WO2001031136A2 - Reinforced concrete systems - Google Patents
Reinforced concrete systems Download PDFInfo
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- WO2001031136A2 WO2001031136A2 PCT/US2000/041485 US0041485W WO0131136A2 WO 2001031136 A2 WO2001031136 A2 WO 2001031136A2 US 0041485 W US0041485 W US 0041485W WO 0131136 A2 WO0131136 A2 WO 0131136A2
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- layer
- steel reinforcement
- steel
- cement
- concrete
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Classifications
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
- C23F11/00—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
- C04B28/02—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing hydraulic cements other than calcium sulfates
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- 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
- E04C5/015—Anti-corrosion coatings or treating compositions, e.g. containing waterglass or based on another metal
- E04C5/017—Anti-corrosion coatings or treating compositions containing cement
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- 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
- C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
- C04B2111/20—Resistance against chemical, physical or biological attack
- C04B2111/26—Corrosion of reinforcement resistance
Definitions
- the present invention is directed to reinforced concrete systems, and more particularly, is directed to steel reinforced concrete having improved corrosion and/or mechanical performance.
- Steel-reinforced concrete is a remarkably versatile and ubiquitous material. It is easily formed from a cement-based slurry which hydrates with water, without extensive volume change, to form solid, compressively strong structures of virtually unlimited size and shape.
- the structural weakness of concrete in tension is compensated by relatively inexpensive steel reinforcement, which fortuitously approximates the thermal expansion of concrete over a broad temperature range.
- steel reinforcement is subject to corrosion (rusting), even when embedded in the high-pH, passivating environment of the hydrated cement paste.
- the pressure from the increased volume of the confined iron oxide corrosion product spalls and cracks the concrete, destroying its functional integrity long before the end of its potential design life.
- Estimates of the repair cost for existing highway bridges in the U.S. have been put at over $50 billion, and $1 to $3 trillion for all concrete structures M. Fickleburn, "Editorial", Materials and Structures Journal, RILEM, Vol. 23, No. 137, p. 317 (1990).
- steel-reinforced concrete has many desirable attributes which have made it a dominant "Infrastructure" material for roads, bridges, buildings and dams throughout the world.
- An enormous design, manufacturing and construction industry has developed which is efficient and skilled in its use and application. In the absence of corrosion, its behavior is relatively predictable and reliable.
- Conventional steel reinforcement is relatively inexpensive, particularly in comparison to inherently expensive alternatives such as Fiber Reinforced Plastic (FRP) and stainless steel.
- FRP Fiber Reinforced Plastic
- Corrosion of steel reinforcement is greatly accelerated in the presence of chloride ions, which catalyze iron oxidation. Even if not present in the original concrete, chlorides can penetrate throughout the pore structure of the concrete when the external surfaces of the concrete are exposed to deicing salts or marine environments [J.A. Gonzalez, et al., "Some Considerations On The Effect Of Chloride Ions On The Corrosion Of Steel Reinforcements Embedded In Concrete Structures", Magazine Of Concrete Research, Vol. 50, pp. 189-199 (1998)].
- a wide variety of approaches has been attempted to overcome the problem of corrosion in reinforced concrete. For example, steel reinforcement with a relatively expensive epoxy coating is commonly used in bridges and highways. However, the soft epoxy coating is easily damaged during transportation and placement.
- the epoxy coating also prevents bonding of the rebar with the cement matrix, and itself tends to debond from the steel surface because its bond can be thermodynamically unstable in the alkaline cement environment.
- the epoxy layer When debonded from the steel surface, the epoxy layer may be associated with underfilm and crevice corrosion.
- Another expensive approach has been the use of reinforcing materials which do not corrode.
- Stainless steel reinforcing bars meeting appropriate specifications ASASTM A955 and BS 6744
- have been used in selected applications [F.N. Smith, et al., "Stainless Steel Reinforcing Bars", Proc.
- FRP Fiber-reinforced plastic
- FRP reinforcements typically comprise carbon, aramid and/or glass fibers embedded in a resin matrix, to provide a high tensile strength-to-weight ratio [O. Chaallal, et al., "Physical and Mechanical Performance of an innovative Glass-Fiber Reinforced Plastic Rod for Concrete and Grouted Anchorages, " Canadian Journal of Civil Engineering, V. 20, No. 2,1993, pp. 254-268.].
- radial force transmission among adjacent fibers may be poor, and failure in fiber reinforced plastic composites may occur at relatively low strains (about 1-3 percent).
- FIGURE I is a schematic illustration of a conventional, freshly-poured, aqueous cement slurry at a steel reinforcement surface
- FIGURE 2 is a schematic illustration of a conventional, fully-reacted cement paste, at the steel reinforcement surface of FIGURE 1 ;
- FIGURE 3 is a schematic illustration of a fully percolated conventional concrete showing a chloride percolation path to, and along, the steel reinforcement surface;
- FIGURE 4 is a schematic illustration of a thermal spray system for integrally applying corrosion resistant and hydraulically reactive layers on hot reinforcing bar stock
- FIGURE 5 is a schematic cross sectional view of a steel reinforcing bar having an integrally bonded, thermally sprayed layer of silicon or ferrosilicon alloy on the steel surface, and an integrally bonded, thermally sprayed layer of hydraulically reactive cementitious material such as blast furnace slag integrally adherently bonded to the silicon or ferrosilicon layer;
- FIGURE 6 is a schematic cross-sectional view of a steel reinforcing bar having a thermally sprayed, dense adherent layer of hydraulically reactive cementitious material such as blast furnace slag integrally adherently bonded directly on the exterior steel surface;
- FIGURE 7 is a schematic illustration of a freshly-poured aqueous cement slurry at a layered, adherent, reactive steel reinforcement surface prepared in accordance with the embodiment of FIGURE 5; and
- FIGURE 8 is a schematic illustration of a cured cement layer at the non-corroding steel reinforcement surface of the embodiment of FIGURE 5, which has a relatively strong interface and which is protected from corrosion;
- FIGURE 9 is a photomicrograph of an undeformed steel reinforcing bar which has been plasma sprayed with an adherent integrally thermally bonded coating of blast furnace slag which is hydraulically reactive in a high-pH cement paste environment
- FIGURE 10 is a photomicrograph of a steel reinforcing bar which has been plasma sprayed with an adherent silicon coating and an adherent, integral blast furnace slag coating which is hydraulically reactive in a high-pH cement paste environment.
- the present disclosure is directed to corrosion-prevention and property-enhancing technology for steel-reinforced concrete, to facilitate the continued use of conventional, relatively inexpensive carbon steel in highways, buildings, bridges and tunnels.
- the present invention is directed to steel reinforcement for concrete which has the capability of forming an adherent bond with a cement matrix, and/or to methods for providing functionally graded, strongly adherent interfaces between steel reinforcement and a bulk cement matrix.
- the present invention is also directed to corrosion-resistant steel reinforced concrete, and to methods for manufacturing corrosion-resistant concrete having an interface between the bulk cement matrix and the steel reinforcement which is at least as strong as the cement paste of the bulk cement, and preferably stronger.
- the present invention is also directed to corrosion-resistant steel reinforcement.
- the interfaces may be provided by thermally spraying very thin, adherently bonded integrally functional layer(s) on the steel surface.
- the outer layer will at least partially react with the hydrating cement to produce a dense, adherent interface.
- Thermal spray application of a variety of functionally graduated interface materials on steel reinforcement bar surfaces may be utilized to more finely control the interface reaction in cement, as will be discussed in more detail.
- the purpose of the thermal spraying is to produce relatively dense, strongly adherent layers which are integrally and durably attached to, and protect, the steel surface.
- Various thermal spray systems such as plasma spray, HVOF (high velocity oxygen flame), and other combustion spray systems may be utilized.
- a key feature of the present disclosure is the thermal bonding of a calcium silicate or other cementreactive layer to the steel surface, or corrosion-passivated steel surface, to provide a strongly adherent interface.
- Suitable reactive coating materials might also include thermally sprayed cohesive layers of alumina, calcium aluminate(s), calcium phosphate/apatite, ferrotitanates, and other materials which can react with hydraulic cement.
- Dicalcium silicate e.g., from inexpensive pulverized fly ash or ground slag such as blast furnace slag, or pulverized burned oil shale
- Dicalcium silicate is a particularly preferred material, because of its relatively low cost and its ability to react in the high alkalinity environment of the cement mix, while being relatively inert under more neutral conditions of transport and storage.
- integrally adherent layers may be provided which are relatively inert and unreactive in storage and under construction site environmental conditions, but which are hydraulically reactive in the highly alkaline cement paste environment of an aqueous concrete mix.
- the thermally sprayed layers may also include strong fiber materials which strengthen the interface zone.
- the layers bond strongly with and protect the steel, and also may partially react with and become part of an enhanced, relatively dense interface with the bulk cement. It is important in the practicalities of the constructions sites and construction practices that the thermally sprayed reinforcing steel can be made so it is relatively durable for transport and handling prior to use. It is relatively inexpensive to apply the coating(s) to the reinforcing steel, which is also an important consideration for providing commercially effective reinforcement products.
- an adhesion promotion layer may be selected to improve the adherence between the steel reinforcement surface and the thermally sprayed cement-reactive layer.
- Adhesion promoting materials include boron, silicon, chromium, titanium, nickel and their lower oxides, which can form a chemical bond with, or from within, the iron surface, and with a calcium silicate, aluminate and/or phosphate thermally sprayed layer.
- the adhesion promotion layer may be very thin, for example, 10-2000 Angstroms, so that the amount of material applied is very small in proportion to the steel reinforcement.
- An optional metallic corrosion-resistant layer which is desirably integrally alloyed with or diffused in the steel reinforcement surface, may also be interposed between the steel and the cementitious hydraulically reactive bonding layer.
- This corrosion-resistant layer may also be relatively thin (e.g., 1000 Angstroms to 25 microns) and comprise or be combined with the adhesion promoting layer.
- the corrosion-resistant layer may be an integral silicon, boron, titanium or chromium diffusion or alloy which resists chloride catalyzed oxidation of iron.
- the present disclosure is directed to corrosion-prevention and property-enhancing technology for steel-reinforced concrete, to facilitate the continued use of conventional, relatively inexpensive carbon steel in highways, buildings, bridges and tunnels.
- Various aspects of the disclosure are directed to steel reinforcement for concrete which has the capability of forming an adherent bond with a cement matrix, and/or to methods for providing functionally graded, strongly adherent interfaces between steel reinforcement and a bulk cement matrix.
- the present disclosure is also directed to corrosion-resistant steel reinforced concrete, and to methods for manufacturing corrosion-resistant concrete having an interface between the bulk cement matrix and the steel reinforcement which is at least as strong as the cement paste of the bulk cement, and preferably stronger.
- the present invention is also directed to corrosion- resistant steel reinforcement.
- the interfaces may be provided by thermally spraying one or more very thin, functional layer(s) on the steel surface.
- the outer layer will at least partially react with the hydrating cement to produce a dense, adherent interface.
- Thermal spray application of a variety of functionally graduated interface materials on steel reinforcement bar surfaces may be utilized to more finely control the interface reaction in cement, as will be discussed in more detail.
- the purpose of the thermal spraying is to produce relatively dense, strongly adherent layers which are integrally and durably attached to, and protect, the steel surface.
- Various thermal spray systems such as plasma spray, HVOF (high velocity oxygen flame), and combustion spray systems may be utilized.
- a key feature of the present disclosure is the thermal bonding of a calcium silicate or other cement-reactive layer to the steel surface, to provide a strongly adherent interface.
- Suitable reactive coating materials might also include thermally sprayed cohesive layers of alumina, calcium aluminate(s), calcium phosphate/apatite, and other materials which can react with hydraulic cement.
- Dicalcium silicate e.g., from inexpensive pulverized fuel ash or ground slag such as blast furnace slag, burned oil shale
- integrally adherent layers may be provided which are relatively inert and unreactive in storage and under potentially difficult construction site environmental conditions, but which are hydraulically reactive in the highly alkaline cement paste environment of an aqueous concrete mix.
- the layers bond strongly with and protect the steel, and also may partially react with and become part of an enhanced, relatively dense interface with the bulk cement. It is important in the practicalities of construction sites and construction practices that the thermally sprayed reinforcing steel can be made so it is relatively durable for transport and handling prior to use. It is relatively inexpensive to apply the coatings to the reinforcing steel, which is also an important consideration for providing commercially effective reinforcement products.
- Methods for manufacturing steel reinforcement for concrete structures can comprise the steps of providing a steel reinforcement element for a concrete structure, thermally applying an adherent layer of hydraulically reactive alkaline earth oxide, aluminate, silicate or phosphate or silica to the external surface of the steel reinforcing element, to form a cohesive layer having a thickness of preferably from about 5 to about 500 microns.
- This layer is adherently bonded to the steel surface, either directly, or indirectly through an adherently bonded corrosion passivating layer such as a silicon or ferrosilicon layer.
- interfacial zones can be relatively porous compared to the bulk of the cement matrix, and may therefor be a "weak link" in reinforced concrete [Z. Li, et al., “Enhancement Of Re-Bar (Smooth Surface)-Concrete Bond Properties By Matrix Modification And Surface Coatings", Magazine Of Concrete Research, Vol. 50, pp. 4957 (1998)].
- the relatively porous interfacial zones typically can have a thickness of about 20-50 microns.
- the porosity of the "weak link" zone adjacent a steel reinforcing bar may actually increase during the curing of the cement, as interfacial void content or microcracking increase at the interface when the cement cures.
- X. Fu, et al. "Effects of Water-Cement Ratio, Curing Age, Silica Fume, Polymer Admixtures, Steel Surface Treatments, and Corrosion on Bond Between Concrete and Steel Reinforcing Bars", A CI Materials Journal, November-December, 1998, pp. 725-733.
- FIGURE I schematically illustrated in FIGURE I is a magnified view of a conventional, freshly-poured aqueous cement slurry at a steel reinforcement surface.
- the aqueous cement slurry comprises a plurality of unreacted cement particles 12 surrounded by water 14, which is adjacent the steel reinforcement surface 16.
- the unreacted cement particles are typically 20-60 microns in length, and accordingly are shown in schematically magnified view in FIGURE 1.
- the cement particles immediately adjacent the steel reinforcement surface 16, the cement particles may pack less efficiently than in the bulk cement packing zone.
- the unreacted cement particles may pack relatively more efficiently and uniformly to provide a bulk cement packing zone 20.
- FIGURE 2 Schematically illustrated in FIGURE 2 is a conventional fully-reacted cement paste at a steel reinforcement surface like that of FIGURE 1.
- the cement particles 12 of the bulk of the cement paste react with water to provide various hard, hydrated cement paste products to provide a bulk density cement paste zone 22.
- the hydrated cement paste is not uniform at a microscopic level, in that it contains pores and may contain partially unreacted cement grains which are not fully hydrated at their cores, this cement paste zone is illustrated as a relatively dense, uniform zone in FIGURE I for purposes of this discussion.
- the fully reacted cement paste in the bulk density zone 22 may be relatively dense, the reacted cement paste immediately adjacent the steel reinforcement surface 16 has reduced density, for reasons previously discussed.
- the reduced density zone may be, for example, 20-50 microns in thickness and may form a relatively porous zone 24 immediately adjacent the steel reinforcement surface 16.
- the tensile strength of the steel reinforcement is relatively high in comparison to the tensile strength 28 of the bulk density cement paste.
- cement and concrete have a tensile strength which is significantly lower than its compressive strength, and significantly lower than that of the steel reinforcement. In fact, this is the principal reason for providing steel or other reinforcement in concrete.
- the tensile strength of the relatively porous interface between the bulk density cement paste and the steel reinforcement surface is even lower in tensile strength than the fully reacted bulk cement paste 22.
- This relatively weak, porous interface zone 24 is accordingly a "weak link" between the cured concrete mass and the steel reinforcement.
- the porosity of the interface promotes corrosion by permitting contact with corrosioninducing chloride ions and oxidizing agents, and adversely affects the environmental durability of the concrete, causing accelerated deterioration.
- the porous interface zones around each of the inclusions, including the steel reinforcement and the aggregate particles form an interconnected network which can foster the percolation of chloride ions through the concrete cover to the steel reinforcement [Y.F. Houst, et al., "Influence of aggregate concentration on the diffusion of C02 and 02", Interfaces in Cementitious Composites, ed. by J. Maso (E and FN Spon, London, 1992), 279-288].
- interfacial zone weakness and porosity adjacent the steel reinforcement can be exacerbated by inhomogeneities which occur during pouring of the reinforced concrete, such as caused by component settling in the concrete mix or structure before hardening.
- relatively heavy aggregate and cement particles can settle in freshly poured concrete, to displace free water upwardly where it is trapped at the undersurfaces of aggregate and reinforcement [K.H. Khayat, "Use Of Viscosity-Modifying Admixture To Reduce
- FIGURE 3 schematically illustrated in FIGURE 3 is a fully permeated conventional concrete mass illustrating a chloride percolation path to, and along, the steel reinforcement surface of an embedded reinforcing bar 30.
- the scale of FIGURE 3 is substantially less than that of FIGURES 1 and 2.
- the inclusions such as aggregate pieces 32 and sand particles (not shown) generally all have relatively porous interfacial zones, and because at relatively high loadings of sand and aggregate in conventional concrete, the surfaces of the sand and aggregate particles are closely spaced together.
- porous interfacial zones of each of the aggregate particles tend to become connected, thereby forming a pathway through the concrete which includes the porous interfacial zone 34 at the steel reinforcement surface. Accordingly, chloride ions and other materials can permeate through the concrete at a rate much faster than the permeation rate through bulk cement paste.
- a corrosion-resistant layer or alloy is provided at the steel reinforcement surface, between the steel and the cement-reactive layer, to further protect the steel from corrosion.
- a passivating, corrosion-resisting layer such as an iron suicide surface layer may be readily applied to steel reinforcement such as "rebar", beams, wire or mesh, by reaction with silicon at elevated temperatures in the presence of chlorides ("Ihrigizing").
- Other materials such as chromium, boron/borides, nickel, stainless steel, titanium, aluminum, etc. may also be vapor-reacted and/or thermally sprayed onto the steel reinforcement to serve as a very thin, hard, adherent protective layer which is inexpensively applied by plasma, HVOF or combustion thermal spraying onto the surface of the steel reinforcement.
- the corrosion-resistant layer such as an iron suicide, iron-titanium, or ferrochrome layer, may be relatively thin, on the order of 0.1 to 100 microns. Silicon, chromium and titanium readily alloy with iron, with Gibbs Free Energy release, so that the iron suicide or other alloy layer is integral with the steel reinforcement, and mechanically much stronger than the bulk cement paste.
- the ferrosilicon or other intermetallic alloy or silicon coating is thermodynamically less reactive than the untreated steel surface to oxidation in the high pH cement paste environment of the concrete, and/or relatively more passivated with respect to catalytic oxidation in the presence of chloride ion.
- the corrosion-passivating layer may be very thin, but should be capable of strong chemical (not just mechanical) bonding to a cement- reactive layer, as will be further described. It is desirable to provide a continuous layer of the alloyed diffused or otherwise chemically passivated surface layer over the steel reinforcing member.
- the surface may be useful to subject the surface to vapor-phase chemical reaction and diffusion, such as by treatment with SiCl 4 , BC1 3 , silanes, boron hydrides, titanium chloride (in a reducing environment) or mixtures thereof, at an elevated temperature (e.g., about 400-1300° C. see, e.g., U.S. Patent Nos. 5,064,691 and 5,089,061), to insure surface reaction.
- the diffused or alloyed surface layer containing B, Si, Ti, Cr or mixtures thereof may be very thin, e.g., 0.5 + 15 microns, but should best be continuous.
- the corrosion passivating layer may be applied during forging or as the steel reinforcement is exiting the rolling mill where it is manufactured, while it is still heated to a rolling/forging temperature of 800-1200° C.
- Conventional plasma spraying particularly if applied to a heated reinforcing steel surface, may produce a dense, thin surface zone which at least partially interdiffuses with the steel surface.
- Fine silicon, boron, titanium, chromium or nickel powders or compounds can be heated to vaporization temperature in a plasma gun system and applied to a hot steel reinforcing bar so that these materials diffuse at the steel surface to form a passivated integral surface layer.
- High temperature electric arc plasma spraying can also provide high velocity particles and may also heat the steel surface momentarily to cause binding and interdiffusion.
- High velocity oxygen flame (HVOF) plasma spraying of passivating materials such as silicon or ferrosilicon may also produce a dense surface layer, particularly in view of the ultrahigh velocity of the sprayed particles, which melt and interact upon impacting of the particles at the surface, where the kinetic energy is converted to thermal energy in a relatively instantaneous manner.
- a reducing atmosphere, and particularly a sputtering of the hot steel surface is best for chemical bonding and diffusion.
- a particularly useful method for applying a passivating alloy surface which is continuous, even on a microscopic basis, is by partially transferred arc and/or rf/plasma arc plasma coating.
- the electric heating arc is transferred internally to the accelerating gun nozzle.
- the steel surface to be coated with the alloy and/or passivating material is biased with a negative voltage in respect to a positive current source at the interior of the nozzle of the plasma spray device.
- the positive electrode may be the regular cathode of the plasma spray gun, or may be a separate electrode located slightly downstream of the plasma gun.
- a plasma column is provided between the plasma gun and the steel surface which is being coated, which conducts current between the reinforcing steel surface and the plasma gun cathode.
- Steel reinforcement may form a native oxide surface (e.g., FeO) during its manufacture in a rolling mill, which is removed by the
- sputtering effect of a transferred arc or rf plasma.
- the plasma functions to ionize and clean oxides and other electronegative components on the surface of the steel, so that they are removed, and to attract ionized metals or silicon or positively charged silicon particles or other passivating materials, which become metallurgically bonded to the cleaned steel surface to form an impervious passivating layer.
- the plasma is a reducing plasma (e.g., contains hydrogen), this may also aid in the formation of a metallurgical bond.
- a radio frequency plasma can be provided to assist maintenance of the arc between the plasma gun and the steel substrate to be coated and alloyed with a passivating material.
- an outer layer of an inorganic ceramic or glass such as an alkaline earth silicate, (e.g., calcium silicate), aluminate, a phosphate, and/or a silica or alumina layer, which is also integrally bonded to the iron suicide layer, and which is reactive with the hydraulic cement paste. It is also stronger than the bulk cement paste, and has a relatively strong bond to the steel reinforcement such that the steel-ceramic composite is itself stronger than the bulk cement paste.
- thermal spraying is conventionally used for applying strongly bonded ceramic and metal layers for mechanically demanding applications such as turbine blades, so the strength and bonding capabilities of thermal spray systems are more than adequate for reinforced concrete bonding needs.
- the composition of the inorganic ceramic or glass layer may be primarily in the mono- to di-silicate range (e.g., powdered blast furnace or other slag, fly ash, burned shale ash or other such material, which is compatible with and participates in and participates in cement hydration reactions and makes an inexpensive raw material source), so that it remains stable in unhydrated form for storage of the reinforcing bars prior to use.
- powdered silica and/or alumina may also be used as a reactive interface material.
- the calcium silicate layer may also be relatively thin, but should desirably be sufficiently thick that it does not become fully hydrated throughout its thickness during the hydration of concrete.
- a thickness of 50-100 microns of a less reactive lower calcium silicate layer should be more than adequate.
- a vitreous or ceramic layer may also be quite mechanically strong compared to the cement paste, and is integrally bonded to the iron suicide, iron titanide or other iron-passivating layer.
- the calcium silicate layer may also be applied by relatively inexpensive high-temperature plasma, HVOF or combustion thermal spraying.
- the thin, refractory, adherent, unitary, inorganic layers may readily be applied during steel rebar manufacture. There are some adhesion and efficiency advantages in high-speed application of the layers in the rolling mill before the steel reinforcement bars have completely cooled.
- the outer surface of the calcium silicate layer may preferably be applied with a somewhat greater degree of open porosity (e.g., 5-20%) than the interior layer (e.g., 015% porosity) to further assist the formation of a functionally graded interface with the bulk cement matrix. Because of the relatively low thermal spray temperatures required for calcium silicate application, the low cost of the materials (e.g., fly ash or blast furnace slag) and the thinness of the layers, the cost of application is relatively low. As indicated earlier, an adhesion-promoting layer may be utilized to promote chemical bonding of the metallic steel or steel alloy surface with the ceramic vitreous coating.
- An extremely thin layer of boron or silicon oxide groups may be formed at the surface of the iron suicide and/or boride layer formed at the surface of the reinforcing steel, which can chemically bond with the thermally applied glass or ceramic layer.
- a very thin layer of chromium, titanium or nickel oxide may form an adhesion-promoting layer, particularly if in a partially-oxidized metallic, or lower oxidation state.
- FIGURE 4 illustrates a thermal spray system 40 for applying corrosion resistant and hydraulically reactive layers on steel reinforcing bar stock as produced by a conventional rolling mill.
- a finished steel reinforcing bar 42 from a rolling mill 44 is continuously transported through a thermal spray station 46.
- the reinforcing bar (or "rebar") stock may still be at elevated temperature such as 500- 1200° C. from its manufacture.
- the thermal spray station 46 comprises a thermal spray station 48 for applying a passivating corrosion-resistant layer such as a silicon or ferrosilicon layer 49, and thermal spray station 50 for applying a hydraulically reactive ceramic material layer 51 on the corrosion-resistant layer 49.
- the thermal spray station 48 desirably comprises at least three thermal spray guns spaced radially around the reinforcing bar, so that the entire surface of the bar is coated on a continuous basis as it is conducted through the thermal spray station. Because the steel bar may form a native oxide (such as FeO) on its surface during its manufacture in the rolling mill, the thermal spray may also desirably be operated with a reducing atmosphere. Preferably, the thermal spray guns function to "sputter-clean" the reinforcing bar surface as the corrosion-resistant layer 49 and/or diffusion is applied.
- a relatively fine silicon or ferrosilicon powders are preferably used, with relatively high plasma operating temperatures, so that at least a portion of the silicon or ferrosilicon is vaporized, for subsequent condensation on this heated steel reinforcing bar surface, to provide a continuous layer.
- the silicon/fe ⁇ o silicon will quickly diffuse/alloy with the steel rebar at its elevated temperature.
- An adhesion-promoting layer may be applied between the silicon/ferrosilicon layer.
- a fine aqueous spray of a chromium, nickel or titanium oxide-based solution or slurry may be directly applied to the hot steel surface, which will promote fusion and bonding at the elevated processing temperatures (e.g., 400- 1200° C.) with the subsequently applied ceramic or vitreous layer.
- the thermal spray station for the ceramic layer application may also desirably be a low-cost combustion system or HVOF system.
- FIGURE 7 is a schematic illustration of a freshly poured aqueous cement slurry at the surface of a thermally sprayed steel reinforcing bar embedded in the cement slurry.
- the steel reinforcing bar 72 has an adherent, thin, thermally sprayed ferrosilicon or silicon layer 74 at its surface, which is substantially more passive with respect to both rusting, and chloride ioncatalyzed oxidation, than the bulk steel of the reinforcing bar 72.
- Silicon can be used to produce a surface which is relatively inert to oxidation catalyzed by the chloride ion.
- the silicon readily alloys with and diffuses into iron at moderately elevated temperatures, which are present immediately after manufacture of the rebar in a steel rolling mill, and/or which can be briefly applied to the surface of the reinforcing bar without damaging the internal metallo graphic structure, to form a variety of ferrosilicon compounds or solid solutions.
- a passivating silicon alloy layer can be provided by exposure to silicon-containing gases such as SiC14 at elevated temperatures (see, e.g., U.S. Patents 3,433,253 and 5,200,145). Pure silicon powder can also be thermally sprayed to produce a relatively inert layer of silicon and/or ferrosilicon alloy.
- ferrosilicon can also be used to provide a surface which is relatively passivated with respect to oxidation under chloridecatalyzed conditions.
- Fe ⁇ osilicon can be produced at very low expense, and provided in powdered form for thermal spray volitalization and/or application to the surface of the steel reinforcement to produce an intimately bonded, alloyed layer at the surface.
- boride materials may be provided and plasma-vaporized at lower expense than boron hydride materials.
- the corrosion-resistant fe ⁇ osilicon layer 72 has an intimately adherent cementitious layer 74, which is thermally sprayed thereon and bonded thereto.
- the illustrated cementitious layer may be an industrial-grade calcium silicate, such as the primarily dicalcium silicate materials of blast furnace slag waste products.
- the thermally-applied cementitious layer may desirably be graded, either continuously, or discreetly, so that it is more dense and/or more unreactive in the high pH environment of a cement mix, immediately adjacent the fe ⁇ osilicon layer 74.
- the layer 76 may be more porous and/or more hydraulically reactive at the exterior surface 78 facing the aqueous cement mix.
- a calcium silicate powder which crystallizes to form a relatively inert material such as wollastonite may be applied using HVOF thermal spraying to produce a very dense, relatively crystalline layer which strongly adheres to the fe ⁇ osilicon or silicon surface 74.
- An external layer of predominantly dicalcium. silicate, such as fly ash or blast furnace slag, may be applied over the calcium silicate layer, using a lower velocity HVOF or plasma spray gun, to produce and external layer which is relatively more hydraulically reactive in the aqueous high pH environment of the cement mix.
- the amount of reaction may be precisely controlled, to ensure that an adherent, dense, protective inorganic oxide layer remains adjacent the steel surface to contribute to the protection of the underlying steel reinforcement.
- An extremely thin adhesion-promoting layer (not shown), for example of chromium oxide, titanium dioxide or lower oxide, or nickel oxide may be present between the fe ⁇ osilicon surface of the steel bar, and the cementitious calcium silicate layer 76.
- the external surface 78 of the thermally sprayed reactive layer 76 need not to be completely smooth, and may also have some degree of porosity, which may permit a denser aggregation of cement particles adjacent the surface.
- the physical density of the calcium silicate layer 76 at the external surface should best be at least 75 percent solid (less than 25% porosity), as compared to a lower concentration of cement particles in the cement mix, and accordingly, the unreacted cement particles 82 of the freshly poured aqueous cement slurry may form a relatively dense surface reaction zone 80 together with the thermally sprayed reactive layer 76.
- the unreacted cement particles in the water matrix 84 away from the immediate surface of the zone 80 may be in a zone 86 having the conventional bulk cement packing density.
- the thermal spray guns may also apply relatively inert fibers, such as alumina fibers or zirconiabased high-pH-stable cement fibers with the cementitious layers. These fibers may be relatively small in diameter (e.g., 2-25 microns) and length (e.g., 25-200 microns), but can considerably strengthen the hydrated cement layer which is formed around the steel reinforcement.
- the volume of reinforcing fibers may desirably be in the range of 2-25 percent of the volume of the cementitious thermally sprayed layer 76.
- the ceramic external layer 76 of the treated steel reinforcement presents a reactive surface which partially hydrates with the bulk cement paste. It preferably does not completely hydrate, however, because it is thicker and less reactive than the cement particles, which themselves may not fully hydrate.
- a strongly adherent, unhydrated layer of the calcium silicate is accordingly retained on the steel surface.
- the high density, unhydrated calcium silicate at the steel surface, and the graded participation of the surface in the cement hydration reaction inhibits the formation of a porous weak interface zone. Co ⁇ osion-causing chloride percolation along the steel surface is therefor restricted, because there is no weak, porous zone adjacent the steel surface.
- the net result is a dense interface, adherently chemically bonded to the steel surface, which is thereby protected from corrosion, and which transmits mechanical forces between the steel reinforcement and the bulk cement matrix.
- the interface is desirably stronger than the bulk cement paste.
- the interface is not porous, and does not promote the percolation of water or corrosioninducing chloride ions through the cured concrete or along the surface of the steel reinforcement. Because the interface integrally bonds the steel reinforcement to the bulk cement matrix with an adhesion strength desirably at least equal to the strength of the cement matrix, the mechanical properties of the reinforced concrete are maximized, rather than minimized by a porous interface zone.
- the reactive calcium silicate layer 76 interacts with the cement particles to prevent the formation of a relatively porous and weak interfacial zone between the steel reinforcement and the bulk cement paste.
- schematically illustrated in Figure 8 is a cured, adherent cement layer at a dense, non co ⁇ oding steel reinforcement surface.
- the steel reinforcement 72 upon curing or partial curing of the cement particles in the cement mix, the steel reinforcement 72 still retains its adherent fe ⁇ osilicon layer 74 which passivates the iron against chloride-catalyzed oxidation, and a portion of the calcium silicate layer 76, which is itself strongly adherent to the fe ⁇ osilicon layer 74 by virtue of the thermal spray processing of its application.
- the presence of silicon, titanium or other similar strong matrix oxide forming elements in the co ⁇ osion-passivating layer facilitates the formation of a strong, adherent chemical bond therebetween.
- the exterior surface of the calcium silicate layer 76 has reacted by hydration with the cement mix to form a relatively dense, strong adherent surface reaction zone 88 which may be denser and stronger than the fully hardened cement paste 90 which is formed at the bulk density of the original cement mix.
- the tensile strength of the composite structure is schematically shown in the graph below the structure illustrated in Figure 8, and in registration therewith.
- the tensile strength of the steel reinforcement is relatively high, and the ferrosilicon, ferrochrome or ferrotitanium layer 74 is generally relatively lower in view of its increased brittleness.
- the tensile strength of the unreacted calcium silicate layer 76 is relatively lower than that of the silicon, fe ⁇ otitanium, fe ⁇ ochrome or fe ⁇ osilicon layer 74, but still substantially higher than the bulk density cement paste.
- the surface reaction zone (like the zones immediately su ⁇ ounding the individual cement particles) is denser and stronger in the direction of the hydration reaction adjacent the unreacted surface zone, and tapers toward the tensile strength of the bulk density cement paste.
- the composite structure of Figure 8 does not produce a "weak link" of porosity adjacent the steel reinforcement. Rather, a functionally graded interface is produced which has a gradient of properties which gradually transitions to that of the bulk density cement paste 90.
- the fe ⁇ osilicon layer 74 and the partially unreacted calcium silicate layer 76 physically limit the access of chloride ion and oxygen to the iron surface, thereby restricting oxidation.
- the functional layers may be applied by thermal spraying, which is an economical technology for applying thin, adherent layers of refractory materials.
- thermal spraying very small molten particles (e.g., 10-50 microns) and vaporized portions of the material to be applied are accelerated by combustion gases or an electric arc plasma, followed by deposition or impacting onto the steel reinforcement surface.
- the steel surface may be heated so that the passivating components can diffuse into the steel surface to form an integrally-passivated layer.
- solidification typically occurs at very rapid rates, so that the as-sprayed deposit is ultra-fine grained. This fast cooling should stabilize calcium silicates in the high-density gamma crystalline form desirable for use in hydraulic cements.
- Thermal spray application of the functional layers is a relatively inexpensive and efficient method for integrally applying the functional layers to the reinforcing steel.
- a wide range of materials has been successfully plasma-sprayed for a variety of applications, including gas turbine components having complex geometries [M.R. Jackson, et al, "Production of Metallurgical Structures by Rapid Solidification Plasma Deposition", J Metals, 33, Nov. 1981, 23-27; S. Sampath and H.Herman, J. Metals, 45(7) (1993) 42; R. Tiwari, et al., "Plasma Spray Consolidation of High Temperature Composites", Mat. Sci. and Eng. A144 (1991) 127-131; M. Moss, Acta Met., 16 (1968) 321 ; V.
- the temperature of a plasma may be as high as 15,000° C. for a typical dc plasma torch, but the application of calcium silicate does not require such high temperatures.
- Other thermal spray processes such as High Velocity Oxy-Fuel Spraying (HVOF), in which a high temperature oxygen-fuel flame undergoes free-expansion from the torch nozzle, to accelerate the particles to a high velocity (e.g., over Mach 3) may be used to produce dense, adherent coatings.
- HVOF High Velocity Oxy-Fuel Spraying
- Porosity should desirably be controlled in the application of the calcium silicate layers, for example in the range of from about 2-25 percent porosity (95-98 percent solid calcium silicate or calcium silicate plus reinforcing fibers).
- porosity decreases.
- the smaller the particle size the lower the porosity for typical thermal spray systems
- Example I Three steel reinforcing bars (or dowels) without ribs or surface deformations, nominally 1/2 inch in diameter and 2 feet long, are cleaned of rust and surface oxidation by sand blasting. All bars receive the same sand blasting treatment.
- One of the bars is placed on a rotating mandrel and coated with a very thin layer of silicon using a high temperature helium plasma Praxair/Miller Thermal SG-100 Plasma Spray System, so that substantially the entire surface of the bar is coated with the silicon layer.
- the SG- 100 plasma spray gun uses a non-transfe ⁇ ed dc plasma torch configuration with powers up to 100 kW (here, about 40 kW).
- the basic design of the plasma gun consists of two electrodes: a cone-shaped cathode inside a cylindrical anode, which forms a nozzle.
- Gases e.g. argon, hydrogen, helium
- the primary gas is argon (100 scfh) and the secondary gas is helium (60 scfh).
- the powder carrier gas is typically argon (15 scfh).
- a four hole gas ring is utilized to induce vortex flow in the electrode.
- Powders injected into the plasma are accelerated and melted by its high temperature.
- the molten droplets i.e. splats
- the molten droplets are propelled onto the substrate where they solidify and accumulate to form a well-bonded coating.
- the first bar (Bar 1) was placed on a rotating mandrel, and silicon was applied by plasma spray along its outer surface. Silicon was applied to the second bar (Bar 2) by plasma spray along a longitudinal strip along the bar length, without mandrel rotation. The silicon is applied at a low feed rate, in order to heat the bar and provide an opportunity for some diffusion of the silicon into the surface of the bars. The bars are not preheated, so diffusion was limited, and the silicon formed a surface layer. All three bards were subsequently coated with ground blast furnace slag using the same helium plasma gun. The third bar (Bar 3) was accordingly directly coated by plasma spray of ground blast furnace slag to the sand blasted surface of the steel reinforcing bar, without an intermediate silicon layer.
- the ground granulated blast furnace slag (GGBFS) used was a product commercially available under the tradename GranCem from Holnam, Inc., 6211 Ann Arbor Road, Dundee, Michigan 48131. It was thermally sprayed using the plasma spray gun operated at about 40 kW.
- the GGBFS had the following specifications:
- the GGBFS is intended for use in admixture with portland cement and is accordingly compatible therewith.
- the GranCem cement is made to meet the requirements of ASTM C 989 (equivalent AASHTO specification is M 302), which lists three grades of GGBF slag: Grade 80, Grade 100 and Grade 120. Grade 100 was utilized in the present example.
- the sample used has the following characteristics according to the Chicago Grinding Facility of Holnam, Inc.: SLAG ACTIVITY INDEX SPECIFICATIONS MININUM
- FIGURE 9 is a photomicrograph of Bar 3, showing an abraded surface of the steel about 3 min wide, and the surface texture of the applied GGBFS.
- FIGURE 10 is similarly a photomicrograph of Bar 1, showing the abraded steel about 3 min wide, and the surface texture of the GGBFS layer.
- the intermediate silicon layer can also be seen In FIGURE 10.
- Bars 1, 2 and 3 and an uncoated steel reinforcing bar were cast in (Sakrete brand) mortar mix, which appear to be "lean” in cement. The bars will be examined after the mortar mix cures.
Abstract
Description
Claims
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AU29174/01A AU2917401A (en) | 1999-10-27 | 2000-10-24 | Reinforced concrete systems |
US10/125,969 US6929865B2 (en) | 2000-10-24 | 2002-04-19 | Steel reinforced concrete systems |
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US16183899P | 1999-10-27 | 1999-10-27 | |
US60/161,838 | 1999-10-27 |
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Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6929865B2 (en) * | 2000-10-24 | 2005-08-16 | James J. Myrick | Steel reinforced concrete systems |
CN109824312A (en) * | 2019-03-21 | 2019-05-31 | 徐州工程学院 | A kind of preparation method improving Marine Reinforced Concrete Structures corrosion resistance of chloride ion ability |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3954482A (en) * | 1973-05-24 | 1976-05-04 | High Performance Coatings, Inc. | Corrosion resistant coating material and method |
US4725491A (en) * | 1986-07-09 | 1988-02-16 | Solomon Goldfein | Reinforced cement products with improved mechanical properties and creep resistance |
US5100738A (en) * | 1990-07-12 | 1992-03-31 | Rebar Couplerbox, Inc. | Reinforced concrete containing coated steel reinforcing member |
-
2000
- 2000-10-24 WO PCT/US2000/041485 patent/WO2001031136A2/en active Application Filing
- 2000-10-24 AU AU29174/01A patent/AU2917401A/en not_active Abandoned
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3954482A (en) * | 1973-05-24 | 1976-05-04 | High Performance Coatings, Inc. | Corrosion resistant coating material and method |
US4725491A (en) * | 1986-07-09 | 1988-02-16 | Solomon Goldfein | Reinforced cement products with improved mechanical properties and creep resistance |
US5100738A (en) * | 1990-07-12 | 1992-03-31 | Rebar Couplerbox, Inc. | Reinforced concrete containing coated steel reinforcing member |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6929865B2 (en) * | 2000-10-24 | 2005-08-16 | James J. Myrick | Steel reinforced concrete systems |
CN109824312A (en) * | 2019-03-21 | 2019-05-31 | 徐州工程学院 | A kind of preparation method improving Marine Reinforced Concrete Structures corrosion resistance of chloride ion ability |
CN109824312B (en) * | 2019-03-21 | 2021-07-27 | 徐州工程学院 | Preparation method for improving chlorine ion erosion resistance of marine reinforced concrete |
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