Compositions suitable for self-healing concrete, methods for manufacturing the same, and uses thereof

Abstract

The present invention relates to a particulate composition suitable for self-healing concrete, comprising limestone-forming bacteria or spores of limestone-forming bacteria and bacterial nutrients dispersed in a lactic acid-based oligomer matrix. The present invention also relates to a method for producing the particulate composition, which comprises the steps of mixing a lactic acid-based oligomer in a liquid phase with limestone-forming bacteria or spores of limestone-forming bacteria and bacterial nutrients, and solidifying the resulting mixture to form solid particles. The mixing step is preferably carried out in an extruder. The formation of the solid particles can be carried out with a water pelletizer.

Description

Technical Field

[0001] The present invention relates to a particulate composition suitable for use in self-healing concrete, and is also presented herein as an agent for self-healing concrete. The present invention also relates to a method of manufacturing such a composition, and its use in virgin concrete and concrete repair.

Background Art

[0002] Concrete is a strong and sustainable material that is currently widely used in art, housing, offices, roads, and other civil structures, such as bridges, basements, and parking lots. Generally, concrete is composed of a hardened mixture of cement and additives such as sand, water, and (optionally) gravel. The material has high compressive strength, relatively low tensile strength, provides great freedom in structure formation, and it is relatively inexpensive. However, concrete has the drawback of being prone to small cracks, which can have a profound impact on the strength characteristics of the concrete, and as a result, may affect the safety and sustainability of objects made of concrete. Especially in reinforced concrete structures, water carried through such concrete can cause oxidation of the steel structure. As a result, the area around the steel structure may expand, and the concrete surrounding the steel may be damaged. Therefore, this process can ultimately lead to the destruction of the concrete structure.

[0003] Due to these harmful phenomena, the repair mechanisms of concrete have been widely studied and repair processes have been developed. These repair processes can potentially be preventive (applied before cracks occur) or curative (applied after cracks have occurred). Among the many approaches described in the literature, an interesting and promising method relates to the use of special bacteria or (dormant) spores of such bacteria. When these bacteria are supplied with a specific substrate, they seem to be able to produce limestone or other stone species under the conditions of crack formation in the presence of nutrients. When a mixture of bacteria (spores), nutrients (for bacterial growth), and substrate (for limestone formation) is applied in and / or on the concrete, it seems possible to prevent cracks or repair (or heal) such cracks after they have formed. When cracks are formed, the strength of the damaged concrete material can be improved so that such formed cracks can be completely repaired, and in some cases even fully restored to the original strength. Therefore, as a preventive measure against future crack formation in hardened concrete structures, such mixtures (or agents) can be added and / or mixed into virgin uncured concrete. However, as a curative measure, such mixtures (or agents) can also be applied to existing cracks in hardened concrete.

[0004] International Publication No. WO201 / 1126361 (A1) describes a method for manufacturing a cementitious material, which includes mixing a cement starting material and a particulate healing agent. The healing agent includes coated particles, particularly coated particles formed as tablets, where these particles include a bacterial material and one or more additives. The bacterial material may be composed of (lyophilized) bacteria or their spores. The additives may include calcium compounds and optionally organic compounds, trace elements, and / or phosphorus compounds. The particles or tablets are coated with a cement and concrete compatible layer, which may include a (co)polymer-based coating based on one or more monomers selected from the group consisting of glycolide, lactide, ε-caprolactone, δ-valerolactone, N-vinylcaprolactam, 3,6-dimethyl-1,4-dioxane-2,5-dione, glycoxysyethyl methacrylate, 1,6-bis(p-acetoxycarbonylphenoxy)hexane, and (3S)-cis-3,6-dimethyl-1,4-dioxane-2,5-dione. In the examples, an epoxy resin coating is used. The particles are manufactured using a two-step process that includes a first step of compressing the bacterial material and one or more additives to form the particles or tablets, and a second step of applying the coating.

[0005] U.S. Patent Application Publication No. US2014 / 248681 describes microcapsules for encapsulation in concrete, which are adapted to reduce the defective area in the concrete by at least 45 percent once a certain amount of the microcapsules ruptures. Here, each of the microcapsules includes a polymeric shell encapsulating a liquid core, where the polymeric shell comprises a substantially impermeable polymer layer, and the liquid core contains carbonatogenic bacterial spores and optionally bacterial nutrients dispersed in a liquid medium. Also disclosed are a concrete composition containing a certain amount of such microcapsules and a method for reducing the defective area in concrete. The polymer is selected from gelatin, polyurethane, polyolefin, polyamide, polysaccharide, silicone resin, epoxy resin, chitosan, and aminoplast resin.

[0006] U.S. Patent Application Publication No. US2017 / 044420A describes a method for delivering a microorganism or an enzyme to a selected location, particularly downhole in cementing applications of a well. The method includes transporting a coated aggregate to the selected location, where the coated aggregate includes an aggregate and a coating disposed on the aggregate, and the coating includes a polymer matrix and a calcium carbonate producing agent containing a microorganism or an enzyme. Exemplary thermoplastics used in the polymer matrix include polyethylene, acrylonitrile-butadiene-styrene, polystyrene, polyvinyl chloride, fluororesin, polysulfide, polypropylene, styrene acrylonitrile, nylon, and polyphenylene oxide. Exemplary thermosetting resins include epoxy resin, phenolic resin, polyester resin, polyurethane, epoxy-modified phenolic resin, and their derivatives. SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

[0007] The healing particles described in the art and their production have many drawbacks. The first drawback lies in their production, which often requires separate coating steps. A further drawback is the fact that the coating needs to be cracked in order to release the active compound. Yet another drawback is the fact that many of the cited polymers are not biodegradable.

Means for Solving the Problems

[0008] It is an object of the present invention to overcome or at least mitigate the associated problems described for known healing agents. More particularly, the present invention provides an agent which can be suitably used in pre-cured concrete in order to avoid or reduce the formation of cracks in hardened or solid concrete, which can be produced in a simple and cost-effective manner, which does not rely on the destruction of a coating, and which relies on biodegradable and renewable materials. The healing agent should also be suitable for use in repairing cracks in solid or hardened concrete. The present invention is also directed to a method for producing the healing agent.

[0009] In one embodiment, the present invention relates to a particulate composition suitable for self-healing concrete, comprising limestone-forming bacteria or spores of limestone-forming bacteria and bacterial nutrients dispersed in a lactic acid-based oligomer matrix.

[0010] In another embodiment, the present invention relates to a method for producing a particulate composition suitable for self-healing concrete, the method comprising the steps of mixing a lactic acid-based oligomer in a liquid phase with limestone-forming bacteria or spores of limestone-forming bacteria and bacterial nutrients, and solidifying the resulting mixture to form solid particles.

[0011] In a further embodiment, the present invention relates to the use of the particulate composition in virgin concrete and to the use of the particulate composition in concrete repair.

BRIEF DESCRIPTION OF THE INVENTION

[0012] Without wishing to be bound by theory, it is believed that the particles of the present invention act as follows when incorporated into concrete: When cracks occur in the concrete, water enters the cracks. The presence of water, in combination with the alkaline environment within the concrete, results in the hydrolysis of the OLA, releasing bacteria or spores and nutrients. The bacteria grow on the nutrients and lactate released from the OLA, forming calcium carbonate, i.e., limestone, to seal the cracks. When the particles of the present invention are used in a composition for mending cracks in existing concrete, the particles are applied onto the concrete in the presence of water. Also in this case, the prevailing alkaline conditions in the presence of the concrete cause the hydrolysis of the OLA.

[0013] The present invention will also be described hereinafter in terms of the problems solved by various aspects and embodiments of the present invention and the advantages associated with the various aspects and embodiments of the present invention.

[0014] The present invention uses a lactate-based oligomer (also denoted herein as OLA). The OLA is a polyester oligomer consisting of at least 50 mol% of lactic acid monomers, the remainder being monomers selected from lactic acid compatible monomers.

[0015] Suitable lactic acid-compatible monomers can be selected from monomers having a single alcohol group and a single carboxylic acid group. Aliphatic hydroxy acids may be used, for example, and in particular, compounds having 2 to 10 carbon atoms, particularly 2 to 8, more particularly 2 to 6, carbon atoms may be used. These compounds can form cyclic esters with themselves or with other compounds containing hydroxy and carboxylic acid groups. Thus, suitable monomers of this type include glycolic acid, but also glycolide, a cyclic ester of glycolic acid, lactones, and cyclic esters of glycolic acid and lactic acid. 2-Hydroxybutyric acid is another example of a suitable compound.

[0016] Interesting further lactic acid-comparable monomers can be selected from aliphatic monomers having two alcohol groups in combination with aliphatic monomers having two carboxylic acid groups.

[0017] Examples of suitable aliphatic monomers having two hydroxyl groups are alkanediols such as ethanediol, propanediol and butanediol, and glycol compounds such as ethylene glycol, diethylene glycol and triethylene glycol. Bio-based compounds, such as compounds produced through fermentation or derived from annually renewable resources, are considered preferable.

[0018] Examples of suitable dicarboxylic acids are succinic acid, fumaric acid, adipic acid, maleic acid, oxalic acid and malic acid.

[0019] Lactic acid-compatible monomers selected from the group consisting of glycolic acid (in the form of glycolide, often a cyclic diester of glycolic acid), and lactones, in particular epsilon-caprolactone, are considered preferable.

[0020] OLA preferably consists of at least 70 mol% lactic acid monomer, in particular at least 80 mol%, more particularly at least 90 mol%, in some embodiments at least 95 mol%, or at least 99 mol%.

[0021] Since lactic acid serves as a substrate for bacteria, the larger the amount of lactic acid, the more preferable it is considered.

[0022] Generally, OLA will have a number-average molecular weight of less than 50 kg / mol as determined by conventional gel permeation chromatography (GPC) relative to the PS standard measured in CHCl 3 If the number-average molecular weight exceeds this value, the viscosity of the polymer in the liquid phase becomes relatively high, making it difficult to mix OLA with further components. The number-average molecular weight is generally at least 1 kg / mol. If the number-average molecular weight is below this value, it will be difficult to produce suitable particles.

[0023] The number-average molecular weight (Mn, relative to PS) of OLA is preferably in the range of 5 to 30 kg / mol, particularly 10 to 25 kg / mol.

[0024] In the production of the particles according to the present invention, OLA will be mixed with further components in the liquid phase, i.e., above the melting point or glass transition temperature of OLA. Since bacteria or bacterial spores may be more sensitive to higher temperatures, particularly when the mixing time and processing time are long, it is preferable for OLA to have a relatively low processing temperature. For this reason, and for further reasons described below, it is preferable for OLA to be amorphous. This is because amorphous OLA has a relatively low glass transition temperature, particularly when compared to the melting point of crystalline OLA.

[0025] The melting temperature (in the case of crystalline materials) and the glass transition temperature depend on the molecular weight of OLA and its chemical composition.

[0026] As shown above, OLA is based on at least 50 mol% lactic acid monomer. Lactic acid can exist as two different enantiomers (L and D). The optical purity of OLA increases when it consists substantially of only one of these two enantiomers. OLA with high optical purity has the ability to crystallize in the solid phase and can therefore exhibit a relatively high melting temperature, often above 140 °C in many cases. OLA with low optical purity often has little or no ability to crystallize and thus may have a melting temperature of only 110 - 140 °C. When the optical purity is low, for example, when the L / D enantiomer ratio is in the range of 85 / 15 to 15 / 85, crystallization is no longer possible and it can only exist in the amorphous state in the solid state. As a result, the melting point no longer exists and only the glass transition temperature measured by DSC remains, and that temperature is in the range of 30 - 60 °C depending on the average chain length and the L / D ratio. Above 200 °C, there is a realistic risk of thermal degradation of OLA, which is considered an obvious drawback.

[0027] In one embodiment, the OLA in solid form has an amorphous - i.e., non - crystalline - structure. In addition to having a glass transition point and thus enabling processing at a temperature lower than the melting point, a further distinct advantage of this type of OLA is that the decomposition rate of the amorphous material in concrete appears to be significantly higher than that of (semi) crystalline materials not only in concrete but also under all decomposition or compounding conditions of polylactic acid (PLA). The prepared amorphous OLA is defined as having a net enthalpy value of 5 joules per gram (J / g) or less measured by differential scanning calorimetry (DSC) at a heating rate of 5 K / min from room temperature to 200 °C. In this regard, it has been found advantageous to use an OLA characterized in that it is a copolymer of L - lactic acid monomer and D - lactic acid monomer and the amount of minor lactate units is at least 10% of all lactate units. The OLA that meets this prerequisite has an amorphous structure in the solid state. Preferably, the amount of minor lactate units ranges from 10% to 30% of all lactate units in the OLA.

[0028] In one embodiment, the OLA is a product obtained from a depolymerized PLA material. For this purpose, recycled PLA materials or off - specification PLA materials can be used, which are depolymerized into OLA materials having the required molecular weight from the high - molecular - weight PLA materials. By using such materials, the material cost is reduced.

[0029] The self - healing agent of the present invention contains limestone - forming bacteria or spores of limestone - forming bacteria and bacterial nutrients dispersed in a lactic - acid - based oligomer matrix. Of course, the bacteria and spores may also be used in combination (even if not explicitly stated elsewhere in this specification). Since spores are generally less temperature - sensitive than bacteria, the use of spores may be preferred in some cases.

[0030] The specific type of limestone-forming bacteria or spores of limestone-forming bacteria is not important for the present invention. Particularly suitable organisms are those having the ability to form spores, where the spores are resistant to high temperatures and elevated pH values and have the ability to ferment lactic acid under aerobic or facultatively anaerobic conditions.

[0031] Bacteria used in the art, such as those described in US Patent Application Publication No. US2017 / 044420, may also be used in the present invention. Examples of suitable organisms include genera such as Bacillus sp. and Sporosarcina sp. Specific examples include Sporosarcina pasteurii (formerly known as Bacillus pasteurii), Bacillus megaterium, Bacillus sphaericus, Bacillus subtilis, and the like. Sporosarcina pasteurii is particularly preferred.

[0032] The bacterial nutrients used in the present invention generally include nutrients for bacterial growth. Suitable nutrient compositions are known in the art.

[0033] An interesting embodiment of the present invention is characterized in that the bacterial nutrient contains yeast. This organic material has proven to be very useful in agents for self-healing concrete applications. Yeast plays an important role in the growth and proliferation of bacterial spores and / or bacteria. The use of yeast appears to be superior to the use of comparative bacterial nutrients, such as urea.

[0034] The particulate composition of the present invention generally has a particle size distribution such that at least 90% by weight, particularly at least 95% by weight, of the particles have a diameter of 5.0 mm to 0.50 mm, particularly 3.0 mm to 0.50 mm, more particularly 2.0 mm to 0.50 mm. The particle size distribution is determined by sieve analysis. The particle size of the composition according to the present invention is relatively narrow, the number of fines is limited, and there may be very large particles. This results in a composition having attractive properties, for example, good mixing behavior when it is mixed into a concrete composition and a composition without dust generation. Depending on the properties of the concrete into which the composition is to be mixed, it is within the scope of those skilled in the art to select a suitable particle size.

[0035] Preferably, the particulate composition of the present invention contains at least 95% by weight, preferably at least 97% by weight, of OLA, at least 1.0 to 3.0% by weight or less of nutrients, and at least 0.01 to less than 0.5% by weight of bacteria or bacterial spores. Agents containing at least these three components in the indicated amounts have been shown to demonstrate excellent results in concrete repair experiments.

[0036] It is a special feature of the composition of the present invention that the bacteria or spores and the nutrients are uniformly mixed and embedded in the OLA matrix. The particles have a uniform composition, but do not exhibit a core-shell structure that may be found in prior art particles. This means that the release profiles of the bacteria or bacterial spores, nutrients, and OLA degradation products are relatively uniform over time.

[0037] The resulting agent material contains a large number of bacteria or spores and a large number of nutrient grains per particle. This results in a composition containing fine particles containing nutrients or bacteria or their spores, which is different from a composition where the spores and / or nutrients are individually encapsulated in the coating.

[0038] In another embodiment, the present invention is a method for producing a particulate composition suitable for self-healing concrete, the method comprising the steps of mixing a lactic acid-based oligomer (OLA) in a liquid phase with limestone-forming bacteria or spores of limestone-forming bacteria and bacterial nutrients, solidifying the resulting mixture, and forming solid particles.

[0039] The bacteria or bacterial spores and the nutrients can be added separately or as a mixture to the OLA in the liquid phase. When added separately, there is no preferred order of addition of these components. In one embodiment, the nutrients and bacteria or spores are combined to form a premix, and the premix is incorporated into the OLA in the liquid phase.

[0040] The nutrients and the limestone-forming bacteria or spores of limestone-forming bacteria are mixed in the liquid phase through the OLA. Care should be taken to add the compounds in a manner and at a temperature such that they do not decompose. In particular, exposure of the limestone-forming bacteria or spores of limestone-forming bacteria to elevated temperatures for extended periods of time should be avoided. Depending on the molecular weight of the OLA, the liquid OLA will have a low or high viscosity at a suitable temperature. Selecting a suitable mixing device taking into account the general viscosity is within the scope of those skilled in the art.

[0041] The liquid mixture containing the OLA is solidified, and solid particles are formed. Generally, although not necessarily, the processes of particle formation and solidification are combined in that particles are formed when the mixture has a high viscosity but is not yet fully solidified. Suitable methods include those adapted from providing particles of a polymer composition. Selecting a suitable method is within the scope of those skilled in the art.

[0042] The method according to the present invention is considered to be relatively cost-effective compared to known methods since individual particles or tablets do not need to be coated. Moreover, the solid particles prepared using the method of the present invention can be made relatively small and can thus be suitably used for repairing microcracks formed in hardened concrete or solid concrete. Generally, it seems rather difficult to prepare small coated particles. Further, by including bacteria and / or spores and nutrients in the OLA, separation or segregation of these components can be prevented when the agent is stored in large quantities over a long period. Such separation or segregation can occur particularly in a physical mixture of the separate components (powders) of the self-healing agent.

[0043] In one embodiment, an extrusion device is used to mix a lactic acid-based oligomer in a liquid phase with limestone-forming bacteria or spores of limestone-forming bacteria and bacterial nutrients. The use of an extrusion device has the advantage that the temperature in the mixing step of the OLA, the bacterial spores and the nutrient agent can be carefully selected so as to prevent damage to any of the components, particularly the spores, during the mixing step. More particularly, an extrusion device, particularly a twin-screw extrusion device, has the particular advantage that the components described above can be mixed at a low temperature such that all components, particularly the bacteria and / or bacterial spores, can withstand the production of the agent and can be homogenized despite the relatively high melt viscosity of the mixture.

[0044] In particular, the OLA is first supplied to the extruder and, in the first part of the extrusion device, can be brought to a temperature at which the OLA softens and becomes a liquid or molten phase, which temperature is typically well above the temperature at which bacteria or bacterial spores are destroyed. After the OLA is heated in the extrusion device to become a liquid or molten phase, the OLA is still plasticized and in a viscous liquid phase and can be transported to the next part of the extruder having a lower temperature than the temperature at which the bacterial spores can survive. In this part, the spores are supplied to the extruder and mixed with the OLA in the viscous liquid or molten phase. Nutrients can be added before, during, or after adding the bacteria or spores to the OLA, depending on their composition. After all components are added to and mixed in the extrusion device, the mixture exits the extruder, solidifies at a low temperature, and subsequently is processed into particles.

[0045] For reasons of efficiency, the OLA can be preheated and melted before entering the extruder by melt-feeding.

[0046] In one embodiment, the bacteria or spores and the nutrients are added to and mixed with the OLA in the extruder when the temperature of the OLA in the liquid phase is in the range of 100 to 200 °C, preferably in the range of 110 to 140 °C. As described above, the temperature at which the OLA melts and thus reaches the liquid phase depends inter alia on the molecular weight of the OLA and its optical purity.

[0047] As described above, in one embodiment, the OLA is a product obtained from a depolymerized PLA material. For this purpose, recycled PLA material or off-spec PLA material can be used, which is depolymerized to an OLA material having the required molecular weight from the high molecular weight PLA material. Depolymerization can be carried out using methods known in the art, such as glycolysis or hydrolysis, with hydrolysis, particularly hydrolysis under alkaline conditions, being particularly preferred. The depolymerization conditions are known in the art and need not be described herein.

[0048] An attractive embodiment in this context is a method in which the depolymerization and the production of the agent are carried out in a single extruder or in two connected extruders. In this case, PLA is fed into the first part of the extruder, where it is subjected to depolymerization conditions, as a result of which OLA is formed in the liquid phase, and subsequently, bacteria or spores and nutrients are fed into the second part of the extruder or into the second extruder to form a mixture containing these components, and subsequently, the resulting mixture is solidified and solid particles are formed.

[0049] The extruded mass can be converted into particles through methods known in the art. In one embodiment, the mass is extruded through a die plate, and subsequently a knife incises the particles into an extrudate of the desired size. Optionally, the particles can be subjected to a spheronizer treatment.

[0050] A preferred embodiment of the method according to the invention is characterized by processing a material solidified by an underwater pelletizer into solid particles. The use of such a pelletizer type provides an easy and convenient way to obtain solid or nearly solid mixtures of OLA, bacteria or spores and nutrients as small particles. In practice, the mixed material is discharged from the extruder in liquid or viscous form through small bores of a hot die plate attached to the extruder. Upstream of the die plate, usually, a gear pump for flow control and pressure generation and a melt filtration system or screen changer for preventing the back side of the die plate from being clogged with impurities are arranged. The strands emerging from the bores of the hot die plate solidify upon contact with the water of the pelletizer, and the solidified strands are cut into particles in water by a rotating cutting knife which is part of the pelletizer. The formed particles are carried away from the vicinity of the die plate by a water stream, pass through a water / granulate separation system and can subsequently be obtained as small particles that can be dried when necessary. Depending on the type of pelletizer and the details of the machine such as cutter speed and mass flow through each bore, the average particle size of the solid particles can be adjusted to less than 3 mm, preferably less than 2 mm, most preferably less than 1 mm. Underwater pelletizers are routinely applied in industrial polymer production, for example for polyolefins and polyesters, and can be commercially obtained from companies such as MAAG Gala, BKG and Econ. The production of fine particles of 1 - 2 mm is generally referred to as microgranulation or micropelletisation.

[0051] The present invention also relates to a method of using the agent of the present invention in virgin concrete (i.e., pre-cured concrete that has not yet been hardened) and in concrete repair, for example, in the repair of a cured concrete or hardened concrete body in which cracks have formed.

[0052] In one embodiment, the particulate composition is incorporated into the concrete composition prior to its shaping.

[0053] In another embodiment, the particulate composition is provided on the concrete in which cracks have formed.

[0054] As will be apparent to those skilled in the art, different embodiments of the present invention can be combined as long as they are not mutually exclusive. All percentages used herein are weight percentages unless otherwise specified. When amounts, concentrations, dimensions and other parameters are expressed in the form of ranges, preferred ranges, upper limit values, lower limit values, or preferred upper and lower limit values, any range that can be obtained by combining any upper limit value or preferred value with any lower limit value or preferred value should be understood to be specifically disclosed, whether or not the resulting range is explicitly recited in the context.

[0055] In the claims, the term "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain means are recited in mutually different dependent claims does not indicate that a combination of these means cannot be used advantageously. Any reference signs in the claims should not be construed as limiting the scope.

[0056] The following examples illustrate the practice of the present invention in some of the preferred embodiments. Other embodiments within the scope of the claims will be apparent to those skilled in the art.

[0057] Example

[0058] Example 1: General preparation method

[0059] Examples 1a) and 1b) below illustrate embodiments of the present invention in which OLA is melt mixed with a 2% yeast masterbatch using an extrusion device and then in-line formed into micropellets (1 - 3 mm) by a laboratory scale underwater pelletizer.

[0060] OLA is a lactic acid oligomer based on more than 99% lactic acid monomer and is produced via the ring-opening polymerization of L - and D - lactide (90 / 10) in batch in the presence of SnOct 2 as a polymerization catalyst and an initiator for molecular weight control, and is provided in the form of a powder (ground lactic acid oligomer). To determine Mn and Mw, conventional GPC was carried out using CHCl 3 as the eluent and PS as the standard substance for calibration. OLA had a Mn of 20 kg / mol and a Mw of 30 kg / mol, and a glass transition temperature of 35 - 45°C.

[0061] The dry powder masterbatch contained bacterial spores and yeast. This “basic +” formulation is a fine brown powder formulation consisting of bacteria and yeast spores that produce CaCO 3 for self - healing concrete applications. The spores are dormant in the dry state and protect themselves against temperature / pH changes until they come into contact with moisture (and nutrients). The spores are relatively resistant to high temperatures up to 120°C for short periods, and thus processing and / or mixing at low temperatures is possible.

[0062] The extrusion device was a state - of - the - art ZE 42x40D BluePower co - rotating twin - screw extruder (TSE) from KraussMaffei Berstorff. The device had a screw diameter of 42 mm and a (temperature - controlled) barrel length of 40D.

[0063] A water-cooled feed port was used to add the OLA powder from a gravimetric Brabender solids feeder. After heating and plasticizing the amorphous oligomer in the initial zone of the TSE, the yeast masterbatch (MB) was added at L = 20D using a twin-screw side feeder (type ZSE 42A). The solid MB was metered and fed to the side-feeder (75 rpm) using a twin-screw feeder device made by Colortronic. Further downstream, melt-mixing to gently homogenize the OLA and the yeast MB was achieved using a conveying screw configuration with two mild melt sections. The first section consisted of a neutral kneading element (type 42BP-KB1.25 / 5 / 45L / 2) followed by a narrow reversed mixing element (type 42BP-KB0.75 / 5 / 45R / 2). The second section consisted of the same neutral kneading element (type 42BP-KB1.25 / 5 / 45L / 2), then a positive mixing element (type 42BP-KB0.75 / 5 / 45L / 2), and again, a reversed mixing element (type 42BP-KB0.75 / 5 / 45R / 2).

[0064] At the die of the extruder, there was a breaker plate with a coarse (400 micron) filter mesh, a gear pump, and a diverter valve before an underwater pelletizer (Gala LPU) used to make microgranulate (micro pellets).

[0065] Typically, the processing speed of the extruder for OLA powder was set at 15 - 30 kg / h, while the screw rotation speed was set at 100 - 125 rpm. The addition level of yeast MB was 2%, and thus, it was 0.6 kg / h at a feed rate of 30 kg / h.

[0066] The temperature profile of the extruder barrel started from the water-cooled feed zone and was 25 - 70 - 125 - 120 - 110 - 110 - 110 - 120 (all in °C), and the adapter, filter, melt pump, switching valve, and die head of the LPU UWP were 125 - 120 - 120 - 120 - 200 (all in °C), respectively.

[0067] Further important data of the Maag-Gala LPU underwater pelletizer are as follows: the die plate had 12 bores with a diameter of 0.8 mm, the 7-spoke cutter hub was set at 5000 rpm, and the temperature of the cooling water was controlled at 20 - 40 °C.

[0068] Example 1a

[0069] The above-described OLA microgranulate was produced using the setup described above operating at 15 kg / hour and 100 rpm without first adding 2% yeast and spore MB. The die plate temperature of the pelletizer was 230 °C, and the cooling water temperature was 30 °C. Due to the low internal pressure (10 bar) before the die plate and filter screen and the OLA melt temperature of 135 °C, the OLA microgranulate was produced in a stable operation. The particle size distribution of the solid microgranulate particles was determined by sieving a known amount of the product through sieves with different mesh sizes using a standard laboratory sieve shaker (Haver & Boecker). Data from these mechanical sieving fractions are shown in Table 1 below for Example 1, and more than 98 wt% of the microgranulate had a particle size of 1.25 - 0.71 mm. For comparison, the OLA powder after mechanical grinding typically has an average particle size of 500 microns and 95 wt% is all less than 850 microns. Thus, the microgranulation process enables the production of OLA particles with few fines and a much higher fraction of particles in the preferred particle size range of several millimeters.

[0070] Example 1b

[0071] OLA microgranulate mixed with 2% yeast masterbatch (375 gr / hour) was produced as follows using the extruder setup described above operating at 15 kg / hour and 100 rpm. The die plate temperature of the pelletizer was 275 °C, and the cooling water temperature was 33 °C. Due to the low internal pressure (10 bar) before the die plate and filter screen and the melt temperature of 135 °C, the microgranulate was produced. The microgranulate was slightly darker in color than pure OLA and showed the presence of yeast and spores.

[0072] The particle size data of these hand sieving fractions are shown in Table 1 below for Example 1b. Approximately 36% by weight of the microgranulate was over 1.25 mm, approximately 95% by weight was over 1 mm, and 64% by weight of the microgranulate had a particle size of 1.25 - 0.710 mm.

[0073]

Table 1

[0074] Example 2

[0075] This example shows an example of the present invention on an enlarged scale compared to Example 1.

[0076] An 8-barrel compounding extruder (KraussMaffei Berstorff ZE 42x36D BluePower co-rotating twin-screw extruder (TSE)) with a screw diameter of 42 mm and a barrel length of 36D was used.

[0077] The extruder had a polymer supply position at the main throat (barrel 1 in the solid conveyance section) and an additive supply position at barrel 5. A solid yeast masterbatch (MB) was added into barrel 5. Venting was performed at barrel 4 to facilitate the rear removal of residual moisture and air from the yeast MB. The connection of a vacuum pump for degassing of the extruder was at barrel 7.

[0078] To add the OLA powder at the polymer supply position, a single-screw, gravimetric Brabender solids feeder was used. After heating and softening the amorphous oligomer in the initial zone of the TSE, the yeast masterbatch (MB) was added using a top feeder (Brabender's loss-in-weight feeder) equipped with a single screw and a stirrer. Further downstream, the melt mixing for gentle homogenization of the OLA and the yeast MB was achieved using a conveying screw configuration with two gentle melt mixing sections to achieve proper distributive mixing of the yeast additive in the OLA melt.

[0079] The powder supply zone of the extruder ensured a stable powder supply to the melt zone section. In addition to the positive and reverse mixing elements, a pressure build-up zone at the end of the extruder was used to make the inlet pressure before the gear pump high enough.

[0080] At the die of the extruder, there was a screen changer equipped with an 80-mesh filter, a gear pump, and a diverter valve in front of the underwater pelletizer (UWP, MAAG SPHERO 登録商標 100 type) used to produce microgranulates (micro pellets).

[0081] Typically, the mass throughput rate of the extruder for OLA powder was set at 95 - 415 kg / h, while the screw rotation speed was set at 200 - 900 rpm. The addition level of yeast MB was typically set at 2.1%. For example, when the total throughput rate of the extruder was 180 kg / h, yeast MB and OLA powder were supplied at rates of 3.8 kg / h and 176.2 kg / h, respectively, resulting in a mass ratio of 2.1 / 97.9.

[0082] The temperature profile of the extruder barrel started from the water-cooled feed zone and was 30 - 100 - 120 - 120 - 120 - 140 (all in degrees Celsius), while the downstream adapter, filter, melt pump, switching valve, and die head of the UWP were 125 - 120 - 120 - 120 - 210 (all in degrees Celsius), respectively.

[0083] The UWP was equipped with a MAAG SPHERO with 12 cutting blades 登録商標 100, while the die plate always had 192 holes. The two selected die plate holes had a diameter D (0.65 mm and 0.5 mm), a spoke cutter hub with 12 spokes, and it was operated at a rotational speed of 3500 - 4800 rpm, and the cooling water temperature was controlled at 20 - 40°C. The rotating speed of the cutter hub of the UWP was used to adapt to process conditions, such as the total mass throughput rate, to control the average particle weight of the granules within the target window.

[0084] Example 2a

[0085] Pure OLA microgranulates were manufactured as follows using the aforementioned extruder setup operating at 180 kg / hour and 380 rpm. The selected die plate size had 192 holes with a diameter of 0.65 mm, the die plate temperature was set at 210 °C, and the cooling water temperature was maintained at 30 °C. Solid microgranulates were produced when the internal pressure in front of the die plate and the filter screen (80 mesh) was low (less than 10 bar) and had a melt temperature of 140 °C.

[0086] Example 2b

[0087] OLA microgranulates mixed with 2.1% yeast masterbatch (MB) were produced using the aforementioned extruder and processing parameters described in Example 2a. The gravimetric top feeder for the yeast MB was set at a feed rate of 3.78 kg / hour, and the feed rate of the OLA powder was set at 176.22 kg / hour. The microgranulates were slightly darker in color than pure OLA after melt extrusion and showed the presence of yeast and spores.

[0088] Example 2c

[0089] OLA microgranulate material mixed with yeast masterbatch (MB) was produced using the extruder setup and processing conditions described in Example 2b, except that the addition amounts of the yeast and spore MB were 4%, resulting in a yeast MB feed rate of 7.2 kg / hour and an OLA powder feed rate of 172.8 kg / hour.

[0090] Example 2d

[0091] OLA microgranulates combined with 2.1% yeast masterbatch were produced from this example using the same extruder conditions as described in Example 2b, except that the selected die plate holes for UWP were 0.5 mm.

[0092] Example 2e

[0093] The microgranulate of OLA mixed with 2.1% of the yeast master batch from this example was produced using the same extruder setup and UWP as in Example 2a, except that the throughput rate of the extruder was set to 425 kg / hour and the screw speed was set to 900 rpm.

[0094] The particle size data shown in Table 2 were measured using a Malvern particle size analyzer. The microgranulates of OLA using MB produced by extrusion granulation and in - water granulation showed similar particle size distributions, with 90% being less than 1600 microns and more than 700 microns as desired.

[0095] The results in Table 2 also show that the molecular weight data (Mn, Mw, and molecular weight distribution) of all microgranulate samples are similar when determined by GPC analysis, indicating that there is no change in the molecular weight values when the throughput rate and screw speed of the extruder are increased, when compared with the pure raw OLA C10 powder.

[0096]

Table 2

Claims

1. A particulate composition suitable for self-healing concrete, comprising limestone-forming bacteria or spores of limestone-forming bacteria and bacterial nutrients dispersed in a lactic acid-based oligomer matrix.

2. The composition according to claim 1, wherein the bacterial nutrients include yeast.

3. The lactic acid-based oligomer (OLA) has a number average molecular weight of less than 50 kg / mol as determined by GPC relative to a PS standard, measured in CHCl 3 The composition according to claim 1 or 2.

4. The composition according to any one of claims 1 to 3, wherein the OLA in solid form has an amorphous structure.

5. The composition according to any one of claims 1 to 4, wherein the OLA is a copolymer of L-lactic acid monomer and D-lactic acid monomer, and the amount of minor lactate units is at least 10% of all lactate units.

6. The composition according to any one of claims 1 to 5, wherein the OLA is obtained from a depolymerized polylactic acid (PLA) material.

7. The composition according to any one of claims 1 to 6, wherein the depolymerization of the PLA is brought about through hydrolysis.

8. The composition according to any one of claims 1 to 7, wherein at least 90% by weight, particularly at least 95% by weight, of the particles have a particle size distribution with diameters in the range of 5.0 mm to 0.50 mm, particularly in the range of 3.0 mm to 0.50 mm, more particularly in the range of 2.0 mm to 0.5 mm, and wherein the particle size distribution is determined via sieve analysis.

9. The composition according to any one of claims 1 to 8, wherein the particulate composition comprises at least 95% by weight, preferably at least 97% by weight, of OLA, at least 1.0% to 3.0% by weight or less of nutrients, and at least 0.01% to less than 0.5% by weight of bacteria or bacterial spores.

10. A method for producing a particulate composition suitable for self-healing concrete according to any one of claims 1 to 9, the method comprising the steps of mixing a lactic acid-based oligomer in a liquid phase with limestone-forming bacteria or spores of limestone-forming bacteria and bacterial nutrients, and solidifying the resulting mixture to form solid particles.

11. The method according to claim 10, wherein an extrusion device is used to mix the OLA, the bacteria or bacterial spores, and the nutrients.

12. The method according to claim 11, wherein the bacteria or bacterial spores are added to and mixed with the OLA in the extruder device when the temperature of the OLA in the liquid phase is in the range of 100 to 200 °C, preferably in the range of 110 to 140 °C.

13. The method according to any one of claims 10 to 12, wherein the solidified material is processed into solid particles by a underwater pelletizer.

14. Use of the composition according to any one of claims 1 to 9 in virgin concrete or in concrete repair.

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