Microcapsules and concrete containing the same

Abstract

Microcapsules for inclusion in concrete are disclosed. The microcapsules are adapted to reduce the area of defects in the concrete. The microcapsules may include carbonatogenic bacteria spores in a liquid core, contained in a polymer layer. Also disclosed are concrete compositions including the microcapsules.

Claims

1. A concrete composition comprising: a cementitious material; one or more aggregate materials; a liquid binder; and a quantity of microcapsules said microcapsules each further comprising a polymeric shell encapsulating a liquid core, wherein the liquid core further comprises carbonatogenic bacterial spores dispersed in a liquid medium and the polymeric shell further comprises a polymer layer substantially impermeable to the liquid core, such that the quantity of microcapsules is sufficient, so that, once the compositions is set into concrete, the area of a defect therein is reduced by at least 45% by action of the carbonatogenic bacteria as compared to an initial area of the defect after at least some of said quantity of microcapsules have been ruptured.

2. The composition as claimed in claim 1 wherein the liquid core further comprises bacterial nutrients.

3. The composition as claimed in claim 1 wherein the ratio of cementitious material to aggregate material to water is in the ranges of (0.5 to 1.5):(1 to 15):(0.1 to 1).

4. The composition as claimed in claim 1 wherein the quantity of microcapsules comprised in the composition, based on their dry weight, is in the range of 1% to 10%-by weight of the cementitious material.

5. The composition of claim 4, wherein the quantity of microcapsules comprised in the composition, based on their dry weight, is in the range of 2% to 8%, by weight, of the cementitious material.

6. The composition as claimed in claim 1 wherein the microcapsules are added to the composition in the form of an emulsion having the microcapsules dispersed therein.

7. The composition as claimed in claim 6 wherein the emulsion is a water-based emulsion.

8. The composition of claim 1, wherein at least one of the following criteria (i)-(iii) is fulfilled: (i) said polymer layer comprises a polymer selected from the group consisting of: gelatines, polyurethanes, polyolefins, polyamides, polysaccharides, silicone resins, epoxy resins, chitosan, aminoplast resins, and mixtures thereof, and/or (ii) said bacterial spores are from a microorganism that is capable of reducing the area of the defect by producing a mineral or extracellular polymeric substance (EPS) and/or (iii) said liquid medium 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.

9. The composition as claimed in claim 8 wherein any two of the three criteria (i)-(iii) are fulfilled.

10. The composition as claimed in claim 8 wherein all three of criteria (i)-(iii) are fulfilled.

11. The composition claimed in claim 8 wherein, in each microcapsule, the concentration of the bacterial spores is at least 10.sup.9 spores per gram (dry weight) of microcapsule.

12. A concrete composition comprising: a cementitious material; one or more aggregate materials; a liquid binder; and a quantity of microcapsules, the microcapsules further comprising a polymeric shell encapsulating a liquid core, wherein the liquid core comprises carbonatogenic bacterial spores and bacterial nutrients dispersed in a liquid medium and the polymeric shell comprises a polymer layer substantially impermeable to the liquid core, the quantity of microcapsules being sufficient to reduce the area of a defect in said concrete once said quantity of microcapsules has ruptured or is exposed at an interface of the defect.

13. The composition claimed in claim 1, wherein, in each microcapsule, the concentration of the bacterial spores is at least 10.sup.9 spores per gram (dry weight) of microcapsule.

14. The composition as claimed in claim 12 wherein the polymer layer comprises a polymer selected from the group consisting of: gelatines, polyurethanes, polyolefins, polyamides, polysaccharides, silicone resins, epoxy resins, chitosan, aminoplast resins, and mixtures thereof.

15. The composition as claimed in claim 12 wherein the bacterial spores are from a microorganism that is capable of reducing the area of the defect by producing a mineral or extracellular polymeric substance (EPS).

16. The composition as claimed in claim 12, wherein the liquid medium is selected from the group consisting of: organic oils, mineral oils, silicone oils, fluorocarbons, fatty acids, plasticizers, esters, and mixtures thereof.

17. The composition as claimed in claim 12, wherein the bacterial spores are selected from the group of bacteria consisting of: Bacillus sphaericus, Bacillus pasteurii and Bacillus cohnii.

18. The composition as claimed in claim 12, wherein the liquid medium is a silicone oil.

19. The composition as claimed in claim 12, wherein the microcapsule each have an average diameter of greater than 0.5 m.

20. The composition as claimed in claim 12, wherein the bacterial spores dispersed in the liquid medium together amount to 40-70% by volume of the volume within the polymeric shell of each microcapsule.

21. The composition as claimed in claim 12 wherein the bacterial spores amount to at least 1% by volume of the volume of the liquid medium within each microcapsule.

22. The composition as claimed in claim 12, wherein the bacterial nutrients comprise one or more of: urea, a suitable carbon and nitrogen source, such as nutrient broth, yeast, yeast extract, organic oil and a suitable source of calcium, such as hydrated calcium nitrate, calcium chloride, calcium acetate or calcium lactate.

23. The composition as claimed in claim 1, further comprising bacterial nutrients, wherein the bacterial nutrients are incorporated by at least one of direct admixture into the composition, admixture of a quantity of different microcapsules containing the nutrients, admixture of a hydrogel or other such suitable carrier, e.g. porous aggregate, clays or diatomaceous earth, containing the nutrients.

24. The composition as claimed in claim 12, wherein the polymer layer comprises a polymer is selected from the group consisting of: vinyl polymers, acrylate polymers, acrylate-acrylamide copolymers, melamine-formaldehyde polymers, urea-formaldehyde polymers, and mixtures thereof.

25. The composition as claimed in claim 24 wherein the polymer layer comprises melamine formaldehyde resin.

26. The composition as claimed in claim 12, wherein the polymer layer comprises reactive functional groups, extending outwardly of the microcapsule, whereby the microcapsule is chemically bondable within the concrete.

27. The composition as claimed in claim 26, wherein a reactive functional group comprises a reactive moiety adapted to provide covalent bonding within the concrete.

28. The composition as claimed in claim 1, further comprising bacterial nutrients, wherein the quantity of bacterial nutrients comprised in the composition is in the range of 10% to 20%, by weight of the cementitious material.

29. The composition of claim 28, wherein the quantity of bacterial nutrients comprised in the composition is in the range of 12% to 18%, by weight, of the cementitious material.

30. The composition as claimed in claim 12 wherein, the-quantity of said microcapsules present in concrete is sufficient so that the area of the defect therein is reduced by at least 60% by action of the carbonatogenic bacteria as compared to an initial area of the defect after at least some of said quantity of microcapsules have been ruptured.

31. The composition as claimed in claim 30 wherein the quantity of said microcapsules present in concrete is sufficient so that the area of the defect in the concrete is reduced by at least 80% by action of the carbonatogenic bacteria as compared to the initial area of said defect after at least some of said quantity of microcapsules have been ruptured.

32. The composition as claimed in claim 30 wherein the reduced area of the defect is determined after 4 weeks of continuous wet-dry cycling, in which the wet phase comprises immersion of the concrete in water for 16 hours, followed by the dry phase of leaving the concrete in air (at 20 C. at 60% relative humidity) for 8 hours.

33. The composition as claimed in claim 12 wherein, the quantity of microcapsules is sufficient so that once the composition is set into concrete, the area of a defect therein is reduced by at least 70% as compared to an initial area of the defect by action of the carbonatogenic bacteria after at least some of said quantity of microcapsules have been ruptured.

34. The composition as claimed in claim 33 wherein the quantity of microcapsules is sufficient so that the area of the defect in the concrete is reduced by at least 80% by action of the carbonatogenic bacteria as compared to the initial area of said defect after at least some of said quantity of microcapsules have been ruptured.

35. The composition as claimed in claim 33 wherein the reduced area of the defect is determined after 4 weeks of continuous wet-dry cycling, in which the wet phase comprises immersion of the concrete in water for 16 hours, followed by the dry phase of leaving the concrete in air (at 20 C. at 60% relative humidity) for 8 hours.

36. A method of reducing the area of a defect in concrete, concrete-based material and/or concrete-like material comprising the steps of: (i) providing a concrete, concrete-based material and/or concrete-like material composition as claimed in claim 1 incorporating the quantity of microcapsules; (ii) setting the composition; and (iii) causing at least some of said quantity of microcapsules to rupture in response to the creation and/or worsening of a defect in said set composition, thereby releasing their encapsulated contents to effect defect reduction.

Description

(1) 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:

(2) 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);

(3) 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);

(4) 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);

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

(6) FIG. 5 is an SEM micrograph of the quantity of aminoplast microcapsules shown in FIG. 4 but at greater magnification;

(7) FIG. 6 is an SEM micrograph of a quantity of silica-based material microparticles/microcapsules according to another embodiment of the invention;

(8) FIG. 7 is an SEM micrograph of an alginate microparticle according to a further embodiment of the invention;

(9) 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

(10) FIG. 9 is a series of plots (a) to (c) showing the degree of bacterial spore germination under different temperature conditions (28 C., 20 C. and 10 C. respectively) by measuring the concentration (g/L) of urea decomposed over time (days) for varying concentrations (g/L) of nutrient at a fixed initial concentration (g/L) of urea.

(11) 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.

(12) 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%

(13) 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.

(14) For each of the six composition groups, five long reinforced prisms (having dimensions of 3030360 mm, with the internal rebar having a length of 660 mm and a diameter of 6 mm) were madethus thirty specimens in total. After casting, the moulds were placed in an air-conditioned room (at 20 C., >90% RH). The specimens in control Group R were de-moulded after 24 hours, while the specimens of other Groups were de-moulded after 48 hours because of their slower hardening in the first 24 hours due to the additives. After de-moulding, all specimens were stored in the same air conditioned room until the time of testing.

(15) 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.

(16) After crack creation, the long reinforced prisms were subjected to five incubation conditions: (1) 20 C., >90% RH (2) full and continuous immersion in water (3) full and continuous immersion in a deposition medium (4) continuous wet-dry cycling with water (5) continuous wet-dry cycling with the deposition medium.

(17) The deposition medium was composed of 0.2 M urea and 0.2 M Ca(NO.sub.3).sub.2.

(18) During the wet-dry cycles, the specimens were immersed in water/deposition medium for 16 hours and then exposed to air for 8 hours. The incubation conditions of (2), (3), (4) and (5) were performed in an air-conditioned room (20 C., 60% RH). When the specimens were subjected to immersion, they were not in contact with the bottom of the immersion container but some distance (about 5 mm) was maintained in between. Four 360 mm30 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.

(19) The cracks formed in each specimen, per incubation condition, were identified and counted; the results are shown in Table 2 below.

(20) 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

(21) 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.

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

(23) 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 m to 900 m.

(24) 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).

(25) 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.

(26) $r=\frac{A_i-A_f}{A_i}100\%$
where: r is the crack healing ratio A.sub.i is the initial crack area (mm.sup.2) A.sub.f is the final crack area (mm.sup.2)

(27) 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.f) crack area, which is shown in accompanying FIG. 1.

(28) 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 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.f) being represented by the right hand bar in each pair.

(29) 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.

(30) 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 (autogenous 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.

(31) 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.

(32) 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).

(33) 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).

(34) 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 m, which was much wider than that in the specimens of non-bacterial groups (maximum 250 m).

(35) 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.

(36) The SEM micrograph images 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.

(37) 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.

(38) 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.

(39) FIGS. 9(a), 9(b) and 9(c) show the variation in germination of B. sphaericus spores at different temperatures (28 C., 20 C. and 10 C. respectively) for different concentrations of yeast extract (m/n in the legend indicates the concentration of yeast extract (m) and urea (n) respectively). As shown in FIG. 9(a), at 28 C., spores in the media with yeast extract concentrations of 20 g/L and 5 g/L exhibited a faster revival of ureolytic activity. From around 70% to around 95% of the urea in the media was decomposed in the first day. Spores in the media with 2 g/L and 0.2 g/L yeast extract showed a greatly increased ureolytic activity after 3 days. Within one week, all the urea in the media of yeast extract was completely decomposed. For the spores in the media without yeast extract, the revival of ureolytic activity was much slower but still gradually increased. About 50% (10 g/L) and 85% (17 g/L) of the urea was decomposed after 7 and 28 days respectively. Spores at 20 C. exhibited similar germination behaviour to those at 28 C., as shown in FIG. 9(b).

(40) The revival of spores' ureolytic activity was much slower at 10 C., as shown in FIG. 9(c). In the media with 20 g/L YE, about 34 g/L of urea was decomposed in the first 3 days. A significant increase of ureolytic activity occurred between the 3rd and 7th days; 1517 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.

(41) 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 C.28 C., not at low temperatures).

(42) Various example embodiments comprise 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 may each comprise: 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.

(43) In some example embodiments, the core of the microparticles may be provided with a surrounding shell. In some example embodiments, the core has liquid present in substantially all of its pores. In some example embodiments, the core comprises a silica-based material. In some example embodiments, the core comprises a carbohydrate-based material.

(44) Various example embodiments are directed to a concrete composition comprising: a cementitious material, one or more aggregate materials, a liquid binder and a quantity of microparticles, for example, as described herein above.

(45) Various example embodiments are directed to methods of reducing the area of a defect in concrete, concrete-based material and/or concrete-like material. The methods may comprise providing a concrete, concrete-based material and/or concrete-like material composition as described herein above; incorporating a quantity of microparticles; 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, thereby releasing their contents to effect defect reduction.