CN101042328B - Monitoring methods for reinforcement corrosion of long period optical fiber grating and sensor thereof - Google Patents

Abstract

This invention relates to one long circle fiber grating steel rib erosion monitor method and its sensor in structure engineer field and fiber sensor technique field, which comprises the following steps: putting one long rib fiber grating by use of adhesive steel rib and periodically observing the circle fiber grating transparent spectrum change by spectrum device to judge whether there is bending and to induce steel rib erosion degree and rate. This invention can realize lone time monitor on steel rib erosion under any situations without loss of concrete surface.

Description

The monitoring methods for reinforcement corrosion of long period fiber grating and sensor thereof

Technical field:

The invention belongs to Structural Engineering field and technical field of optical fiber sensing, particularly based on the monitoring method of long period fiber grating to reinforcement corrosion in the reinforced concrete member.

Background technology:

Reinforced concrete is most important a kind of fundamental construction material, and it is to combine a kind of compound substance that the characteristic of the high breaking strength of concrete high compressive strength and reinforcing bar is made.Discover that from the disease of a large amount of engineering structures when reinforced concrete was in the environment that the chlorion existence is arranged, the etching problem of reinforcing bar was one of most important endurance issues in the reinforced concrete.Therefore grasp the corrosion condition of reinforcing bar in the xoncrete structure early, prevent the further aggravation of corroding so that in time take preventive measures, significant to the serviceable life that prolongs xoncrete structure, also be the focus in the concrete durability research.Ripe measurement reinforcement corrosion all is to use electrochemical method in the research means at present, as measure biasing resistor, electrochemical impedance, methods such as half current potential, these methods all are to determine the extent of corrosion of reinforcing bar in the concrete or the chemical measure of speed etc. by the electrochemical properties of measuring the steel reinforced concrete erosion system, workload is big, testing result is subjected to the extraneous factor influence easily, to the body structure surface that is difficult to arrive (as the long span bridge beam, the beam slab bottom surface of sea port dock etc.) can't detect, therefore application reliability is relatively poor, be subjected to external interference big, be difficult to directly react the reinforcement corrosion situation.

Owing to volume after the reinforcement corrosion in the concrete will change, therefore the vary in diameter amount of volumetric expansion takes place by reinforcement corrosion in the measurement xoncrete structure, just can monitor the corrosion condition of reinforcing bar in the xoncrete structure in real time.That fiber-optic grating sensor has is highly sensitive, wide dynamic range, be not subjected to that electromagnetic interference (EMI), essence are explosion-proof, corrosion-resistant, light weight, volume be little, be easy to imbed in the material series of advantages such as constituting smart material and structure, and long period fiber grating have more be easy to make, added losses are little, without male offspring to reflection and with distinct advantages such as polarization irrelevant, and because its high susceptibility to bending can remedy the deficiency on galvanochemistry and other corrosion monitoring process.

The long period fiber grating monitoring reinforcement corrosion degree of adopting is also arranged at present, but mainly be utilize the long period fiber grating refractive index high susceptibility and to the monitoring of corrosion environment parameter, and environmental monitoring is for the judgement of reinforcement corrosion state, actual is a kind of indirect method of testing, its defective is: the environmental parameter that causes reinforcement corrosion is a lot, as rebar surface humidity, O ₂, CO ₂, Cl ^-Concentration and pH value etc., these factors influence each other, can not set up single mathematical relation with reinforcement corrosion, the variation of therefore necessary these parameters of comprehensive monitoring, set up expert system, could more reasonably judge the steel bar corrosion situation, this method belongs to the indirect monitoring reinforcement corrosion, can not judge the etch state of reinforcing bar exactly.In addition, the method of utilizing Bragg grating to monitor to the high susceptibility of strain and to reinforcement corrosion is also arranged, but being bragg grating, the shortcoming of this method make it in observation process, inevitably have the intersection sensing of temperature and strain to the sensitivity characteristic of temperature, therefore in observation process, must carry out temperature compensation, and need in the sensor production process grating is sticked with glue on bar reinforcement, this life-span for grating also is disadvantageous.So far, also nobody proposes to utilize the flexural property of long period fiber grating to realize monitoring corrosion of steel in the reinforced concrete member.

Summary of the invention:

The objective of the invention is at the deficiency in the existing monitoring method, the monitoring method of reinforcement corrosion in a kind of reinforced concrete member is provided, and the method need not to use glue in the grating section, avoided the cross influence of environmental factor temperature, refractive index simultaneously, under the prerequisite of not damaging concrete surface, can accurately, nondestructively monitor out the etch state of reinforcing bar under the actual working environment.

A kind of based on long period fiber grating to monitoring methods for reinforcement corrosion in the reinforced concrete member, it is characterized in that may further comprise the steps:

(a), sensor production: choose a bar reinforcement identical with the used reinforcing bar material of engineering, put it in the pedestal, with around the elasticity thing filling bar reinforcement of good penetrability and between the pedestal, long period fiber grating overcoat protection flexible pipe, vertical and lie against rebar surface, two ends ride over the pedestal two ends, the protection flexible pipe of one end is pasted with epoxide-resin glue and pedestal, and this end optical fiber is also pasted with epoxide-resin glue and protection flexible pipe, the optical fiber two ends pass and guarantee that from pedestal grating is in the stretching state of level, fill the fiber grating upper end with the elasticity thing of above-mentioned good penetrability again, cover tight capsule, pedestal and capsule are stamped aperture in advance, so sensor production is finished;

(b), sensor is in place: sensor is fixed in the concrete component, and guarantees reinforcing bar sensor surface level, deposit concrete then;

(c), transducer calibration: optical fiber one end of etched diffraction grating is linked to each other with wideband light source, the other end links to each other with spectrometer, sensor is carried out periodic monitoring, observe grating transmission spectrum drift situation, be the transmissivity size of resonance wave strong point, can judge the degree of crook of grating thus, thereby infer the vary in diameter amount of reinforcing bar, and then obtain reinforcement corrosion degree and speed, wherein main formulas is: Δ D=K _L(P _L2-P _L1), wherein Δ D is the vary in diameter amount of reinforcing bar, P _L1Be the transmittance values of long period fiber grating resonance wavelength under original state, P _L2Be the transmittance values at the Resonant Wavelengths of Long Period Fiber Gratings place that records in the observation process, K _LBe the reinforcement corrosion sensitivity coefficient;

K _LScaling method be: when making this sensor, do N group and the identical test block of sensor condition in addition again, guarantee that bar reinforcement length is identical, the sand-cement slurry grade thickness of cast is identical, but in this N group test block, do not place grating, optical fiber, in the drift of periodic monitoring grating transmission spectrum, in this N group, get 1 group of damaged etching extent that directly detects bar reinforcement at every turn, the etch state of bar reinforcement in the alternative sensor of the corrosion of these bar reinforcements, measure by the N group thus, can obtain N and organize under the different etch states corresponding grating transmission spectrum measurement data, with this again linear regression can calibrate K _LValue, the N value is 8-10.

A kind of based on long period fiber grating to steel reinforcement corrosion sensor in the reinforced concrete member; it is characterized in that: the housing of forming by pedestal and capsule; place the bar reinforcement of housing; horizontally disposed in bar reinforcement surface and perpendicular to the long period fiber grating of bar reinforcement; be placed in the outer protection flexible pipe of above-mentioned long period fiber grating; be filled in the elastic filler of the good penetrability between bar reinforcement and long period fiber grating and the pedestal; the elastic filler that is filled in the good penetrability between long period fiber grating and the capsule is formed; above-mentioned housing also is provided with permeability hole, and above-mentioned long period fiber grating two ends connect optical fiber and pass and the stretching state of maintenance level from pedestal.

Discuss long period fiber grating (Long-period-fiber grating, LPFG) sensing principle below.The grating cycle of long period fiber grating is generally more than 100 μ m; it is based on the coupling of the resonance between the pattern in the same way of satisfying phase-matching condition in the optical fiber; be to be coupled between the guided mode of fl transmission and other forward direction guided modes or the forward radiation mould; coupling light to of certain frequency band in the light wave gone in the covering and lost, therefore without male offspring to reflection.

The resonance wavelength of long period fiber grating satisfies expression formula:

${\mathrm{\λ}}_L=(n_{\mathrm{eff}}^{\mathrm{co}}-n_{\mathrm{eff}}^{\mathrm{cl},m})\·\mathrm{\Λ}---\left(1\right)$

Wherein: λ _LBe resonance wavelength,

Be respectively the effective refractive index of fiber core effective refractive index and m cladding mode.

When in optical fiber, introducing certain perturbation, can cause the coupling between different communication modes.When LPFG is crooked, optical fiber has become curved waveguide, the xsect run-off the straight (for refractive index xsect modulated in first cycle) of each modulated refractive index among the LPFG simultaneously, therefore crooked LPFG can equivalence be straight inclined optical fiber grating.When flexibility became big (radius-of-curvature reduces), the coupling coefficient between fibre core and the cladding mode reduced, and the amplitude of harmonic peak reduces.Study from the flexural property to LPFG, when LPFG bends, its transmission spectrum will move to right along with the increase of flexibility, and the transmissivity of resonance wave strong point also will increase, and promptly whole spectrum shape moves to right and to compose deformation shallow.Find the transmissivity of LPFG resonance wave strong point and the linear variation of grating flexibility by the transmissivity of research resonance wave strong point and the relation of flexibility.Therefore, can utilize this characteristic to know its crooked situation, thereby judge the vary in diameter amount that the bar reinforcement corrosion in the xoncrete structure causes by the transmission spectrum of observing LPFG.

Because long period fiber grating is all very responsive to environmental factors such as temperature, strain, bendings, therefore, the making of sensor also must be considered the cross influence of these environmental factors.But the advantage of utilizing the flexural property of LPFG to carry out the monitoring of concrete reinforcement erosion degree also just is being this.

Owing to variation of temperature, can cause the wave length shift of long period fiber grating, temperature raises, and resonance wavelength moves to right; Temperature reduces, and resonance wavelength moves to left.But the drift of the LPFG transmission spectrum that temperature causes does not influence the spectrum shape of transmission spectrum, and promptly variation of temperature does not influence the transmittance values of resonance wave strong point.Same, also be so for strain, the variation of strain does not influence the transmittance values of resonance wave strong point and only changes the position of resonance wavelength.Therefore, adopt the transmittance values of the resonance wave strong point of observing the LPFG transmission spectrum, the influence that can avoid environmental factor temperature, strain to cause, when the transmissivity of finding the resonance wave strong point changes, promptly be that bending has taken place grating, this bending is then caused by the increase of bar reinforcement volume, diameter increase.

The transmissivity of the resonance wave strong point of LPFG and the relation of flexibility are linear, have:

$\mathrm{\ΔC}=\frac{P_{L2}-P_{L1}}{K_c}---\left(2\right)$

P wherein _L1Be the transmittance values of long period fiber grating resonance wavelength under original state, P _L2Be the transmittance values at the Resonant Wavelengths of Long Period Fiber Gratings place that records in the observation process, Δ C is the grating flexibility variable quantity that reinforcing bar expands and causes, K _cThe transmissivity of resonance wave strong point and the scale-up factor of flexibility during for the grating bending.

And the vary in diameter magnitude relation that grating flexibility variable quantity and reinforcing bar expand is:

$\mathrm{\ΔC}=\frac{2\·\mathrm{\ΔD}}{{(a/2)}^2+{\left(\mathrm{\ΔD}\right)}^2}---\left(3\right)$

Wherein Δ D is the vary in diameter amount of reinforcing bar, and a is the distance between the pedestal both upper ends thereof.

But go out Δ D=K by above-mentioned two formula Theoretical Calculation _L(P _L2-P _L1) middle K _LThe reinforcement corrosion sensitivity coefficient, itself and K _c, a is relevant, in the real process, also needs to demarcate by experiment again, scaling method is as mentioned above.

The present invention can be by arranging detecting sensor respectively at the different parts of structure (as the profundal zone of bridge post, spatter Lang Qu, dry section), arrange a plurality of points simultaneously in each zone, and, can determine reinforcement corrosion degree and speed exactly by regularly sensor being carried out data acquisition.Its accuracy comprises double implication: one for reinforcement corrosion degree and speed are reinforcement corrosion degree and speed under the actual detected environment really, two determination methods for reinforcement corrosion degree and speed be accurately, feasible.Since the present invention be directly at corrosion take place carrier--reinforcing bar is measured, that measures buries as for the different reinforcing bar of inside concrete (on-site sampling obtains) in advance to liking, by specific detection means, etch state to tested reinforcing bar is judged, closely obtain reinforcement corrosion degree and speed, this method can guarantee the first heavy implication of accuracy.And owing in sensor base and capsule many apertures are arranged; and wrapping up tested bar reinforcement sand-cement slurry and on-site concrete is same label; can guarantee that the sensor internal corrosion environment is identical with the corrosion environment of on-site concrete inside; in addition; what monitored is the transmission change of grating transmission spectrum resonance wave strong point; irrelevant with factors such as temperature, strains again; and simultaneously; because grating overcoat protection flexible pipe; isolated with the variations in refractive index in the environmental factor; also avoided the influence of refractive index, therefore this method also can guarantee the second heavy implication of accuracy.Detecting sensor of the present invention is simple in structure, easy to process, need not to use glue in the grating section, guaranteed the serviceable life of grating, the reinforcing bar of employing is gathered materials on the spot, or choose and the identical reinforcing bar of the used reinforcing bar material of engineering, test environment and actual components environmental facies with, measure simply and directly perceived, accurately, be easy to judge the etch state of reinforcing bar, can under the prerequisite of not damaging concrete surface, determine reinforcement corrosion degree and speed accurately and easily.

Description of drawings:

Fig. 1 is a sensor construction synoptic diagram of the present invention.

Label title among Fig. 1: 1, bar reinforcement, 2, long period fiber grating, 3, connect optical fiber, 4 protection flexible pipes, 5, pedestal, 6, epoxide-resin glue, 7, capsule, 8, screw.

Embodiment:

Fig. 1 is a sensor one-piece construction synoptic diagram of the present invention.The housing that it is made up of pedestal 5 and capsule 7; place the bar reinforcement 1 of housing; vertical and level places the long period fiber grating 2 of the overcoat protection flexible pipe 4 on bar reinforcement 1 surface; the filling material that is filled between bar reinforcement 1 and long period fiber grating 2 and the pedestal 5 is formed; its middle shell also is provided with permeability hole, and the long period fiber grating two ends connect optical fiber 3 and pass and the stretching state of maintenance level from pedestal.Pedestal 5 is a groove shape as shown in the figure, and a small amount of glue of bar reinforcement 1 usefulness and pedestal 5 bottoms are fixed, and is difficult for rolling so that reinforcing bar is put into; To leave certain space between capsule 7 and the reinforcing bar 1, so that give the grating bending with enough spaces; The space is left in the centre on capsule 7 both sides, so that the optical fiber of overcoat protection flexible pipe passes; Screw 8 is at the Si Jiaochu of whole housing.

Below in conjunction with Fig. 1 the specific embodiment of the present invention is described in further detail.

Choose a reinforcing bar 1 identical, be about 8cm, make stainless steel pedestal 5 simultaneously with the used reinforcing bar material of engineering, pedestal is groove shape, bar reinforcement 1 as figure place, and the elastic filler of filling good penetrability then is filled to bar reinforcement surface and filling material level around bar reinforcement 1 always.Long period fiber grating 2 overcoats protection flexible pipe 4; grating section 2 is lain against rebar surface; two ends connect optical fiber 3 and ride over stainless steel pedestal two ends; the protection flexible pipe 4 usefulness epoxide-resin glues 6 and the stainless steel pedestal 5 of one end are pasted, and this end optical fiber is also done slight fixing with epoxide-resin glue 6 and 4 stickups of protection flexible pipe.The optical fiber two ends pass and give some microstrains of grating to be in the stretching state of level to guarantee grating from pedestal 5 upper ends, continue to fill the elastic filler of identical good penetrability again above bar reinforcement, and cover stainless steel capsule 7, tighten the screws 8.Put into behind the mould casting cement mortar outside, steel reinforcement corrosion sensor is made and is finished.

In work progress, when at joints cement mortar in sensor, note the sensor level of trying one's best, record detects structure reinforcing bars position, position simultaneously.

Deposit concrete after the maintenance form removal, should be put lead in order, and with polybag lead be wrapped.

Detecting the instrument that needs is spectrometer and wideband light source, during measurement optical fiber one end is linked to each other with wideband light source, the other end links to each other with spectrometer, the transmissivity of transmission spectrum spectrum shape and resonance wavelength correspondence when noting original state, the periodic logging measurement data, spectrum shape begins drift explanation corrosion beginning, and the variable quantity of the transmissivity of resonance wavelength correspondence and pace of change directly reflect reinforcement corrosion degree and speed.Δ D=K _L(P _L2-P _L1), P _L1Be the transmittance values of long period fiber grating resonance wavelength under original state, P _L2Be the transmittance values at the Resonant Wavelengths of Long Period Fiber Gratings place that records in the observation process, Δ D is the vary in diameter amount of bar reinforcement, because reinforcing bar length does not become, therefore can directly reflect the volumetric expansion of reinforcing bar, is converted to quality again, i.e. etching extent.The speed of grating strain is converted to corrosion rate too.

K _LBe the reinforcement corrosion sensitivity coefficient, the method of determining is: when making this sensor, do N group and the identical test block of sensor condition in addition again, guarantee that bar reinforcement length is identical, the sand-cement slurry grade thickness of cast is identical, but in this N group test block, do not place grating, optical fiber, in the drift of periodic monitoring grating transmission spectrum, in this N group, get 1 group of damaged etching extent that directly detects bar reinforcement at every turn, the etch state of bar reinforcement in the alternative sensor of the corrosion of these bar reinforcements, measure by N group thus, can obtain the grating transmission spectrum measurement data that N organizes correspondence different etch states under, with this again linear regression can calibrate K _LValue, the N value is 8-10.

Sensor is carried out periodic monitoring, can find As time goes on, the transmission spectrum waveform drifts about gradually, shoals.

The present invention can be by arranging above detecting device respectively at the different parts of structure (as the profundal zone of bridge post, spatter Lang Qu, dry section), and arrange a plurality of points simultaneously in each zone, and buildings is effectively guarded.

Claims (4)

1. a steel bar corrosion monitoring method of long-period fiber grating, is characterized in that comprising the following steps: (a) Sensor production: select a steel bar with the same material as the steel bar used in the project, put it into the base, fill the area around the steel bar and the base with elastic materials with good permeability, and coat the long-period fiber grating The protective hose is placed vertically and flatly on the surface of the steel bar, and the two ends are placed on the two ends of the base. The protective hose at one end is glued to the base with epoxy glue, and the optical fiber at this end is also glued to the protective hose with epoxy resin glue. Paste, the two ends of the optical fiber pass through the base and ensure that the grating is in a horizontal and straight state, then fill the upper end of the optical fiber grating with the above-mentioned elastic material with good permeability, cover the casing tightly, and punch small holes in the base and the casing in advance, so the sensor manufacture complete; (b), the sensor is in place: fix the sensor in the concrete member, and ensure that the surface of the steel sensor is level, and then pour concrete; (c) Sensor calibration: Connect one end of the optical fiber etched with the grating to a broadband light source, and the other end to a spectrometer, monitor the sensor regularly, and observe the drift of the grating transmission spectrum, that is, the transmittance at the resonance wavelength. Judging the bending degree of the grating, so as to infer the diameter change of the steel bar, and then obtain the corrosion degree and rate of the steel bar. The main formula is: ΔD=K _L (P _L2 -P _L1 ), where ΔD is the diameter change of the steel bar, P _L1 is the transmittance value of the long-period fiber grating at the resonant wavelength in the initial state, P _L2 is the transmittance value at the resonant wavelength of the long-period fiber grating measured during the monitoring process, and K _L is the corrosion sensitivity coefficient of the steel bar; The calibration method of K _L is: while making the sensor, make N groups of test blocks with the same conditions as the sensor to ensure that the length of the steel bars is the same, and the thickness of the poured cement mortar is the same, but in the N groups of test blocks No grating or optical fiber is placed, and while regularly monitoring the drift of the grating transmission spectrum, each time a group of N groups is damaged to directly detect the corrosion amount of the steel bar. The corrosion of these steel bars can replace the corrosion state of the steel bar in the sensor. Therefore, through N groups of measurements, the corresponding grating transmission spectrum measurement data in N groups of different corrosion states can be obtained, and then linear regression can be used to calibrate the K _L value, and the value of N is 8-10. 2. A steel bar corrosion monitoring sensor for long-period fiber gratings, characterized in that: a housing composed of a base (5) and a casing (7), placed in a steel bar (1) in the housing, horizontally arranged on A long-period fiber grating (2) on the surface of the steel bar (1) and perpendicular to the steel bar (1), a protective hose (4) set outside the above-mentioned long-period fiber grating (2), filled in the steel bar (1) and An elastic filler with good permeability between the long-period fiber grating (2) and the base (5), and an elastic filler with good permeability filled between the long-period fiber grating (2) and the casing (7) , the casing is also provided with a penetration hole, and the connecting optical fibers (3) at both ends of the long-period fiber grating pass through the base and maintain a horizontally straightened state. 3. The long-period fiber grating steel bar corrosion monitoring sensor according to claim 2, characterized in that: the base (5) is groove-shaped. 4. The long-period fiber grating steel bar corrosion monitoring sensor according to claim 2, characterized in that: the housing is made of stainless steel.

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