AU2020430725B2

AU2020430725B2 - Sprayable cementitious composition

Info

Publication number: AU2020430725B2
Application number: AU2020430725A
Authority: AU
Inventors: Victor C. Li; Chung Wai SO; He ZHU
Original assignee: Individual
Current assignee: Individual
Priority date: 2020-02-18
Filing date: 2020-05-14
Publication date: 2023-08-03
Anticipated expiration: 2040-05-14
Also published as: MX2022009511A; CN115038676A; WO2021167635A1; JP2023513865A; TW202138334A; AU2020430725A1; TWM628911U

Abstract

A sprayable ductile metal-like cementitious composition (SDMCC) comprising: a composite binder, fibres, and water; wherein the composite binder comprises a cement component and a pozzolan component. The SDMCC may exhibit expansion on curing and strain hardening behaviour. The SDMCC is useful for repairing and/or retrofitting building structures such as pipelines. Also described are methods for the preparing the SDMCC.

Description

SPRAYABLE CEMENTITIOUS COMPOSITION TECHNICAL FIELD

[0001] The present invention relates to a sprayable ductile metal-like cementitious composition (SDMCC). The present invention also relates to use of the SDMCC for repairing or retrofitting building structures, such as underground pipelines, and a method for the use thereof.

BACKGROUND ART

[0002] Underground pipelines are vital infrastructure and may be used to transport and distribute water for a variety of purposes, including drinking water and wastewater. Pipelines used for these purposes often experience severe mechanical load and environmental stresses. As a result, both metal pipes and concrete pipes are susceptible to problems such as cracking, spalling, and debris built-up. Metal pipes may corrode or deform. If left without repair, these issues can lead to pipeline failure.

[0003] Trenchless pipeline repair technologies are useful techniques for repairing existing pipelines with minimal disruption. Reduced construction cost, reduced environmental impact, and reduced public disturbance mean that trenchless pipeline repair technology is often preferred over open-trench methods. Known trenchless pipeline repair methods include cure-in place pipe (CIPP) methods, slip lining, close-fit pipe methods, spiral wound lining methods, splice segment lining and sprayed lining. Compared to other methods, sprayed lining with cement-based materials may offer advantages such as lower cost and faster construction. Spray lining can also be formed continuously without joints.

[0004] Sprayed lining methods involve spraying a cementitious or polymer-based material onto the internal surface of an existing pipeline. Cementitious materials are low cost but typically have poor corrosion protection of steel host pipes. Polymer-based materials typically have better corrosion resistance but are more expensive. Once sprayed onto the substrate, the material must have good adhesion and cohesion to build up the desired thickness. The internal surfaces of pipelines are typically adverse to coating materials. Although pipelines are usually cleaned before spraying, lack of adhesion between the sprayed material and the internal pipe wall remains a major challenge.

[0005] Conventional cementitious materials are brittle, with no tensile ductility. To attain high strength and dense microstructure, cementitious repair materials usually contain a large quantity of fine and reactive powders and require low water content. This combination results in high shrinkage of the cementitious material, which can lead to restrained shrinkage cracking. After cracking, the fluid in the pipeline penetrates the cracks and further corrodes the pipe. In addition, if there is poor adhesion, the cracked repair materials may spall off. Consequently, the use of conventional cementitious materials often results in the repaired pipeline being less durable and requiring repeated maintenance.

[0006] To overcome the inherent brittleness of cement-based materials, fibre-reinforced composites called engineered cementitious composites (ECCs) have been developed for spray repair. An ECC exhibits a high strain capacity, larger than 3% under uniaxial tension. The high ductility of an ECC is realised by multiple tight cracks instead of a single crack typical of normal concrete. However, ECC mixes generally have a higher volume of cement and no coarse aggregate when compared with normal concrete, so drying shrinkage may reach -1500 με at 28 days. Increased shrinkage may result in microcracking when deformation is restrained. The presence of microcracks in an aggressive environment may affect the durability of the spray repair. Examples of ECCs are disclosed in the following patents.

[0007] US patent No. 7,241,338 discloses a sprayable cementitious composition comprising a hydraulic cement such as Portland cement, a non-Newtonian additive, a viscosity agent, a superplasticizer, a short discontinuous fibre, a lightweight aggregate, and water.

[0008] US patent No. 7,572,501 discloses cementitious composites comprising a cement such as Portland cement, water, sand, fly ash, water reducing agent, and discontinuous short fibres such as polyethylene (PE) fibres. The rheology of the composition can be adjusted to provide a composite that can be pumped, cast or sprayed.

[0009] US patent No. 7,799,127 discloses a class of polyvinyl alcohol (PVA) fibre-reinforced high early strength ECC materials. The materials comprise a hydraulic cement, a chemical accelerator admixture, polyvinyl alcohol fibres, non-matrix interactive crack initiators, one or more fine grained aggregates, and a chemical dispersant admixture.

[0010] It is an object of the present invention to go some way to avoiding the above disadvantages; and/or to at least provide the public with a useful choice.

[0011] Other objects of the invention may become apparent from the following description which is given by way of example only. [0012] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date.

SUMMARY OF THE INVENTION

[0013] In a first aspect, the present invention provides a sprayable cementitious composition comprising: a composite binder, fibres, and water; wherein the composite binder comprises a cement component and a pozzolan component.

[0014] In some embodiments, the ratio of water to composite binder is about 0.2 to about 0.5.

[0015] In some embodiments, the ratio of water to composite binder is about 0.2 to about 0.4.

[0016] In some embodiments, the ratio of water to composite binder is about 0.3.

[0017] In some embodiments, the cement component comprises a hydraulic cement and an expansion agent.

[0018] In some embodiments, the expansion agent is a calcium sulfoaluminate.

[0019] In some embodiments, the amount of the expansion agent is, based on the total cement component weight, about 10 to about 60 wt%.

[0020] In some embodiments, the amount of the expansion agent is, based on the total cement component weight, about 20 to about 50 wt%. [0021] In some embodiments, the average particle size of the expansion agent is about 2 μm to about 500 μm, or about 10 μm to about 30 μm.

[0022] In some embodiments, the hydraulic cement comprises ordinary Portland cement.

[0023] In some embodiments, the amount of the hydraulic cement is, based on the total cement component weight, about 1 to about 80 wt%. [0024] In some embodiments, the amount of the hydraulic cement is, based on the total cement component weight, about 20 to about 80 wt%. [0025] In some embodiments, the amount of the hydraulic cement is, based on the total cement component weight, about 50 to about 80 wt%.

[0026] In some embodiments, the amount of the hydraulic cement is, based on the total cement component weight, about 60 to about 80 wt%.

[0027] In some embodiments, the cement component comprises a reactive aluminosilicate, a calcium carbonate, or a mixture thereof.

[0028] In some embodiments, the reactive aluminosilicate is a calcined clay.

[0029] In some embodiments, the reactive aluminosilicate is a metakaolin.

[0030] In some embodiments, the calcium carbonate is a limestone.

[0031] In some embodiments, the cement component comprises a reactive aluminosilicate, a calcium carbonate, or a mixture thereof in an amount of, based on the total cement component weight, about 1 to about 80 wt%, or about 30 to about 60 wt %, or about 40 to 50 wt%.

[0032] In some embodiments, the cement component comprises a reactive aluminosilicate in an amount of, based on the total cement component weight, 0 to about 50 wt%, or about 20 to about 40 wt%, or about 30 wt%.

[0033] In some embodiments, the cement component comprises a calcium carbonate in an amount of, based on the total cement component weight, about 0 to about 30 wt%, or about 10 to about 20 wt%, or about 15 wt%.

[0034] In some embodiments, the ratio of reactive aluminosilicate to calcium carbonate is 2: 1.

[0035] In some embodiments, the cement component comprises, based on the total cement mixture weight, about 10 to about 50 wt% ordinary Portland cement (OPC), about 20 to about 40 wt% metakaolin, and about 10 to about 20 wt% limestone.

[0036] In some embodiments, the average particle size of the reactive aluminosilicate is about

2 μm to about 40 μm, or about 2 μm to about 10 μm.

[0037] In some embodiments, the average particle size of the calcium carbonate is about 2 μm to about 100 μm, or about 2 μm to about 20 μm. [0038] In some embodiments, the amount of the pozzolan component is about 1 to about 3 times, by weight, of the cement component.

[0039] In some embodiments, the amount of the pozzolan component is about 2 to about 3 times, by weight, of the cement component.

[0040] In some embodiments, the amount of the pozzolan component is about 2 to about 2.5 times, by weight, of the cement component.

[0041] In some embodiments, the pozzolan component comprises a material selected from the group consisting of fly ash, steel slag, granulated blast furnace slag, diatomaceous earth, silica fume, calcined clay such as metakaolin, calcined shale, volcanic ash, pumice, burnt silica-rich organic matter such as rice husk ash, and mixtures of any two or more thereof.

[0042] In some embodiments, the fly ash is selected from the group consisting of type C fly ash, type F fly ash, and mixtures thereof.

[0043] In some embodiments, the fibres are selected from the group consisting of polymeric fibres, inorganic fibres, metal fibres, carbon fibres, plant-based fibres, and mixtures of any two or more thereof.

[0044] In some embodiments, the polymeric fibres comprise a polymeric material selected from the group consisting of a polyolefin, a polyacrylic, a polyester, a polyvinyl alcohol, a polyamide, and combinations of any two or more thereof.

[0045] In some embodiments, the polymeric fibres are selected from the group consisting of polyethylene fibres, high tenacity polypropylene fibres, polyvinyl alcohol fibres, and mixtures of any two or more thereof.

[0046] In some embodiments, the amount of the fibres is, based on the total composition volume (i.e. the volume of the composition including water), from about 0.1 to less than 4 v/v%, or about 1 to about 3 v/v%, or about 1.5 to about 2.3 v/v%.

[0047] In some embodiments, the fibre length is about 4 mm to about 25 mm, or about 6 mm to about 20 mm, or about 8 mm to about 12 mm.

[0048] In some embodiments, the fibre diameter is about 10 μ tmo about 150 , μ omr about 10 pm to about 60 μm. [0049] In some embodiments, the sprayable cementitious composition further comprises one or more components selected from the group consisting of a superplasticizer, an aggregate, a viscosity agent, and a retarder agent.

[0050] In some embodiments, the amount of the superplasticizer is, based on the total composition weight, about 0.1 to 10 wt%, or about 0.3 to about 3 wt%, or about 0.5 to about 1.5 wt%.

[0051] In a further aspect, the present invention provides a sprayable cementitious composition comprising: a composite binder, fibres, and water; wherein the composite binder comprises a cement component and a pozzolan component, and wherein the sprayable cementitious composition, when cured, achieves one or more properties selected from the group consisting of:

(i) a tensile strength of at least about 2.50 MPa,

(ii) a tensile strain capacity of at least about 3% at 28 days,

(iii) a crack width of less than about 100 μ amt e < 2%, and (iv) a maximum expansion of at least about 1210 me.

[0052] In a yet further aspect, the present invention provides a method of preparing a sprayable cementitious composition, the method comprising:

(i) providing a binder composition comprising a cement component and a pozzolan component, (ii) mixing the binder composition with water to form a wet mixture,

(iii) adding fibres to the wet mixture.

[0053] In some embodiments, the method further comprises mixing the cement component and the pozzolan component to provide the binder composition.

[0054] In some embodiments, a superplasticizer is added to the water before step (ii). [0055] In a still further aspect, the present invention provides a method of repairing and/or retrofitting a building structure comprising the steps of: (i) providing a sprayable cementitious composition of the invention;

(ii) spraying the cementitious composition on a surface of the building structure to at least partially coat the surface with the cementitious composition; and

(iii) allowing the cementitious composition to set on the surface.

[0056] In some embodiments, the spraying step (ii) is carried out by a manual spray system or an automated spray system.

[0057] In some embodiments, the building structure is a pipeline.

[0058] In some embodiments, the surface is the internal surface of the pipeline.

[0059] In some embodiments, the pipeline is retrofitted to increase the lifetime of the pipeline, increase the load bearing capacity of the pipeline, and/or strengthen the pipeline.

[0060] In another aspect, the present invention provides use of the sprayable cementitious composition of the invention for repairing and/or retrofitting a building structure.

[0061] In some embodiments, the building structure is a pipeline.

[0062] In another aspect, the present invention provides a dry pre-mix for preparing a sprayable cementitious composition of the invention, the dry pre-mix comprising a composite binder, and fibres; wherein the composite binder comprises a cement component and a pozzolan component.

[0063] In another aspect, the present invention provides a method of preparing a sprayable cementitious composition of the invention, the method comprising:

(i) providing the dry pre-mix of the invention,

(ii) mixing the dry pre-mix with water to form the sprayable cementitious composition.

[0064] This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth. [0065] In addition, where features or aspects of the invention are described in terms of Markush groups, those persons skilled in the art will appreciate that the invention is also thereby described in terms of any individual member or subgroup of members of the Markush group.

[0066] As used herein “(s)” following a noun means the plural and/or singular forms of the noun.

[0067] As used herein the term “and/or” means “and” or “or” or both.

[0068] The term “comprising” as used in this specification means “consisting at least in part of’. When interpreting each statement in this specification that includes the term “comprising”, features other than that or those prefaced by the term may also be present. Related terms such as “comprise” and “comprises” are to be interpreted in the same manner.

[0069] It is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range (for example, 1, 1.1, 2,

3, 3.9, 4, 5, 6, 6.5, 7, 8, 9 and 10) and also any range of rational numbers within that range (for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7) and, therefore, all sub-ranges of all ranges expressly disclosed herein are hereby expressly disclosed. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.

[0070] Although the present invention is broadly as defined above, those persons skilled in the art will appreciate that the invention is not limited thereto and that the invention also includes embodiments of which the following description gives examples.

BRIEF DESCRIPTION OF THE DRAWINGS

[0071] The invention will now be described with reference to the Figures in which:

[0072] Figure 1 illustrates the shrinkage/expansion of SDMCCs prepared with OPC and CSA-K cement (wherein CSA-K comprises 7, 10, and 13 wt% of the composite binder, respectively); [0073] Figure 2 illustrates the shrinkage/expansion of SDMCCs prepared with OPC and LC3/CSA-K cement (wherein CSA-K comprises 10 and 13 wt% of the composite binder, respectively);

[0074] Figure 3 illustrates the shrinkage/expansion of SDMCCs prepared with CSA-R cement (wherein anhydrite comprises 0, 10, 15, and 20 wt% of the CSA-R, respectively);

[0075] Figure 4 illustrates the maximum allowable expansion of a SDMCC for repairing a C40 concrete pipe;

[0076] Figure 5 illustrates the average strain of a steel ring measured by 3 strain gauges for SDMCCs prepared with LC3/CSA-K cement and CSA-K cement (wherein CSA-K comprises 13 wt% of the composite binder);

[0077] Figure 6 illustrates the residual interface pressure between the steel ring and SDMCCs prepared with LC3/CSA-K cement and CSA-K cement (wherein CSA-K comprises 13 wt% of composite binder);

[0078] Figure 7 illustrates the 28-day tensile stress-strain behaviour of the compositions shown in Figures 1 and 2;

[0079] Figure 8 illustrates the self-healing of ultimate tensile strength and strain capacity of SDMCCs prepared with OPC, LC3, and LC3/CSA-K cement after 7 wet-dry cycles;

[0080] Figure 9 illustrates the permeability coefficients of SDMCCs prepared with OPC and LC3/CSA-K cement tested on the 14th day after the specimens were pre-cracked on 28 days; [0081] Figure 10 illustrates a pipe repair protocol cast with kraft tubes; and

[0082] Figure 11 illustrates the relationship between crush load and displacement of a concrete pipe and a SDMCC-repaired pipe.

DETAILED DESCRIPTION OF THE INVENTION

[0083] The inventor has surprisingly discovered a SDMCC having advantageous properties compared to conventional cements and concretes. For example, the SDMCC may exhibit expansion on curing and strain hardening behaviour. [0084] Accordingly, in one aspect, the present invention provides a SDMCC comprising: a composite binder, fibres and water; wherein the composite binder comprises a cement component and a pozzolan component. The sprayable cementitious composition is useful, e.g., for repairing and/or retrofitting of pipelines.

[0085] The cement component comprises a hydraulic cement, and may further comprise additional materials such as an expansion agent, a reactive aluminosilicate and/or calcium carbonate.

[0086] The SDMCC may further comprise other components, such as a superplasticizer, aggregates and/or other additives.

Hydraulic cement

[0087] Hydraulic cements are materials that set and harden when mixed with water.

Hydraulic cements include, but are not limited to, Portland cement, blended Portland cement, phosphate cement, and belite cement (dicalcium silicate). Mixtures of any two or more thereof are also contemplated. Preferably the hydraulic cement is a Portland cement.

[0088] Portland cement is a finely ground powder produced by grinding clinker consisting essentially of hydraulic calcium silicates. The cement may contain up to about 5% gypsum. The amount of gypsum present affects the set time. The standards for Portland cement are defined in ASTM C 150, Standard Specification for Portland Cement, which defines eight types of Portland cement: type I, type IA, type II, type IIA, type III, type IIIA, type IV, and type V. Type I cement is a general purpose ordinary Portland cement (OPC) suitable for all uses where the special properties of other types are not required. Type III cements are chemically and physically similar to Type I cements except they are ground finer to produce higher early strengths.

[0089] The cement component may comprise a hydraulic cement in an amount of, based on the total cement component weight, about 1 to about 80 wt%, or about 20 to about 80 wt%, or about 50 to about 80 wt%, or about 60 to about 80 wt%.

[0090] In some embodiments, the cement component comprises a reactive aluminosilicate such as calcined clay and/or a calcium carbonate such as limestone. Advantageously, replacing a portion of the hydraulic cement with a reactive aluminosilicate and/or calcium carbonate provides a more environmentally friendly composition by reducing the amount of carbon released during the manufacturing process. [0091] SDMCC comprising a reactive aluminosilicate and/or calcium carbonate may provide other advantages. For example, limestone calcined clay cement (LC3) paste has been found to have a finer pore structure than paste made with OPC. Advantageously, the pore refinement provides excellent resistance to chloride ingress and good performance in the presence of sulfates, which is especially significant for the complex environment in pipelines.

[0092] Additionally, the SDMCC comprising LC3 has surprisingly been found to have larger strain capacity and smaller crack width than prior art ECCs prepared with OPC. The decreased crack width results in a lower permeability. This may prevent, for example, an original pipe from being corroded by a fluid. The larger strain capacity SDMCC is expected to have larger deformability. This may result, for example, in a repaired pipe having a higher loading and deflection capacity.

[0093] The cement mixture may comprise a reactive aluminosilicate, a calcium carbonate, or a mixture thereof in an amount of, based on the total cement component weight, about 1 to about 80 wt%, or about 30 to about 60 wt%, or about 40 to 50 wt%. For example, the cement component may comprise a reactive aluminosilicate in an amount of, based on the total cement component weight, 0 to about 50 wt%, or about 20 to about 40 wt%, or about 30 wt%. For example, the cement component may comprise a calcium carbonate in an amount of, based on the total cement component weight, about 0 to about 30 wt%, or about 10 to about 20 wt%, or about 15 wt%. In some embodiments, the ratio of reactive aluminosilicate to calcium carbonate is 2:1.

[0094] In some embodiments, the average particle size of the reactive aluminosilicate is about 2 μm to about 40 μm, or about 2 μm to about 10 μm . In some embodiments, the average particle size of the calcium carbonate is about 2 μm to about 100 μ,m or about 2 μ tom about 20 . μm

[0095] In some embodiments, the cement component comprises, based on the total cement mixture weight, about 10 to about 50 wt% OPC, about 20 to about 40 wt% metakaolin, and about 10 to about 20 wt% limestone.

[0096] In some embodiments, a portion of the hydraulic cement may be replaced with mining tailings. For example, the cement component may comprise mining tailings in an amount of, based on the total cement component weight, about 1 to about 30 wt%. Expansion agent

[0097] An expansion agent is a material that augments the expansion of the SDMCC during the hydration process. In some embodiments, the expansion agent may be used to reduce shrinkage that occurs during curing of the composition. In other embodiments, the expansion agent may be used to provide a SDMCC that expands during curing. Advantageously, augmenting the expansion of the SDMCC may reduce the risk of cracking that occurs during shrinkage.

[0098] The expansion agent may be used to tailor the expansive properties of the SDMCC such that, when applied to an internal surface of a pipeline and cured, the SDMCC exerts an expansive force against the internal surface of the pipeline. The expansive force reduces any space between the SDMCC and the internal surface, and increases the mechanical friction between them. Advantageously, the increased mechanical friction may increase adhesion between the SDMCC and the internal surface. As a result, the repaired or retrofitted pipeline may have a higher loading and deflection capacity compared with the original host pipe. Additionally, the increased adhesion may reduce delamination of the SDMCC from the surface, as well as wrinkle and even buckling of the repair layer during post-repair service. The controlled expansive force exerted by the SDMCC onto the host pipe may result in coupling of the repair layer to the host pipe wall, and lead to a combined structural and functional repair, rather than only a functional repair, such as repairing water leakage. However, those persons skilled in the art will appreciate that, in some embodiments, excessive expansion should be avoided because it may lead to deformation of the surface or even damage to the host pipe to which the SDMCC is applied.

[0099] In addition to exerting pressure against the pipeline, the expansion properties also distinguish the SDMCC from known sprayable ECCs, which typically have a large drying shrinkage around -1500 με after 28 days. The expansive SDMCC reduces the restrained shrinkage cracking risk, further increases the durability of the repaired pipeline, and lowers post repair leakage risk.

[00100] Those persons skilled in the art will appreciate that the preferred expansion properties of the SDMCC depend on various factors, such as the diameter and tensile strength of the host pipe that is to be repaired or retrofitted, whether the host pipe is under a confining pressure, and the intended thickness of the SDMCC. In some embodiments, the expansion of the SDMCC is at least about 1200 με. In some other embodiments, the expansion of the SDMCC is at least about 3000 me. The maximum expansion of the SDMCC may be, e.g., about 3000 με, about 3375 με, about 4000 με, or about 4450 με.

[00101] Preferred expansion agents include calcium aluminate cement (CAC) and calcium sulfoaluminate cement (CSA). Preferably the expansive agent is CSA. The amount of CaSO₄· nH₂O in the CSA is preferably, based on the weight of the CSA, about 1 to 50 wt%, wherein n may be 0, 0.5, 1 or 2.

[00102] The composite binder may comprise an expansive agent in an amount of, based on the total cement component weight, about 10 to about 60 wt%, or about 20 to about 50 wt%. In some embodiments, the average particle size of the expansion agent is about 2 μm to about 500 , μm or about 10 μm to about 30 μm.

Pozzolans

[00103] Pozzolans are siliceous or siliceous and aluminous materials that are typically provided in a finely divided form. Pozzolans alone have little or no cementitious properties, However, in the presence of water, pozzolans react with calcium hydroxide released by the hydration of hydraulic cement to form calcium silicate hydrate and other cementitious compounds. Advantageously, pozzolans may improve the binder fracture toughness of cementitious materials leading to higher ductility of the cured SDMCC. Pozzolans may also be used to modulate the rheology of the SDMCC. Advantageously, the rheology of the SDMCC may be modulated to improve the pumpability and/or sprayability of the composition.

[00104] Generally, any siliceous or siliceous and aluminous materials that react with calcium hydroxide in the presence of water may be suitable for use in the binder. Examples of suitable pozzolans include, but are not limited to, fly ash, steel slag, granulated blast furnace slag, diatomaceous earth, silica fume, calcined clay such as metakaolin, calcined shale, volcanic ash, pumice, burnt silica-rich organic matter such as rice husk ash, and mixtures of any two or more thereof. Preferably, the pozzolan component comprises a fly ash, e.g. as defined in ASTM C618. In some embodiments, the fly ash is type C fly ash and/or type F fly ash.

[00105] In some embodiments, the pozzolan component comprises silica fume. Advantageously, silica fume may increase the compressive strength of the SDMCC and/or improve the fibre/matrix interface bond. [00106] The composite binder may comprise the pozzolan component in an amount of about 0 to about 3 times the weight of the cement component. Preferably, the composite binder comprises the pozzolan component in an amount of about 1 to about 3 times, by weight, the cement component, more preferably about 2 to about 3 times, more preferably about 2 to about 2.5 times.

Fibres

[00107] The fibres are intended to reinforce the cured SDMCC. Suitable fibres may be selected based on various characteristics, including the desired cost, mechanical properties, physical properties and bond properties of the fibres. The properties of the SDMCC may be influenced by factors such as the length, diameter, chemical composition, stiffness, density, and strength of the fibres. The fibres may be selected to transmit load across cracks when the composite is loaded to beyond the elastic stage. Their load-carrying behaviour may be tuned to balance fibre fracture and fibre slippage, i.e. controlled fibre bridging behaviour. During imposed loading on the composite, excessive fibre fracture or fibre slippage is undesirable, as this may limit the composite ductility or result in crack width that is excessively large as to compromise composite durability. Advantageously, the fibres may improve the strain hardening and tensile ductility of the composite, and limit crack width.

[00108] Fibres suitable for use in the SDMCC include, but are not limited to, polymeric fibres, inorganic fibres (e.g. basaltic fibres and glass fibres), metal fibres (e.g. steel fibres), carbon fibres, plant-based fibres (e.g. cellulosic fibres and lignocellulosic fibres), and mixtures of any two or more thereof. Preferably, the fibres are polymeric fibres, i.e. fibres composed of a polymeric material such as a polyolefin (e.g. polyethylene or polypropylene), a polyacrylic, a polyester, a polyvinyl alcohol, a polyamide (e.g. nylon), or combinations of any two or more thereof. More preferably, the fibres are polypropylene fibres, more preferably high tenacity polypropylene fibres. In some embodiments, the fibres are short discontinuous fibres.

[00109] The upper limit of fibre concentration is dictated by pumpability and sprayability requirements, while the lower limit is dictated by the ability to provide strain hardening (ductile) behaviour as opposed to brittle or quasi-brittle behaviour. For example, the fibres may be present in an amount of, based on the total composition volume (i.e. the volume of the composition including water), from about 0.1 to less than 4 v/v%, or about 1 to about 3 v/v%, or about 1.5 to about 2.3 v/v%. In some embodiments, the fibre length is about 4 mm to about 25 mm, or about 6 mm to about 20 mm, or about 8 mm to about 12 mm. In some embodiments, the fibre diameter is about 10 mhi to about 150 mhi, or about 10 mhi to about 60 mih.

Superplasticizer

[00110] In some embodiments, the SDMCC further comprises a superplasticizer, also known as a high range water reducer. A superplasticizer may be added to the SDMCC to affect the rheology of the composition. Advantageously, the superplasticizer may reduce the amount of water that is required to maintain the pumpability and sprayability of the SDMCC.

[00111] Accordingly, the superplasticizer is typically added to the SDMCC in an amount effective to achieve a composition with the desired pumpability and sprayability. Those persons skilled in the art will appreciate the amount of superplasticizer required to achieve the desired pumpability and sprayability may depend on other components of the composition, such as the water content of the composition. For example, the superplasticizer may be included in the SDMCC in an amount of, based on the total composition weight, about 0.1 to 10 wt%, or about 0.3 to about 3 wt%, or about 0.5 to about 1.5 wt%.

[00112] Generally, any superplasticizer known in the art is suitable for use in the SDMCC. Such superplasticizers include, but are not limited to, sulfonated melamines (e.g. sulfonated melamine formaldehyde condensates), sulfonated naphthalenes (e.g. sulfonated naphthalene formaldehyde condensates), polycarboxylate ethers (e.g. ADVA^® 190), modified lignosulfonates, and mixtures of any two or more thereof.

Aggregate

[00113] The SDMCC may further comprise aggregate, such as sand, ground stone and lightweight aggregate. Incorporation of lightweight aggregates may decrease the density of the SDMCC. Incorporation of lightweight aggregates may also allow increased thicknesses to be sprayed, particularly on horizontal overhead surfaces. If the amount of lightweight aggregate is significant, then the particle size becomes important, otherwise strain hardening cannot be achieved. In general, the average particle size is about 10 μm to about 1000 , μm or about 10 μm to about 200 μm, or about 30 μm to about 100 μm.

[00114] Lightweight aggregates may comprise, but are not limited to, grounded rubber (e.g. from waste tires), hollow glass spheres, cenosphere, expanded mica, and microballoons (e.g. glass, ceramic or polymer microballoons). [00115] In addition to, or instead of, lightweight aggregate, the SDMCC may further comprise gas bubbles. The gas may be introduced during processing of the cementitious composition by physical means, e.g. frothing or aeration. Alternatively, the gas may be chemically induced, e.g. as hydrogen gas created by reaction of aluminium powder with the alkaline composition or reaction of Si-H functional silanes with water. In some embodiments, stabilising substances are added to assist in preventing coalescence of adjoining bubbles. In some embodiments, the volume percent is limited to provide a cured density of about 1400 kg/m³ or higher, preferably 1500 kg/m³ or higher. If significant coalescence to large voids occurs, strength properties of the composite, particularly strain hardening behaviour, may be compromised. Gas bubbles may be used in conjunction with other lightweight aggregates. Advantageously, the volume fraction of gas bubbles in such formulations can be kept small so that coalescence will be minimal. For example, in a composite with a target density of 1300 kg/m³, a gas or gas precursor may be added to obtain a density of about 1600 kg/m³ or higher, and other lightweight filler added to lower the density to the target range.

Other additives

[00116] The SDMCC may further comprise other additives as are known in the art, such as a viscosity agent and/or a retarder agent.

[00117] For example, the viscosity agent may be a cellulose derivative, such as hydroxypropyl methylcellulose (HPMC). The viscosity agent may be included in the SDMCC in an amount of, based on the total binder weight (i.e. the weight of the composition excluding water), about 0 to about 1 wt%, or about 0.03 to about 0.5 wt%, or about 0.05 to about 0.2 wt%. The viscosity agent enhances the ability of the composite to build up thickness on a substrate, and also helps the fibres disperse evenly in the matrix.

[00118] The SDMCC may comprise a retarder agent. A conventional retarder agent can be used. A preferred retarder agent is citric acid, which, advantageously, is compatible with use of CSA. The retarder agent may be included in an amount of, based on the total binder weight, about 0.01 to about 10 wt%, or about 0.1 to about 2 wt%, or about 0.2 to about 1.5 wt%. The retarder agent can increase the working time of the SDMCC during a spray process. However, those persons skilled in the art will appreciate that excess retarder agent may decrease the strength and ductility of the SDMCC. Water

[00119] The amount of water in the SDMCC affects various properties of the composition. The water content should be sufficient to obtain a pumpable and sprayable composition. In general, a higher water content reduces the viscosity and increases sprayability, while a lower water content increases cohesion and allows for thicker application. The amount of water required to provide a pumpable and sprayable composition may be readily determined by routine experimentation and may be decreased by including a superplasticizer as discussed above.

[00120] In some embodiments, the water-to-binder ratio is about 0.2 to about 0.5. Preferably, the water-to-binder ratio is about 0.2 to about 0.4, more preferably about 0.3.

Preparation of the cementitious composition

[00121] The SDMCCs of the present invention can be prepared by conventional techniques. The ingredients may be mixed with water separately or certain ingredients may be pre-mixed. In some embodiments, water is added to a pre-mix of the dry binder ingredients to obtain a wet mixture, to which the fibres are added. In some embodiments, a superplasticizer is mixed with water to form a solution that is added to a pre-mix of the dry binder ingredients to obtain a wet mixture, to which the fibres are added. In some other embodiments, the dry ingredients may be provided in a “ready-mix” composition, e.g. a pre-mix of the dry binder ingredients and the fibres, that is mixed with water prior to use to form the SDMCC.

Repairing and retrofitting pipelines

[00122] The SDMCCs of the present invention are useful for repairing pipelines, such as gravity pipelines or pressure pipelines, particularly underground gravity pipelines or pressure pipelines. Such pipelines are found in various applications, e.g. water pipes, drainage pipes, sewage pipes and oil pipes. For example, the SDMCCs are useful in a trenchless pipeline repair method. The method of repairing a pipeline of the present invention is compatible with various pipe geometries, e.g. pipes having a circular or non-circular cross-section, pipes having a narrow or wide diameter, straight pipes or bent pipes.

[00123] The present inventor has also determined that the SDMCCs of the present invention are useful for retrofitting pipelines. In contrast to a repair method that aims to recover the original function of the damaged host pipe, retrofitting refers to methods in which a property of the pipeline is enhanced. For example, a pipeline may be retrofitted to increase the lifetime of the pipeline, increase the load bearing capacity of the pipeline, and/or strengthen the pipeline. In some embodiments, a pipeline is retrofitted for earthquake strengthening of the pipeline. For this purpose, the SDMCC may be applied to pipes to reduce the risk of leakage or contamination of drink water or subsurface water caused by a seismic event.

[00124] The method of repairing or retrofitting pipelines of the present invention may protect against common failure modes that occur in pipelines repaired or retrofitted by other methods, such as CIPP, slip lining or spiral wound lining methods, or spray lining with known materials. Common failure modes that may be avoided include local buckling, lining or pipeline fracture, water leakage, and corrosion of the lining or pipeline.

[00125] The method of repairing or retrofitting a pipeline comprises providing the SDMCC as a wet mixture, applying the wet mixture to at least a portion of a surface of the pipeline, e.g. an internal wall of a pipeline, and curing the mixture. In some embodiments, the SDMCC is applied to the entire internal surface of a length of the pipeline. Advantageously, coating the entire internal surface may essentially result in a new internal pipe. Continuous spraying of cementitious material along the length of a deteriorated pipeline may provide an internal coating with a reduced number of joints, and in some embodiments, no joints. Joints are typically a weak point in pipelines and therefore, advantageously, reducing the number of joints in a repaired pipeline may extend the service life of the pipeline. A pipeline having a continuous internal coating with a reduced number of joints or no joints is also less susceptible to leakages, including under hazardous conditions such as an earthquake.

[00126] The cementitious composition may be applied to a surface of the pipeline by conventional methods. The SDMCC may be applied by a manual spray system or an automated spray system. For example, the SDMCC may be applied manually by pneumatically projecting the composition at a high velocity through a nozzle onto a surface. Alternatively, the SDMCC may be applied by an automated, centrifugal spray system that sprays the material onto the internal surface of an existing pipeline.

[00127] The cementitious composition is in a fluid state during pumping but sets after spray application to a surface. The setting speed should be fast enough to allow build-up of thickness against the pull of gravity. The SDMCC of the present invention may have a thickness of about 10 mm to about 50 mm when sprayed onto a horizontal or vertical surface, including an overhead surface. In some embodiments, the SDMCC has a thickness of about 20 mm to about 40 mm when sprayed onto a horizontal or vertical surface. In some embodiments, the SDMCC has a thickness of about 20 mm to about 30 mm when sprayed onto a horizontal or vertical surface.

[00128] The SDMCCs of the present invention are useful for repairing and retrofitting pipelines. However, those persons skilled in the art will appreciate that the SDMCCs of the present invention may be useful in the repairing and/or retrofitting other building structures. Particularly, building structures wherein one or more of the improved properties described herein would be beneficial. For example, suitable building structures may include tunnels, culverts, manholes, bridges, slabs, and roads.

[00129] The following non-limiting examples are provided to illustrate the present invention and in no way limit the scope thereof.

EXAMPLES

1. Material composition and processing

[00130] The exemplary mixtures are listed in Table 1. The cement was Type I Portland cement (PCI) from Lafarge Cement Co., MI, USA. Two classes of expansive cement from CTS Cement Manufacturing Corp. and from Royal White Cement Inc were used and defined as CSA-K and CSA-R, respectively. Metakaolin (MK) was Sikacrete® M-100 from Sika Corporation, NJ, USA. Anhydrite was Terry-Alba No.1 from USG. Limestone (LS) was Snowhite® 12-PT from Omya Canada Inc. Fly ash (FA) was class C fly ash with a size distribution from 10 to 100 μm from Boral Material Technologies Inc. The superplasticizer (SP) was AVDA® 190 from GCP Applied Technologies. Hydroxypropyl methylcellulose (HPMC), a viscosity agent, was from Fisher Scientific. The amount of polypropylene (PP) fibres was 2% volume fraction with 12 μm diameter, 10 mm length, 6 GPa Young’s modulus, and 850 MPa tensile strength, and was Brasilit from Saint-Gobain Brazil.

[00131] The nomenclature in Table 1 reflects the binder composition. OPC and LC3 refer to binders prepared with ordinary Portland cement and limestone calcined clay cement, respectively. K07, K10, and K13 refer to a CSA-K to binder ratio of 7, 10, and 13 wt%. R13- CO, 10, 15, and 20 represent a CSA-R and anhydrite to binder ratio of 13 wt%, wherein the anhydrite proportion is 0, 10, 15, and 20 wt% of the total weight of CSA-R and anhydrite. The wt% ratio of PCI, MK, and LS in LC3 cement is 55%, 30%, and 15%.

[00132] The SDMCC was prepared by mixing all the dry ingredients (PCI, CSA, anhydrite, MK, LS, FA, and HPMC) in a drum mixer for 10 minutes. Water together with SP was added gradually and mixed for 6 minutes. PP fibres were added last, then mixed for 6 minutes.

2. Sprayability of the cementitious composition

[00133] The fresh property of a sprayable (often referred to as “shotcreting”) ECC is important. A sprayable cementitious composition requires high initial deformability for pumping, a fast build-up ability when spraying onto a substrate, and optimal rest time. The rest time, defined as the time interval from mixing finishing to spraying beginning, should be long enough to accommodate the time required for pumping and short enough for a desirable build- up thickness upon spraying.

[00134] The composition of the SDMCC was the same as LC3-K13 in Table 1 except for a different SP content. Compared with a prior art sprayed ECC comprising 2 v/v% PVA fibres, the present SDMCC employed 2 v/v% PP fibres, which is advantageously lower cost than PVA fibres. However, under the same dosage and fibre length, the quantity of PP fibres (12 μm) in SDMCC was 10.56 times the quantity of fibres in the prior art sprayed PVA-ECC (39 ) μ. m The large amount of small-diameter fibres required careful control of the fresh rheology of sprayable SDMCC.

[00135] A CARROUSEL pump and multi-air jet pole gun from Quikspray Inc. were used for spraying in the examples described below. The multi-air jet pole gun was particularly suitable for spraying cementitious materials with reinforcing fibres. The materials were mixed in a Hobart mixer, and then the material was pumped by the CARROUSEL pump. After passing through a 1.25" (31.75 mm) diameter material hose and to the multi-air jet pole gun, the SDMCC was sprayed with a 560 kPa air pressure onto a plywood substrate. The spray tests included spraying from both vertical and overhead directions onto the substrate.

[00136] Using a series of flowability tests with varying amounts of superplasticizer, the optimal superplasticizer content was determined to be 0.8 wt% of the composite binder. For the vertical plywood substrate spray test, the build-up thickness was 15 mm after a rest time of 20 minutes. The maximum build-up thickness could reach 50 mm when the rest time was 40 minutes for the vertical plywood substrate. For the overhead substrate, the maximum thickness could reach 25 mm after a rest time of 20 minutes.

[00137] Although the fibre quantity in the SDMCC was 10.56 times that of the prior art sprayed PVA-ECC, the sprayed SDMCC was found to have good atomization, allowing the material to be sprayed onto the substrate evenly. The SDMCC showed nearly no rebound, and did not drip or sag after being sprayed onto the substrate, demonstrating significant advantages over traditional coating materials.

3. Expansion characteristics

[00138] The specimens for measuring shrinkage/expansion were cast into a prism mould (25x25x300 mm). The shrinkage/expansion measurements were taken after demoulding as early as possible without damaging the specimens and marked as the “zero time” of the deformation. For the mixtures in Table 1, the demoulding time was 20 hours for OPC; 10 hours for K07; 5 hours for K10, K13, and LC3-K13; 8 hours for LC3-K10; 3 hours for R13-C0, R13-C10, R13- C15, and R13-C20. The specimens were stored in a 20±2°C and 40±5% relative humidity (RH) environment. The length changes of the specimens were tested according to ASTM C490/C490M-17. 3.1 Drying shrinkage/expansion

[00139] The shrinkage/expansion versus age curves of the compositions in Table 1 are shown in Figures 1-3, wherein the negative sign (on the y-axis) represents shrinkage and the positive sign represents expansion. Table 2 lists the characteristic values of shrinkage/expansion at 28 days. For the SDMCC prepared with OPC, the shrinkage continuously increased to -1434 aμtε 28 days. Such relatively large shrinkage could lead to cracking under restrained conditions, which decreases the durability of the material. The SDMCC utilising CSA-K showed the characteristics of expansion initially followed by shrinkage. The maximum expansion occurred around 2 days age. The magnitude of the maximum expansion was 779 me, 2418 me, and 3756 me for compositions K07, K10, and K13, varying with the CSA-K ratios. However, with 7 wt% CSA-K cement in the composite binder, the SDMCC still showed -832 με shrinkage at 28 days. The expansion of K10 and K13 was 1139 με and 2026 me, respectively, at 28 days. The expansion of ECC employing LC3 was a little lower than OPC. The expansion was 838 με and 1722 με for LC3-K10 and LC3-K13.

[00140] The type of CSA cement may also influence the magnitude of expansion. CSA-R is a CSA binder with less CaSO₄ than CSA-K. Even when the content of CSA-R was 13 wt% of the composite binder (R13-C0), the shrinkage of R13-C0 was -834 με at 28 days and did not show expansion. Increased replacement of CSA-R with anhydrite, reduced the shrinkage and R13- C20 had a 489 με expansion at 28 days. Without wishing to be bound by theory, it is thought the CaSO₄ (gypsum or anhydrite) amount in CSA cement affects the production of ettringite. Ettringite is the main expansive hydration product of CSA cement.

3.2 Minimum expansion

[00141] Assuming linear material constitutive behaviour, the pressure caused by expansion can be expressed as: where p is the pressure applied from expansive SDMCC; ε₁ is the maximum expansion of SDMCC; ε₂ is the difference between maximum expansion and the residual strain at 28 days; E₁ is the effective modulus between time zero and maximum expansion time and; E₂ is the effective modulus between maximum expansion time and 28 days. ε₁ and ε₂ can be tested by the drying shrinkage/expansion test according to ASTM C490/C490M-17, and the values are listed in Table 2. E₁ and E₂ are the effective modulus, influenced by stress relaxation and time development. During early age (before 3 days), creep is more significant than at later age (3-28 days). Additionally, the elastic modulus is smaller at an early age, even for the rapid hardening SDMCC materials. [00142] Assuming that E₁ = kE₂, the pressure can also be expressed as: where k is defined as the coefficient of effective modulus. k is determined by the combined effect of material elastic modulus development and boundary restrained condition. Advantageously, to ensure the SDMCC creates a coupling effect against the host pipe, / should be larger than 0. In other words, kε₁ — ε₂ should be larger than 0. According to Zhu H. et al., Double feedback control method for determining early-age restrained creep of concrete using a temperature stress testing machine. Materials, 2018, 11(7), 1079, it seems plausible to assume k = 0.5.

[00143] For the mixtures in Table 2, the maximum expansion and the expansion of OPC after 28 days differ from K07, K10, and K13; however, the difference between the maximum expansion and the 28 day expansion (i.e. e₂ ) is similar for OPC, K07, K10, and K13. Experimentally, ε₂ is found to be approximately 1531με for the OPC -based SDMCC and 605 με for the LC3-based SDMCC. Therefore, for the OPC-based SDMCC, the maximum expansion ε₁ = ε₂/k is preferably at least 3062 με (1531/0.5) to provide a desirable coupling effect. The maximum expansion for the LC3-based SDMCC is preferably at least 1210 με (605/0.5). 3.3 Maximum allowable expansion

[00144] While expansion of the SDMCC is desirable, as explained above, excessive expansion should be avoided because it could cause damage to the host pipe. According to the elastic theory of steel ring (Hossain A B, Weiss J. Assessing residual stress development and stress relaxation in restrained concrete ring specimens. Cement and Concrete Composites, 2004, 26(5): 531-540), the elastic pressure applied by the SDMCC against the host pipe can be expressed as equation (3) and the maximum elastic stress of the host pipe can be calculated by equation (4): where As_ex is the expansion of the SDMCC; E_c and E_s are the elastic modulus of the host pipe and SDMCC; and C_1R, C_2R, C_3R can be assumed to be constant for a given geometry as shown in equations (5) to (7): where v_c and v_s are the Poisson’s ratio of the host pipe and the SDMCC; R_IS and R_0S are the inner and outer radius of the SDMCC respectively; and R_Ic and R_oc are the inner and outer radius of the host pipe, respectively.

[00145] Equations (3) to (7) indicate the maximum tensile strength in the host pipe is affected by the SDMCC thickness, inner diameter (ID) of the host pipe, expansion of the SDMCC, and the materials’ mechanical properties. C40 concrete pipes with different diameters [ID=48" (1219 mm), 60" (1524 mm), and 90" (2286 mm)] were employed as examples. The tensile strength was 5 MPa and the elastic modulus was 40 GPa. The average elastic modulus of the SDMCC during zero time and maximum expansion time was assumed to be 5 GPa. The Poisson’s ratio of the host pipe and the SDMCC was assumed to equal 0.18. Assuming that the relaxation stress during early age (0-3 days) is 0.5 of the total elastic stress, the maximum allowable expansion can be calculated using equations (3) to (7) under the condition that the maximum allowable tensile stress in the host pipe is half of the tensile strength (2.5 MPa).

[00146] Figure 4 plots the maximum allowable expansion of the SDMCC for repairing a C40 concrete pipe, and the characteristic values are listed in Table 3. The tensile stress in the host pipe increases with the SDMCC thickness. For a 48" (1219 mm) host pipe repaired with 1.5" (38 mm) thickness of the SDMCC, the maximum allowable expansion is 3375 me, which is smaller than the maximum of K13 (3756 me). Accordingly, the thickness of K13 should not exceed 1"

(25 mm) when used for repairing a 48" (1219 mm) pipe. For repairing a larger diameter pipe, the thickness could increase. For example, the maximum allowable expansion is 4450 με for a 90"

(2286 mm) pipe repaired with a 2" (51 mm) thickness of the SDMCC.

[00147] Pipelines are usually buried underground with confining pressure. The confining pressure mitigates the tensile stress of the host pipe caused by expansion of the SDMCC. Assuming a 0.3 MPa confining pressure as shown in Table 3, the maximum allowable expansion increases significantly compared to that for pipes without confining pressure.

[00148] With confining pressure, K13 can be also used for repairing 48" (1219 mm) pipelines with 2" (51 mm) thickness of the SDMCC. Without wishing to be bound by theory, the inventor suggests a maximum allowable expansion of the SDMCC of 3000 με and 4000 με for repairing pipes without and with confining pressure, respectively.

3.4 Restrained expansion test using a steel ring

[00149] Concrete was cast in an annular zone around a steel ring according to the restrained shrinkage test method ASTM C1581/C1581M-18a. The strain caused by concrete shrinkage applying pressure against the steel ring was monitored and used for calculating the interface pressure.

[00150] The expansion steel ring test method was based on ASTM C 1581/C 1581—18a, but differed in that the K13 or LC3-K13 was solid cast inside a steel ring with an outer diameter of 405 mm and inner diameter of 385 mm, rather than a hollow ring as used in the restrained test. The expansion of K13 or LC3-K13 applied pressure against the steel ring and the resulting strain of the steel ring was monitored by 3 strain gauges, starting 5 hours after casting.

[00151] Figure 5 plots the average strain of 3 strain gauges. Similar to the drying expansion described in Section 3.1, the restrained expansion also initially increased and then decreased.

The maximum drying expansion occurred between 2 to 3 days as shown in Figures 1 and 2. However, due to creep and relaxation, the maximum restrained expansion occurred around the first day after cast. The maximum expansion was 123 με for K13 and 104 μ fεor LC3-K13, which then decreased to 6 με for K13 and 56 με for LC3-K13 on day 28. The LC3-K13 had a smaller expansion reduction than K13, which indicates that LC3-K13 may provide a better coupling effect than K13.

[00152] The residual interface pressure between the steel ring and K13/ LC3-K13 can be calculated by equation (8): where P_residual(t) is the residual interface pressure, ε_steel(t) is the strain measured by 3 strain gauges, E_steel is Young's modulus of the steel ring, and R_0steel and R_Isteel are the outer and inner diameter of the steel ring.

[00153] Figure 6 plots the residual interface pressure calculated by equation (8). After 1 day, the maximum pressure of K13 was 1.18 MPa and the maximum pressure of LC3-K13 was 1.00 MPa. After 28 days, the pressure of K13 was only 0.06 MPa, nearly 0 MPa, while the pressure of LC3-K13 was 0.54 MPa.

[00154] Compared with traditional repair materials, the SDMCC (K13 or LC3 K13) is designed to apply pressure against the host pipe. The experimental data herein demonstrates this concept. Without wishing to be bound by theory, it is thought the pressure improves coupling between the host pipe and the SDMCC, reducing or eliminating the problems of buckling and debonding due to poor adhesion. The inventor surprisingly found that, advantageously, LC3 may provide lower expansion reduction over time compared to OPC, resulting in a sustained pressure applied against the outer pipe. The coupling may be achieved without adhesive, but by mechanical friction that increases with the normal (radial) pressure exerted by the SDMCC on the host pipe.

4. Tensile properties

[00155] For tension testing, the specimens were cast into a dogbone-shaped mould (see Felekoglu, B., et ah, Influence of matrix flowability, fiber mixing procedure, and curing conditions on the mechanical performance ofHTPP-ECC Composites Part B: Engineering,

2014, 60, 359-370 for the dog bone geometry). Uniaxial tensile tests were performed with an Instron servo-hydraulic testing machine under displacement control with a 0.5 mm/min rate. The strain was measured by two linear variable displacements (LVDT) with an 80 mm gauge length. The average crack width was calculated by dividing the displacement with crack numbers. The tension results listed in Table 2 are the average values of 3 specimens at 28 days.

[00156] Figure 7 plots the representative tensile stress and strain curves of the SDMCCs in Table 1. The ultimate tensile strength and tensile strain capacity of OPC were 3.41 MPa and 3.69%. For SDMCCs mixed with CSA-K, the ultimate tensile strength was 3.67 MPa, 3.62 MPa, and 3.85 MPa for K07, K10, and K13, respectively. Including CSA-K increased the ultimate tensile strength. The tensile strain capacity was 4.79%, 5.17%, and 5.04% for K07, K10, and K13, respectively, each of which is greater than OPC. The average crack widths were around 60 pm, 80 μm, and 90 μm when strains were 1%, 2%, and 3%. The crack width of the SDMCC prepared with CSA-K is smaller than OPC. The tensile strain capacity and crack width of LC3- K10 and LC3-K13 were comparable with the SDMCC prepared with OPC. However, the ultimate tensile strength was lower than 3 MPa. Although LC3 resulted in a lower strength, SDMCCs prepared with LC3 had larger strain capacity and used less cement. Such SDMCCs may, advantageously, have good durability, lower cost, and be more environmentally friendly than those prepared with OPC. The durability and permeability of the SDMCC are further discussed below.

[00157] Even though SDMCCs may experience microcracking damage under external loads, the material can undergo self-healing, which can be enhanced under the wet-dry environmental conditions commonly found inside pipelines. After curing for 28 days, the specimens were precracked to 1% and 2% strain to deliberately cause damage to the SDMCC. Subsequently, the specimens were exposed to seven wet-dry cycles. Figure 8 plots the strength and strain capacity results after self-healing. Although the specimens were pre-cracked, the tensile strengths of the specimens after self-healing were all higher than that of the virgin specimen. The SDMCC prepared with LC3 cement showed a higher strain capacity than that prepared with OPC, which indicates that the SDMCC prepared with LC3 has a comparable or even better self-healing performance.

[00158] After curing for 28 days, the specimens were pre-cracked to 1% and 2% strain prior to permeability testing, following the procedure in Liu, H., et al., “ Influence of micro-cracking on the permeability of Engineered Cementitious Composites ”, Cement and Concrete Composites, 2016, 72, 104-113. Figure 10 presents the permeability coefficient results after 14 days. As expected, the permeability coefficient increases with crack width. The permeability of the SDMCC (LC3-K13) is smaller than that of the SDMCC (OPC) due to its tight crack width pattern. The permeability coefficient of SDMCCs is nearly two orders of magnitude smaller than conventional reinforced mortar subjected to the same pre-crack strains (crack width > 150 μm). This low permeability of SDMCC should significantly improve the service life performance of the pipeline and prevent leakage. The low permeability, even under a 2% pre-crack strain, is expected to reduce the risk of loss of drinking water or contamination of subsurface water, e.g., after a seismic event.

5. Pipe retrofitting test

[00159] To demonstrate the retrofitting ability of SDMCCs, pipe crush tests were conducted according to ASTM C497M-19a. Figure 10 shows the pipe section before and after being repaired with a SDMCC (LC3-K13). The SDMCC repair layer thickness shown in Figure 10 is by way of example only. Those persons skilled in the art will appreciate that an actual SDMCC thickness can be selected depending on the mechanical and functional demands of a specific application. The length of the pipe was 36" (914 mm). The original concrete pipe was mixed with 500 g/L OPC, 1200 g/L river sand, 200 g/L water, and 6g/L water reducer. The mixture of the SDMCC was the same as LC3-K13 in Table 1. 7 days after concrete casting, the concrete and kraft tube was placed into a water tank. The kraft tube was demoulded after 3 hours of immersion in water, after which the SDMCC (LC3-K13) was cast.

[00160] After 28 days curing in air, the pipe was cut by a diamond saw into 8" (203 mm) length, which was used in a crushing test. The crushing test was conducted with the concrete pipe and a pre-cracked pipe repaired with LC3-K13. The pre-cracked concrete pipe was used to simulate the effect of repairing a cracked pipe using an SDMCC. [00161] When the load exceeded the crushing strength, the concrete pipe collapse suddenly due to its brittleness. However, the pre-damaged pipe repaired with SDMCC was able to carry the load after macrocracks occurred in the concrete pipe. Many microcracks occurred in the SDMCC. The crack first occurred in the interior surface of SDMCC, and then more cracks appeared as the load increased. Instead of one macrocrack in the concrete pipe, there were many tight cracks distributed throughout the SDMCC.

[00162] This test also demonstrated that the SDMCC eliminated buckling, a common problem in pipes repaired with the CIPP method. Buckling typically occurs due to a gap between the repair layer and the host pipe, which is commonly observed in the CIPP method. The expansion properties of the SDMCC may provide a SDMCC coating that couples seamlessly with the host pipe resulting in little or no gap between them.

[00163] Figure 11 plots the results of crushing strength versus displacement testing. Both the crushing strength and displacement capacity of the pipe repaired with LC3-K13 were greater than that of the concrete pipe. This demonstrates that retrofitting a pipe with the SDMCC improves both the strength and displacement capacity of the pipe (also shown in Table 4). Even after the peak load, the SDMCC retains residual load capacity. When the residual load dropped to 4.89 kN, equal to the load capacity of the original sound concrete pipe, the displacement was 3.63 times the displacement capacity of the sound concrete pipe.

6. Leakage test

[00164] A SDMCC repaired pipe was used to conduct a leakage test. After the peak load was reached, the bottom part of the cracked SDMCC pipe was sealed with cement on plywood. This system was then filled with water. There was no leakage from the system 24 hours after being filled with water, despite macrocracks in the host concrete pipe and microcracks in SDMCC. The microcracks in the SDMCC extended from the interior surface to the outer pipe. Without wishing to be bound by theory, it is thought the multiple tight cracks worked as a plastic hinge and redistributed the stress. The microcracks did not propagate to a macrocrack, and no local crack occurred in the SDMCC. Consequently, there was no leakage even after the peak load had been reached.

[00165] It is not the intention to limit the scope of the invention to the abovementioned examples only. As would be appreciated by a skilled person in the art, many variations are possible without departing from the scope of the invention as set out in the accompanying claims.

Claims

1. A sprayable cementitious composition comprising: a composite binder, fibres, and water; wherein the composite binder comprises a cement component and a pozzolan component.

2. The sprayable cementitious composition of claim 1 , wherein the ratio of water to composite binder is about 0.2 to about 0.5.

3. The sprayable cementitious composition of claim 1 or 2, wherein the cement component comprises a hydraulic cement and an expansion agent.

4. The sprayable cementitious composition of claim 3, wherein the expansion agent is a calcium sulfoaluminate.

5. The sprayable cementitious composition of claim 3 or 4, wherein the amount of the expansion agent is, based on the total cement component weight, about 10 to about 60 wt%.

6. The sprayable cementitious composition of any one of claims 3 to 5, wherein the hydraulic cement comprises ordinary Portland cement.

7. The sprayable cementitious composition of any one of claims 3 to 6, wherein the amount of the hydraulic cement is, based on the total cement component weight, about 1 to about 80 wt%.

8. The sprayable cementitious composition of any one of claim 1 to 7, wherein the cement component comprises a reactive aluminosilicate, a calcium carbonate, or a mixture thereof.

9. The sprayable cementitious composition of claim 8, wherein the reactive aluminosilicate is a calcined clay.

10. The sprayable cementitious composition of claim 8, wherein the calcium carbonate is a limestone.

11. The sprayable cementitious composition of any one of claims 1 to 10, wherein the amount of the pozzolan component is about 1 to about 3 times, by weight, of the cement component.

12. The sprayable cementitious composition of any one of claims 1 to 11, wherein the pozzolan component comprises a material selected from the group consisting of fly ash, steel slag, granulated blast furnace slag, diatomaceous earth, silica fume, calcined clay such as metakaolin, calcined shale, volcanic ash, pumice, burnt silica-rich organic matter such as rice husk ash, and mixtures of any two or more thereof.

13. The sprayable cementitious composition of claim 12, wherein the fly ash is selected from the group consisting of type C fly ash, type F fly ash, and mixtures thereof.

14. The sprayable cementitious composition of any one of claims 1 to 13, wherein the fibres are selected from the group consisting of polymeric fibres, inorganic fibres, metal fibres, carbon fibres, plant-based fibres, and mixtures of any two or more thereof.

15. The sprayable cementitious composition of claim 14, wherein the polymeric fibres comprise a polymeric material selected from the group consisting of a polyolefin, a polyacrylic, a polyester, a polyvinyl alcohol, a polyamide, and combinations of any two or more thereof.

16. The sprayable cementitious composition of claim 14 or 15, wherein the polymeric fibres are selected from the group consisting of polyethylene fibres, high tenacity polypropylene fibres, polyvinyl alcohol fibres, and mixtures of any two or more thereof.

17. The sprayable cementitious composition of any one of claims 1 to 16, wherein the sprayable cementitious composition further comprises one or more components selected from the group consisting of a superplasticizer, an aggregate, a viscosity agent, and a retarder agent.

18. A sprayable cementitious composition comprising: a composite binder, fibres, and water; wherein the composite binder comprises a cement component and a pozzolan component, and wherein the sprayable cementitious composition, when cured, achieves one or more properties selected from the group consisting of:

(i) a tensile strength of at least about 2.50 MPa,

(ii) a tensile strain capacity of at least about 3% at 28 days,

(iii) a crack width of less than about 100 μm at ε < 2%, and

(iv) a maximum expansion of at least about 1210 με.

19. A method of preparing a sprayable cementitious composition, the method comprising: (i) providing a binder composition comprising a cement component and a pozzolan component,

(ii) mixing the binder composition with water to form a wet mixture,

(iii) adding fibres to the wet mixture.

20. The method of claim 19, wherein the method further comprises mixing the cement component and the pozzolan component to provide the binder composition.

21. The method of claim 19 or 20, wherein a superplasticizer is added to the water before step (ii).

22. A method of repairing and/or retrofitting a building structure comprising the steps of: (i) providing a sprayable cementitious composition of any one of claims 1 to 18;

(iii) allowing the cementitious composition to set on the surface.

23. The method of claim 22, wherein the spraying step (ii) is carried out by a manual spray system or an automated spray system.

24. The method of claim 22 or 23, wherein the building structure is a pipeline.

25. The method of claim 24, wherein the surface is the internal surface of the pipeline.

26. The method of claim 24 or 25, wherein the pipeline is retrofitted to increase the lifetime of the pipeline, increase the load bearing capacity of the pipeline, and/or strengthen the pipeline.

27. Use of the sprayable cementitious composition of any one of claims 1 to 18 for repairing and/or retrofitting a building structure.

28. The use of claim 27 wherein the building structure is a pipeline.

29. A dry pre-mix for preparing a sprayable cementitious composition of any one of claims 1 to 18, the dry pre-mix comprising a composite binder, and fibres; wherein the composite binder comprises a cement component and a pozzolan component.

30. A method of preparing a sprayable cementitious composition of any one of claims 1 to 18, the method comprising:

(i) providing the dry pre-mix of claim 29,