Fibres and material comprising same.

Method for the manufacture of cement-based material and synthetic fiber bundles used therein

The invention relates to a method according to the preamble of claim 1 and to synthetic fiber bundles according to the preamble of claim 17.

The use of different types of fibers in the manufacture of concrete to provide additional tensile strength and reinforcement against impact damage and fracture propagation is known and has been practiced for a long time. It is also known that while conventional reinforcing and coarser fibers can reduce the greater visible cracking that tends to occur in concrete, only very fine fibers are truly effective in preventing the development of smaller fractures. However, fibers commonly used in concrete, e.g., synthetic fibers of materials such as polypropylene, are relatively coarse due to the difficulty of achieving satisfactory dispersion in concrete with very fine fibers, and especially fibers with high aspect ratios, using conventional mixing procedures and equipment. In fact, even the even dis20 of relatively coarse fibers can also be difficult to disperse into concrete.

It is common for such fibers to be made as a unitary fibrillate strip and to rely on concrete to break the fibrillation and disperse the individual filaments, which are still relatively coarse, after prolonged mixing. This system may not always be reliable and the fibrillated tape will not always break into the desired individual filaments, especially since the required degree of long-term mixing is often not achieved in practice. Even when the fibers are effectively separated, they may still be too coarse to achieve maximum effectiveness in fracture prevention, especially against microcracking.

Concrete is prone to endogenous fracture and because it is a brittle material, these fractures easily propagate at relatively low stresses. Concrete breaks in tension with the gradual development of fracture and not with the more common way of breaking technical materials.

It is generally assumed that the discrepancy between the actual and theoretical strength of concrete can be explained by the presence of cast blisters (Neville, AM, Properties of Concrete, 1981). Thus, concrete does not fracture because it is weak in tension, but rather it is weak in traction because it already contains fractures. These fractures and casting vesicles vary in size, so scale is very important when dealing with the fracture mechanism, because the actual strength of the whole is a statistical probability that depends on the distribution of fractures in the material. The effective strength of the concrete can therefore be improved and cracking, i.e., large-scale cracks and fractures, can be prevented by preventing the development and propagation of cracks.

Intrinsic, non-structural cracks develop in large masses of pre-mixed concrete due to small cracks that form at an early stage and these then propagate under the influence of stresses caused by changes in the dimensions of such relatively large structures. Pavement concrete units are typically about n in size. 3 x 10 m and 200 mm thick; small cracks in such concrete can easily progress, creating a weak loop that leads to subsequent cracking. This clearly visible cracking is often the only form of cracking that is perceived to be important, but it is a direct result of much smaller and probably substantially invisible previous crack development.

EP-A-0 235 577 discloses fibrous agglomerates with improved dispersibility in viscous organic and inorganic matrices, e.g. cement-based matrices, which agglomerates consist of acrylic staple fibers each having a diameter better than 50 mm and a length greater than 3 mm with a substance dissolved in the matrix to be reinforced, swells or melts therein. A cohesion enhancer, e.g. polyvinyl alcohol, 1-30% by weight of fiber is used. The fibers preferably have a high modulus of elasticity.

EP-A-0 225 404 discloses a process for producing a fiber-reinforced cast cement body, in which filaments of several fibers are dispersed in an uncured cementitious material and then the material is cured, at least some of the filaments being impregnated with a binder so that the fibers are weakly bound to each other. the strands are dispersed in the cementitious material, the fibers are released from each other. A binder, e.g. epoxy resin, the amount used is such that the ratio of fibers to binder is 5: 5-9: 1 by volume.

Previous applications of the fiber have been directed to conventional reinforcement using fibers of sufficiently high modulus of elasticity to support tensile stress bases. While this is possible in materials with a high cement content, this approach may not work effectively with more conventional concretes, not even steel fibers with excellent mechanical properties. This may be due to the following:

a. The amount of fiber required may be too large to fit into the mortar phase of the concrete.

b. The benefit provided by the fibers can be achieved after the matrix has ruptured and can therefore, in such cases, simply be described as a gradual rupture instead of the useful strength.

c. Costs and difficulties in use do not always justify an application.

d. The three-dimensional orientation of the fibers in premix use and the use of fibers throughout the material often make the use of reinforcement ineffective.

It has become increasingly apparent that the main commercial contribution of fibers is to improve the properties of the concrete itself and not to act independently as a reinforcement.

However, the reinforcement is easy to calculate and although the reinforcement of other advantages, i.e. the concrete itself, may be recognized as relevant, the difficulty in measuring and determining them has been a factor slowing down the use of this fiber in concrete.

According to the invention, it has been found possible to use very small amounts of very fine synthetic fibers, e.g. polypropylene, to improve the properties and performance of concrete and mortar, in particular to prevent cracking caused by dimensional changes in concrete and to prevent this cracking at an important micro level, before as cracks develop visually perceptible. The fibers thus act to improve the inherent strength of the concrete and in particular to prevent endogenous cracks from developing at the micro level and also to prevent their propagation instead of providing a separate stand-alone reinforcement.

The method according to the invention is known mainly from the characterizing part of claim 1 and the fiber bundles according to the invention from the characterizing part of claim 17, respectively.

The fibers are added to the concrete or mortar in the form of fiber bundles which, as will be described below, allow the desired substantially homogeneous distribution of fine fibers in the material to be achieved. One aspect of the present invention therefore relates to synthetic fiber bundles designed for use in concrete, mortar or cement, the fibers containing 10 to 10,000 filaments per bundle; the filaments consisting essentially of a polyolefin such as polypropylene or polyethylene, polyester or a mixture of the foregoing and having a length of

1-30 mm, an average cross-sectional dimension of 5-30 μm and an aspect ratio of 100-1000, which the fibers are held together in each bundle by a wetting agent which provides the individual filaments with a surface tension which allows them to be dispersed substantially homogeneously in concrete, mortar or mortar by conventional mixing in conventional concrete mixing equipment.

In another aspect, the present invention relates to a method of making a cement-based material, the method comprising:

adding to the concrete, mortar or cement mixture to which water has been added less than 1% by weight of the cementitious materials, calculated from synthetic fiber bundles containing ΙΟΙ 5 to 10 000 filaments per bundle, the filaments consisting of a polyolefin such as polypropylene or polyethylene, polyester or a mixture thereof having a length of 1 to 30 mm, a mean cross-sectional dimension of 5 to 30 μm and an aspect ratio of 100 to 1000, which filaments in each bundle are held together by a wetting agent, which wetting agent imparts a surface tension to the individual filaments which allows them to disperse substantially homogeneously into the mixture by conventional mixing in conventional concrete mixing equipment, mixing the resulting mixture for at least about 20 seconds to obtain a concrete, mortar or cement mixture in which the individual filaments are substantially homogeneously distributed; the mortar or cement mixture to the desired shape, optionally with the addition of additional ingredients such as reinforcement during casting.

It has been found that the very fine fibers in the form of the fiber bundles according to the invention can be efficiently dispersed in all types of concretes, mortars or cements using all types of existing conventional mixers, such as the rotating drum of a ready-mixed concrete truck. Because these fibers are well dispersed, they can provide many important advantages to the properties and performance of concrete and other cement-based materials, even with very small addition rates. These benefits include:

Prevention of cracks resulting from plastic shrinkage, plastic settling, early thermal shrinkage, chemical shrinkage and carbonation.

Prevention of cracks resulting from drying shrinkage, varying cyclic stresses due to loads caused by loads, reversible moisture movements, and thermal changes.

Possible elimination of the need for a steel mesh to combat the worst problems caused by endogenous cracking.

Improved durability due to crack prevention and reduced water absorption and consequent improved inherent strength.

Reduction of frost damage due to reduced permeability and improved cracking resistance as a result of increased concrete strength and uniformity and improved resistance to crack propagation.

Improved shock and wear damage resistance.

Greater cohesion of wet concrete and the achievement of thixotropic Theology leading to:

more homogeneous and uniform concrete with smoother and more reliable properties, easier pumping, molding and finishing, and prevention of deposition and excessive sweating, less tendency to form plastic settling cracks as a result of reduced deposition; and the advantages of applying concrete to sloping surfaces because the material has a lower tendency to continue to move, which would otherwise result in an increased tendency to crack.

Better resistance to fire damage, as the fine synthetic fibers melt at high temperatures, thus forming a large number of capillaries on the superheated steam generated in the concrete, through which it can escape.

Better resistance to degradation by corrosive chemicals due to reduced penetration of such chemicals into concrete.

More uniform and homogeneous concrete by improving the performance of the mix and preventing aggregation according to particle size and subsequent deposition.

The cohesiveness provided by the fiber bundles of this invention works to improve the surface quality of the concrete. The patterning of the surface to form a non-slip outer surface is improved and the effect obtained is not deteriorated due to subsequent settling due to the thixotropic property provided by the fibers.

The fibers do not degrade the surface quality and are themselves essentially invisible to the naked eye in concrete. The thixotropic effect may also be interesting in enabling new and more interesting aesthetic finishes and effects to be achieved, including decorative on-site and pre-casting applications.

It is increasingly common to use higher concentrations of cement in concrete and other cement-based materials to improve their durability. However, this results in a greater inherent tendency to crack and, because these materials are relatively brittle, greater crack propagation. As mentioned above, the fibers of this invention can be effectively dispersed in all types of concretes and mortars. Due to the ability of the fibers to prevent cracking, they make it possible to improve concrete and other cement-based materials both directly and indirectly in terms of durability requirements.

The use of poszolane materials is also increasing and because these materials, such as microsilica, are very finely divided, they can reduce the rate of sweating and water migration and lead to increased plastic cracking.

When less fine pozzolanic materials are used, such as pulverized fuel ash, the rate of strength increase is reduced and the period of time during which the concrete or other cement-based material is weak and prone to plastic or early shrinkage cracking is extended. The use of ground granulated blast furnace slag cement has a similar effect on the development of early strength. Similarly, when polymer emulsions are added to concrete or cement-based materials, susceptibility to early drying cracks is known to increase.

In all these cases, the addition of small amounts of the fiber bundles according to the invention is effective in reducing the tendency of the material to crack and thus makes it possible to achieve the potential of these materials to a greater extent.

Cements with a high alumina content suffer from highly exothermic temperature rises, which also lead to cracking problems and limit the effectiveness of these materials. The fiber bundles of the invention are effective in preventing such cracks and improving the performance of these cements.

Cements that can be designed to provide long-term controlled expansion to compensate for long-term drying shrinkage, such as calcium sulfoaluminates, nevertheless suffer from plastic and early drying shrinkage. The fibers of this invention are therefore also of interest in allowing these cements to retain their integrity for a sufficient period of time to allow long-term shrinkage compensating benefits of these cements to be achieved.

Fiber bundles are added to concrete or other cement-based material. They may consist essentially of polyolefin, polyester, polyamide or a mixture of the above. Typically, the fibers consist of a polyolefin, such as polypropylene or polyethylene. Polypropylene is a well-known material for synthetic fibers and has been used as such for many years due to its resistance to acids and bases, its advantageous strength properties, its low density, and low cost.

Although there will always be some variation in the number of filaments in the fiber bundles, they will typically contain about 50-5000 filaments per bundle, such as 1002000 filaments per bundle, especially about 500-1500 filaments per bundle, such as about 1000 filaments per bundle.

In contrast to the fine fibers used, e.g., in the manufacture of carpet yarns, the fibers of this invention are preferably substantially uncurled to facilitate their dispersion in concrete or other cementitious material.

The length of the individual filaments is typically about 3-30 mm, e.g. about 5-25 mm, especially about 6-18 mm and the central cross-sectional dimension about 3-30, such as about 5-25, especially about 10-20. .

The aspect ratio of the individual filaments, i.e. the length to diameter ratio, is typically about 200-800, especially about 400-700, such as about 600. Although an aspect ratio of at least about 100 is considered to be the least desirable to achieve efficiency in the use of fibers in concrete or cementitious materials, in the past, it has proved difficult to achieve good dispersion even with fibers with smaller aspect ratios. In addition, the dispersion of fibers with aspect ratios of only 100 has often required special mixing equipment and the use of special additives in the mixture to facilitate dispersion. The individual filaments of this invention thus have a high aspect ratio compared to the fibers commonly used in concrete and are preferred as such. Nevertheless, these fibers can be dispersed in concrete in the form of fiber bundles even when the aspect ratio of the individual filaments is about 1000.

The fact that the fibers of this invention can be easily dispersed in a cementitious mixture using standard mixing times, procedures and equipment is believed to be due to 1) the dispersibility of the fiber bundle units in the cement mixture with added water and 2) the delicate separation of the bundles into sub-bundles and individual filaments. The individual filaments have a surface tension that allows them to be substantially homogeneously dispersed in concrete, mortar or cement by conventional mixing in conventional concrete mixing equipment. The surface of the filaments is thus substantially hydrophilic, so that the filaments are easy to disperse in water or mixtures containing water, e.g. a concrete, mortar or cement mixture to which water has been added. A suitable surface tension of the filaments is approx. 65-80 dynes / cm 2, such as about 70-75 dynes / cm 2, especially about 72-74 dynes / cm 2.

The desired surface tension is typically achieved by treating the bundles of filaments with a wetting agent. As an additional surface treatment, the fiber bundles can optionally be subjected to an electrical treatment known as corona treatment. These lost ones are described in more detail below.

The fibers described above are typically made as follows:

The first step in the production of fiber bundles is the melting of fiber raw materials. This often occurs in an extruder, although the extruder may not need to be used. The temperature used to melt the fiber components obviously depends on the materials used in a given fiber.

The type of spinner used to spin the molten pulp into a spun bundle of filaments is not critical because both short spinning and long spinning can be used. Short spinning is a one-step process in which the fiber bundles are both spun and stretched in a single operation, while long spinning or conventional melt spinning, as it is also known, is a two-step process in which the first step of en100239 is the extrusion of molten pulp .

The spun fibers are cooled as they are pulled out of the spinning nozzle and cooling is typically achieved by a stream of air blown past the fibers.

The bundles of filaments, which at this stage typically contain several thousand fibers, are then stretched. Stretching is typically accomplished using a series of hot rollers and a hot air oven or liquid medium such as hot water or oil, typically stretching a plurality of bundles simultaneously. The bundles of filaments first pass through one set of rollers, followed by passage through a hot air oven or hot liquid, and then pass through another set of rollers. The temperature of the hot rolls is typically about 70-130 ° C and the temperature of the hot air oven or hot liquid is typically about 80-140 ° C. The speed of the second set of rolls is higher than the speed of the first set, and the heated bundles of filaments therefore stretch according to the relationship between the two speeds (called the stretch ratio or draw ratio). A second furnace or liquid and a third set of rollers can also be used (two-stage stretching), whereby the speed of the third set of rollers is higher than that of the second set. In this case, the draw ratio is the ratio between the speeds of the last and the first set of rollers. Additional roller sets and ovens or fluids can also be used.

The fibers of this invention are typically stretched using a stretch ratio of about 1.5.1 to 8: 1, normally about 2.Ί to 6.Ί, preferably about 2.5: 1 to 4: 1, and especially about 2.5: 1. 3.5: 1, resulting in the appropriate diameter or center cross-dimension, as discussed above.

The bundles of filaments are dried and then attached. The stretching process can cause stresses to develop in the fibers. These can be triggered by placing the stretched bundles of filaments in heating, which also works by drying the fibers. This is conveniently done by passing bundles of filaments through an oven where the fibers are allowed to shrink.

As mentioned above, the bundles of filaments are then treated with an ingredient to provide the filaments with a desired surface tension, i.e., a surface tension of about 65-80 dynes / cm 2, such as about 70-75 dynes / cm 2, and especially about 72-74 dynes / cm 2. . This is typically accomplished by conducting bundles of so-called through a series of lubricant brush rollers to which a wetting agent is fed. In addition to providing easy dispersion of the individual filaments in the cement mix, the wetting agent also works by holding the filaments of the bundle together during light handling before adding the fiber bundles to the mix. The wetting agent is typically selected from wetting agents normally used for application to synthetic fibers to be rendered hydrophilic, such as wetting agents intended for application to fibers used in so-called a wet laid nonwoven processes. Such wetting agents are commercially available and are typically compositions containing compounds normally used as emulsifiers, surfactants or detergents and may consist of mixtures of such compounds.

Examples of such compounds are fatty acid esters of glycerides, fatty acid amides, polyglycol esters, polyethoxylated amides, nonionic and cationic surfactants.

Typical examples of compounds that can be used as wetting agents or ingredients in wetting agents are polyethylene glycol lauryl ether having the formula:

CH₃(CH₂) i 10 - (CH₂CH₂O)_of-H, glycerol monostearate of formula:

(C17H3 ₅) COOCH₂CHOHCH₂OH, erucic acid amide of formula:

C₂H₄₁CONH₂, a stearic acid amide of formula:

CH₃(CH₂)₁₆CONH₂, a trialkyl phosphate of the formula:

O

RO-P-OR, R = C_ofB_2n+ 1, (*) R lauryl phosphate amine ester of formula:

O

CH 3 (CH₂) II-O'-O- (CH₂) iiCH₃ Science₂ch₂nh₂ potassium salt of lauryl phosphate of formula:

or

O

CH₃(CH₂) 11-0- U- (CH₂) i iCH₃D + K

O

CH 3 (CH₂) NO-Lo-K⁺

DH and ethylenediamine-polyethylene glycol of formula:

CH₂N ((CH₂CH₂O)_I1H) 2

CH₂N ((CH₂CH₂O) 'H)₂

An example of a preferred wetting agent is SW-T, available from Nissin Kagaku Kenkyosho Ltd., Japan, consisting essentially of the sodium salt of bis (2-ethylhexyl) ester of sulfosuccinic acid (anionic wetting / dispersing compound) and also containing isopropyl alcohol, siloxane soridone, siloxanes, siloxanes, .

In addition to being treated with a wetting agent, the bundles of fibers may optionally be subjected to a corona treatment, which is an electrical treatment commonly used in the manufacture of synthetic fibers. This treatment is a strong electrical discharge from the special electrode to the fiber bundles. A fairly high voltage (about 25 kV and 20 kHz) is required for the electrons to receive sufficient energy to pass through the surface of the fibers. Kim electrons hit the polymer chains at high speed, many of which break down, thus making it possible to form carboxyl groups with ozone (O3) in the air. The formation of carboxyl groups makes the surface of the fibers polar and thus more easily dispersible in aqueous mixtures. Optional Corona treatment is normally performed prior to application of the wetting agent.

After the bundles of filaments have been treated with a wetting agent, they split themselves into smaller bundles, each containing fewer filaments than the original bundles. Thus, the bundles of filaments then contain about 50-5000 filaments per bundle, such as about 100-2000 filaments per bundle, especially

about 500-1500 filaments per bundle. It must be borne in mind that there is always a certain natural variation in the number of filaments per bundle.

The bundles of filaments are then passed to a cutter where the fibers are cut to the desired length. The cutting is typically performed by passing the bundles over a wheel containing radially spaced blades. The fibers are pressed against the blades by the pressure exerted by the rollers and are thus cut to a desired length equal to the distance between the blades. As described above, the bundles of filaments are cut so that the length of the fibers is about 1-30 mm, typically about 3-30 mm, e.g. about 525 mm and especially about 6-18 mm, which gives them the aspect ratio described above.

Filament bundles made by the above method are, as described above, designed for use in concrete, mortar or cement, and the individual filaments of the bundles can be efficiently dispersed in all types of concrete, mortar or cement using all types of existing conventional mixers.

In this context, the term cement is meant to mean all Portland cement type cements such as Portland cement, low alkali cements, sulphate resistant cements, Portland slag cement and Portland cement cement and masonry cement and highly refractory or aluminate type cements such as cementitious alumina hemi- and anhydrite versions, magnesium oxychlorate and magnesium chloride and other similar inorganic cement systems, both hydraulic and non-hydraulic, or combinations of the above, optionally with additives or polymer additives. Lime mortar refers to a mixture of cement and water.

The term mortar, as used herein, refers to a mixture of cement and particles, such as sand and fine crushed stone or stone, including special lightweight aggregates, with the particles being able to pass through a sieve or mesh with an opening of 2.4 mm. The term concrete, as used hereinafter, refers to mortar or cement containing larger aggregates. The term cementitious mate100239 refers to the concentration of the aforementioned cementitious materials in concrete, mortar or cement.

It will be apparent to one skilled in the art that the phrase substantially homogeneously distributed therein suggests that the fibers of this invention are substantially homogeneously distributed throughout the mortar phase of the material, as such fibers clearly cannot be distributed into larger aggregates in concrete.

Concrete or other cement-based materials can be considered to be in situ10 or pre-cast materials from which in situ materials are cast in situ. In situ concrete is usually of the pre-mixed type, although it can also be mixed on site.

The cement content of the mortar or concrete containing the fiber bundles of the invention is generally in the range of about 200-1200 kg / rrA. In conventional in situ concrete to which the fibers of this invention are often added, the cement content is typically about 200-600 kg / πΑ, especially about 250-450 kg / πΑ while in precast concrete using the fibers of this invention, the cement content is typically about 300-500 kg / rrA. The mortar has a cement content of typically about 400-1200 kg / πΑ, especially n. 60020 1000 kg / m 2. Special high-strength concretes or mortars may have a cement content of about 500-1200 kg / πΑ, typically about 500-1000 kg / nA

The water to cement ratio of the cementitious material prepared in accordance with the invention is typically in the range of about 0.25 to 0.8 by weight. In situ concrete, the ratio of water to cement is typically about 0.4 to 0.6, while the ratio of water to cement in precast concrete is typically about 0.25 to 0.35 when compacted under pressure, and n 0.4-0.6 when wet cast and vibrated. However, the addition of fiber bundles to cement-based materials with a water-to-cement ratio of less than 0.25, e.g., dense materials containing ultrafine microsilicon dioxide, is also of interest.

The concrete thus prepared typically contains at least about 0.2 parts by weight of mortar. The amount of mortar phase in conventional concrete is generally limited to a maximum of 0.6 parts by weight due to the fact that the tendency of the concrete to crack increases as the amount of mortar increases. However, since the addition of fiber bundles to the concrete results in a small tendency to crack, it is possible to produce concretes with a larger mortar phase than is normally used without the risk of excessive cracking. Thus, the concrete may contain a relatively large mortar phase, such as up to about 0.8 parts by weight or more.

The fibers of the fiber bundles of the invention are typically present in the material in an amount of about 0.05-0.5%, especially about 0.1-0.3%, such as 0.15-0.25% by weight of the cementitious materials.

Typically in situ concrete with a cement content of about 250-400 kg / m 2³, the fiber content is thus less than about 4 kg / m 2³, typically n, 0.1-2.0 kg / m 2³, such as about 0.3-1.0 kg / m 2³, especially n, 0.4-0.8 kg / m 2³, e.g., about 0.5-0.7 kg / m³.

The concrete or mortar prepared according to the invention may contain additives which reduce the water requirement, improve the workability, change the Theology, reduce the permeability, entrain air or slow or accelerate the reaction of the cement with water. It may also contain various types of organic polymers added as solids or aqueous emulsions, including polymer impregnated concrete or polymer cement concrete. In addition, it may contain a reinforcement contained therein either in the form of rods or nets, including ferro-cement and metal plaster, or in the form of additional fibers, e.g. metal, glass or synthetic material.

As described above, it has been found that the addition of even very small amounts of fiber bundles results in the cement-based material in question, which has various advantages. The fact that these advantages can be obtained with such small amounts of fibers can be explained by the fineness of the fibers together with the fact that they can be dispersed substantially homogeneously in the material. The fiber bundles of the present invention having e.g. 300 x 10 ^ individual 12 mm long filaments / kg provide approx. 2000 km of fiber / m³, when added to a cement-based material, eg 0.6 kg in fiber bundles / m³. Viewed in this light, it is clear that even small amounts of fibers can provide significant benefits when added to a cementitious material.

The cement-based material is prepared according to the invention by adding less than 1% by weight of the fiber-containing bundles of this invention to a concrete, mortar or cement mixture to which water has been added, mixing the resulting mixture for at least about 20 seconds to obtain a concrete, mortar or cement mixture. into which the individual filaments are distributed substantially homogeneously and by casting the mortar or cement mixture to the desired configuration by optionally adding additional ingredients such as reinforcement during casting. Fiber bundles are typically added in an amount of about 0.05-0.5%, especially about 0.1-0.3%, such as about 0.150.25% by weight of cementitious materials.

Because the individual filaments of the fiber bundles are easily dispersed in all types of concrete and cement-based materials, the length of the mixing cycle is dictated by the need to produce good concrete and not the need to disperse the fibers. The fiber bundles of this invention can be used in all forms of mixing, including rotary drum and paddle mixers, and in particular truck mixers for pre-mixed concrete, and do not require any special mixing arrangements or equipment. In cases where a precast concrete, mortar or cement mixture to which fiber bundles have been added is mixed in a paddle mixer (also known as a forced action mixer), mixing is performed for at least about 20 seconds, typically at least about 30 seconds to obtain a concrete, mortar or cement mixture. , into which the individual filaments are distributed substantially homogeneously. In cases where an in situ concrete, mortar or cement mixture to which fiber bundles have been added is mixed in a tumble mixer (also known as a barrel mixer), mixing is typically performed for at least about 2 minutes to obtain a concrete, mortar or cement mixture in which the individual filaments are substantially homogeneous. .

The fiber bundles of this invention are often added to a concrete mix in a truck mixer, which mixer is a device consisting of a spiral inside a tilted drum. As the drum rotates, the material to be mixed simply falls to the bottom of the spiral and this creates a mixing effect. The fiber bundles can also be added to already mixed concrete and good dispersion can be achieved with a ready-mixed drum which rotates e.g. 15 rpm for e.g. 3 minutes.

The truck mixer can be designed for mixing or just for mixing. In some systems, the concrete is mixed and placed in the drum of the truck mixer, so the truck is used only to mix the already mixed concrete, while in other systems the concrete materials are placed in the drum of the truck mixer and the truck mixer actually mixes the materials. It is possible to mix the fiber bundles with the dry components of the cement or concrete mix, e.g. to premixed, dry-blended materials that require only the addition of water, but this is currently not considered preferred or necessary because ar100239 is considered to be at least as advantageous as adding fiber bundles to a wet blend or mixture to which water has already been added due to the substantially hydrophilic surface properties of the fibers.

Mixed concrete, mortar, or cement containing the fibers of this invention substantially homogeneously dispersed therein can be cast in a conventional manner to the desired configuration. The material can thus be compacted and shaped either by a simple mixer or by gravity or with a trowel, plastering, stuffing, filling, pressing, water suction, vacuum, extrusion, pumping, spraying, dry cellulating, spinning, rolling or a combination of these processes. Additional pieces, such as reinforcement, can be added to the material during casting if desired or necessary.

The materials made in accordance with this invention are considered to be particularly important in all types of in-situ cast concrete, such as pavements, foundations, roads, floors, bridge decks, concrete buildings, structural concrete, retaining walls, water retaining structures and precast concrete, such as concrete used for marine and military purposes. cladding of panels, floors, beams and beams, in concrete used for decorative and architectural products, prefabricated structures, pipes, tunnel cladding, etc.

The present invention is further illustrated by the following non-limiting examples.

Example 1

Manufacture of fiber bundles

The production of fiber bundles involved the following steps:

- smelting the fibrous raw material to obtain a molten mass,

- spinning of the molten mass into a spun bundle of filaments,

- stretching of the bundle of filaments,

- drying and fixing of the bundle of filaments,

treating the bundle of filaments with a wetting agent, and

cutting of bundles of filaments.

The fibers consisted of a homopolymer isotactic polypropylene (Petrofina 10060, manufactured by Pertrofina, Belgium) with a melting point of about 160 ° C and a melt of 100239 dex 35. The polypropylene was melted and then spun at a temperature of about 280 ° C using a spinning nozzle with 22,880 sulfur and at a draw speed of 22.5 m / min. The spun bundle of filaments was then passed through a hot water bath at 100 ° C and then stretched at 60.7 m / min to give a stretch ratio of 2.7. The drying and fixing of the bundle of filaments was carried out by passing the bundle through an oven at 150 ° C at a speed of 54.2 m / min, which allowed the fibers to shrink by about 12% and the stresses caused by the stretching of the fibers to be released. The fibers were given the desired surface tension by treating the bundle with a wetting agent (SW-T, Nissin Kagaku Kenkyosho Ltd, Japan, as above) by passing through a pair of brush rollers. Finally, the fiber bundles were cut to a length of 12 mm.

The finished fibers, which contained roughly 1000 individual filaments per bundle, had a moisture content of less than 17% and contained about 0.5% wetting agent. The fineness of the individual filaments was 2.8 dtex, which corresponds to a diameter of about 20 μm, whereby the aspect ratio of the fibers becomes about 600.

Example 2

Manufacture of concrete beams

Concrete beams were made at the factory from a premixed concrete mix consisting of fast-curing Portland cement, standard rough concrete sand and gravel that passed through a 20 mm sieve in a ratio of 2: 3: 6 with a cement content of 400 kg cement / mT. was 20 ° C, as with the fiber bundles of Example 1. The ratio of water to cement was 0.6 and fiber bundles were added in an amount of 0.2% by weight of the cementitious materials. The concrete was mixed in a rotary tumble mixer with a capacity of about 100 L using a speed of about 25 rpnrn and a total mixing time of 4 minutes and adding fiber bundles after the first 2 minutes of mixing. The individual filaments were substantially homogeneously distributed in the mixture at the end of the mixing period. Concrete beams with a square cross-sectional side length of 150 mm and a beam length of 550 mm were prepared by infiltrating the mixture into a multi-compartment mold and compacting by hand.

For comparison purposes, beams were prepared as above, but without adding fibers. Beams with and without fibers were cast alternately in a multi-compartment mold.

Example 3 Bending tests

Laboratory tests were performed on the concrete beams prepared in Example 2, which contained either 0.2% by weight of fibers from the cementitious materials or no fibers at all. The beams were subjected to early drying and then subjected to a standard 4-point elastic bending test with a distance of 450 mm for the outer rolls and 150 mm for the inner rollers.

The results of these experiments are summarized as follows:

Fibers without fibers without fibers 0,2% fibers 0,2% fibers

Murtomoduli

2.83 MPa 2.31 MPa 3.17 MPa

3.22 MPa

It is found that the modulus of fracture is significantly higher for beams containing the fibers of Example 1. The fracture modulus was also more consistent with beam containing fibers.

Example 4

Periodic load tests

Concrete beams were prepared as in Example 2 and subjected to a 4-point elastic bending test as in Example 3 with the following exceptions: 1) the beams were not subjected to early drying and 2) the load was kept below the shape modulus and switched on continuously at 2000 cycles / h. The load was increased after 4000 cycles to shorten the duration of the experiment. The results are summarized as follows:

Maximum Number of cycles under load

<td>Fiber</td><td>murtomoduli</td><td>15 kN</td><td>16 kN</td><td>17kN</td><td>18 kN</td><td>19 kN</td>

<td>No</td><td>2.13 MPa</td><td> 1540</td><td> 425</td><td></td><td></td><td></td>

<td>No</td><td>2.27 MPa</td><td></td><td> 4160</td><td> 17</td><td></td><td></td>

<td>Yes</td><td>2.40 MPa</td><td></td><td> 4000</td><td> 4000</td><td> 925</td><td></td>

<td>Yes</td><td>2.53 MPa</td><td></td><td> 4000</td><td> 4000</td><td> 4000</td><td> 1875</td>

The experiments clearly showed a noticeable improvement in both load levels and fatigue resistance with fiber-containing beams. The combination of both increased load levels and the number of pre-fracture cycles with fibrous concrete shows significantly improved fatigue resistance.

Example 5

Manufacture of in situ concrete containing the fiber bundles of this invention

The fiber bundles of Example 1 have been added in an amount of 0.2% by weight of cementitious materials to various types of concretes, including in situ concrete, using conventional unmodified mixing equipment and without the need for other additives as follows:

(a) 30 MPa concrete with a cement content of 300 kg / m 2 and 20 mm of aggregate, with a water / cement ratio of 0.56 and 50 mm cone penetration.

(b) 30 MPa concrete as in (a) above, but with 320 kg / m 2 of cement and a water-to-cement ratio of 0,52 and containing an air-entraining substance.

(c) 30 MPa concrete as in (a) above, but with 210 kg of ordinary Portland cement and 105 kg of powdered fuel ash per cubic meter.

(d) 30 MPa concrete with 350 kg / m 2 of cement and roughly equal amounts of 10 mm of aggregate and sand at a water-cement ratio with a cone penetration of 0.58 and 100 mm.

e) 40 MPa concrete with 400 kg / ln ^ cement and 10 mm aggregate in a water to cement ratio with a cone penetration of 0.50 and 100 mm.

All of the above concretes were mixed with conventional truck mixers manufactured by Mulder and Stothert &amp; Pitt containing 6 rrP of concrete. In all cases, complete dispersion of the fibers was achieved in 3 minutes with the drum rotating at 15 rpm. This complete dispersion was also achieved when the fibers were added to the already mixed concrete by simply feeding the fibers to the back of the truck mixer on site.

Example 6

Manufacture of precast concrete

The following pre-cast concrete materials were prepared containing the fiber bundles of this invention, which were added as the fiber bundles of Example 1 in an amount of 0.2% by weight of the cementitious materials:

(a) 40 MPa concrete with 400 kg / m 2 of cement and roughly equal amounts of 5 mm gravel and sand with a water / cement ratio of 0.31.

b) 40 MPa concrete with 350 kg / m 2 of cement and roughly equal amounts of 10 mm of gravel and sand in a water to cement ratio of 0.30.

Complete dispersion of the fibers was achieved in 1 minute with a forced paddle mixer (Teka and Liner Cumflow). In both cases, the concrete compacted well and there were no adverse surface effects in the products.

Example 7

Concrete Pavement

A 30 MPa concrete was prepared containing about 300 mg / m 2 of cement and 20 mm of aggregate in a water to cement ratio of 0.55 and containing 0.2% by weight of the fibers of the cementitious materials of this invention. 200 mm thick in situ concrete pavement areas were cast from the outside into 2.5 m wide decks with continuous lengths of 50 m, without shrinkage control joints. No cracking occurred within 2 months, so no cracking is expected.

Similar experiments, which gave similar results, had been performed 9 months earlier with 20 m long continuous concrete decks.

Example 8

Practical experience with concrete

a) A 200 mm thick concrete carriageway with a width of about 5 m and a length of just over 80 m and a pitch of about 1/15 was cast using 0.7 kg of the fibers / m ^ of concrete of Example 1. The concrete had a strength of 30 MPa, with a total cement content of air containing 330 kg / m 2 and containing 25% blast furnace slag.

The entire 80 m was cast in one day as a continuous slab formed from the upper end of the slope to its lower end. No shrinkage control joints were formed. The upper end of the concrete was thickened so that it was anchored effectively and the end of the carriageway was stopped before the associated concrete at the lower end and this was filled later.

After a few weeks, a single crack appeared across the road approximately to the center and in line with the seam in the associated concrete. After nearly a year of continuous operation of heavy trucks, ore trucks, etc., the road has not been damaged or further cracked. The central crack has not opened and no distinct vertical movement has taken place on either side of the crack, the crack being in fact only visible with a careful examination.

These and other applications show that the production of continuous bands of always about 50 running meters without shrinkage control joints seems to be entirely possible with the fiber bundles of this invention and without any steel reinforcement.

b) The fiber bundles of this invention were used in a factory floor of laser-corrected concrete.

The concrete was applied in two castings, each on the same day, with the first casting at 2300 m 2 and the second casting at 3200 m 2 and the concrete being standard 30 MPa concrete with 330 kg / iZ of ordinary Portland cement. The concrete contained the fibers of Example 1 in an amount of 0.6 kg / rrZn. The surface was mechanically rubbed and treated the next day with sodium silicate as a surface hardener. The concrete was applied to a thickness of 150 mm on top of a polyethylene vapor barrier.

Two days after application, the concrete was sawn at column intervals or roughly every seven meters to a depth of approximately 50 mm to form long-term shrinkage control joints.

After several months, numerous of the sawn adjustment joints had opened, but no cracking of the concrete had otherwise occurred.

Due to the very cold weather following the pouring of the concrete, the factory radiant gas heaters were left on for 48 hours, but nevertheless no shrinkage cracking occurred.

(c) More than 4 tonnes of the fibers of this invention have been used in coastal embankment to protect large areas of lowland land in Lincolnshire, England from flooding in the North Sea. Two grades of concrete have been used, 30 MPa and 40 MPa concrete, each with large amounts of cement substitutes to control the alkali content.

Serious plastic cracking has always occurred in beach concrete due to very windy and weather-prone conditions. It was found that the addition of 0.9 kg of the fibers of Example 1 resulted in a dramatic reduction in the incidence of cracking and the overall results obtained have proved to be very satisfactory.

d) Approximately 100,000 m 2 of ground floor car parking concrete containing the fibers of this invention was poured into a shopping center new building.

150 mm thick concrete slabs were prepared by adding steel mesh to the bottom, but without adding surface steel mesh, but instead preparing concrete using 0.9 kg of fiber bundles of Example 1 per cubic meter. The concrete was 30 MPa concrete weighing 330 kg / m 2 with air entrained with 25% slag as a substitute for cement.

The production of such large concrete slabs with a size of 8 x 16 m would normally be very difficult, as the use of a base steel mesh retains the total shrinkage of the slab and thus provides higher shrinkage heating to the concrete. However, no cracking occurred in the concrete slabs containing the fibers of this invention and the overall results obtained have been excellent.

e) A factory floor of more than 6000 m ^ with an overall thickness of 150 mm was cast using standard deck casting with sawn shrinkage control joints.

The concrete was a high-strength concrete containing microsilicon dioxide with a cement content of 350 kg / m 2 and was prepared using a standard superplasticizer to reduce the water-cement ratio below 0.5. The fibers of Example 1 were used in an amount of 0.6 kg / nP.

It was found that the cubic strengths actually achieved were consistently higher than expected. The results have proven to be excellent and show that an extra strong concrete, which is generally known to be more susceptible to cracking, together with the anti-cracking effect of the fibers, is an excellent combination.