Method for judging service life of concrete based on saline invasion

Abstract

The invention discloses a method for judging the service life of concrete based on brine intrusion, and relates to the technical field of concrete salt prevention. On the basis of the basic principle of a chloride ion transmission model in concrete, the model is optimized, so that the chloride ion diffusion coefficient of the concrete to be predicted can be accurately obtained, and the accuracy of concrete service life prediction is remarkably improved; meanwhile, a relation function between the concrete surface chloride ion concentration and the age attenuation coefficient is obtained through an experiment, so that the service life range of the concrete can be accurately determined according to the value range of the age attenuation coefficient of the concrete, and a reference range is provided for the design of the service life of the concrete; the method is favorable for optimal design of a concrete formula and is suitable for large-scale application to judgment of the service life of saline water invaded concrete.

Description

Technical Field

[0001] The present invention relates to the technical field of seawater intrusion prevention and control, in particular to the technical field of concrete anti-salinity, and in particular to a method for judging the service life of concrete based on saltwater intrusion. Background Art

[0002] According to domestic and foreign statistics, the economic losses caused by structural corrosion and durability diseases are huge. From the 1970s to the 1980s, the economic losses caused by structural corrosion in the United States reached 70 billion to 168 billion US dollars. The 11 reinforced concrete viaducts on the central ring expressway of the Isle of England, UK, cost 28 million pounds to build, and the cost of repair due to corrosion was 45 million pounds, about 1.6 times the initial cost; in the subsequent 15 years, it continued to cost about 120 million pounds, which is close to 6 times the original project cost. Foreign scholars use the "five-fold law" to quantitatively describe the importance of considering structural durability in the design stage, that is, if $1 is saved in anti-corrosion / protection during the structural design stage, then when steel corrosion is found, remedial measures will add $5 in repair costs; when concrete cracks along the reinforcement, additional measures will add $25 in repair costs; when the structure suffers serious durability damage, additional measures will add $125 in repair costs. It can be seen that in the corrosive environment of seawater intrusion, the durability of concrete structures should be taken seriously during the design process, otherwise the economic losses caused by repairs and reinforcements during the later operation and maintenance process will be difficult to estimate. The service life prediction of the designed concrete structure in the saltwater intrusion environment is one of the main means to judge whether the concrete anti-salinity measures meet the design requirements, which is of great significance to the design and construction of concrete anti-salinity structures.

[0003] In the prior art, there are a variety of methods for predicting and judging the service life of concrete, but most of the existing methods cannot accurately judge the service life of concrete in a saltwater intrusion environment. In addition, the methods are complex and have poor operability, and are not suitable for large-scale judgment and prediction of the service life of concrete in a saltwater intrusion environment. Summary of the invention

[0004] The purpose of the present invention is to propose a method for predicting the service life of concrete based on salt water intrusion, which is targeted at the defect that the existing method for predicting the service life of concrete is poor in accuracy when used to judge the service life of concrete under salt water intrusion environment.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides a method for judging the service life of concrete based on salt water intrusion, comprising the following steps:

[0006] S1. Prepare a concrete specimen using the concrete to be predicted, and obtain basic parameters of the concrete specimen;

[0007] S2. Based on the basic parameters of the concrete specimen, obtain the relationship function between the chloride ion concentration on the concrete surface and the age attenuation coefficient;

[0008] S3, determining the design thickness and critical chloride ion concentration of the concrete to be predicted, and then obtaining the relationship function between the predicted service life and the age attenuation coefficient of the concrete based on the chloride ion transmission optimization model in the concrete;

[0009] S4. Based on the value of the age attenuation coefficient, the predicted service life of the concrete is obtained.

[0010] The invention discloses a method for judging the service life of concrete based on salt water intrusion. The method is based on the basic principle of the chloride ion transmission model in concrete, and not only optimizes the model, so as to accurately obtain the chloride ion diffusion coefficient of the concrete to be predicted, and significantly improves the accuracy of the prediction of the service life of the concrete; at the same time, the relationship function between the chloride ion concentration on the surface of the concrete and the age attenuation coefficient is obtained through experiments, so as to accurately determine the service life range of the concrete according to the value range of the concrete age attenuation coefficient, thereby providing a reference range for the design of the service life of the concrete, facilitating the optimization design of the concrete formula, and being suitable for large-scale application in judging the service life of the salt water intrusion concrete.

[0011] Wherein, in step S1, preferably, the basic parameters of the concrete specimen include initial age of concrete, initial chloride ion concentration of concrete and initial chloride ion diffusion coefficient.

[0012] Preferably, the initial chloride ion concentration of the concrete is measured using a rapid chloride ion content tester.

[0013] Preferably, the initial diffusion coefficient of chloride ions is measured by a natural diffusion method.

[0014] Wherein, in step S2, preferably, the method for obtaining the relationship function between the chloride ion concentration on the concrete surface and the age attenuation coefficient comprises the following steps:

[0015] (1) Pre-treat the concrete specimens;

[0016] (2) subjecting the pretreated concrete specimens to a saltwater intrusion test based on the predicted use environment of the concrete;

[0017] (3) Grinding and sampling the concrete specimens after the saltwater intrusion test layer by layer along the saltwater diffusion depth direction to obtain concrete sample powders with different exposure times and different grinding depths;

[0018] (4) After the concrete sample powder is sieved and dried, the chloride ion concentration in the different concrete sample powders is measured;

[0019] (5) Based on the chloride ion concentration in the concrete sample powder, the chloride ion transport model was used for regression fitting analysis to obtain the fitting equation of the chloride ion concentration on the concrete surface and the age attenuation coefficient, which is the relationship function between the chloride ion concentration on the concrete surface and the age attenuation coefficient.

[0020] Wherein, in step (1), preferably, the pretreatment is to apply epoxy resin on the five non-diffusion surfaces of the concrete specimen and air-dry them to form a sealed epoxy resin layer; through the pretreatment, it can be ensured that chloride ions only invade one surface of the concrete specimen (one-dimensional corrosion).

[0021] Wherein, in step (2), preferably, the mixed brine has a mass concentration that is the same as the brine concentration of the brine intrusion.

[0022] Preferably, the time of the salt water intrusion test is 30d, 60d, 100d, 150d and 200d.

[0023] Wherein, in step (3), preferably, when grinding and sampling layer by layer, each 2 mm depth is considered as one layer, and the number of sampling layers is not less than 10 layers.

[0024] Wherein, in step (4), preferably, the particle size of the sieved concrete sample powder is not greater than 0.63 mm.

[0025] Preferably, the drying temperature is 105±5° C. and the drying time is 1.5-2.5 h.

[0026] Preferably, the test method for the chloride ion concentration in concrete sample powder comprises: stirring and soaking a certain amount of concrete sample powder with distilled water, taking the supernatant and measuring it with a rapid chloride ion content tester; wherein the stirring time is not less than 20 minutes, and the soaking time is not less than 1 hour.

[0027] Wherein, in step (5), preferably, the chloride ion transport model is:

[0028]

[0029] Where: C 0 Indicates the initial concentration of chloride ions in concrete (%); C s Indicates the chloride ion concentration on the concrete surface (%); t 0 represents the initial age; t represents the exposure time; x represents the chloride ion diffusion depth (mm); C(x,t) represents the chloride ion concentration at the depth x in the concrete specimen at time t (%); D(t) represents the chloride ion diffusion coefficient at time t; n is the age attenuation coefficient, erf is the error function, and D 0 is the initial diffusion coefficient of chloride ions.

[0030] Wherein, in step S3, preferably, the critical chloride ion concentration of the concrete is obtained by detecting by a dynamic potentiometry method or an electrostatic potential method based on the initial rust criterion of steel bars and the environmental action level of salt water intrusion.

[0031] Preferably, the environmental impact level is determined based on GB 50476-2008.

[0032] Preferably, the optimization model for chloride ion transmission in concrete is:

[0033]

[0034] Among them, C 0 Indicates the initial chloride ion concentration in concrete (%); C s Indicates the chloride ion concentration on the concrete surface (%); t 0 represents the initial age of concrete; t represents the service life; x represents the thickness of concrete (mm); C(x,t) represents the critical chloride ion concentration of concrete (%); D(t) represents the chloride ion diffusion coefficient at time t; n is the age attenuation coefficient; erf is the error function, D 0 is the initial diffusion coefficient of chloride ions; D is the diffusion coefficient of chloride ions during service; K e With K c They are the environmental coefficient and the curing coefficient respectively; T is the absolute temperature (K); U is the activation energy in the diffusion process, which is related to the water-cement ratio of concrete; and R is the molar gas constant.

[0035] Among them, in step S4, preferably, the value of the age attenuation coefficient is based on the relevant provisions of DB 45 / T 1828-2018; specifically: when the concrete to be predicted uses silicate cement concrete, the age attenuation coefficient n=0.23; when the concrete to be predicted uses mineral admixture concrete, the age attenuation coefficient ranges from n=0.48 to 0.67.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. The method for judging the service life of concrete based on salt water intrusion of the present invention is based on the basic principle of the chloride ion transmission model in concrete, and not only optimizes it, so as to accurately obtain the chloride ion diffusion coefficient of the concrete to be predicted, but also significantly improves the accuracy of concrete service life prediction.

[0038] 2. The method for judging the service life of concrete based on salt water intrusion of the present invention is based on the basic principle of the chloride ion transmission model in concrete. The relationship function between the chloride ion concentration on the concrete surface and the age attenuation coefficient is obtained through experiments. Therefore, the service life range of the concrete can be accurately determined according to the value range of the concrete age attenuation coefficient, thereby providing a reference range for the design of the service life of the concrete, which is beneficial to the optimal design of the concrete formula and is suitable for large-scale application in judging the service life of concrete invaded by salt water. DETAILED DESCRIPTION

[0039] The present invention is further described in detail below in conjunction with specific embodiments. However, it should not be understood that the scope of the above subject matter of the present invention is limited to the following embodiments, and all technologies realized based on the content of the present invention belong to the scope of the present invention.

[0040] Embodiment 1:

[0041] A method for judging the service life of concrete (ship lock concrete, in a 1:1 dry-wet alternating environment, an ambient temperature of 20-35°C, and a salt water concentration of 10‰) based on salt water intrusion, comprising the following steps:

[0042] S1. Prepare a concrete specimen using the concrete to be predicted, and obtain basic parameters of the concrete specimen;

[0043] (1) Determine the raw materials and mix ratio of concrete specimens;

[0044] The raw materials and mix ratio of concrete to be predicted are:

[0045] Raw material types cement Fly ash Mineral powder sand gravel water Water reducing agent <![CDATA[1m 3 Amount of raw materials used for concrete (kg)]]> 189 130 72 788 1089 150 11.7

[0046] ; Cement is PO.42.5 ordinary Portland cement from the same batch; Fly ash is Class F I, fineness 10.1%, water requirement ratio 93.6%; Mineral powder is S95, 7d activity index not less than 78%, 28d activity index not less than 100%, specific surface area 436m 2 / kg; the apparent density of sand is 2.61×10 3 kg / m 3 Continuously graded natural river sand; the crushed stone has an apparent density of 2.69×10 3 kg / m 3 , continuous graded natural crushed stone with a nominal particle size of 5 to 40 mm; the water reducing agent has a water reducing rate of 10% to 18%; the water is ordinary tap water;

[0047] (2) Mixing of raw materials;

[0048] The concrete specimens were prepared by machine mixing. The mixing process of the mixture included: wetting the inside of the concrete mixer with a wet cloth, pouring fine aggregate (river sand), fly ash, mineral powder and other raw materials into it, adding coarse aggregate (natural crushed stone) after stirring for 30 seconds, and slowly adding the water reducer and mixing water together after stirring for 2 minutes and stirring for 3 minutes. After the mixing is completed, the mixture in the mixer is poured onto the mixing board.

[0049] (3) Moulding and shaping of the mixture;

[0050] Check carefully beforehand 100×100×100mm 3 Check whether the appearance of the standard plastic mold of concrete is intact, brush the inside and let it air dry; before the mixture is molded, a layer of mineral grease should be applied to the side wall and bottom of the plastic mold to facilitate the demolding of cement mortar and concrete specimens; put the evenly mixed mixture into the plastic mold, and place the specimen and the mold (referred to as: test mold) on a vibration table for compaction; when using a vibration table to mold concrete specimens, the concrete mixture can be loaded into the test mold at one time, and there should be a little surplus when loading; during the vibration process, the test mold should be prevented from jumping freely on the vibration table. According to the provisions of the "Test Procedures for Concrete in Water Transport Engineering (JTJ 270-1998)", the vibration time should be at least enough to allow the surface to slurry out, vibrate and form;

[0051] (4) Maintenance of specimens;

[0052] After each molded test mold is covered with a plastic film coated with mineral grease, it is then covered with a clean rag soaked in distilled water (to prevent water loss); then, the test mold is placed in a standard concrete curing box with an ambient temperature of 20±5℃ and a relative humidity of more than 50% for initial setting curing for 24 hours;

[0053] After the initial setting and curing is completed, the test specimens have achieved initial strength. Take out the test mold, carefully peel off the wet cloth and plastic film on its surface, and demold all the test specimens; then, immediately move the demolded test specimens into a saturated Ca(OH) 2 The concrete specimens were cured in the solution for 28 days (ensuring that the age of all test specimens was 28 days). After the curing was completed, the initial diffusion coefficient of chloride ions in the concrete specimens was measured (the initial diffusion coefficient measured by the natural diffusion method was 4.98×10 -12 m 2 / s) and the initial chloride ion concentration in the concrete (the initial chloride ion concentration was measured by PXS-270 type chloride ion content rapid determination instrument and was 0.021%), and the initial age of the concrete was determined to be 28d.

[0054] S2. Based on the basic parameters of the concrete specimen, the relationship function between the chloride ion concentration on the concrete surface and the age attenuation coefficient is obtained, including the following steps:

[0055] (1) Pretreatment of the concrete specimens; the pretreatment is to apply epoxy resin on the five non-diffusion surfaces of the concrete specimens and air-dry them to form a sealed epoxy resin layer;

[0056] (2) subjecting the pretreated concrete specimens to a saltwater intrusion test based on the predicted use environment of the concrete;

[0057] The pretreated concrete specimens were subjected to a dry-wet cycle test using a high-frequency dry-wet cycle test system;

[0058] The high-frequency dry-wet cycle test system includes a time-controlled socket, two water pumps, mixed brine, a test box, a water storage tank and a storage table; the time-controlled socket is electrically connected to the water pump to control the water pump to circulate according to the set time; the storage table is set in the test box for placing concrete specimens; the water storage tank is used to store mixed brine; one water pump can pump the mixed brine in the water storage tank into the test box through a water pipe, and the other water pump can pump the mixed brine in the test box into the water storage tank through a water pipe;

[0059] The storage table is a hollow PVC pad; the storage table can ensure that the concrete remains as dry as possible during the alternating dry and wet drying process;

[0060] The mixed brine is a sodium chloride aqueous solution with a mass concentration of 10‰;

[0061] In the dry-wet cycle test, the dry-wet time ratio of the concrete specimens was 1:1, and the cycle frequency was 2 h / time;

[0062] The duration of the dry-wet cycle test is 30d, 60d, 100d, 150d and 200d;

[0063] (3) Grinding and sampling the concrete specimens after the saltwater intrusion test layer by layer along the saltwater diffusion depth direction to obtain concrete sample powders with different exposure times and different grinding depths;

[0064] The epoxy resin cured on the surface of various test pieces at different exposure times was peeled off, and a concrete powder sample layered grinding and collection device was used to grind and sample layer by layer starting from the remaining diffusion surface and along the diffusion depth direction. Within the depth range of 0 to 20 mm, the grinding sampling was carried out at 2 mm / layer; each layer of the ground concrete powder sample was collected and placed in a clean and transparent plastic sealing bag, and corresponding labels were made according to different exposure times and different grinding depths;

[0065] (4) After the concrete sample powder is sieved and dried, the chloride ion concentration in the different concrete sample powders is measured;

[0066] According to the provisions of Section 7.16 of the Test Procedure for Concrete in Water Transport Engineering (JTJ 270-1998) on the determination of water-soluble chloride ion content in concrete, the ground concrete powder sample was sieved with a standard sieve with an aperture of 0.63 mm. The sieved powder sample was placed in a drying oven at a temperature of 105±5℃ for about 2 hours, and then taken out and cooled to room temperature for use;

[0067] Take out 5g of the dried powder sample with a microbalance and place it in a clean beaker. Then measure 100ml of distilled water and pour it into the beaker containing the powder. Then place the suspension on a H01-1D magnetic stirrer and stir it for 20min and let it stand for 1h. Then use a disposable syringe to take 60ml of the upper clear liquid into another clean small beaker. Use a PXS-270 chloride ion content rapid tester to measure the free chloride ion concentration in the supernatant, which is the chloride ion concentration in the concrete.

[0068] (5) Based on the chloride ion concentration in the concrete sample powder, the chloride ion transport model was used to perform regression fitting analysis to obtain the fitting equation of the chloride ion concentration on the concrete surface and the age attenuation coefficient, which is the relationship function between the chloride ion concentration on the concrete surface and the age attenuation coefficient;

[0069] The chloride ion transport model is:

[0070]

[0071] Where: C 0 Indicates the initial concentration of chloride ions in concrete (%); C s Indicates the chloride ion concentration on the concrete surface (%); t 0 represents the initial age; t represents the exposure time; x represents the chloride ion diffusion depth (mm); C(x,t) represents the chloride ion concentration at depth x in the concrete specimen at time t (%); D(t) represents the chloride ion diffusion coefficient at time t, n is the age attenuation coefficient, erf is the error function, and D 0 is the initial diffusion coefficient of chloride ions;

[0072] S3, determine the design thickness (65mm) and critical chloride ion concentration of the concrete to be predicted (the environmental action level is L4, and its critical chloride ion concentration is judged to be 0.4%), and then obtain the relationship function between the predicted service life of the concrete and the age attenuation coefficient based on the chloride ion transmission optimization model in the concrete;

[0073] The optimization model of chloride ion transport in concrete is:

[0074]

[0075] Among them, C0 Indicates the initial chloride ion concentration in concrete (%); C s Indicates the chloride ion concentration on the concrete surface (%); t 0 represents the initial age of concrete; t represents the service life; x represents the thickness of concrete (mm); C(x,t) represents the critical chloride ion concentration of concrete (%); D(t) represents the chloride ion diffusion coefficient at time t; n is the age attenuation coefficient; erf is the error function, D 0 is the initial diffusion coefficient of chloride ions; D is the diffusion coefficient of chloride ions during service; K e With K c They are the environmental coefficient (0.192) and the curing coefficient (0.179) respectively; T is the absolute temperature (ambient temperature + 273k) (K); U is the activation energy in the diffusion process (2700K), which is related to the water-cement ratio of concrete; R is the molar gas constant (8.314472J / (K·mol)).

[0076] S4. Based on the value of the age attenuation coefficient, the predicted service life of concrete is obtained, as shown in the following table:

[0077]

Claims

1. A method for judging the service life of concrete based on salt water intrusion, characterized in that: The following steps are involved: S1. Prepare a concrete specimen using the concrete to be predicted, and obtain basic parameters of the concrete specimen; the basic parameters of the concrete specimen include the initial age of the concrete, the initial chloride ion concentration of the concrete, and the initial chloride ion diffusion coefficient; S2. Based on the basic parameters of the concrete specimen, obtain the relationship function between the chloride ion concentration on the concrete surface and the age attenuation coefficient; S3, determining the design thickness and critical chloride ion concentration of the concrete to be predicted, and then obtaining the relationship function between the predicted service life and the age attenuation coefficient of the concrete based on the chloride ion transmission optimization model in the concrete; S4. Based on the value of the age attenuation coefficient, the predicted service life of the concrete is obtained.

2. The method for judging the service life of concrete based on saltwater intrusion according to claim 1, characterized in that: The initial chloride ion concentration of the concrete is measured by a rapid chloride ion content tester; the initial chloride ion diffusion coefficient is measured by a natural diffusion method.

3. The method for judging the service life of concrete based on saltwater intrusion according to claim 2 is characterized in that: In step S2, the method for obtaining the relationship function between the chloride ion concentration on the concrete surface and the age attenuation coefficient comprises the following steps: (1) Pre-treat the concrete specimens; (2) subjecting the pretreated concrete specimens to a saltwater intrusion test based on the predicted use environment of the concrete; (3) Grinding and sampling the concrete specimens after the saltwater intrusion test layer by layer along the saltwater diffusion depth direction to obtain concrete sample powders with different exposure times and different grinding depths; (4) After the concrete sample powder is sieved and dried, the chloride ion concentration in the different concrete sample powders is measured; (5) Based on the chloride ion concentration in the concrete sample powder, the chloride ion transport model was used for regression fitting analysis to obtain the fitting equation of the chloride ion concentration on the concrete surface and the age attenuation coefficient, which is the relationship function between the chloride ion concentration on the concrete surface and the age attenuation coefficient.

4. The method for judging the service life of concrete based on saltwater intrusion according to claim 3 is characterized in that: In step (1), the pretreatment is to apply epoxy resin on the five non-diffusion surfaces of the concrete specimen and air-dry it to form a sealed epoxy resin layer; through the pretreatment, it can be ensured that chloride ions only invade one surface of the concrete specimen.

5. The method for judging the service life of concrete based on saltwater intrusion according to claim 3 is characterized in that: In step (3), when grinding and sampling layer by layer, each 2 mm depth is considered as one layer, and the number of sampling layers is not less than 10 layers.

6. The method for judging the service life of concrete based on saltwater intrusion according to claim 3 is characterized in that: In step (5), the chloride ion transport model is: Where: C0 represents the initial concentration of chloride ions in concrete (%); C s represents the chloride ion concentration on the concrete surface (%); t0 represents the initial age; t represents the exposure time; x represents the chloride ion diffusion depth (mm); C(x,t) represents the chloride ion concentration at the depth x in the concrete specimen at time t (%); D(t) represents the chloride ion diffusion coefficient at time t; n is the age attenuation coefficient, erf is the error function, and D0 is the initial chloride ion diffusion coefficient.

7. The method for judging the service life of concrete based on saltwater intrusion according to claim 1, characterized in that: In step S3, the critical chloride ion concentration of the concrete is obtained by detecting by a dynamic potentiometry method or an electrostatic potential method based on the initial rust criterion of steel bars and the environmental action level of salt water intrusion.

8. The method for judging the service life of concrete based on saltwater intrusion according to claim 1, characterized in that: In step S3, the environmental impact level is determined based on GB 50476-2008.

9. The method for judging the service life of concrete based on saltwater intrusion according to claim 1, characterized in that: In step S3, the optimization model of chloride ion transmission in concrete is: Where, C0 represents the initial chloride ion concentration in concrete (%); C s represents the chloride ion concentration on the concrete surface (%); t0 represents the initial age of concrete; t represents the service life; x represents the thickness of concrete (mm); C(x,t) represents the critical chloride ion concentration of concrete (%); D(t) represents the chloride ion diffusion coefficient at time t; n is the age attenuation coefficient; erf is the error function, D0 is the initial chloride ion diffusion coefficient; D represents the chloride ion diffusion coefficient during service; K e With K c They are the environmental coefficient and the curing coefficient respectively; T is the absolute temperature (K); U is the activation energy in the diffusion process, which is related to the water-cement ratio of concrete; and R is the molar gas constant.

10. The method for judging the service life of concrete based on salt water intrusion according to claim 9, characterized in that: In step S4, the value of the age attenuation coefficient is based on the relevant provisions of DB 45 / T 1828-2018; specifically: when the concrete to be predicted is silicate cement concrete, the age attenuation coefficient n=0.23; when the concrete to be predicted is concrete with admixtures added with minerals, the age attenuation coefficient ranges from n=0.48 to 0.67.

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