Classifications

• • 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
  • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
  • C04B28/02—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing hydraulic cements other than calcium sulfates
• • 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
  • C04B24/00—Use of organic materials as active ingredients for mortars, concrete or artificial stone, e.g. plasticisers
  • C04B24/24—Macromolecular compounds
  • C04B24/38—Polysaccharides or derivatives thereof
• • 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
  • C04B24/00—Use of organic materials as active ingredients for mortars, concrete or artificial stone, e.g. plasticisers
  • C04B24/24—Macromolecular compounds
  • C04B24/38—Polysaccharides or derivatives thereof
  • C04B24/383—Cellulose or derivatives thereof

Definitions

• the invention relates to a method for preparing a concrete shaped body from a moist concrete, to moist concrete and to a concrete body prepared from moist concrete.
• Formed concrete bodies are made by filling moulds with concrete.
• Examples of such concrete bodies are blocks, slabs (paving stones), curbstones, etc.
• After removal of the moulds the shape of the concrete bodies has to be retained.
• the removal of the mould is at such a short time after filling that setting of cement cannot play a significant role in retaining the shape. Therefore, retaining the shape of the bodies is a critical step in the production process.
• Concrete products are in direct competition with other forms of construction materials, such as metals, plastics, wood, asbestos-cement etc.
• concrete with a very low amount of water is used, so-called earth moist concrete.
• This concrete has a much higher so-called green strength than concrete with a high amount of water, such as self-compacting concrete.
• the green strength is the strength of fresh concrete before setting of cement plays a role.
• a low amount of water also ensures that the concrete does not stick to the moulds or the press.
• EP-A-O 955 277 describes a self-compacting concrete comprising a polysurfactant-like additive, which provides the concrete with desirable properties making it very easy to pour or place.
• DE-A- 102 09 812 is directed to the use of water soluble polysaccharide derivatives as dispersion agent in particular for mortar and concrete.
• the polysaccharide derivatives consist of partial hydrolysed celluloses and/or starches, wherein the starches preferably have a polymerisation degree of 40 to 500.
• US-A-5 575 840 describes an additive for aiding the water retention of cementitious and adhesive compositions.
• the additive comprises a mixture of cold-water-soluble, unmodified starch and a polysaccharide.
• the additive is free of modified starches.
• US-A-3 847 630 describes a sprayable water-permeable porous concrete with a water-cement ratio of between 0.32 and 0.48, which concrete comprises a macromolecular compound.
• US-A-4 487 864 describes the use of a modified carbohydrate polymer comprising a polyacrylamide as a water retention aid in various cementitious compositions.
• US-B-6 387 171 is directed to a light weight concrete composition comprising granular starch. It is an object of the invention to provide a novel method for preparing a concrete shaped body from a moist concrete, that can be used as an alternative to known methods.
• An additional object is to provide a method for preparing a concrete shaped body from a moist concrete with good filling properties for filling a mould with the concrete, whilst maintaining sufficient retaining properties of the shape, also if the mould is removed before the concrete has substantially set.
• Another object is to provide a method which allows the use of a higher amount of water than in conventional methodology making use of moist concrete, whilst maintaining good shape retaining properties of the concrete, before substantial setting of the concrete.
• the present invention relates to a method for preparing a concrete shaped body from a moist concrete, comprising
• the moist concrete is a concrete according to compaction class CO, Cl, or C2 as defined in EN 206-1.
• an aggregate sand and/or gravel is usually present in the moist concrete.
• the term "at least partially modified starch” herein means that at least part of the starch which is used in the mixture for forming the moist concrete is modified.
• the modified starch can be any modified starch, such as chemically, biologically and/or physically modified starch.
• the starch according to the invention is preferably soluble in cold water.
• Concrete can be classified in terms of the compaction class.
• the term "moist concrete” is in particular used for a concrete having a compaction class CO, Cl or C2 as defined in EN 206-1.
• the degree of compactability (C) of a moist concrete is in particular at least 1.11.
• C is more than 1.20, in particular more than 1.25 (i.e. class CO or Cl).
• EN 206-1 the consistence of earth moist concrete, i.e. concrete with a low water content designed to be compacted in special processes, is not classified.
• NEN 8005 classify earth moist concrete in compaction class Cl.
• C is defined herein as (ho/(h o -s), wherein ho is the initial height of a column of concrete, s the difference between ho and h wherein h is the height after sagging (see figure 1).
• C may be determined according to NEN 5958.
• the exact water to cement ratio of the concrete generally depends on for instance the application (the product being made), the raw materials including the use of a (super)plasticizer, and the production equipment.
• sufficient dimension stability of the shaped body is usually reached shortly after shaping (e.g. in a mould), typically within a few seconds to a couple of minutes.
• Starch and starch derivatives and combinations of these with other polymers have been found to improve the production process and/or the concrete properties in a number of ways.
• the internal friction of the concrete and the friction between the concrete and production equipment may be decreased so that filling the moulds may improve. As a consequence pressing and vibration may be reduced, which leads to less wear and tear of the production machinery.
• the reduced internal friction can also lead to increased homogeneity of the concrete and/or an increased density of the concrete.
• An increased density may be desired for providing a concrete with a relatively low pore volume and/or a small average pore size.
• An increased density may contribute to improved thaw/frost resistance, a low efflorescence of salts (in particular free lime), a better wear resistance of the concrete and/or a higher colour intensity of an article made from the concrete.
• the use of starch or a combination of starch with one or more other polymers increases the green strength of the concrete which contributes to retaining the shape of the concrete body. This leads to a reduction in B-grade production (products with a relatively low quality, yet still useful for less demanding applications), and thus to an increase in
• A- grade production (high quality products; usually not showing a substantial amount of visible deformations).
• a method according to the invention allows the use of a higher amount of water and/or plasticizer, whilst maintaining good stability and/or strength. Increase of the amount of water is thought to lead to a more complete cement hydration. This makes it possible to increase the strength of the concrete and/or offers the opportunity to decrease the amount of cement in the formulation. A better cement hydration may also change the pore size distribution and lead to a decreased pore volume. As a consequence the thaw/frost resistance of the concrete may be improved because the tendency of water from the environment to penetrate into the concrete is reduced.
• any cement suitable for preparing concrete may be used, in particular any cement as defined in NEN-EN 206-1 and more specifically in EN197-1.
• any aggregate suitable for preparing concrete may be used as, in particular any aggregate as defined in NEN-EN 206-1 and more specifically in prEN 12620:2000 for normal and heavy-weight aggregate and prEN 13055-1:1997 for light-weight aggregates.
• the starch may in principle be any starch, including modified starches, such as chemically, biologically and/or physically modified starches.
• a starch from any starch may be used.
• a starch may be selected from potato, tapioca, maize and wheat, including starch from varieties having a high amylopectin content, such as amylopectin potato starch and waxy maize starch.
• amylopectin potato starch and waxy maize starch are examples having a high amylopectin content.
• good results have been achieved with a potato starch.
• At least part of the starch is a chemically modified starch.
• Such starches are commercially available or may be made by a method known in the art.
• Suitable chemically modified starches include starch ethers, starch esters and crosslinked starches.
• Preferred examples include starch ethers and crosslinked starch, including cross-linked starch ethers.
• a starch that is hydroxyalkylated and/or carboxyalkylated, in particular a starch that is hydroxypropylated and/or carboxymethylated.
• hydroxyalkylated and/or carboxyalkylated starch is cross-linked.
• the degree of modification may be chosen within wide limits.
• the degree of hydroxyalkylation (DS) of the starch is between 0.01 and 2.0 hydroxyalkylations per monosaccharide unit. In a particular embodiment the degree of hydoxyalkylation is in the range of 0.05-0.8.
• the degree of carboxyalkylation of the starch is between 0.01 and 0.5 carboxyalkylations per monosaccharide unit.
• a high degree of polymerisation (DP) of the polysaccharide is preferred with respect to the degradation of the starch. Therefore, the DP is preferably 100 or more, more preferably 500 or more, and most preferably 1000 or more. It is believed that a high degree of polymerization has a positive effect on the increase of the green strength.
• the starch may be cross-linked with any cross-linking agent known in the art, including epichlorohydrin, linear dicarboxylic acid anhydrides, citric acid acrolein, phosphorus oxychloride, adipic/acetic mixed acid anhydrides, dichloro acetic acid, trimetaphosphate salts, acrolein, polyphosphates (e.g. hexametaphosphate), biphenyl compounds, N,N,-dimethylol-imidzolidon-2 (DMEU), formaldehyde, cyanuric chloride, diioscyanates, dimethylolethylene urea and divinyl sulfones.
• any cross-linking agent known in the art, including epichlorohydrin, linear dicarboxylic acid anhydrides, citric acid acrolein, phosphorus oxychloride, adipic/acetic mixed acid anhydrides, dichloro acetic acid, trimetaphosphate
• the cross-linking reaction may be carried out under any conditions which are known to be suitable for this type of reaction.
• Crosslinking may very suitably be done to a cross-linking degree (DS) of about 0.0001 to about 0.05, in particular with epichlorohydrine as the crosslinking agent.
• DS cross-linking degree
• the starch ester can e.g. suitably be prepared as described in EP A-I 225 268 (in particular page 5, lines 25-28). Thus, it may be prepared by reacting an aqueous suspension of the starch with an alkali (such as NaOH) at a pH in the range of 6-9.5, usually at a temperature of about 20-40 °C.
• an alkali such as NaOH
• the degree of esterification of the starch (DS) is between 0.02 and 2 ester moieties per monosaccharide unit.
• the amount of starch in the concrete may be chosen in wide limits. In practice, an amount of starch in the range of 0.01 to 1.0 wt.%, based upon the weight of cement, usually suffices. An amount in the range of about 0.05 to 0.3 % has been found advantageous in terms of good performance to cost ratio.
• one or more components may be added to the concrete.
• At least one second (organic) polymer is present, in particular a polysaccharide, preferably at least one polysaccharide selected from the group consisting of cellulose, xanthane gum, tamarind, welan gum and guar.
• the further polysaccharide is preferably chemically modified, more preferably a polysaccharide ether.
• the further polysaccharide is cross-linked.
• the further polysaccharide may generally be modified in a manner as indicated for the starch.
• a preferred further polysaccharide is an alky Ip oly saccharide - in particular a alkylcellulose, more in particular a methylcellulose - which has a DS of about 1-2. More preferably the alkylpolysaccharide (alkylcellulose) is additionally (hydroxyl) alkylated, in particular with a DS of 0.05 to 0.5.
• the total amount of the further polymer(s), in particular the polysaccharide other than starch, more in particular a cellulose (such as cellulose ether), is preferably 3-50 wt.% based on the combined weight of the polymer (s) including the starch, more preferably up to 20 wt.%.
• a further polymer in particular a polysaccharide other than starch, more in particular a cellulose (such as cellulose ether), in an amount of at least about 5 wt.% based on the combined weight of the polymer(s) including the starch.
• a further polymer in particular a polysaccharide other than starch, more in particular a cellulose (such as cellulose ether), in an amount of at least about 5 wt.% based on the combined weight of the polymer(s) including the starch.
• one or more other additives may be present in the concrete.
• an additional plasticizer and/or a water adsorbing agent may be present.
• Particular suitable plasticizers may be selected from the group consisting of lignosulfonates, melamine-based or naphtalene-based stiperplasticizers, polycarboxylates and the like; a particularly suitable water adsorbing agent is limestone powder.
• the method of the invention involves shaping of the moist concrete into the desired shape. This may be done based upon a method known in the art. Preferably, the shaping is accomplished by filling a mould with the moist concrete.
• the moist concrete can be distributed in a highly homogenous manner in the mould.
• the moist concrete in the mould is subjected to vibratory ramming until it is dense and ready for removal from the mould. This facilitates densification of the concrete, which improves the dimension stabilisation of the concrete.
• the required vibration may be reduced, compared to a moulding method wherein use is made of a concrete not comprising the starch, or substantial vibration may even be omitted.
• the concrete in the mould is compressed by an upper press. The method may be carried out with reduced pressurisation (compared to a method wherein use is made of a concrete not comprising the starch) or even without subjecting the concrete to substantial pressing on an upper surface of the concrete in the mould.
• the thickness, width and length of the flag does not deviate more than +/- 2 mm.
• the difference between the length of two diagonals of a paving flag may not be more than 2 mm for flags having a diagonal of at most 850 mm, and not more than 4 mm for flags having a diagonal of more than 850 mm.
• the deviation of flatness and straightness may not be more than +/- 1.5 mm for kerbs having a length of gauge of 300 mm, not more than +/- 2.0 mm for kerbs having a length of gauge of 400 mm, and +/- 2.5 mm for kerbs having a length of gauge of 500 mm.
• the length of a kerb may not deviate more than +/- 1% to the nearest millimetre with a minimum of 4 mm, and not exceeding 10 mm.
• the other dimensions, except radius, for faces may not deviate more than +/- 3% to the nearest millimetre with a minimum of 3 mm, and not exceeding 5 mm, and for other parts not more than +/- 5% to the nearest millimetre with a minimum of 3 mm and not exceeding 10 mm.
• the length and width may not deviate more than +/- 2 mm, while the thickness may not deviate more than +/- 3 mm.
• the length and width may not deviate more than +/- 3 mm, while the thickness may not deviate more than +/- 4 mm.
• the difference between any two measurements of the thickness of a single block shall be at most 3 mm.
• a residence time of about 1 min or more suffices. If desired, shorter residence times are feasible though, such as a residence time of less than about 30 sec, or even less than 10 sec; it is an option within the present invention to separate the shaped body from the mould, immediately after filling the mould. From a practical point of view, the upper limit is about 45 minutes.
• the residence time is not longer than 30 minutes, more preferably not longer than 20 minutes, even more preferably not longer than 10 minutes.
• These residence times are in sharp contrast to the residence times necessary when demoulding depends on the strength development resulting from the setting of cement. These residence times are in the order of magnitude of several hours. Thus, the present invention allows for a remarkable increase in production speed.
• the invention further relates to a shaped concrete body, in particular a moulded body, obtainable by a method according to the invention.
• the invention relates to a shaped concrete article wherein the concrete comprises a starch as defined above, and optionally one or more ingredients as mentioned above.
• the article is in particular made from moist concrete, which concrete has set.
• a shaped article according to the invention usually has a good appearance, such as a smooth surface and/or good strength properties.
• the concrete article is selected from the group consisting of blocks, slabs, paving stones, curbstones, garden ornaments, street furniture and tiles.
• the invention in particular relates to a shaped concrete body, meeting the requirements put in the respective NEN-EN standards for concrete articles, such as NEN-EN 1338 for concrete paving blocks, NEN-EN 1339 for concrete paving flags or EN-EN 1340 for concrete kerb units.
• NEN-EN 1338 for concrete paving blocks
• NEN-EN 1339 for concrete paving flags
• EN-EN 1340 for concrete kerb units.
• a moist concrete which may be used in a method according to the invention.
• the composition of the moist concrete generally is as described above when describing the method of the invention in detail.
• Advantages of the use of a moist concrete according to the invention, compared to conventional (earth) moist concrete include: reduction of energy costs during the production of shaped articles of the concrete, reduction of wear and tear and/or maintenance of machinery, increased strength, shorter cycle times and/or saving on cement use by using less cement to realise the same strength.
• the concrete may further lead to one or more other advantages (in a product made from the moist concrete), which are thought to be at least partially caused by the inci'ease in density, in the presence of the starch and optionally another polymer (such as cellulose or a further polysaccharide).
• advantages include: increased freeze/thaw resistance, less efflorescence, high(er) wear resistance, intensified colour, improved surface properties.
• the moist concrete has a degree of compactability of at least 1.11, as determined by NEN-EN 5958, preferably of at least 1.20, more preferably of at least 1.26.
• the moist concrete preferably has a degree of compactability of up to 1.5, in particular of up to 1.45.
• An additional aspect of the invention is the use of a starch, in particular a starch as defined above, such as a starch ether, in a concrete - in particular a moist concrete such as earth moist concrete - as a reducer of the internal friction of the concrete, as a concrete-homogenising aid or as a flowing- aid.
• the invention relates to the use of a starch, as defined above, such as a starch ether, in a concrete - in particular a moist concrete such as earth moist concrete - to increase the strength of the concrete.
• the starch may be used to increase any of the following strengths, alone or in combination: compressive strength, flexural tensile strength, tensile splitting strength and green strength.
• the invention relates to the use of a starch, as defined above, such as a starch ether, in a concrete - in particular a moist concrete such as earth moist concrete - to improve smoothness of the surface of a shaped body formed of the concrete.
• a starch as defined above, such as a starch ether
• the invention relates to the use of a starch, as defined above, to increase the density of a concrete.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Ceramic Engineering (AREA)
• Materials Engineering (AREA)
• Structural Engineering (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Inorganic Chemistry (AREA)
• Curing Cements, Concrete, And Artificial Stone (AREA)

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• 2004
  • 2004-12-29 EP EP04078567A patent/EP1676821A1/de not_active Withdrawn
• 2005
  • 2005-12-28 EP EP05822971A patent/EP1831128A1/de not_active Withdrawn
  • 2005-12-28 WO PCT/NL2005/000896 patent/WO2006071116A1/en not_active Ceased

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