CN112390662B - Electrochemical repair method for dual degradation of alkali aggregate damage and steel bar corrosion - Google Patents

Electrochemical repair method for dual degradation of alkali aggregate damage and steel bar corrosion Download PDF

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CN112390662B
CN112390662B CN202011165004.7A CN202011165004A CN112390662B CN 112390662 B CN112390662 B CN 112390662B CN 202011165004 A CN202011165004 A CN 202011165004A CN 112390662 B CN112390662 B CN 112390662B
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concrete
aggregate
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CN112390662A (en
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刘清风
毛丽璇
胡志
夏晋
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Shanghai Jiaotong University
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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
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/60—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone of only artificial stone
    • C04B41/61—Coating or impregnation
    • C04B41/65—Coating or impregnation with inorganic materials
    • 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
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/45—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements
    • C04B41/50—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements with inorganic materials
    • 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
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/53—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone involving the removal of at least part of the materials of the treated article, e.g. etching, drying of hardened concrete
    • C04B41/5369—Desalination, e.g. of reinforced concrete
    • C04B41/5376—Electrochemical desalination
    • 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
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/60—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone of only artificial stone
    • C04B41/72—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone of only artificial stone involving the removal of part of the materials of the treated articles, e.g. etching
    • E—FIXED CONSTRUCTIONS
    • E04—BUILDING
    • E04G—SCAFFOLDING; FORMS; SHUTTERING; BUILDING IMPLEMENTS OR AIDS, OR THEIR USE; HANDLING BUILDING MATERIALS ON THE SITE; REPAIRING, BREAKING-UP OR OTHER WORK ON EXISTING BUILDINGS
    • E04G23/00—Working measures on existing buildings
    • E04G23/02—Repairing, e.g. filling cracks; Restoring; Altering; Enlarging

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  • Ceramic Engineering (AREA)
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Abstract

The invention provides a concrete electrochemical repair method aiming at dual degradation of alkali aggregate damage and steel bar corrosion, which comprises the following steps: monitoring the aggregate activity and the chloride ion content of the concrete test piece, and evaluating the deterioration degree of different concrete test pieces; determining the optimal electrochemical repair technical parameters based on the evaluated degradation degree of the concrete test piece; the technical parameters comprise electrolyte concentration, current density and electrifying time; the concrete sample is electrochemically repaired by adopting a lithiated solution as an electrolyte and adopting optimal electrochemical repair technical parameters, so that the aim of inhibiting the alkali aggregate reaction inherent in the existing structure and the alkali aggregate reaction induced by the alkalinity improvement caused by the electrochemical reaction on the surface of the steel bar is achieved while removing chlorine. The method can set the optimal repair parameter set according to concrete samples with different degradation degrees in different environments, and improve the repair efficiency, thereby achieving the dual purposes of effectively preventing alkali aggregate damage and reinforcing steel bar corrosion.

Description

Electrochemical repair method for dual degradation of alkali aggregate damage and steel bar corrosion
Technical Field
The invention relates to the field of electrochemical durability repair of concrete structures, in particular to a concrete electrochemical repair method aiming at double degradation of alkali aggregate damage and steel bar corrosion.
Background
Chloride attack and alkali-aggregate reactions (also known as alkali-silicon reactions, alkali-aggregate reactions) are important causes of reduced structural durability. The corrosion of the steel bars can be induced by the corrosion of the chloride, and hydroxide radicals released by a cement matrix in the corrosion process can cause or aggravate alkali-aggregate reaction to cause the durability damage of the existing structure; and microcracks generated when alkali aggregate gel is damaged by expansion not only influence the mechanical property of concrete, but also aggravate the corrosion of harmful media such as chloride ions, sulfate ions and the like, thereby further aggravating the premature damage of a service structure. The economic loss caused by the two can generally reach 2 to 10 percent of the total economic value of the nations. Therefore, how to solve the deterioration of concrete durability caused by these two problems has become a worldwide problem to be solved.
The Chinese patent with the application number of CN201210127351.X is found through retrieval, and discloses a bidirectional electroosmosis repairing method for a corroded concrete structure, wherein a rust inhibitor is injected into electrolyte, a steel bar in concrete is used as a cathode, a stainless steel net is laid on the surface of the concrete and used as an anode, the anode is immersed into the electrolyte containing the rust inhibitor, a direct current power supply is applied between the anode and the cathode, and the applied current density is controlled to be 1-5A/m in terms of the total surface area of the steel bar2And after the electrifying time is 10-20 days, ending the electrifying. However, this patent has the following problems: the corrosion potential of the rusted steel bar is improved by removing chlorine and simultaneously transferring different rust inhibitors, but the defect that alkali-aggregate reaction is possibly induced or inherent in a concrete member cannot be overcome.
Chinese patent application No. CN201611199386.9 discloses a device and method for improving the efficiency of electrochemically repairing concrete, the device includes a first temperature sensor disposed at the cathode, a display connected to the first temperature sensor, and a temperature controller; the temperature control device comprises a stirrer immersed in electrolyte, a resistance wire and a second temperature sensor, wherein one end of the resistance wire is connected with one end of the stirrer, and the other end of the resistance wire, the other end of the stirrer and the second temperature sensor are connected with a temperature controller. However, this patent has the following problems: the method only aims at the problem of durability of the concrete structure caused by chlorine salt erosion, and does not relate to treatment of alkali aggregate reaction which can be induced or inherent in the concrete member; and the electrochemical repair parameters can not be adjusted according to concrete members with different chloride corrosion and aggregate activity degrees.
Chinese patent with application number CN201210004797.3 discloses a concrete admixture capable of inhibiting alkali silicic acid reaction, which comprises the following components in percentage by mass: 20-90 parts of spherical superfine inorganic industrial waste with high vitreous content, 0-60 parts of crystalline aluminum hydroxide and 10-70 parts of inorganic industrial waste silicon with high amorphous SiO2 content. The blending amount is 10-30% of the total mass of the cementing material. The content of the glass body in the spherical superfine inorganic industrial waste with high glass body content is more than or equal to 95 percent, the granularity characteristic parameter D50 is less than or equal to 1.0 mu m, and the physicochemical factor Ipc calculated by adopting a formula is more than or equal to 1.20 multiplied by 107. The crystalline aluminum hydroxide is of industrial grade, the content of Al2O3 is more than or equal to 63.5 percent, and the fineness is 180-6000 meshes. The content of SiO2 in the inorganic industrial waste silica fume with high content of amorphous SiO2 is more than or equal to 85 percent. However, the patent has the following problems: the method of adding the concrete admixture in the early stage of engineering construction can only prevent the alkali aggregate reaction and cannot treat the existing structure in which the alkali aggregate reaction has already occurred. Moreover, studies have shown that the alkali-aggregate reaction in existing structures can be inhibited by transferring lithium ions into concrete through electrochemical techniques.
According to the search of the applicant for the prior art, the existing electrochemical repair methods focus on improving the dechlorination efficiency and inhibiting the corrosion of the steel bars, and do not propose or consider the possible alkali-aggregate reaction caused by the large increase of the alkalinity and the temperature of the internal steel bar area in the electrochemical dechlorination process; meanwhile, in the prior art, the alkali aggregate damage of the concrete is prevented mainly by adding the admixture at the early stage of construction, and a solution for solving the inherent alkali aggregate damage in the existing structure is not provided.
Therefore, in order to improve the durability of the concrete structure and prolong the service life of the concrete structure, it is necessary to develop a method for removing harmful ions inside the concrete while solving the alkali aggregate reaction which may be induced by electrochemical repair and the alkali aggregate damage inherent in the existing structure.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a concrete electrochemical repairing method aiming at the dual deterioration of alkali aggregate damage and steel bar corrosion.
According to the purpose of the invention, the concrete electrochemical repair method aiming at the dual deterioration of alkali aggregate damage and steel bar corrosion comprises the following steps:
monitoring the aggregate activity and the chloride ion content of the concrete test piece, and evaluating the deterioration degree of different concrete test pieces;
determining the optimal electrochemical repair technical parameters based on the evaluated degradation degree of the concrete test piece; the technical parameters comprise the type and concentration of electrolyte, current density and electrifying time;
the concrete sample is electrochemically repaired by adopting a lithiated solution as an electrolyte and adopting optimal electrochemical repair technical parameters, so that the aim of inhibiting the alkali aggregate reaction inherent in the existing structure and the alkali aggregate reaction induced by the alkalinity improvement caused by the electrochemical reaction on the surface of the steel bar is fulfilled while removing chlorine.
Preferably, the aggregate activity and the chloride ion content of the concrete test piece are monitored, and the evaluation of the degradation degree of different concrete test pieces comprises the following steps:
determining the activity of the concrete protective layer aggregate by a rapid mortar bar method; when the expansion rate of the test piece is lower than 0.10% in 14 days, the deterioration degree of the concrete test piece is A1; when the expansion rate of the test piece is between 0.1 and 0.20 percent in 14 days, the degradation degree of the concrete test piece is A2; when the expansion rate of the test piece is higher than 0.20% in 14 days, the deterioration degree of the concrete test piece is A3;
measuring the content of chloride ions in the concrete protective layer by a chloride ion rapid measurement method; when the concentration of chloride ions is lower than 100mol/m3When the concrete sample is degraded, the degradation degree of the concrete sample is B1; when the concentration of chloride ions is 100mol/m3～400mol/m3When the concrete sample is degraded, the degradation degree of the concrete sample is B2; when the concentration of chloride ions is higher than 400mol/m3The degree of deterioration of the concrete specimen was B3.
Preferably, said determining optimal electrochemical repair technique parameters comprises:
when the aggregate activity of the concrete sample is high and the content of chloride ions is low, namely the deterioration degree of the concrete sample is A3B 1; the optimal electrochemical repair parameters are: the concentration of the lithiated solution is higher than 1500mol/m3Current density higher than 2A/m2The electrifying time is 14 to 21 days;
when the aggregate activity of the concrete sample is low and the chloride ion content is low and high, namely the deterioration degree of the concrete sample is A1B 3; optimized electrochemistryThe repair parameters are: the concentration of the lithiated solution is less than 500mol/m3Current density higher than 2A/m2The electrifying time is 14 to 21 days;
when the aggregate activity and the chloride ion content of the concrete sample are both high, namely the deterioration degree of the concrete sample is A3B 3; the optimal electrochemical repair parameters are: the concentration of the lithiated solution is 800mol/m3～1200mol/m3Between, the current density is higher than 3A/m2The electrifying time is 14 to 21 days;
when the aggregate activity and the chloride ion content of the concrete sample are lower, namely the deterioration degree of the concrete sample is A1B 1; the optimal electrochemical repair parameters are: the concentration of the lithiated solution is less than 500mol/m3The current density is between 1A/m and 2A/m2The electrifying time is 7 to 14 days;
when the aggregate activity and the chloride ion content of the concrete test piece are A1B2, A2B1, A2B2, A2B3 and A3B2, the optimal electrochemical repair parameters are as follows: the concentration of the lithiated solution is 500mol/m3～1000mol/m3Between, the current density should be 2A/m2The energization time was about 14 days.
Preferably, the concrete test piece is subjected to electrochemical repair, wherein
And paving a metal net on the side surface of the concrete sample, placing the metal net in a lithiated solution to serve as an anode to be connected with the positive pole of a direct-current power supply, and connecting a reinforcing steel bar in the concrete sample serving as a cathode to be connected with the negative pole of the direct-current power supply.
Preferably, after the electrochemical repairing of the concrete sample, the method further comprises: and arranging strain gauges in the areas near the steel bars in the concrete test piece, continuously monitoring the crack development condition of the sensitive area, and determining the repairing effect in real time so as to determine whether secondary repairing is needed.
Preferably, the species of the lithiated solution includes LiOH, Li2CO3Or LiNO3Any of the solutions.
In recent years, it has been found that lithium salts can inhibit the swelling of alkali-aggregate gels by altering the alkali-aggregate reaction progress and product characteristics. Therefore, a series of methods for lithium salt infiltration into concrete, such as vacuum impregnation, spraying, and electrochemical techniques, have begun to be applied to inhibit damage to the alkali aggregate of existing structures. Research shows that the effect of inhibiting the alkali aggregate by electrochemically migrating lithium ions is optimal. Therefore, based on the existing electrochemical dechlorination method, the electrochemical repairing method capable of simultaneously preventing the corrosion of the steel bars and the alkali aggregate reaction is provided. By means of an external electric field, migration rate of lithium ions to the interior of concrete is accelerated, and harmful ions such as chloride ions and sulfate ions are removed, so that dual purposes of preventing alkali aggregate damage and reinforcing steel bar corrosion are achieved, and the method has great significance for improving durability of a concrete structure and prolonging service life of the concrete structure.
Compared with the prior art, the invention has at least one of the following beneficial effects:
the method disclosed by the invention is simple and convenient to operate, and can be used for migrating lithium ions into concrete in a short time without damage and high efficiency, so that the alkali-aggregate reaction in the existing concrete structure and the alkali-aggregate reaction possibly induced in the electrochemical process are inhibited, and the development of micro cracks caused by the alkali-aggregate reaction is further prevented; meanwhile, harmful ions such as chloride ions and sulfate ions possibly existing in the concrete can be removed, so that the reinforcing steel bars in the concrete are prevented from being corroded, the dual purposes of preventing alkali aggregate damage and reinforcing steel bars from being corroded are achieved, the durability of the concrete structure is improved, and the service life of the concrete structure is prolonged.
According to the method, the concentration and the type of the lithium compound solution can be adjusted according to different pollution degrees of the concrete by monitoring the aggregate activity and the chloride ion content of the concrete sample, and the infiltration rate of lithium ions and the removal rate of harmful ions such as chloride ions and sulfate ions are maximized.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
FIG. 1 is a schematic diagram of the state of a concrete electrochemical repair method for dual deterioration of alkali aggregate damage and reinforcing steel corrosion according to a preferred embodiment of the present invention;
FIG. 2 is a diagram illustrating the lithium ion concentration distribution in a concrete sample after electrochemical repair according to a preferred embodiment of the present invention;
FIG. 3 is a diagram illustrating the concentration distribution of chloride ions in a concrete sample after electrochemical repair according to a preferred embodiment of the present invention;
FIG. 4 shows Li in a concrete sample after electrochemical repairing according to a preferred embodiment of the present invention+/Na+Molar mass ratio of (a);
FIG. 5 is a graph illustrating A, B, C, D the lithium ion concentration distribution in four concrete samples according to a preferred embodiment of the present invention;
FIG. 6 is a graph illustrating the concentration distribution of chloride ions in A, B, C, D four concrete samples according to a preferred embodiment of the present invention;
the scores in the figure are indicated as: 1 is a concrete sample, 2 is a metal net, 3 is a steel bar, 4 is electrolyte and 5 is a direct current power supply.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications can be made by persons skilled in the art without departing from the spirit of the invention. All falling within the scope of the present invention.
Referring to fig. 1, a schematic diagram of a state of a concrete electrochemical repair method for alkali aggregate damage and steel bar corrosion dual deterioration according to a preferred embodiment of the present invention is shown, wherein the repair method includes the following steps:
and S1, monitoring the aggregate activity and the chloride ion content of the concrete sample 1, and evaluating the deterioration degree of different concrete samples 1.
S2, determining the optimal electrochemical repair technical parameters based on the evaluated degradation degree of the concrete sample 1; the technical parameters comprise electrolyte concentration, current density and electrifying time.
And S3, adopting a lithiated solution as the electrolyte 4 and adopting the optimal electrochemical repair technical parameters to carry out electrochemical repair on the concrete sample 1, thereby achieving the effect of inhibiting the alkali aggregate reaction inherent in the existing structure and the alkali aggregate reaction induced by the alkalinity improvement caused by the electrochemical reaction on the surface of the steel bar 3 while removing chlorine.
In other embodiments, the step S1 is to monitor the aggregate activity and the chloride ion content of the concrete sample, and the evaluating the deterioration degree of different concrete samples includes: and (4) detecting the activity of the aggregate and the content of chloride ions by drilling and sampling.
Determining the activity of the concrete protective layer aggregate by a rapid mortar bar method; when the expansion rate of the concrete test piece is lower than 0.10% in 14 days, the deterioration degree of the concrete test piece is A1; when the expansion rate of the concrete test piece is between 0.1 and 0.20 percent in 14 days, the deterioration degree of the concrete test piece is A2; when the expansion rate of the concrete test piece is higher than 0.20% in 14 days, the deterioration degree of the concrete test piece is A3;
measuring the content of chloride ions in the concrete protective layer by a chloride ion rapid measurement method; when the concentration of chloride ions is lower than 100mol/m3When the concrete sample is degraded, the degradation degree of the concrete sample is B1; when the concentration of chloride ions is 100mol/m3～400mol/m3When the concrete sample is degraded, the degradation degree of the concrete sample is B2; when the concentration of chloride ions is higher than 400mol/m3The degree of deterioration of the concrete specimen was B3.
The embodiment may be implemented by the following steps: the concrete column with the set diameter and the height being the thickness of the concrete protective layer is obtained from the concrete structure to be repaired by a drilling and sampling method and is used as a concrete test piece, and the set diameter of the concrete column can be 45-60 mm. And (3) determining the activity of the aggregate in the concrete protective layer by a rapid mortar rod method for the concrete test piece. And (3) determining the content of chloride ions in the concrete protective layer of the concrete test piece by a chloride ion rapid determination method. The concrete specimen was removed in the area where severe alkali aggregate expansion cracks had occurred.
In other embodiments, the determining the optimal electrochemical repair technique parameters in S2 includes:
when the aggregate activity of the concrete sample is high and the content of chloride ions is low, namely the deterioration degree of the concrete sample is A3B 1; the optimal electrochemical repair parameters are: the concentration of the lithiated solution is higher than 1500mol/m3Current density higher than 2A/m2The electrifying time is 14 to 21 days;
when the aggregate activity of the concrete sample is low and the chloride ion content is low and high, namely the deterioration degree of the concrete sample is A1B 3; the optimal electrochemical repair parameters are: the concentration of the lithiated solution is less than 500mol/m3Current density higher than 2A/m2The electrifying time is 14 to 21 days;
when the aggregate activity and the chloride ion content of the concrete sample are both high, namely the deterioration degree of the concrete sample is A3B 3; the optimal electrochemical repair parameters are: the concentration of the lithiated solution is 800mol/m3～1200mol/m3Between, the current density is higher than 3A/m2The electrifying time is 14 to 21 days;
when the aggregate activity and the chloride ion content of the concrete sample are lower, namely the deterioration degree of the concrete sample is A1B 1; the optimal electrochemical repair parameters are: the concentration of the lithiated solution is less than 500mol/m3The current density is between 1A/m and 2A/m2The electrifying time is 7 to 14 days;
when the aggregate activity and the chloride ion content of the concrete test piece are A1B2, A2B1, A2B2, A2B3 and A3B2, the optimal electrochemical repair parameters are as follows: the concentration of the lithiated solution is 500mol/m3～1000mol/m3Between, the current density should be 2A/m2The energization time was about 14 days.
The current density and the electrifying time of the surface of the steel bar are mainly adjusted based on the thickness of a concrete test piece protective layer, the activity of aggregate and the pollution degree of harmful ions.
In the above embodiment, as the concentration of lithium ions in the electrolyte is higher, more lithium ions will migrate into the concrete, and in order to maintain the electrical neutrality of the concrete pore liquid system, the removal rate and total amount of chloride ions will be limited, therefore, as the activity of the aggregate is stronger, a high-concentration and high-mobility lithiated solution should be selected; or when the pollution degree of chloride ions in the concrete is higher, a lithium compound solution with low concentration and low mobility is selected. In the case of high aggregate activity and chloride concentration, the necessary conditions for alkali-aggregate reaction are active aggregate, moisture and high alkaline environment, while in the case of high chloride ion concentration, the alkalinity of the internal pore liquid of the concrete is reduced and alkali-aggregate reaction does not occur, so in this case, a low-concentration and low-mobility lithiated solution is still selected. Therefore, the concentration of the lithium solution is adjusted according to different pollution degrees of concrete, and the infiltration rate of lithium ions and the removal rate of harmful ions such as chloride ions are maximized.
In other embodiments, the above-mentioned S3 is performed to perform electrochemical repairing on the concrete sample, wherein,
referring to fig. 1, a metal mesh 2 is laid on the side surface of a concrete sample 1, the metal mesh 2 is placed in a lithiated solution and used as an anode to be connected with a positive electrode of a direct current power supply 5, and a steel bar 3 in the concrete sample 1 is used as a cathode to be connected with a negative electrode of the direct current power supply 5. After the constant direct-current power supply 5 is switched on, under the action of an external electric field, harmful ions such as chloride ions, sulfate ions and the like in the protective layer of the concrete sample 1 migrate to the outside of the concrete into electrolyte on the surface of the concrete sample, so that the aim of preventing the reinforcing steel bars 3 from being corroded is fulfilled; at the same time, lithium ions start to accelerate the migration into the concrete protective layer, so as to inhibit the alkali aggregate reaction inherent to the existing structure and the alkali aggregate reaction induced by the increase in alkalinity due to the electrochemical reaction (O2+2H2O +4e ═ 4OH-) occurring on the surface of the steel bar 3. As a preferable mode, in order to avoid the anode corrosion to cause the pollution on the concrete surface, the metal net 2 is preferably selected from metals or alloys which are not easily oxidized. Specifically, but not limited to, a titanium alloy mesh or a stainless steel mesh can be selected.
In some other preferred embodiments, the concrete electrochemical repairing method for alkali aggregate damage and steel bar corrosion comprises the following steps after the concrete sample is electrochemically repaired: and arranging strain gauges in the areas near the steel bars in the concrete sample, continuously monitoring the crack development condition of the sensitive area, and determining the repair effect in real time so as to determine whether secondary repair is needed.
In other preferred embodiments, the concrete electrochemical repair method aiming at the dual deterioration of alkali aggregate damage and steel bar corrosion can spray waterproof paint on the surface of a repaired concrete sample after the concrete sample is electrochemically repaired, so as to provide a new alkali aggregate inducing environment after preventing the re-erosion of harmful ions such as chloride ions, sulfate ions and the like and the water infiltration; and grouting and repairing the drill hole sampling area and the local area removed due to the irreversible expansion of the alkali aggregate by using any one of cement, ultra-fine cement or epoxy resin.
The object and effect of the concrete electrochemical repairing method for alkali aggregate damage and steel bar corrosion dual deterioration described in the above embodiment are further described below with reference to a specific application example. Two groups of experimental examples and one group of control examples are provided in the application example, and the repairing results of the two groups of experimental examples and the control group are compared to show the repairing effect of the two groups of experimental examples.
Three concrete columns with a cross section of 100mm x 100mm and a height of 200mm were prepared to obtain three concrete samples. The reinforcing steel bar of each concrete sample selects the Q235 reinforcing steel bar with the diameter of 12mm, and is positioned in the center of the concrete sample. The weight contents of each component in each cubic meter of the concrete of the three concrete samples are respectively as follows: 300kg of cement, 180kg of water, 780kg of fine aggregate, 580kg of non-active coarse aggregate, 390kg of active coarse aggregate (deterioration degree A2), and 11.9kg of sodium chloride, namely 200mol/m3(degree of deterioration B2). After the three concrete samples are subjected to standard curing for 28 days, the three concrete samples are placed in a climatic environment box with the humidity of 100% and the temperature of 40 ℃ for two months so as to accelerate the alkali aggregate reaction in the concrete samples.
Taking two concrete samples as B, C groups of experimental examples, and repairing by adopting a concrete electrochemical repair method aiming at dual deterioration of alkali aggregate damage and steel bar corrosion; one of the remaining concrete samples was used as a group A control group, and the group A was left at room temperature without being electrochemically treated.
Based on the component proportions of the concrete samples, the deterioration degree of the B, C group concrete samples is A2B 2. Determining optimal electrochemical repair technical parameters based on the degradation degree of B, C groups of concrete samples; the concentration of the lithiated solution is 500mol/m3～1000mol/m3Between, the current density should be 2A/m2The energization time was about 14 days.
Arranging a titanium alloy net on the side surface of B, C groups of concrete samples as an anode to be connected with a direct current power supply anode, and respectively placing B, C groups of concrete samples with lithium ion concentration of 500mol/m3LiOH solution of (3), Li2CO3In the solution, B, C groups of titanium alloy nets on the outer surfaces of concrete samples are respectively soaked in LiOH solution and Li2CO3In solution.
B, C groups of concrete samples, steel bars are used as cathodes to be connected with a negative electrode of a direct current power supply, and the current density applied to the surfaces of the steel bars is 2A/m2The energization time was 15 days. The entire repair process was performed at room temperature. Measuring the concentration of the electrolyte every two days, and replenishing the electrolyte to maintain the lithium ion concentration at 500mol/m3And (4) up and down to improve the migration rate of lithium ions to the interior of the concrete.
After the electrochemical repair of the B, C sets of concrete samples was completed. In order to avoid boundary effect, A, B, C three groups of concrete samples are drilled and powdered in the depth direction of the protective layer every 12.5mm from the depth of 6 mm.
Then, the cations (K) in A, B, C three groups of concrete samples are measured by adopting Atomic Absorption Spectrometry (AAS)+、Na+、Li+) Reference is made to fig. 2, which is a schematic diagram of the lithium ion concentration distribution of A, B, C three groups of concrete samples. Meanwhile, the content of chloride ions in A, B, C three groups of concrete samples is measured by a chloride ion rapid measurement method (RCT), and is shown in fig. 3 as a schematic diagram of the concentration distribution of chloride ions in A, B, C three groups of concrete samples. As can be seen from FIG. 3, after two weeks of electrochemical repair, the chloride ion concentration in the B, C groups of concrete samples was significantly reduced; as can be seen from FIG. 2, in contrast, the amount of migration of lithium ions was small, but as can be seen from FIG. 4, in the B, C group of concrete samples, particularly in the region Li near the reinforcing steel bars+/Na+The molar concentration ratio of the Li is more than 1.0, and the research shows that when the Li is used+/Na+The molar concentration ratio of (A) is more than 1.0, which is sufficient to suppress the alkali-aggregate reaction in the concrete.
The invention aims and effects of the concrete electrochemical repairing method aiming at the dual deterioration of alkali aggregate damage and steel bar corrosion in the embodiment are further described in the following with another specific application example.
Four concrete columns with the cross sections of 100mm x 100mm and the heights of 200mm are prepared, and Q235 reinforcing steel bars with the diameters of 12mm are selected and located in the centers of the concrete test pieces. Wherein A, B groups of test pieces have the following components in each cubic meter of concrete: 300kg of cement, 180kg of water, 780kg of fine aggregate, 580kg of non-active coarse aggregate and 390kg of active coarse aggregate, and 11.9kg of sodium chloride is doped simultaneously. C. The D group of test pieces respectively comprise the following components in each cubic meter of concrete: 300kg of cement, 180kg of water, 780kg of fine aggregate, 580kg of non-active coarse aggregate and 390kg of active coarse aggregate, and 23.8kg of sodium chloride is doped simultaneously. A. B, C, D after standard curing for 28 days, the four test pieces are all placed in a climatic environment box with the humidity of 100% and the temperature of 40 ℃ for two months to accelerate the alkali aggregate reaction in the concrete test pieces.
The method is adopted to carry out electrochemical repair on A, B, C, D four groups of concrete samples, and the surfaces of the samples are provided with titanium alloy nets as anodes to be connected with the positive pole of a direct current power supply, and steel bars in the concrete samples are used as cathodes to be connected with the negative pole of the direct current power supply. The electrolyte of group A is a lithium ion electrolyte with the concentration of 500mol/m3In a solution of LiOH; the electrolyte in the group B has a lithium ion concentration of 1500mol/m3Li of (2)2CO3In solution; the electrolyte in group C has a lithium ion concentration of 500mol/m3In a solution of LiOH; the electrolyte in the group D has a lithium ion concentration of 1500mol/m3Li of (2)2CO3In solution. The current density applied to the surfaces of the reinforcing steel bars of A, B, C, D four groups of concrete samples is 2A/m2The energization time was 15 days. The entire repair process was performed at room temperature. The concentration of the electrolyte was measured every two days, and the solution was replenished so that the lithium ion concentrations in A, C and B, D groups were maintained at 500mol/m3、1500mol/m3And the rate of lithium ion migration into the concrete is improved.
After the electrochemical repair is finished, in order to avoid the boundary effect, A, B, C, D four groups of concrete test pieces are drilled and powdered along the depth direction of the protective layer every 12.5mm from the 6mm depth position. The lithium ion content in the concrete test piece was then determined by Atomic Absorption Spectroscopy (AAS). Meanwhile, the content of chloride ions in the concrete sample is measured by adopting a chloride ion rapid measurement method (RCT). Referring to fig. 5 and 6, which are schematic diagrams of concentration distributions of lithium ions and chloride ions of A, B, C, D four groups of concrete samples, it can be seen that after two weeks of electrochemical repair, the chloride ion content of the four groups of concrete samples is significantly reduced, and the lithium ion content is significantly increased. And the penetration depth and the content of lithium ions are obviously improved in B, D two groups of high-concentration high-mobility lithiated solutions. The results are in direct opposition to the chloride ion. The higher the concentration and mobility of the lithiated solution, the more chloride ions remain in the concrete specimen. And the inhibition phenomenon is more obvious along with the increase of the initial chloride ion pollution degree of the concrete. It is indicated that different electrochemical technical parameters should be given for concrete samples which suffer from different degrees of chlorine salt pollution and alkali aggregate reaction so as to achieve the highest repairing efficiency and the best repairing effect.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention.

Claims (4)

1. A concrete electrochemical repair method aiming at dual deterioration of alkali aggregate damage and steel bar corrosion is characterized by comprising the following steps:
monitoring the aggregate activity and the chloride ion content of the concrete test piece, and evaluating the deterioration degree of different concrete test pieces;
determining the optimal electrochemical repair technical parameters based on the evaluated degradation degree of the concrete test piece; the technical parameters comprise electrolyte concentration, current density and electrifying time;
the concrete sample is electrochemically repaired by adopting a lithiated solution as electrolyte and adopting optimal electrochemical repair technical parameters, so that the effects of removing chlorine and inhibiting the inherent alkali aggregate reaction of the existing structure and the alkali aggregate reaction induced by the alkalinity improvement caused by the electrochemical reaction on the surface of the steel bar are achieved;
the aggregate activity and the chloride ion content of the concrete test piece are monitored, and the degradation degree of different concrete test pieces is evaluated, wherein the method comprises the following steps:
determining the activity of the concrete protective layer aggregate by a rapid mortar bar method; when the expansion rate of the test piece is lower than 0.10% in 14 days, the deterioration degree of the concrete test piece is A1; when the expansion rate of the test piece is between 0.1 and 0.20 percent in 14 days, the degradation degree of the concrete test piece is A2; when the expansion rate of the test piece is higher than 0.20% in 14 days, the deterioration degree of the concrete test piece is A3;
measuring the content of chloride ions in the concrete protective layer by a chloride ion rapid measurement method; when the concentration of chloride ions is lower than 100mol/m3When the concrete sample is degraded, the degradation degree of the concrete sample is B1; when the concentration of chloride ions is 100mol/m3～400mol/m3When the concrete sample is degraded, the degradation degree of the concrete sample is B2; when the concentration of chloride ions is higher than 400mol/m3The deterioration degree of the concrete sample is B3;
the determining of the optimal electrochemical repair technology parameters comprises:
when the aggregate activity of the concrete sample is high and the content of chloride ions is low, namely the deterioration degree of the concrete sample is A3B 1; the optimal electrochemical repair parameters are: the concentration of the lithiated solution is higher than 1500mol/m3Current density higher than 2A/m2The electrifying time is 14 to 21 days;
when the aggregate activity of the concrete sample is low and the chloride ion content is high, namely the deterioration degree of the concrete sample is A1B 3; the optimal electrochemical repair parameters are: the concentration of the lithiated solution is less than 500mol/m3Current density higher than 2A/m2The electrifying time is 14 to 21 days;
when the aggregate activity and the chloride ion content of the concrete sample are both high, namely the deterioration degree of the concrete sample is A3B 3; the optimal electrochemical repair parameters are: the concentration of the lithiated solution is 800mol/m3～1200mol/m3Between, the current density is higher than 3A/m2The electrifying time is 14 to 21 days;
when the aggregate activity and the chloride ion content of the concrete sample are both low, the concrete sample is inferiorDegree of conversion is A1B 1; the optimal electrochemical repair parameters are: the concentration of the lithiated solution is less than 500mol/m3The current density is between 1A/m and 2A/m2The electrifying time is 7 to 14 days;
when the aggregate activity and the chloride ion content of the concrete test piece are A1B2, A2B1, A2B2, A2B3 and A3B2, the optimal electrochemical repair parameters are as follows: the concentration of the lithiated solution is 500mol/m3～1000mol/m3Between, the current density should be 2A/m2The energization time was 14 days.
2. The electrochemical repair method for concrete aiming at double degradation of alkali aggregate damage and steel bar corrosion according to claim 1, characterized in that the electrochemical repair is carried out on the concrete sample, wherein,
and paving a metal net on the side surface of the concrete sample, placing the metal net in a lithiated solution to serve as an anode to be connected with the positive pole of a direct-current power supply, and connecting a reinforcing steel bar in the concrete sample serving as a cathode to be connected with the negative pole of the direct-current power supply.
3. The method for electrochemically repairing concrete with respect to dual deterioration of alkali aggregate damage and steel bar corrosion according to claim 2, further comprising, after the electrochemically repairing the concrete sample: and arranging strain gauges in the areas near the steel bars in the concrete test piece, continuously monitoring the crack development condition of the sensitive area, and determining the repairing effect in real time so as to determine whether secondary repairing is needed.
4. The method for electrochemically repairing concrete against dual deterioration of alkali aggregate damage and steel bar corrosion according to any one of claims 1 to 3, wherein the types of the lithiated solution include LiOH, Li2CO3Or LiNO3Any of the solutions.
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