CN109946414B - Method for representing amount of combined chloride ions by using content of cement-based material oxide - Google Patents
Method for representing amount of combined chloride ions by using content of cement-based material oxide Download PDFInfo
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- CN109946414B CN109946414B CN201910235806.1A CN201910235806A CN109946414B CN 109946414 B CN109946414 B CN 109946414B CN 201910235806 A CN201910235806 A CN 201910235806A CN 109946414 B CN109946414 B CN 109946414B
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Abstract
The invention discloses a method for representing the amount of combined chloride ions by using the content of cement-based material oxides, which comprises the following steps: firstly, slag and/or fly ash are added into portland cement to prepare cement paste samples with different oxide compositions, the cement paste samples are soaked in different salt solutions, the chloride ion adsorption capacity of each sample is tested by an isothermal adsorption method, so that a series of chloride ion binding capacities under different oxide content compositions are obtained, a ternary linear relation between the chloride ion binding capacities and the samples is fitted by software, a method for representing the binding capacity of chloride ions by using the oxide content is realized, and therefore, cement-based materials which can maximally bind the chloride ions and are composed of different oxides are prepared under the same external condition.
Description
Technical Field
The invention belongs to the field of cement-based materials, and particularly relates to a method for representing chloride ion binding capacity by using the content of an oxide of a cement-based material.
Background
The cement-based material is widely applied in production and life, but under the chloride salt environmental conditions of oceans, deicing salts, salt lakes and the like, reinforced concrete faces a serious problem of chloride ion corrosion, and the corrosion of steel bars caused by the corrosion is one of the most important reasons for the failure of concrete structures. Therefore, the durability of the concrete structure in the chlorine salt environment is a major concern.
Research shows that when the content of chloride ions in the reinforced concrete pore solution reaches critical concentration, a passive film on the surface of a reinforcing steel bar can be damaged, the reinforcing steel bar is corroded, and concrete cracks and even the whole structure is damaged. The chloride ions exist in the concrete in two forms of free chloride ions and combined chloride ions, steel bar corrosion can be caused and accelerated only when the concentration of the free chloride ions reaches a critical value, and the combined chloride ions have no influence on the steel bar corrosion.
The current research considers that the combination of chloride ions is divided into two modes of chemical combination and physical adsorption: the chemical combination mainly refers to the process of combining aluminum phase in cement clinker or AFm phase in hydration product with chloride ion to generate Friedel salt, and the process is rooted in the end and Al in raw materials2O3The amount of (c) is closely related; the physical adsorption mainly refers to the process of physically adsorbing chloride ions by various hydration products of the cementing material. The method for improving the chloride ion binding capacity of the cement-based material by doping the mineral admixture is always concerned, and the research focuses on the particle size, the shape, the structure and the like of the doped mineral, but the influence of the doped mineral on the chloride ion of the cement-based material is not further researched, so that the reinforcement corrosion in the doped cement-based material is neglected by the existing research.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the problems in the prior art, the invention provides a method for representing the chloride ion binding capacity by using the oxide content of a cement-based material, which is used for preparing the cement-based material resistant to chloride corrosion under the same condition.
The technical scheme is as follows: the invention discloses a method for characterizing the amount of bound chloride ions by using the content of cement-based material oxides, which comprises the following steps:
(1) preparing cement-based materials containing different oxide contents by adding slag and/or fly ash, wherein in the cement-based materials, Al2O3、SiO2The total amount of the CaO and the calcium oxide accounts for 85-90% of the mass of the cement-based material, the mixture is crushed to a specified size after forming and curing, and the moisture is removed and dried;
(2) weighing the crushed cement-based material, and placing the crushed cement-based material in a sealed bottle containing a salt solution to achieve adsorption balance;
(3) filtering and collecting the soak solution in the sample bottle, and sealing and storing;
(4) determining the amount of bound chloride ions in the sample;
(5) calculating the oxide content of the cement-based material in the step (1), obtaining the binding capacity of the cement-based material with different oxide contents and corresponding chloride ions, and establishing a sample chloride ion binding capacity CbWith oxide content chi1，χ2Hexix-3The relationship between the three elements is as follows:
Cb＝A×χ1+B×χ2+C×χ3+D
wherein C isbIs the combination amount of chloride ions of cement-based materials, chi1Represents Al2O3Based on the total mass of the cement-based material, chi2Represents SiO2Based on the total mass of the cement-based material, chi3Expressing the percentage of CaO in the total mass of the cement-based material;
(6) fitting Al through different oxide contents and corresponding chloride ion binding amounts in the step (5)2O3Correlation coefficient A, SiO of content and chloride ion binding capacity2And measuring the content of the oxide in the cement-based material through an obtained equation to determine the chloride ion binding capacity of the cement-based material, wherein the content of the correlation coefficient B, CaO of the content and the chloride ion binding capacity, the chloride ion binding capacity C of the cement-based material and a constant D are obtained.
The invention researches the binding capacity of the cement-based material to chloride ions from the aspect of chemical composition, and discovers the binding capacity of the chloride ions and Al in the cement-based material2O3、SiO2Is closely related to the content of CaO, overcomes the defect that only the combination amount of chloride ions and Al are studied in the prior art2O3Without considering the combination amount of the chlorine ions and the shortage of the three oxides involved in the reaction. The invention uses the oxide content of the cement-based material to represent the chloride ion binding capacity, and then reasonably configures the cement-based material with corresponding oxide content according to different salt solutions, thereby improving the chloride ion corrosion resistance of the reinforced concrete and prolonging the service life of the reinforced concrete.
In the step (1), the particle size range of the crushed cement-based material is 0.25 mm-2.00 mm. The invention breaks the cement-based material and eliminates the influence of chloride ions in the aperture of the cement-based material, because the adsorption capacity of the aperture wall to the chloride ions is very small and can be ignored, and the content of the chloride ions adsorbed by the cement-based material is obtained on the premise of not considering the transmission and diffusion of the chloride ions.
In the step (1), the drying is carried out in a vacuum drying oven, the vacuum degree is-1 MPa to-2 MPa, the drying temperature is 20 +/-1 ℃, and the drying time is 3-4 d.
In the step (2), the salt solution is a chloride salt solution prepared by saturated calcium hydroxide and a chloride salt and sulfate salt solution.
In the step (4), the measuring method of the chloride ion amount is an isothermal adsorption method, and the specific measuring method refers to the standard 'test procedure for concrete for water transportation engineering' (JTJ 270-98).
In the step (1), the water cement ratio of the cement-based material is 0.25-0.5.
In the step (1), the Al is2O3、SiO2The total amount of the CaO and the Al accounts for 85-90% of the mass of the cement-based material2O3The content of SiO accounts for 5-15% of the mass of the cement-based material2The content of the CaO is 20-30% of the mass of the cement-based material, and the content of the CaO is 45-65% of the mass of the cement-based material.
In the step (1), the water cement ratio of the cement-based material is 0.48-0.5.
Has the advantages that: (1) the invention simultaneously considers Al2O3、SiO2And the influence of the content of CaO on the chloride ion binding capacity, obtaining the relation between the chloride ion binding capacity and the oxide, obtaining the cement-based material with the maximum chloride ion capacity, and providing theoretical reference for better preparing the chloride ion binding capacity consisting of any oxide content under the same condition of the concrete resistant to chloride salt erosion; (2) the method eliminates the influence of pore structure and ion transmission, considers the essential problem of chloride ion combination from the chemical component perspective, obtains more essential significance of chloride ion combination amount, and is simple and easy to obtain.
Drawings
FIG. 1 is a graph of oxide content versus chloride ion binding for example cement-based materials soaked in chloride solution 28d for a curing age of 28 d.
FIG. 2 is a graph of oxide content versus chloride ion binding for example cement-based materials having a curing age of 28 days soaking in a chloride plus sulfate solution 28 d.
FIG. 3 is a flow chart of the method of the present invention.
Detailed Description
Firstly, preparing raw materials
1.1 preparation of Cement-based materials
Because the slag and the fly ash are beneficial to improving the anti-chlorine salt erosion performance and are most widely used, the method selects the two mineral admixtures to replace part of cement, researches the relation between the oxide content and the chloride ion binding capacity of the cement-based material, and the specific sample preparation method comprises the following steps: the process of the present invention is illustrated with a neat paste sample as a typical cement-based material. Ordinary portland cement (C) with the reference number of 52.5 is selected, 10%, 30% and 50% of fly ash (FA, F type i low-calcium fly ash) and 10%, 30% and 50% of slag (BS, S95 slag) are added to the ordinary portland cement (C), a cement paste sample with the water-cement ratio of 0.48 is prepared, and the cement paste sample is tested after standard curing for 28 days.
1.2 preparing saturated calcium hydroxide solution, preparing chlorine salt solution by using the prepared saturated calcium hydroxide solution, and respectively preparing 1mol/L NaCl solution, 1mol/L NaCl solution and 0.35mol/L Na2SO4The mixed salt solution simulates different water body environments.
Determination of the amount of bound chloride ion
Example 1:
step 1: and wiping and crushing the surface water of the maintained cement-based material into particles to obtain a particle sample with the particle size range of 0.25-2.00 mm. Placing the crushed granular sample with the specified size into a vacuum drying oven with the vacuum degree of-1 MPa and the temperature of 20 +/-1 ℃, drying to remove water to ensure that the quality of the granular sample is constant, then placing the granular sample into a dryer filled with silica gel and soda lime for continuous drying, and storing to remove CO in the air2。
Step 2: weighing 10g of the treated sample, placing the sample in a sealed bottle, transferring 20ml of a chloride solution prepared by saturated calcium hydroxide by using a pipette, wherein the concentration of the chloride solution is 1mol/L, and standing and soaking the sample at normal temperature for 28 days to achieve adsorption balance.
And step 3: and filtering the soaking solution which reaches the balance in the sample bottle, and collecting, sealing and storing.
And 4, step 4: the amount of bound chloride ions in the sample was determined by isothermal adsorption.
And 5: in the solution with the concentration of the chloride salt solution of 1mol/L, only Al is changed2O3、SiO2And influence of the contents of the three oxides including CaO on the chloride ion binding capacity of the cement-based material, firstly calculating the oxide content of each sample in the step 1, and using chi1Represents Al2O3Content, χ2Represents SiO2Content, χ3Represents CaO content (85%<χ1+χ2+χ3<90%) to obtain a series of different oxide contents and corresponding chloride ion binding capacities (see table 1). Establishing the chloride ion binding capacity C of the samplebWith oxide content chi1，χ2Hexix-3Ternary linear relationship between Cb＝A×χ1+B×χ2+C×χ3+ D. Substituting the series of different oxide contents and corresponding chloride ion binding amounts, and obtaining coefficients A, B, C and D through software fitting to obtain a complete equation:
Cb＝21.683×χ1+91.964×χ2-23.291×χ3+7.810
then, knowing the oxide content composition of a certain cement-based material, knowing the maximum chloride ion binding capacity of the material under the corrosion of 1mol/L NaCl solution according to a formula, and obtaining the proportion of the oxide content according to the expected chloride ion binding capacity, wherein in the figure 1, the cement-based material cured for 28d can be intuitively obtained, and after being soaked in 1mol/L chloride salt solution for 28d, the chloride ion binding capacity and the Al content are2O3、SiO2The content is in direct proportion relation and in inverse proportion relation with the CaO content, and Al is correspondingly improved when the cement-based material is prepared2O3、SiO2The content of (3) can increase the binding amount of the chloride ions.
Example 2:
step 1: and wiping and crushing the surface water of the maintained cement-based material into particles to obtain a particle sample with the particle size range of 0.25-2.00 mm. Placing the crushed granular sample into a vacuum drying oven with vacuum degree of-1 MPa and temperature of 20 + -1 deg.C, drying to remove water to make the quality of the granular sample constant, placing the granular sample into a drier filled with silica gel and soda lime, drying, and storing for 2 days to remove CO in air2。
Step 2: weighing 10g of the treated sample, placing the sample in a sealed bottle, and transferring 20ml of a compound salt solution prepared from a saturated calcium hydroxide solution by using a pipette, wherein the solution comprises 1mol/L NaCl solution and 0.35mol/L Na2SO4And (5) standing the solution at normal temperature and soaking for 28d to achieve adsorption equilibrium.
And step 3: and filtering the soaking solution which reaches the balance in the sample bottle, and collecting, sealing and storing.
And 4, step 4: the amount of bound chloride ions in the sample was determined by isothermal adsorption.
And 5: calculating the oxide content of each sample in the step 1, and using chi1Represents Al2O3Content, χ2Represents SiO2Content, χ3Represents CaO content (85%<χ1+χ2+χ3<90%) were obtained in a series of different oxide contents and corresponding chloride ion binding capacities (see table 1). Establishing the chloride ion binding capacity C of the samplebWith oxide content chi1，χ2Hexix-3Ternary linear relationship between Cb＝A×χ1+B×χ2+C×χ3+ D. Substituting the series of different oxide contents and corresponding chloride ion binding amounts, and obtaining coefficients A, B, C and D through software fitting to obtain a complete equation:
Cb＝47.453×χ1+75.486×χ2-26.165×χ3+4.437
then the oxide content composition of a certain cement-based material is known, and 1mol/L NaCl solution and 0.35mol/L Na solution can be known according to the formula2SO4Maximum of this material under solution attackThe content of the oxide can be obtained according to the expected chloride ion binding amount.
As can be seen from FIG. 2, the cement-based material cured for 28 days was soaked in 1mol/L NaCl solution and 0.35mol/L Na2SO4After mixing the solution 28d, the combined amount of chloride ions and Al2O3、SiO2The content is in a direct proportion relation and in an inverse proportion relation with the CaO content. When the cement-based material is prepared, Al is correspondingly improved2O3、SiO2The content of (3) can increase the binding amount of the chloride ions.
TABLE 1 oxide content and chloride ion binding amount in each sample
The invention considers the essential problem of chloride ion combination from the aspect of chemical components, namely the oxide which has the most important influence on the adsorption capacity of the chloride ions of the cement-based material, does not consider the problems of pore structure and ion transmission, obtains the chloride ion combination amount, establishes the essential relation between the oxide content of the admixture and the chloride ion combination amount, and is used as reference for preparing the cement-based material with chloride corrosion resistance under the same condition.
In summary, the present invention is only a specific embodiment, but the scope of the present invention is not limited thereto, and any person skilled in the art can be covered within the scope of the present invention without any changes or substitutions that may be conceived by inventive efforts within the technical scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope defined by the claims.
Claims (4)
1. A method for characterizing the amount of bound chloride ions using the oxide content of a cement-based material, comprising the steps of:
(1) by adding slag and/orPreparing cement-based material containing different oxide contents with fly ash, wherein Al in the cement-based material2O3、SiO2The total amount of the CaO and the calcium oxide accounts for 85-90% of the mass of the cement-based material, the mixture is crushed to a specified size after forming and curing, and the moisture is removed and dried; the Al is2O3、SiO2The total amount of the CaO and the Al accounts for 85-90% of the mass of the cement-based material2O3The content of SiO accounts for 5-15% of the mass of the cement-based material2The content of the CaO is 20-30% of the mass of the cement-based material, and the content of the CaO is 45-65% of the mass of the cement-based material; the crushed cement-based material has a particle size range of 0.25 mm-2.00 mm;
(2) weighing the crushed cement-based material, and placing the crushed cement-based material in a sealed bottle containing a salt solution to achieve adsorption balance; the salt solution is a chlorine salt solution prepared by saturated calcium hydroxide and a chloride salt and sulfate solution;
(3) filtering and collecting the soak solution in the sample bottle, and sealing and storing;
(4) determining the amount of bound chloride ions in the sample; the measuring method of the chloride ion amount is an isothermal adsorption method;
(6) fitting Al through different oxide contents and corresponding chloride ion binding amounts in the step (5)2O3Correlation coefficient A, SiO of content and chloride ion binding capacity2And measuring the content of the oxide in the cement-based material through an obtained equation to determine the chloride ion binding capacity of the cement-based material, wherein the content of the correlation coefficient B, CaO of the content and the chloride ion binding capacity, the chloride ion binding capacity C of the cement-based material and a constant D are obtained.
2. The method for characterizing the amount of the bound chloride ions by using the oxide content of the cement-based material in the claim 1, wherein in the step (1), the drying is drying in a vacuum drying oven, the vacuum degree is-1 MPa to-2 MPa, the drying temperature is 20 +/-1 ℃, and the drying time is 3-4 d.
3. The method for characterizing the amount of the bound chloride ions by using the oxide content of the cement-based material according to claim 1, wherein in the step (1), the water cement ratio of the cement-based material is 0.25-0.5.
4. The method for characterizing the amount of the bound chloride ions by using the oxide content of the cement-based material according to claim 3, wherein in the step (1), the water cement ratio of the cement-based material is 0.48-0.5.
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