EP2961715A1

EP2961715A1 - Microcapsules and concrete containing the same

Info

Publication number: EP2961715A1
Application number: EP14709589.7A
Authority: EP
Inventors: Hugo SOENS; Nele De Belie; Jianyun WANG; Maxime DURKA
Original assignee: Universiteit Gent; Devan Chemicals NV
Current assignee: Universiteit Gent; Devan Chemicals NV
Priority date: 2013-03-01
Filing date: 2014-03-03
Publication date: 2016-01-06
Also published as: WO2014131913A1

Abstract

Microcapsules, for inclusion in concrete, adapted to reduce the area of a defect by at least 45 % in said concrete once a quantity of said microcapsules has ruptured, said microcapsules each comprising: a polymeric shell encapsulating a liquid core, wherein the polymeric shell comprises a substantially impermeable polymer layer and the liquid core comprises carbonatogenic bacterial spores, and optionally bacterial nutrients, dispersed in a liquid medium. Also disclosed is a concrete composition comprising a quantity of such microcapsules, and a method of reducing the area of a defect in concrete.

Description

MICROCAPSULES AND CONCRETE CONTAINING THE SAME

The present invention relates to microparticles, especially microcapsules, for inclusion in concrete or like materials, containing microorganisms in the form of bacterial spores and / or bacterial nutrients, which microparticles (e.g. microcapsules) are adapted to reduce the area of a defect in said concrete (or like material) once a quantity of said microparticles (e.g. microcapsules) has fractured/ruptured. The invention also relates to a concrete or like material composition containing a quantity of such microparticles, especially microcapsules, which is "self-healing" in respect of any defects therein.

Concrete, concrete-based and concrete-like materials are often used in civil engineering projects as the building material of choice because of their high compressive strength, high durability and low cost. Projects in which such materials are used include constructions such as bridges, road projects, underground projects, water conservancy and hydropower projects, nuclear power plants, ports and marine engineering, etc, as well as smaller scale projects such as ramps, paving slabs, etc. Constructions which include concrete or like materials typically have long lifetimes (of at least 50 years), however, in this time frame usage and the influence of external environmental factors can lead to defects forming therein. Defects include visible cracks (of millimetres in width), micro-cracks (of micrometres in width), indentations and crevices. If left untreated, one or more of such defects could reduce the lifetime of a construction and/or may pose an immediate threat to the safety of said construction and its users. Although a concrete composition per se may be optimized to improve its inherent defect resistance, for example by appropriate selection of the raw materials used, their mixing ratio, inclusion or omission of particular additives, the manufacturing process, casting processes and methods, defects are known to still occur with varying degrees of severity and over the course of varying numbers of years since setting of the concrete. Therefore, the timely and effective repair of defects in concrete and like material is of continued concern to those in the field, including scientists and engineers.

It is known that under certain circumstances, some concrete compositions may exhibit a degree of autogenous healing, i.e. autogenous repair, of defects therein. Typically, with relatively freshly laid concrete and high strength concrete, un-hydrated cement particles are present in the concrete matrix; when water becomes available in defects that may have formed in such concrete, any un-hydrated cement particles present in/on the defect begin to hydrate, leading to a certain degree of healing or repair of the defect in question. In general, it is thought that there are two mechanisms by which autogenous repair may occur based around secondary hydration of un-hydrated cement particles present in the concrete composition: (1 ) the consequential precipitation of calcium carbonate, and (2) swelling of the hydration products to decrease the area of the defect. With mechanism (1 ), carbon dioxide (C0₂) from the surrounding atmosphere may dissolve in water to generate carbonate anions (C0₃ ^2~) in the alkaline environment of the concrete (the pH of concrete is around 12.5-13). Free dissolved calcium cations (Ca²⁺) arising from the defect may then react with the carbonate anions to form calcium carbonate. However, any such autogenous healing is greatly dependent on the age of the concrete, the water to cement ratio and the available water in the vicinity of the defect. It is also known, for example from EP2239242A1 , to provide a self-repairing or "self- healing" concrete which has distributed throughout a number of urea-formaldehyde, melamine-formaldehyde and/or urea-melamine-formaldehyde resin polymer microcapsules containing adhesive. The disclosed adhesives include mono- component adhesives, such as polyurethanes, organo-silico anaerobes, acrylic resins, and chloroprene rubbers, and multi-component adhesives, such as epoxy resins. Once a crack occurs in the concrete, microcapsules in the vicinity of the crack rupture due to induced stress caused by the crack, releasing the encapsulated adhesive to repair the crack. However, a number of technical problems may be encountered and require a solution to be provided with such teaching, including interface compatibility between the walls of the crack in the concrete and the adhesive materials used for repair, the extent to which the adhesive will flow to repair the crack prior to it setting, the durability of the adhesive, and the consequential effects (such as localized weakening) on the concrete immediately surrounding the repaired crack.

Accordingly, there is still a need to address the repair of defects in concrete and like materials, preferably by means of auto-reparation so as to avoid the need for human or mechanical intervention in the identification and actioning of a repair, in as timely a manner as possible to provide a compatible and durable solution. First Aspect

In a first aspect, the present invention thus provides microcapsules, for inclusion in concrete, concrete-based material and concrete-like material, adapted to reduce the area of a defect in said material once a quantity of said microcapsules has rupture or is exposed at an interface of the defect, said microcapsules each comprising:

a polymeric shell encapsulating a liquid core,

wherein the polymeric shell comprises a substantially impermeable polymer layer and the liquid core comprises carbonatogenic bacterial spores dispersed in a liquid, and

wherein at least one of the following criteria (i)-(iii) is fulfilled:

(i) said polymer layer comprises a polymer selected from the group consisting of: gelatines, polyurethanes, polyolefins, polyamides, polysaccharides, silicone resins, epoxy resins, chitosan, aminoplast resins and derivatives and mixtures thereof, and/or

(ii) said bacterial spores are in the form of a microorganism that is capable of reducing the area of the defect by means of mineral or extracellular polymeric substance ("EPS") production, and are preferably selected from the group of bacteria consisting of: Bacillus cereus, Bacillus subtilis, Bacillus sphae cus, Bacillus lentus, Bacillus pasteu i, Bacillus megate um, Bacillus cohnii, Bacillus halodurans, Bacillus pseudofirmas, Myxococcus Xanthus and mixtures thereof, and/or

(iii) said liquid is a non-aqueous, water-immiscible liquid selected from the group consisting of: organic oils, mineral oils, silicone oils, fluorocarbons, fatty acids, plasticizers, esters and mixtures thereof,

such that, when a quantity of said microcapsules is present in the material, the area of the defect therein is reducible by at least 45 % as compared to an initial area of the defect once at least some of said quantity of microcapsules have been ruptured. Such microcapsules have the ability, once included in a concrete or like material composition, to reduce the area of a defect, such as a crack or an indentation therein, once a quantity of said microcapsules has ruptured. Rupture of the microcapsules is achieved by locally induced internal stress in the concrete around the area of the defect, however, an external influence such as force or increased/decreased temperature, may be applied in addition to the internal stress to act on the inherent friability of the microcapsules to achieve rupture. Once ruptured, the relevant microcapsules will release their encapsulated contents, thus facilitating repair of the defect in as timely a manner as possible to provide a compatible and durable solution.

Microcapsules according to the invention may be made by any suitable microencapsulation technique known in the art, including, but not limited to, coacervation, interfacial polycondensation polymerization, addition or in-situ emulsion polymerization, addition or in-situ suspension polymerization, spray-drying and fluidized bed-drying to produce microcapsules of a desired size, friability and water-insolubility. Generally, methods such as coacervation and interfacial polymerization can be employed in known manner to produce microcapsules of the desired characteristics. Such methods are described in US3870542, US3415758 and US3041288.

For the avoidance of doubt, the rupture of as few as a single microcapsule would facilitate some degree of defect area reduction, however for the results to be non- negligible and for a discernible reparation to be observed, a quantity of microcapsules (being greater in number than a single microcapsule, preferably at least 10⁴ microcapsules per cm² of defect area, and generally of the order of 10⁶ microcapsules per cm² of defect area) are required to rupture. Preferably, in microcapsules according to the first aspect of the invention, any two of the three criteria (i)-(iii) may be fulfilled, with criteria (i) and (ii) being preferred. Further preferably however, in such microcapsules all three of criteria (i)-(iii) may be fulfilled. To achieve the percentage reduction in defect area discussed, in each microcapsule, the concentration of the bacterial spores may preferably be at least 10⁹ spores per gram (dry weight) of microcapsule.

Second Aspect

In a second aspect, the invention provides microcapsules, for inclusion in concrete, concrete-based material and concrete-like material, adapted to reduce the area of a defect in said material once a quantity of said microcapsules has ruptured or is exposed at an interface of the defect, said microcapsules each comprising:

a polymeric shell encapsulating a liquid core,

wherein, in each microcapsule, the concentration of the bacterial spores is at least 10⁹ spores per gram (dry weight) of microcapsule, such that, when a quantity of said microcapsules is present in the material, the area of the defect therein is reducible by at least 45 % as compared to an initial area of the defect once at least some of said quantity of microcapsules have been ruptured. The liquid in which the bacterial spores are dispersed may preferably be a nonaqueous, water-immiscible liquid.

As with the first aspect of the invention, such microcapsules have the ability, once included in a concrete or like material composition, to reduce the area of a defect, such as a crack or an indentation therein, once a quantity of said microcapsules has ruptured, with all the attendant benefits described earlier. Again, such microcapsules may be made by any suitable microencapsulation process, such as those described earlier. Advantageously, in either of the first or second aspects of the invention, the liquid core of some or all of the microcapsules may further comprise bacterial nutrients, i.e. the nutrients may be co-encapsulated with the carbonatogenic bacterial spores in some or all of the microcapsules. With such co-encapsulation, on rupture of a relevant microcapsule and dispersal of its contents, the bacterial nutrients are readily available to act with atmospheric oxygen and ambient water to enable germination of the bacterial spores to form vegetative bacteria, thus facilitating calcium carbonate production, as will described in more detail later in the specification. Furthermore, encapsulated nutrients may have a less detrimental effect on the surrounding concrete matrix than if the nutrients were freely distributed throughout.

Third Aspect

In a third aspect, the invention provides microcapsules, for inclusion in concrete, concrete-based material and concrete-like material, adapted to reduce the area of a defect in said material once a quantity of said microcapsules has ruptured or is exposed at an interface of the defect, said microcapsules each comprising:

a polymeric shell encapsulating a liquid core,

wherein the polymeric shell comprises a substantially impermeable polymer layer and the liquid core comprises carbonatogenic bacterial spores and bacterial nutrients dispersed in a liquid medium.

In this third aspect of the invention, the nutrients are co-encapsulated with the carbonatogenic bacterial spores in the microcapsules, regardless of the concentration or variety of the bacterial spores (other than being carbonatogenic), the nature of the polymer layer and the nature of the liquid medium.

As with each of the first and second aspects of the invention, such microcapsules have the ability, once included in a concrete or like material composition, to reduce the area of a defect, such as a crack or an indentation therein, once a quantity of said microcapsules has ruptured, with all the attendant benefits described earlier. Again, such microcapsules may be made by any suitable microencapsulation process, such as those described earlier.

In a preferred embodiment according to the third aspect of the invention, when a quantity of such microcapsules is present in the concrete or like material, the area of the defect therein may preferably be reducible by at least 45 % as compared to an initial area of the defect once at least some of said quantity of microcapsules have been ruptured. To achieve the percentage reduction in defect area discussed, in each microcapsule, the concentration of the bacterial spores may preferably be at least 10⁹ spores per gram (dry weight) of microcapsule.

Fourth Aspect

In a fourth aspect, the invention provides microcapsules, for inclusion in concrete, concrete-based material and concrete-like material, adapted to reduce the area of a defect in said material once a quantity of said microcapsules has ruptured or is exposed at an interface of the defect, said microcapsules each comprising:

a porous solid core, comprising a silica-based material, having bacterial nutrients dispersed therein.

Surrounding said porous solid core, there may be provided a surrounding shell, which may also comprise a silica-based material, which may the same as or different to the silica-based material of the core.

As with the previous aspects of the invention, such microcapsules have the ability, once included in a concrete or like material composition, to reduce the area of a defect, such as a crack or an indentation therein, once a quantity of said microcapsules has at least partially released its encapsulated nutrients, with all the attendant benefits described earlier. Again, such microcapsules may be made by any suitable microencapsulation process, such as those described earlier. In a preferred embodiment according to the fourth aspect of the invention, when a quantity of such microcapsules is present in the concrete or like material, the area of the defect therein may preferably be reducible by at least 45 % as compared to an initial area of the defect once at least some of said quantity of microcapsules have been ruptured or exposed at the crack surface. To achieve the percentage reduction in defect area discussed, the microcapsules may have come into contact with humidity and/or water; the bacterial spores may be provided in accordance with any of the previous aspects if the invention and/or by a natural occurrence of such spores in the area surrounding the concrete defect.

Fifth Aspect

In a fifth aspect, the invention provides microcapsules, for inclusion in concrete, concrete-based material and concrete-like material, adapted to reduce the area of a defect in said material once a quantity of said microcapsules has ruptured or is exposed at the interface of the defect, said microcapsules each comprising:

a porous solid core, comprising a carbohydrate-based material, having carbonatogenic bacterial spores and/or bacterial nutrients dissolved and/or dispersed therein. Surrounding said porous solid core, there may be provided a surrounding shell, which may also comprise a carbohydrate-based material, which may the same as or different to the carbohydrate-based material of the core.

As with the previous aspects of the invention, such microcapsules have the ability, once included in a concrete or like material composition, to reduce the area of a defect, such as a crack or an indentation therein, once a quantity of said microcapsules has at least partially released its encapsulated nutrients and/or bacterial spores, with all the attendant benefits described earlier. Again, such microcapsules may be made by any suitable microencapsulation process, such as those described earlier.

In a preferred embodiment according to the fifth aspect of the invention, when a quantity of such microcapsules is present in the concrete or like material, the area of the defect therein may preferably be reducible by at least 45 % as compared to an initial area of the defect once at least some of said quantity of microcapsules have been ruptured or exposed at the crack surface. To achieve the percentage reduction in defect area discussed, the microcapsules may have come into contact with humidity and/or water (and if not provided in the microcapsules, the bacterial spores may be provided in accordance with any of the previous aspects of the invention and/or by a natural occurrence of such spores in the area surrounding the concrete defect).

Reducible Defect Area

With the microcapsules according to any of the previous aspects of the invention, the area of the defect in the concrete or like material may be reducible by at least 50 %, preferably by at least 60 %, further preferably by at least 70 % and most preferably by at least 80 % as compared to the initial area of said defect once at least some of said quantity of microcapsules have been ruptured.

Advantageously, the reducible area of the defect may be determined after 4 weeks of continuous wet-dry cycling, beginning with a wet phase which comprises immersion of the concrete or like material, or at least the surface in which the defect is located, in water for 12-20 hours, preferably 16 hours, followed by a dry phase in which the concrete or like material, or at least the surface in which the defect is located, in air (at ambient temperature, such as 20 °C, at 50-70 %, preferably 60 %, relative humidity) for 6-10 hours, preferably 8 hours. Such conditions are believed to facilitate the at least 45 % reduction in defect area discussed above. Polymer Layer

The polymer layer of the microcapsules according to any of the previous aspects of the invention may comprise a polymer selected from the group consisting of: gelatines, polyurethanes, polyolefins, polyamides, polysaccharides, silicone resins, epoxy resins, chitosan, aminoplast resins and derivatives and mixtures thereof. These are the same polymers as for the first aspect of the invention. Many of these types of polymeric microcapsule shell materials are further described and exemplified in US3870542.

Preferably, the polymer layer of any of the aforementioned aspects of the invention comprises a polymer selected from the group consisting of: vinyl polymers, acrylate polymers, acrylate-acrylamide copolymers, melamine-formaldehyde polymers, urea- formaldehyde polymers and mixtures and derivatives thereof.

Highly preferred materials for the microcapsule shell wall are aminoplast polymers comprising the reactive products of, for instance, urea or melamine and an aldehyde, e.g. formaldehyde. The polymer layer therefore further preferably may be a melamine formaldehyde resin or include a layer of this polymer. Such materials are those which are capable of acid-condition polymerization from a water-soluble prepolymer or precondensate state. Polymers formed from such precondensate materials under acid conditions are water-insoluble and can provide the requisite microcapsule friability characteristics to allow subsequent rupture of the microcapsule. The microcapsule shell wall may further preferably by formed by a cross-linked network of polymers comprising a melamine-formaldehyde : acrylamide-acrylic acid copolymer.

Microcapsules made from aminoplast polymer shell materials can be made by an interfacial polymerization process, such as is described in US3516941 : an aqueous solution of a precondensate (methylol urea) is formed containing from about 3 % to 30 % by weight of the precondensate. A non-aqueous, water-immiscible liquid is dispersed throughout this solution in the form of microscopically-sized discrete droplets. Whilst maintaining a solution temperature of between 20 °C and 90 °C, acid is added to catalyze polymerization of the dissolved precondensate. If the solution is rapidly agitated during this polymerization step, shells of water-insoluble aminoplast polymer form around, so as to encapsulate, the dispersed droplets of liquid forming a liquid core. Microcapsules according to the present invention may be produced by a similar method, with the carbonatogenic bacterial spores and/or bacterial nutrients (as appropriate) being dispersed in the liquid core prior to polymerization. The polymer layer comprised in the microcapsules of any of the aforementioned aspects of the invention may further comprise reactive functional groups, extending outwardly of the microcapsule, whereby the microcapsule is chemically bondable within the concrete or like material. Such a reactive functional group preferably comprises a reactive moiety adapted to provide covalent bonding within the concrete.

Silica-Based Materials

Suitable silica-based materials for use in accordance with any of the previous aspects of the invention include those made from precursors such as sodium silicate and those selected from organically modified alkoxides ("ORMOSIL") such as tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), methyltrimethoxysilane (MTMS) and mixtures thereof. In general, the encapsulation process used may use silicon precursors of Si-O-Si bonds employed in sol-gel processes. To such silica precursors may be added colloidal silica nanoparticles (such as Ludox™ colloidal silica series), from 0 wt% to 10 wt% of the total silica content, to reinforce the shell and core structure of the obtained microparticles and/or microcapsules. Many of these types of sol-gel microcapsules are further described and exemplified in EP2335818 A1 , US7255874 and US6303149.

Highly preferred precursors for microcapsulation are ORMOSIL comprising the reactive product of TMOS, TEOS and MTMS. Such materials are capable of acid-condition condensation in a compatible solvent or water-soluble monomers or precondensates. Silica-based microparticles and/or microcapsules formed from such monomers and/or precondensate materials under acid conditions may be partially to totally insoluble in the solvents used and thus may provide the requisite microcapsule friability and/or porosity characteristics to allow subsequent release of the nutrients from microcapsules.

By way of example, the following describes the preparation of ORMOSIL microparticles and/or microcapsules containing bacterial nutrients using a sol-gel process:

- dissolve from 0.1 g to 1 g of calcium nitrate and/or from 0.1 g to 1 g of urea in 2 to 5 ml_ of a 2M hydrochloric acid aqueous solution at room temperature;

- dissolve from 0.01 g to 1 g of a polyethylene glycol sorbitan monooleate surfactant (such as, for example TWEEN™ 80) in the above aqueous mixture;

- optionally add a water suspended solution of colloidal silica nanoparticles (such as Ludox™ colloidal silica series), from 0 wt% to 10 wt% of the total silica content, to the above aqueous mixture;

- dropwise, add the above aqueous mixture to 20 ml_ to 100 ml_ of a non-miscible organic solvent (such as cyclohexane, petroleum ether) containing from 0.5 g to 4 g of a sorbitan monooleate surfactant (such as Span™ 80);

- emulsify the resultant biphasic mixture with vigorous agitation until the desired emulsion is reached;

- dropwise, add from 1 to 4 mL of a commercial TEOS solution to the above emulsion whilst mixing;

- continue to stir at room temperature for the desired period of condensation (from 1 to 24h);

- filter and wash (with previous organic solvents) the resultant silica-based microparticles and/or microcapsules to remove the remaining surfactants, then dry.

Carbohydrate-Based Materials

Suitable carbohydrate-based materials for use in accordance with any of the previous aspects of the invention include those made from precursors such as sodium alginate and those selected from natural source carbohydrate polymers (such as xanthan gums, arabic gums, agar, chitosan, pectin, pullulan, carrageenan, cellulosic materials), oligomers and mixtures thereof. In general, the encapsulation processes used may employ ionic exchange (exchange of sodium ions to calcium or barium ions). To such carbohydrate-based precursors may be added colloidal silica particles (such as Ludox™ colloidal silica series), from 0wt% to 10wt% of the total silica content, to reinforce the shell and core structure of the obtained microparticles and/or microcapsules. Many of these types of alginate microspheres are further described and exemplified in US5766907 A, US5508041 A and W01991/0091 19A1 .

The most highly preferred precursor for microcapsulation is sodium alginate. Such a material may be capable of gelation and coacervation in compatible solvents. Gelatine- based microcapsules and/or microspheres formed from carbohydrate materials are partially to totally insoluble in the used solvents and can provide the requisite microcapsule friability and/or porosity characteristics to allow subsequent release of the nutrients and/or bacterial spores from microcapsules. By way of example, the following describes the preparation of sodium alginate microparticles and/or microcapsules containing bacterial nutrients by a sol-gel or coacervation process:

- dissolve from 0.1 g to 5 g of urea in 4 ml_ of water;

- added from 1 to 5 wt% of sodium alginate powder to the above and stir the mixture until a homogeneous viscous liquid is obtained;

- dropwise, add the above mixture to a calcium-containing solution (preferably of calcium nitrate (for example 25g/L) and dissolved urea (to avoid a gradient of concentration that will reduce the urea content of the microcapsules and/or microspheres during the shell formation) and stir gently;

- filter and dry the resultant alginate-based microparticles and/or microcapsules.

The microcapsules obtained of any of the aforementioned aspects of the invention may further comprise reactive functional groups on its surface, extending outwardly thereof, whereby the microcapsule is chemically bondable within the concrete or like material. Such a reactive functional group preferably comprises a reactive moiety adapted to provide covalent bonding within the concrete. Bacterial Spores

The bacterial spores of the microcapsules according to any of the second to fifth aspects of the invention may be in the form of a microorganism that is capable of reducing the area of the defect by means of mineral or EPS production, and may be preferably selected from the group of bacteria consisting of: Bacillus cereus, Bacillus subtilis, Bacillus sphaericus, Bacillus lentus, Bacillus pasteurii, Bacillus megaterium, Bacillus cohnii, Bacillus halodurans, Bacillus pseudofirmas, Myxococcus Xanthus and mixtures thereof. Such carbonatogenic bacteria, i.e. carbonate- (C0₃ ^2~) and bicarbonate- (HC0₃ ^~) producing bacteria, may be used to generate calcium carbonate to achieve the desired concrete (or like material) defect reparation, as will be discussed in more detail below.

Preferably, the bacterial spores of any of the aforementioned aspects of the invention may be selected from the group of bacteria consisting of: Bacillus sphaericus, Bacillus pasteurii and Bacillus cohnii as being the best performing for present purposes in terms of carbonatogenesis. Further preferably, the bacterial spores may be selected from the group of bacteria consisting of: Bacillus sphaericus and Bacillus pasteurii.

Liquid

The liquid, preferably a non-aqueous, water-immiscible, of the microcapsules according to the second of third aspects of the invention may be selected from the group consisting of: organic oils, mineral oils, silicone oils, fluorocarbons, fatty acids, plasticizers, esters and mixtures thereof. By "non-aqueous" it is meant that the liquid contains less than 0.1 % by weight of water. By "water-immiscible" it is meant that the liquid has less than 1 % solubility in water (and vice versa), as this assists in the formation of the microcapsules by an emulsion polymerization route.

It is preferred that the liquid is a silicone oil, preferably having a kinematic viscosity of 500 centistokes (mm²/sec) or less, preferably 350 centistokes (mm²/sec) or less at 25 °C.

Size & Content

Microcapsules according to any of the aforementioned aspects of the invention may each have average dimensions in the range of from 1 x 10^~7 m to less than 1 x 10^~3 m, i.e. from 0.1 to less than 1000 μιη, which may be spherical or non-spherical. Preferably, microcapsules may have an average diameter greater than 0.5 μιη, preferably greater than 1 μιη. The average diameters of the microcapsules may, for example, fall in the range of from 0.5 to 900 μιη, of from 0.5 to 500 μιη, or of from 1 to 100 μιη.

Preferably, the bacterial spores dispersed in the liquid in each microcapsule according to any of the aforementioned aspects of the invention together may amount to 40-70 % by volume of the volume within the polymeric shell of each microcapsule.

Further preferably, the bacterial spores may amount to at least 1 %, preferably at least 2 %, by volume of the volume of the liquid within each microcapsule.

Bacterial Nutrients

By the term "bacterial nutrients" used throughout this specification, it is meant not only nutrients that may be required for germination and/or growth of bacteria, but also the calcium source used by the bacteria to provoke formation of calcium-containing minerals, i.e. the "healing" ingredients. Bacterial nutrients described with respect to the microcapsules of any of the aforementioned aspects of the invention may comprise (but are not limited to): urea (CO(NH₂)₂), a suitable carbon and nitrogen source, such as nutrient broth, yeast, yeast extract, organic oil and a suitable source of calcium, such as hydrated calcium nitrate (Ca(N0₃)2-4H₂0), calcium chloride, calcium acetate, calcium lactate and the like.

In addition to provision of novel and inventive microcapsules per se, the present invention also provides novel and inventive concrete compositions, which are "self- healing", containing such microcapsules.

Advantageously, the bending strength of concrete, concrete-based material or concrete-like material compositions comprising said microcapsules (such as described in the aspects and embodiments below) is not adversely affected by inclusion of said microcapsules as seen in the examples. In embodiments are thus provided microcapsules adapted to provide a composition bending strength when incorporated into a concrete, concrete-based material or concrete-like material composition (such as described in aspects and embodiments below) of 90% or more, such as 95% or more, 98% or more, preferably 99% or more of a corresponding composition that is devoid of the microcapsules.

In embodiments, the microcapsules are adapted to provide a composition bending strength when incorporated into a concrete, concrete-based material or concrete-like material composition comprising said microcapsules (such as described in aspects and embodiments below) of at least 4 MPa, such as at least 4.5 MPa, suitably at least 4.8 MPa (as measured according to a three-point bending test based on the standard NBN EN 12390-5 (2009) method as described in the examples section). In embodiments, the microcapsules are adapted to provide a composition bending strength when incorporated into a concrete, concrete-based material or concrete-like material composition comprising said microcapsules (such as described in aspects and embodiments below) of from 4 to 7 MPa, such as from 4.5 to 6.5 MPa, suitably, from 4.8 to 6.2 MPa. Typically, these values are obtained when the microcapsules are present in the composition in a concentration of from 1 % to 5% wt., such as 1 , 2, 3, 4, or 5 % wt. relative to the weight of cement in the concrete, concrete-based material or concrete-like material in the composition. In embodiments having a microcapsule dosage of around 1 % by weight relative to the weight of the cement in the concrete, concrete-based material or concrete-like material in the composition, the bending strength may be at least 4.5 MPa, 4.8 MPa, or suitably at least 5.0 MPa, such as from 4.5 to 6.0 MPa (such as from 4.8 to 5.5 MPa, e.g. around 5.2 ± 0.3 MPa). In embodiments having a microcapsule dosage of around 3% by weight relative to the weight of the cement in the concrete, concrete-based material or concrete-like material in the composition, the bending strength may be at least 5.0 MPa, 5.3 MPa, or suitably at least 5.6 MPa, such as from 5.0 to 6.5 MPa (such as from 5.3 to 6.2 MPa, e.g. around 5.9 ± 0.3 MPa). In embodiments having a microcapsule dosage of around 5% by weight relative to the weight of the cement in the concrete, concrete-based material or concrete-like material in the composition, the bending strength may be at least 4.5 MPa, 4.8 MPa, or suitably at least 5.0 MPa, such as from 4.5 to 6.0 MPa (such as from 4.8 to 5.5 MPa, e.g. around 5.2 ± 0.3 MPa) Bending strength was calculated according to a three-point bending test based on the standard NBN EN 12390-5 (2009) method as described in the examples section.

Advantageously, the inclusion of microcapsules may mean that concrete, concrete- based material or concrete-like material compositions (such as described in the sixth to eighth aspects and embodiments) show a decreased open porosity compared to analogous compositions devoid of the microcapsules, as detailed in the examples. Suitably the inclusion of microcapsules in the compositions (such as described in the sixth to eighth aspects and embodiments above) therefore has a beneficial effect in reducing water absorption. Microcapsules of the invention may thus suitably provide a decrease in capillary water absorption and / or (preferably and) final saturated water absorption when incorporated into concrete compositions (such as described in the aspects and embodiments below) compared to analogous compositions that are devoid of the microcapsules.

In embodiments, the microcapsules are thus adapted to provide a reduction in capillary water absorption in a concrete, concrete-based material or concrete-like material composition (such as described in aspects and embodiments below) compared to analogous compositions devoid of said microcapsules by at least 20%, suitably at least 25%, typically at least 30%, such as at least 35%, 40%, 45%, 50% or 55%. Typically, these values are obtained when the microcapsules are present in the composition in a concentration of from 1% to 5% wt., such as 1 , 2, 3, 4, or 5 % wt relative to the weight of cement in the concrete, concrete-based material or concrete-like material in the composition, such as at a microcapsule concentration of 1 % wt., 3% wt. or 5% wt., suitably 3% wt. and preferably 5% wt. of microcapsules relative to the weight of the cement in the concrete, concrete-based material or concrete-like material in the composition. In embodiments, said microcapsules are configured to reduce capillary water absorption by no more than 60%, for instance, no more than 55%, 50%, 45% 40%, 35% or 30% compared to analogous compositions that are devoid of the microcapsules, particularly at a microcapsule concentration of 1 % wt., 3% wt. or 5% wt., suitably 3% wt. and preferably 5% wt. of microcapsules relative to the weight of the cement in the concrete, concrete-based material or concrete-like material in the composition. In embodiments having a microcapsule dosage of around 3% by weight relative to the weight of the cement in the concrete, concrete-based material or concrete-like material in the composition, the water absorption may be reduced by 30- 45% (such as 35-40%) relative to a composition devoid of the microcapsules, or from 40-60%, preferably around 50%, e.g. 48% in embodiments having a microcapsule dosage of around 5% by weight relative to the weight of the cement in the concrete, concrete-based material or concrete-like material in the composition.

In embodiments, the microcapsules are thus adapted to provide concrete, concrete- based material or concrete-like material compositions (such as described in aspects and embodiments below) having a capillary water absorption of 0.25 g/cm² or less, suitably 0.22 g/cm² or less, such as 0.20 g/cm² or less, preferably 0.15 g/cm² or less, more preferably 0.13 g/cm² or less at a time period of 72 h. Typically these values are obtained when the microcapsules are present in the composition in a concentration of from 1 % to 5% wt., such as 1 , 2, 3, 4, or 5 % wt relative to the weight of cement in the concrete, concrete-based material or concrete-like material in the composition. Capillary water absorption may be calculated as described in the examples section. In embodiments, the microcapsules are configured to provide a reduction in the saturated water absorption in said compositions compared to analogous compositions devoid of microcapsules by at least 15% or 20%, suitably at least 25%, typically at least 30%, such as at least 35%, 40%, 45%, 50% or 55%, such as at a microcapsule concentration of around 1 % wt., 3% wt. or 5% wt., suitably around 3% wt. and preferably around 5% wt. of microcapsules relative to the weight of the cement in the concrete, concrete-based material or concrete-like material in the composition. In embodiments, microcapsules are configured to provide a reduction in the saturated water absorption in said compositions compared to analogous compositions devoid of microcapsules by no more than 60%, for instance, no more than 55%, 50%, 45% 40%, 35% or 30%, particularly at a microcapsule concentration of around 1 % wt., 3% wt. or 5% wt., suitably 3% wt. and preferably 5% wt. of microcapsules relative to the weight of the cement in the concrete, concrete-based material or concrete-like material in the composition. In embodiments having a microcapsule dosage of around 3% by weight relative to the weight of the cement in the concrete, concrete-based material or concrete-like material in the composition, the water absorption may be reduced by 20- 30% (such as 20-25%, e.g. around 23%) relative to a composition devoid of the microcapsules, or from 30-50% (such as 33-38%), preferably around 36%, in embodiments having a microcapsule dosage of around 5% by weight relative to the weight of the cement in the concrete, concrete-based material or concrete-like material in the composition.

In particular embodiments, the microcapsules are thus adapted to provide concrete, concrete-based material or concrete-like material compositions (such as described in aspects and embodiments below) having a saturated water absorption of 3.0% w/w or less, (i.e. weight water relative to the total weight of the composition), suitably 2.5% w/w or less, such as 2.2% w/w or less, for instance 2.0% w/w or less, preferably 1 .8% w/w or less, more preferably 1 .6% w/w or less, even more preferably 1 .5% w/w or less. Typically, these values are obtained when the microcapsules are present in the composition in a concentration of from 1 % to 5% wt., such as 1 , 2, 3, 4, or 5 % wt relative to the weight of cement in the concrete, concrete-based material or concretelike material in the composition. Saturated water absorption may be calculated as described in the examples section.

Suitably, the microcapsules of the above aspects and embodiments may be configured to provide concrete, concrete-based material or concrete-like material compositions (such as described in aspects and embodiments below) that exhibit hydration levels similar to those exhibited by compositions devoid of microcapsules.

Sixth Aspect

Accordingly, a sixth aspect of the present invention provides a concrete, concrete- based material and concrete-like material composition comprising:

a cementitious material, one or more aggregate materials, a liquid binder and a quantity of microcapsules according to the first, second, fourth and/or fifth aspects of the invention,

whereby, once set into concrete, the area of a defect therein is reducible by at least 45 % as compared to an initial area of the defect once at least some of said quantity of microcapsules have been ruptured.

Seventh Aspect

An seventh aspect of the present invention provides a concrete, concrete-based material and concrete-like material composition comprising:

a cementitious material, one or more aggregate materials, a liquid binder and a quantity of microcapsules according to the third, fourth or fifth aspects of the invention.

Eighth Aspect

A eighth aspect of the present invention provides a method of reducing the area of a defect (as compared to an initial area of the defect) in concrete, concrete-based material and/or concrete-like material comprising the steps of:

(i) providing a concrete, concrete-based material and/or concrete-like material composition according to the sixth and/or seventh aspects of the invention incorporating a quantity of microcapsules;

(ii) setting the composition; and

(iii) causing at least some of said quantity of microcapsules to rupture in response to the creation and/or worsening of a defect in said set composition, thereby releasing their contents to effect defect reduction.

Once set into concrete, the area of a defect therein may be reducible by at least 45 % as compared to an initial area of the defect once at least some of said quantity of microcapsules have been ruptured.

The presence of microcapsules according to any of the aforementioned aspects of the invention into such concrete or like material compositions mean the area of a defect, such as a crack or an indentation therein, is reducible by at least 45 % once a quantity of said microcapsules has ruptured, i.e. a degree of self-repair is achievable. Rupture of the microcapsules is achieved by locally induced internal stress in the concrete around the area of the defect, however, an external influence such as force or increased/decreased temperature, may be applied in addition to the internal stress to act on the inherent friability of the microcapsules to achieve rupture. Once ruptured, the relevant microcapsules will release their encapsulated contents, thus facilitating repair of the defect in as timely a manner as possible to provide a compatible and durable solution.

For the avoidance of doubt, the rupture of as few as a single microcapsule would facilitate some degree of defect area reduction, however for the results to be non- negligible and for a discernible reparation to be observed, a quantity of microcapsules (being greater in number than a single microcapsule, preferably at least 10⁴ microcapsules per cm² of defect area, and generally of the order of 10⁶ microcapsules per cm² of defect area are required to rupture.

Surprisingly, the inventors found that the bacterial spores were able to withstand the manufacturing (e.g. microencapsulation) process, such that they were still able to germinate, and for ureolytic activity to decompose urea (present in bacterial nutrients) to begin. The bacterial spores thus remain dormant inside the microcapsules.

Without wishing to be bound by any theory, the repair mechanism is thought to follow the following pathway:

(1 ) Rupture of microcapsule → release of bacterial spores, for exposure to germination activators: oxygen, water and bacterial nutrients

(2) Germination of bacterial spores→ production of vegetative bacterial cells for use in hydrolysis

(3) Precipitation of calcium carbonate for defect repair via:

(a) CO(NH₂)₂ + 2H₂0→ 2NH₄ ⁺ + C0₃ ^2" [catalyzed by bacterial urease]

(b) Ca²⁺ + C0₃ ^2"→CaC0₃

Defect formation, for example formation of a crack, triggers breakage of the microcapsules in the vicinity of the crack, which enables exposure of the liquid core. In the presence of oxygen, water and bacterial nutrients, the bacterial spores in the liquid core begin to germinate so that ureolytic activity may begin. Urea is decomposed into C0₃ ^2~ and NH₃/NH₄ ⁺ by the germinated bacteria (catalyzed by bacterial urease) under alkaline pH. When C0₃ ^2" ions meet with Ca²⁺ ions (e.g. from calcium nitrate), CaC0₃ is formed.

A concrete composition according to either the sixth or seventh aspects of the invention is thus advantageous over prior art concrete compositions in that it possesses the desired interface compatibility between the walls of a defect in the concrete and the in- situ generated calcium carbonate used for repair. Furthermore, there is no limit to the extent to which the in-situ generated calcium carbonate is generated to enable repair of the defect provided microcapsules are evenly distributed throughout the concrete composition. Moreover, because of the compatibility of the repair material with the concrete, the repair possesses the desired longevity and durability. Also, any consequential effects (such as localized weakening) on the concrete immediately surrounding the repaired crack are minimized, again because of the compatibility of the repair material with the concrete.

The area of the defect in the concrete formable from the composition of either the sixth or seventh aspects of the invention may be reducible by at least 50 %, preferably by at least 60 %, further preferably by at least 70 % and most preferably by at least 80 % as compared to the initial area of said defect once at least some of said quantity of microcapsules have been ruptured.

Advantageously, the reducible area of the defect may be determined after 4 weeks of continuous wet-dry cycling, beginning with a wet phase which comprises immersion of the concrete or like material, or at least the surface in which the defect is located, in water for 12-20 hours, preferably 16 hours, followed by a dry phase in which the concrete or like material, or at least the surface in which the defect is located, in air (at ambient temperature, such as 20 °C, at 50-70 %, preferably 60 %, relative humidity) for 6-10 hours, preferably 8 hours. Such conditions are believed to facilitate the at least 45 % reduction in defect area discussed above.

Advantageously, the bending strength of the concrete, concrete-based material or concrete-like material compositions of the invention comprising said microcapsules (such as described in the sixth to eighth aspects and embodiments above) is not adversely affected by inclusion of said microcapsules as seen in the examples. In embodiments are thus provided compositions wherein the bending strength of the composition is 90% or more, such as 95% or more, 98% or more or preferably 99% or more of a corresponding composition that is devoid of the microcapsules. In embodiments, the composition has a bending strength (such as described in aspects and embodiments below) of at least 4 MPa, such as at least 4.5 MPa, suitably at least 4.8 MPa (as measured according to a three-point bending test based on the standard NBN EN 12390-5 (2009) method as described in the examples section). In embodiments, the compositions have a bending strength of from 4 to 7 MPa, such as from 4.5 to 6.5 MPa, suitably, from 4.8 to 6.2 MPa. Typically, these values are obtained when the microcapsules are present in the composition in a concentration of from 1% to 5% wt., such as 1 , 2, 3, 4, or 5 % wt. relative to the weight of cement in the concrete, concrete-based material or concrete-like material in the composition. In embodiments having a microcapsule dosage of around 1 % by weight relative to the weight of the cement in the concrete, concrete-based material or concrete-like material in the composition, the bending strength may be at least 4.5 MPa, 4.8 MPa, or suitably at least 5.0 MPa, such as from 4.5 to 6.0 MPa (such as from 4.8 to 5.5 MPa, e.g. around 5.2 ± 0.3 MPa). In embodiments having a microcapsule dosage of around 3% by weight relative to the weight of the cement in the concrete, concrete-based material or concrete-like material in the composition, the bending strength may be at least 5.0 MPa, 5.3 MPa or suitably at least 5.6 MPa, such as from 5.0 to 6.5 MPa (such as from 5.3 to 6.2 MPa, e.g. around 5.9 ± 0.3 MPa). In embodiments having a microcapsule dosage of around 5% by weight relative to the weight of the cement in the concrete, concrete-based material or concrete-like material in the composition, the bending strength may be at least 4.5 MPa, 4.8 MPa, or suitably at least 5.0 MPa, such as from 4.5 to 6.0 MPa (such as from 4.8 to 5.5 MPa, e.g. around 5.2 ± 0.3 MPa). Bending strength was calculated by a three-point bending test based on the standard NBN EN 12390-5 (2009) as described in the examples section.

Advantageously, compositions of the invention (such as described in the sixth to eighth aspects and embodiments above) show a decreased open porosity compared to analogous compositions devoid of the microcapsules, as detailed in the examples. Compositions of the invention thus suitably show a decrease in capillary water absorption and / or (preferably and) final saturated water absorption compared to analogous compositions that are devoid of the microcapsules.

Suitably, the inclusion of microcapsules in the compositions (such as described in the sixth to eighth aspects and embodiments above) has a beneficial effect in reducing the concrete porosity and thus reducing water absorption. In embodiments, the capillary water absorption in the composition is reduced compared to analogous compositions devoid of microcapsules by at least 20%, suitably at least 25%, typically at least 30%, such as at least 35%, 40%, 45%, 50% or 55%, such as at a microcapsule concentration of 1 % wt., 3% wt. or 5% wt., suitably 3% wt. and preferably 5% wt. of microcapsules relative to the weight of cement in the concrete, concrete-based material or concrete-like material in the composition. In embodiments, the capillary water absorption in the compositions may be reduced by no more than 60%, for instance, no more than 55%, 50%, 45% 40%, 35% or 30% compared to analogous compositions that are devoid of the microcapsules, particularly at a microcapsule concentration of 1 % wt., 3% wt. or 5% wt., suitably 3% wt. and preferably 5% wt. of microcapsules relative to the weight of cement in the concrete, concrete-based material or concretelike material in the composition. In embodiments having a microcapsule dosage of around 3% by weight relative to the weight of cement in the concrete, concrete-based material or concrete-like material in the composition, the water absorption is reduced by 30-45% (such as 35-40%) relative to a composition devoid of the microcapsules, or from 40-60%, preferably around 50%, e.g. 48% in embodiments having a microcapsule dosage of around 5% by weight relative to the weight of the cement in the concrete, concrete-based material or concrete-like material in the composition.

In particular embodiments, the compositions (such as described in aspects and embodiments above) have a capillary water absorption of 0.25 g/cm² or less, suitably 0.22 g/cm² or less, such as 0.20 g/cm² or less, preferably 0.15 g/cm² or less, more preferably 0.13 g/cm² or less at a time period of 72 h. Typically these values are obtained when the microcapsules are present in the composition in a concentration of from 1 % to 5% wt., such as 1 , 2, 3, 4, or 5 % wt. relative to the weight of cement in the concrete, concrete-based material or concrete-like material in the composition. Capillary water absorption may be calculated as described in the examples section.

In embodiments, the saturated water absorption in the composition is reduced compared to analogous compositions devoid of microcapsules by at least 15% or 20%, suitably at least 25%, typically at least 30%, such as at least 35%, 40%, 45%, 50% or 55%, such as at a microcapsule concentration of around 1 % wt., 3% wt. or 5% wt., suitably around 3% wt. and preferably around 5% wt. of microcapsules relative to the weight of the cement in the concrete, concrete-based material or concrete-like material in the composition. In embodiments, the saturated water absorption in the compositions may be reduced by no more than 60%, for instance, no more than 55%, 50%, 45% 40%, 35% or 30% compared to analogous compositions that are devoid of the microcapsules, particularly at a microcapsule concentration of around 1 % wt., 3% wt. or 5% wt., suitably 3% wt. and preferably 5% wt. of microcapsules relative to the weight of the cement in the concrete, concrete-based material or concrete-like material in the composition. In embodiments having a microcapsule dosage of around 3% by weight relative to the weight of the cement in the concrete, concrete-based material or concrete-like material in the composition, the water absorption is reduced by 20-30% (such as 20-25%, e.g. around 23%) relative to a composition devoid of the microcapsules, or from 30-50% (such as 33-38%), preferably around 36%, in embodiments having a microcapsule dosage of around 5% by weight relative to the weight of the concrete, concrete-based material or concrete-like material in the composition.

In particular embodiments, the compositions (such as described in aspects and embodiments above) have a saturated water absorption of 3.0% w/w or less, (i.e. weight water relative to the total weight of the composition), suitably 2.5% w/w or less, such as 2.2% w/w or less, for instance 2.0% w/w or less, preferably 1 .8% w/w or less, more preferably 1 .6% w/w or less, even more preferably 1 .5% w/w or less. Typically, these values are obtained when the microcapsules are present in the composition in a concentration of from 1 % to 5% wt., such as 1 , 2, 3, 4, or 5 % wt. relative to the weight of cement in the concrete, concrete-based material or concrete-like material in the composition. Saturated water absorption may be calculated as described in the examples section.

Suitably, the compositions of the above aspect and embodiments may exhibit hydration levels similar to those exhibited by compositions devoid of microcapsules.

Microcapsule Dosage

Advantageously, the quantity of microcapsules comprised in the composition according to either the sixth or seventh aspects of the invention, based on their dry weight, is in the range of 1 % to 10 %, preferably 2 % to 8 %, by weight of the cementitious material.

In one embodiment, the microcapsules may be added to the composition in the form of an emulsion having the microcapsules dispersed therein, particular when the microcapsules have been formed by an emulsion polymerization method. Further preferably, the emulsion may be a water-based emulsion. Bacterial Nutrients

A concrete composition according to the sixth or seventh aspects of the invention may comprise or further comprise bacterial nutrients, which are preferably added to the concrete composition per se alongside the cementitious material, aggregate material, liquid binder and microcapsules, which may or may not themselves also contain bacterial nutrients.

The bacterial nutrients may be thus incorporated into the composition by any one or more of the following means:

- by direct admixture into the composition;

- by admixture of a quantity of different microcapsules containing the nutrients;

- by admixture of a hydrogel or other such suitable carrier, e.g. porous aggregate, clays or diatomaceous earth, containing the nutrients. The quantity of bacterial nutrients comprised in the composition may beneficially be in the range of 10 % to 20 %, preferably 12 % to 18 %, by weight of the cementitious material.

Concrete Ingredients

In a concrete composition according to the sixth and seventh aspects of the invention, the cementitious material is preferably cement. A typically suitable cement is Portland cement, however any other suitable cementitious material may be used.

In a concrete composition according to the sixth and seventh aspects of the invention, the aggregate material is preferably a mixture of fine and coarse aggregates, of differing particles sizes, including materials such as sand, natural gravel, crushed stone and/or recycled materials obtained from construction, demolition and/or excavation waste. In a concrete composition according to the sixth and seventh aspects of the invention, the liquid binder is preferably water.

Advantageously, the ratio of cementitious material to aggregate material to water in a concrete composition according to the sixth and seventh aspects of the invention may be in the ranges of (0.5 to 1 .5) : (1 to 15) : (0.1 to1 ), with the ratio 1 : 5 : 0.5 being preferred. For a better understanding, the present invention will now be more particularly described by way of non-limiting examples only, with reference to the accompanying Figures in which: Figure 1 illustrates a series of plots (a) to (f) for a number of different cement samples (Groups R, N, C, NC, NCS3% and NCS5% respectively) of initial crack area (mm²) compared to final crack area (mm²) after being subjected to different incubation conditions (1 ) to (5); Figure 2 is a plot of the absolute value of healed crack area (mm²) for the cement samples shown in Figures 1 (a) to 1 (f) for incubation conditions (1 ) to (5);

Figure 3 is a plot of the healing ratio for the cement samples shown in Figures 1 (a) to 1 (f) and Figure 2 for incubation conditions (1 ) to (5);

Figure 4 is a scanning electron microscope (SEM) micrograph of a quantity of aminoplast microcapsules according to one embodiment of the invention;

Figure 5 is an SEM micrograph of the quantity of aminoplast microcapsules shown in Figure 4 but at greater magnification;

Figure 6 is an SEM micrograph of a quantity of silica-based material microcapsules according to another embodiment of the invention; Figure 7 is an SEM micrograph of an alginate microparticle according to a further embodiment of the invention;

Figure 8 is a plot of the absolute concentration of bacterial cells against time (hours) for varying concentrations (g/L) of nutrient at a fixed concentration (g/L) of urea; and

Figure 9 is a series of plots (a) to (c) showing the degree of bacterial spore germination under different temperature conditions (28 °C, 20 °C and 10°C respectively) by measuring the concentration (g/L) of urea decomposed over time (days) for varying concentrations (g/L) of nutrient at a fixed initial concentration (g/L) of urea. Figure 10 shows microscopy images taken before (Figure 10a) and after (Figure 10b) mixing of microcapsules with concrete as described in example d). The images were acquired from a sample taken from the 5% sample as described in example d). Figure 1 1 shows the bending strength data for cement samples having no microcapsules (reference "R"), as well as samples containing 1 %, 3% and 5% wt. microcapsules, respectively (relative to the weight of cement in the concrete) as detailed in example e). Figure 12 shows the capillary water absorption data in g/cm² against time in hours for cement samples having no microcapsules (reference "R" - upper line with diamond points), 1 % wt. microcapsules (second line to top with square points), 3% wt. microcapsules (third line to top with triangular points) and 5% wt. microcapsules (bottom line with circular points), respectively (relative to the weight of cement in the concrete) as detailed in example f).

Figure 13 shows the saturated water absorption data provided as weight water versus total weight concrete sample against time in hours for cement samples having no microcapsules (reference "R" - upper line with diamond points), 1 % wt. microcapsules (second line to top with square points), 3% wt. microcapsules (third line to top with triangular points) and 5% wt. microcapsules (bottom line with circular points), respectively (relative to the weight of cement in the concrete) as detailed in example f).

Figure 14 shows hydration heat production data as heat production rate (J/gh) plotted against time (minutes) for three samples having different microcapsule concentrations (no microcapsules, i.e. sample "R", 3% wt. microcapsules and 5% wt. microcapsules relative to the weight of cement in the concrete) prepared as in example g). The graph shows cumulative heat production data (lines progressing to top right) and heat production rate (lines peaking on left and fall to bottom right). For the cumulative heat production data, R is the top of the three lines at the top right of the graph, 3% is the middle and 5% is the bottom, For the heat production rate date, looking at the peak at the left of the graph, R is the top of the three lines, 3% is the middle and 5% is the bottom. Figure 15 shows a schematic diagram of the three-point bending test as described in example e) wherein 1 is the loading roller; and 2 and 3 are supporting rollers. Examples

a) Self-healing tests

Six example cement compositions were prepared, as detailed in Table 1 below. The "Group R" specimens are the control specimens, prepared without any additions to the basic cement, sand and water composition. The "Group N" specimens were prepared with bacterial nutrients of (i) yeast, (ii) urea and (iii) calcium nitrate tetrahydrate in amounts of 0.85 %, 4 % and 8 % by weight of cement as the only additions as compared to the control specimens. The "Group C" specimens were prepared with control microcapsules (containing no bacterial spores) in an amount of 3 % by weight of cement. Thus the "Group NC" specimens were prepared as per the "Group N" and "Group C" specimens combined, with both bacterial nutrients and 3 % by weight of microcapsules containing no bacterial spores. The "Group NCS3%" and "Group NCS5%" were prepared containing bacterial nutrients (as per the "Group N" specimens) and 3 % and 5% (by weight of cement) respectively microcapsules containing encapsulated bacterial spores in a concentration of 10⁹ spores per gram (dry weight) of microcapsule.

Table 1

In the specimens having bacterial nutrients added (Groups N, NC, NCS3% and NCS5%), to offset the 30.5 wt% provided by the water of hydration in the calcium nitrate tetrahydrate, the amount of water added to the composition was accordingly reduced from 225 g. Similarly, in the specimens having microcapsules added (Groups C, NC, NCS3% and NCS 5%), to offset the water provided from the emulsion (in which the microcapsules were added to the compositions), the amount of water added to the composition was accordingly reduced, or further reduced, from 225 g. For each of the six composition groups, five long reinforced prisms (having dimensions of 30 x 30 x 360 mm, with the internal rebar having a length of 660 mm and a diameter of 6 mm) were made - thus thirty specimens in total. After casting, the moulds were placed in an air-conditioned room (at 20^°C, > 90 % RH). The specimens in control Group R were de-moulded after 24 hours, while the specimens of other Groups were de-moulded after 48 hours because of their slower hardening in the first 24 hours due to the additives. After de-moulding, all specimens were stored in the same air conditioned room until the time of testing.

28 days after casting, each of the long reinforced prisms were subjected to a tensile test to create multiple cracks. The rebar of the prism was clamped into a test machine (Amsler 100, SZDU 230, Switzerland), with the distance between the clamp and the side surface of the prism being 50 mm. After unloading, the rebar was cut off (leaving around 140 mm protruding from each end of the prisms) and the remaining rebar was wrapped with aluminium tape to prevent iron corrosion during subsequent immersion.

After crack creation, the long reinforced prisms were subjected to five incubation conditions:

(1 ) 20^°C, > 90 % RH

(2) full and continuous immersion in water

(3) full and continuous immersion in a deposition medium

(4) continuous wet-dry cycling with water

(5) continuous wet-dry cycling with the deposition medium.

The deposition medium was composed of 0.2 M urea and 0.2 M Ca(N0₃)₂.

During the wet-dry cycles, the specimens were immersed in water/deposition medium for 16 hours and then exposed to air for 8 hours. The incubation conditions of (2), (3), (4) and (5) were performed in an air-conditioned room (20^°C, 60 % RH). When the specimens were subjected to immersion, they were not in contact with the bottom of the immersion container but some distance (about 5 mm) was maintained in between. Four 360 mm x 30 mm surfaces were named A, B, C and D to represent different contact conditions with water: surfaces B and C were the upper and lower surfaces, while surfaces A and D were the two side surfaces, respectively. The cracks formed in each specimen, per incubation condition, were identified and counted; the results are shown in Table 2 below.

Table 2

Group Incubation No. of Cracks per Surface Total No.

Condition of Cracks

Surface Surface Surface Surface per A B C D Specimen

R (1 ) 8 8 8 7 31

(2) 5 6 5 6 22

(3) 6 6 5 6 23

(4) 7 6 6 5 24

(5) 6 6 6 5 23

N (1 ) 6 6 5 6 23

(2) 6 7 6 7 26

(3) 7 5 5 6 23

(4) 8 7 8 8 31

(5) 6 6 6 6 24

C (1 ) 4 3 3 3 13

(2) 3 4 4 4 15

(3) 4 4 4 5 17

(4) 4 4 4 4 16

(5) 5 5 5 5 20

NC (1 ) 7 6 5 6 24

(2) 5 6 6 6 23

(3) 5 5 6 6 22

(4) 7 6 8 7 28

(5) 5 7 7 6 25

NCS3% (1 ) 10 7 9 9 35

(2) 4 6 6 4 20

(3) 10 9 7 6 32

(4) 7 4 6 7 24 (5) 5 5 5 5 20

NCS5% (1 ) 4 3 2 5 14

(2) 4 5 4 5 18

(3) 9 5 5 5 24

(4) 4 9 7 7 27

(5) 9 7 5 5 26

Initial optical microscope images of the cracks in the specimens were taken immediately after multiple cracking. Each crack was divided into 10-1 1 portions by pencil markers to make sure the whole crack would be photomicrographed with minimal overlap of the area among the images.

During the incubation period under different conditions, the specimens were subjected to light microscopy every week in the first month and at the end of the second month. The values of the initial and final cracking area in the images were determined by a Leica™ image analysis program.

Although the same methodology was applied to create cracks in each of the specimens, the cracking behaviour was clearly different due to different mechanical properties of the specimens, on account of their different compositions. As shown in Table 2, the number of cracks per specimen varied from 13 to 35 and the crack widths varied from 50 μιη to 900 μιη.

The self-healing efficiency, or extent of defect (crack) repair, of each of the samples was evaluated by determination of the absolute healed cracking area (A_h).

Crack healing efficiency was also evaluated by the healing ratio (the amount of crack area filled by the precipitation), which was calculated based on the equation shown below. The healing ratio can indicate the potential healing effect in the absence of specific information about the cracks (widths, area, etc.) in practice.

where:

"r" is the crack healing ratio "A," is the initial crack area (mm²)

"A_f" is the final crack area (mm²)

It was clearly observed that the crack area gradually decreased over time. Within three weeks, the crack area was almost completely healed. However, in order to quantify the healing efficiency, the cumulative healed crack area in each specimen after eight weeks was calculated based on its total initial (A,) and total final (A_f) crack area, which is shown in accompanying Figure 1 . As shown in Figure 1 , the crack area was decreased after eight weeks in all specimens (shown in plots (a) to (f)) except for those incubated under condition (1 ) (in an air- conditioned room at 20 °C at 95 % RH), in which no obvious healing was visualized under light microscopy. In each plot, a set of "paired" bars is plotted per incubation condition (1 ) to (5), with the total initial crack area (A,) being represented by the left hand bar in each pair, and the total final crack area (A_f) being represented by the right hand bar in each pair.

The absolute value of the healed crack area (A_h) shown in Figure 2 provides a straight comparison of healing efficiency, while the healing ratio (r) provides a means to compare healing efficiencies relative to the original crack area per specimen as shown in Figure 3.

Crack healing was observed in all specimens except for those stored at 95 % RH. For the specimens without microencapsulated bacteria, a considerable amount of crack healing (autogeneous healing) was observed when they were subjected to submersion or wet-dry cycles. The healed crack area (A_h) varied from 12.6 mm² to 57.8 mm² depending on the specific specimen and its incubation condition.

Compared with the specimens without encapsulated bacteria, those with microencapsulated bacteria showed much higher healing efficiency (r). The healed crack area (A_h) varied from 49.3 mm² to 80 mm². In view of the overall healed crack area, no significant difference was observed between the series of NCS3% and NCS5%, however, the specific healing efficiency of each specimen of NCS3% and NCS5% was different depending on the incubation conditions. The maximum healed crack area (around 80 mm²) was observed in the specimens which were subjected to the condition of wet-dry cycles with water, although the specimens under other incubation conditions exhibited similar healing efficiencies. The crack healing ratio (r) in each specimen of the different series is shown in Figure 3. The specimens without encapsulated bacteria had a healing ratio (r) in the range of 18 % to 50 %. No significant difference in the overall healing ratio (r) was observed among different series (R, N, C and NC).

The specimens with microencapsulated bacteria had a much higher healing ratio (r) which ranged from 48 % to 80 %. The highest value was obtained in the specimen of NCS3%, which was subjected to incubation condition (4).

The specimens with microencapsulated bacteria incorporated showed much higher self-healing efficiency; around six times the crack area was healed compared with the control "Group R" series when the specimens were subjected to incubation condition (4). In view of the healed crack area, the specimens in non-bacterial groups (R, N, C, NC) had a healed area range of 12.6 mm² to 57.8 mm² while the bacterial-containing groups (NCS3% and NCS5%) had 49.3 mm² to 80 mm² of the crack area healed. The maximum crack width healed in the specimens of the bacterial-containing groups was 970 μιη, which was much wider than that in the specimens of non-bacterial groups (maximum 250 μιη).

The micrograph of Figure 4 shows a quantity of microcapsules having an aminoplast shell containing bacterial spores and bacterial nutrients in the form of yeast extract. The magnified micrograph of Figure 5 shows a number of the quantity of said microcapsules having been ruptured, such that a number of bacterial spores along with its surround yeast extract is released from those number of microcapsules.

The SEM micrographs of Figures 6 and 7 respectively show a quantity of microparticles/microcapsules having a silica-based material core and/or shell containing only bacterial nutrients and a microparticle of alginate core material containing only bacterial nutrients. b) Nutrient effects on spore germination/outgrowth

The plots shown in Figures 8 and 9 are a result of further investigative work undertaken to determine the effect of a particular bacterial nutrient (yeast extract "YE") on the activity of bacterial spores, in particular the germination and outgrowth of spores, and the subsequent formation of bio-precipitation. Figure 8 shows that, in a series of media with different concentrations of yeast extract, the higher the concentration of yeast extract (from 0 g/L to 20 g/L) for a given initial concentration of urea ("U") (20 g/L), the higher absolute concentration of bacterial cells present, particularly after a period of fifteen hours. Clearly, the outgrowth of spores was much more remarkable at YE20/U20 and YE5/U20 than in other series with lower concentrations of yeast extract. c) Temperature / nutrient concentration effects on spore germination/outgrowth

Figures 9(a), 9(b) and 9(c) show the variation in germination of B. sphaericus spores at different temperatures (28 °C, 20 °C and 10°C respectively) for different concentrations of yeast extract (m/n in the legend indicates the concentration of yeast extract ("m") and urea ("n") respectively). As shown in Figure 9(a), at 28^°C, spores in the media with yeast extract concentrations of 20 g/L and 5 g/L exhibited a faster revival of ureolytic activity. From around 70 % to around 95 % of the urea in the media was decomposed in the first day. Spores in the media with 2 g/L and 0.2 g/L yeast extract showed a greatly increased ureolytic activity after 3 days. Within one week, all the urea in the media of yeast extract was completely decomposed. For the spores in the media without yeast extract, the revival of ureolytic activity was much slower but still gradually increased. About 50 % (10 g/L) and 85 % (17 g/L) of the urea was decomposed after 7 and 28 days respectively. Spores at 20^°C exhibited similar germination behaviour to those at 28^°C, as shown in Figure 9(b). The revival of spores' ureolytic activity was much slower at 10^°C, as shown in Figure 9(c). In the media with 20 g/L YE, about 3-4 g/L of urea was decomposed in the first 3 days. A significant increase of ureolytic activity occurred between the 3rd and 7th days; 15-17 g/L urea was decomposed by the 7th day. For the media with 5 g/L and 2 g/L YE, the major revival of ureolytic activity occurred between the 7th and 14th days and between the 14th and 21 st days respectively. Urea was completely hydrolyzed after 21 days in the media with 20 g/L, 5 g/L and 2 g/L YE. However, the spores in the media with 0.2 g/L and 0 g/L YE showed no noticeable decomposition of urea within 28 days. It thus appears that, especially when in an unfavourable environment, such as low temperature and in the presence of a high concentration of calcium ions, any negative effect on bacterial ureolytic activity may be counteracted by the presence of yeast extract (YE). Without yeast extract, bacterial spores could still germinate (but without outgrowth) and precipitate CaC0₃ ^~, however precipitation formation was much slower, and that the process only happened at moderate temperatures (20^°C ~ 28^°C, not at low temperatures). d) Survival of microcapsules in concrete

A concrete composition described below in Table 3 was prepared. Based on the standard EN 206-1 , the w/c is 0.5, the content of cement is 300kg/m³.

Table 3

Composition of the concrete mixture

Four batches (40L per batch) of concrete were prepared by adding various amounts of microcapsules to the above concrete composition. For this, a microcapsule emulsion containing 40-50% wt. microcapsules, 5% wt. of an anionic surfactant and the remaining weight water (relative to the total weight of the emulsion) was first formed before mixing with the concrete mixture. The size of the microcapsules was from 3-20μιη. The four compositions are represented below in Table 4. "R" is a reference sample containing no microcapsules. The remaining batches contained 1 %, 3% and 5% microcapsules relative to the weight of the cement.

Table 4

Compositions of the concrete with or without microcapsules

Sand Aggregate Aggregate CEMI H₂0 Super- MicroMicro¬

0/4 2/8 (kg) 8/16 (kg) 52.5N (kg) plasticizer capsule capsule

(kg) (kg) (mUkg (kg) emulsion cement) (kg)

R 29.2 21 .04 27.44 12.00 6.00 5 0 0

1% 29.2 21 .04 27.44 12.00 5.86 2.5 0.12 0.26

3% 29.2 21 .04 27.44 12.00 5.58 5 0.36 0.78

5% 29.2 21 .04 27.44 12.00 5.3 6 0.6 1 .30

Microscopy images illustrated in Figure 10 were taken before (Figure 10a) and after (Figure 10b) the mixing. It can be seen that after being mixed in concrete, most microcapsules survived the mixing process. e) Concrete strength - bending test

Samples of the four batches (R, 1 %, 3% and 5%) as prepared in example d) were subject to a bending test after 28 days. For this test, prisms of concrete from the above batches R, 1%, 3% and 5% (100 mm x 100 mm x 500 mm, n=3) were prepared and used. The results of the test are shown in Figure 1 1 . It can be seen that inclusion of the microcapsules did not substantially affect the tensile strength.

The bending test was conducted as follows: The concrete prisms (100mm 100mm x500mm) were subjected to a three-point bending test based on the standard NBN EN 12390-5 (2009). As shown in Figure 15, the span between two support rollers was 320mm. The load was applied in the center of the specimen by means of a server hydraulic jack with maximum load capacity of 10OkN.

The loading rate was determined by the formula:

2 x s x d-, x df

R is the required loading rate, in N/s;

s is the stress rate, in MPa/s (N/mm².s);

d₁ and d₂ are the lateral dimensions of the specimen, in mm;

/ is the distance between the supporting rollers, in mm; and the flexural (i.e. bending) strength is calculated by the following equation:

3 X F X I where: f_Cf is the flexural (i.e. bending) strength, in MPa (N/mm²);

Fis the maximum load, in N;

/ is the distance between the supporting rollers, in mm;

d₁ and d₂ are the lateral dimensions of the specimen, in mm; f) Water absorption test

Samples of the four batches (R, 1 %, 3% and 5%) as prepared according to example d) were subject to a water absorption test over 72 hours. The data are presented in Figures 12 and 13. As seen in Figures 12 and 13, the water absorption (both capillary water absorption and final saturated water absorption) decreased after the addition of microcapsules. A significant decrease occurred for concrete having microcapsule concentrations higher than 1 %. The capillary water absorption in the concrete specimens was reduced by 39% and 48% at the microcapsule dosage of 3% and 5%, respectively. The saturated water absorption in the series of 3% and 5% was decreased by 23% and 36%, respectively. This means that the addition of microcapsules can beneficially decrease the open porosity of the concrete.

Capillary water absorption test: A modified capillary water absorption test based on RILEM 25 PEM II-6 (NBN B 24-213) was performed. The concrete slices (100mm ^χ 100mm ^χ 60mm) were cut from the concrete prisms and then were dried at 40 ^°C in an oven until weight changes were less than 0.1 % at 24 h intervals. The initial weight of the specimens was recorded. Before the test, the four sides adjacent to the cutting surface (100mm ^χ 100mm) were wrapped by an aluminum tape to prevent water evaporation through the sides during the water absorption test. The initial weight of the wrapped specimens was also recorded. Subsequently, the specimens were brought into a water bath with a water level of 10±1 mm and the cut surface facing downwards. At regular time intervals (30min, 1 , 2, 3, 4, 5, 6, 24h, 48h and 72h), the specimens were taken out from the water bath and weighed after removing the surface water with a wet towel. After the measurement, the specimens were immediately put back into the water bath. The test was done in an air-conditioned room with a temperature of 20^°C and a relative humidity of 60%. The amount of water absorbed per unit (cm²) after certain time can be obtained using the following equation: q_t = (Q_t-Qo)/S

where:

q_t is the amount of water absorbed per unit after certain time, in g/cm²;

Q_t is the weight of the specimens at time t; Qo is the weight of the specimen at time 0;

S is the contact area with water, in cm².

Saturated water absorption test: After the capillary water absorption test, the concrete slices were taken out from the water bath and put in the 40 ^°C oven until weight changes were less than 0.1 % at 24 h intervals. Subsequently, the completely dry specimens were subjected to the vacuum saturation test (NBN B 24-213). The specimens in dry state were placed in a container and were subjected to vacuum for 3h and then de-ionized water was added into the container till the specimens were completely immersed. The vacuum was maintained during water addition and lasted 1 h more at constant water level. After the vacuum was stopped, the specimens were kept submersed for another 12h. The final weight of the water saturated specimens was measured. The saturated water absorption was calculated by the following formula.

where:

W_s: saturated water absorption ratio

W_d: dry weight of the specimen

W_w: wet weight of the water saturated specimen q) Influence of microcapsules on cement hydration

To investigate the influence of the microcapsules on cement hydration, hydration heat production was measured for various concrete samples prepared as described below. Hydration heat production is used as an indicator for hydration degree. Three kinds of cement paste mixtures of the same water to cement ratio (0.5) were made: a reference cement paste R, and cement pastes with μ-capsules (3%), μ-capsules (5%), respectively. The dosage of the additives was versus cement weight. The hydration heat production (at 20°C) was determined by a TAM AIR isothermal heat conduction calorimeter. The results are shown in Figure 14. It can be seen that the addition of microcapsules delayed somewhat the appearance of the second hydration peak, the higher dosage used, more delay was observed. However, the cumulative heat production after 7 days was quite similar for R, μ-capsule 3% and μ-capsule 5%, i.e. in the range of 355-364 J/g. Thus, the difference is not significant. It can be concluded that the microcapsules have no adverse effect on cement hydration. Further embodiments of the invention

In a further aspect, the present invention provides microparticles, for inclusion in concrete, concrete-based material and concrete-like material, adapted to reduce, or to assist in the reduction of, the area of a defect in said material once a quantity of said microparticles has fractured or is exposed at an interface of the defect, said microparticles each comprising:

a core, in the form of a porous solid and/or a liquid, having carbonatogenic bacterial spores and/or bacterial nutrients dissolved and/or dispersed therein. Thus the core may be a porous solid, in which case it may or may not be provided with a surrounding shell, i.e. there may be a shell which surrounds the porous solid core, or the core may be a liquid, it which case it may be provided with a surrounding shell, i.e. the shell may encapsulate the liquid core therein. Alternatively, the core may be a porous solid having liquid present in substantially all of its pores, surrounding which there may be provided a surrounding shell.

For the avoidance of any doubt, said core may have carbonatogenic bacterial spores dispersed therein in the absence of any bacterial nutrients (which may be provided in the concrete or like material from another source), or said core may have bacterial nutrients dispersed and/or dissolved therein in the absence of any bacterial spores (which may be provided in the concrete or like material from another source), or said core may have both bacterial spores and bacterial nutrients dissolved and/or dispersed therein. Once released, the bacterial nutrients are readily available to act with atmospheric oxygen and ambient water to enable germination of the bacterial spores to form vegetative bacteria, thus facilitating calcium carbonate production, as will described in more detail later in the specification

The "other source" of bacterial nutrients includes other microparticles containing said nutrients and naturally occurring, environmental nutrients found in situ. The "other source" of carbonatogenic bacterial spores includes other microparticles containing said spores and naturally occurring, environmental spores found in situ.

A "microparticle" as described herein is a particle with dimensions from 1 x 10^~7 m to less than 1 x 10^~3 m, i.e. from 0.1 to less than 1000 μιη, which may be spherical or non- spherical. Such microparticles have the ability, once included in a concrete or like material composition, to reduce, or assist in the reduction of, the area of a defect, such as a crack or an indentation therein, once a quantity of said microparticles has fractured. Fracture of the microparticles is achieved by locally induced internal stress in the concrete around the area of the defect, however, an external influence such as force or increased/decreased temperature, may be applied in addition to the internal stress to act on the inherent friability of the microparticles to achieve fracture. Once fractured, the relevant microparticles will release their dissolved and/or dispersed contents, thus facilitating repair of the defect in as timely a manner as possible to provide a compatible and durable solution.

In embodiments, said microparticles have a core provided with a surrounding shell. In embodiments, the core is a porous solid having liquid present in substantially all of its pores.

In embodiments, the core comprises a silica-based material. In embodiments, the core comprises a carbohydrate-based material.

In a further aspect is provided a concrete composition comprising:

a cementitious material, one or more aggregate materials, a liquid binder and a quantity of microparticles as described above.

In a still further aspect is provided a method of reducing the area of a defect in concrete, concrete-based material and/or concrete-like material comprising the steps of:

(i) providing a concrete, concrete-based material and/or concrete-like material composition, such as described above, incorporating a quantity of microparticles as described above;

(ii) setting the composition; and

(iii) causing at least some of said quantity of microparticles to fracture in response to the creation and/or worsening of a defect in said set composition, thereby releasing their contents to effect defect reduction.

In the further aspects and embodiments above, the microparticles may be microcapsules according to any aspect or embodiment of the invention as described herein. In the further aspects and embodiments above, the composition containing the microparticles may be as defined for any of the above aspects and embodiments containing microcapsules (i.e. wherein said microcapsules are microparticles as described above), In the method above, the method steps may be as defined according to methods relating to microcapsules as disclosed above (i.e. wherein said microcapsules are microparticles as described above),

Claims

Microcapsules, for inclusion in concrete, adapted to reduce the area of a defect in said concrete once a quantity of said microcapsules has ruptured or is exposed at an interface of the defect, said microcapsules each comprising: a polymeric shell encapsulating a liquid core,

wherein at least one of the following criteria (i)-(iii) is fulfilled:

(ii) said bacterial spores are in the form of a microorganism that is capable of reducing the area of the defect by means of mineral or extracellular polymeric substance ("EPS") production, and are preferably selected from the group of bacteria consisting of: Bacillus cereus, Bacillus subtilis, Bacillus sphaericus, Bacillus lentus, Bacillus pasteu i, Bacillus megaterium, Bacillus cohnii, Bacillus halodurans, Bacillus pseudofirmas, Myxococcus Xanthus and mixtures thereof, and/or

(iii) said liquid is a non-aqueous, water-immiscible liquid selected from the group consisting of: organic oils, mineral oils, silicone oils, fluorocarbons, fatty acids, plasticizers, esters and mixtures thereof, such that, when a quantity of said microcapsules is present in concrete, the area of the defect therein is reducible by at least 45 % as compared to an initial area of the defect once at least some of said quantity of microcapsules have been ruptured.

Microcapsules as claimed in claim 1 wherein any two of the three criteria (i)-(iii) are fulfilled.

Microcapsules as claimed in claim 2 wherein all three of criteria (i)-(iii) are fulfilled. Microcapsules as claimed in any preceding claim wherein, in each microcapsule, the concentration of the bacterial spores is at least 10⁹ spores per gram (dry weight) of microcapsule.

wherein, in each microcapsule, the concentration of the bacterial spores is at least 10⁹ spores per gram (dry weight) of microcapsule,

such that, when a quantity of said microcapsules is present in concrete, the area of the defect therein is reducible by at least 45 % as compared to an initial area of the defect once at least some of said quantity of microcapsules have been ruptured.

Microcapsules as claimed in any preceding claim wherein the liquid core further comprises bacterial nutrients.

Microcapsules as claimed in claim 7 wherein, when a quantity of said microcapsules is present in concrete, the area of the defect therein is reducible by at least 45 % as compared to an initial area of the defect once at least some of said quantity of microcapsules have been ruptured.

Microcapsules as claimed in any of claims 1 -6 and 8 wherein the area of the defect in the concrete is reducible by at least 50 %, preferably by at least 60 %, further preferably by at least 70 % and most preferably by at least 80 % as compared to the initial area of said defect once at least some of said quantity of microcapsules have been ruptured.

Microcapsules as claimed in any of claims 1 -6, 8 and 9 wherein the reducible area of the defect is determined after 4 weeks of continuous wet-dry cycling, in which the wet phase comprises immersion of the concrete in water for 16 hours, followed by the dry phase of leaving the concrete in air (at 20 °C at 60 % relative humidity) for 8 hours.

Microcapsules as claimed in claim 5 or claim 7 wherein the polymer layer comprises a polymer selected from the group consisting of: gelatines, polyurethanes, polyolefins, polyamides, polysaccharides, silicone resins, epoxy resins, chitosan, aminoplast resins and derivatives and mixtures thereof.

Microcapsules as claimed in any of claims 5, 7 or 1 1 wherein the bacterial spores are in the form of a microorganism that is capable of reducing the area of the defect by means of mineral or extracellular polymeric substance ("EPS") production, and are preferably selected from the group of bacteria consisting of: Bacillus cereus, Bacillus subtilis, Bacillus sphaericus, Bacillus lentus, Bacillus pasteuni, Bacillus megatenum, Bacillus cohnii, Bacillus halodurans, Bacillus pseudofirmas, Myxococcus Xanthus and mixtures thereof.

Microcapsules as claimed in any of claims 5, 7, 1 1 or 12 wherein the liquid is selected from the group consisting of: organic oils, mineral oils, silicone oils, fluorocarbons, fatty acids, plasticizers, esters and mixtures thereof.

14. Microcapsules as claimed in claim 1 or claim 1 1 wherein the polymer layer comprises a polymer is selected from the group consisting of: vinyl polymers, acrylate polymers, acrylate-acrylamide copolymers, melamine-formaldehyde polymers, urea-formaldehyde polymers and mixtures and derivatives thereof.

15. Microcapsules as claimed in claim 14 wherein the polymer layer comprises melamine formaldehyde resin.

16. Microcapsules as claimed in any of claims 1 , 1 1 , 14 or 15 wherein the polymer layer comprises reactive functional groups, extending outwardly of the microcapsule, whereby the microcapsule is chemically bondable within the concrete.

Microcapsules as claimed in claim 16 wherein a reactive functional group comprises a reactive moiety adapted to provide covalent bonding within the concrete.

Microcapsules as claimed in claim 1 or claim 12 wherein the bacterial spores are selected from the group of bacteria consisting of: Bacillus sphaericus, Bacillus pasteu i and Bacillus cohnii.

Microcapsules as claimed in claim 1 or claim 13 wherein the liquid is a silicone oil.

Microcapsules as claimed in any preceding claim each having an average diameter of greater than 0.5 μιη, preferably greater than 1 μιη.

Microcapsules as claimed in any preceding claim wherein the bacterial spores dispersed in the liquid together amount to 40-70 % by volume of the volume within the polymeric shell of each microcapsule.

Microcapsules as claimed in any preceding claim wherein the bacterial spores amount to at least 1 %, preferably at least 2 %, by volume of the volume of the liquid within each microcapsule.

Microcapsules as claimed in claim 6 or claim 7 wherein the bacterial nutrients comprise one or more of: urea, a suitable carbon and nitrogen source, such as nutrient broth, yeast, yeast extract, organic oil and a suitable source of calcium, such as hydrated calcium nitrate, calcium chloride, calcium acetate or calcium lactate.

A concrete composition comprising:

a cementitious material, one or more aggregate materials, a liquid binder and a quantity of microcapsules as claimed in claim 1 or claim 5, whereby, once set into concrete, the area of a defect therein is reducible by at least 45 % as compared to an initial area of the defect once at least some of said quantity of microcapsules have been ruptured.

25. A concrete composition comprising:

a cementitious material, one or more aggregate materials, a liquid binder and a quantity of microcapsules as claimed in claim 7.

A concrete composition as claimed in claim 25 wherein, once set into concrete, the area of a defect therein is reducible by at least 45 % as compared to an initial area of the defect once at least some of said quantity of microcapsules have been ruptured.

A concrete composition as claimed in claim 24 or 26 wherein the area of the defect in the concrete is reducible by at least 50 %, preferably by at least 60 %, further preferably by at least 70 % and most preferably by at least 80 % as compared to the initial area of said defect once at least some of said quantity of microcapsules have been ruptured.

A concrete composition as claimed in any of claims 24, 26 and 27 wherein the reducible area of the defect is determined after 4 weeks of continuous wet-dry cycling, in which the wet phase comprises immersion of the concrete in water for 16 hours, followed by the dry phase of leaving the concrete in air (at 20 °C at 60 % relative humidity) for 8 hours.

A concrete composition as claimed in any of claims 24 to 28 wherein the quantity of microcapsules comprised in the composition, based on their dry weight, is in the range of 1 % to 10 %, preferably 2 % to 8 %, by weight of the cementitious material.

A concrete composition as claimed in any of claims 24 to 29 wherein the microcapsules are added to the composition in the form of an emulsion having the microcapsules dispersed therein.

A concrete composition as claimed in claim 30 wherein the emulsion is a water- based emulsion.

32. A concrete composition as claimed in any of claims 24 to 31 further comprising bacterial nutrients. A concrete composition as claimed in claim 32 wherein the bacterial nutrients are incorporated by any one or more of the following means: by direct admixture into the composition, by admixture of a quantity of different microcapsules containing the nutrients, by admixture of a hydrogel or other such suitable carrier, e.g. porous aggregate, clays or diatomaceous earth, containing the nutrients.

A concrete composition as claimed in claims 32 or 33 wherein the quantity of bacterial nutrients comprised in the composition is in the range of 10 % to 20 %, preferably 12 % to 18 %, by weight of the cementitious material.

A concrete composition as claimed in any of claims 24 to 34 wherein the ratio of cementitious material to aggregate material to water is in the ranges of (0.5 to 1 .5) : (1 to 15) : (0.1 to 1 ), preferably 1 : 5 : 0.5.

A method of reducing the area of a defect in concrete, concrete-based material and/or concrete-like material comprising the steps of:

(i) providing a concrete, concrete-based material and/or concrete-like material composition as claimed in any of claims 24 to 35 incorporating a quantity of microcapsules;

(ii) setting the composition; and

(iii) causing at least some of said quantity of microcapsules to rupture in response to the creation and/or worsening of a defect in said set composition, thereby releasing their encapsulated contents to effect defect reduction.

Microcapsules, for inclusion in concrete, adapted to reduce the area of a defect in said concrete once a quantity of said microcapsules has ruptured substantially as hereinbefore described.

A concrete composition substantially as hereinbefore described.

39. A method of reducing the area of a defect in concrete substantially as hereinbefore described.