CN111896428A - Device and method for measuring diffusion coefficient of sulfate ions in mortar and concrete - Google Patents
Device and method for measuring diffusion coefficient of sulfate ions in mortar and concrete Download PDFInfo
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- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 title claims abstract description 103
- 238000009792 diffusion process Methods 0.000 title claims abstract description 81
- 239000004567 concrete Substances 0.000 title claims abstract description 54
- 239000004570 mortar (masonry) Substances 0.000 title claims abstract description 33
- 238000000034 method Methods 0.000 title claims abstract description 28
- 238000012360 testing method Methods 0.000 claims abstract description 101
- 239000000243 solution Substances 0.000 claims abstract description 93
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims abstract description 90
- 239000007864 aqueous solution Substances 0.000 claims abstract description 24
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 16
- 239000003822 epoxy resin Substances 0.000 claims description 15
- 229920000647 polyepoxide Polymers 0.000 claims description 15
- 229910052742 iron Inorganic materials 0.000 claims description 8
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 7
- 230000005684 electric field Effects 0.000 claims description 4
- 239000011248 coating agent Substances 0.000 claims description 3
- 238000000576 coating method Methods 0.000 claims description 3
- 229920002379 silicone rubber Polymers 0.000 claims description 3
- 239000012466 permeate Substances 0.000 abstract 1
- 239000004568 cement Substances 0.000 description 13
- 239000000463 material Substances 0.000 description 11
- 239000011148 porous material Substances 0.000 description 11
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 8
- BHPQYMZQTOCNFJ-UHFFFAOYSA-N Calcium cation Chemical compound [Ca+2] BHPQYMZQTOCNFJ-UHFFFAOYSA-N 0.000 description 6
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 6
- 229910001424 calcium ion Inorganic materials 0.000 description 6
- 150000002500 ions Chemical class 0.000 description 6
- 238000012512 characterization method Methods 0.000 description 5
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 description 4
- OSGAYBCDTDRGGQ-UHFFFAOYSA-L calcium sulfate Chemical compound [Ca+2].[O-]S([O-])(=O)=O OSGAYBCDTDRGGQ-UHFFFAOYSA-L 0.000 description 4
- 230000009545 invasion Effects 0.000 description 4
- 239000010410 layer Substances 0.000 description 4
- 238000011160 research Methods 0.000 description 4
- 238000006243 chemical reaction Methods 0.000 description 3
- 230000007797 corrosion Effects 0.000 description 3
- 238000005260 corrosion Methods 0.000 description 3
- 230000003628 erosive effect Effects 0.000 description 3
- 229910001653 ettringite Inorganic materials 0.000 description 3
- 239000010881 fly ash Substances 0.000 description 3
- 229910052500 inorganic mineral Inorganic materials 0.000 description 3
- 230000005012 migration Effects 0.000 description 3
- 238000013508 migration Methods 0.000 description 3
- 239000011707 mineral Substances 0.000 description 3
- 230000035515 penetration Effects 0.000 description 3
- 230000008569 process Effects 0.000 description 3
- 239000000741 silica gel Substances 0.000 description 3
- 229910002027 silica gel Inorganic materials 0.000 description 3
- 239000002893 slag Substances 0.000 description 3
- JXHZRQHZVYDRGX-UHFFFAOYSA-M sodium;hydrogen sulfate;hydrate Chemical compound [OH-].[Na+].OS(O)(=O)=O JXHZRQHZVYDRGX-UHFFFAOYSA-M 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 230000009471 action Effects 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 229910000019 calcium carbonate Inorganic materials 0.000 description 2
- AXCZMVOFGPJBDE-UHFFFAOYSA-L calcium dihydroxide Chemical compound [OH-].[OH-].[Ca+2] AXCZMVOFGPJBDE-UHFFFAOYSA-L 0.000 description 2
- 239000000920 calcium hydroxide Substances 0.000 description 2
- 229910001861 calcium hydroxide Inorganic materials 0.000 description 2
- 239000000378 calcium silicate Substances 0.000 description 2
- 229910052918 calcium silicate Inorganic materials 0.000 description 2
- JGIATAMCQXIDNZ-UHFFFAOYSA-N calcium sulfide Chemical compound [Ca]=S JGIATAMCQXIDNZ-UHFFFAOYSA-N 0.000 description 2
- OYACROKNLOSFPA-UHFFFAOYSA-N calcium;dioxido(oxo)silane Chemical compound [Ca+2].[O-][Si]([O-])=O OYACROKNLOSFPA-UHFFFAOYSA-N 0.000 description 2
- 230000006378 damage Effects 0.000 description 2
- 238000005034 decoration Methods 0.000 description 2
- HOOWDPSAHIOHCC-UHFFFAOYSA-N dialuminum tricalcium oxygen(2-) Chemical compound [O--].[O--].[O--].[O--].[O--].[O--].[Al+3].[Al+3].[Ca++].[Ca++].[Ca++] HOOWDPSAHIOHCC-UHFFFAOYSA-N 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 229910052602 gypsum Inorganic materials 0.000 description 2
- 239000010440 gypsum Substances 0.000 description 2
- 230000036571 hydration Effects 0.000 description 2
- 238000006703 hydration reaction Methods 0.000 description 2
- 239000011159 matrix material Substances 0.000 description 2
- 229910021487 silica fume Inorganic materials 0.000 description 2
- 238000010998 test method Methods 0.000 description 2
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 229910052925 anhydrite Inorganic materials 0.000 description 1
- 239000011575 calcium Substances 0.000 description 1
- 229910052791 calcium Inorganic materials 0.000 description 1
- XFWJKVMFIVXPKK-UHFFFAOYSA-N calcium;oxido(oxo)alumane Chemical compound [Ca+2].[O-][Al]=O.[O-][Al]=O XFWJKVMFIVXPKK-UHFFFAOYSA-N 0.000 description 1
- 239000011083 cement mortar Substances 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 238000007716 flux method Methods 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 description 1
- 229910052753 mercury Inorganic materials 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 230000000149 penetrating effect Effects 0.000 description 1
- 230000002829 reductive effect Effects 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 239000004576 sand Substances 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 239000013535 sea water Substances 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 239000002689 soil Substances 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
- 230000036962 time dependent Effects 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N13/00—Investigating surface or boundary effects, e.g. wetting power; Investigating diffusion effects; Analysing materials by determining surface, boundary, or diffusion effects
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N13/00—Investigating surface or boundary effects, e.g. wetting power; Investigating diffusion effects; Analysing materials by determining surface, boundary, or diffusion effects
- G01N13/04—Investigating osmotic effects
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
- G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N13/00—Investigating surface or boundary effects, e.g. wetting power; Investigating diffusion effects; Analysing materials by determining surface, boundary, or diffusion effects
- G01N2013/003—Diffusion; diffusivity between liquids
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- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
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- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
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Abstract
The invention discloses a device and a method for measuring diffusion coefficients of sulfate ions in mortar and concrete, wherein the device comprises a direct-current power supply, an anode plate, a cathode plate, an anode end solution loading tank, a cathode end solution loading tank and a test piece loading tank; the anode end solution loading tank is filled with a sodium hydroxide aqueous solution, and the anode plate is positioned in the sodium hydroxide aqueous solution in the anode end solution loading tank; a mixed aqueous solution of sulfate and sodium hydroxide is filled in the cathode end solution loading tank, and the cathode plate is positioned in the mixed aqueous solution of sulfate and sodium hydroxide in the cathode end solution loading tank; the test piece loading groove is used for placing a test piece, is positioned between the anode end solution loading groove and the cathode end solution loading groove, and is communicated with the anode end solution loading groove and the cathode end solution loading groove respectively at two ends; the anode plate and the cathode plate are respectively connected with the positive electrode and the negative electrode of the direct current power supply through leads. The diffusion coefficient of the sulfate ions is calculated by measuring the initial time for the sulfate ions to permeate the test sample into the target solution.
Description
Technical Field
The invention relates to the technical field of concrete durability test, in particular to a device and a method for measuring diffusion coefficients of sulfate ions in mortar and concrete.
Background
Sulfate attack is one of the main causes affecting the durability of cement-based materials, including internal and external sulfate attack. The internal sulfate corrosion mainly comes from excessive gypsum or sulfate introduced by additives, and the external sulfate corrosion mainly causes structural expansion cracking caused by the fact that a large amount of sulfate in seawater, underground water, river water and saline-alkali soil invades into the interior of a cement-based material and reacts with calcium hydroxide which is a cement hydration product and mono-sulfur calcium sulphoaluminate or tricalcium aluminate which is an incompletely hydrated mineral to generate expansive products such as ettringite, gypsum and the like. For calcium carbonate containing cement-based materials, the sulfate or sulfate product will also chemically react with calcium carbonate and calcium silicate hydrate or unreacted calcium silicate minerals to form calcium sulfosilicate, causing the cement-based material structure to collapse.
External sulfate attack occurs from the intrusion, diffusion, penetration and destruction of sulfate ions. The erosion process can be divided into three processes according to the ionic action: (1) sulfate ions enter water in a diffusion mode, exist in a water-soluble sulfate ion mode, and are spread into the pores of the cement-based material through a water medium; (2) the hydration product calcium hydroxide and sulfate ions in the pore solution are chemically reacted to generate CaSO with lower solubility4Small fraction of CaSO4Dissolving in water, and separating out in the form of hydrated calcium sulfate after most of the solution reaches ion saturation to generate crystal expansion; (3) calcium sulfate reacts with tricalcium aluminate, hydrated calcium aluminate and monosulfur calcium sulfoaluminate to generate ettringite with low solubility, and the ettringite is quickly crystallized, so that the outer wall of a pore is pressed, and a cement matrix is expanded and cracked. The external sulfate erosion action gradually extends from the surface layer of the cement-based material to the interior of the structure, and continuously generates chemical reaction with the cement matrix to generate an expansive product, so that the cement-based material is damagedThe degree is then severe. The research on the sulfate diffusion coefficient can represent the sulfate diffusion and penetration degree of cement mortar and concrete structures and evaluate the sulfate corrosion damage condition of the mortar and the concrete.
At present, sulfate diffusion research is mainly characterized by measuring sulfate products or sulfate ion dissolution concentration of cement-based materials at different depths, can qualitatively characterize the sulfate invasion and reaction degree, but cannot quantitatively characterize the diffusion coefficient of sulfate ions. At present, the chloride ion diffusion coefficient of the concrete material is mainly determined by adopting an electric flux method, a steady-state electromigration test method, an unsteady-state electromigration test method and a saturated salt conductivity method, and meanwhile, a calcium ion diffusion coefficient determination method is also provided. Among them, the chloride ion diffusion coefficient measuring method (RCM) calculates the diffusion coefficient from the diffusion depth, and the calcium ion diffusion coefficient measuring method (CN201210106775) calculates the diffusion coefficient from the calcium ion migration rate. However, no apparatus or method has been reported which is specifically used for measuring the diffusion coefficient of sulfate ions.
Disclosure of Invention
The purpose of the invention is as follows: the invention aims to solve the technical problem of the prior art and provides a device and a method for measuring the diffusion coefficient of sulfate ions in mortar and concrete, so as to quantitatively represent the invasion and diffusion characteristics of external sulfate in the mortar and concrete.
In order to solve and achieve the purpose, the technical scheme adopted by the invention is as follows:
a device for measuring the diffusion coefficient of sulfate ions in mortar and concrete comprises a direct-current power supply, an anode plate, a cathode plate, an anode end solution loading groove, a cathode end solution loading groove and a test piece loading groove;
the anode end solution loading tank is filled with a sodium hydroxide aqueous solution, and the anode plate is positioned in the anode end solution loading tank and is immersed in the sodium hydroxide aqueous solution;
the cathode end solution loading tank is filled with a mixed aqueous solution of sulfate and sodium hydroxide, and the cathode plate is positioned in the cathode end solution loading tank and is immersed in the mixed aqueous solution of sulfate and sodium hydroxide;
the test piece loading groove is used for placing a test piece and is positioned between the anode end solution loading groove and the cathode end solution loading groove, and two ends of the test piece loading groove are respectively communicated with the anode end solution loading groove and the cathode end solution loading groove;
the anode plate and the cathode plate are respectively connected with the positive electrode and the negative electrode of the direct current power supply through conducting wires.
Specifically, the anode end solution loading tank and the cathode end solution loading tank are both right-angle bent pipes, and the test piece loading tank is a straight pipe;
the top end openings of the anode end solution loading groove and the cathode end solution loading groove are respectively used for connecting the corresponding anode plate and cathode plate with the positive and negative electrodes of the direct current power supply through leads, and the bottom end openings are respectively fixed with the two end openings of the test piece loading groove.
Preferably, the anode plate and the cathode plate are thin iron plates, and the tops of the anode plate and the cathode plate are respectively connected with the anode and the cathode of the direct current power supply through leads.
Preferably, the side surface of the test specimen is coated with a layer of epoxy resin, is mutually attached to the inner wall of the specimen loading groove, and is sealed through the epoxy resin; both sides of the test piece contacting the solution were flat.
Preferably, the anode end solution loading tank and the cathode end solution loading tank are both right-angled bends made of PVC materials; the test piece loading groove is a straight hose made of silicon rubber, the test piece loading groove is conveniently sealed with the side face of the test piece through epoxy resin, and meanwhile the straight hose is convenient to replace.
Furthermore, the invention also provides a method for measuring the diffusion coefficient of sulfate ions in mortar and concrete by adopting the device, which comprises the following steps:
s1: cutting the mortar and concrete test block cured to the age into test pieces with the same cross sections as the test piece loading grooves, and simultaneously ensuring the flatness of the cut surfaces;
s2: uniformly coating a layer of epoxy resin on the side surface of the obtained test specimen, standing and curing, and then placing the test specimen in the middle of the specimen loading groove, so that the side surface of the test specimen is attached to the inner wall of the specimen loading groove, and the sections at two ends are parallel to the openings at two ends of the specimen loading groove; then, a needle cylinder is used for absorbing epoxy resin to be uniformly coated on the side surface of the test piece and the inner contact surface of the test piece loading groove, so that the side surface of the test piece is ensured to be sealed;
s3: opening two ends of a test piece loading groove loaded with a test piece, and respectively fixing and communicating the test piece loading groove with an anode end solution loading groove and a cathode end solution loading groove;
s4: respectively connecting the anode plate and the cathode plate with the positive electrode and the negative electrode of a direct current power supply through leads, and respectively fixing the anode plate and the cathode plate in an anode end solution loading tank and a cathode end solution loading tank;
s5: injecting a sodium hydroxide aqueous solution into the anode end solution loading tank, injecting a mixed aqueous solution of sulfate and sodium hydroxide into the cathode end solution loading tank, and completely submerging the anode plate, the cathode plate and the test piece;
s6: setting working voltage, switching on a direct-current power switch, continuously measuring the concentration of sulfate ions in the solution loading tank at the anode end after the direct-current power switch is switched on, and obtaining the initial time t of sulfate ion diffusion and permeation by drawing a sulfate ion concentration curve and fitting according to the curve0；
S7: calculating the diffusion coefficient of sulfate ion
Wherein d is the thickness of the test specimen, R is the gas constant, T is the temperature, F is the Faraday constant, E is the electric field strength, z is the charge number, T is0Is the initial time for diffusion and permeation of sulfate ions.
Diffusion coefficient of sulfate ion
The formula (2) is calculated according to the Nernst-Einstein equation
And
and deriving deformation.
Preferably, in step S5, the concentration of the sodium hydroxide aqueous solution is 0.1-1.0 mol/L; in the mixed water solution of the sulfate and the sodium hydroxide, the concentration of the sulfate is 0.1-1.0mol/L, and the concentration of the sodium hydroxide is 0.1-1.0 mol/L.
Preferably, in step S6, the operating voltage is 30-60V.
Preferably, the measured test temperature T is controlled at 5-45 ℃.
The invasion depth calculation adopted by the chloride ion diffusion coefficient and the migration rate calculation adopted by the calcium ion diffusion coefficient can not effectively cover the part for representing the ions to participate in the chemical reaction. Compared with a rapid chloride ion electromigration measurement (RCM) method for calculating the diffusion coefficient according to the invasion depth of chloride ions and a determination method for calculating the calcium ion diffusion coefficient according to the electron migration rate, the sulfate ion diffusion coefficient is calculated according to the initial time of the sulfate ions penetrating through a test sample to enter a target solution, and the method is more accurate and has a simpler calculation process.
Has the advantages that:
based on the unsteady state electromigration test principle, the sulfate ion diffusion coefficient is calculated by measuring the initial time of sulfate ion diffusion and permeation for the first time, so that the quantitative characterization of the sulfate ion diffusion performance is realized, and a new characterization method is provided for the research of sulfate erosion; accelerating the diffusion of sulfate ions in mortar and concrete through an electric field to realize the rapid analysis of the diffusion coefficient of the sulfate ions; the device has simple structure and convenient operation, has no special requirements on experimental conditions such as fields, environments and the like, and is very favorable for the development of tests.
Drawings
The foregoing and/or other advantages of the invention will become further apparent from the following detailed description of the invention when taken in conjunction with the accompanying drawings.
FIG. 1 is a schematic structural view of a sulfate ion diffusion coefficient measuring apparatus according to the present invention.
FIG. 2 is a time-dependent sulfate ion concentration curve of a mortar M1 test piece measured by a sulfate ion diffusion coefficient measuring device.
FIG. 3 is a graph showing the change of sulfate ion concentration with time in a test piece of concrete C1 using a sulfate ion diffusion coefficient measuring apparatus.
Wherein each reference numeral represents: 1, a direct current power supply; 2, an anode plate; 3, a cathode plate; 4, an anode end solution loading groove; 5 cathode end solution loading tank; 6, a test piece loading groove; test specimens were tested 7.
Detailed Description
The invention will be better understood from the following examples.
As shown in fig. 1, the apparatus for measuring the diffusion coefficient of sulfate ions in mortar and concrete includes a dc power supply 1, an anode plate 2, a cathode plate 3, an anode-side solution loading tank 4, a cathode-side solution loading tank 5, and a test piece loading tank 6.
Wherein, the anode end solution loading tank 4 is filled with sodium hydroxide aqueous solution, and the anode plate 2 is positioned in the anode end solution loading tank 4 and is immersed in the sodium hydroxide aqueous solution. The cathode end solution loading tank 5 is filled with a mixed aqueous solution of sulfate and sodium hydroxide, and the cathode plate 3 is positioned in the cathode end solution loading tank 5 and is immersed in the mixed aqueous solution of sulfate and sodium hydroxide. The test piece loading groove 6 is used for placing a test piece 7 and is positioned between the anode end solution loading groove 4 and the cathode end solution loading groove 5, and two ends of the test piece loading groove are respectively communicated with the anode end solution loading groove 4 and the cathode end solution loading groove 5. The anode plate 2 and the cathode plate 3 are respectively connected with the positive pole and the negative pole of the direct current power supply 1 through conducting wires.
The direct current power supply 1 adopts a commercial 40V/5A adjustable direct current power supply and is provided with a positive electrode connecting wire and a negative electrode connecting wire; the anode plate 2 and the cathode plate 3 are both thin iron plates with the length of 5cm, the width of 5cm and the thickness of 1cm, and the tops of the thin iron plates are respectively connected with the anode and the cathode of the direct current power supply 1 through leads.
The anode end solution loading tank 4 and the cathode end solution loading tank 5 are both right-angle bent pipes made of PVC materials, and the inner diameter of the right-angle bent pipes is 50 mm; the test piece loading groove 6 is a straight hose made of silicon rubber, the inner diameter of the straight hose is 50mm, the straight hose is convenient to seal with the side face of a test piece through epoxy resin, and the straight hose is convenient to replace.
The top end openings of the anode end solution loading tank 4 and the cathode end solution loading tank 5 are respectively used for connecting the corresponding anode plate 2 and cathode plate 3 with the positive and negative electrodes of the direct current power supply 1 through leads, and the bottom end openings are respectively fixed with the two end openings of the test piece loading tank 6.
When the mortar or concrete test piece curing liquid is used, a cutting machine is adopted to cut a mortar or concrete test piece cured to 28-day age into a cylindrical test piece (the diameter of the mortar test piece is 8mm, the height of the concrete test piece is 8mm, and the height of the concrete test piece is 20mm) with the diameter of 50mm and the height of 8mm or 20mm, two surfaces in contact with a solution are ensured to be flat surfaces, and a thin layer of epoxy resin is uniformly coated on the side surface of the cylindrical test piece and is statically cured. And placing the sample to be tested in the middle of the silica gel hose, and absorbing the epoxy resin by using the needle cylinder to uniformly coat the side surface of the sample and the inner contact surface of the silica gel hose to ensure the side surface of the sample to be sealed. The sulfate-sodium hydroxide solution loading groove and the sodium hydroxide solution loading groove adopt PVC bent pipes with the inner diameter of 50mm, two ends of a silica gel hose loaded by the test piece are fixedly connected with the sulfate-sodium hydroxide solution loading bent pipes and the sodium hydroxide solution loading bent pipes respectively, and the lengths of the two ends are kept equal. And placing the anode iron sheet in a sodium hydroxide solution tank, placing the cathode iron sheet in a sulfate-sodium hydroxide solution loading tank and fixing, and respectively connecting the anode and the cathode to the positive and negative poles of a direct current power supply through leads. The whole testing device can be fixed by adopting an iron stand.
The method for measuring the sulfate ion diffusion coefficients of the mortar and the concrete test block by adopting the device comprises the following specific steps:
s1: respectively cutting the mortar and concrete test blocks which are cured to 28d age into cylindrical to-be-tested pieces with the diameters of 50mm and 8mm, and the diameters of 50mm and 20mm, and simultaneously ensuring the cut surfaces to be smooth;
s2: uniformly coating a layer of epoxy resin on the side surface of the obtained test piece 7, standing and curing, and then placing the test piece 7 in the middle of the test piece loading groove 6, so that the side surface of the test piece 7 is attached to the inner wall of the test piece loading groove 6, and the sections at two ends are parallel to the openings at two ends of the test piece loading groove 6; a needle cylinder is adopted to absorb epoxy resin to be uniformly coated on the side surface of the test specimen 7 and the inner contact surface of the specimen loading groove 6, so that the side surface of the specimen is ensured to be sealed;
s3: opening two ends of a test piece loading groove 6 loaded with a test piece 7, and respectively fixing and communicating the test piece loading groove with an anode end solution loading groove 4 and a cathode end solution loading groove 5;
s4: respectively connecting the anode plate 2 and the cathode plate 3 with the positive electrode and the negative electrode of the direct current power supply 1 through leads, and respectively fixing the anode plate 2 and the cathode plate 3 in an anode end solution loading tank 4 and a cathode end solution loading tank 5;
s5: 800ml of a 0.3mol/L NaOH aqueous solution was poured into the anode side solution-charging tank 4, and 800ml of a 0.5mol/LNa aqueous solution was poured into the cathode side solution-charging tank 52SO40.3mol/LNaOH solution, and completely submerged in the anode plate 2, cathode plate 3 and test coupon 7;
s6: setting the working voltage to be 30 +/-0.2V, switching on a switch of a direct current power supply 1, continuously measuring the concentration of sulfate ions in the solution loading tank 4 at the anode end after electrifying, and cutting off the power supply after electrifying for 168 hours; obtaining a sulfate ion concentration curve, and obtaining the initial time t of sulfate ion diffusion and permeation according to curve fitting0(ii) a The test is carried out at room temperature (20 ℃), and after the test is finished, the power supply is turned off and the sample is taken out.
S7: calculating the diffusion coefficient of sulfate ions: according to the Nernst-Einstein equation
And
to obtain
Wherein d is the thickness of the test specimen, R is the gas constant, T is the temperature, F is the Faraday constant, E is the electric field strength, z is the charge number, T is0Is the initial time for diffusion and permeation of sulfate ions.
The mortar M1 test piece is prepared by adopting 450g of cement, 1350g of sand and 0.5 water-cement ratio. Table 1 shows the mixing ratio of the concrete test pieces, and table 2 shows the sulfate ion diffusion coefficient of each test piece measured by the above method.
TABLE 1
Measuring the sulfate ion diffusion coefficient of mortar and concrete, and measuring the initial time t of sulfate ion diffusion and penetration of a mortar M1 test piece0For 420min (as shown in FIG. 2), the calculated sulfate ion diffusion coefficient is as follows:
Initial time t of sulfate ion diffusion and permeation of concrete C1 test piece0For 1250min (as shown in fig. 3), the calculated sulfate ion diffusion coefficient is as follows:
TABLE 2
| Numbering | t0(min) | 28 days sulfate ion diffusion coefficient (10)-11m2/s) |
| M1 | 420 | 2.69 |
| C1 | 1250 | 2.26 |
| C2 | 1347 | 2.09 |
| C3 | 1469 | 1.92 |
| C4 | 1398 | 2.02 |
Due to the lack of similar sulfate ion diffusion coefficient evaluation methods, the accuracy of sulfate ion diffusion coefficient test data or calculation results cannot be directly compared, and the accuracy of sulfate ion diffusion coefficient test can only be indirectly evaluated through the concrete pore structure performance. The embodiment of the invention adopts common concrete, fly ash, slag and silica fume-doped concrete, and measures the diffusion coefficient of sulfate ions in 28 days. Mineral admixtures such as fly ash, slag and silica fume in the concrete are beneficial to the refinement of the concrete structure and reduce the porosity, thereby reducing the diffusion of sulfate ions.
The concrete pore structure characterization method adopts a mercury intrusion method and a nitrogen adsorption method for characterization. In the past, concrete diffusion characteristics are tested, chloride ion diffusion coefficients are calculated and characterized more, and research results of consistency of porous structure performance and chloride ion diffusion coefficients are found in many documents. The structural performance or compactness of concrete pores has a direct relation with ion diffusion, the fewer the pores are, the smaller the pore size is, the denser the structure is, the more difficult the ions are to diffuse by permeation (chloride ions, calcium ions and sulfate ions have the same rule), and the smaller the diffusion coefficient is, so that the influence relation between the structural performance of the pores and the diffusion coefficient can be directly judged.
The ion diffusion coefficient has a certain relation with the concrete pore structure, and the concrete is doped with admixtures such as fly ash, slag, silica fume and the like, so that the concrete pore structure is refined, and the ion permeation diffusion is reduced. As can be seen from table 2, the diffusion coefficient of sulfate ions in concrete: the slag-doped concrete C3, the silica-doped concrete C4, the fly ash-doped concrete C2, the common concrete C1 and the mortar M1 show that the admixture is beneficial to inhibiting the diffusion and permeation of sulfate ions in the concrete and reducing the diffusion coefficient, and the test result is consistent with the characterization of the concrete performance and has regularity and accuracy.
The invention provides a device and a method for measuring diffusion coefficient of sulfate ions in mortar and concrete, and a method and a way for implementing the method, and the above description is only a preferred embodiment of the invention, and it should be noted that, for those skilled in the art, a plurality of improvements and decorations can be made without departing from the principle of the invention, and these improvements and decorations should be regarded as the protection scope of the invention. All the components not specified in the present embodiment can be realized by the prior art.
Claims (9)
1. A device for measuring diffusion coefficients of sulfate ions in mortar and concrete is characterized by comprising a direct-current power supply (1), an anode plate (2), a cathode plate (3), an anode end solution loading groove (4), a cathode end solution loading groove (5) and a test piece loading groove (6);
the anode end solution loading tank (4) is filled with a sodium hydroxide aqueous solution, and the anode plate (2) is positioned in the anode end solution loading tank (4) and is immersed in the sodium hydroxide aqueous solution;
the cathode end solution loading tank (5) is filled with a mixed aqueous solution of sulfate and sodium hydroxide, and the cathode plate (3) is positioned in the cathode end solution loading tank (5) and is immersed in the mixed aqueous solution of sulfate and sodium hydroxide;
the test piece loading groove (6) is used for placing a test piece (7) and is positioned between the anode end solution loading groove (4) and the cathode end solution loading groove (5), and two ends of the test piece loading groove are respectively communicated with the anode end solution loading groove (4) and the cathode end solution loading groove (5);
the anode plate (2) and the cathode plate (3) are respectively connected with the positive electrode and the negative electrode of the direct current power supply (1) through conducting wires.
2. The device for measuring the diffusion coefficient of sulfate ions in mortar and concrete according to claim 1, wherein the anode end solution loading tank (4) and the cathode end solution loading tank (5) are both right-angled bent pipes, and the test piece loading tank (6) is a straight pipe;
the top end openings of the anode end solution loading tank (4) and the cathode end solution loading tank (5) are respectively used for connecting the corresponding anode plate (2) and cathode plate (3) with the positive and negative electrodes of the direct current power supply (1) through leads, and the bottom end openings are respectively fixed with the two end openings of the test piece loading tank (6).
3. The device for measuring the diffusion coefficient of sulfate ions in mortar and concrete according to claim 2, wherein the anode plate (2) and the cathode plate (3) are both thin iron plates, and the tops of the thin iron plates are respectively connected with the positive electrode and the negative electrode of the direct current power supply (1) through leads.
4. The sulfate ion diffusion coefficient measuring device of mortar and concrete according to claim 2, wherein the side surface of the test piece (7) is coated with a layer of epoxy resin, and is attached to the inner wall of the test piece loading groove (6) and sealed by epoxy resin; the two surfaces of the test piece (7) contacting the solution are both flat surfaces.
5. The device for measuring the diffusion coefficient of sulfate ions in mortar and concrete according to claim 2, wherein the solution loading tank (4) at the anode end and the solution loading tank (5) at the cathode end are both right-angled bends made of PVC; the test piece loading groove (6) is a straight hose made of silicon rubber.
6. A method for determining the diffusion coefficient of sulfate ions in mortar and concrete using the apparatus of claim 1, comprising the steps of:
s1: cutting the mortar and concrete test block cured to the age into a test specimen (7) with the same section as that of the specimen loading groove (6), and simultaneously ensuring that the cut surface is flat;
s2: uniformly coating a layer of epoxy resin on the side surface of the obtained test piece (7) and standing and curing the epoxy resin, and then placing the test piece (7) in the middle of the test piece loading groove (6) to ensure that the side surface of the test piece (7) is attached to the inner wall of the test piece loading groove (6), and the sections at two ends are parallel to the openings at two ends of the test piece loading groove (6); epoxy resin is sucked by a needle cylinder and evenly smeared on the inner contact surface of the side surface of the test specimen (7) and the specimen loading groove (6), so that the side surface of the specimen is ensured to be sealed;
s3: two ends of a test piece loading groove (6) loaded with a test piece (7) are opened and are respectively fixed and communicated with an anode end solution loading groove (4) and a cathode end solution loading groove (5);
s4: respectively connecting the anode plate (2) and the cathode plate (3) with the positive electrode and the negative electrode of the direct current power supply (1) through leads, and respectively fixing the anode plate (2) and the cathode plate (3) in an anode end solution loading tank (4) and a cathode end solution loading tank (5);
s5: injecting a sodium hydroxide aqueous solution into the anode end solution loading tank (4), injecting a mixed aqueous solution of sulfate and sodium hydroxide into the cathode end solution loading tank (5), and completely submerging the anode plate (2), the cathode plate (3) and the test specimen (7);
s6: setting working voltage, switching on a direct current power supply (1) switch, continuously measuring the concentration of sulfate ions in the anode end solution loading tank (4) after electrifying, and obtaining the initial time t of sulfate ion diffusion and permeation according to curve fitting by drawing a sulfate ion concentration curve0；
S7: calculating the diffusion coefficient of sulfate ion
Wherein d is the thickness of the test specimen, R is the gas constant, T is the temperature, F is the Faraday constant, E is the electric field strength, z is the charge number, T is0Is the initial time for diffusion and permeation of sulfate ions.
7. The method for determining the diffusion coefficient of sulfate ions in mortar and concrete according to claim 6, wherein in step S5, the concentration of the aqueous solution of sodium hydroxide is 0.1-1.0 mol/L; in the mixed water solution of the sulfate and the sodium hydroxide, the concentration of the sulfate is 0.1-1.0mol/L, and the concentration of the sodium hydroxide is 0.1-1.0 mol/L.
8. The method for determining the diffusion coefficient of sulfate ions in mortar and concrete according to claim 6, wherein in step S6, the operating voltage is 30-60V.
9. The method for determining the diffusion coefficient of sulfate ions in mortar and concrete according to claim 6, wherein the determination of the experimental temperature T is carried out at 5 to 45 ℃.
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