may be any one type of fibers selected from a group consisting of polyvinyl alcohol fibers, ethyl vinyl acetate fibers, polyethylene fibers, acrylic fibers, polypropylene fibers, and acrylamide fibers.
• a percentage of the one or more fibers in the cementitious composition by volume may be any one percentage value selected from a range from 0.5% to 10%.
• Each of the one or more fibers may include a coating of an oiling agent.
• Various embodiments may relate to a cementitious composition formed from any method described herein.
• the fiber-reinforced cementitious composition may be prepared in any suitable manner.
• a method of preparing the fiber-reinforced cementitious composition may follow the steps of 1 ) mixing dry powders including reactive MgO cement and supplementary binders like fly ash; 2) mixing of the above with water and Na(P03) 6 solution for several minutes; 3) adding fibers, such as PVA fibers into the fresh mixture and mixing until a homogenous mixture is achieved.
• a cement-based structure may be formed from the composition by curing in ambient air or elevated carbon dioxide (CO2) conditions in a manually controlled environment until it achieves desirable mechanical strength.
• CO2 carbon dioxide
• Various embodiments may relate to a method of forming a cement-based structure.
• FIG. 4 is a schematic showing a method of forming a cement-based structure according to various embodiments.
• the method may include, in 402, forming a matrix including one or more hydrated magnesium carbonates.
• One or more fibers may be embedded in the matrix.
• various embodiments may relate to a method of forming a cement-based structure, such as concrete or mortar, including a matrix containing of hydrated magnesium carbonates, and a plurality of fibers within the matrix.
• the method may include embedding or dispersing the one or more fibers in the matrix.
• forming the matrix, wherein the one or more fibers are embedded in the matrix may include forming a cementitious composition.
• the cementitious composition may include a mixture including a binder component (including reactive magnesium oxide cement), and water.
• Forming the matrix may further include curing the cementitious composition by exposing the cementitious composition to carbon dioxide (CO2) so that the one or more hydrated magnesium carbonates is formed from the reactive magnesium oxide cement.
• CO2 carbon dioxide
• curing may be carried out for any suitable duration. In various embodiments, curing may be carried out for any suitable duration from 7 days to 28 days. An increased curing duration may lead to an improvement in ultimate tensile strength, and reduction in strain hardening.
• Curing may be carried out in a carbonation chamber or in air under ambient conditions. Curing may take place at any suitable temperature, e.g. any temperature selected from a range from 25 °C to 40 °C, e.g. from 30 °C to 35 °C. Curing may be carried out at any suitable C0 2 concentration, e.g. any concentration selected from 5% to about 20%, by volume, e.g. about 10% by volume. Curing may be carried out at any suitable relative humidity, e.g. a relative humidity of above 50%, e.g. above 60%, above 70%, above 80% e.g. about 90%.
• any suitable relative humidity e.g. a relative humidity of above 50%, e.g. above 60%, above 70%, above 80% e.g. about 90%.
• Forming the one or more hydrated magnesium carbonates may include forming brucite (Mg(OH) 2 ) from the reactive magnesium oxide cement, and forming the one or more hydrated magnesium carbonates from brucite.
• the magnesium oxide from the reactive magnesium oxide cement may react with water to form brucite.
• Brucite may react with carbon dioxide to form hydrated magnesium carbonates, such as such as nesquehonite (MgC0 3 -3H 2 0), hydromagnesite (4MgC0 Mg(OH) 2 -4H 2 0), dypingite (4MgC0 Mg(OH) 2 -5H 2 0), and/or artinite (MgC0 3 Mg(OH) 2 -3H 2 0).
• Various embodiments may involve sequestration of carbon dioxide from the atmosphere or surroundings.
• the one or more fibers may be bonded to the matrix.
• the cement-based structure may be concrete or mortar.
• the cement-based structure may achieve tensile ductility or tensile strain capacity of above 1%.
• Various embodiments may have an average crack width of less than 150 ⁇ , e.g. less than 100 ⁇ .
• Two exemplary mixes are presented for preparing strain hardening reactive MgO composites (SHMC). These mixes may include reactive MgO cement, coal fly ash, water, Na(P0 3 ) 6 , and fibers.
• the mix proportions are tabulated in Table 1.
• Reactive MgO cement provided by International Scientific Ltd. of Singapore, coal fly ash provided by Bisley Asia Pte Ltd. of Singapore, and Na(P0 3 ) 6 provided by VMR Pte Ltd. of Singapore, were used in both mixes.
• Reactive MgO and fly ash were used as the main binders, while the Na(P0 3 ) 6 was used as a water reducer to achieve the required workability for good fiber dispersion.
• the polyvinyl alcohol (PVA) fibers were manufactured by Kuraray Co. Ltd., Japan.
• the fiber length was 12 mm and the fiber diameter was 39 ⁇ .
• Two different fiber surface oil-coating contents at 0.0% and 1.2% relative to mass of the fibers were used respectively for the two example mixes (Mix 1 and Mix 2).
• compositions (Mix 1 and Mix 2) were prepared in a mixer with a planetary rotating blade.
• the mixing process followed the following steps: 1) Na(P03) 6 was dissolved into the water, forming a Na(P03) 6 solution; 2) all the solid raw materials in powder form, i.e. MgO cement and fly ash, were dry-mixed for more than five minutes; 3) the Na(P03) 6 solution was slowly added into the dry powder mixture; 4)this blend was mixed for over three minutes until the liquid and solid were uniformly mixed; 5) PVA fibers were added into the mixture; 6) the mixing process continued for another three minutes.
• the PVA fibers were not coated with oiling agent, while in Mix 2, the PVA fibers were coated oiling agent.
• FIG. 5 A is a plot of weight percentage (in percent or %) /heat flow (in milli-Watts or mW) as a function of temperature (in degrees Celsius or °C) showing the thermogravimetric analysis (TGA) and differential thermal analysis (DGA) results of samples formed from Mix 1 and Mix 2 according to various embodiments.
• TGA thermogravimetric analysis
• DGA differential thermal analysis
• a weight loss (lines (i) and (ii)), corresponding to the decomposition of hydrated magnesium carbonates (HMC), may be observed between 388 °C to 900 °C. Heat absorption may also be observed in the same temperature range (lines (iii) and (iv)).
• the amount of carbon dioxide (CO2) sequestrated during curing may be determined quantitatively with the weight loss.
• Table 2 shows the CO2 sequestration measured by the TGA/ DTA methods, as well as the hydrochloric acid (HC1) decarbonation method.
• FIG. 5B is a plot of tensile stress (in mega-Pascals or MPa) as a function of tensile strain (in percent or %) showing the uniaxial tensile stress-strain curves of samples formed from Mix 1 according to various embodiments.
• FIG. 5C is a plot of tensile stress (in mega-Pascals or MPa) as a function of tensile strain (in percent or %) showing the uniaxial tensile stress-strain curves of samples formed from Mix 2 according to various embodiments. It can be seen that both Mix.l and Mix.2 may achieve ultra-high tensile ductility of at least 1%.
• Commercial applications of the compositions as well as structures/composites may include the manufacturing of unreinforced structural and building components, which include bricks, blocks and pavers, the market size of which is estimated to reach 8.9 billion USD in 2018.
• FIG. 6 is a plot of fiber-bridging stress ( ⁇ ) as a function of crack opening displacement ( ⁇ ) showing the tensile stress-crack opening displacement curve and strain-hardening criteria, illustrating the fiber-bridging constitutive law.
• the hardened composites may need to satisfy the two strain-hardening criteria.
• the complementary energy of the fiber-bridging curve, Jt i.e. the hatched area
• Jt the complementary energy of the fiber-bridging curve
• ⁇ 0 is the maximum fiber-bridging strength
• ⁇ 0 is the crack opening corresponding to the maximum fiber-bridging strength
• a ss is the steady-state cracking strength
• S ss is the crack opening corresponding to the steady-state cracking strength, a ss .
• the maximum fiber-bridging strength, ⁇ 0 (i.e. the curve peak), may be required to be higher than the tensile cracking strength of the matrix, o c , as shown in Equation (2).
• Various embodiments may relate to RMC-based strain-hardening composites (SHC) or structures.
• SHC strain-hardening composites
• Various embodiments relating to various composites or structures may be influenced by key parameters during the process of forming the composites or structures.
• the first part of Experiment 2 focuses on the effect of water/binder (w/b) ratio and fly ash (FA) content on the rheological properties of RMC compositions or pastes, with the goal of determining a suitable mix design that leads to a desired viscosity and sufficient flowability for good fiber dispersion.
• the second part of Experiment 2 focuses on the inclusion of fibers within the mix design determined in the first stage and investigates the effect of certain factors such as the w/b ratio, fiber aspect ratio, fiber surface treatment and curing age on the performance of the developed formulations.
• Reactive magnesium oxide cement obtained from International Scientific Ltd. (Singapore) was the main binder used in this study.
• Class F fly ash (FA) obtained from Bisley Asia Ltd. (Malaysia), was used to adjust the rheology of the fresh mixtures and function as a binder via its pozzolanic reaction with brucite.
• Table 3 shows the chemical compositions of reactive magnesium oxide cement (RMC) and fly ash (FA).
• FIG. 7 is a plot of cumulative fraction (in percent or %) as a function of particle diameter (in micrometers or ⁇ ) showing particle size distribution of reactive magnesium oxide cement (RMC) and fly ash (FA) used in compositions according to various embodiments.
• RMC reactive magnesium oxide cement
• FA fly ash
• Fiber type i.e.
• the first part of Experiment 2 studied the effect of water/binder (w/b) and fly ash/binder (FA/b) ratios on the rheology of fresh mixtures before the inclusion of fibers.
• the goal of this part was to determine a suitable mix design (i.e. w/b ratio and FA content) that led to a desired plastic viscosity and flowability for good fiber dispersion.
• the second part during which PVA fibers were introduced into the mix design determined in the first part, studied the effect of the w/b ratio, fiber aspect ratio, fiber surface treatment (i.e. oil content) and curing age on the mechanical properties of the RMC -based strain-hardening composite (SHC).
• sample names followed a format of FA(X)-(Y), where X represented the FA content (i.e. as a percentage of the total binder) and Y represented the w/b ratio.
• X represented the FA content (i.e. as a percentage of the total binder)
• Y represented the w/b ratio.
• a range of w/b (0.47-0.58) and FA/b (0-0.6) ratios were determined from preliminary samples prepared for each formulation.
• the sample preparation process started with the dissolving of Na(P0 3 ) 6 in the predetermined amount of water. This solution was then added to the dry mix of RMC and FA during the mixing process. A stopwatch was set to notify two minutes from the moment the solution was added to the dry RMC-FA mix. After two minutes of mixing, one spoon of the fresh mixture was placed onto a 39 mm proliferated base plate on the rheometer, equipped with a 39 mm P35 TiL top plate pressed against the mixture at 0.5 N.
• FIG. 8A shows the rheometer used to measure the samples according to various embodiments.
• FIG. 8B shows the test setup used to measure the samples according to various embodiments.
• results from the first part of the study were used in the selection of w/b and FA/b ratios to be incorporated in the mix designs in the second part.
• Previous literature has shown that while the fiber dispersion coefficient increased with plastic viscosity, tensile ductility stabilized after a threshold fiber dispersion coefficient. This value corresponded to a plasticity of about 3.5 Pa s, which was also adopted in this study for the preparation of samples used in the testing of tensile properties.
• the four mix proportions listed in Table 6 were prepared to assess the effect of w/b ratio, fiber aspect ratio, fiber surface treatment (i.e. oil content), and curing age on the tensile performance of the RMC -based strain-hardening composite (SHC).
• FIG. 9A shows the top view and side view of a dog-bone shaped mold according to various embodiments.
• FIG. 9B shows the test setup for conducting the uniaxial tensile test for the samples according to various embodiments.
• the loading rate was set at 0.02 mm/min and two linear variable differential ransformers (LVDTs) were used to determine the extension of the gauged length (about 60 mm to about 70 mm).
• LVDTs linear variable differential ransformers
• the crack width and spacing on each specimen were determined with a Nikon DS-Fi2 high resolution camera at a magnification of about 420x. For each mix design, three to six specimens were analyzed to evaluate their crack patterns.
• FIG. 10A is a plot of torque ⁇ (in Pascals or Pa) as a function of shear rate N (per second or 1/s) showing the torque-shear rate ( ⁇ - N) of sample FA60-0.53 at 6 minutes (mins), 12 minutes (mins), and 18 minutes (mins) according to various embodiments.
• FIG. 10B is a plot of torque ⁇ (in Pascals or Pa) as a function of shear rate N (per second or 1/s) showing the magnified plot of the box outlined in FIG. 10A according to various embodiments.
• FIGS. 10A-B may illustrate the relationship between the shear resistance ⁇ (Pa) and shear rate N (/s) of a fresh RMC mixture at different elapsed times.
• the curves show that the fresh mixtures (i.e. without the fibers) were Bingham liquids, in which the shear force exceeded the initial mixture resistance to initiate rotation, after which the shear resistance increased linearly with the rotation speed N (/s), showing no shear thinning or thickening effect.
• the fresh mixtures do not contain fibers.
• Equation 3 The relationship between ⁇ and N of Bingham liquids is quantitatively described by Equation 3, where g (Pa), the intercept on the y-axis, is the yield stress needed to break the network of interactions between particles and initiate rotation; and h (Pa-s), the slope of the curve, is the plastic viscosity.
• g and h are constants that represent the rheological properties of that mixture.
• shear resistance which varies with shear rate (N) and solid volume fraction (V s ), depends on several types of particle interactions (i.e. Van der Waals forces, direct contact forces between particles and hydrodynamic forces, for which the friction between fluid layers increases with velocity).
• the yield stress (g) may be mainly determined by Van der Waals or direct contact forces.
• a generally increasing trend in g and h may be observed with elapsed time. This may be possibly associated with the precipitation of brucite (Mg(OH) 2 ) on the surface of RMC particles, which increased the direct contact between particles by enlarging the solid particle sizes, leading to additional drag between fluid layers.
• brucite Mg(OH) 2
• FIGS. 11A-B show the effects of water and FA contents on the rheological properties of RMC samples.
• FIGS. 11A-B show declining trends in both yield stress (g) and plastic viscosity (h) were observed with increasing water content.
• FIG. 11 A shows a plot of plastic viscosity (in Pascals second or Pa s) as a function of fly ash / binder ratio (FA/b) (in percent or %) illustrating the effects of the water and fly ash contents on the plastic viscosity of the mixture according to various embodiments.
• FIG. 11 A shows a plot of plastic viscosity (in Pascals second or Pa s) as a function of fly ash / binder ratio (FA/b) (in percent or %) illustrating the effects of the water and fly ash contents on the plastic viscosity of the mixture according to various embodiments.
• FIG. 11 A shows a plot of plastic viscosity (in Pascals second or Pa s) as a function of fly ash /
• IB shows a plot of yield stress (in Pascals or Pa) as a function of fly ash / binder ratio (FA/b) (in percent or %) illustrating the effects of the water and fly ash contents on the yield stress of the mixture according to various embodiments.
• the crack spacing may be computed by:
• FIGS. 12A-E show the relationship between the tensile stress and strain of composites formed from each mix.
• the notation for sample names followed a format of (X)-(Y)-(Z), where X, Y and Z represented the fiber surface treatment, fiber length and w/b ratio, respectively.
• the term 'OC for (X) refers to oil coating, while the term 'NC refers to no oil coating.
• the unit for (Y) is in millimeters (mm).
• FIG. 12A is a plot of tensile stress (in mega Pascals or MPa) as a function of tensile strain (in percent or %) illustrating tensile stress-strain curves of the samples NC- 12-0.41 after curing for 7 days according to various embodiments.
• FIG. 12B is a plot of tensile stress (in mega Pascals or MPa) as a function of tensile strain (in percent or %) illustrating tensile stress-strain curves of the samples NC- 12-0.41 after curing for 28 days according to various embodiments.
• FIG. 12A is a plot of tensile stress (in mega Pascals or MPa) as a function of tensile strain (in percent or %) illustrating tensile stress-strain curves of the samples NC- 12-0.41 after curing for 28 days according to various embodiments.
• FIG. 12C is a plot of tensile stress (in mega Pascals or MPa) as a function of tensile strain (in percent or %) illustrating tensile stress-strain curves of the samples OC- 12-0.41 after curing for 7 days according to various embodiments.
• FIG. 12D is a plot of tensile stress (in mega Pascals or MPa) as a function of tensile strain (in percent or %) illustrating tensile stress-strain curves of the samples OC- 12-0.53 after curing for 7 days according to various embodiments.
• FIG. 12C is a plot of tensile stress (in mega Pascals or MPa) as a function of tensile strain (in percent or %) illustrating tensile stress-strain curves of the samples OC- 12-0.41 after curing for 7 days according to various embodiments.
• FIG. 12D is a plot of tensile stress (in mega Pascals or MPa) as a function of tensile
• 12E is a plot of tensile stress (in mega Pascals or MPa) as a function of tensile strain (in percent or %) illustrating tensile stress-strain curves of the samples OC-8-0.53 after curing for 7 days according to various embodiments.
• FIG. 13 is an image showing the typical crack distribution of a failed specimen (NC-12- 0.41 with 7 days of curing) after unloading according to various embodiments.
• FIG. 13 illustrates the occurrence of multiple cracks in RMC -based samples.
• the typical fracture surface may be seen in FIG. 14 A, where the layout of fibers at the location of the crack at failure is revealed.
• FIG. 14A is an image showing the fracture surface of the specimen shown in FIG. 13 according to various embodiments. The fracture surface has several pulled fibers.
• FIGS. 14B and 14C are shown in FIGS. 14B and 14C respectively.
• FIG. 14B is a field emission scanning electron microscopy (FESEM) image of a pulled-out fiber shown in FIG. 14A according to various embodiments.
• FIG. 14C is a field emission scanning electron microscopy (FESEM) image of a left-over tunnel in the matrix after the fiber shown in FIG. 14B is pulled out according to various embodiments.
• FESEM field emission scanning electron microscopy
• the fiber surface was smooth with a very small amount of matrix debris attached on it, showing that a majority of the fibers were pulled out instead of ruptured. This suggests the fiber strength may not be fully utilized in the developed formulations, and the limiting factor may be the fiber-matrix interface, which may be further strengthened.
• the effect of fiber surface treatment in terms of the presence of the oil coating on sample performance may be assessed via a comparison of a sample having fibers with an oil coating (OC- 12-0.41) and a sample having fibers without an oil coating (NC-12-0.41). Both samples may be cured for 7 days before being tested.
• the effect of fiber aspect ratio caused by the differences in fiber lengths can be evaluated via a comparison of sample OC-8-0.53 containing fibers with lengths of 8 mm, and sample OC- 12-0.53 containing fibers with lengths 12 mm.
• An increase in the fiber aspect ratio may lead to a significant improvement in tensile strength and ductility.
• the effect of w/b on the compressive and tensile strength of RMC-SHC formulations may be determined via a comparison of sample OC-12-0.41 and sample OC-12-0.53.
• a reduction in the compressive strength was observed with an increase in the w/b ratio from 0.41 to 0.53.
• This may be associated with a decrease in the diffusion rate of carbon dioxide (CO2) within the saturated pore system at higher water contents, which would reduce the extent of carbonation and the associated formation of strength providing carbonate phases; as well as the increased porosity through the presence of additional free water.
• CO2 carbon dioxide
• the fiber- matrix interface may also be weakened, causing a reduction in the strength of the bonding between the fiber and the matrix.
• the effect of curing duration on sample performance may be determined via an investigation of a sample of NC- 12-0.41 that has been cured for 7 days and another sample of NC- 12-0.41 that has been cured for 28 days.
• the enhanced ultimate strength may be associated with the improvements in fiber-bridging, which may be attributed to the continued formation of carbonate phases that strengthened the fiber-matrix interface over the 28-day curing period.
• An increase in the crack spacing and average crack width was observed with an increase in curing duration from 7 days to 28 days, indicating a reduction in strain-hardening, which was influenced by the enhanced matrix toughness at longer curing durations.
• FIG. 15 is a plot of mass (in percent or %) / heat flow (in milli-Watts or mW) as a function of temperature (in degree Celsius or °C) showing the thermogravimetric analysis (TGA) curve and the differential scanning calorimetry (DSC) curve of a sample of OC-12-0.53 according to various embodiments.
• the mass loss ⁇ 100 °C due to the loss of hydroscopic water was followed by two distinct endothermic peaks.
• the first peak at around 320 °C may correspond to the removal of water of crystallization in Mg-carbonates that formed during carbonation curing, and the decomposition of uncarbonated hydrates (Mg(OH) 2 ) into MgO.
• the second peak at around 460 °C may correspond to the decarbonation of carbonate phases, leaving MgO at the end of the analysis.
• the quantification of the mass loss at > 460 °C which was associated with the loss of CO2 from the carbonated RMC system, revealed an average carbonation degree of around 10%.

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• 2018
  • 2018-09-18 WO PCT/SG2018/050475 patent/WO2019054950A1/en active Application Filing
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