Method for predicting life of concrete under alkali-aggregate reaction damage

Abstract

This invention provides a method for predicting the service life of concrete under alkali-aggregate reaction failure. Based on the kinetics of alkali-aggregate reaction expansion and the theory of temperature acceleration, the method first determines the activation energy Ea of the alkali-silica reaction expansion of reactive aggregates through accelerated tests at different temperatures. Then, concrete specimens are prepared using actual engineering mix proportions, and accelerated temperature tests are conducted in a simulated pore solution at 70℃ to obtain the time t1 required for the expansion rate to reach the failure threshold of 0.040%. Finally, based on the Arrhenius equation, a mathematical model is established comparing the failure time of the concrete specimens under accelerated temperature conditions with the failure time of the concrete in the engineering structure, and the service life t2 of the concrete under engineering conditions is calculated. This invention solves the problems of existing technologies lacking a unified physical basis and being difficult to quantitatively extrapolate, improving the engineering applicability and universality of service life assessment, and providing a scientific basis for the long-term safety evaluation of major infrastructure such as hydraulic engineering and transportation.

Description

Technical Field

[0001] This invention belongs to the field of concrete durability and service life assessment technology, specifically involving a method for predicting the service life of concrete based on alkali-aggregate reaction (AAR / ASR) expansion kinetics and temperature acceleration theory. It is applicable to the long-term safety evaluation of concrete structures in hydraulic engineering, transportation engineering and major infrastructure. Background Technology

[0002] Alkali-aggregate reaction is one of the most harmful internal chemical damages to concrete structures during service. Essentially, it involves the reaction of alkaline ions in the cement pore solution with the active siliceous components in the aggregate, generating water-absorbing and swelling alkali-silica gel, causing volume expansion, cracking, and degradation of the concrete's mechanical properties. Extensive engineering practice has shown that alkali-aggregate reaction is characterized by a long latency period, slow development, and irreversibility; once it occurs, it seriously threatens the long-term safety of concrete structures.

[0003] For practical engineering projects, it is necessary to use rapid and effective methods to evaluate the long-term safety and durability of concrete in a short period of time. Many acceleration methods can be used to assess the behavior of concrete subjected to alkali-aggregate reaction damage. The most common acceleration methods are increasing the curing temperature and humidity of the specimens and increasing the alkali content of the concrete. Excessive alkali content can sometimes cause non-alkali-reactive quartz crystals to expand due to the alkali-silica reaction; therefore, most tests use increased curing temperature to accelerate the test process. To date, although many tests have used various curing temperatures to accelerate the alkali-aggregate reaction, the results of these acceleration methods cannot be directly used to evaluate the long-term safety of concrete because they do not consider the differences between concrete structures in the actual environment and accelerated test specimens.

[0004] The alkali-aggregate reaction process involves a series of physicochemical processes, but studies have shown that the Arrhenius equation is an effective tool for studying the alkali-aggregate reaction rate. The accelerating effect of temperature on the alkali-aggregate reaction and its expansion can be quantitatively described by the Arrhenius equation, which provides a feasible way to predict the safety of alkali-aggregate reaction in actual engineering concrete structures through short-term experimental studies.

[0005] To address the aforementioned problems, this invention proposes a method for predicting the alkali-aggregate reaction life, distinct from methods based on specific experimental approaches and empirical correlations. This method utilizes concrete specimens with actual engineering mix proportions. The 0.04% expansion rate, determined by the concrete prism method to assess aggregate alkali reactivity, is used as the threshold for concrete failure; that is, when the expansion rate of the concrete specimen exceeds 0.04%, the concrete structure is considered to have failed. The method studies the expansion behavior of engineering mix concrete under accelerated heating conditions, determining the time required for the expansion rate to reach 0.04%. Then, by measuring the activation energy of the alkali-silica reaction or the activation energy of the alkali-silica reaction expansion, and based on the Arrhenius equation describing the effect of temperature on the alkali-aggregate reaction or its expansion, a mathematical model is established comparing the failure time of concrete specimens under accelerated heating conditions with the safe service life of engineering structural concrete. This model is used to evaluate the alkali-aggregate reaction safety of engineering structural concrete, ultimately predicting the service life of concrete under alkali-aggregate reaction, thus improving the engineering applicability and universality of the life assessment method. Summary of the Invention

[0006] To address the lack of a unified physical basis and the difficulty in quantitative extrapolation in existing technologies for predicting the service life of alkali-aggregate reaction, this invention provides a method for predicting the service life of concrete under alkali-aggregate reaction failure. This method introduces the Arrhenius reaction kinetics theory to establish a quantitative relationship between the alkali-aggregate reaction expansion rate and temperature, and combines it with the concrete expansion failure threshold to achieve long-term service life prediction of engineering concrete based on accelerated testing.

[0007] The technical solution adopted in this invention is: a method for predicting the service life of concrete under alkali-aggregate reaction damage, comprising the following steps: S1. Determining the effect of curing temperature on the expansion of concrete due to alkali-silica reaction. Concrete prism specimens were cured in 1 mol / L NaOH solution at 30-80℃, and the expansion rate was measured periodically. S2. Determine the activation energy Ea of the alkali-silica reaction expansion in concrete. The expansion rate constant k was obtained by linear fitting of the relationship between the expansion rate and age at different temperatures, and the activation energy Ea was obtained by using the Arrhenius equation. S3. Determine the failure time t1 of the engineering mix concrete under accelerated conditions. Specimens were prepared according to the actual mix proportion of the project, and accelerated curing was carried out in a simulated pore solution at 70℃. The time t1 required for the expansion rate to reach 0.040% was measured and determined. S4. Calculate the service life t2 of concrete under service conditions. The average temperature of the project site over many years is collected as the service environment temperature T2. The failure time t2 under the service environment is calculated using the following formula: , Where Ea is the activation energy, J / mol; and R is the gas constant, which is 8.314 J·mol. -1 ·K -1 T1 is the accelerated curing temperature of the concrete specimen, which is 343.14K; t1 is the time required for the expansion rate of the concrete specimen to reach 0.040% during accelerated curing, in days; T2 is the service environment temperature of the engineering concrete, in K; t2 is the time required for the expansion rate of the engineering concrete in the service environment to reach 0.040%, in days.

[0008] Preferably, the concrete in S1 uses silicate cement, with an alkali content adjusted to 2.0% and a cement dosage of 420 kg / m³. 3 The coarse aggregate is 5-25mm crushed stone, the fine aggregate is sand with a fineness modulus of 2.7±0.2, the ratio of coarse aggregate to fine aggregate is 6:4, and the water-cement ratio is 0.50-0.55.

[0009] Preferably, the activity of the aggregate needs to be determined according to the actual situation of the engineering concrete: when both coarse and fine aggregates are active aggregates, each is mixed with 50% active aggregate and 50% inactive aggregate; when only coarse aggregate is active aggregate, fine aggregate is inactive aggregate; when only fine aggregate is active aggregate, coarse aggregate is inactive aggregate.

[0010] Preferably, the concrete prism specimen described in S1 has dimensions of 75mm*75mm*285mm.

[0011] Preferably, the mass ratio of the NaOH solution to the concrete prism specimen in S1 is 1:2.

[0012] Preferably, the Arrhenius equation in S2 is: , Where A is the pre-exponential factor; R is the gas constant, which is 8.314 J·mol⁻¹. -1 ·K -1 Ea is the activation energy, J / mol; T is the reaction temperature, K.

[0013] Preferably, the simulated pore solution in S3 is based on K calculated according to the alkali content and water-cement ratio of the engineering concrete. + and Na + The content is prepared accordingly.

[0014] Preferably, in S3, if the expansion rate of the specimen does not reach 0.040% within the test cycle, t1 is calculated by establishing a fitting equation between the expansion rate and time.

[0015] If the predicted service life t2 of the concrete is less than the design service life, the alkali-aggregate reaction prevention measures of the concrete need to be adjusted.

[0016] Compared with the prior art, the present invention has the following significant technical effects: This invention provides a method for predicting the service life of concrete under alkali-aggregate reaction failure. This method introduces the Arrhenius reaction kinetics theory to establish a quantitative relationship between the alkali-aggregate reaction expansion rate and temperature, and combines it with the concrete expansion failure threshold to achieve long-term service life prediction of engineering concrete based on accelerated testing. It is applicable to the long-term safety evaluation of concrete structures in hydraulic engineering, transportation engineering and major infrastructure.

[0017] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] Figure 1 The expansion rate of concrete specimens at different curing temperatures in Example 1 of this invention; Figure 2 The fitting result of the expansion rate of the concrete specimen in Example 1 of the present invention; Figure 3 The relationship between lnk and 1 / T is given for the concrete prism specimen in Example 1 of this invention. Figure 4 This is the fitting result of the expansion rate of C60 concrete specimens prepared from tuff during 70℃ simulated pore solution curing in Example 1 of the present invention. Detailed Implementation

[0019] This invention provides a method for predicting the life of concrete under alkali-aggregate reaction failure, comprising the following steps: S1. The effect of curing temperature on the expansion of concrete due to alkali-silica reaction Concrete prism specimens were used, with dimensions of 75mm × 75mm × 285mm. The concrete used was silicate cement with an alkali content of 2.00%, and the cement dosage was 420 kg / m³. 3 The coarse aggregate is 5-25mm crushed stone, and the fine aggregate is sand with a fineness modulus of 2.7±0.2. The ratio of coarse to fine aggregate is 6:4. The water-cement ratio of the concrete is 0.50-0.55. The activity of the aggregate needs to be determined according to the actual situation of the engineering concrete: when both coarse and fine aggregates of the engineering concrete are active aggregates, the coarse aggregate used in the test consists of 50% active aggregate and 50% inactive aggregate, and the fine aggregate consists of 50% active aggregate and 50% inactive aggregate; when only active aggregates are used as coarse aggregates in the engineering concrete, the coarse aggregates used in the test are active aggregates, and the fine aggregates are inactive aggregates; when only active aggregates are used as fine aggregates in the engineering concrete, the coarse aggregates used in the test are inactive aggregates, and the fine aggregates are active aggregates.

[0020] Concrete prism specimens were cured at different temperatures using a 1 mol / L NaOH solution as the curing medium. The mass ratio of the curing solution to the concrete specimen was 1:2. The curing temperatures were 30℃, 40℃, 50℃, 60℃, 70℃, and 80℃. The expansion rate of the concrete prisms was measured periodically.

[0021] S2. Determine the activation energy Ea of the alkali-silica reaction expansion in concrete. By linearly fitting the relationship between the expansion rate of concrete at different temperatures and the curing age, the alkali-silica reaction expansion rate constant k is obtained.

[0022] The Arrhenius equation used to describe the effect of temperature on the rate of a chemical reaction is equation (1): (1) In the formula, A is the pre-exponential factor. R is the gas constant, which is 8.314 J·mol⁻¹. -1 ·K -1 , Ea-Arrhenius activation energy, J / mol T - Reaction temperature (absolute temperature), K; Taking the logarithm of both sides of equation (1) yields equation (2), which shows a linear relationship between lnk and 1 / T, with a slope of -Ea / R and an intercept of lnA.

[0023] (2) The good linear relationship between ln k and 1 / T obtained from fitting the expansion rate data of concrete specimens indicates that the effect of curing temperature on the alkali-silica reaction expansion of concrete basically conforms to the Arrhenius equation. By linearly fitting the logarithm of the expansion rate constant lnk with the reciprocal of the curing temperature (absolute temperature) 1 / T, the slope of the straight line can be used to determine the activation energy Ea of the alkali-silica reaction expansion of concrete. This parameter represents the degree of influence of curing temperature on the accelerating effect of the alkali-silica reaction expansion of tuff.

[0024] S3. Determine the failure time t1 of the engineering mix concrete under accelerated conditions. Concrete prism specimens were prepared according to the engineering concrete mix proportion that met the design requirements for strength and other properties. These specimens were cured in a simulated pore solution at 70℃, and the expansion rate of the concrete specimens was measured periodically to determine the time t1 required for the engineering mix concrete to reach an expansion rate of 0.040%. The concentration of the simulated pore solution was calculated based on the alkali content and water-cement ratio of the concrete, using the K0 value of the concrete pore solution. + and Na + Once the content was determined, a simulated pore solution for curing was prepared using KOH and NaOH reagents.

[0025] If the experiment can directly determine the time t1 for the alkali-silica reaction expansion rate of the concrete in the engineering mix to reach 0.040% under accelerated conditions, then the experimental data shall be adopted; if the concrete prism specimen does not reach the expansion rate of 0.040% within the test period, then the time t1 required for the expansion rate of the concrete prism specimen to reach 0.040% shall be calculated by establishing a fitting equation between the expansion rate and time.

[0026] S4. Calculate the service life t2 of concrete under service conditions. The average temperature of the project site over many years is collected from meteorological websites and used as the temperature of the service environment. The service life of the concrete in the service environment (i.e., the time required to reach 0.040% expansion rate) t2 is calculated according to formula (3).

[0027] (3) In the formula, Ea is the activation energy of the alkali-silica reaction expansion of the active aggregate in concrete, in J / mol; T1 -- the accelerated curing temperature of the concrete specimen, which is 343.14K; T2 -- the service temperature of the engineering concrete, in K; t1 -- the time required for the expansion rate of the concrete specimen to reach 0.040% during accelerated curing, in days; t2 -- the time required for the expansion rate of concrete in the service environment to reach 0.040%, expressed in days; R is the gas constant, which is 8.314 J·mol⁻¹. -1 ·K -1 ; The aforementioned t2 represents the predicted service life of concrete, which is the time required for concrete to undergo alkali-silica reaction failure in the service environment, at which point cracking occurs. If the alkali-silica reaction failure time t2 is greater than or equal to the design service life, the alkali-silica reaction prevention measures for active aggregates in concrete can be used for engineering concrete. If the alkali-silica reaction failure time is less than the design service life, the alkali-silica reaction prevention measures need to be adjusted to meet the design service life requirements. Example 1

[0028] This embodiment describes a method for predicting the life of concrete under alkali-silica reaction damage caused by tuff, including the following steps: S1. The effect of curing temperature on the alkali-silica reaction expansion of reactive tuff was evaluated using concrete prism specimens.

[0029] The experiment selected tuff as the active aggregate and limestone as the inactive aggregate. The active tuff and inactive limestone blocks were crushed into 5-25mm gravel and sand with a fineness modulus of 2.8, respectively. 50% tuff and 50% limestone gravel were uniformly mixed to form coarse aggregate, and 50% tuff and 50% limestone sand were uniformly mixed to form fine aggregate, with a coarse aggregate to fine aggregate ratio of 6:4.

[0030] P·II 52.5 cement with an alkali content of 0.51% was selected, and the alkali content was adjusted to 2.00% using NaOH solution. The cement dosage was 420 kg / m³. 3 The water-cement ratio is 0.55. After molding, the specimens are cured in humid air at 20℃ and relative humidity greater than 95% for 24±2 hours before demolding, and the initial length of the specimens is measured.

[0031] The specimens were then cured in 1 mol / L NaOH solutions at 30℃, 40℃, 50℃, 60℃, 70℃ and 80℃ respectively until the specified age (7d, 14d, 28d, 56d, 90d, 120d, 182d and 210d). The specimens were then removed to complete the length measurement. After the measurement, the specimens were returned to the curing device for further curing. Figure 1 The results show the effect of curing temperature on the expansion rate of concrete specimens. As the curing temperature increases, the expansion rate of concrete prism specimens increases significantly.

[0032] S2. Determine the activation energy Ea of the alkali-silica reaction expansion in concrete. Will Figure 1 A linear fit was performed on the relationship between the concrete expansion rate at different temperatures and the curing age, such as... Figure 2 The obtained tuff alkali silicate reaction expansion rate constant k and correlation coefficient R 2 As shown in Table 1, the correlation coefficients range from 0.9076 to 0.9978, indicating a good linear correlation between the expansion rate of concrete prism specimens and the curing age.

[0033] Table 1. Slope and linear correlation coefficient of the fitted line between the alkali-silica reaction expansion of tuff in concrete prism specimens and the curing age. Plot the logarithm of the slope k of the fitted straight line against the reciprocal of the curing temperature (absolute temperature) 1 / T, and perform linear fitting to obtain... Figure 3 The result showed that the slope of the straight line was -3768.24, and the calculated activation energy Ea for the expansion of alkali silicate reaction in tuff was 31.3 kJ / mol.

[0034] S3. Determine the failure time t1 of the engineering mix concrete under accelerated conditions. Concrete prism specimens were molded according to the C60 concrete mix proportions (see Table 2), where crushed stone 1 is 5-16mm and crushed stone 2 is 16-25mm. After molding, the specimens were cured in humid air at 20℃ and relative humidity greater than 95% for 24±2 hours before demolding, and the initial length of the specimens was measured. The curing solution was prepared according to the simulated pore solution concentration calculated in Table 3, and the curing temperature was 70℃. The expansion rate of the concrete prisms was measured periodically.

[0035] Table 2 Concrete Mix Proportions for Engineering Projects Table 3 Initial concentration of pore solution in concrete simulation Since the expansion rate of the concrete specimens in the engineering mix proportion did not reach 0.040% within 2 years, the time t1 required for the expansion rate of the concrete prism specimens to reach 0.040% was determined by fitting. Figure 4 The fitted curve is given by the equation E = 0.044 - 0.048Exp(-t / 1296.90). According to the equation, when E = 0.04, t1 is 3223 days, approximately 8.83 years. This indicates that at 70℃, it takes 8.83 years for concrete to undergo alkali-silica reaction failure.

[0036] S4. Calculate the service life t2 of concrete under service conditions. According to meteorological records, the average annual temperature at the location of the concrete project is 14-18℃. Taking the average temperature of 16℃ as the service environment temperature T2, we substitute it into equation (3) to calculate... The result is t2 = 24999d, approximately 68.49 years. This means that the current concrete mix design would require 68.49 years to undergo alkali-silica reaction failure under engineering conditions, which does not meet the 100-year design requirement. Therefore, the mix design should be redesigned.

[0037] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for predicting the service life of concrete under alkali-aggregate reaction failure, characterized in that, Includes the following steps: S1. Determining the effect of curing temperature on the expansion of concrete due to alkali-silica reaction. Concrete prism specimens were cured in 1 mol / L NaOH solution at 30-80℃, and the expansion rate was measured periodically. S2. Determine the activation energy Ea of the alkali-silica reaction expansion in concrete. The expansion rate constant k was obtained by linear fitting of the relationship between the expansion rate and age at different temperatures, and the activation energy Ea was obtained by using the Arrhenius equation. S3. Determine the failure time t1 of the engineering mix concrete under accelerated conditions. Specimens were prepared according to the actual mix proportion of the project, and accelerated curing was carried out in a simulated pore solution at 70℃. The time t1 required for the expansion rate to reach 0.040% was measured and determined. S4. Calculate the service life t2 of concrete under service conditions. The average temperature of the project site over many years is collected as the service environment temperature T2. The failure time t2 under the service environment is calculated using the following formula: ， Where Ea is the activation energy, J / mol; and R is the gas constant, which is 8.314 J·mol. -1 ·K -1 T1 is the accelerated curing temperature of the concrete specimen, which is 343.14K; t1 is the time required for the expansion rate of the concrete specimen to reach 0.040% during accelerated curing, in days; T2 is the service environment temperature of the engineering concrete, in K; t2 is the time required for the expansion rate of the engineering concrete in the service environment to reach 0.040%, in days.

2. The method according to claim 1, characterized in that, The concrete described in S1 uses silicate cement with an alkali content adjusted to 2.0% and a cement dosage of 420 kg / m³. 3 The coarse aggregate is 5-25mm crushed stone, the fine aggregate is sand with a fineness modulus of 2.7±0.2, the ratio of coarse aggregate to fine aggregate is 6:4, and the water-cement ratio is 0.50-0.

55.

3. The method according to claim 2, characterized in that, The activity of the aggregates needs to be determined based on the actual conditions of the concrete project: when both coarse and fine aggregates are active aggregates, each is mixed with 50% active aggregate and 50% inactive aggregate; when only coarse aggregate is active aggregate, fine aggregate is inactive aggregate; when only fine aggregate is active aggregate, coarse aggregate is inactive aggregate.

4. The method according to claim 1, characterized in that, The concrete prism specimen described in S1 has dimensions of 75mm*75mm*285mm.

5. The method according to claim 1, characterized in that, The mass ratio of the NaOH solution to the concrete prism specimen in S1 is 1:

2.

6. The method according to claim 1, characterized in that, The Arrhenius equation described in S2 is: ， Where A is the pre-exponential factor; R is the gas constant, which is 8.314 J·mol⁻¹. -1 ·K -1 Ea is the activation energy, J / mol; T is the reaction temperature, K.

7. The method according to claim 1, characterized in that, The simulated pore solution described in S3 uses K calculated based on the alkali content and water-cement ratio of the engineering concrete. + and Na + The content is prepared accordingly.

8. The method according to claim 1, characterized in that, If the expansion rate of the specimen does not reach 0.040% within the test cycle in S3, t1 can be calculated by establishing a fitting equation between the expansion rate and time.

9. The method according to claim 1, characterized in that, If the predicted service life t2 of the concrete is less than the design service life, the alkali-aggregate reaction prevention measures of the concrete need to be adjusted.

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