Functional gradient bacterial capsules for concrete self-repair

Abstract

Disclosed herein is a capsule that can be incorporated into a cementitious material for use in repairing cracks in the cementitious material. The capsule can include an inorganic particle having a surface and a core region, wherein the core region houses bacterial spores for use in repairing cracks, or the core region houses bacterial spores for use in repairing cracks and the capsule houses nutrients separate from the bacterial spores, wherein the density and strength of the inorganic particle decrease in a direction from the surface to the core region, and the density at the surface is sufficient to hinder penetration of alkaline substances. Disclosed herein is a nutrient capsule that can be incorporated into a cementitious material for use in housing nutrients that aid bacterial spores in repairing cracks in the cementitious material. The nutrient capsule can include an inorganic particle having a surface and a core region, wherein the density and strength of the inorganic particle decrease in a direction from the surface to the core region, and the core region houses the nutrients, and the capsule is free of bacterial spores. Disclosed herein is a cementitious material incorporating (i) the capsule or (ii) the capsule and the nutrient capsule. Also disclosed herein are methods of forming the respective capsule, nutrient capsule, and cementitious material.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to Singapore Patent Application No. 10202103685S, filed on April 12, 2021, the contents of which are incorporated herein by reference in their entirety for all purposes. Technical Field

[0003] This disclosure relates to a capsule that can be incorporated into a cementitious material for repairing cracks in the cementitious material. This disclosure relates to a nutrient capsule that can be incorporated into a cementitious material for containing nutrients that facilitate the repair of cracks in the cementitious material by bacterial spores. This disclosure relates to a cementitious material incorporating (i) a capsule, or (ii) a capsule and a nutrient capsule. This disclosure also relates to methods of forming capsules, nutrient capsules, and cementitious materials. Background Technology

[0004] Crack repair is crucial for concrete structures because crack formation allows corrosive substances to penetrate, leading to decreased durability and shortened service life. However, traditional manual repair methods are labor-intensive, inconvenient, and costly. It is estimated that in the United States alone, annual costs for concrete repair range from $1.8 billion to $21 billion. To avoid these drawbacks of manual repair, researchers have investigated a bacteria-based self-healing technology to achieve self-healing of cracks in Portland cement (PC). This method involves directly embedding dormant bacterial spores along with compounds such as nutrients and calcium sources into the concrete mix during pouring. As the crack expands, the bacterial spores are exposed and activated by the introduction of water and oxygen, precipitating a carbonate phase within the crack through bacterial metabolic activity.

[0005] However, studies have shown that when bacteria are directly encapsulated in PC (i.e., without any protection) for 28 days, no precipitation occurs, indicating that bacteria cannot achieve self-repair within the PC under these conditions. This inactive state of the bacteria is likely related to the high pH of PC (approximately 13), leading researchers to develop encapsulation methods to protect bacteria from adverse environments. Traditionally, polymers (such as melamine and hydrogels), porous carriers (such as expanded clay, expanded perlite, and fibers), and low-alkalinity cementitious materials that gain strength primarily through hydration are perhaps the most widely used encapsulation materials. While these encapsulations can extend bacterial lifespan, there are limitations to using these materials. Numerous studies have shown that using polymers as capsules often results in a significant reduction in matrix strength, primarily due to two reasons. First, polymers are soft materials with lower strength than cementitious materials, thus becoming a weak point in the system. Second, the introduction of polymer capsules tends to create larger pores within the matrix, and higher porosity leads to decreased concrete strength. As for using porous materials to encapsulate bacteria, the high porosity of these materials does not provide sufficient protection for the bacteria. After bacteria are embedded in these porous carriers through soaking or vacuum impregnation, they can still come into contact with the surrounding environment during mixing. Because the porous structure of the carrier allows bacteria to penetrate the interior, it also allows alkaline components in the binder to permeate, thus hindering the bacteria from "repairing" the concrete. For hydration-based cementitious materials, the continuous hydration of cement often leads to the continuous densification of the capsule's microstructure. Therefore, bacteria may be compressed due to insufficient space. Furthermore, the fairly uniform density of the capsule throughout can make it difficult for bacteria to be exposed when cracks propagate.

[0006] Therefore, it is necessary to provide a solution to overcome one or more of the above limitations. Summary of the Invention

[0007] In a first aspect, this article provides a capsule that can be incorporated into cement-based materials for repairing cracks in the materials, the capsule comprising: inorganic particles having surface and core regions.

[0008] The core region contains bacterial spores used to repair cracks, or

[0009] The core region contains bacterial spores for repairing cracks, and the capsule contains nutrients separate from the bacterial spores.

[0010] The density and strength of the inorganic particles decrease along the direction from the surface to the core region, and

[0011] The density at the surface is sufficient to prevent the penetration of alkaline substances.

[0012] On the other hand, this document provides a method for forming the capsules described in various embodiments of the first aspect, the method comprising:

[0013] Provides bacterial spores for repairing cracks in cement-based materials;

[0014] Forming a slurry containing the bacterial spores and water, or forming a slurry containing the bacterial spores, water, and nutrients;

[0015] The slurry is then hardened.

[0016] To convert hardened slurry into granules; and

[0017] The particles are solidified in the presence of carbon dioxide to form capsules.

[0018] On the other hand, this article provides a nutrient capsule that can be incorporated into cementitious materials to contain nutrients that help bacterial spores repair cracks in cementitious materials. The nutrient capsule contains:

[0019] Inorganic particles, wherein the inorganic particles have a surface region and a core region.

[0020] The density and strength of the inorganic particles decrease along the direction from the surface to the core region, and

[0021] The core area contains nutrients, and the capsule is free of bacterial spores.

[0022] On the other hand, this document provides a method for forming the nutritional capsules described in the various embodiments of this document, the method comprising:

[0023] Provides nutrients that help bacterial spores repair cracks in cement-based materials;

[0024] A slurry containing the nutrients and water is formed;

[0025] The slurry is then hardened.

[0026] To convert hardened slurry into granules; and

[0027] The particles are solidified in the presence of carbon dioxide to form a nutrient capsule.

[0028] On the other hand, this document provides a cement-based material incorporating (i) the capsules described in the various embodiments of the first aspect, or (ii) the capsules described in the various embodiments of the first aspect and the nutritional capsules described in the various embodiments of this document.

[0029] On the other hand, this document provides a method for forming the cement-based materials described in the various embodiments herein, the method comprising:

[0030] Provide (i) the capsules described in the various embodiments of the first aspect, or (ii) the capsules described in the various embodiments of the first aspect and the nutritional capsules described in the various embodiments herein; and

[0031] The capsules and the existing nutrient capsules are mixed with cement to form a cement-based material. Attached Figure Description

[0032] The accompanying drawings are not necessarily drawn to scale, but generally focus on illustrating the principles of this disclosure. In the following description, various embodiments of this disclosure will be described with reference to the following drawings, wherein:

[0033] Figure 1A A servo-hydraulic universal testing machine is shown for inducing cracks in self-healing samples (e.g., cylindrical samples).

[0034] Figure 1B A pre-cracked sample with markings is shown.

[0035] Figure 2 The X-ray diffraction (XRD) pattern of the capsule of this disclosure containing 20 wt% fluorite is shown.

[0036] Figure 3 SEM images of two different RMC-based capsules of this disclosure, manufactured by the method of this disclosure, are shown. The SEM images show that the two different RMC-based capsules have a uniform morphology.

[0037] Figure 4A Microscopic images of crack self-healing before and after using samples from group P are shown.

[0038] Figure 4B Microscopic images of crack self-healing before and after using samples from the PNB group are shown.

[0039] Figure 4C Microscopic images of crack self-healing before and after using samples from the PNC group are shown.

[0040] Figure 5 These are the 28-day compressive strength graphs for P, PNC, PN, and PC* samples.

[0041] Figure 6 The particle size distribution of the reactive magnesium cement-based bacterial spore (RMC-B) capsules of the present invention is shown.

[0042] Figure 7 The quantitative procedure for bacterial activity in RMC-B and PC-B capsules is shown.

[0043] Figure 8A A steel mesh placed in a semi-filled mold for self-healing sample preparation is shown.

[0044] Figure 8B A fully filled mold for preparing self-healing samples is shown.

[0045] Figure 9 The water flow rate measuring device is shown.

[0046] Figure 10A This is a schematic diagram of extracting samples for SEM examination of the repaired product to demonstrate surface repair.

[0047] Figure 10B This is a schematic diagram of extracting samples for SEM examination of repaired products to demonstrate internal repairs.

[0048] Figure 10C This is a schematic diagram of extracting samples for SEM examination of repaired products to demonstrate the deposition on the sample surface.

[0049] Figure 11 An SEM image of an RMC-B capsule according to an embodiment of the present disclosure is shown.

[0050] Figure 12 This is a graph showing the weight loss of RMC raw materials.

[0051] Figure 13 This is a schematic diagram of the gradient structure of an RMC-B capsule with a dense shell and a porous core.

[0052] Figure 14 This is a graph showing the activity of bacterial spores in PC-B capsules.

[0053] Figure 15 This is a graph showing the activity of bacterial spores in RMC-B capsules.

[0054] Figure 16 The isothermal calorimetric test results of Mix P and Mix PC according to an embodiment of this disclosure are shown.

[0055] Figure 17 This is a graph showing the compressive strength of PC slurry with and without RMC-B capsules.

[0056] Figure 18 The crack widths of different samples before and after five wet / dry cycles are shown.

[0057] Figure 19A Optical microscopic images of cracks in the PNC sample before and after five wet / dry conditioning cycles are shown.

[0058] Figure 19B Optical microscopic images of cracks in the PNS sample are shown before and after five wet / dry conditioning cycles.

[0059] Figure 19C Optical microscopic images of the cracks in sample P before and after five wet / dry conditioning cycles are shown.

[0060] Figure 20 The decrease in water throughput of samples PNC, PNS, and P after 5 wet / dry conditioning cycles is shown.

[0061] Figure 21A This is a SEM image of the repair product on the cracked surface of the PNC sample.

[0062] Figure 21B This is a SEM image of the repair product inside the crack of the PNC sample.

[0063] Figure 21C This is a SEM image of the repaired product on the surface of a PNC sample.

[0064] Figure 22 This is a SEM image of RMC-BN capsules.

[0065] Figure 23 The XRD pattern of the RMC-BN capsule is shown.

[0066] Figure 24A Crack widths of different samples (P-BNC and P) before and after 10 wet / dry cycles are shown.

[0067] Figure 24B Crack widths of different samples (P-BNC and P) before and after 20 wet / dry cycles are shown.

[0068] Figure 24C Crack widths of different samples (P-BNC and P) before and after 30 wet / dry cycles are shown.

[0069] Figure 25A A photograph of a 235 μm wide crack from the P-BNC group before repair is shown.

[0070] Figure 25B The image shows a crack with an initial width of 235 μm from the P-BNC group after 10 conditioning cycles.

[0071] Figure 25C The image shows a crack with an initial width of 235 μm from the P-BNC group after 20 conditioning cycles.

[0072] Figure 26 The study showed that the average water throughput decreased for different samples at 10, 20, and 30 conditioning cycles.

[0073] Figure 27This is a graph showing the compressive strength of samples with and without (P)RMC-BN capsules.

[0074] Figure 28 This is a graph showing the compressive strength of different samples with added PC nutritional capsules and RMC-B capsules.

[0075] Detailed Explanation

[0076] The present disclosure will now be described in detail with reference to the accompanying drawings, which illustrate by way of example specific details and embodiments in which the present disclosure may be practiced.

[0077] Features described in the context of an embodiment may be adapted accordingly to the same or similar features in other embodiments. Features described in the context of an embodiment may be adapted accordingly to other embodiments, even if not explicitly described in those other embodiments. Furthermore, additions and / or combinations and / or substitutions described with respect to features in the context of an embodiment may be adapted accordingly to the same or similar features in other embodiments.

[0078] This disclosure relates to a capsule that can be incorporated into cementitious materials for repairing cracks in those materials. The capsule can be used as a cement additive to participate in the self-healing of concrete and other cementitious materials. Hereinafter, the capsule may be referred to as a "functionally graded bacterial capsule" because the density and strength of the capsule decrease along the direction from the surface to the core region, and bacterial spores are incorporated (restricted) in this core region. In other words, the capsule of the present invention differs from the conventional capsules discussed in the background section above because the capsule of the present invention has a gradient density and strength, i.e., the density and strength gradually decrease from the surface to the core region of the capsule.

[0079] This disclosure also relates to a method for forming the capsule. To prepare the capsule, an inorganic material with low alkalinity (e.g., pH below 12 or below 11), a porous structure, and capable of forming particles with a dense surface and the aforementioned density and strength transitions can be used. As a non-limiting example, reactive magnesium cement (RMC) or any RMC-based mixture (e.g., RMC incorporating waste / aggregate / additives) can be used to prepare the capsule of the present invention. Taking a pure RMC mixture as a non-limiting example, RMC is a low-alkalinity cementitious material (pH approximately 10.5) that acquires strength primarily through carbonation. The strength evolution process involves two steps. For example, firstly, MgO hydrates to form brucite, a mineral with high porosity and low strength. Brussels silica then undergoes carbonation to form a series of hydrated magnesium carbonates (HMCs), such as nesquehonite (MgCO3·3H2O), hydromagnesite (4MgCO3·Mg(OH)2·4H2O), and dypingite (4MgCO3·Mg(OH)2·5H2O), which are dense and robust. Carbonation is primarily a surface reaction, thus the HMC phase forms in the surface region. Under accelerated carbonation at high CO2 concentrations, a dense shell forms on the carbonation surface, hindering further CO2 penetration into the core region of the capsule, keeping the core region porous, and the dominant phase within the sample remains brussels silica. Due to this characteristic of RMCs, the capsules of this invention exhibit gradient density and strength, with density and strength gradually decreasing from the surface region to the core region.

[0080] The present invention also relates to a nutrient capsule that can be incorporated into cementitious materials to contain nutrients that help bacterial spores repair cracks in the cementitious materials. This disclosure also relates to cementitious materials incorporating (i) the capsule or (ii) the capsule and the nutrient capsule. The present invention also relates to methods for forming the capsule, the nutrient capsule, and the cementitious material.

[0081] Details of various embodiments of the capsules, nutritional capsules, cement-based materials incorporating (i) capsules or (ii) capsules and nutritional capsules of the present invention, their methods of formation, and advantages associated with the various embodiments are now described below. Where embodiments or advantages have already been further described in the Examples section below, they will not be repeated for the sake of brevity.

[0082] This disclosure provides a capsule that can be incorporated into cementitious materials for repairing cracks in the materials. The capsule may contain inorganic particles having surface and core regions.

[0083] In various non-limiting embodiments, the core region contains (i) bacterial spores for repairing cracks, or (ii) the core region contains bacterial spores for repairing cracks and the capsule contains nutrients separate from the bacterial spores.

[0084] In various embodiments, the density and strength of the inorganic particles decrease from the surface to the core region, and the density at the surface is sufficient to impede the penetration of alkaline substances. Due to the dense surface of the capsule, it advantageously protects the bacterial spores within from any harmful external factors. Structures formed from concrete or cement-based materials may crack over time. Advantageously, the capsule can be incorporated into the concrete or cement-based material before the structure is formed. Over time, cracks will appear in the concrete or cement-based material, and cracks will also appear in the capsule, thereby exposing the bacterial spores to repair the cracks.

[0085] In various embodiments, the core region can be porous. Porosity advantageously allows bacterial spores to be contained within the capsule away from the surface.

[0086] In various embodiments, the core region may comprise brucite and the surface may comprise magnesia or magnesia. Magnesia and magnesia advantageously provide the capsule surface with a degree of strength to better withstand any compressive forces that may damage bacterial spores.

[0087] In some non-limiting embodiments, the capsule may be nutrient-free when the core region contains bacterial spores for repairing cracks.

[0088] In various embodiments, the nutrients may comprise yeast extract. In some non-limiting embodiments, the nutrients may comprise yeast extract when the capsule contains nutrients separated from bacterial spores.

[0089] In various embodiments, the bacterial spores are dormant bacteria. In other words, the bacterial spores in the capsule are in a dormant state and can be activated by nutrients to repair cracks. Compared to active bacteria (i.e., vegetative bacteria), dormant bacterial spores are more resistant to external factors (adverse temperature, pH, etc.). In other words, in the context of this disclosure, bacteria in a dormant state are referred to as bacterial spores, while bacteria in an active state are referred to as vegetative bacteria. In various embodiments, the bacterial spores may include Bacillus coliformis, Bacillus halophilus, and / or Bacillus pseudostrongylus.

[0090] In various embodiments, the capsule may also contain a calcium precursor. Non-limiting examples of calcium precursors may include calcium lactate, calcium acetate, calcium glutamate, and calcium formate. Bacterial spores can precipitate calcium from the calcium precursor, thereby sealing the calcium mineralization crack.

[0091] This disclosure provides a method for forming capsules as described in various embodiments of the first aspect. The method includes: providing bacterial spores for repairing cracks in a cementitious material; forming a slurry comprising the bacterial spores and water, or forming a slurry comprising the bacterial spores, water, and nutrients; hardening the slurry; converting the hardened slurry into particles; and solidifying the particles in the presence of carbon dioxide to form capsules. The method will be described in more detail in the following embodiments section.

[0092] The embodiments and advantages described with respect to the capsule in the first aspect can be similarly applied to the methods described below, and vice versa. Since various embodiments and advantages have already been described in the examples above and below, they will not be repeated for the sake of brevity.

[0093] In various embodiments, the slurry comprising bacterial spores and water, or the slurry comprising bacterial spores, water, and nutrients, may also comprise reactive magnesium cement. In various embodiments, in addition to reactive magnesium cement, the slurry may also comprise waste material incorporating reactive magnesium cement, wherein the waste material is harmless to bacteria, whether in a spore state or a vegetative state.

[0094] In various embodiments of forming a slurry containing bacterial spores, water, and nutrients, the method may include first mixing the bacterial spores and water with reactive magnesium cement. After the bacterial spores are sufficiently dispersed, nutrients are added. In various embodiments, the nutrients may be added in the form of a dry powder. Advantageously, when water, along with the bacterial spores, is first mixed with the reactive magnesium cement, the reactive magnesium cement particles may react with the water first during the mixing process. Subsequently, when nutrients are added (e.g., in dry powder form), the amount of water present is insufficient to dissolve the nutrients, causing the nutrients to remain in a dry powder state and not react with the bacterial spores (i.e., the nutrients are present in a slurry separate from the bacterial spores). If the bacterial spores, water, and nutrients are mixed together simultaneously in the reactive magnesium cement, the bacterial spores may come into contact with the nutrients and be activated. Once activated, the bacterial spores become fragile and easily die during the mixing process or the addition of other substances. Therefore, starting from this step of mixing the bacterial spores and water with the nutrients, the incorporation of nutrients and bacteria into the same capsule may lead to additional bacterial death. Furthermore, some nutrients may be consumed due to bacterial spore activation, leading to a reduction in nutrients available for self-repair. That is, when bacterial spores, water, and nutrients are mixed together, the nutrients are in an aqueous state (i.e., dissolved). In other words, if bacterial spores are mixed with dry nutrient powder (and / or the amount of water present therein is insufficient to dissolve the nutrients, as previously described), the bacterial spores advantageously remain inactive and do not react with the nutrients.

[0095] In various embodiments, the cured particles may include particles cured under conditions of 10% volume fraction of carbon dioxide and 80% relative humidity.

[0096] In various embodiments, the weight ratio of water to reactive magnesium cement can be from 0.5 to less than 2 (i.e., 0.5:1 to less than 2:1). For example, the weight ratio of water to reactive magnesium cement can be 0.5:1 or less than 2:1. When the weight ratio of water to reactive magnesium cement exceeds 2, it may impair the strength of the capsule.

[0097] This disclosure also provides a nutrient capsule that can be incorporated into cementitious materials to contain nutrients that facilitate the repair of cracks in the cementitious materials by bacterial spores. The nutrient capsule comprises inorganic particles having surface and core regions, wherein the density and strength of the inorganic particles decrease along the direction from the surface to the core region, and the core region contains the nutrients while the capsule is free of bacterial spores. The nutrient capsule of the present invention differs from the capsule of the first aspect in that the nutrient capsule contains nutrients instead of bacterial spores. Therefore, it is understood that the embodiments and advantages described with respect to the capsule of the first aspect can be similarly applied to the nutrient capsule described herein, and vice versa. Since various embodiments and advantages have already been described in the examples above and below, they will not be repeated for the sake of brevity.

[0098] In various embodiments, the nutrient capsules may be formed from Portland cement or derived from any RMC-based material. Nutrients may be present in the core region, near the surface, and / or in any area between the core region and the surface.

[0099] This disclosure also provides a method for forming nutrient capsules. The method includes: providing nutrients that help bacterial spores repair cracks in a cementitious material; forming a slurry containing the nutrients and water; hardening the slurry; converting the hardened slurry into particles; and solidifying the particles in the presence of carbon dioxide to form nutrient capsules.

[0100] The embodiments and advantages described with respect to the capsules and nutritional capsules of the first aspect can be similarly applied to the method of forming nutritional capsules described below, and vice versa. Since various embodiments and advantages have already been described in the examples above and below, they will not be repeated for the sake of brevity. The following embodiments section illustrates the method in more detail.

[0101] This disclosure also provides a cement-based material incorporating (i) the capsules described in the various embodiments of the first aspect, or (ii) the capsules and nutrient capsules described in the various embodiments of the first aspect.

[0102] The embodiments and advantages described with respect to the capsule in the first aspect can be similarly applied to the cement-based materials described below, and vice versa. Since various embodiments and advantages have already been described in the examples above and below, they will not be repeated for the sake of brevity.

[0103] In various embodiments, the cement-based material may further comprise nutrients incorporated into the cement-based material, wherein the nutrients may be incorporated into the cement-based material and, in (i) the capsule exterior described in the various embodiments of the first aspect, and in (ii) the exterior of the nutrient capsule (when present). In other words, even if the nutrient capsule is incorporated into the cement-based material, the (additional) nutrients may be present in the capsule and on the exterior of the nutrient capsule (when present).

[0104] In various embodiments, the cement-based material may be derived from cement, including Portland Cement.

[0105] In various embodiments, the cement-based material may also contain a calcium precursor. As a non-limiting example, the calcium precursor may include calcium lactate, calcium acetate, calcium glutamate, and / or calcium formate.

[0106] This disclosure also provides a method for forming the cement-based material described in the various embodiments. The method includes: providing (i) the capsules described in the various embodiments of the first aspect, or (ii) the capsules and nutrient capsules described in the various embodiments of the first aspect; and mixing the capsules and the nutrient capsules present (when present) with cement to form the cement-based material. The embodiments and advantages described with respect to the capsules and nutrient capsules of the first aspect are similarly applicable to the method for forming the cement-based material described herein, and vice versa. Since various embodiments and advantages have already been described in the examples above and below, they will not be repeated for the sake of brevity. The following embodiments section illustrates the method in more detail.

[0107] In various embodiments, the step of providing (i) a capsule or (ii) a capsule and a nutrient capsule includes: uniformly dispersing the capsule and any present nutrient capsule (if present) in water to form an aqueous suspension, and then mixing the aqueous suspension with cement. In some non-limiting embodiments, the step of providing (i) a capsule or (ii) a capsule and a nutrient capsule includes: preparing an aqueous solution containing nutrients, and mixing the capsule and any present nutrient capsule (if present) into the aqueous solution to form a mixture, and then mixing the mixture with cement.

[0108] In various embodiments, the method may further include mixing the calcium precursor with the capsule, as well as any existing nutrient capsules (if present), and cement. As a non-limiting example, the calcium precursor may include calcium lactate, calcium acetate, calcium glutamate, and / or calcium formate.

[0109] In various embodiments, the cement may include Portland cement.

[0110] The word “substantially” does not exclude “completely”, for example, a composition that is “substantially free” of Y can be completely free of Y. The word “substantially” may be omitted from the definition in this disclosure if necessary.

[0111] In the context of various embodiments, the articles “a,” “an,” and “the” used with respect to features or elements include references to one or more features or elements.

[0112] In the context of various embodiments, the term “about” or “approximately” applied to numerical values ​​covers both precise values ​​and reasonable variances.

[0113] As used herein, the term “and / or” includes any and all combinations of one or more of the related listed items.

[0114] Unless otherwise stated, the terms “contain” and “include” and their grammatical variations are intended to indicate “openness” or “inclusiveness” in language, such that they include the listed elements, but also allow for the inclusion of additional, unlisted elements. Example

[0115] This disclosure relates to functionally graded bacterial capsules that can be used as cement additives to participate in the self-healing of concrete and cement-based materials. For brevity, the functionally graded bacterial capsules of the present invention may be referred to herein as "capsules". The capsules have gradient density and strength, exhibiting a gradual decrease in density and strength from the capsule surface to the core region.

[0116] Compared to the softness and fragility of traditional polymer-based porous capsules, the functionally graded capsules of this invention are rigid and robust. Unlike the addition of traditional polymer-based capsules, which leads to a decrease in concrete strength, the inclusion of the functionally graded capsules of this invention in concrete and cement-based materials can improve the strength of concrete and cement-based materials.

[0117] Because inorganic-based materials (such as RMC, i.e., reactive magnesium cement) are used as capsule binders, the capsules have better compatibility with the surrounding cement matrix.

[0118] Compared to traditional carriers that fail to provide adequate protection for bacteria and bacterial spores, the capsule of this invention has a dense outer shell that hinders the penetration of alkaline components in the cement matrix and provides better protection for bacteria. Simultaneously, the porous core with low alkalinity provides a host space for bacteria and ensures the long-term survival of bacterial spores.

[0119] This disclosure also relates to a nutrient capsule that can be incorporated into cementitious materials (e.g., concrete) to contain nutrients that help bacterial spores repair cracks in the cementitious materials.

[0120] This disclosure also relates to methods for forming the above-described capsules and nutritional capsules. The capsules, nutritional capsules, and methods of the present invention will be further described in detail below through non-limiting examples.

[0121] Example 1: Introductory discussion of the capsule of the present invention

[0122] This embodiment discusses the functionally graded bacterial capsules of the present invention as a cement additive for self-healing in concrete and cement-based materials. The capsules exhibit a gradient density and strength from the capsule surface to the core. The dense surface provides better protection for the bacteria, while the porous internal environment facilitates long-term bacterial survival and exposure during crack propagation. The applications of these capsules are not limited to PC-based self-healing concrete. With the development of alternative adhesives, these capsules can be applied to any cementitious building material requiring encapsulation of bacteria (e.g., high-alkalinity geopolymers).

[0123] To illustrate the preparation and use of capsules, capsules prepared using RMC are discussed as a non-limiting example.

[0124] For bacterial preparation, specific bacteria are cultured using appropriate culture media and conditions. After the bacteria are prepared, they need to be centrifuged to separate them from the used culture medium. Then, the supernatant is removed, leaving only the precipitate.

[0125] For capsule preparation, generally, after separately measuring the RMC and water for mixing, the prepared bacterial precipitate is resuspended in water. After uniformly dispersing the bacteria in water, the suspension is poured into the RMC. The slurry is mixed for about 5 minutes until homogeneous. Then, the fresh slurry is poured into a mold. There are no restrictions on the size of the mold. After initial hardening for about 2 to 3 days, the hardened slurry is demolded and pulverized into powder using a mortar and pestle. The powder is then spread on a tray and subjected to accelerated carbonation and curing at 10% CO2 and 80% relative humidity for 7 days.

[0126] The following is a general discussion of the use of the capsules of this invention in a cement-based system for self-healing. After the capsules have undergone carbonation and curing, they are removed and weighed according to the specific application requirements. The composition of the mixture is then measured accordingly, and the capsules can be mixed with cement or suspended in water first. If the capsules are mixed with cement, they should be stirred using a mixer for at least 1 minute to ensure uniform distribution of the capsules in the cement. If the capsules are mixed with water, the suspension should also be mixed until the capsules are fully dispersed. After the capsules are mixed with cement / water, the remaining mixing process can follow the standard mixing process for the corresponding cement-based system. In short, for the standard mixing process, after the capsules are mixed with cement and / or water, nutrients are added to dissolve them to form an aqueous mixture. The aqueous mixture is then added to the cement (if not already there) and mixed in a mixer (e.g., for about 5 minutes) until the slurry becomes homogeneous.

[0127] Example 2: Overview and characterization of the method for forming capsules

[0128] To illustrate the working principle of this invention, the preparation of RMC-based capsules and their application in the self-healing of Portland cement (PC)-based mixtures are described below.

[0129] In this example, *Bacillus coli* was encapsulated in RMC. To prepare the bacteria, vegetative cells were aerobically grown in a sterile growth medium consisting of 5 g / L peptone, 3 g / L meat extract, 4.2 g / L NaHCO3, and 5.3 g / L Na2CO3. After incubation for 24 hours at 25°C on a rocker (200 rpm), the vegetative culture was inoculated into sterile sporulation medium (1% inoculum) for 3–7 days under the same incubation conditions. The spore formation medium consisted of 0.2 g / L NH₄Cl, 0.02 g / L KH₂PO₄, 0.225 g / L CaCl₂, 0.2 g / L KCl, 0.2 g / L MgCl₂·6H₂O, 1 ml of trace element solution SL12B (for 1 L of spore formation medium), 0.1 g / L yeast extract, 4.2 g / L NaHCO₃, 5.3 g / L Na₂CO₃, and 5.16 g / L sodium citrate. Spores were harvested by centrifugation at 8000–9000 rpm for 10 minutes, and the precipitate was resuspended in sterile water. To kill all vegetative cells, the spore suspension was pasteurized (20 minutes in an 80°C water bath, followed by 5 minutes on crushed ice). The colony-forming unit (CFU) concentration of the spore suspension was determined using serial dilution and plating techniques. The suspension was then centrifuged at 8000–9000 rpm for 10 minutes. Remove the supernatant and preserve the precipitate for capsule preparation.

[0130] To prepare the capsules, RMC, bacteria, and water were measured separately, as shown in Table 1 below. First, the bacteria were suspended in water and mixed thoroughly. Then, the suspension was poured into the RMC and mixed for approximately 5 minutes until homogeneous. The fresh slurry was poured into 2.5 cm³ molds and cured under ambient conditions for 3 days. After demolding, the cubes were pulverized into powder using a 150 μm sieve and spread on a tray, where accelerated carbonation and curing were carried out for 7 days under 10% CO₂ and 80% relative humidity.

[0131] Table 1: Ingredient Configuration of RMC-Based Capsules

[0132]

[0133] After capsule preparation, the composition of the capsules was examined by X-ray diffraction (XRD). XRD scans were performed on a Panalytical XpertPro using Cu Ka radiation (40 kV, 30 mA) at a scan rate of 0.017°2θ / step and a scan range from 5° to 80°2θ.

[0134] The RIR (Reference Intensity Ratio) technique was employed, using a standard phase of known proportions and comparing its integrated intensity with that of the target phase to quantitatively analyze the existing phase. The internal standard used for quantification was 20 wt% fluorite (CaF2). Calibration curves for the magnesia and brucite components used for quantitative analysis were straight lines passing through the origin, i.e., y = kx, where x is the RIR of the analyzed phase and y is the weight fraction of the studied component. The k-value was 0.2886 for magnesia and 0.3651 for brucite. The RIR was obtained by dividing the integrated intensity of the strongest phase line by the integrated intensity of the standard line. Furthermore, the morphology of the capsules was examined using scanning electron microscopy (SEM). Approximately 0.1 g of capsules were coated with platinum for 40 seconds at 20 mA using an automated fine coating machine (JEOL JFC1600). The coated samples were studied using a JEOL JSM-7600F instrument at 5.0 kV in SEI mode.

[0135] To investigate the effectiveness of this capsule in protecting bacteria, encapsulated and unencapsulated bacteria were prepared and applied to PC to examine self-healing properties. The amounts of capsule, PC, and corresponding bacterial nutrients were measured according to Table 2 below.

[0136] Table 2: Compositional Design of P, PNB, and PNC Samples Used for Self-Healing Tests

[0137]

[0138] In Table 2, group P represents pure PC slurry without any additives, group PNB represents PC slurry containing bacteria (unencapsulated) and corresponding nutrients, and group PNC represents PC slurry containing prepared capsules and the same nutrients as group PNB. The total bacterial count in the capsules used in group PNC is the same as that used in group PNB. First, the nutrients are dissolved in water. After complete dissolution, the capsules are added to the solution and mixed until they are evenly distributed in the suspension. Then, the mixture is added to the PC and mixed with a mixer for about 5 minutes until homogeneous. The fresh slurry is poured into cylindrical molds with a diameter of 7.5 cm and a height of 2.5 cm. The samples are sealed twice with airtight plastic bags to prevent moisture evaporation. After initial hardening for 1-2 days, the samples are demolded and cured under the same conditions for up to 28 days.

[0139] On day 28, the sample was loaded onto a servo-hydraulic universal testing machine, where an initial crack was induced at a loading rate of 0.01 mm / s. Figure 1A As shown. The initial crack width was then measured using a Nikon stereomicroscope. All samples were then subjected to wet / dry repair cycles. Each wet / dry repair cycle consisted of immersion in water for one day and drying under ambient conditions for one day. After five repair cycles, the crack closure of the same crack was examined under a microscope.

[0140] To investigate the effect of RMC-based capsules on the mechanical properties of the matrix, compressive strength tests were performed on P and PNC samples, as shown in Table 2. However, to further investigate the individual effects of nutrients and capsules on the matrix, two additional groups of samples were prepared, one with added nutrients and the other with added capsules. The composition of the cast samples used for compressive strength testing is shown in Table 3. The casting and curing methods were the same as described above, except that the mold size used for strength testing was 50×50×50 mm. After curing for 28 days, the samples were tested at a constant loading rate of 55 kN / min.

[0141] Table 3: Composition of samples for compressive strength testing

[0142]

[0143] Figure 2 The XRD patterns of capsules incorporating 20% ​​CaF2 are shown. As shown, strong peaks are observed for fluorite (at 28.2° and 47.0°), unhydrated MgO (at 42.9° and 62.2°), and uncarbonated brucite (at 18.6°, 38.0°, and 50.8°). Smaller peaks for hydromagnesite (9.6° and 15.2°) and magnesite (32.8°) are also observed. The presence of magnesite is due to incomplete calcination during RMC production, while the formation of hydromagnesite is due to accelerated carbonation solidification. The composition of the capsules, calculated by RIR, is shown in Table 4. As mentioned above, only the surface of the RMC-based sample can be carbonized; the core region of the sample remains brucite. Therefore, approximately 50% of the capsules are uncarbonated and retain porous brucite, while only about 17% exhibit the carbonated phase.

[0144] Table 4: Ingredients of RMC-based capsules

[0145]

[0146] The morphology of the capsule is shown in Figure 3 In the middle. For example Figure 3As shown, the capsule surface is completely covered with rosette-shaped hydromagnesia. XRD shows that a large amount of hydromagnesia is formed on the capsule surface, and there is also a large amount of hydromagnesia inside the capsule, which fully demonstrates that the RMC-based capsule of this disclosure has density gradient characteristics.

[0147] Figures 4A to 4C The self-healing properties of groups P, PNB, and PNC are shown separately. Cracks with a width of approximately 200 μm are presented for comparison in each group. Figure 4A The results showed that although sparse crystal formation was observed at the crack edges in the PC samples, the cracks were far from fully repaired. The crystal formation within the cracks was due to further hydration of unreacted cement or carbonation of Ca(OH)₂ in the matrix, which is inherent to the self-healing properties of PC. Similarly, Figure 4B Some crystal formation was observed along the crack, but the PNB sample could not be completely repaired. This result indicates that self-healing performance is limited when bacteria are added without any protection, mainly because the bacteria cannot survive in such a harsh environment. This observation is consistent with a study in which bacteria failed to produce precipitation after being embedded in PC for 28 days. Unlike the P group and the PNB group, the PNC group ( Figure 4C Encapsulating bacteria in RMC-based capsules resulted in significant precipitation formation and complete crack repair under the same curing cycle. The significant difference in crack repair between the PNB group (without encapsulated bacteria) and the PNC group (bacteria encapsulated in RMC-based capsules) demonstrates the protective efficiency of the proposed RMC-based capsules. Furthermore, since bacteria require exposure to access nutrients for precipitation, the results indicate that bacteria are exposed as cracks propagate.

[0148] Figure 5 The compressive strength of P, PNC, PN, and PC* samples at 28 days is shown. No significant difference was observed when comparing pure PC samples with PC+capsule samples, indicating that adding capsules does not impair the strength of the matrix. However, when comparing PC samples with PC+nutrient samples, the addition of nutrients resulted in a decrease of approximately 17%. When capsules and nutrients were applied together in PC (PC+nutrient+capsule sample), a slight increase (approximately 8%) was observed compared to the PC sample. This increase may be related to the pre-consumption of nutrients and the pre-precipitation of the carbonate phase during the 28-day curing process. During the preparation of RMC capsules, some bacteria may be present on the capsule surface. During mixing and early curing, these bacteria on the surface are exposed to nutrients and Ca(OH)2 in the matrix. Therefore, bacterial spores can be activated with the help of yeast extract, subsequently converting calcium lactate (CaL) into calcium carbonate, as shown in equation (1). Other calcium precursors, such as calcium acetate, calcium glutamate, and / or calcium formate, can be used in addition to calcium lactate. Simultaneously, the CO2 produced by the reaction can further carbonate the Ca(OH)2 in the matrix.

[0149]

[0150] Example 3A: General Discussion of a Non-limiting Example of the Capsule Containing Bacterial Spores of the Present Invention

[0151] Examples 3A to 3L demonstrate and discuss the development of functionally graded reactive magnesium cement-based bacterial spore (RMC-B) capsules for self-healing concrete. These capsules possess a graded structure—a dense outer shell and a porous, low-alkaline core—which better protects and enhances the viability of the bacterial spores. Results showed that the addition of RMC-B capsules did not negatively impact the hydration and freshness properties of the PC slurry and increased the 28-day compressive strength of the hardened PC slurry by 18%. Samples containing RMC-B capsules exhibited strong crack-healing properties, closing cracks of several hundred micrometers in size and densely forming layered orthorhombic calcite along the entire crack from surface to interior, thus reducing transport properties.

[0152] Concrete is the most widely used man-made building material in the world, with an annual production exceeding 6 billion tons. Due to its limited tensile strength, concrete structures are prone to cracking under external loads. Once cracks form, they allow moisture, carbon dioxide, and corrosive substances to seep in, shortening the lifespan of infrastructure. Repairing cracks in concrete structures typically involves manual methods, which are labor-intensive, inconvenient, and costly. In the United States, the annual cost of concrete repair is estimated at between $1.8 billion and $21 billion. To avoid these drawbacks of manual repair, this disclosure describes an environmentally friendly, bacteria-based technology for the self-healing of cracks in concrete structures. The mechanism involves applying dormant bacterial spores (in capsules) along with necessary compounds (such as nutrients and calcium sources) to the concrete during mixing. When a crack appears, the bacterial spores are exposed and activated upon the introduction of oxygen and water. Subsequently, the activated bacteria precipitate out through their metabolic activity, causing the crack to close.

[0153] Based on this bacteria-based approach, studies have been conducted to investigate its feasibility, and cases have been reported where bacteria failed to settle after 28 days when directly (without capsules) embedded in Portland cement (PC)-based mixtures. It is generally believed that bacterial inactivation in concrete is related to high alkalinity (e.g., pH > 12) and the densification of the microstructure during hydration. Due to this harsh environment of concrete, encapsulation is beneficial for protecting bacteria. Traditionally, commonly used bacterial encapsulation materials in self-healing concrete are polymer-based coating materials (e.g., melamine, hydrogels, and epoxy resins) and porous carriers (e.g., expanded clay, biochar, and cellulose fibers). These encapsulation materials have been reported to extend the lifespan of bacteria in concrete and enhance self-healing capabilities, but they also have significant drawbacks. First, the strength of the matrix has been reported to decrease significantly when using polymer-based materials. For example, adding 5% melamine-based microcapsules resulted in a 34% decrease in compressive strength after 28 days, and adding 1% modified alginate hydrogel capsules resulted in a 23% decrease. The strength reduction is mainly because these polymer-based capsules are typically soft materials with much lower strength and stiffness than the PC-based matrix. Adding such capsules creates multiple weak points in the matrix, thus reducing strength. Furthermore, using porous carriers does not provide adequate protection for bacteria. Generally, after encapsulating bacteria within a porous carrier through soaking or vacuum impregnation, no further surface treatment is performed to seal the openings of the porous carrier. This allows alkaline compounds in the PC-based mixture to permeate into the porous carrier and come into contact with the bacteria during mixing.

[0154] To overcome these drawbacks and address mechanical performance issues, the use of low-alkalinity cementitious materials for encapsulation was explored. These materials not only possess low alkalinity, potentially enabling bacterial survival within, but also exhibit high compatibility with the PC-based matrix. It has been reported that encapsulating bacteria with low-alkalinity sulfoaluminate cement can achieve self-healing of cracks. Simultaneously, when the capsule dosage was 12% of the cement mass, the 28-day compressive strength of the matrix was maintained. In another reported example, the use of cementitious materials prepared from carbide slag, fly ash, and desulfurized gypsum to encapsulate bacteria for self-healing was investigated. Results showed that the biocapsules could self-heal cracks around 500 μm, and the matrix strength remained unchanged when the capsule dosage was less than 5% of the cement mass. Furthermore, capsule rupture after cracking was observed, indicating high compatibility between the cementitious materials and the PC matrix. However, continuous hydration of these cementitious materials leads to microstructural densification and reduces the porosity of the bacterial capsules. Therefore, the long-term survival capacity of the bacteria within the capsules is compromised.

[0155] Contrary to reported examples, this disclosure provides a gradient reactive magnesium cement (RMC)-based bacterial spore capsule for self-healing concrete. RMC is a low-alkaline binder (i.e., pH approximately 10.5) used to encapsulate bacterial spores. Unlike most cementitious materials that gain strength through hydration, RMC primarily enhances its strength through carbonation, resulting in a unique, stable gradient structure in the resulting RMC-based bacterial capsule (RMC-B)—a dense outer shell and a porous core. The porous core contains the bacterial spores, while the dense outer shell protects the spores from direct contact with the surrounding cement matrix and provides mechanical strength. The stable microstructure of the RMC-B capsules promotes the long-term viability of the bacterial spores.

[0156] Generally, bacterial spore capsules are made by encapsulating Bacillus coli spores in RMC slurry. Bacillus coli is a non-urea-decomposing bacterium that oxidizes calcium lactate to form calcium carbonate. Unlike urea-decomposing bacteria that lead to ammonia formation during calcium carbonate precipitation, the metabolic precipitation pathway of Bacillus coli does not impose any ammonia burden on the environment. We characterized the composition and morphology of the RMC-B capsules. The viability of the bacterial spores in the RMC capsules was evaluated. The effects of adding RMC-B capsules on the hydration, freshness, and hardening properties of the PC slurry were investigated. The capsules were then incorporated into the PC slurry along with nutrients (as a non-limiting example) to evaluate self-healing properties. These nutrients included calcium lactate (CaL) and yeast extract (YE), where YE contributes to spore activation, and CaL is a precursor for calcium carbonate precipitation. In addition to calcium lactate, other calcium precursors, such as calcium acetate, calcium glutamate, and / or calcium formate, can also be used. Self-healing properties were evaluated by observing crack closure and water flow rate tests.

[0157] Example 3B: Materials and Methods – Preparation of Bacterial Spores

[0158] Vegetative cells of Bacillus coli (ATCC 51227) were grown aerobically in a sterile growth medium. The vegetative growth medium consisted of 5 g / L peptone, 3 g / L meat extract, 4.2 g / L NaHCO3, and 5.3 g / L Na2CO3. After incubation at 25°C on a rocker (200 rpm) for 1 day, the vegetative culture was inoculated into sterile sporulation medium (1% inoculum) under the same incubation conditions for 5 days. The spore formation medium consisted of 0.2 g / L NH₄Cl, 0.02 g / L KH₂PO₄, 0.225 g / L CaCl₂, 0.2 g / L KCl, 0.2 g / L MgCl₂·6H₂O, 1 ml of trace element solution SL12B (for 1 L of spore formation medium), 0.1 g / L yeast extract, 4.2 g / L NaHCO₃, 5.3 g / L Na₂CO₃, and 5.16 g / L sodium citrate. The spores were then centrifuged at 8000 rpm for 10 minutes. The supernatant was removed, and the precipitate was retained and resuspended in sterile water. Centrifugation and resuspension were repeated twice to wash the bacterial cells and ensure the cells were free of used medium. To kill all vegetative cells, the spore suspension was pasteurized (20 minutes in an 80°C water bath, followed by 5 minutes on crushed ice). The colony-forming unit (CFU) concentration of the spore suspension was determined using serial dilution and plating techniques. Then, store the spores in a 4°C refrigerator for later use.

[0159] Example 3C: Materials and Methods—Preparation of the RMC-based Bacterial Spore Capsules (RMC-B Capsules) of the Present Invention

[0160] To prepare functionally graded RMC-based bacterial spore capsules (RMC-B capsules), spore particles (1.02 x 10 u CFU) were first mixed with 20 g of water to form a well-dispersed suspension. The spore suspension was then added to 40 g of RMC powder and mixed with a hand stirrer for approximately 5 minutes until homogeneous. The RMC used in this non-limiting example was purchased from Richard Baker Harrison Ltd. (UK), and its chemical composition is shown in Table 5 below. The reactivity was measured by the time required for 5 g of RMC to neutralize 0.25 M acetic acid, which was recorded as 520 s.

[0161] Table 5: Chemical Composition of RMC

[0162]

[0163] The fresh slurry was then poured into 2.5 cubic centimeter molds and cured under ambient conditions for 3 days. After demolding, the blocks were pulverized into powder using a mortar and pestle and sieved through a 150 μm sieve. The powder was spread on a tray and subjected to accelerated carbonation and curing at 30°C, 10% CO2, and 80% relative humidity (RH) for 7 days. After carbonation, the particle size distribution of the capsules was studied using a laser diffraction particle size analyzer (Beckman Coulter LS13 320), and the results are as follows. Figure 6 As shown.

[0164] Approximately 0.1 g of capsules were freeze-dried for one day, and then platinum was deposited on them for 40 seconds at 20 mA using an automated fine coating machine (JEOL JFC1600). The coated capsules were examined using a scanning electron microscope (SEM, JEOL JSM-7600F) at 5.0 kV in secondary electron imaging (SEI) mode.

[0165] XRD and RIR methods were used to quantify the crystal structure of the capsules. The carbonated capsules were further pulverized and sieved through a 75 μm sieve. 20 wt% fluorite (CaF2) was added as an internal standard to the pulverized and sieved capsules. The mixture was freeze-dried for one day and then scanned using a Panalytical Xpert Pro scanner with Cu Ka radiation (40 kV, 30 mA) at a scan rate of 0.017°2θ / step and a scan range from 5° to 80°2θ. In the RIR calculations, the calibration curves for the MgO and Bruxite components used for quantitative analysis were straight lines through the origin, i.e., y = kx, where x is the RIR of the analyzed phase and y is the weight fraction of the studied component. The k-value for MgO was 0.2886, and the k-value for Bruxite was 0.3651. The RIR was obtained by dividing the integrated intensity of the strongest phase line by the integrated intensity of the standard line. When calculating the HMC phase in the capsules, the original content of magnesite present in the raw material (RMC) was subtracted from the remainder. To determine the magnesite content in RMC, thermogravimetric analysis (TGA) was performed on a Perkin Elmer TGA4000 instrument at a heating rate of 10 °C / min under nitrogen flow from 50 °C to 900 °C.

[0166] The activity of bacterial spores in RMC-B capsules was quantified using the following method. First, the RMC-B capsules were pulverized using a mortar and pestle and sieved through a 53 μm sieve. Then, 1 g of the sieved powder was suspended in 10 ml of distilled water and vortexed for approximately 1 minute. Next, the suspension was treated in an ultrasonic water bath (70 W, 42 kHz) for 20 minutes. The supernatant was then collected, serially diluted, and plate counts were performed. The subsequent procedures are as follows: Figure 7As shown. Each test was repeated three times. As a control, the viability of bacterial spores in the PC capsules was also evaluated. Following the same mixing procedure as the RMC-B capsules, 1.15 × 10⁻⁶ spores were mixed. 9 CFU bacterial spores were added to PC slurry (50g cement and 16g water) and pulverized into powder following the same mixing steps as for RMC-B capsules. The viability of the bacterial spores in PC-B capsules at 1, 8, 14, and 28 days was then quantitatively studied in the same manner.

[0167] Example 3D: Materials and Methods – Effects of RMC-B Capsules on Hydration and Fresh and Cured Properties of PC Slurry Impact

[0168] The effects of incorporating RMC-B capsules into PC slurry on the heat of hydration, flowability, initial setting time, and compressive strength of the PC slurry were investigated. Table 6 shows the composition of the PC slurry containing RMC-B capsules. In addition, a control composition with the same composition but without RMC-B capsules was prepared.

[0169] Table 6: Component formulation for studying the effects of adding RMC-B capsules on the hydration, freshness, and curing properties of PC slurry.

[0170]

[0171] First, RMC-B capsules are mixed with water to prepare the PC mixture. Then, the suspension is added to the PC and mixed in a mixer for approximately 5 minutes until homogeneous. The heat of hydration is measured using an I-Cal 8000HPC calorimeter (Calmetrix) at 30°C via isothermal calorimetry, according to ASTM C1679. The slurry flowability is determined using a flow meter (63-L0040 / A, control), according to ASTM C1437. The initial setting time is measured using an automated Vicat apparatus (EN 196-3, Testing Bluhm & Feuerherdt GmbH), according to ASTM 191.

[0172] To determine compressive strength, fresh slurry was poured into 50 cubic millimeter molds, sealed in airtight plastic to prevent moisture evaporation, and then placed under ambient conditions (25°C, 80% RH). The block samples were demolded after 2 days and cured for another 26 days under the same conditions. The compressive strength of the samples was then tested at 7, 14, and 28 days on a compressor (ToniTechnik Baustoffprüfsysteme) at a loading rate of 55 kN / min.

[0173] Example 3E: Materials and Methods – Self-Healing Properties of Capsules

[0174] Samples (sample PNC) were prepared using the prepared RMC-B capsules to evaluate self-healing properties, as shown in Table 7 below. In addition, two control compositions were prepared: (i) Sample P, a PC slurry without RMC-B capsules and nutrients, to reveal crack repair (if any) due to further hydration or carbonation of the PC matrix; and (ii) Sample PNS, to investigate the self-healing properties of the PC slurry after the addition of the same concentration (CFU) level of unprotected bacterial spores.

[0175] Table 7: Composition of samples prepared for self-healing testing

[0176]

[0177] The PC used in this embodiment was purchased from EnGro Ltd (Singapore) and complies with SS EN 197-1:2014. The chemical composition of the PC is shown in Table 8 below. Calcium lactate and yeast extract were purchased from Sigma-Aldrich. In addition to calcium lactate, other calcium precursors, such as calcium acetate, calcium glutamate, and / or calcium formate, can also be used.

[0178] Table 8: Chemical Composition of PC

[0179]

[0180] To prepare the composition, first mix the nutrients (CaL and YE) with water until completely dissolved. Then add the RMC-based capsules (or bacterial spores) to the solution and mix until well dispersed. Add the suspension to the PC dry powder and mix for about 5 minutes until homogeneous. Pour the fresh slurry into a cylindrical mold (2.5 cm high, 7.5 cm in diameter), filling the mold halfway. Then place a circular steel mesh (7 cm in diameter) inside, cover the mesh with fresh slurry, and fill the mold completely. Figure 8A and Figure 8B As shown. The sample was sealed in an airtight plastic container to prevent moisture evaporation. After 2 days, the sample was demolded and cured for another 26 days under the same conditions.

[0181] Cylindrical samples were pre-cracked for 28 days using a servo-hydraulic universal testing machine (MTS Landmark 250kN) at a constant rate of 0.01mm / s for splitting tensile testing. Figure 1A As shown. After pre-cracking and unloading, a splitting crack formed at the center of the sample. Using a stereo microscope (Nikon SMZ 745T), five marked locations along the crack line were observed (…). Figure 1B )Measure the crack width.

[0182] In addition, the water flow rate of the pre-cracked samples was determined using the constant head method. For example... Figure 9As shown, a constant water head was formed by a PVC pipe 10 cm high and 6 cm in diameter. The pipe was connected to the top surface of the sample and sealed with waterproof plastic clay. A constant water head of 10 cm was maintained for 5 minutes to allow water to pass through the pre-cracked sample. The amount of water collected in the bowl below was measured and the water flow rate was calculated as shown in Equation (2), where V is the volume of water passing through the sample; L is the sample thickness in the direction of water flow; A is the flow cross-sectional area; h is the constant water head; and t is the duration of water flow. Three tests were performed on each sample, and the mean and standard deviation values ​​were reported.

[0183]

[0184] Three samples were prepared for each group, and then the samples were subjected to wet / dry conditioning, during which they were completely immersed in water (25°C) for 24 hours, and then dried in ambient air (25°C, 80% RH) for 24 hours. Samples of different mixture designs were not placed in the same container for wet / dry conditioning to avoid cross-contamination between different mixtures. The conditioning water was replaced and replenished after each cycle. Crack widths at five marked locations and water throughput after five wet / dry conditioning cycles were measured. Crack closure rate (%) and water throughput reduction (%) were calculated according to formulas (3) and (4), respectively.

[0185]

[0186]

[0187]

[0188] Then, using a precision saw (Buehler IsoMet 1000), small samples are cut from the Mix PNC sample, such as... Figures 10A to 10C As shown. Samples were extracted from the crack location, and the repair products (if any) on the sample surface were observed. Figure 10A To examine the internal repair products, the sample was broken to expose the interior of the repaired crack. Figure 6 B). Extract samples from locations where no cracks have been found and observe any deposits on the sample surface. Figure 6 C). The samples were freeze-dried for 3 days to completely remove internal moisture, and then platinum was deposited for 40 seconds at 20mA using an automated fine coating machine (JEOL JFC1600). All samples were inspected by SEM (JEOL JSM-7600F) at 5.0kV in SEI mode.

[0189] Example 3F: Results and Discussion – RMC-B Capsules

[0190] Figure 11SEM images of the prepared RMC-B capsules are shown. The surface morphology of the capsules consists of disc-shaped crystals, similar to the morphology of hydromagnesite.

[0191] XRD pattern of the capsule as follows Figure 2 As shown, strong fluorite peaks were observed at 28.3° and 47.0°2θ due to the addition of 20% standard phase. Main peaks for MgO (at 42.9° and 62.3°2θ) and brucite (at 18.6° and 38.0°2θ) were also recorded, indicating the presence of uncarbonated brucite even after accelerated carbonation solidification. Smaller peaks for brucite and magnesite appeared at 15.2° and 32.8°2θ, respectively. The presence of magnesite is attributed to incomplete calcination of the parent material during RMC production, while brucite is the main carbonation product formed during accelerated carbonation solidification.

[0192] To calculate the carbonate phase (hydromagnesite) content in RMC-B capsules, the amount of magnesite (MgCO3) needs to be subtracted. Therefore, based on the weight loss of RMC between 500-900℃, the percentage of magnesite in the raw material (RMC) is calculated, such as... Figure 12 As shown in the figure, the decomposition phases and corresponding weight losses at different temperatures are marked accordingly. From 50℃ to 300℃, the weight loss is mainly due to the loss of free water in the RMC, followed by the weight loss caused by the decomposition of magnesite from 300℃ to 500℃. From 500℃ to 900℃, the weight loss is related to the decarburization of magnesite in the RMC, as shown in equation (5).

[0193] MgCO3→MgO+CO2 (5)

[0194]

[0195] The weight loss related to decarbonization is 2.61%, corresponding to a magnesite content of 5% in RMC, calculated by formula (6), where W Ms The weight fraction of magnesite is Mw(Ms), the molecular weight of magnesite is Mw(CO2), and the molecular weight of CO2 is Mw(CO2). The composition of the capsules was calculated by XRD analysis and is shown in Table 9 below. The RMC-B capsules consist of approximately 31% unhydrated MgO, 51% brucite, and 13% HMC phase.

[0196] Table 9: Ingredients of RMC-B Capsules

[0197]

[0198] Based on surface morphology observation and phase composition results, the structural schematic diagram of the RMC-B capsule is shown below. Figure 13As shown, the obtained RMC-B capsules exhibit a gradient structure, with a dense HMC shell (12.6%) and a porous core (52% brucite and 31% unreacted MgO). This is because MgO is initially hydrated to form brucite. After carbonation, the brucite near the capsule surface transforms into a series of HMCs with a dense microstructure, while the core is mainly composed of brucite and unhydrated RMC, exhibiting high porosity. The dense HMCs formed on the capsule surface (i.e., the shell) hinder further CO2 penetration into the capsule core. Therefore, RMC-B capsules should possess a stable microstructure (i.e., a hard shell and a soft core), unlike other cement-based capsules, which continuously hydrate to refine their internal microstructure. The porous core accommodates bacterial spores, while the dense shell protects the spores from direct contact with the surrounding cement matrix and provides mechanical strength. The obtained RMC-B capsules possess a stable microstructure that promotes long-term survival of bacterial spores.

[0199] Example 3G: Results and Discussion – Viability of Bacterial Spores in RMC-B Capsules

[0200] Figure 14 The number of surviving bacterial spores in the PC-B capsules was plotted. It can be seen that after one day in the PC matrix, the number of surviving bacterial spores decreased sharply by four orders of magnitude. With increasing PC age, the number of surviving bacterial spores continued to decrease until it fell below the detection limit of the method used at 28 days. This highlights how easily bacterial spores are destroyed in the PC matrix due to the harsh PC environment.

[0201] Figure 15 The number of surviving bacteria in the RMC-B capsules is shown. It can be seen that the bacterial spore activity in the RMC matrix is ​​much higher than in the PC matrix. This is likely due to the lower alkalinity of the RMC system, reportedly with an internal pH of approximately 9.9-10.5, which provides a more favorable environment for bacterial spore survival. Furthermore, the porous core of the RMC-B capsules preferably provides space to accommodate bacterial spores.

[0202] Example 3H: Results and Discussion – Effects of RMC-B Capsules on the Hydration and Fresh and Cured Properties of PC Slurry Impact

[0203] Figure 16 The changes in hydration heat and corresponding cumulative heat in the first 72 hours are shown for PC slurry with RMC-B capsules (sample PC) and PC slurry without RMC-B capsules (sample P). It can be seen that the hydration peak for both mixtures occurs around hour 9, indicating that the addition of RMC-B capsules did not change the hydration rate of the PC slurry. Furthermore, the cumulative heat after 72 hours of hydration for both mixtures is comparable, indicating that the capsules have little effect on the early hydration process.

[0204] Table 10 below summarizes the flowability and initial setting time of the PC and P mixture. It can be seen that the flowability of the control group (sample P) was 69%, and the initial setting time was 187 minutes. The addition of RMC-B capsules (Mix PC) did not significantly affect the flowability and initial setting time of the PC slurry. This is likely because the functionally graded RMC-B capsules form an HMC (mainly magnesite) shell through carbonation, which is chemically stable in alkaline environments such as PC slurry. Therefore, the addition of RMC-B capsules did not significantly affect the hydration and freshness properties of the PC slurry.

[0205] Table 10: Flowability and initial setting time of Mix P and Mix PC

[0206]

[0207] Figure 17 The compressive strength of the two mixtures was compared at 7, 14, and 28 days. It can be seen that the PC slurry containing RMC-B capsules (sample PC) exhibited higher compressive strength than the control mixture (sample P). This was particularly evident at the early stages. The 7-day strength of sample PC (63.4 MPa) was 26% higher than that of sample P (50.3 MPa). At 14 days, the strength of sample PC (69.5 MPa) was 21% higher than that of sample P (57.6 MPa). Even at 28 days, the strength of sample PC (74.1 MPa) was still 18% higher than that of Mix P (62.8 MPa). This indicates that, unlike typical soft self-healing capsules, RMC-B capsules are not a strength-limiting phase in hardened PC slurries. Furthermore, this also indicates that the resulting functionally graded RMC-B capsules are robust and highly compatible with the PC matrix, likely due to the formation of a hard HMC shell through carbonation. Further research is necessary to better understand the interfacial transition zone between the RMC-B capsule and the surrounding PC matrix and to reveal the strength enhancement mechanism.

[0208] Overall, these results indicate that the addition of RMC-B capsules does not alter the heat of hydration, flowability, or initial setting time of the PC slurry. Furthermore, the addition of capsules increases the compressive strength of the matrix. This suggests that the newly developed functionally graded RMC-B capsules with a rigid HMC shell are chemically stable and compatible with the surrounding PC matrix.

[0209] Example 3I: Self-healing performance – Surface crack closure

[0210] Plot the crack width after 5 wet / dry conditioning cycles relative to the original crack width, as shown below. Figure 18As shown in the figure. For each mixture, three samples were measured, with five observation points on each sample. Therefore, there are a total of 15 data points in each figure. The 45° black solid line represents no crack closure, while the gray dashed line represents 50% crack closure. It can be seen that all crack widths in sample PNC decreased significantly after 5 wet / dry conditioning cycles, while samples PNS and P had the lowest crack closure rates. Table 11 calculates the average crack closure rate for each mixture. It can be seen that before wet / dry conditioning, the crack widths of the three mixtures were comparable, approximately 220-250 μm. After 5 wet / dry conditioning cycles, the marginal crack closure rates of PNS and Mix P samples were approximately 20%, while the crack closure rate of PNC was as high as approximately 92%. This highlights the effectiveness of RMC-B capsules in self-healing in PC slurry. The closure of the edge cracks in the PNS and P samples is likely due to further hydration and carbonation, as the water-cement ratio of the mixture is low, at only 0.32, and therefore a large amount of unhydrated cement is expected to be produced at 28 days.

[0211] Table 11: Average crack closure rate after 5 wet / dry conditioning cycles

[0212]

[0213] Figures 19A to 19C Representative optical microscopic images of cracks in each mixture before and after 5 dry / wet conditioning cycles are shown. Compared with sample PNS (… Figure 19B ) and P( Figure 19C Compared to sample PNC, Figure 19A The PNC sample exhibited significant repair. Therefore, the PNC sample achieved complete crack closure by forming a large amount of repair products within the crack, while samples PNS and P showed sparse formation of white crystals along the crack edges. Notably, the formation of repair products was not limited to within the crack but also appeared on the entire surface of the PNC sample after wet / dry conditioning cycles. This indicates that the RMC-B capsules in the PC slurry possess high bioactivity.

[0214] Example 3J: Self-healing performance – water flow rate

[0215] Figure 20The reduction in average water flow rate for the three mixtures was compared. Overall, the results were consistent with the crack closure rate results. The water flow rate reduction for PNS and Mix P samples was less than 25%, while that for PNC exceeded 80%. The resistance to water flow through the repaired crack is a key parameter for evaluating crack repair performance, as cracks may be weak points in the matrix, allowing water and corrosive substances to enter. The resistance is directly related to crack closure performance and the density of crystal formation within the crack. The repaired PNC sample exhibited high resistance to water flow, indicating the dense nature of the repair product, and the RMC-B capsules in the PC slurry generally demonstrated high repair efficiency.

[0216] Example 3K: Self-healing properties – Microstructure of the repair products

[0217] Figures 21A to 21C The morphology and microstructure of the repair products at different locations in the Mix PNC sample are shown. It can be seen that all three images show the formation of layered orthorhombic calcite, consistent with previous findings using the same type of bacteria and nutrients. The repair products form not only on the crack surface but also along the crack depth. The dense formation of calcite along the entire crack from surface to interior leads to a significant reduction in water permeability in the PNC sample. The formation of a large amount of repair products occurs not only within the crack but also on the sample surface, such as... Figure 21C As shown, dense formation of calcite crystals and gel-like CSH formed by further hydration can be observed.

[0218] Example 3L: Summary of Examples 3A to 3K

[0219] Examples 3A to 3K demonstrate the development of the gradient RMC-B capsules of the present invention for self-healing concrete. These capsules possess a gradient structure—a dense HMC shell and a porous, low-alkaline core—to better protect and enhance the viability of bacterial spores. Results showed that the addition of the RMC-B capsules did not negatively affect the hydration, initial setting time, or flowability of the PC slurry. Furthermore, the 28-day compressive strength of the hardened PC slurry with the RMC-B capsules was 18% higher than the control group. This indicates that the capsules are robust and highly compatible with the PC matrix. The developed functionally gradient RMC-B capsules with a rigid HMC shell are chemically stable and compatible with the surrounding PC matrix.

[0220] Samples using the RMC-B capsules exhibited strong crack repair performance, achieving a crack closure rate of up to 93% and a water permeability reduction of 80% for wide cracks of several hundred micrometers after only 5 wet / dry conditioning cycles. Microstructural observation revealed that layered orthorhombic calcite densely formed along the entire crack line from the surface to the interior. This highlights the effectiveness of the gradient RMC-B capsules of this invention for self-healing concrete.

[0221] Example 4A: Non-limiting Example of RMC-BN Capsules

[0222] Examples 4A and 4B relate to RMC-BN capsules, which are standalone systems in which bacteria and nutrients are encapsulated together in RMC.

[0223] Bacillus spores were prepared according to the same procedure as in the RMC-B capsule system. Subsequently, RMC, water, bacteria, and nutrients were measured and prepared according to Table 12 to prepare RMC-BN capsules. First, the bacteria were suspended in water and mixed thoroughly. Then, the suspension was poured into the RMC and mixed for approximately 5 minutes until homogeneous. This allows the RMC to react with water first. Then, pre-mixed yeast extract (YE) and calcium lactate (CaL) powder were slowly added to the slurry. Since the RMC had already reacted with water, the amount of water present was insufficient to dissolve the nutrients (e.g., yeast extract) when added. Other calcium precursors, such as calcium acetate, calcium glutamate, and / or calcium formate, can be used in addition to calcium lactate. The mixture was further mixed in a mixer for 5 minutes until homogeneous again. The fresh slurry was poured into 2.5 cm³ molds and cured under ambient conditions for 3 days. After demolding, the blocks were crushed into smaller pieces and subjected to accelerated carbonation curing for 1 day under 10% CO₂ and 80% relative humidity. The fragments were then removed, further ground in a mortar, and sieved through a 150μm sieve. The sieved particles were then spread on a plate and cured for another 6 days under the same accelerated carbonation curing conditions.

[0224] Table 12: Ingredient Configuration of RMC-Based Capsules

[0225]

[0226] After capsule preparation, the composition of the capsules was examined by XRD. XRD scans were performed on a Panalytical Xpert Pro using Cu Ka radiation (40 kV, 30 mA) at a scan rate of 0.017°2θ / step and a scan range from 5° to 80°2θ.

[0227] RIR (Resonant Infrared) technology was employed, using a standard phase of known proportions and comparing its integrated intensity with that of the target phase to quantitatively analyze the existing phase. The internal standard used for quantification was 20 wt% fluorite (CaF2). The calibration curves for the magnesium oxide and brucite components used for quantitative analysis were straight lines passing through the origin, i.e., y = kx, where x is the RIR of the analyzed phase and y is the weight fraction of the studied component. The k-value for magnesium oxide was 0.2886, and for brucite, it was 0.3651. The RIR was obtained by dividing the integrated intensity of the strongest phase line by the integrated intensity of the standard line. Furthermore, the morphology of the capsules was examined using scanning electron microscopy (SEM). Approximately 0.1 g of capsules were coated with platinum for 40 seconds at 20 mA using an automated fine coating machine (JEOL JFC1600). The coated samples were studied using a JEOL JSM-7600F instrument at 5.0 kV in SEI mode.

[0228] To investigate the self-healing properties of RMC-BN capsules, the P-BNC group was designed to incorporate the capsules into PC slurry. As a comparison, a pure PC slurry without capsules was also designed. The specific mixing ratios for both groups are shown in Table 13. For the P-BNC group, the prepared capsules were weighed and mixed with PC in a mixer for 3-5 minutes until the capsules were fully dispersed in the cement. Then, the prepared water and powder were mixed in a mixer for about 5 minutes until homogeneous. For the P group, water and cement were directly mixed for about 5 minutes until homogeneous. Fresh slurry was poured into a cylindrical mold (2.5 cm high, 7.5 cm in diameter), filling half of the mold initially. A circular steel mesh (7 cm in diameter) was then placed inside, and fresh slurry was used to cover the mesh and fill the mold completely. The sample was sealed in an airtight plastic container to prevent moisture evaporation. The sample was demolded after 2 days and cured under the same conditions for another 26 days.

[0229] Table 13: Composition of samples used for self-healing tests

[0230]

[0231] At 28 days, the samples were pre-cracked using the same procedure as the RMC-B capsule system. Initial crack width and water flow rate were measured and calculated using the same method demonstrated in the RMC-B capsule system. After the initial measurement, the samples underwent wet / dry conditioning cycles in water. Specifically, each conditioning cycle consisted of complete immersion in water (25°C) for 24 hours, followed by drying in ambient air (25°C, 80% RH) for 24 hours. Crack width and water flow rate were measured and calculated again after every 10 conditioning cycles. Crack closure rate (%) and water flow rate reduction (%) were calculated according to formulas (7) and (8), respectively.

[0232]

[0233]

[0234]

[0235] To investigate the effect of RMC-BN capsules on the mechanical properties of the matrix, the compressive strength of the P-BNC group and the P group was measured. The mixing and preparation process of the slurry was the same as described above. Fresh slurry was then poured into 50 m³ molds, sealed in airtight plastic to prevent moisture evaporation, and placed under ambient conditions (25°C, 80% RH). The cube samples were demolded after 2 days and cured for another 26 days under the same conditions. The compressive strength of the samples was then tested at 7, 14, and 28 days on a compressor (ToniTechnikBaustoffprüfsysteme) at a loading rate of 55 kN / min.

[0236] Example 4B: Results and Discussion of RMC-BN Capsules from Example 4A

[0237] Figure 22 SEM images of the manufactured RMC-BN capsules are shown. The surface morphology of the capsules consists of needle-like crystals, similar to the morphology of hydrated magnesium oxide.

[0238] The XRD pattern of the obtained RMC-BN capsules is as follows: Figure 23 As shown, strong fluorite peaks were observed at 28.3° and 47.0°2θ due to the addition of 20% standard phase. A MgO peak at 42.9° and a brucite peak at 62.3°2θ were also recorded, indicating the presence of uncarbonated brucite even after accelerated carbonation curing. Characteristic peaks of brucite were observed at 23.1° and 29.5°, and magnesite was found at 32.6°2θ. The presence of magnesite is attributed to the incomplete calcination of the parent material during RMC production, while brucite is the main carbonation product formed during accelerated carbonation curing.

[0239] The composition of the RMC-BN capsules, calculated by XRD analysis, is shown in Table 14 below. The RMC-BN capsules consist of approximately 11.9% unhydrated MgO, 7.7% brucite, 9.5% HMC phase, and 65.9% nutrients. The morphology and composition of the capsules show that the surface is dense HMC, while the core region is mainly composed of porous brucite, MgO, and nutrients. Essentially, the obtained RMC-BN capsules are also a functionally graded capsule system.

[0240] Table 14: Ingredients of RMC-BN Capsules

[0241]

[0242] Plot the crack widths after 10, 20, and 30 wet / dry conditioning cycles relative to the original crack width, as shown below. Figures 24A to 24C As shown in the figures. For each component configuration, three samples were measured, with five observation points on each sample. Therefore, there are a total of 15 data points in each figure. The 45° black solid line indicates no crack closure, while the gray dashed line indicates 50% crack closure. As can be seen from the figures, after the wet / dry conditioning cycle, both the P-BNC group and the P group showed crack repair effects, with a reduction in crack width compared to the original crack width before conditioning. However, there was a significant difference in repair efficiency between the two groups. Figure 24A It is clearly shown that after 10 cycles of repair, all cracks in group P fall between the two lines, representing a crack closure rate of less than 50%. In contrast, in group P-BNC, most cracks, except for a few larger than 300 μm, fall below the gray dashed line, representing a crack closure rate exceeding 50%. Meanwhile, some cracks between 200 μm and 300 μm almost lie on the x-axis, representing 100% crack closure. As the adjustment cycles progress to 20 and 30 cycles, the cracks in group P remain near the gray line (i.e., 50% crack closure). In contrast, the number of cracks in group P-BNC decreases continuously, and by 30 cycles, most cracks are located near the x-axis. Specifically, cracks between 200 μm and 300 μm exhibit strong repair capabilities, as almost all cracks in this range achieve 100% closure. Figures 25A to 25C Crack photographs of the P-BNC group under different conditioning cycles are shown to illustrate the repair process.

[0243] The average water passage rate of the P-BNC group and the P group decreased as follows: Figure 26 As shown in the figure. Throughout the conditioning process, both groups exhibited recovery of transport performance, which is related to crack repair. Comparing the two groups, it is evident that regardless of the conditioning cycles, the reduction in water throughput in the P-BNC group was significantly higher than that in the P group. In the initial conditioning phase (i.e., 10 cycles), the reduction in P-BNC group was close to 60%, while that in P group was close to 10%. Finally, at 30 cycles, the water throughput reduction in P group was approximately 23.8%, while that in P-BNC group was approximately 73.8%, more than three times that of the control group. Overall, the crack closure and water throughput test results confirm the effectiveness of RMC-BN capsules in crack repair and transport performance recovery.

[0244] To investigate the effect of RMC-BN capsules on the strength of PC slurry, the compressive strength of PC slurry with and without capsules was tested, as shown below. Figure 27As shown. Generally, adding capsules does not impair the strength of the matrix throughout the curing period. At 28 days, the addition of RMC-BN capsules even increased the strength by 8.7%, with the P-BNC group having a strength of 68.75 MPa and the P group having a strength of 62.76 MPa.

[0245] Example 5: General discussion of non-limiting examples of RMC-N and RMC-B capsule systems (dual capsule systems)

[0246] This example illustrates the RMC-N and RMC-B dual-capsule system. The RMC-N capsule contains nutrients only within the carbonated RMC capsule, while the RMC-B capsule encapsulates bacteria only within the carbonated RMC capsule. The RMC-B capsule has been described in Examples 1 to 3L. When used as a self-healing additive, both the RMC-B and RMC-N capsules should be incorporated into the PC (dual-capsule system).

[0247] For this dual-capsule system, since the encapsulation of nutrients does not require a specific alkalinity for the encapsulation material, a certain amount of PC in the matrix can be used to encapsulate the nutrients instead of using RMC carbonate. Furthermore, PC typically has higher strength than RMC, so using PC to manufacture nutrient capsules may reduce mechanical loss of the matrix or have no impact on the matrix itself. We prepared three different PC-based nutrient capsules, as shown in Table 15 below.

[0248] Table 15: Ingredient Configuration of PC-Based Capsules

[0249]

[0250] To prepare the capsules, water and PC were mixed in a mixer for 5 minutes until homogeneous. Premixed YE and CaL powders were then added to the slurry and mixed for another 5 minutes until homogeneous. The fresh slurry was then poured into a 2.5 cm³ mold. After curing for 2 days, the cube was demolded and then cured for another 5 days in a sealed plastic bag. After 7 days, the cube was pulverized into powder and sieved through a 150 μm sieve. After preparing three different capsules, they were incorporated into the PC slurry along with RMC-B capsules, and their effects on matrix strength were investigated. The composition configurations for incorporating different PC-N capsules are shown in Table 16 below.

[0251] Table 16: Composition of PC slurry containing RMC-B and PC-N capsules

[0252]

[0253] In preparing the slurry, the prepared RMC-B and PC-N capsules were first mixed with PC in a mixer for approximately 5 minutes. Water was then added, and the mixture was stirred for another 5 minutes until homogeneous. The fresh slurry was poured into 50 cubic millimeter molds, sealed in airtight plastic to prevent moisture evaporation, and placed under ambient conditions (25°C, 80% RH). The block samples were demolded after 2 days and cured under the same conditions for another 26 days. The compressive strength of the samples was then tested at 7, 14, and 28 days on a compressor (ToniTechnikBaustoffprüfsysteme) at a loading rate of 55 kN / min.

[0254] The compressive strength results are as follows Figure 28 As shown in the figure (28-day strength of P-Dual80 was not tested). It can be seen from the figure that the mixtures of these three PC-based nutrient capsules significantly reduced the strength of the matrix. This reduction in matrix strength may be related to two reasons. First, adding a large amount of nutrients to the capsules may significantly impair the capsule strength, resulting in very low nutrient capsule strength. Second, nutrients may leach out of the capsules during mixing and hydration, thus impairing the matrix strength. However, this study compared RMC-BN capsules with PC-N capsules and found that incorporating RMC-BN capsules into the matrix did not cause any loss of strength when the same amount of nutrients (45g) was encapsulated in the same amount of gelling material (23.3g RMC). The results indicate that carbonation is a key step in the preparation of nutrient capsules, as the dense shell formed during carbonation prevents nutrients from leaching out of the capsules.

[0255] Example 6: Commercial Applications and Potential Applications

[0256] Concrete is the most widely used man-made material, with a global annual production exceeding 25 billion tons. In most developed countries, the maintenance and repair costs of concrete account for approximately 50% of infrastructure expenditures. Damage to concrete infrastructure is related to the formation of cracks. Therefore, enabling concrete to self-heal—that is, for cracks to repair themselves in the natural environment without human intervention—is highly desirable. The functionally graded bacterial capsules of this invention can be used as an additive in concrete and other cementitious materials.

[0257] While this disclosure has been specifically shown and described with reference to specific embodiments, those skilled in the art will understand that various changes to its form and details may be made without departing from the spirit and scope of this disclosure as defined by the appended claims. Therefore, the scope of this disclosure is defined by the appended claims and all modifications thereof, and all modifications within the meaning and equivalent scope of the claims should be included.

Claims

1. A capsule that can be incorporated into cement-based materials for repairing cracks in the cement-based materials, said capsule comprising: Inorganic particles, wherein the inorganic particles have a surface region and a core region. The core region contains bacterial spores used to repair cracks, or The core region contains bacterial spores for repairing cracks, and the capsule contains nutrients separate from the bacterial spores. The density and strength of the inorganic particles decrease along the direction from the surface to the core region. The density at the surface is sufficient to impede the penetration of alkaline substances, and The core region contains brucite and the surface contains magnesia or magnesia.

2. The capsule according to claim 1, wherein the core region is porous.

3. The capsule of claim 1, wherein the core region contains bacterial spores for repairing cracks, and the capsule is free of nutrients.

4. The capsule of claim 1, wherein when the capsule contains nutrients separate from the bacterial spores, the nutrients comprise yeast extract.

5. The capsule according to claim 1, wherein the bacterial spores comprise Bacillus coliformis, Bacillus halophilus, and / or Bacillus pseudostrongylus.

6. A method for forming a capsule that can be incorporated into a cementitious material for repairing cracks in the cementitious material, the method comprising: Provides bacterial spores for repairing cracks in cement-based materials; Forming a slurry containing the bacterial spores and water, or forming a slurry containing the bacterial spores, water, and nutrients; The slurry is then hardened. To convert hardened slurry into granules; and The particles are solidified in the presence of carbon dioxide to form capsules, wherein the capsules comprise: Inorganic particles, wherein the inorganic particles have a surface region and a core region. The core region contains bacterial spores used to repair cracks, or The core region contains bacterial spores for repairing cracks, and the capsule contains nutrients separate from the bacterial spores. The density and strength of the inorganic particles decrease along the direction from the surface to the core region. The density at the surface is sufficient to impede the penetration of alkaline substances, and The core region contains brucite and the surface contains magnesia or magnesia.

7. The method of claim 6, wherein the slurry comprising (i) the bacterial spores and water, or (ii) the bacterial spores, water and nutrients further comprises reactive magnesium cement.

8. The method of claim 6, wherein the step of curing the particles comprises curing the particles under conditions of 10% volume fraction carbon dioxide and 80% relative humidity.

9. A nutrient capsule that can be incorporated into cementitious materials to contain nutrients that help bacterial spores repair cracks in the cementitious materials, said nutrient capsule comprising: Inorganic particles, wherein the inorganic particles have a surface region and a core region. The density and strength of the inorganic particles decrease along the direction from the surface to the core region. The core region contains nutrients, and the capsule is free of bacterial spores. The core region contains brucite and the surface contains magnesia or magnesia.

10. A method for forming nutrient capsules that can be incorporated into cementitious materials to contain nutrients that help bacterial spores repair cracks in the cementitious materials, the method comprising: Provides nutrients that help bacterial spores repair cracks in cement-based materials; A slurry containing the nutrients and water is formed; The slurry is then hardened. To convert hardened slurry into granules; and The particles are solidified in the presence of carbon dioxide to form a nutrient capsule, wherein the nutrient capsule comprises: Inorganic particles, wherein the inorganic particles have a surface region and a core region. The density and strength of the inorganic particles decrease along the direction from the surface to the core region. The core region contains nutrients, and the capsule is free of bacterial spores. The core region contains brucite and the surface contains magnesia or magnesia.

11. A cement-based material incorporating (i) the capsule of any one of claims 1 to 5, or (ii) the capsule of any one of claims 1 to 5 and the nutritional capsule of claim 9.

12. The cement-based material according to claim 11, further comprising nutrients incorporated into the cement-based material, wherein the nutrients are incorporated into: The cement-based material is present in (i) the outside of the capsule, and in (ii) the outside of the nutrient capsule.

13. The cement-based material of claim 11, wherein the cement-based material is derived from cement including Portland cement.

14. The cement-based material according to claim 11 further comprises a calcium precursor, wherein the calcium precursor comprises calcium lactate, calcium acetate, calcium glutamate, or calcium formate.

15. A method for forming a cement-based material incorporating (i) any one of claims 1 to 5, or (ii) any one of claims 1 to 5 and the nutritional capsule of claim 9, said method comprising: Provide (i) the capsule, or (ii) the capsule and the nutritional capsule; as well as The capsules and the existing nutrient capsules are mixed with cement to form a cement-based material.

16. The method of claim 15, wherein the step of providing (i) the capsule, or (ii) the capsule and the nutritional capsule, comprises: (I) The capsule and the nutrient capsule present are uniformly dispersed in water to form an aqueous suspension, and then the aqueous suspension is mixed with cement; or (II) Prepare an aqueous solution containing nutrients, and mix the capsule and the nutrient capsule present in the aqueous solution to form a mixture, and then mix the mixture with cement.

17. The method of claim 15, further comprising mixing the calcium precursor with the capsule, the present nutrient capsule, and the cement.

18. The method of claim 15, wherein the cement comprises Portland cement.

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