U.S. patent application number 14/771963 was filed with the patent office on 2016-01-14 for microcapsules and concrete containing the same.
The applicant listed for this patent is DEVAN CHEMICALS NV, UNIVERSITEIT GENT. Invention is credited to Nele DE BELIE, Maxime DURKA, Hugo SOENS, Jianyun WANG.
Application Number | 20160009596 14/771963 |
Document ID | / |
Family ID | 48142259 |
Filed Date | 2016-01-14 |
United States Patent
Application |
20160009596 |
Kind Code |
A1 |
SOENS; Hugo ; et
al. |
January 14, 2016 |
MICROCAPSULES AND CONCRETE CONTAINING THE SAME
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 micro-capsules 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.
Inventors: |
SOENS; Hugo; (Kaster,
BE) ; DE BELIE; Nele; (Brakel, BE) ; WANG;
Jianyun; (Gent, BE) ; DURKA; Maxime; (Ronse,
BE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DEVAN CHEMICALS NV
UNIVERSITEIT GENT |
Ronse-Renaix
Gent |
|
BE
BE |
|
|
Family ID: |
48142259 |
Appl. No.: |
14/771963 |
Filed: |
March 3, 2014 |
PCT Filed: |
March 3, 2014 |
PCT NO: |
PCT/EP2014/054100 |
371 Date: |
September 1, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13962638 |
Aug 8, 2013 |
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14771963 |
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Current U.S.
Class: |
435/182 ;
106/674; 106/677; 106/802; 106/823; 524/597; 524/6 |
Current CPC
Class: |
C04B 20/1029 20130101;
C04B 40/0675 20130101; C12N 1/20 20130101; C04B 20/1033 20130101;
C04B 2103/0001 20130101; C04B 24/00 20130101; C12N 11/04 20130101;
C04B 20/1029 20130101; C04B 2103/0001 20130101; C04B 20/1033
20130101; C04B 2103/0001 20130101; C04B 40/0675 20130101; C04B
28/02 20130101; C04B 40/0641 20130101 |
International
Class: |
C04B 24/00 20060101
C04B024/00; C12N 11/04 20060101 C12N011/04; C04B 40/06 20060101
C04B040/06 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 1, 2013 |
GB |
1303690.0 |
Aug 8, 2013 |
GB |
1314220.3 |
Claims
1.-39. (canceled)
40. Microparticles, for inclusion in a concrete, concrete-based, or
concrete-like material, said microparticles each comprising: a
core, in the form of a porous solid and/or a liquid; carbonatogenic
bacterial spores dissolved and/or dispersed in the core, wherein
said microparticles are adapted to reduce, or to assist in the
reduction of, the area of a defect in said material by
carbonatogenesis by the carbonatogenic bacteria once a quantity of
said microparticles has fractured or is exposed at an interface of
the defect.
41. Microparticles as claimed in claim 40, further comprising: a
shell surrounding the core.
42. Microparticles as claimed in claim 41 wherein the core of each
of the microparticles comprises the porous solid.
43. Microparticles as claimed in claim 42, wherein liquid is
present in substantially all of the pores of the porous solid, and
the carbonatogenic bacterial spores are dispersed in the liquid and
bacterial nutrients are dispersed or dissolved in the liquid.
44. Microparticles as claimed in 41, wherein the shell further
comprises a polymer layer, the polymer further comprising melamine
formaldehyde resin, the polymer having reactive functional groups,
extending outwardly of the microparticle, whereby the microparticle
is chemically bondable within the material.
45. Microparticles as claimed in claim 42 wherein the porous solid
of each of the microparticles comprises a silica-based material or
a carbohydrate-based material.
46. Microparticles according to claim 40, wherein the
microparticles are 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 the polymeric
shell comprises a substantially impermeable polymer layer and the
liquid core comprises carbonatogenic bacterial spores dispersed in
a liquid, and 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.
47. A concrete, concrete-based, or concrete-like composition,
comprising: a cementitious material; one or more aggregate
materials; a liquid binder; and a quantity of microparticles as
claimed in claim 40.
48. The composition of claim 47, wherein the core of each the
microparticles is provided with a surrounding shell.
49. The composition of claim 48, wherein the core of each of the
microparticles comprises the porous solid.
50. The composition of claim 49, wherein liquid is present in
substantially all of the pores of the porous solid, and the
carbonatogenic bacterial spores are dispersed in the liquid and
bacterial nutrients are dispersed or dissolved in the liquid.
51. The composition of claim 48, wherein the shell further
comprises a polymer layer, the polymer further comprising melamine
formaldehyde resin, the polymer having reactive functional groups,
extending outwardly of the microparticles, whereby the
microparticles are chemically bonded to the cementitious
material.
52. The composition as claimed in claim 49 wherein the porous solid
of each of the microparticles comprises a silica-based material or
a carbohydrate-based material.
53. The composition as claimed in claim 49 wherein the
microparticles are microcapsules adapted to reduce the area of a
defect in the composition 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 dispersed in a liquid, and wherein,
in each microcapsule, the concentration of the bacterial spores is
at least 109 spores per gram (dry weight) of microcapsule, such
that the area of the defect in the composition 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.
54. A method of reducing the area of a defect in a concrete,
concrete-based, or concrete-like material, the method comprising:
providing a composition as claimed in claim 47; setting the
composition; and 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; effecting defect
reduction in said set composition by release of the contents of the
quantity of microparticles followed by carbonatogenesis by the
carbonatogenic bacteria.
55. The method of claim 54, wherein each of the microparticles is
provided with a surrounding shell.
56. The method of claim 55, wherein the core of each of the
microparticles comprises the porous solid.
57. The method of claim 56, wherein liquid is present in
substantially all of the pores of the porous solid, and the
carbonatogenic bacterial spores are dispersed in the liquid and
bacterial nutrients are dispersed or dissolved in the liquid.
58. The method as claimed in claim 54 wherein the porous solid of
each of the microparticles comprises a silica-based material.
59. The method as claimed in claim 54 wherein the porous solid of
each of the microparticles comprises a carbohydrate-based material.
Description
[0001] 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.
[0002] 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.
[0003] 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.
[0004] 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
(CO.sub.2) from the surrounding atmosphere may dissolve in water to
generate carbonate anions (CO.sub.3.sup.2-) in the alkaline
environment of the concrete (the pH of concrete is around
12.5.about.13). Free dissolved calcium cations (Ca.sup.2+) 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.
[0005] 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.
[0006] 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.
[0007] 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.
[0008] First Aspect
[0009] 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:
[0010] a polymeric shell encapsulating a liquid core,
[0011] wherein the polymeric shell comprises a substantially
impermeable polymer layer and the liquid core comprises
carbonatogenic bacterial spores dispersed in a liquid, and
[0012] wherein at least one of the following criteria (i)-(iii) is
fulfilled: [0013] (i) said polymer layer comprises a polymer
selected from the group consisting of: gelatines, polyurethanes,
polyolef ins, polyamides, polysaccharides, silicone resins, epoxy
resins, chitosan, aminoplast resins and derivatives and mixtures
thereof, and/or [0014] (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 pasteurii, Bacillus
megaterium, Bacillus cohnii, Bacillus halodurans, Bacillus
pseudofirmas, Myxococcus Xanthus and mixtures thereof, and/or
[0015] (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.
[0016] 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.
[0017] 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 U.S. Pat. No.
3,870,542, U.S. Pat. No. 3,415,758 and U.S. Pat. No. 3,041,288.
[0018] 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 10.sup.4 microcapsules per cm.sup.2 of defect area, and
generally of the order of 10.sup.6 microcapsules per cm.sup.2 of
defect area) are required to rupture.
[0019] 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 10.sup.9 spores per
gram (dry weight) of microcapsule.
[0020] Second Aspect
[0021] 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: [0022] a polymeric shell encapsulating a liquid core,
[0023] wherein the polymeric shell comprises a substantially
impermeable polymer layer and the liquid core comprises
carbonatogenic bacterial spores dispersed in a liquid, and [0024]
wherein, in each microcapsule, the concentration of the bacterial
spores is at least 10.sup.9 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.
[0025] The liquid in which the bacterial spores are dispersed may
preferably be a non-aqueous, water-immiscible liquid.
[0026] 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.
[0027] 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.
[0028] Third Aspect
[0029] 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:
[0030] a polymeric shell encapsulating a liquid core, [0031]
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.
[0032] 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.
[0033] 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.
[0034] 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
10.sup.9 spores per gram (dry weight) of microcapsule.
[0035] Fourth Aspect
[0036] 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: [0037] a porous solid core, comprising a silica-based
material, having bacterial nutrients dispersed therein.
[0038] 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.
[0039] 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.
[0040] 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.
[0041] Fifth Aspect
[0042] 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:
[0043] a porous solid core, comprising a carbohydrate-based
material, having carbonatogenic bacterial spores and/or bacterial
nutrients dissolved and/or dispersed therein.
[0044] 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.
[0045] 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.
[0046] 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).
[0047] Reducible Defect Area
[0048] 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.
[0049] 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 .degree. 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.
[0050] Polymer Layer
[0051] 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.
[0052] 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.
[0053] 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.
[0054] Microcapsules made from aminoplast polymer shell materials
can be made by an interfacial polymerization process, such as is
described in U.S. Pat. No. 3,516,941: 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.degree. C. and 90.degree. 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.
[0055] 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.
[0056] Silica-Based Materials
[0057] 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.sup.lM
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.
[0058] Many of these types of sol-gel microcapsules are further
described and exemplified in EP2335818 A1, U.S. Pat. No. 7,255,874
and U.S. Pat. No. 6,303,149.
[0059] 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.
[0060] By way of example, the following describes the preparation
of ORMOSIL microparticles and/or microcapsules containing bacterial
nutrients using a sol-gel process: [0061] 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;
[0062] dissolve from 0.01 g to 1 g of a polyethylene glycol
sorbitan monooleate surfactant (such as, for example TWEEN.sup.TM
80) in the above aqueous mixture; [0063] optionally add a water
suspended solution of colloidal silica nanoparticles (such as
Ludox.sup.lM colloidal silica series), from 0 wt % to 10 wt % of
the total silica content, to the above aqueous mixture; [0064]
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.sup.TM 80); [0065] emulsify the resultant biphasic
mixture with vigorous agitation until the desired emulsion is
reached; [0066] dropwise, add from 1 to 4 mL of a commercial TEOS
solution to the above emulsion whilst mixing; [0067] continue to
stir at room temperature for the desired period of condensation
(from 1 to 24h); [0068] filter and wash (with previous organic
solvents) the resultant silica-based microparticles and/or
microcapsules to remove the remaining surfactants, then dry.
[0069] Carbohydrate-Based Materials
[0070] 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.TM. 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.
[0071] Many of these types of alginate microspheres are further
described and exemplified in U.S. Pat. No. 5,766,907 A, U.S. Pat.
No. 5,508,041 A and WO1991/009119A1.
[0072] 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.
[0073] 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: [0074]
dissolve from 0.1 g to 5 g of urea in 4 mL of water; [0075] added
from 1 to 5 wt % of sodium alginate powder to the above and stir
the mixture until a homogeneous viscous liquid is obtained; [0076]
dropwise, add the above mixture to a calcium-containing solution
(preferably of calcium nitrate (for example 25 g/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; [0077] filter and dry the
resultant alginate-based microparticles and/or microcapsules.
[0078] 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.
[0079] Bacterial Spores
[0080] 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-
(CO.sub.3.sup.2-) and bicarbonate- (HCO.sub.3.sup.-) 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.
[0081] 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.
[0082] Liquid
[0083] 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.
[0084] It is preferred that the liquid is a silicone oil,
preferably having a kinematic viscosity of 500 centistokes
(mm.sup.2/sec) or less, preferably 350 centistokes (mm.sup.2/sec)
or less at 25.degree. C.
[0085] Size & Content
[0086] Microcapsules according to any of the aforementioned aspects
of the invention may each have average dimensions in the range of
from 1.times.10.sup.-7 m to less than 1.times.10.sup.-3 m, i.e.
from 0.1 to less than 1000 .mu.m, which may be spherical or
non-spherical. Preferably, microcapsules may have an average
diameter greater than 0.5 .mu.m, preferably greater than 1 .mu.m.
The average diameters of the microcapsules may, for example, fall
in the range of from 0.5 to 900 .mu.m, of from 0.5 to 500 .mu.m, or
of from 1 to 100 .mu.m.
[0087] 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.
[0088] 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.
[0089] Bacterial Nutrients
[0090] 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(NH.sub.2).sub.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(NO.sub.3).sub.2.4H.sub.2O), calcium
chloride, calcium acetate, calcium lactate and the like.
[0091] 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.
[0092] 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.
[0093] 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.
[0094] 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.
[0095] 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.
[0096] 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/cm.sup.2 or less,
suitably 0.22 g/cm.sup.2 or less, such as 0.20 g/cm.sup.2 or less,
preferably 0.15 g/cm.sup.2 or less, more preferably 0.13 g/cm.sup.2
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.
[0097] 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.
[0098] 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 concrete-like material in
the composition. Saturated water absorption may be calculated as
described in the examples section.
[0099] 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.
[0100] Sixth Aspect
[0101] Accordingly, a sixth aspect of the present invention
provides a concrete, concrete-based material and concrete-like
material composition comprising: [0102] 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, [0103] 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.
[0104] Seventh Aspect
[0105] An seventh aspect of the present invention provides a
concrete, concrete-based material and concrete-like material
composition comprising: [0106] 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.
[0107] Eighth Aspect
[0108] 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: [0109] (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; [0110]
(ii) setting the composition; and [0111] (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.
[0112] 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.
[0113] 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.
[0114] 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 10.sup.4 microcapsules per cm.sup.2 of defect area, and
generally of the order of 10.sup.6 microcapsules per cm.sup.2 of
defect area are required to rupture.
[0115] 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.
[0116] Without wishing to be bound by any theory, the repair
mechanism is thought to follow the following pathway: [0117] (1)
Rupture of microcapsule.fwdarw.release of bacterial spores, for
exposure to germination activators: oxygen, water and bacterial
nutrients [0118] (2) Germination of bacterial
spores.fwdarw.production of vegetative bacterial cells for use in
hydrolysis [0119] (3) Precipitation of calcium carbonate for defect
repair via: [0120] (a)
CO(NH.sub.2).sub.2+2H.sub.2O.fwdarw.2NH.sub.4.sup.++CO.sub.3.sup.2-[catal-
yzed by bacterial urease] [0121] (b)
Ca.sup.2++CO.sub.3.sup.2-.fwdarw.CaCO.sub.3
[0122] 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 CO.sub.3.sup.2- and NH.sub.3/NH.sub.4.sup.+ by
the germinated bacteria (catalyzed by bacterial urease) under
alkaline pH. When CO.sub.3.sup.2- ions meet with Ca.sup.2+ ions
(e.g. from calcium nitrate), CaCO.sub.3 is formed.
[0123] 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.
[0124] 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.
[0125] 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 .degree. 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.
[0126] 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.
[0127] 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.
[0128] 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.
[0129] 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
concrete-like 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.
[0130] In particular embodiments, the compositions (such as
described in aspects and embodiments above) have a capillary water
absorption of 0.25 g/cm.sup.2 or less, suitably 0.22 g/cm.sup.2 or
less, such as 0.20 g/cm.sup.2 or less, preferably 0.15 g/cm.sup.2
or less, more preferably 0.13 g/cm.sup.2 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.
[0131] 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.
[0132] 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.
[0133] Suitably, the compositions of the above aspect and
embodiments may exhibit hydration levels similar to those exhibited
by compositions devoid of microcapsules.
[0134] Microcapsule Dosage
[0135] 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.
[0136] 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.
[0137] Bacterial Nutrients
[0138] 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.
[0139] The bacterial nutrients may be thus incorporated into the
composition by any one or more of the following means: [0140] by
direct admixture into the composition; [0141] by admixture of a
quantity of different microcapsules containing the nutrients;
[0142] by admixture of a hydrogel or other such suitable carrier,
e.g. porous aggregate, clays or diatomaceous earth, containing the
nutrients.
[0143] 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.
[0144] Concrete Ingredients
[0145] 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.
[0146] 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.
[0147] In a concrete composition according to the sixth and seventh
aspects of the invention, the liquid binder is preferably
water.
[0148] 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.
[0149] 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:
[0150] FIG. 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 (mm.sup.2) compared to final
crack area (mm.sup.2) after being subjected to different incubation
conditions (1) to (5);
[0151] FIG. 2 is a plot of the absolute value of healed crack area
(mm.sup.2) for the cement samples shown in FIGS. 1(a) to 1(f) for
incubation conditions (1) to (5);
[0152] FIG. 3 is a plot of the healing ratio for the cement samples
shown in FIGS. 1(a) to 1(f) and FIG. 2 for incubation conditions
(1) to (5);
[0153] FIG. 4 is a scanning electron microscope (SEM) micrograph of
a quantity of aminoplast microcapsules according to one embodiment
of the invention;
[0154] FIG. 5 is an SEM micrograph of the quantity of aminoplast
microcapsules shown in FIG. 4 but at greater magnification;
[0155] FIG. 6 is an SEM micrograph of a quantity of silica-based
material microcapsules according to another embodiment of the
invention;
[0156] FIG. 7 is an SEM micrograph of an alginate microparticle
according to a further embodiment of the invention;
[0157] FIG. 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
[0158] FIG. 9 is a series of plots (a) to (c) showing the degree of
bacterial spore germination under different temperature conditions
(28.degree. C., 20.degree. C. and 10.degree. 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.
[0159] FIG. 10 shows microscopy images taken before (FIG. 10a) and
after (FIG. 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).
[0160] FIG. 11 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).
[0161] FIG. 12 shows the capillary water absorption data in
g/cm.sup.2 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).
[0162] FIG. 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).
[0163] FIG. 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.
[0164] FIG. 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
[0165] a) Self -Healing Tests
[0166] 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
10.sup.9 spores per gram (dry weight) of microcapsule.
TABLE-US-00001 TABLE 1 Bacterial Microcapsule Dry Weight of Cement
Sand Water Nutrients Emulsion Microcapsules Bacterial Group (g) (g)
(g) (g) (g) (g) Spores? R 450 1350 225 0 0 0 N N 450 1350 214 57.84
0 0 N C 450 1350 212.4 0 26.1 13.5 N NC 450 1350 201.4 57.84 26.1
13.5 N NCS 450 1350 192.8 57.84 34.7 13.5 Y 3% NCS 450 1350 178.7
57.84 57.84 22.5 Y 5%
[0167] 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.
[0168] For each of the six composition groups, five long reinforced
prisms (having dimensions of 30.times.30.times.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.degree. C.,
>90% RH). The specimens in control
[0169] 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.
[0170] 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.
[0171] After crack creation, the long reinforced prisms were
subjected to five incubation conditions: [0172] (1) 20.degree. C.,
>90% RH [0173] (2) full and continuous immersion in water [0174]
(3) full and continuous immersion in a deposition medium [0175] (4)
continuous wet-dry cycling with water [0176] (5) continuous wet-dry
cycling with the deposition medium.
[0177] The deposition medium was composed of 0.2 M urea and 0.2 M
Ca(NO.sub.3).sub.2.
[0178] 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.degree. 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.
[0179] The cracks formed in each specimen, per incubation
condition, were identified and counted; the results are shown in
Table 2 below.
TABLE-US-00002 TABLE 2 Total No. No. of Cracks per Surface of
Cracks Incubation Surface Surface Surface per Group Condition A B C
Surface 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
[0180] Initial optical microscope images of the cracks in the
specimens were taken immediately after multiple cracking. Each
crack was divided into 10-11 portions by pencil markers to make
sure the whole crack would be photomicrographed with minimal
overlap of the area among the images.
[0181] 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.sup.TM image analysis program.
[0182] 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 .mu.m to 900 .mu.m.
[0183] 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.sub.h).
[0184] 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.
r = A i - A f A i .times. 100 % ##EQU00001##
where: [0185] "r" is the crack healing ratio [0186] "A.sub.i" is
the initial crack area (mm.sup.2) [0187] "A.sub.1" is the final
crack area (mm.sup.2)
[0188] 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.sub.i) and
total final (A.sub.1) crack area, which is shown in accompanying
FIG. 1.
[0189] As shown in FIG. 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.degree. 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.sub.i) being represented by the left hand bar
in each pair, and the total final crack area (A.sub.1) being
represented by the right hand bar in each pair.
[0190] The absolute value of the healed crack area (A.sub.h) shown
in FIG. 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 FIG. 3.
[0191] 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.sub.h) varied from 12.6
mm.sup.2 to 57.8 mm.sup.2 depending on the specific specimen and
its incubation condition.
[0192] Compared with the specimens without encapsulated bacteria,
those with microencapsulated bacteria showed much higher healing
efficiency (r). The healed crack area (A.sub.h) varied from 49.3
mm.sup.2 to 80 mm.sup.2. 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
mm.sup.2) 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.
[0193] The crack healing ratio (r) in each specimen of the
different series is shown in FIG. 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).
[0194] 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).
[0195] 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 mm.sup.2 to
57.8 mm.sup.2 while the bacterial-containing groups (NCS3% and
NCS5%) had 49.3 mm.sup.2 to 80 mm.sup.2 of the crack area healed.
The maximum crack width healed in the specimens of the
bacterial-containing groups was 970 .mu.m, which was much wider
than that in the specimens of non-bacterial groups (maximum 250
.mu.m).
[0196] The micrograph of FIG. 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 FIG. 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.
[0197] The SEM micrographs of FIGS. 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.
[0198] b) Nutrient Effects on Spore Germination/Outgrowth
[0199] The plots shown in FIGS. 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.
[0200] FIG. 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.
[0201] c) Temperature/Nutrient Concentration Effects on Spore
Germination/Outgrowth
[0202] FIGS. 9(a), 9(b) and 9(c) show the variation in germination
of B. sphaericus spores at different temperatures (28.degree. C.,
20.degree. C. and 10.degree. 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 FIG. 9(a), at 28.degree. 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.degree. C. exhibited
similar germination behaviour to those at 28.degree. C., as shown
in FIG. 9(b).
[0203] The revival of spores` ureolytic activity was much slower at
10.degree. C., as shown in FIG. 9(c). In the media with 20 g/L YE,
about 3.about.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.about.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 21st 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.
[0204] 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 CaCO.sub.3.sup.-,
however precipitation formation was much slower, and that the
process only happened at moderate temperatures (20.degree.
C.-28.degree. C., not at low temperatures).
[0205] d) Survival of Microcapsules in Concrete
[0206] 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/m.sup.3.
TABLE-US-00003 TABLE 3 Composition of the concrete mixture Per
batch Per m.sup.3 Abs v m Volume (40 L) kg (kg/m.sup.3) (m.sup.3)
kg Sand 0/4 730.00 2650 0.275 29.2 Aggregate 2/8 526.00 2650 0.198
21.04 Aggregate 8/16 686.00 2650 0.259 27.44 CEM I 52.5 N 300.00
3100 0.097 12.00 Water 150.00 1000 0.15 6.00
[0207] 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 3-20 .mu.m.
[0208] 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-US-00004 TABLE 4 Compositions of the concrete with or without
microcapsules Super- Micro- Sand CEMI plasticizer Micro- capsule
0/4 Aggregate Aggregate 52.5N H.sub.2O (mL/kg capsule emulsion (kg)
2/8 (kg) 8/16 (kg) (kg) (kg) cement) (kg) (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
[0209] Microscopy images illustrated in FIG. 10 were taken before
(FIG. 10a) and after (FIG. 10b) the mixing. It can be seen that
after being mixed in concrete, most microcapsules survived the
mixing process.
[0210] e) Concrete Strength--Bending Test
[0211] 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 FIG. 11. It can be seen that
inclusion of the microcapsules did not substantially affect the
tensile strength.
[0212] The bending test was conducted as follows: The concrete
prisms (100 mm.times.100 mm.times.500 mm) were subjected to a
three-point bending test based on the standard NBN EN 12390-5
(2009). As shown in FIG. 15, the span between two support rollers
was 320 mm. The load was applied in the center of the specimen by
means of a server hydraulic jack with maximum load capacity of 100
kN.
[0213] The loading rate was determined by the formula:
R = 2 .times. s .times. d 1 .times. d 2 2 3 .times. I
##EQU00002##
[0214] where
[0215] R is the required loading rate, in N/s;
[0216] s is the stress rate, in MPa/s (N/mm.sup.2.s);
[0217] d.sub.1 and d.sub.2 are the lateral dimensions of the
specimen, in mm;
[0218] l is the distance between the supporting rollers, in mm;
and
[0219] the flexural (i.e. bending) strength is calculated by the
following equation:
f cf = 3 .times. F .times. I 2 .times. d 1 .times. d 2 2
##EQU00003##
[0220] where:
[0221] f.sub.cf is the flexural (i.e. bending) strength, in MPa
(N/mm.sup.2);
[0222] F is the maximum load, in N;
[0223] l is the distance between the supporting rollers, in mm;
[0224] d.sub.1 and d.sub.2 are the lateral dimensions of the
specimen, in mm;
[0225] f) Water Absorption Test
[0226] 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 FIGS. 12 and 13. As seen
in FIGS. 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.
[0227] Capillary water absorption test: A modified capillary water
absorption test based on RILEM 25 PEM 11-6 (NBN B 24-213) was
performed. The concrete slices (100 mm.times.100 mm.times.60 mm)
were cut from the concrete prisms and then were dried at 40
.degree. 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
(100 mm.times.100 mm) 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 (30 min, 1, 2, 3, 4, 5, 6, 24
h, 48h and 72 h), 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.degree. C. and a relative humidity of 60%. The
amount of water absorbed per unit (cm.sup.2) after certain time can
be obtained using the following equation:
q.sub.i=(Q.sub.t-Q.sub.0)/S
[0228] where:
[0229] q.sub.t is the amount of water absorbed per unit after
certain time, in g/cm.sup.2;
[0230] Q.sub.t is the weight of the specimens at time t;
[0231] Q.sub.0 is the weight of the specimen at time 0;
[0232] S is the contact area with water, in cm.sup.2.
[0233] 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 .degree. 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 3 h 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.
W s = W w - W d W d .times. 100 % ##EQU00004##
[0234] where:
[0235] W.sub.s: saturated water absorption ratio
[0236] W.sub.d: dry weight of the specimen
[0237] W.sub.w: wet weight of the water saturated specimen
[0238] g) Influence of Microcapsules on Cement Hydration
[0239] 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
p-capsules (3%), p-capsules (5%), respectively. The dosage of the
additives was versus cement weight. The hydration heat production
(at 20.degree. C.) was determined by a TAM AIR isothermal heat
conduction calorimeter. The results are shown in FIG. 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, p-capsule 3% and p-capsule
5%, i.e. in the range of 355.about.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
[0240] 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: [0241] 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.
[0242] 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.
[0243] 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
[0244] 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.
[0245] A "microparticle" as described herein is a particle with
dimensions from 1.times.10.sup.-7 m to less than 1.times.10.sup.-3
m, i.e. from 0.1 to less than 1000 .mu.m, which may be spherical or
non-spherical.
[0246] 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.
[0247] 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.
[0248] In embodiments, the core comprises a silica-based material.
In embodiments, the core comprises a carbohydrate-based
material.
[0249] In a further aspect is provided a concrete composition
comprising: [0250] a cementitious material, one or more aggregate
materials, a liquid binder and a quantity of microparticles as
described above.
[0251] 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: [0252] (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; [0253] (ii) setting
the composition; and [0254] (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.
[0255] 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),
* * * * *