Patent Application
20110083585
This invention relates to aqueous formulations comprising a pozzolan and a substantially inert filler in particulate form, which formulations may be used in the preparation of concrete and mortar.
A pozzolan is described in Lea's Chemistry of Cement and Concrete, 4th edition, published by Arnold, as an inorganic material, natural or synthetic, which hardens in water when mixed with calcium hydroxide (lime) or with a material which can release calcium hydroxide (such as Portland Cement clinker). A pozzolan is generally a siliceous or siliceous and aluminous material which, alone, possesses little or no cementitious value but which is capable, in the presence of moisture, of reacting chemically with calcium hydroxide at ambient temperature to form compounds having cementitious properties. Silica fume generally comprises more than 80% silicon dioxide and is very widely used as a pozzolan but is becoming increasingly expensive.
The expression “substantially inert” in relation to the filler means that the filler possesses substantially no pozzolanic activity.
The present invention seeks to provide aqueous formulations (slurries) comprising a particulate pozzolan which pozzolan contains less than 80% silicon dioxide, the formulations having high dry matter content, good rheology (for example being pumpable) and/or good sedimentation characteristics (for example to render the slurry less subject to sedimentation and/or reagglomeration of pozzolans).
The present invention accordingly provides an aqueous slurry comprising:
The slurry of the invention may consist essentially, or consist, of water, the pozzolan and filler as hereinbefore defined. It will be understood that all or substantially all of the elementary particles in the slurry of the invention have a particle size less than 100 μm; the presence of a small but insignificant number of particles having a particle size greater than the specified value will not substantially affect the slurry's properties. Particulate materials in aqueous suspensions, such as slurries, may comprise individual, elementary particles. The individual particles may group together to form agglomerates. The agglomerates may group together to form clusters. Unless otherwise specified particle sizes in this specification and the accompanying claims are particle sizes as measured by laser granulometry.
The particulate pozzolan preferably comprises a high percentage of amorphous silica, for example between 50 and 80%, more preferably between 70 and 80%, of amorphous silica. Crystalline silica may also be present provided that, for practical purposes, it stays in suspension.
Pozzolans containing less than 80% silica include artificial pozzolans and natural pozzolans. Artificial pozzolans include for example, fly ash, rice husk ash, burned shales and thermally activated materials of natural origin. Naturally occurring pozzolans include: pyroclastic rocks which may be incoherent rocks (for example Italian pozzolana, Tuffasche, Santorin earth and vitreous rhyolites) and coherent rocks (for example zeolitised material such as Trass and tuff) and clastic rocks which include materials of organic origin (such as diatomaceous earth) and materials of mixed origin (such as moler and gaize); a mixture of pozzolans may also be used. Silica fume generally has a silica content of 80% or more. In the present invention, the pozzolan is different from silica fume. Moreover, the pozzolan is preferably different from metakaolin.
The particulate substantially inert filler may be, for example a ground natural calcium carbonate (GCC) (for example chalk, calcite, marble or other naturally occurring calcium carbonate), a precipitated (also known as synthetic) calcium carbonate (PCC), barium carbonate, dolomite, talc, a crystalline silica, fumed titanium dioxide, iron oxides, manganese oxides, titanium dioxide, kaolin, clays, mica, slag, calcium sulphate, basalt, barium sulphate, aluminium hydroxide, bauxite or a mixture thereof. Ground calcium carbonate and precipitated calcium carbonate are preferred.
The filler preferably has a Moh hardness greater than 1.
The dry matter in the slurry of the invention (i.e. the pozzolan and filler excluding water) generally comprises from 20% to 100% pozzolan and from 80% to 0% filler, preferably from 20% to 80% pozzolan and from 80% to 20% filler, more preferably from 30% to 70% pozzolan and from 70% to 30% filler.
The mean particle size of the elementary particles is preferably less than 10 μm, more preferably less than 5 μm. The overall particle size range is generally 0.05 μm to 100 μm as measured by laser granulometry in water.
The BET surface area of the solid, dried materials in the slurry is preferably from 1 to 30 m2/g, preferably from 1 to 20 m2/g.
The Blaine specific surface of the solid, dried materials in the slurry is generally from 2000 to 15000 cm2/kg.
In order to produce the micro-fine slurry according to the invention wet milling is generally employed. Wet milling according to the invention seeks to provide a process in which: agglomeration and/or blocking are reduced; the rise in temperature during milling is reduced; monodisperse particles of a single material, for example pozzolan, having a narrow granulometric distribution are produced; and/or, when pozzolan and filler are ground together, the slurry is stabilized by reducing sedimentation and/or reagglomeration of the pozzolan.
According to a further feature of the invention the slurry according to the invention is prepared by wet milling a mixture of pozzolan and substantially inert filler in water. The mill may be, for example, a bar mill, a ball mill or an impact mill. Suitable mills are known, for example those available from Netzsch and WAB. The milling is intended to produce particles having a high BET surface area, a high Blaine surface area and/or small particle size, three parameters which provide a measure of particle fineness. BET specific surface values reflect particle texture, Blaine specific surface values reflect the separation of agglomerates and laser granulometry provides a measure of agglomerated particle fineness. High Blaine fineness in the slurries of the invention render them suitable for use in, for example, self-compacting ultra high performance concrete (UHPC).
Milling may be carried out in one or more stages, depending on the starting materials and the desired properties of the slurry to be obtained. Milling may effect grinding (to reduce particle size) and/or homogenisation.
The wet milling is conducted in an aqueous medium, generally water. The pH of the aqueous medium is chosen to avoid gelling or possible setting which might arise due to activation of the pozzolan under alkaline conditions. The milling process may be continuous or batch-wise.
The mill is generally cooled to avoid overheating of the slurry by heat generated in the milling process.
The slurry obtained by milling may be concentrated by removal of water. Known methods for such removal include heating, optionally under reduced pressure; allowing the slurry to settle followed by removal of liquid from the surface; and centrifugation.
The slurry of the invention is preferably stable. After storage for a long period, for example more than a month, it may require agitation to redisperse the particles.
The pozzolan and filler before milling may have similar or different granulometries. The pozzolan and filler after milling may also have similar or different granulometries. When the pozzolan and filler have similar granulometries before milling they may have different granulometries after milling, for example when the pozzolan and filler have different hardnesses.
The granulometries of pozzolan and filler in the slurry of the invention may be similar but are preferably different. The granulometries are preferably such that particles of one material, for example the pozzolan, may occupy interstices between particles of the other. When this occurs the concentration of particles (dry matter) in the slurry may be increased. The packing density (C0) of dry monodisperse particles, having similar size, for random close packing is about 0.60. When a second, smaller, set of particles which can pack in the interstices between the first particles is added the overall packing density is increased. The space between the first particles (1-0.6, i.e. 0.4) is ideally packed at a similar density (0.6) giving an additional solids content of 0.6×0.4 (i.e. 0.24). The total solids content might then reach 0.84. When this principle is applied to slurries it will be understood that the use of particles of differing sizes allows increased solid contents to be achieved. The use of such slurries, containing a smaller proportion of water, affords more flexibility in their use to prepare concretes, particularly concretes designed to have a low water to cement (W/C) ratio.
The granulometries of the pozzolan and filler may be the same or different.
In the slurries according to the invention the mean particle size of one material, for example the inert filler (d1) is preferably greater than the mean particle size (d2) of the other, for example the pozzolan.
The ratio d1:d2 is generally such that: (d1) is greater than or equal to (d2), preferably (d1) is greater than or equal to 5(d2), more preferably (d1) is greater than or equal to 7(d2).
The slurry preferably comprises a superplasticizer. The superplasticizer may be added at the start of milling, during milling or after milling when the desired particle sizes have been achieved. The superplasticizer is generally added at the start of milling.
The term “superplasticizer” as used in this specification and the accompanying claims is to be understood as including both water reducers and superplasticizers as described in the Concrete Admixtures Handbook, Properties Science and Technology, V.S. Ramachandran, Noyes Publications, 1984.
A water reducer is defined as an additive which reduces the amount of mixing water of concrete for a given workability by typically 10-15%. Water reducers include, for example lignosulphonates, hydroxycarboxylic acids, carbohydrates, and other specialized organic compounds, for example glycerol, polyvinyl alcohol, sodium alumino-methyl-siliconate, sulfanilic acid and casein.
Superplasticizers belong to a new class of water reducers chemically different from the normal water reducers and capable of reducing water contents by about 30%. The superplasticizers have been broadly classified into four groups: sulphonated naphthalene formaldehyde condensate (SNF) (generally a sodium salt); or sulphonated melamine formaldehyde condensate (SMF); modified lignosulfonates (MLS); and others. More recent superplasticizers include polycarboxylic compounds such as polyacrylates. The superplasticizer is preferably a new generation superplasticizer, for example a copolymer containing polyethylene glycol as graft chain and carboxylic functions in the main chain such as a polycarboxylic ether. Phosphonic acid derivatives may also be used. Sodium polycarboxylate-polysulphonates and sodium polyacrylates may also be used. The amount of superplasticizer required generally depends on the reactivity of the cement. The lower the reactivity the lower the amount of superplasticizer required. In order to reduce the total alkali content the superplasticizer may be used as a calcium rather than a sodium salt.
Other additives may be included in the composition according to the invention, for example, a defoaming agent (e.g. polydimethylsiloxane). These also include silicones in the form of a solution, a solid or preferably in the form of a resin, an oil or an emulsion, preferably in water. More particularly suitable are silicones comprising (RSiO0.5) and (R2SiO) moieties.
In these formulae, the R radicals, which may be the same or different, are preferably hydrogen or an alkyl group of 1 to 8 carbon atoms, the methyl group being preferred. The number of moieties is preferably from 30 to 120.
The amount of such an agent in the final cement is generally at most 5 parts in weight relative to the cement.
The slurry according to the invention preferably comprises a viscosity and/or yield stress modifying agent (generally to increase viscosity and/or yield stress). Such agents include: cellulose derivatives, for example water-soluble cellulose ethers, such as the sodium carboxymethyl, methyl, ethyl, hydroxyethyl and hydroxypropyl ethers; alginates; and xanthan, carrageenan or guar gum. A mixture of such agents may be used.
Water-soluble additives may be added at the start of milling, during milling or after milling when the desired particle sizes have been achieved.
The inert filler, before milling to produce a slurry according to the invention, may be a particulate calcium carbonate (for example ground or precipitated). It is preferably a ground calcium carbonate.
The preferred BET surface area is 2-10 m2/g, generally less than 8 m2/g, for example 4 to 7 m2/g, preferably less than 6 m2/g, The inert filler may be, for example, Durcal®1.
The inert filler before milling may have a mean particle size of less than 5 μm, for example 1 to 4 μm.
The non-pozzolan may be a ground silica, for example quartz, having a particle size <100 μm, preferably <80 μm, for example C800 which is a substantially non-pozzolanic silica filler having a D90 of 1.3 μm available from Sifraco, France.
The inert filler before milling may also be a precipitated calcium carbonate. Individual (primary) particles generally have a particle size of about 20 nm. Individual particles agglomerate into clusters having a (secondary) particle size of about 0.1 to 1 μm. The clusters themselves form agglomerates having a (ternary) particle size greater than 1 μm. The BET surface area before milling (determined by known methods) may be 20-40 m2/g.
The concentration of starting material before milling is generally 20 to 90%, preferably 20 to 75%, more preferably 20 to 60%. The milling time depends on the starting materials and the operating parameters of the mill. Dispersion of solid material in the aqueous suspending medium may be conducted for about half an hour. Milling may be conducted for about two hours.
A mill may be operated either in recirculatory mode (in which the recirculated product is returned to the feed, for example via a storage tank) or in multi-pass mode (in which the product circulates one or more times as a batch). Milling is optimised by a suitable choice of:
The slurry according to the invention may be used in the preparation of a concrete. The term “concrete” as used hereinafter in this specification, including the accompanying claims, also embraces mortar. The concrete may be a high performance concrete (HPC), for example according to C60/80, generally having a compressive strength of 50 to 100 MPa, or an ultra high performance concrete (UHPC), for example Ductal®, generally having a compressive strength of more than 100 MPa. The concrete may also be self-levelling, self-consolidating or self-placing. The concrete may also be a low cement content concrete or a conventional concrete, for example according to C25/30.
When the slurry is used to prepare a concrete mix the invention seeks to provide a reduced time of mixing required to achieve design flow or slump, improved workability of the mix, and/or higher strength (for example of a HPC) for a given ultrafine particle content.
The invention also seeks to provide a formulation which is adaptable to the preparation of a pourable concrete mix or a pressable concrete mix (for example by the inclusion of superplasticizer and/or additional water); to reduce the mixing time, the ultra-fine materials having been already dispersed; to improve safety, as ultrafine components in the slurry are not dispersed into the atmosphere, where they may constitute a health risk by possible inhalation during preparation of the concrete mix; to permit the preparation of UHPC without using silica fume (which has come to be regarded as a vital component of UHPC) or HPC; and/or to permit the preparation of a concrete mix which is adapted to provide good compressive strength after heat curing (the strength after curing may be increased substantially compared with the 48 hours strength).
The present invention accordingly provides a first example of concrete which comprises up to 30% by weight of a slurry according to the invention. The first example of concrete may comprise, for example, in relative parts by weight:
The amount of slurry is preferably up to 70, or is more preferably about 30 parts by weight.
The sand is generally a silica sand, a calcined bauxite or a particulate metallurgical residue; the fine sand may also comprise a ground hard dense mineral material, for example a ground vitrified slag. A preferred mixture of sands comprises a mixture of sands (preferably two sands), the finest sand having a D10 to D90 between 0.063 and 1 mm and the coarsest sand having a D10 to D90 between 1 and 2 mm.
The first example of concrete according to the invention may be a self-placing concrete.
The total setting shrinkage may be reduced by the inclusion of 2 to 8, preferably 3 to 5, for example about 4 parts, of quicklime, burnt lime or calcium oxide in the mixture before addition of slurry.
The first example of concrete according to the invention may also be a high performance concrete (HPC): such concretes generally have a compressive strength greater than 100 MPa.
The slurry according to the invention may also be used in the preparation of a second example of a concrete composition comprising in proportions by mass:
The expression “selected Portland cement” means, for example, a cement on which an operation of preparation is made in order to keep particles having a given granulometric class, for example a stronger milling than the milling provided for the obtention of a common Portland cement, selection or sizing, for example by screening or pneumatic selection.
The second example of the concrete composition has high early compression strength, superior or equal to 50 MPa at short term, in particular after 48 hours. The composition satisfies the need to produce an ultra high performance concrete with reduced associated carbon dioxide emissions. Indeed, the quantity of cement (and in particular) of clinker used for the preparation of the ultra high performance concrete is inferior to the quantity commonly used for the preparation of a common ultra high performance concrete.
The second example of the concrete composition preferably comprises in proportions by mass:
The second example of the concrete composition may also comprise materials in a larger particle size range comprising particles the D10 which is superior to 5 mm. According to an embodiment of the present invention, the second example of the concrete composition comprises in proportions by mass:
The materials which make up the second example of the concrete composition are present in the form of particles, i.e. unitary elements of materials. The particle-size distribution makes it possible to establish a division of the constituents into several “particle size ranges”, i.e. into essentially separate compartments.
Thus, the ultrafine particle size range is made up of:
The fine particle size range corresponds to a set of particles the D10 and the D90 of which are comprised between 1 μm and 120 μm and the specific BET surface area of which is less than 5 m2/g. The average particle size range corresponds to a set of particles the D10 and the D90 of which are comprised between 120 μm and 5 mm And the larger particle size range corresponds to a set of particles the D10 of which is greater than 5 mm.
The D90, also noted DV90, corresponds to the 90th percentile of the particle-size distribution, i.e. 90% of the particles are smaller than the D90 and 10% are larger than the D90. Similarly the D10, also noted DV10, corresponds to the 10th percentile of the particle-size distribution, i.e. 10% of the particles have a size less than the D10 and 90% have a size greater than the D10.
In other words: at least 80% of the particles in the fine particle size range (preferably at least 90%, in a particularly preferred manner at least 95% or even at least 99%) have a size comprised between 1 μm and 120 μm; at least 80% of the particles in the average particle size range (preferably at least 90%, in a particularly preferred manner at least 95% or even at least 99%) have a size comprised between 120 μm and 5 mm; at least 90% of the particles in the larger particle size range (preferably at least 95% or even at least 99%) have a size greater than 5 mm; and, according to the embodiments corresponding to cases (i) and (iii) above, at least 90% of the particles in the ultrafine particle size range (preferably at least 95%, in a particularly preferred manner at least 99%) have a size of less than 1 μm. The four particle size ranges (ultrafine, fine, average and larger) then correspond to essentially separate size compartments. The D10or D90 of a set of particles can be generally determined by laser particle-size analysis for particles smaller than 63 μm, or by sieving for the particles larger than 63 μm.
The specific BET surface area is a measurement of the total real surface area of the particles which takes into account the presence of reliefs, irregularities, surface or internal cavities, and porosity.
According to an alternative embodiment, there can be an overlap between the sizes of the particles in the fine and ultrafine ranges, i.e. more than 10% of the particles in the ultrafine and fine ranges respectively can be situated in the same size range.
An example of a case where the ultrafine and fine ranges differ only by the specific BET surface area and not by the size of the particles can be that where the ultrafine particles are constituted by hydrated hydraulic binder grinds. In this example, the ultrafine particles can have a size of the order of 10 μm, for a specific surface area which can be of the order of 100 m2/g (due to the porosity of this material). In the compositions of the second example of the concrete as defined above, the cement is Portland cement chosen from the standard CPA-type (Artificial Portland Cement) Portland cements, and in particular from the cements described in European Standard EN 197-1. It is possible to use for example a CEM1 or CEM2 52.5 N or R or PM (for marine construction) cement or PMES (for marine construction, sulfated water). The cement can be of the HR1 type (High Initial Strength). In some instances, notably for type CEM2, the Portland cement is not made of pure clinker but is provided admixed with at least one additional material (slag, pozzolana, fly ash, calcinated schist, lime etc.) in an amount of up to 37%. In these instances, the abovementioned amounts of cement more particularly correspond to the clinker amounts, whereas the additional materials are counted among the relevant particle size range.
The larger particle size range can comprise aggregates and/or gravel and/or pebbles and/or stone chippings.
The average particle size range can in particular comprise sand or fine sand. The fine particle size range can comprise one or more materials chosen from fly ash, pozzolanas (natural or artificial), limestone powders, siliceous powders, lime, calcium sulfate (in particular gypsum in anhydrous or semi-hydrated form), slag. The word “fillers” is sometimes used to designate most of materials of the fine particle size range.
The ultrafine particle size range can comprise materials chosen from the group consisting of limestone powders, precipitated carbonates, natural and artificial pozzolanas, pumice stones, ground fly ash, hydrated or carbonated siliceous hydraulic binder grinds, and mixtures or co-grinds thereof, in dry form or aqueous suspension. In particular, materials from the ultrafine particle size range comprise substantially no silica fume. The expression “substantially no” means that the amount of silica fume is inferior to 1% in weight of the total amount of materials of the ultrafine particle size range.
The term “hydrated siliceous hydraulic binder grinds” designates in particular the products described in the document FR 2708592.
Any standard plasticizer (or superplasticizer) can advantageously be added to the second example of the concrete composition according to the invention, preferably at a concentration of 0.05 to 3%, preferably from 0.5 to 2%, expressed as a mass ratio of dry extract of the plasticizer to the mass of concrete composition. The amount of plasticizer is also determined as a function of the desired quality of the paste, notably depending on whether a self-compacting concrete is desired or not. Slump measurements make it possible to determine the type and quantity of plasticizer that should be used in the formulation.
The second example of the concrete according to the invention is prepared by mixing the slurry according to the invention with cement, water, materials in the average particle size range, and if necessary in the larger particle size range. The W/B ratio, where W designates the quantity of water and B the quantity of binder (materials of the mixture (Portland cement+fine particle size range)), for the second example of the concrete according to the invention, is therefore reduced relative to a standard concrete, and is typically situated between 0.1 and 0.5, preferably between 0.13 and 0.30. The W/C ratio, where W designates the quantity of water and C the quantity of cement, is greater than in the case of standard concrete, due to the small quantity of cement which is present. The W/C ratio is preferably comprised between 0.2 and 2, quite particularly between 0.5 and 1
For the second example of the concrete according to the invention, the quantity of mixing water is from 150 to 3001/m3, preferably from 180 to 2501/m3. According to an embodiment, the compositions of the second example of concrete formulated according to the invention are the result of a complex optimization of the different parameters involved (choice of materials and concentration thereof) in order to guarantee an optimized packing (choice of particle size and choice of admixtures), optimized hydration chemistry (in fact numerous components participate in the reaction: limestone powder, fly ash, etc.) and an optimized water demand.
The compositions of the second example of concrete according to the invention have a compressive strength greater than or equal to 50 MPa 48 hours after mixing, and/or greater than or equal to 100 MPa, 28 days after mixing, and/or greater than or equal to 120 MPa after mixing and after a cure treatment, for example 2 days at 20° C. after the setting and then 2 days at 90° C.
The different purposes and advantages of the invention are obtained by means of full optimization of all of the formulation parameters, and in particular by means of:
Preferably, the concretes according to the invention are fluid or self-compacting concretes.
The concrete according to the present invention may be prepared according to methods known to a person skilled in the art, comprising mixing of the slurry, the solid compounds and water, forming (for example molding, pouring, injection, pumping, extrusion or calendaring) and hardening.
The invention also relates to an object made of hardened concrete, comprising:
The cements of the invention may comprise metal and/or organic fibres, for example, for the preparation of the first and second concretes of the invention. The amount by weight of fibres is generally from 15 to 25 parts per 100 parts of cement. The amount of metal fibres, expressed in terms of the volume of the final set concrete is generally less than 4%, for example from 0.5 to 3.5%, preferably about 2%. The amount of organic fibres, expressed on the same basis, is preferably 2 to 4.5%. Concrete is generally batched by weight with the weight of additives expressed relative to the weight of cement, not the total weight of concrete. The weight of cement in a cubic metre of the first example of concrete containing metal fibres is about 750 kg/m3. The weight of metal fibres relative to the weight of cement is preferably 120 to 170 kg/m3, more preferably about 160 kg/m3. The weight of cement in a cubic metre of the first example of concrete containing organic fibres is about 700 kg/m3. The weight of organic fibres relative to the weight of cement is preferably 25 to 60 kg/m3, more preferably about 55 kg/m3. When such fibres are included the concrete according to the invention is preferably an ultra high performance concrete: such concretes generally have a compressive strength greater than 100 MPa, preferably greater than 150 MPa.
Metal fibres are generally chosen from steel fibres, such as high strength steel fibres, amorphous steel fibres or stainless steel fibres. Optionally, the steel fibres may be coated with a non-ferrous metal such as copper, zinc, nickel (or their alloys). The individual length (1) of the metal fibres is generally at least 2 mm and is preferably 10-30 mm. The 1/d ratio (d being the diameter of the fibres) is generally at least 30, and preferably at most 100.
Fibres having a variable geometry may be used: they may be crimped, corrugated or hooked at the ends. The roughness of the fibres may also be varied and/or fibres of variable cross-section may be used; the fibres may be obtained by any suitable technique, including by braiding or cabling several metal wires, to form a twisted assembly.
Bonding between the fibres and matrix may be promoted by several means, which may be used individually or in combination.
According to a first means, the bonding of the metal fibres in the cementitious matrix may be promoted by treating the surface of the fibres. This fibre treatment may be carried out by one or more of the following processes: fibre etching; or deposition of a mineral compound on the fibres, especially by depositing silica or a metal phosphate.
The etching may be carried out, for example, by contacting the fibres with an acid, followed by neutralization.
Silica may be deposited by contacting the fibres with a silicon compound, such as a silane, a siliconate or a silica sol. It will be understood that the silica or phosphate is then substantially confined to the surface of the metal fibres in the concrete matrix and is not uniformly dispersed in the matrix.
Phosphatizing treatments are known and are described, for example, in the article by G. LOR1N entitled “The Phosphatizing of Metals” (1973), Pub.Eyrolles.
In general, a metal phosphate is deposited using a phosphatizing process, which comprises introducing prepickled metal fibres into an aqueous solution comprising a metal phosphate, preferably manganese phosphate or zinc phosphate, and then filtering the solution in order to recover the fibres: the fibres are then rinsed, neutralized and rinsed again. Unlike in the usual phosphatizing process, the fibres obtained do not have to undergo grease-type finishing; they may, however, optionally be impregnated with an additive either in order to provide anticorrosion protection or to make it easier for them to be processed with a cementitious medium. The phosphatizing treatment may also be carried out by coating or spraying a metal phosphate solution onto the fibres.
According to a second means, bonding of the fibres to the cementitious matrix may be promoted by introducing into the composition one or more compounds selected from: precipitated calcium carbonate, polyvinyl alcohol in aqueous solution, a latex or a mixture thereof.
Organic fibres include polyvinyl alcohol fibres (PVA), polyacrylonitrile fibres (PAN), polyethylene fibres (PE), high density polyethylene fibres (HDPE), polypropylene fibres (PP), homo- or copolymers, polyamide or polyimide fibres, aramid fibres and carbon fibres. Mixtures of these fibres can also be used. The organic reinforcing fibres used in the invention may be classified as: high modulus reactive fibres, low modulus non-reactive fibres and reactive fibres. Examples include non-reactive HDPE fibres, the modulus of which is generally higher than that of the concrete matrix, non-reactive polyamide fibres (PA), the modulus of which is generally lower than that of the concrete matrix and PVA fibres which are capable of reacting with the concrete matrix. The term “modulus” as used in this specification including the accompanying claims, refers to Young's modulus (modulus of elasticity).
A mixture of metal and organic fibres may also be used: a “hybrid” composite is thereby obtained the mechanical behaviour of which may be adapted depending upon the required performance (for elastic and cold working and post-peak performance).
The presence of organic fibres makes it possible to modify the behaviour of the concrete to heat or fire.
Melting of organic fibres makes it possible to develop pathways through which steam or water under pressure can escape when the concrete is exposed to high temperatures.
Hybrid metal and organic reinforcing elements may be produced by combining fibres of various natures and/or lengths. Examples include short PVA organic fibres (6 mm) and long metal fibres (13 mm) which may show a reinforcing synergistic effect; PVA or HDPE short fibres (6 mm) and PVA long fibres (20 mm), short steel cords (5 mm) and PVA long fibres (20 mm).
The organic fibres may be present as a monostrand or multistrand; the diameter of the mono- or multistrand is preferably from 10 μm to 800 μm. The organic fibres may also be used in the form of woven or non-woven structures or of a hybrid strand comprising a different filament.
The individual length of the organic fibres is preferably 5 mm to 40 mm.
The amount of organic fibres is generally such that their volume is from 1% to 8% and preferably less than 5% of the concrete volume after setting. The optimum quantity of organic fibres used generally depends on the fibre geometry, their chemical nature and their intrinsic mechanical properties (e.g. elastic modulus, flowing threshold, mechanical strength).
The L/Φ ratio, Φ being the fibre diameter and L the length, is generally at least 30 and preferably 300 at the most.
The use of blends of fibres having different properties permits modification of the properties of the concrete containing them.
Adherence of polymeric fibre to a concrete matrix may be promoted by various methods used alone or in combination. Adherence is promoted by using reactive fibres: adherence can be enhanced by thermal treatment of the concrete, for example by curing. Adherence can also be promoted by surface treatment of the fibres.
Fibre adherence to the cement matrix can be promoted by including in the concrete composition a compound selected from: precipitated calcium carbonate; an aqueous solution of polyvinyl alcohol; phosphates; latexes; a surfactant (for example a defoaming agent or wetting agent); or a mixture thereof.
The ratio R of the average length L of the fibres to the grain size D of the sand is generally at least 5, particularly when the sand has a maximum grain size of 1 mm The cement in the concrete of the invention may be, for example a type I, II, III, IV or V cement according to ENV 197-1 or may be a masonry cement for the preparation of mortar. The Portland cements include slag; silica fume; pozzolana; fly ash; burnt shale; limestone; and composite cements. A preferred cement for use in the invention is CEM I.
The water/binder ratio used for the cement according to the invention may vary with the amount and type of the pozzolan and filler. The water/binder ratio (W/B), where W is the weight of water and B is the combined weight of cement and pozzolan used for the concrete according to the invention may vary with the amount and type of the pozzolan and filler. The water-binder ratio is generally less than about 0.7, for example less than about 0.6, and more than about 0.08; it is generally from 0.08 to 0.3, preferably from 0.13 to 0.25, for example about 0.2. The water/binder ratio may be adjusted using, for example water-reducing agents and/or superplasticizers.
In using a slurry according to the invention to prepare a concrete mix the slurry is generally added after the aggregates or to a premix. The slurry may provide all of the water required or more may be added if necessary. In the preparation of UHPC all of the water required may be provided by the slurry; for HPC more water may be added, either separately or by using a more dilute slurry.
The following order of mixing may, for example, be adopted: mixing of the pulverulent constituents of the matrix; introduction of the slurry and a fraction, for example half, of the admixtures; mixing; introduction of the remaining fraction of the admixtures; mixing; introduction of the reinforcing fibres and the additional constituents; mixing. The first and second examples of concrete may be subjected to a cure to improve its mechanical properties. Curing is generally conducted at a temperature from ambient temperature (e.g. 20° C. to 90° C.), preferably from 60° C. to 90° C. The curing temperature should be less than the boiling point of water at the ambient pressure. The curing temperature is generally less than 100° C. Autoclaving in which curing is conducted at elevated pressures allows higher curing temperatures to be used.
The cure time may be, for example, 6 hours to 4 days, preferably about 2 days. Curing may be started before or after setting, preferably at least one day after setting has started, and preferably on concrete which is 2 days up to about 7 days old, at 20° C.
The cure may be performed in dry or wet conditions or in cycles alternating both environments, for example, a 24 hour cure in a humid environment followed by a 24 hour cure in a dry environment.
The first and second examples of concrete may be pretensioned, by bonded wires or by bonded tendons, or post-tensioned, by single unbonded tendons or by cables or by sheaths or bars, the cable comprising an assembly of wires or comprising tendons. Prestressing, whether in the form of pretensioning or in the form of post-tensioning, is particularly well suited to products made of the concrete according to the invention. Metal prestressing cables have a very high, under-used, tensile strength since the brittleness of the matrix which contains them does not allow the dimensions of the concrete structural elements to be optimized.
The reduction in volume obtained, because of this increase in mechanical strength, allows the production of prefabricated elements. There is then the possibility of having long-span concrete elements that are easily transportable because of their lightness; this is particularly well suited to the construction of large structures in which the use of post-tensioning is widely employed. In the case of this type of structure, the solution provides particularly favourable savings to be made in terms of worksite duration times and assembly.
In addition, in the case of a thermal cure, the use of pre-tensioning or post-tensioning significantly reduces shrinkage.
The invention will be illustrated by the following non-limiting Examples in relation with the accompanying
In this specification including the accompanying claims:
compressive strength values are measured after moist curing for two days at 20° C., and then moist curing for 2 days at 90° C. on cylindrical test samples having a diameter of 7 cm and a height of 14 cm; the force applied to the sample is increased at a rate of 3.85 kN/sec during testing;
flexural strengths are measured after moist curing as described for compressive strength values on prism-shaped test samples measuring 4×4×16 cm supported at two points, force being applied in the middle; the force applied to the sample is increased at a rate of 0.05 kN/sec during testing;
The invention is illustrated by the following non-limiting Examples. In the Examples materials used are available from the following suppliers:
A slurry was prepared using an LME1 (Netzsch) mill. The mill comprises a horizontal tank in the interior of which a stirring shaft equipped with pierced disks agitates a bed of monomodal ceramic balls whose diameter can be chosen as necessary for the desired milling (minimum dimension: 0.4 mm). A cage system at the end of the tree allows a first separation of the balls and product. A second static separation system, arranged at the centre of cage comprises a cartridge having openings of 0.1 mm. The mill can be operated either in recirculatory mode (in which the recirculated product is returned directly to the feed via a storage tank) or in multi-pass mode (in which the product circulates one or more times as a batch). Milling is optimised by a suitable choice of:
the dimension of the milling balls (the smaller these are the smaller the milled particles);
the concentration of solids in the suspension being milled (more dilute suspensions are better adapted to milling);
the use of an appropriate grinding agent (superplasticizer) which ensures good deflocculation in order to improve the effectiveness of grinding.
Yali pozzolan was ground in known manner to produce a starting material having a particle size less than 80 μm (all of the material passed through an 80 μm sieve).
The starting material thus prepared was then milled to prepare 6 litres of a slurry containing 30% solid material.
Zirconia/silica 04/06 mm balls were used.
The loading level was 80% (about 1400 g).
Milling with recirculation was carried out for 5 hours.
Mill speed 2500 tpm
Pump speed 2.5
Slurry output 650 g/min
The particle size distribution of the slurry was measured on a diluted sample and the results obtained are shown by the dotted line A1 in
The procedure used similar to that described in Example 1.
Jojobera fly ash was ground in a know manner to produce a starting material having a particle size of less than 80 μm. The starting material thus produced was then milled using a Netzsch mill to prepare 6 litres of a slurry containing 30% solid material.
Zirconia/silica 04/06 mm balls were used.
The loading level was 80% (about 1400 g).
Milling with recirculation was carried out for 3 hours.
Mill speed 2500 tpm
Pump speed 2
Slurry output 560 g/min
The slurry produced was allowed to stand 4 weeks followed by aspiration of surface water to yield a slurry product containing 52.3% solid matter.
The particle size distribution of the slurry was measured on a diluted sample and the results obtained are shown by the dotted line B1 in
A slurry was prepared with silica fume NS980 of SEPR and a limestone filler (Durcal 1). The powder mixture comprises 40% silica fume and 60% limestone filler. The powder mixture was ground in a know manner to produce a starting material having a particle size of less than 80 μm. The starting material thus produced was then milled using a Netzsch mill to prepare 6 litres of a slurry containing 30% solid material.
Zirconia/silica 04/06 mm balls were used.
The loading level was 80% (about 1400 g).
Milling with recirculation was carried out for 45 minutes.
Mill speed 2500 tpm
Pump speed 2.5
Slurry output 760 g/min
The slurry produced was allowed to stand 4 weeks followed by aspiration of surface water to yield a slurry product containing 58.5% solid matter. More precisely, the slurry comprises 22.72% silica fume, 33.98% limestone filler, 1.76% superplasticizer (F2) and 41.54% water.
The particle size distribution of the slurry was measured on a diluted sample and the results obtained are shown by the solid line C1 in
A slurry was prepared with silica fume 971U of ELKEM and a limestone filler (Durcal 1). The powder mixture comprises 40% silica fume and 60% limestone filler. The powder mixture was ground in a know manner to produce a starting material having a particle size of less than 80 μm. The starting material thus produced was then milled using a Netzsch mill to prepare 6 litres of a slurry containing 30% solid material.
Zirconia/silica 04/06 mm balls were used.
The loading level was 80% (about 1400 g).
Milling with recirculation was carried out for 45 minutes.
Mill speed 2500 tpm
Pump speed 2.5
Slurry output 850 g/min
The slurry produced was allowed to stand 4 weeks followed by aspiration of surface water to yield a slurry product containing 54.5% solid matter. More precisely, the slurry comprises 20.92% silica fume, 31.36% limestone filler, 2.27% superplasticizer (F2) and 45.45% water.
The particle size distribution of the slurry was measured on a diluted sample and the results obtained are shown by the solid line D1 in
The use of a superplasticizer was necessary for the preparation of the slurries of Examples 3 and 4 with silica fume. On the contrary, the slurries of Examples 1 and 2, respectively with Yali pozzolan and Jojobera fly ash were prepared without superplasticizer.
The slurries prepared in Examples 1 and 2 were used to replace silica fume in a concrete mix having the following composition:
Mixing was carried out in a Rayneri mixer.
The following results were obtained:
The slurry prepared in Examples 3 was used to replace silica fume in a concrete mix having the following composition:
Mixing was carried out in a Rayneri mixer.
The slurry prepared in Example 4 was used to replace silica fume in a concrete mix having the following composition:
Mixing was carried out in a Rayneri mixer.
The following results for Examples 6 and 7 were obtained:
The flexural strengths after thermal curing of the concretes made with the slurries of Examples 1 and 2 are superior to the flexural strengths after thermal curing of the concretes made with the slurries of Examples 3 and 4.
The addition of a superplasticizer was necessary for the preparation of the concretes made with the slurries of Examples 3 and 4 in order to obtain a similar static spread, even though the slurries of Examples 3 and 4 already contain a superplasticizer.
The beginning times of the setting of the concretes made with the slurries of Examples 1 and 2 are inferior to the beginning times of the setting of the concretes made with the slurries of Examples 3 and 4. The compressive strengths at 48 hours of the concretes made with the slurries of Examples 1 and 2 are superior to the compressive strengths after thermal curing of the concretes made with the slurries of Examples 3 and 4.
An ultra-high performance concrete reinforced with alkali-resistant glass fibers was prepared with the Yali pozzolan slurry described in Example 1. Before adding this slurry to the concrete composition (shown below), the slurry was concentrated, through evaporation of the liquid, to a final solids concentration of 70% wt. The composition was mixed in a Rayneri mixer by first thoroughly homogenizing the mortar (i.e. cement, slurry, sand, superplasticizer, and water) and then adding the fibers at the end of the mixing procedure.
The fresh concrete mixture was then cast into either cylindrical moulds (70 mm diameter) or into a plate moulds (dimensions 500×450×20 mm). The cylinders were submitted to compressive strength tests, the plates to four-point bending tests. All samples were demoulded 24 hours after contact between cement and water. The demoulded specimens were stored at 20° C. and 100% relative humidity. After 28 days, the plate specimens were cut into 3 pieces (dimensions 450×145×20 mm) before testing.
A summary of other pertinent properties of the mix is shown in the table below.
The ductile (i.e., deflection-hardening) behaviour of the plates was determined in a four point bending test using a hydraulic DARTEC HA 250 (Zwick) apparatus.
| Number | Date | Country | Kind |
|---|---|---|---|
| 08356110.0 | Jul 2008 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB2009/006670 | 7/10/2009 | WO | 00 | 12/9/2010 |
