EP0804648A1 - Procede pour realiser une structure en beton arme - Google Patents

Procede pour realiser une structure en beton arme

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Publication number
EP0804648A1
EP0804648A1 EP95922444A EP95922444A EP0804648A1 EP 0804648 A1 EP0804648 A1 EP 0804648A1 EP 95922444 A EP95922444 A EP 95922444A EP 95922444 A EP95922444 A EP 95922444A EP 0804648 A1 EP0804648 A1 EP 0804648A1
Authority
EP
European Patent Office
Prior art keywords
concrete
reinforcement
crack
cracks
initiated
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP95922444A
Other languages
German (de)
English (en)
Inventor
Anders Henrichsen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Dansk Beton Teknik AS
Original Assignee
Dansk Beton Teknik AS
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Dansk Beton Teknik AS filed Critical Dansk Beton Teknik AS
Publication of EP0804648A1 publication Critical patent/EP0804648A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • E—FIXED CONSTRUCTIONS
    • E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
    • E01C—CONSTRUCTION OF, OR SURFACES FOR, ROADS, SPORTS GROUNDS, OR THE LIKE; MACHINES OR AUXILIARY TOOLS FOR CONSTRUCTION OR REPAIR
    • E01C7/00—Coherent pavings made in situ
    • E01C7/08—Coherent pavings made in situ made of road-metal and binders
    • E01C7/10—Coherent pavings made in situ made of road-metal and binders of road-metal and cement or like binders
    • E01C7/14—Concrete paving
    • 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
    • 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
    • B28B11/00—Apparatus or processes for treating or working the shaped or preshaped articles
    • B28B11/24—Apparatus or processes for treating or working the shaped or preshaped articles for curing, setting or hardening
    • B28B11/245—Curing concrete 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
    • B28B23/00—Arrangements specially adapted for the production of shaped articles with elements wholly or partly embedded in the moulding material; Production of reinforced objects
    • B28B23/02—Arrangements specially adapted for the production of shaped articles with elements wholly or partly embedded in the moulding material; Production of reinforced objects wherein the elements are reinforcing members
    • 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
    • E—FIXED CONSTRUCTIONS
    • E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
    • E01C—CONSTRUCTION OF, OR SURFACES FOR, ROADS, SPORTS GROUNDS, OR THE LIKE; MACHINES OR AUXILIARY TOOLS FOR CONSTRUCTION OR REPAIR
    • E01C11/00—Details of pavings
    • E01C11/16—Reinforcements
    • E01C11/18—Reinforcements for cement concrete pavings
    • E—FIXED CONSTRUCTIONS
    • E04—BUILDING
    • E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
    • E04C5/00—Reinforcing elements, e.g. for concrete; Auxiliary elements therefor
    • E04C5/01—Reinforcing elements of metal, e.g. with non-structural coatings

Definitions

  • This invention relates to a method of producing a reinforced concrete structure, more precisely a reinforced concrete structure, the crack formation of which is controlled by means of the degree of reinforcement.
  • the method of the invention can be used for instance in the construc ⁇ tion of submerged tunnels, ducts, caissons for transmission pipes for heating systems and box caissons for large marine structures, but also for the construction of reinforced concrete pave ⁇ ments for bridges, container terminals, road pavements, sports arenas and airport pavements.
  • the invention also relates to special concrete compositions and the resulting concrete struc- tures as such as produced by this method.
  • the invention relates to the use on any bearing course of a reinforced concrete pavement as the base for a thin wearing course, and the use of a reinforced concrete pavement as an individual load-bearing layer.
  • Background information and background art Concrete is a composite material comprising a hydraulicaliy hardening binder, aggregate and in some cases additives. During mixing the required amount of water is added and fresh concrete is obtained. The mix of the hydraulicaliy hardening binder and water is known as paste. The addition of water initiates a number of different hydration reactions, which of course are de ⁇ pending on the chemical composition of the actual hydraulic binders. The hydration reactions generate heat and consume water, and the reaction products cause a hardening of the con ⁇ crete.
  • the hydration takes place in several phases, the length of which depends on the composition and the amount of the binder.
  • the mixing process itself generates a large amount of heat due to saturation of the powder and transformation of mechanical energy.
  • the con ⁇ crete is characterized by a dormant period where only moderate heat is generated.
  • the con ⁇ crete can be placed and worked on or compacted during this period, which normally lasts from 0 to 3 hours.
  • the next phase (3-24 hours) which includes the hardening (setting) of the con ⁇ crete, one third of the total hydration takes place.
  • the third and final phase includes the slow part of the hydration, which normally, for a Portland cement concrete, is considered to be completed after 28 days.
  • the hydration of the largest cement particles can however continue for several years; likewise, the use of pozzolans, blended cements and/or other binders can cause the hydration process to continue for a long period.
  • Maturity defines the relative extent of hydration at 20°C. Maturity is determined on the basis of the generation of heat in the concrete. The precise course and extent of the hy ⁇ dration depends on the chemical composition of the binder and the amount of binder in the concrete. During the hardening period the maturity is calculated as the actual isothermal heat generation in relation to the overall possible heat generation. The overall heat generation of the concrete can be determined by means of adiabatic calorimetry.
  • the relative maturity during the course of the hardening process can also be determined as the amount of bound water (non-evaporable below 105°C) in relation to the amount of bound water at full hydration.
  • the temperature in the concrete will rise depending on the initial temperature, the amount and type of binder and the ambient tempera ⁇ ture.
  • the concrete temperature usually rises during the first one or two days of the hardening pro- cess, and then it declines under adjustment to the surrounding climate.
  • the hydraulic binder in concrete can be cement, e.g. Portland cement, Pyrament, or calcium aluminate cement; natural pozzolans, such as volcanic ash, typically of basalt origin (described first in antiquity, from Pozzuoli in Italy), liparite (volcanic ash from Iceland), paganite (volcanic ash from Pagan Island), or moler; or artificial pozzolans such as blast furnace slag, fly ash or microsilica.
  • cement e.g. Portland cement, Pyrament, or calcium aluminate cement
  • natural pozzolans such as volcanic ash, typically of basalt origin (described first in antiquity, from Pozzuoli in Italy), liparite (volcanic ash from Iceland), paganite (volcanic ash from Pagan Island), or moler
  • natural pozzolans such as volcanic ash, typically of basalt origin (described first in antiquity, from Pozzuoli in Italy), liparite (volcanic ash from Iceland
  • microsilica in the present application is intended to mean a waste product from the ferro-silicon production, stemming from the cleansing of flue gases and consisting primarily of Si0 2 of spherical shape with an average particle size of approx. 0.1 ⁇ m.
  • cement hydration product any combination of these binders can be used.
  • a sufficient amount of a cement hydration product must be available to react with the pozzolans, otherwise the necessary amount of alkalis must be added separately. Accordingly, it is not vital that cement is used, since for example, alkalis in the form of seawater can be used together with pozzolans. Under normal circumstances, however, concrete typically comprises cement.
  • the aggregate is typically concrete gravel, consisting of sand (0/4 mm) and stone (4/8 mm, 8/16 mm, 16/32 mm and larger). These fractions, which also can have other grading intervals, can be combined according to the purpose. Not all fractions have to be present, and within individual fractions size gaps may occur.
  • mineral additives i.e. fillers such as crushed quartz or limestone, chemical additives such as air entraining agents, plasticizing agents and agents for the regulation of the setting and/or the hardening.
  • chemical additives such as air entraining agents, plasticizing agents and agents for the regulation of the setting and/or the hardening.
  • polymer bin ⁇ ders, viscosity influencing materials (e.g. tylose) and colouring agents can be included.
  • one specific main object of the invention is the development of a cement-based road construction material for use as an independent, flexible bearing layer or as a wearing course on top of existing flexible pavements.
  • a concrete pavement is traditionally placed on top of a layer of bitumen stabilized sand/gravel (asphalt) or cement stabilized sand/gravel, which again is placed on top of a layer of sub-base material.
  • bitumen stabilized sand/gravel asphalt
  • cement stabilized sand/gravel which again is placed on top of a layer of sub-base material.
  • a wearing course if desired, can be placed, for example a thin concrete layer or an asphaltic wearing course, which normally would have a thickness greater than 10 mm, or a surface dressing which typically would be less than 10 mm thick.
  • Such surface dressings are usually produced using cut-back bitumen binders in combination with application of chippings (small stones), or artificial binders such as epoxy resins may be used.
  • This method is based on the cutting of joints with a diamond saw every 5 metres at a point in time corresponding to 12-18 hours of maturity, the joint width is typically 3-5 mm and the joint depth corresponds to 1/3 of the thickness of the concrete layer.
  • the joint is later sealed with an elastic joint filler.
  • steel dowels are placed transversely to the joints in the middle of the pavement at the time of paving.
  • the distance between the dowels is typically 30 cm for pavements up to 25 cm and the dowel diameter is typically 25 mm.
  • the dowel length is set by local practice but would normally be 50 cm.
  • the dimensioning of the dowels is determined on the basis of he traffic load (Beton Teknik 6/08/1983).
  • the dowels are coated with a suitable covering layer, for example bitumen, epoxy or grease.
  • the typical thickness of the concrete layer is approx. 25 cm (20- 27 cm).
  • CRCP Continuous Reinforced Concrete Pavements
  • PIARC Permanent International Association of Road Congresses
  • PIARC Technical Committee on Concrete Roads
  • Subcommittee Continuously Rein ⁇ forced Concrete Pavements dated May 1993.
  • Such pavements are extensively used and have excellent properties; frequently lifetimes of 35-40 years are reported. Their lifetime depends, however, strongly on how well the crack formation can be controlled.
  • methods of calculating the necessary percentage of reinforcement are also described.
  • CRCP pavements are normally placed on top of a layer of cement-stabilised or hydraulicaliy bound gravel of varying thicknesses depending on the sub-base, the thickness of the CRC- layer varying between 20 and 25 cm, depending on the traffic load.
  • FRC Fibre Reinforced Concrete
  • FRC is no real reinforced concrete material in the traditional sense, but rather a con ⁇ crete material of an improved ductility. Thereby the energy required for the formation of cracks is increased.
  • DS 411 (Danish Standard no. 411) and Eurocode 2 provide similar calculation methods for the necessary degree of reinforcement with a view to ensuring that the cracks do not exceed a certain upper limit of width.
  • these standards relate to concrete beams, and calcu ⁇ lations relating to road pavements necessitate taking into account the effect from friction against the basecourse, but nevertheless this technical basis generally seems correct with a view to calculating crack widths in concrete pavements.
  • the required amount of reinforcing material depends basically on the cross-section dimension of the concrete layer, the type of concrete, friction against the basecourse, the temperature at the time of construction versus the potential minimum temperature, and of the properties of the reinforcement material (E-modulus and yield stress).
  • the horizontal degree of reinforcement (for short: the degree of rein ⁇ forcement) is defined as that part of the cross section area which is made up of reinforcement material. This is due to the fact that the reinforcement in the longitudinal direction is the most important - the transverse reinforcement acts mainly to assure the correct location of the longi ⁇ tudinal steel.
  • steel is generally used as continuous reinforcement material, e.g. High Ferrite Steel having a yield stress of 550 MPa.
  • this reinforcement material experience supported by theoretical considerations (see PIARC) has shown that the required degree of reinforcement is 0.7% at least, with a view to establishing a satisfactory crack structure with crack widths of less than 0.2 mm and with a preferred spacing of (distance between) the cracks of between 0.8 and 1.2 m.
  • this shows that this applies to climatic conditions which are prevalent in temperate zones. If a type of steel with a higher tensile strength/yield stress is used, such as 1000 MPa, the degree of reinforcement required is typically reduced to 0.3%. It is therefore important to specify precisely the reinforcement used.
  • Continuously reinforced concrete pavements on roads typically have a layer thickness of ap- prox. 22 cm, whereas fibre reinforced concrete pavements will normally vary from 10 to more than 100 mm when used as a repair layer on old concrete pavements.
  • method (2) is preferred over method (1), because of a longer lifetime, less maintenance and the fact that it constitutes a more comfortable pavement for the drivers.
  • the reinforcement method is disadvantageous in being somewhat more expensive than method (1) (cut joints); about 20% more expensive.
  • This method has been used experimentally recently and involves the initiation of pre-cracks every 2 m in the longitudinal direction of a hardened non-reinforced concrete (with a minimum compressive strength of 60 MPa).
  • This method is called ECOPAVE (Economical Pavement) and is described in a research report to the European Commission, General Directorate XII,
  • the pre-cracks of the hardened concrete are established mechanically with a view to pre-de- termining the outbread of cracks resulting from the loading. But since this initiation of pre- cracks takes place in the hardened concrete, it is not always possible to avoid the crack forma ⁇ tion resulting from thermal fluctuations and the shrinkage during hardening. Experience shows that there is a risk of such pavement in time acting in the same manner as a pavement with joints as mentioned above (1), main cracks breaking out approx. every 5 m resulting in insuffi ⁇ cient load transfer because of a too great width of these cracks. Experience shows that such instability in the crack system never occurs in CRCP as described above under method (2).
  • the present invention is based on the surprising observation that the necessary level of rein ⁇ forcement can be reduced drastically by introducing cracks in the concrete before completion of the hardening process. This applies to concrete structures such as concrete pavements being load bearing per se and to wearing courses on other primary load bearing structures such as asphalt and old concrete, and it applies to continuous reinforcement as well as fibre reinfor- cement or combinations thereof.
  • US Patent no. 3,810,708 discloses a method of anchoring a concrete pavement on a base- course, said method comprising the pushing of clamps through the paved, non-hardened con ⁇ crete pavement and into the basecourse with a view to create holes, to be filled up with con- crete. Allegedly, this constitutes an attempt to influence the crack formation in connection with the hardening in such a way that a finely dispersed crack system results.
  • this prin ⁇ ciple has proved not to work in practice, since the required load transfer ability is not provided simply by creating these cement-filled holes in the basecourse.
  • the method has primarily been developed in order to prevent so-called “welreisen”, which describes the phenomenon that the concrete plates so to speak move in "packets”, since very large cracks arise every 20-30 m.
  • the crack system must be pre-initiated before contraction cracks are formed under the influence of the normal hardening and thermal strains. That is to say before the point in time at which the temperature has decreased below that level which was prevailing when the concrete acquired an E-modulus of a certain magnitude, which typically occurs 4 hours after setting. Cracks are formed inherently when the stresses in the concrete resulting from the setting, a potential drying out and the temperature influence exceed the actual tensile strength of the concrete, and then it is too late to pre-initiate a crack system.
  • Claim 1 relates to various reinforced concrete structures, examples of which are mentioned i.a. in the introduction. So the method of casting the concrete referred to in the pre-characterizing portion of claim 1 includes all conventional methods relating to the various structures, such as, for instance for road constructions, a slip form paver, laying it between forms, laying it using asphalt pavers or other types of suitable road construction equipment.
  • cracks are pre-initiated - they form before the concrete cracks on its own - that part of the reinforcement which is otherwise required to control the formation of an acceptable crack pattern can be omitted.
  • a certain degree of reinforcement is indispensable, since it is still necessary primarily to stabilise the crack system as mentioned above.
  • the reinforcement has served the purpose of controlling the crack formation by overcoming the tensile strength of the concrete material as well as the frictional force which is established against the basecourse, but, according to the invention, with pre-initiated cracks the tensile strength of the material is reduced in the crack zone as is the reinforcement degree required, viz. to a level at which the tensile strength in the material is comparable to the mechanical strength of the crack itself.
  • the reinforcement degree required can be related to a force consisting of the above-mentioned crack strength plus the friction against the basecourse of no more than 1 element, i.e. no more than the friction of a plate with a length equal to the maximum crack distance or spacing.
  • the necessary reinforcement degree depends on the crack strength, the crack spacing and the coefficient of friction to the basecourse, and it can be calculated at a given load as that degree which is sufficient to prevent yield of the reinforcement.
  • a theoretical teaching on the calculation of the necessary degree of reinforcement is given for a construction with pre-initiated so-called macro cracks, on the basis of the above considerations, said teaching more precisely relating to a continuously reinforced structure (see also the analogous considerations regarding fibre reinforcement and micro cracks below).
  • the invention is not limited to concrete pavements but applies to all concrete structures which are traditionally reinforced in order to control the cracking. Examples of such structures are mentioned in the introduction. In the introduction typical concrete compositions are also men ⁇ tioned.
  • the principles of the invention apply to continuously reinforced structures as well as to fibre- reinforced structures and to structures reinforced with a combination thereof.
  • the pre-initiated cracks can be so-called macro cracks, easily observable with the naked eye, or so-called micro cracks of a considerably reduced size.
  • the cracks can be established in many ways, some of which are described below.
  • Claim 3 discloses a first special aspect of the invention, viz. the pre-initiation of macro cracks in continuously reinforced concrete structures
  • a second aspect relating to the introduction in a fibre reinforced concrete structure of an inter ⁇ connected micro crack system is disclosed in claim 4.
  • a concrete pavement constructed in accordance with the principles of this aspect is particularly well suited to accommodate the deformations which occur in connection with a wearing course on asphalt pavements (10-100 mm, preferably 30-50 mm), cfr. claim 26.
  • a third aspect of the invention (cfr. claim 5), relates to the formation of pre-initiated macro cracks and/or micro cracks in a concrete with a combination of continuous reinforcement (using reinforcing bars) and fibre reinforcement.
  • Such a combined reinforced concrete structure with pre-initiated micro cracks can advan ⁇ tageously be used in the wearing course on asphaltic pavements (30-100 mm), cfr. claim 26.
  • a fourth aspect of the invention (claims 6 and 7), the principle of the invention is applied in connection with a composite pavement consisting of at least one layer of concrete with a pre- initiated crack system in relation to the above-mentioned aspects 1 to 3, and with correspon- ding reinforcement and at least one layer of fibre reinforced concrete with a pre-initiated crack system and reinforcement according to the second aspect.
  • materials for traditional ferrous reinforcement can be used to substitute materials for traditional ferrous reinforcement.
  • the use thereof, however, is still at a developmental and experimental stage, but the materials are well-known in connection with fibres.
  • Such materials are, for example, polypropylene, glass, nylon, carbon, aramid, polyaramid, mineral wool, cellulose and asbestos, but as mentioned above all materials that fulfil the functional demands can be used.
  • spun and weldless polypropylene wires spun glass cables, spun and pressed polyaramid thread (Kevlar) etc. can be used.
  • fibre reinforcement typically steel, carbon, glass, asbestos, cellulose, polypropylene, polya ⁇ ramid, aramid, nylon, etc. can be used.
  • the following materials are preferred:
  • the concrete composition is mixed in quite conventional manner; problems of correct dosage and mixing of the fibres is generally a matter for the technology of the 1980's.
  • the pre-initiation of cracks can be performed in several ways according to the invention.
  • Macro cracks can for example be introduced as indicated in claims 8-11 and micro cracks as indicated in claims 12-15.
  • the pre- initiated cracks are formed by means of a preliminary crack formation in a lower layer.
  • a groove (a joint) is made across the layer, e.g. using a Soff-cut diamond cutting machine, immediately following the setting of the concrete, the groove width being less than 3 mm.
  • the depth of the groove corresponds to about 10% of the layer thickness.
  • a piece of hard wood for instance of the dimensions 100 x 100 mm, is placed over the groove, and a falling weight or a falling sword is released so as to hit the wood beam with a drop or fall energy of minimum t x 50,000 J/m 2 (per unity of length of the groove, the expression t being the thickness in meter of the layer).
  • a detonating thread as mentioned in claims 8 and 10
  • a detonating thread is only possible for layers of a thickness above a certain minimum (about 10 cm), since detonating threads having such low charge as would be required for less thick layers are for the moment not marketed (not yet).
  • a detonating thread e.g.
  • Pantrit 3 g/m supplied by Dansk Spraengstofselskab A/S, is placed on the sub base before the laying of the concrete.
  • the detonating thread is ignited, for instance using an electrical detonator supplied by the above mentioned firm. By the detonation, a fine crack is established bottom-to-top with no damage of the surface.
  • a tool comprising cutting organs of the ploughshare type is used.
  • the spraying with a release agent takes place in order to prevent the disappearance of the cracks because of the sides fusing together. Care must be taken to ensure that the release agent is not applied at the top of the groove, since otherwise surface failures might occur involving a risk of shelling or peeling.
  • This method is likewise preferred for layers of a greater thickness than 10 cm.
  • micro cracks are formed, which have shown up to establish a continuous network of inter-connected cracks, separating the structure in a lot of parts, being inter-locked in a sort of a three-dimensional jigsaw puzzle, deformation of the micro cracks however being allowed, and the tensile strength of the material being reduced.
  • the desired point contact can for instance be obtained by using an aggregate mixture in which a heavy jump or discontinuity exists in the particle size distribution curve, typically so as to bring about lack of particles of a full range of order, e.g. a jump between 1 and 10 mm, between 2 and 20 mm, between 4 and 40 mm etc.
  • the concrete then has to be composed so as to allow the filling mixture to flow so easily as to ensure contact between the larger particles, while not completely filling all those cavities of the stone skeleteon which are defined by the coarse aggregates.
  • micro cracks of the desired character will be formed in connection with the chemical shrinkage of the paste.
  • the particles smaller than 0,1 ⁇ as mentioned in claim 12 is for instance micro silica.
  • the shrinkage of the paste depends on the chemical reaction type of the cement. Clay of the lllit type usually forms dehydration cracks in connection with the water consumption during the hydration.
  • the concrete is laid as usual, and at a given point in time, typically in the interval of between the setting time and before a compressive strength of 20 MPa is achieved, viz. usually within 1-3 days after laying, a vibration roller, a vibration plate compacting device, a rubber wheel roller or other static compaction devices are put upon and/or driven upon the layer, following which a nice pattern of micro cracks is formed in the layer.
  • a deflection (deflection bowl) is obtained of the sub base layer, whether asphalt or something else, and when the concrete layer deflects correspondingly, appropriately spaced cracks are formed.
  • Claims 18-21 relate to fresh concrete, binder compositions and paste being particularly useful for the formation of micro cracks, cfr. the corresponding method claims 12-15.
  • Claim 12 dis ⁇ close one example of a paste of poor strain capacity at an early age, viz. a paste of a large hydration shrinkage and/or a low water content etc. Typically, but not exclusively, this is a paste as defined in claim 14.
  • the method of claim 17 is well known, i.a. from Germany, for the positioning of transverse cracks every five meter in the basecourse below non-reinforced concrete layers.
  • the cracks of the cement bound gravel basecourse are positioned immediately below the joints of the concrete pavement. If cracks are made in the basecourse every meter instead of every five meter, cracks are formed in the concrete layer exactly according to this pre-de- termined pattern. The cracks are only formed, however, at a certain difference of about 10°C between the day and the night temperature. If this difference is not obtained, the cracks may be artificially provoked with a knock at the crack zone using a so-called Whip-hammer or using a mechanical impact as mentioned in claim 9.
  • Example 4 a method of calculating the required degree of reinforcement in systems of pre-initiated cracks is presented.
  • test specimens with and without pre-initiated cracks
  • Tensile tests are carried out on test specimens of the following dimensions: A: 500 x 800 x 40 mm (b x I x h)
  • the smaller specimens of type A are used in connection with the methods IV-VI (see below) in tests with pre-initiated micro cracks, and also because the specimens for micro crack testing do not need to be so large.
  • Air entraining agent (Sika) 0 0 1 ,25 0 0
  • the cement is a low-alkali cement from Aalborg Portland, micro-silica is obtained from Elkem, sand 0/4 mm from Frederikssund Sten & Grus, gravel 4/8, 4/25 and 8/25 from Superfos Construction, R ⁇ nne, Sika air-15 and Sika plastiment A40 from Sika, fly ash is supplied by Danaske AS in Aalborg.
  • test specimens are divided into two groups.
  • a crack system is pre-initiated by means of the methods stated below, the other group being a control group with no pre-initiated cracks.
  • a reflective crack is established at 12 hours of maturity by sawing with a diamond saw a 3mm lead groove through 10% of the slab thickness and afterwards loading with a Falling Weight on an ordinary railway sleeper placed across the test specimen.
  • the drop energy should correspond to a 3 tons weight falling 20 cm per m beam width.
  • a reflective crack is established at 14 hours of maturity by setting off a detonating thread placed below the beam, transversely to the longitudinal direction.
  • the detonating thread is supplied by Dansk Spraengstofselskab and has a charge or loading of 3 g/m.
  • a partially reflective crack is established at zero hours of maturity by scraping across the test beam using a brick jointer and spraying bitumen emulsion in the scraped joint. The joint is then carefully closed by manually vibrating both sides of the crack.
  • test specimens are exposed to uni-axial longitudinal tension.
  • the test method is no standard method. The results obtained are shown in the Table below:
  • Method IV seems to be less effective than methods V and VI, but a single less successful test should not absolutely lead to the exclusion of the method as a potential crack-inducing method.
  • the cracks are pre-initiated as follows:
  • the first meter of the slab is cast against a plywood board.
  • the board is removed and the lower two thirds of the casting joint is painted with liquid asphalt.
  • the plywood board is placed 1 m further down and the next section of slab is cast between the asphalt surface and the plywood board. In this way, four weak lines (pre-initiated cracks) are made in the 5 m long slab, see fig. 1.
  • the reinforcement used is a high-strength steel (High Tensile Steel, rib bar, from Lemvigh- M ⁇ ller & Munch, Copenhagen) with a diameter of 6 and 8 mm.
  • the yield stress of the steel is 550 MPa.
  • the number and diameter of the reinforcement bars and the resulting degree of rein ⁇ forcement ⁇ is shown in Table 2 below: Table 2
  • the slabs are tested at an age of three days of maturity in uniaxial tension.
  • the stress-strain- relation and the distribution of cracks is studied for different amounts of reinforcement.
  • the slabs are exposed to an overall elongation of 3 %o.
  • the test arrangement is shown in Fig. 1.
  • the load is applied by means of two hydraulic load cells.
  • a manometer is attached to each load cell in order to record the load applied.
  • the surface of the slabs is painted white in order to make the cracks visible.
  • the strain (the relative elongation) is measured in two ways: (1) By means of two 500 mm slide gauges (the approximate placing of the slide gauges is shown at Fig. 1); and (2) the overall elongation of the slab is measured by recording the distance between the movable traverse and the fixed traverse, to which the load cell are attached (see Fig. 1).
  • L indicates the placing of the slide gauges and the numbering indicates the order in which the cracks were formed.
  • crack no. 1 occurred at one of the pre-initiated cracks.
  • a " ⁇ " indicates the development of cracks no. 5-10
  • a ⁇ indicates the development of cracks no. 1-9.
  • a degree of reinforcement of more than 0.7% will ensure satisfactorily distributed cracks, even if no cracks are pre-initiated in the fresh concrete (slabs no. 7 and 8).
  • the distance between cracks and accordingly also the crack width is inversely proportional to the degree of reinforce- ment (i.e., the greater the degree of reinforcement, the smaller the crack spacing and the nar ⁇ rower the crack width).
  • a degree of reinforcement of 0.06% (slab no. 1) does not suffice in order to activate the pre- initiated cracks and thus only one crack is formed.
  • the results indicate that by pre-initiating a crack system in the slab, the reinforcing degree can be reduced from 0.7% to 0.1%, perhaps even more, to 0,07%, i.e. about 10%.
  • the desired minimum distance betweeen the pre-initiated cracks of the structure depends on the maximum crack width, which can be allowed in the final structure and on the expected maximum load.
  • Melment L-10 is a superplasficizer, supplied by NBK, R ⁇ dekro.
  • the steel fibres used are of the type Dramix ZL 30/.50 from Bekaert.
  • the equation in the last row of the Table corresponds to the Danish Standard calculation of the equivalent water/cement ratio.
  • the size of the slabs are 40 x 500 x 800 mm.
  • a micro crack system is pre-initiated, the rest being control slabs with no micro cracks.
  • Micro cracks are pre-initiated as follows: gravel is mixed with steel fibre and cement, and then water and the superplasticizer (SPT) is added.
  • SPT superplasticizer
  • the viscosity of the paste is sufficiently low to ensure that there is contact between individual gravel particles.
  • a stiff stone skeleton is formed being surrounded by fibre-reinforced paste.
  • the cement paste as such during the set- ting shows high shrinkage. Due to the stiff stone skeleton, however, the shrinkage of the paste is hindered and this leads to the formation of a well-dispersed micro crack pattern.
  • the fibres ensure that stress can be transferred across the shrinkage cracks.
  • the slabs are tested at a maturity of three days in uniaxial tension.
  • the distribution of the cracks formed in the slabs during loading is studied at various fibre reinforcement percentages.
  • the slabs are exposed to a total elongation of 3%o.
  • the maximum crack width at 3%o is measured.
  • the test setup is shown in principle in Fig. 1.
  • the load is applied by means of two hydraulic load cells.
  • a manometer is attached to each load cell in order to record the load applied.
  • the surface of the slabs is painted white in order to ensure that the cracks become visible.
  • the strain is measured with two 500 mm slide gauges.
  • the crack patterns of the slabs are shown at Figs. 18-22.
  • the numbering indicates the order in which the cracks appeared.
  • a fibre reinforcement of 2 to 3 volume percent is generally assumed to be sufficient to obtain a well-dispersed crack system and to control the crack widths in a typical concrete pavement exposed to tensile strain (with no pre-initiated crack system).
  • a fibre percentage reinforcement of 0.2 to 0.5% by volume is sufficient to ensure that a well-dis ⁇ persed crack system is formed, when the slab is exposed to the influence of tensile strain.
  • the spacing between the cracks created and the crack widths are inversely proportional to the degree of reinforcement.
  • the results of this test series indicate that - aiming at a maximum crack width of 0.2 mm at an elongation of 3%o - the fibre reinforcement can be reduced to 17%, viz. from 3% to 0.5%, by pre-initiating a finely dispersed micro crack system in the slab.
  • A a the minimum area of the reinforcement perpendicular to the crack surface (m 2 ) A, ⁇ the cross-sectional area of the slab (pavement) (m 2 )
  • the force of the reinforcement F r must exceed the force necessary to activate the pre-initiated crack F cr plus the force F f generated by the friction between the sub-grade and a section of the pavement of the length /, see Eq. (3.1):
  • the required reinforcing degree can be estimated from eq. (3.3):
  • the fibre reinforcement necessary to ac ⁇ tivate the micro cracks can be calculated using the same principles as applied above.
  • the main difference between the two cases is the distance between pre-initiated cracks.
  • the distance between the macro cracks in the longitudinally reinforced pavement is of the order of 27
  • the widths of the pre-initiated cracks are smaller for the same overall deformation and accordingly the strength of the pre-initiated micro cracks ( ⁇ C ) is higher than that of the pre- initiated macro cracks.
  • the fibres are assumed to be randomly 3-D distributed. According to Aare, T., "Tensile Charac ⁇ teristics of Concrete with Special Emphasis on its Applicability in a Continuous Pavement," Ph.D. thesis, Institute of Supporting Structures at The Technical University of Denmark, the number of fibres bridging a crack per unit area of crack surface N 0 can be determined in accor ⁇ dance with eq. (4.4):
  • N 0 172 - ⁇ r f ⁇ d f Vindicating the fibre volume fraction and df the diameter of the fibres.
  • the emergency lane in question was constructed as follows from the top downwards: 4 cm fibre reinforced concrete, 10 cm reinforced concrete with micro cracks, 10 cm stabilized gravel with micro cracks, 10 cm granular sub-base 0/32 mm, 60 cm frost-proof capping layer.
  • the upper 14 cm which is of relevance for the present test, was constructed as follows: A gravel layer was laid using a standard asphalt paver consisting of crushed R ⁇ nne granite, 45 mm rail track ballast from Superfos Construction, R ⁇ nne. The layer thickness was 10 cm fol- lowing compacting with a light vibrating roller, type Bomag 90. The width of the pavement was 240 cm.
  • composition of the mortar (2.5 m 3 ): Cement, low alkali 2000 kg
  • Peramin F is a suiphonated melamine formaldehyde in a 35% aqueous solution supplied by Perstorp Chemitech AB, Sweden.
  • the fibre concrete was also produced by GH-beton and had the following composition per m 3 :
  • the pavement surface was then inspected and it was found that a crack system had been established with a crack width of less than 0.1 mm and with a crack spacing between 0.4 and 0.8 m in the reinforced sections, whereas the non-reinforced control section had cracks in four places with cracks widths of > 2 mm.
  • the moderate reinforcement of the top layer (0.5 vol-% polypropylene fibre) as expected, did not show up to have any effect on the primary crack formation. Very wide cracks appeared in those sections having no traditional reinforcement, despite the well-established microcrack system in the lower concrete. Accordingly, the reinforcement degree can not be reduced to zero.
  • a test pavement was constructed on an existing asphalt pavement on a local road at the above-mentioned gravel pit.
  • the pavement was 2 m wide and had a thickness of 4 cm.
  • the following concrete composition was used for the pavement:
  • the concrete was mixed at Dansk Beton Teknik's concrete mixing plant at the gravel pit (of the type Rex Chainbe't Porto Paver, 9 cu. yd).
  • the concrete was transported to the paver in a Volvo 860 open dumper.
  • the wearing course was laid by first milling the asphalt surface slightly so as to establish an even base. Then a surfacing of fibre concrete with a thickness of 4 cm was laid with an asphalt paver of the type Vogele 2000, High Compaction, Superscreed. The concrete was compacted by by means of the vibrating beam of the asphalt paver only.
  • the above micro crack system was pre-initiated using the method of establishing point contact in the gravel layer together with a paste of high shrinkage.

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Abstract

L'invention concerne un procédé pour réaliser des structures en béton armé et plus particulièrement des structures en béton armé permettant d'éviter la formation de fissures, du type de celles utilisées dans les tunnels submergés, les conduites utilisées pour le chauffage à distance et les caisssons pour structures de taille importante, comme les tabliers des ponts, les quais, les routes, les pistes d'atterrissage et les terrains de sport. On effectue le pré-amorçage de la formation de macro- ou de micro-fissures dans le béton, alors que le procédé de durcissement n'est pas terminé, à un moment particulier avant l'apparition de fissures de contraction 'spontanées', provoquées par la température, etc., ce qui permet de diminuer le degré de renforcement d'environ 10 % par rapport à ce qui était normalement considéré comme nécessaire. On décrit des procédés de pré-amorçage de macro- et de micro-fissures dans le béton. L'invention concerne également des compositions de béton et de liant spéciales ainsi que les structures en béton ainsi produites utilisant le procédé de l'invention. En particulier, l'invention concerne la réalisation d'une couche de roulement mince en béton renforcé disposée sur une couche portante quelconque et servant de couche portante indépendante.
EP95922444A 1994-06-21 1995-06-20 Procede pour realiser une structure en beton arme Withdrawn EP0804648A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
DK734/94 1994-06-21
DK73494A DK73494A (da) 1994-06-21 1994-06-21 Fremgangsmåde til fremstilling af en armeret betonkonstruktion
PCT/DK1995/000255 WO1995035415A1 (fr) 1994-06-21 1995-06-20 Procede pour realiser une structure en beton arme

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MY118701A (en) 1997-02-12 2005-01-31 Bekaert Sa Nv Combination reinforcement for floor on piles
JP3445932B2 (ja) * 1998-04-17 2003-09-16 新東京国際空港公団 打継用コンクリート及び該打継用コンクリートを用いた打ち継ぎ工法
EP0964113A1 (fr) * 1998-06-11 1999-12-15 N.V. Bekaert S.A. Armature mixte pour dalles de plancher reposant sur des piliers
US6687559B2 (en) 2000-04-04 2004-02-03 Digital Site Systems, Inc. Apparatus and method for a vertically integrated construction business
GB2426994A (en) * 2005-06-07 2006-12-13 Mark Andrew Holden Method for preventing cracks in hydraulically bound materials
WO2009117520A2 (fr) * 2008-03-19 2009-09-24 Hexion Specialty Chemicals, Inc. Modificateur pour des formulations de béton et ciment et procédés de préparation associés
US9254583B2 (en) 2012-01-23 2016-02-09 Quipip, Llc Systems, methods and apparatus for providing comparative statistical information for a plurality of production facilities in a closed-loop production management system
US9836801B2 (en) 2012-01-23 2017-12-05 Quipip, Llc Systems, methods and apparatus for providing comparative statistical information in a graphical format for a plurality of markets using a closed-loop production management system
US10184928B2 (en) 2014-01-29 2019-01-22 Quipip, Llc Measuring device, systems, and methods for obtaining data relating to condition and performance of concrete mixtures
US9194855B2 (en) 2014-02-28 2015-11-24 Quipip, Llc Systems, methods and apparatus for providing to a driver of a vehicle carrying a mixture real-time information relating to a characteristic of the mixture
US9766221B2 (en) 2015-01-30 2017-09-19 Quipip, Llc Systems, apparatus and methods for testing and predicting the performance of concrete mixtures
CN112699520B (zh) * 2020-11-10 2024-04-30 西安建筑科技大学 一种建立hbprc本构模型的方法及装置
CN114577563A (zh) * 2022-02-11 2022-06-03 中国电建集团西北勘测设计研究院有限公司 一种自愈合混凝土裂缝修复检验方法

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GB1481410A (en) * 1973-11-28 1977-07-27 Miers Ltd L Insertion member for use in the construction of concrete slabs

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AU2733995A (en) 1996-01-15
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