CA3129300A1 - Shotcrete composition - Google Patents

Abstract

A shotcrete composition includes a cement, a fine aggregate, a coarse aggregate and water. A
weight ratio of water to cement is between 0.38 and 0.44 and is sufficient for hydraulic setting of the cement. The shotcrete composition also includes a magnesium aluminosilicate material, a colloidal silica material, and a MgO/Ca0 blend. The MgO/Ca0 blend is present in an amount of between 2.5% and 5% of the amount of dry cement, and the MgO/Ca0 blend is between 2% and 6% Ca0 by weight.

Description

Doc. No. 328-18 CA
Green Tech Patent SHOTCRETE COMPOSITION
FIELD
This disclosure relates generally to shotcrete mixtures for use in fanning underground supports, repairing damaged concrete structures, encasing structural steel for fireproofing, etc., and more particularly to shotcrete mixtures that foun substantially waterproof structures after hardening.
BACKGROUND
Shotcrete is a method of applying concrete projected at high velocity primarily onto a vertical or overhead surface. The impact created by the application consolidates the concrete.
Although the hardened properties of shotcrete are similar to those of conventional cast-in-place concrete, the nature of the placement process results in an excellent bond with most substrates, and rapid or instant capabilities, particularly on complex forms or shapes. In the shotcrete method, concrete is applied using a wet- or dry-mix process. The wet-mix shotcrete process mixes all ingredients, including water, before introduction into the delivery hose. The dry-mix shotcrete process adds water to the mix at the nozzle. The shotcrete method of applying concrete is used in new construction and repairs and is suitable for curved and thin elements.
Buildings and construction together account for more than 30% of global final energy use and almost 40% of energy-related carbon dioxide (CO2) emissions when upstream power generation is included. Concrete is one of the biggest contributors to the carbon footprint of buildings and infrastructure. Every year, more than 10 billion tons of concrete are used, which requires more than 4 billion tons of cement, accounting for around 8% of all CO2 emissions worldwide. Despite improvements in processes and control measures, the manufacture of concrete still emits between 70 and 90 kg of CO2 per ton.
The main environmental impact of concrete occurs during manufacture, especially the production of cementitious binder, reinforcing steel, mining, and transport of aggregates, and the energy used to transport the concrete to the job site.

Date Recue/Date Received 2021-08-30 Doc. No. 328-18 CA
Green Tech Patent Reducing the impact of concrete in the construction industry will become increasingly important in coming years as rapid urbanization and economic development increases demand for new buildings and, thus, for concrete and cement, including for use in the shotcrete process. One of the most important and attainable ways of reducing the carbon footprint and other environmental impacts of concrete construction is to extend the life of the buildings, roads and other structures that are built using concrete. Since water permeation leads to corrosion and frost-thaw damage, etc., providing waterproof concrete structures that are resistant to water permeation is an area of intense interest due to the potential to significantly extend the time before it becomes necessary to demolish existing structures and build new ones.
As is well known, concrete is a composite construction material composed primarily of the reaction products of hydraulic cement, aggregates, and water. Water is both a reactant for the cement component and is necessary to provide desired flow characteristics (e.g., spread and/or slump) and ensure consolidation of freshly mixed concrete to prevent formation of strength-reducing voids and other defects. In the shotcrete process, air is entrained in the composition, which must be tailored to provide acceptable workability/pumpability, sprayability and to have suitable rebound and compaction characteristics. Of course, chemical admixtures may be added to modify the characteristics of the composition to suit a particular application using the shotcrete process.
Crack formation at or near the surface of the applied concrete, due to shrinkage of the concrete during hydration and hardening, are a common occurrence and may result in weaker structure and poor aesthetics. Unfortunately, these cracks also provide a pathway that allows water to permeate into the concrete, which may lead to corrosion of internal reinforcements, leaching of the aggregates and binders, and ultimately result in premature failure of the concrete structure and the need to build a replacement. Different mechanisms are known to result in crack formation. For instance, plastic shrinkage occurs in a freshly mixed concrete, with loss of water by evaporation from its surface, after placing and before hardening of the concrete. This can lead to plastic shrinkage cracking if the rate of evaporation is higher than that of the bleeding water rising to the surface of the concrete. Drying shrinkage occurs due to the loss of moisture from concrete after it hardens. Several factors impact shrinkage, for

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Green Tech Patent example: the cement and water content, size of the aggregates, aggregate to cement ratio, excessive fines, admixtures, cement composition, temperature, humidity, curing process, etc.
In general, it is not uncommon for these effects to produce cracks up to 1 mm or more in width in the hardened concrete structure, which is unacceptable for applications in which the concrete structure may be exposed to water.
Various technologies have been used to reduce shrinkage, using chemicals or fibers or mixes thereof. For instance, the use of cellulose fibers, polyethylene fibers, polypropylene fibers etc., has been widely practiced in the concrete industry for many years.
However, current technologies have thus far failed to achieve a reduction in crack size that is necessary to prevent water permeation and avoid premature failure of the concrete structure.
It would therefore be beneficial to provide a solution that overcomes at least some of the above-mentioned drawbacks.
SUMMARY OF EMBODIMENTS
In accordance with an aspect of at least one embodiment, there is provided a shotcrete composition, comprising: a cement, a fine aggregate, a coarse aggregate and water, wherein a weight ratio of water to cement is between 0.38 and 0.44 and is sufficient for hydraulic setting of the cement; a magnesium aluminosilicate material; a colloidal silica material; and a MgO/CaO blend in an amount of between 2.5% and 5% of the amount of dry cement, wherein the MgO/CaO blend comprises between 2% and 6% CaO by weight.
In accordance with an aspect of at least one embodiment, there is provided a shotcrete composition, comprising: a cement, a fine aggregate, a coarse aggregate and water, wherein a weight ratio of water to cement is between 0.38 and 0.44 and is sufficient for hydraulic setting of the cement; a magnesium aluminosilicate material; a colloidal silica material; and a MgO/CaO blend, wherein cracks formed during hardening of the shotcrete composition are less than 0.01 mm in width.
In accordance with an aspect of at least one embodiment, there is provided a hardened shotcrete structure fabricated from a shotcrete composition, wherein prior to hardening the

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Green Tech Patent shotcrete composition comprises: a cement, a fine aggregate, a coarse aggregate and water, wherein a weight ratio of water to cement is between 0.38 and 0.44 and is sufficient for hydraulic setting of the cement; a magnesium aluminosilicate material; a colloidal silica material; and a MgO/CaO blend in an amount of between 2.5% and 5% of the amount of dry cement, wherein the MgO/CaO blend comprises between 2% and 6% CaO by weight, and wherein a surface of the hardened shotcrete structure is free from cracks having a width greater than 0.01 mm.
DETAILED DESCRIPTION
While the present teachings are described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments. On the contrary, the present teachings encompass various alternatives and equivalents, as will be appreciated by those of skill in the art. All statements herein reciting principles, aspects, and embodiments of this disclosure, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perfolm the same function, regardless of structure.
As used herein, the temis "first," "second," and so forth are not intended to imply sequential ordering, but rather are intended to distinguish one element from another, unless explicitly stated to the contrary. Similarly, sequential ordering of method steps does not imply a sequential order of their execution, unless explicitly stated.
As used herein, "Cement" refers to a binder that sets and hardens and brings materials together. The most common cement is Ordinary Portland Cement (OPC) and a series of Portland cements blended with other cementitious materials, such as Portland Pozzolana Cement (PPC) and their typical blends available in the market.
As used herein, "Ordinary Portland cement" refers to a hydraulic cement made from grinding clinker with gypsum. Portland cement contains calcium silicate, calcium aluminate and calcium ferroaluminate phases. These mineral phases react with water to produce strength.

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Green Tech Patent As used herein, "Fibers" refers to a material used to increase shotcrete's structural performance. Fibers are also responsible for reducing cracking, abrasion resistance, surface finishes etc. For example, fibers include steel fibers, glass fibers, synthetic fibers, and natural fibers.
As used herein, "Admixture" refers to a chemical substance used to modify or improve shotcrete's properties in fresh and hardened state. These could be air entrainers, water reducers, set retarders, accelerators, stabilizers, superplasticizers, and others.
As used herein, "Concrete" refers to a combination of cement, fine aggregates, coarse aggregates, and water. Admixture can also be added to provide specific properties such as flow, lower water content, acceleration.
As used herein, "Shotcrete" refers to a concrete composition specifically formulated for high-velocity application onto surfaces by spraying. "Shotcrete" is a specific type of concrete that can either be dry-mix or wet-mix. "Shotcrete" also refers to the method of applying the concrete composition using a nozzle to spray the concrete onto a surface, etc.
As used herein, "Structural applications" refers to a construction material having a compressive strength greater than 25 MPa.
As used herein, "Coarse aggregates" refers to a manufactured, natural or recycled mineral with a particle size typically of about 10 mm for shotcrete applications, but more generally may be in the range between about 9 mm and about 15 mm. Coarse aggregates may also include mineral with a particle size outside this range, such as for instance

5-10%.
As used herein, "Fine aggregates" refers to a manufactured, natural or recycled minerals with a particle size between 0.1 mm and 1 mm. Fine aggregates may also include mineral with a particle size outside this range.
As used herein, "Shrinkage" refers to the reduction in the volume of shotcrete caused by the loss of moisture as shotcrete hardens or dries. Because of the volume loss, shotcrete shrinkage can lead, for example, to cracking when base friction or other restraint occurs.

Date Recue/Date Received 2021-08-30 Doc. No. 328-18 CA
Green Tech Patent As used herein, the water to cement ratio "w/c" refers to the total free water (w) mass in kg divided by the total cement mass in kg.
As used herein "Batch total weight" refers to the combined weight of cement, fine aggregate, coarse aggregate, and water added to form the shotcrete composition but excludes the weight of all admixture components.
According to a first aspect, the present disclosure relates to a shotcrete composition including i) cement, ii) a fine aggregate, iii) a coarse aggregate, iv) a magnesium aluminosilicate, v) colloidal silica, vi) a blend of magnesium oxide (MgO) and calcium oxide (CaO), and vii) water. After curing, a compressive strength in the range between about 20 MPa and 40 MPa, determined using the standard 28-day lab test for compressive strength of a concrete cylinder, is observed. The specific compressive strength may be tailored to suit the requirements of a particular project in which the shotcrete composition is to be used.
Advantageously, the disclosed shotcrete composition, after curing, exhibits reduced cracking and improved waterproof properties relative to known compositions.
The shotcrete composition of this disclosure provides improved performance, primarily against plastic shrinkage cracking, thermal cracking, and drying shrinkage cracking. The performance of the disclosed shotcrete composition is improved relative to prior art compositions by the inclusion of specific admixture components which exhibits a useful and unexpected synergy. The inclusion of an expansion agent (i.e., the MgO/CaO
blend) acts against the tensile forces that develop in the early setting stage of shotcrete hardening and that are responsible for plastic shrinkage cracking. The inclusion of colloidal silica reduces curing requirements and eliminates wet curing, and develops shotcrete strength earlier compared to typical mixes, thus reducing schedule times. The inclusion of colloidal silica furthermore minimizes capillary formation, bleeding of water and hence, drying shrinkage cracking compared to typical mixes. The inclusion of magnesium aluminosilicate provides improved workability and enables reduced water content (w/c ratio).
A currently preferred composition will now be described as a specific and non-limiting embodiment. However, as discussed in more detail below, the relative amount of the various components may be varied depending on the requirements of a specific application. The

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Green Tech Patent currently preferred composition includes a cement, a fine aggregate, a coarse aggregate, and water. The cement is preferably a hydraulic cement, preferably a sulfoaluminous clinker, preferably Portland cement. Portland cement refers to the most common type of cement in general use around the world, developed from types of hydraulic lime and usually originating from limestone. It is a fine powder produced by heating materials in a kiln to foun what is called clinker, grinding the clinker, and adding small amounts of other materials. The Portland cement is made by heating limestone (calcium carbonate) with other materials (such as clay) to >1400 C in a kiln, in a process known as calcination, whereby a molecule of carbon dioxide is liberated from the calcium carbonate to foun calcium oxide, or quicklime, which is then blended with the other materials that have been included in the mix to from calcium silicates and other cementitious compounds. The resulting hard substance, called "clinker" is then ground with a small amount of gypsum into a powder to make ordinary Portland cement (OPC). Several types of Portland cement are available with the most common being called ordinary Portland cement (OPC) which is grey in color. The low cost and widespread availability of the limestone, shales, and other naturally occurring materials used in Portland cement make it one of the low-cost materials widely used throughout the world.
Of course, as will be apparent to a person having ordinary skill in the art, other types of cement, such as for instance Portland Pozzolana Cements (PPC) and their typical blends available in the market, may be used as the cement in the currently preferred composition. Portland Pozzolana Cements are produced by either inter-grinding of OPC clinker along with gypsum and pozzolanic materials in certain proportions or grinding the OPC clinker, gypsum and Pozzolanic materials separately and thoroughly blending them in certain proportions.
The fine aggregate may be of natural or synthetic origin and may have a particle size in the range of 0.1 mm to 1.0 mm. The fine aggregate may be sand or another suitable material having a similar particle size, including manufactured, natural, or recycled minerals. Using manufactured sand is a more environmentally beneficial alternative to typical sand. The benefits arise from the fact that manufactured sand is a by-product of crushing rock. This leads to reduced processing needed compared to typical sand and reduced river dredging for obtaining sand. These factors also help making manufactured sand cheaper to use than typically sourced sand.

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Green Tech Patent The coarse aggregate also may be of natural or synthetic origin and may have a particle size typically of about 9-15 mm, the industry standard being about 10 mm, although the particle size may be either smaller or larger than these values as will be understood by a person having ordinary skill in the art (i.e., 5-10%). The coarse aggregate may be limestone, pea stone, standard crushed stone, or another suitable material. Aggregates, from different sources, or produced by different methods, may differ considerably in particle shape, size, and texture.
Shape of the aggregates of the present disclosure may be cubical and reasonably regular, essentially rounded, or angular and irregular. Surface texture may range from relatively smooth with small, exposed pores to irregular with small to large, exposed pores. Particle shape and surface texture of both the fine aggregate and the coarse aggregate influence proportioning of mixtures in such factors as workability, pumpability, fine-to-coarse aggregate ratio, cement binder content, and water requirement.
A typical batch weight is 2400 kg producing 1 m3 of shotcrete, although the total batch size may be greater or less than this value to suit a particular job requirement.
In the currently preferred composition, a weight ratio of the cement to the fine aggregate is between about 1:2 and about 1:2.5. A weight ratio of the cement to the coarse aggregate is between about 1:1.5 and about 1:2.5. A weight ratio of the fine aggregate to the coarse aggregate is between about 1:0.54 and 1:1.5, preferably between about 1:0.6 and 1:1.25. Specific and non-limiting examples of suitable ratios of cement to fine aggregate to coarse aggregate include 1:2.5:2, 1:2:2.5, 1:2.5:1.5. Of course, other ratios within the above-mentioned ranges may be used. In addition, the ratio of fine aggregate to coarse aggregate may be tailored depending on the specific requirements for a particular job (i.e., vertical, or curved application and site conditions) and the material quality (shape, size etc.). For some applications, a higher weight ratio of fine aggregate to coarse aggregate may be advantageous (i.e., about 1:0.54, which means that about 65 % of the total aggregate weight is the fine aggregate).
The amount of water added to the dry mixture of cement, fine aggregate and coarse aggregate is sufficient for hydraulic setting of the cement. More specifically, the water to cement content (kg/kg) is between about 0.38 and about 0.44 in the currently preferred composition.
The relative amounts of cement, fine aggregate, and coarse aggregate, with a water content between 0.38 and 0.44, yields a shotcrete mixture that is suitable for application via a concrete

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Green Tech Patent gun in known fashion. The currently preferred shotcrete composition may be prepared e.g., in a ready-mix truck at an appropriate time prior to a scheduled delivery at a work site. Suitable amounts of each of the above-mentioned components may be within the following ranges:
400-460 kg of cement; 800-1200 kg of fine aggregates; 650-1100 kg of coarse aggregates;
and 150-200 L of water. The amount of each component is adjustable within the above-mentioned ranges to produce a batch total weight of shotcrete of 2400 kg and yielding 1 m3 of shotcrete.
The currently preferred composition includes chemical admixtures and mineral admixtures to improve the physical properties of the wet mix of the finished shotcrete material. In particular, the currently preferred composition includes i) a blend of magnesium oxide (MgO) and calcium oxide (CaO) (MgO/CaO blend), ii) a magnesium aluminosilicate such as for instance palygorskite and/or attapulgite, and iii) colloidal silica. The currently preferred composition optionally includes additional admixtures, such as for instance iv) plasticizers/water reducers, e.g., lignosulfonate-based additives, v) micro/macro fibers, e.g., steel fibers or synthetic fibers (e.g., polypropylene, polyvinyl alcohol, etc.), and/or vi) supplementary cementitious materials (SCM) used to further enhance the properties of the concrete or to reduce use of cement in the mix (e.g., typically in the form of silica fumes, limestone, flyash, slag etc.). The above-mentioned admixtures is discussed in greater detail in the following paragraphs.
.. The MgO/CaO blend is added, in the dry state, to the mixture of cement, fine aggregate and coarse aggregate described above. More particularly, the MgO/CaO blend is an expansion agent that counteracts the tensile forces across the applied shotcrete during the initial setting state, which leads to a significant reduction in plastic shrinkage cracking after the shotcrete composition hardens. It has been found that a blend, containing the relative amounts of MgO, CaO and silica fume that are disclosed in the following paragraph, has a synergistic effect with the other admixtures resulting in the formation of cracks that are orders of magnitude smaller than the cracks that are formed using prior art shotcrete compositions. For instance, after hardening, the disclosed shotcrete composition may have cracks that are no larger than about 0.01 mm in width, preferably no larger than about 0.001 mm in width.

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Green Tech Patent Preferably, the MgO/CaO blend is added in an amount between about 2.5 wt% and about 5 wt% of the cement, on a dry weight basis. For a typical 2400 kg batch including water, between about 10 kg and about 23 kg of the MgO/CaO blend is added. The relative amount of the two components of the blend may vary depending on the specific application and/or depending on the desired properties of the shotcrete. Preferably, the MgO/CaO
blend contains between 2¨ 6% CaO by weight, with the balance being MgO.
The magnesium aluminosilicate, such as for instance palygorskite and/or attapulgite, is added, either as a slurry or in dry foun, to the currently preferred shotcrete composition described above. The magnesium aluminosilicate admixture acts as a binder, thixotrope, reinforcement additive, anti-settling agent and rheology modifier. The magnesium aluminosilicate can be introduced at any point in the process with similar performance. To avoid making the preferred shotcrete composition too cohesive, the magnesium aluminosilicate dosage typically is reduced relative to the dosage in prior art shotcrete compositions. In the currently preferred composition, the total combined amount of magnesium aluminosilicate is in the range between 0.03% and 0.1% of the batch total weight (i.e., the combined dry weight of cement, fine aggregate and coarse aggregate, and water), or between 0.5 kg and 2.5 kg in a typical 2400 kg batch total weight including added water.
The colloidal silica is provided in slurry foun, such as for instance about 15 wt% to 30 wt%
amorphous silica in 70 wt% to 85 wt% water. The silica particles in the slurry may have a size between about 1 nm and about 100 nm and a surface area of between about 300 m2/g and about 900 m2/g. A currently preferred colloidal silica slurry has silica particle between about 1 nm and about 50 nm in size and a surface area between about 500 m2/g and about 600 m2/g.
As noted above, the colloidal silica enables internal hydration and curing, promotes early strength acceleration, and increases workability by binding to the cement particles. The colloidal silica is added to the preferred shotcrete mix in slurry foim in an amount of about 0.95 L to about 1.15 L in a typical 2400 kg batch total weight including water (i.e., about 0.11 L per 45.35 kg dry weight of cement) and is the last admixture component added. The amount of colloidal silica slurry in a typical 2400 kg batch total weight including water may, however, be as much as 2.43 L. For instance, when the preferred shotcrete mixture is being prepared in a ready-mix truck, prior to adding the colloidal silica slurry the mixer is switched Date Recue/Date Received 2021-08-30 Doc. No. 328-18 CA
Green Tech Patent to discharge mode, and the mixer is turned to the point where the shotcrete mixture is on the final spiral of the mixer and about to fall off the chute. The mixer is then switched to mixing mode. The colloidal silica slurry is added, in a controlled manner, avoiding spillage onto the chute and avoiding contact with the internal surface of the mixer. Finally, the mixer spins at minimum speed of 70 rpm for at least 4 minutes to ensure proper dispersion across the volume of the shotcrete mixture.
The presently preferred shotcrete composition may include additional but optional admixtures, which are in any case added prior to adding the colloidal silica slurry. Optional admixtures include at least plasticizers/water reducers (e.g., lignosulfonate-based additives).
These additives are typically used to reduce water/cement ratio, provide additional fluidity/workability, strength and slow down the settling rates of shotcrete.
The presently preferred shotcrete composition is compatible and consistent with the use of plasticizers falling in the low to mid-range capabilities. A plasticizer admixture component may be added in an amount of about 160 ml to about 1000 ml per 100kg of dry cement, or about 600 ml to about 4600 ml in a typical 2400 kg batch total weight including water.
Another optional admixture includes at least micro/macro fibers, such as for instance glass, steel, nylon or other synthetic fibers (e.g., polypropylene fibers). The inclusion of steel and/or synthetic macro/micro fibers is to avoid all fauns of internal cracking and limit the width of cracks when the presently preferred shotcrete composition is to be used in extreme weather conditions. Some specific and non-limiting examples of suitable synthetic fibers include polyvinyl alcohol (PVA) micro filament fibers with a fiber diameter in the range between about 24 microns to about 100 micron and a fiber length in the range between about 6 mm to about 50 mm. PVA fibers can be suggested as the most preferred option.
Alternatively, polypropylene fibers (PPF) with a fiber diameter in the range between about 50 microns to about 200 microns and a fiber length in the range between about 12 mm to about 65 mm may be used. The type of fiber selected will depend at least partially upon the specific application for the shotcrete batch. A micro/macro fiber admixture component may be added in an amount of about 0.45 kg to about 2.5 kg in a typical 2400 kg batch total weight including water.

Date Recue/Date Received 2021-08-30 Doc. No. 328-18 CA
Green Tech Patent In teims of the present disclosure, the term "composition" may refer to the fresh state solid cement or shotcrete mixture comprising the cement, the fine aggregate, the coarse aggregate, the magnesium aluminosilicate, the colloidal silica, the MgO/CaO blend before the addition of the water and/or additional chemical and/or mineral admixtures. The "composition" may refer to a sprayable fluid shotcrete mixture after the addition of all or a portion of the water and/or additional chemical and/or mineral admixtures. The "composition" may refer to the hardened matrix shotcrete after any period of setting once the hydration process has started.
In a preferred embodiment, all components of the shotcrete composition of the present disclosure are homogeneously dispersed in the composition.
Throughout the description and claims of this specification, the words "comprise", "including", "having" and "contain" and variations of the words, for example "comprising"
and "comprises" etc., mean "including but not limited to", and are not intended to, and do not exclude other components.
When a range is given between "x" and "y" the range is intended to include both "x" and "y."
The term "about" means 10% and preferably 5% when applied to values in a range or to single values.
It will be appreciated that variations to the foregoing embodiments of the disclosure can be made while still falling within the scope of the disclosure. Each feature disclosed in this specification, unless stated otherwise, may be replaced by alternative features serving the same, equivalent or similar purpose. Thus, unless stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.
All of the features disclosed in this specification may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. In particular, the preferred features of the disclosure are applicable to all aspects of the disclosure and may be used in any combination. Likewise, features described in non-essential combinations may be used separately (not in combination).

Date Recue/Date Received 2021-08-30

Claims (22)

Doc. No. 328-18 CA
Green Tech PatentWhat is claimed is:

1. A shotcrete composition, comprising:
a cement, a fine aggregate, a coarse aggregate and water, wherein a weight ratio of water to cement is between 0.38 and 0.44 and is sufficient for hydraulic setting of the cement;
a magnesium aluminosilicate material;
a colloidal silica material; and a MgO/Ca0 blend in an amount of between 2.5% and 5% of the amount of dry cement, wherein the MgO/Ca0 blend comprises between 2% and 6% Ca0 by weight.

2. The shotcrete composition of claim 1, wherein cracks formed during hardening of the shotcrete composition are less than 0.01 mm in width.

3. The shotcrete composition of claim 1, wherein cracks formed during hardening of the shotcrete composition are less than 0.001 mm in width.

4. The shotcrete composition of any one of claims 1 to 3, wherein a weight ratio of the cement to the fine aggregate is between 1:2 and about 1:2.5, a weight ratio of the cement to the coarse aggregate is between 1:1.5 and about 1:2.5, and a weight ratio of the fine aggregate to the coarse aggregate is between 1:0.54 and 1:1.5.

5. The shotcrete composition of claim 4, wherein weight ratio of the fine aggregate to the coarse aggregate is between 1:0.6 and 1:1.25.

6. The shotcrete composition of any one of claims 1 to 4, wherein the magnesium aluminosilicate material is present in an amount between 0.03 wt% and 0.1 wt%
of the batch total dry weight of cement, fine aggregate and coarse aggregate combined.

Date Recue/Date Received 2021-08-30 Doc. No. 328-18 CA
Green Tech Patent

7. The shotcrete composition of claim 5, wherein the magnesium aluminosilicate material is at least one of palygorskite or attapulgite.

8. The shotcrete composition of any one of claims 1 to 6, wherein the colloidal silica material is added as a slurry containing 15 wt% to 30 wt% amorphous silica in 70 wt% to 85 wt% water and is added in an amount of 0.11 L of the slurry per 45.35 kg of dry cement.

9. The shotcrete composition of any one of claims 1 to 7, further comprising natural or synthetic fibers homogeneously distributed throughout the shotcrete composition.

10. The shotcrete composition of claim 8, wherein the natural or synthetic fibers are selected from the following: glass fibers, steel fibers, nylon fibers, polyvinyl alcohol fibers and polypropylene fibers.

11. The shotcrete composition of any one of claims 1 to 10, wherein the fine aggregate has a particle size in the range of 0.1 mm to 1.0 mm.

12. The shotcrete composition of any one of claims 1 to 11, wherein the coarse aggregate has a particle size of about 20 mm.

13. The shotcrete composition of any one of claims 1 to 12, wherein the colloidal silica is amorphous silica having a particle size between 1 nm and 100 nm and a surface area of between 300 m2/g and 900 m2/g.

14. The shotcrete composition of any one of claims 1 to 12, wherein the colloidal silica is amorphous silica having a particle size between 1 nm and 50 nm and a surface area of between 500 m2/g and 600 m2/g.

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Green Tech Patent

15. A shotcrete composition, comprising:
a cement, a fine aggregate, a coarse aggregate and water, wherein a weight ratio of water to cement is between 0.38 and 0.44 and is sufficient for hydraulic setting of the cement;
a magnesium aluminosilicate material;
a colloidal silica material; and a MgO/Ca0 blend, wherein cracks formed during hardening of the shotcrete composition are less than 0.01 mm in width.

16. The shotcrete composition according to claim 15, wherein the cracks formed during hardening of the shotcrete composition are less than 0.001 mm in width.

17. A hardened shotcrete structure fabricated from a shotcrete composition, wherein prior to hardening the shotcrete composition comprises:
a cement, a fine aggregate, a coarse aggregate and water, wherein a weight ratio of water to cement is between 0.38 and 0.44 and is sufficient for hydraulic setting of the cement;
a magnesium aluminosilicate material;
a colloidal silica material; and a MgO/Ca0 blend in an amount of between 2.5% and 5% of the amount of dry cement, wherein the MgO/Ca0 blend comprises between 2% and 6% Ca0 by weight, and wherein a surface of the hardened shotcrete structure is free from cracks haying a width greater than 0.01 mm.

18. The hardened shotcrete structure according to claim 17, wherein the surface of the hardened shotcrete structure is free from cracks haying a width greater than 0.01 mm.

19. The hardened shotcrete structure of claim 17 or 18, wherein:
the magnesium aluminosilicate material is between 0.03 wt% and 0.1 wt% of the batch total dry weight of the of cement, fine aggregate and coarse aggregate combined, and is selected from at least one of palygorskite or attapulgite; and Date Recue/Date Received 2021-08-30 Doc. No. 328-18 CA
Green Tech Patent the colloidal silica material is added as a slurry containing between 15 wt%
and 30 wt% amorphous silica in between 70 wt% and 85 wt% water and is added in an amount of 0.11 L of the slurry per 45.35 kg of dry cement.

20. The shotcrete composition of any one of claims 17 to 19, wherein a weight ratio of the cement to the fine aggregate is between 1:2 and about 1:2.5, a weight ratio of the cement to the coarse aggregate is between 1:1.5 and about 1:2.5, and a weight ratio of the fine aggregate to the coarse aggregate is between 1:0.54 and 1:1.5.

21. The shotcrete composition of claim 20, wherein weight ratio of the fine aggregate to the coarse aggregate is between 1:0.6 and 1:1.25.

22. The hardened shotcrete structure of any one of claims 17 to 21, wherein the shotcrete composition further comprises natural or synthetic fibers homogeneously distributed throughout the shotcrete composition, selected from the following: glass fibers, steel fibers, nylon fibers, polyvinyl alcohol fibers and polypropylene fibers.

Date Recue/Date Received 2021-08-30