Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B28—WORKING CEMENT, CLAY, OR STONE
  • B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
  • B28B3/00—Producing shaped articles from the material by using presses; Presses specially adapted therefor
  • B28B3/20—Producing shaped articles from the material by using presses; Presses specially adapted therefor wherein the material is extruded
  • B28B3/22—Producing shaped articles from the material by using presses; Presses specially adapted therefor wherein the material is extruded by screw or worm
  • B28B3/228—Slipform casting extruder, e.g. self-propelled extruder
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B28—WORKING CEMENT, CLAY, OR STONE
  • B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
  • B28B1/00—Producing shaped prefabricated articles from the material
  • B28B1/08—Producing shaped prefabricated articles from the material by vibrating or jolting
  • B28B1/084—Producing shaped prefabricated articles from the material by vibrating or jolting the vibrating moulds or cores being moved horizontally for making strands of moulded articles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B28—WORKING CEMENT, CLAY, OR STONE
  • B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
  • B28B7/00—Moulds; Cores; Mandrels
  • B28B7/40—Moulds; Cores; Mandrels characterised by means for modifying the properties of the moulding material
  • B28B7/44—Moulds; Cores; Mandrels characterised by means for modifying the properties of the moulding material for treating with gases or degassing, e.g. for de-aerating
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B40/00—Processes, in general, for influencing or modifying the properties of mortars, concrete or artificial stone compositions, e.g. their setting or hardening ability
  • C04B40/02—Selection of the hardening environment
  • C04B40/0231—Carbon dioxide hardening

Definitions

• This invention relates to a method for casting concrete products so that the hardening reaction of the concrete is speeded up by adding to concrete mix an additive which speeds up this reaction and which is led into concrete mix having a consistency suitably stiff for slide casting while compacting the concrete mix in a slide casting machine, before the concrete mix is formed into a final product in an extruding nozzle.
• the invention also relates to equipment for casting concrete products having one or several cavities by slide casting method of pressurized concrete mix, which equipment has a mould part moving on a casting bed and formed by side and top surfaces and also forming a compaction chamber, and in connection with this one or several compacting members, and which equipment is provided with means leading into the compaction chamber at feeding screws for leading the additive into the concrete mix.
• FI patent publication 66139 describes a vacuum concreting method, wherein the concrete product is hardened by first subjecting the concrete mix to negative pressure and by then leading carbon dioxide into the product's capil ⁇ laries.
• FI patent publication 72965 describes a method where ⁇ in carbon dioxide is used to harden concrete sprayed in a fluid state so that carbon dioxide is introduced into the concrete mix before spraying, and carbon dioxide is also used as a propellant in the spraying process.
• US patent publication 4 927 573 describes a method com ⁇ parable with the method described in the above FI patent publication 66139.
• press ⁇ urized carbon dioxide is supplied into concrete mix which is under pressure in a mould to speed up hardening.
• the carbon dioxide is supplied only when compacting of the concrete product is completed and the product has been given its final shape, whereby the gas works only on the surface of the product. Since the gas is supplied into a fixed mould, out- side the finally shaped product, the gas must be under a very high pressure.
• CH patent publication 323 266 describes casting of elongated profile beams of concrete by using an extrusion method.
• the device described in this publication is not a moving casting machine and it is not suitable for casting prestressed concrete products.
• the publication mentions the use of additives which increase elasticity or bring about quick binding. The additives are supplied to the concrete mix during the compaction and forming stages, before final shaping. However, the publication does not describe specifically what kind of additives are used.
• Various liquids or solid materials were generally used in the prior art as concrete additives for the mentioned purposes. They were intended among other things to reduce the stiffness of the concrete mix or to either accelerate or slow down hardening.
• Casting is by the extrusion method and as a continuous process by using concrete mix of a relatively stiff consist- ency. This is brought under pressure into the mould part of a casting machine moving on a bed, which mould part is formed by side faces and a top face located against the bed.
• the mould part also forms a compaction chamber, wherein the concrete mix is compacted with the aid of feeding screws and compacting mandrels.
• the feeding screws bring about a casting pressure in the concrete mix causing the casting machine move on its bed while the concrete is discharged.
• the concrete is of a sufficiently stiff consistency for the cast product to maintain its shape while discharging from the casting machine.
• the method in accordance with the present invention is characterized in that the additive is carbon dioxide gas; that the carbon dioxide discharging from a pressure vessel is heated to keep its temperature above 0°C, preferably at least at 18°C; that the overpressure of the carbon dioxide is about 1 -
• the quantity of the carbon dioxide measured at atmospheric pressure is about 0.1 - 3 times, preferably 0.5 - 1 times the volume of the concrete mix; and that carbon dioxide is supplied to the concrete mix not more than 60 seconds, preferably 1 - 30 seconds before the final compaction of the concrete.
• the equipment according to the invention is characterized in that the means for leading the additive comprise one or several nozzles for feeding pressurized gas and a flow meter connected to each nozzle.
• the volume weight of the concrete mix increases by about 50 kg/m 3 compared with conventional extruder casting not using the treatment by carbon dioxide according to this invention.
• a final product is obtained on an industrial scale with a density which is even as much as 99.7 per cent of the theoretical maximum density.
• This is a significant improvement over previously known concrete products made by slide casting.
• other properties of the product improve, such as waterproofness and durability.
• Previous mechanic compaction methods did not allow such complete removal of air from relatively dry concrete mix suitable for slide casting.
• the strength and density of the product improve not only due to the removal of air but also because they are improved by the calcium carbonate which becomes part of the concrete mix in consequence of the reaction.
• the compacting screw of the casting machine creates a pressure in the concrete mix, which again speeds up the reaction mentioned above. As the reaction is very quick, it is important to feed the gas into the concrete as late as possible before its final shaping.
• the strength of the cast slab after e.g. 6 hours may increase by about 10 - 20 per cent compared with the prior art. This clearly accelerates the production process as a whole. This means that either a quicker process with the same quantity of binder (cement) is obtained, or the quantity of the binder can be reduced while the speed of the process remains the same. In some cases the product's wall thickness may be reduced, because even less strength in the finished product will be sufficient in several applications.
• carbon dioxide is supplied into the concrete mix just before the compaction stage.
• the preferable time between the feeding of carbon dioxide and concrete compaction is about 1 - 30 seconds, depending on the casting speed of the machine producing the product, on the cement quality and on the temperature of the concrete mix.
• carbon dioxide is supplied into the compaction chamber, it displaces air in the concrete mix which has not yet compacted.
• each gas feeding nozzle must be provided with a flow meter of its own, for example, with a rotameter.
• the gas must also be heated constantly, so that when discharging it will not cool but its temperature will remain at over 0°C all the time, preferably at about 18 - 30°C. Heating, too, requires exact control.
• a suitable gas quantity is about 0.1 - 3 times the concrete volume, whereby the gas volume is expressed at atmospheric pressure.
• desired properties may be chosen for the concrete, for example, increased fresh strength.
• Other gaseous substances may also be led into the concrete mix which have desired effects on the properties of the concrete mix.
• FIG 1 is a side view of the equipment according to the invention
• Figure 2 shows the gas supply arrangement of the equipment according to the invention
• Figures 3a and 3b show the shear surfaces of a product made with the method according to the invention and with a prior art method, respectively.
• the slide casting machine is known as such. It moves on a bed 1 carried by wheels 2. Concrete mix is supplied from a hopper 3 onto conical feeding screws 4, of which the equipment has one or several 'in parallel.
• a compacting mandrel 5 is a continuation to each feeding screw. The feeding screws and compacting mandrels are surrounded by a top wall and side walls, which form a compaction chamber together with the casting bed.
• the concrete mix is compacted inside these, around the compacting mandrels, and is formed into a hollow-core slab as the casting machine is moving to the right in the figure under the effect of a reaction force of the concrete mix which is pressurized by the feeding screws.
• the machine moves at a speed of about 0.5 - 3 m/min, preferably about 1 - 2 m/min, depending on the cross- sectional area of the product to be cast. A higher speed can be used with smaller cross-sectional surfaces.
• the slide casting machine is combined with a carbon dioxide vessel 6, from which a gas supply pipe 7 leads to each feeding screw.
• the length of nozzle part 8 of the supply pipe is chosen so that gas will enter the concrete at the right time, that is, about 1 - 30 seconds before final compaction of the concrete.
• the supply point depends on the machine's speed of progress and on the concrete quality.
• the nozzle part has one or several holes, from which the gas is discharged into the concrete mix.
• FIG. 2 shows in greater detail two carbon dioxide bottles 6 and how these are connected to the gas supply pipe
• Figures 3a and 3b show photographs of a product made with the method according to the invention and with a prior art method, respectively. Using a diamond drill, a cylindrical piece was cut off the products made with both methods.
• the product made by using carbon dioxide is perfectly compact, whereas the product obtained without adding any carbon dioxide has large pores and air bubbles.
• the feeding of C0 2 was arranged from below the feeding screw in such a way that the gas flowed into the fresh concrete at the rear end of the screw, about 80 mm before the beginning of the compacting mandrel.
• the corresponding point of time is about 10 seconds before final compaction.
• About 1 litre of gas was supplied for every one litre of concrete mix moving through the casting machine (the gas volume is ex ⁇ pressed at atmospheric pressure, before its compression in the pressurized concrete mix) .
• the fresh strength of compacted concrete was valuated firstly by a pipe loading test by pressing whole cast pipes until they broke and secondly by loading pipe wall pieces with a penetrometer. In the pipe loading test, the pipe rested on its side on a bed and it was pressed by a horizontal loading plane. The loading force was measured. The test samples were tested immediately after casting.
• the pipe loading test showed that C0 2 -treated pieces with ⁇ stood an average load of 450 g per pipe length centimetre, whereas the untreated samples collapsed of their own weight so that no proper measurements were obtained.
• the values for treated pieces were about 1.5 times higher than those for untreated ones.
• Tests were also done by using more gas, whereby fresh strength values which were even 2 - 3 times higher were obtained.
• Other tests were also done both with laboratory equipment and with full-scale production equipment, that is, with a hollow-core slab slide casting machine of the extruder type. In the performed tests, the method was found to work in the expected way. The above is a description of an application of the method to a slide casting machine equipped with feeding screws.
• Hollow-core slabs are cast also by using a so-called slip- form device having none of the feeding screws described above.
• Fresh concrete of sligthly more fluid consistency is used in the device and compaction is by vibration.
• the hydrostatic pressure of the concrete mix creates the casting pressure.
• the method according to the invention can also be applied in such a method. It may then suffice to lead carbon dioxide only onto the top surface of the product. In this way, the top surface is hardened and it is prevented from sagging at the cavities.
• the method is suitable for use not only in casting hollow- core slabs but also when casting other products produced by slide casting.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Ceramic Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Mechanical Engineering (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Health & Medical Sciences (AREA)
• Toxicology (AREA)
• Materials Engineering (AREA)
• Structural Engineering (AREA)
• Organic Chemistry (AREA)
• Devices For Post-Treatments, Processing, Supply, Discharge, And Other Processes (AREA)

Priority Applications (5)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

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Cited By (13)

Families Citing this family (1)

Citations (2)

• 1993
  • 1993-06-02 FI FI932509A patent/FI932509A0/fi not_active Application Discontinuation
• 1994
  • 1994-06-02 AU AU68460/94A patent/AU6846094A/en not_active Abandoned
  • 1994-06-02 EP EP94917000A patent/EP0701503B1/en not_active Expired - Lifetime
  • 1994-06-02 WO PCT/FI1994/000233 patent/WO1994027797A1/en active IP Right Grant
  • 1994-06-02 DE DE69425495T patent/DE69425495T2/de not_active Expired - Fee Related
• 1995
  • 1995-11-29 NO NO954855A patent/NO301698B1/no unknown

Patent Citations (2)

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