Method for evaluating salt frost resistance of airport pavement cement concrete
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HARBIN INST OF TECH
- Filing Date
- 2026-04-03
- Publication Date
- 2026-06-09
Smart Images
Figure CN122171383A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the technical field of evaluation of the freeze-thaw resistance and durability of cement concrete, and specifically relates to a method for evaluating the salt-freezing resistance of airport pavement cement concrete by combining the coupling effects of freeze-thaw cycles, chemical erosion and wheel wear. Background Technology
[0002] Airport pavements in cold regions operate under complex environments. The combined effects of freeze-thaw cycles, de-icing fluid / snow-melting agent erosion, and aircraft wheel loads lead to surface erosion, internal cracking, and reduced durability in concrete, severely impacting pavement lifespan and flight safety. Freeze-thaw resistance is one of the most important indicators for evaluating concrete durability. Current research on concrete freeze-thaw resistance, both domestically and internationally, largely employs single-factor testing methods, such as the rapid freezing method or single-sided salt freezing method in standards like ASTM C666 / C672, GB / T 50082, and MH / T 6083. However, these methods do not consider the continuous or dynamic effects of aircraft wheel loads in actual service environments, nor do they systematically study the freeze-thaw damage caused by various chemical media (such as potassium acetate and ethylene glycol) participating in freeze-thaw cycles. Furthermore, existing tests often differ significantly from actual airport pavement conditions in terms of specimen size, freeze-thaw regime, and load simulation methods, resulting in evaluation results that fail to accurately reflect the salt-freeze resistance durability of airport pavement cement concrete under complex environments. Summary of the Invention
[0003] The purpose of this invention is to address the problems of large errors, long test cycles, and inability to take into account the erosion of de-icing fluids or de-icing agents and wheel wear in current freeze-thaw test methods for determining the salt-freezing resistance of airport pavement cement concrete. The invention provides a new method for evaluating the salt-freezing resistance of airport pavement cement concrete based on a wheeled polisher.
[0004] A wheel-type polishing machine is a type of polishing machine that uses car tires to simulate the polishing of road surfaces. It drives a polishing wheel assembly to rotate horizontally in a circular motion under a certain ground pressure. When the experimental parameters are properly controlled, it can simulate the wear effect of aircraft tires on the pavement during taxiing in the flight area to a certain extent. This invention combines wheel-type accelerated loading polishing tests with single-sided salt-freezing tests. Based on the physical and mechanical mechanism that the concrete surface layer is damaged due to the accumulation of multiple pressures under the coupled action of salt-freezing and aircraft tire wear, resulting in the formation and eventual separation of the damaged layer, the invention collects the spalling material from the concrete surface under different freeze-thaw cycles and polishing cycles, calculates the total composite spalling mass per unit area of the specimen, and evaluates the salt-freezing resistance of the concrete based on the number of freeze-thaw cycles and the total composite spalling mass per unit area. This allows for a more realistic assessment of the salt-freezing resistance of airport pavement concrete.
[0005] A method for evaluating the salt-frost resistance of cement concrete pavement for airports includes the following steps:
[0006] I. Specimen curing: The concrete specimens were cured to an age of 28 days and then sealed to obtain the concrete specimens to be tested;
[0007] 2. Pre-absorption treatment: The molded surface of the concrete specimen to be tested is used as the test surface. The test surface is immersed in the test liquid. The surface area of the test surface is A. The specimen is pre-absorbed with water to obtain the concrete specimen to be tested after water absorption.
[0008] III. Coupled Cycle Test: A coupled cycle test was conducted on the concrete specimens after water absorption, and the samples were collected and dried.
[0009] Exfoliated material and specimen quality were recorded; a single coupled cycle test included two consecutive single-sided freeze-thaw cycles and one wheel-type accelerated loading polishing test.
[0010] IV. Repeat the loop: Repeat step three until the stopping condition is met;
[0011] In step four, the stopping condition includes any of the following situations:
[0012] (1) Achieve 9 consecutive coupling cycle tests;
[0013] (2) After N coupled cycle tests, the total mass of composite spalling per unit area of the specimen is greater than 1500 g / m². 2 ;
[0014] (3) After completing 9 coupled cycle tests, the surface peeling level reached level 4;
[0015] V. Performance Evaluation: When the stopping conditions are met, the concrete’s salt-freezing resistance is characterized by at least one of the following evaluation methods: the number of coupled cycle tests, the total composite spalling mass per unit area of the specimen after N coupled cycle tests, and the surface spalling grade after 9 coupled cycle tests.
[0016] Compared with the prior art, the significant advantages of the present invention are:
[0017] I. This invention uses a wheel grinder to simulate the wear of aircraft wheels and tests the salt-freeze resistance of concrete under the salt-freeze-aircraft wheel wear environment of airports. By calculating the total mass of composite spalling per unit area of the specimen and comparing it with the spalling amount per unit test surface area of concrete specimens under conventional single-sided freeze-thaw conditions, it can more realistically evaluate the salt-freeze resistance of airport pavement cement concrete and better fit the engineering service environment.
[0018] Second, this invention combines industry standards, national standards and international salt-freezing standards to propose a single-sided freeze-thaw test method for airport pavement cement concrete under the coupled effect of multiple factors. It can significantly accelerate the surface erosion process of concrete specimens, greatly reduce the number of freeze-thaw cycles required, improve test efficiency, shorten the test cycle, and is more suitable for the rapid evaluation of the salt-freezing resistance of airport pavement cement concrete.
[0019] Third, this invention optimizes the unit test surface area spalling amount in the GB / T 50082 single-sided freeze-thaw test based on coupling test, defines the grading judgment standard for spalling amount of airport pavement concrete, and can more accurately determine the salt freeze resistance performance of airport pavement concrete in the corresponding chemical medium environment. Attached Figure Description
[0020] Figure 1 This refers to the number of freeze-thaw cycles required for a concrete specimen to reach the failure standard. Detailed Implementation
[0021] Specific Implementation Method 1: This implementation method is a method for evaluating the salt-freezing resistance of cement concrete pavement at airports, including the following steps:
[0022] I. Specimen curing: The concrete specimens were cured to an age of 28 days and then sealed to obtain the concrete specimens to be tested;
[0023] 2. Pre-absorption treatment: The molded surface of the concrete specimen to be tested is used as the test surface. The test surface is immersed in the test liquid. The surface area of the test surface is A. The specimen is pre-absorbed with water to obtain the concrete specimen to be tested after water absorption.
[0024] III. Coupled Cycle Test: A coupled cycle test was conducted on the concrete specimens after water absorption, and the samples were collected and dried.
[0025] Exfoliated material and specimen quality were recorded; a single coupled cycle test included two consecutive single-sided freeze-thaw cycles and one wheel-type accelerated loading polishing test.
[0026] IV. Repeat the loop: Repeat step three until the stopping condition is met;
[0027] In step four, the stopping condition includes any of the following situations:
[0028] (1) Achieve 9 consecutive coupling cycle tests;
[0029] (2) After N coupled cycle tests, the total mass of composite spalling per unit area of the specimen is greater than 1500 g / m². 2 ;
[0030] (3) After completing 9 coupled cycle tests, the surface peeling level reached level 4;
[0031] V. Performance Evaluation: When the stopping conditions are met, the concrete’s salt-freezing resistance is characterized by at least one of the following evaluation methods: the number of coupled cycle tests, the total composite spalling mass per unit area of the specimen after N coupled cycle tests, and the surface spalling grade after 9 coupled cycle tests.
[0032] This implementation method achieves multi-factor coupled simulation of freeze-thaw cycles, chemical erosion, and wheel wear, closely matching the actual service conditions of airport pavements. It can significantly accelerate damage development, shorten the test cycle, and provide more accurate and reliable evaluation results. It can effectively solve the problems of large deviations between traditional single-factor tests and actual operating conditions, and insufficient evaluation accuracy.
[0033] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the concrete specimen dimensions described in step one are 300mm × 300mm × 50mm. All other steps are the same as in Specific Implementation Method One.
[0034] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that: the method for curing the concrete specimen to 28 days and sealing it in step one is as follows: the concrete specimen is cured in water at 18℃~22℃ for 7 days, then placed in an environment with a temperature of 18℃~22℃ and a relative humidity of 55%~65% to dry for 24 days. Then, epoxy resin is used to seal the four surfaces other than the two opposing test surfaces, and drying continues for another 28 days. Other steps are the same as in Specific Implementation Method One or Two.
[0035] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the test liquid mentioned in step two is selected from: a 3.5% sodium chloride solution, a 4% potassium acetate solution, or a 12.5% ethylene glycol solution. The other steps are the same as in Specific Implementation Methods One to Three.
[0036] Specific Implementation Method Five: The difference between this implementation method and Specific Implementation Methods One to Four is that the pre-absorption time mentioned in step two is 7 days. The other steps are the same as those in Specific Implementation Methods One to Four.
[0037] Specific Implementation Method Six: The difference between this implementation method and Specific Implementation Methods One to Five is that the single-sided freeze-thaw cycle in step three is as follows: freezing at -20°C for 16 to 18 hours, followed by thawing at 20°C for 6 to 8 hours. The other steps are the same as in Specific Implementation Methods One to Five.
[0038] Specific Implementation Method Seven: The difference between this implementation method and Specific Implementation Methods One through Six is that: Step Three, the single wheel-type accelerated loading polishing test includes the following steps:
[0039] (1) Two hours before the end of a single freeze-thaw cycle, collect and dry the exfoliated material generated during the freeze-thaw cycle. Record the quality of the test specimens;
[0040] (2) Fix the test specimen with the test surface facing up in the groove of the wheel grinder, so that the tire contacts the test surface, apply pressure to 200 kg, rotate at 23 r / min to 27 r / min for 10 min, collect the peeling material generated during the grinding process, and then rotate the test specimen counterclockwise 90°.
[0041] (3) Repeat step (2) three times. After the test, collect and dry the slough produced by the wheel-type accelerated loading polishing test. ,
[0042] Record the quality of the specimen. Other steps are the same as in specific implementation methods one through six.
[0043] Specific Implementation Method Eight: The difference between this implementation method and Specific Implementation Methods One to Seven is that the formula for calculating the total composite spalling mass per unit area of the specimen after N coupled cycle tests in step (2) is:
[0044] ;
[0045] In the formula: The total composite spalling mass per unit area of the specimen after N coupled cycle tests, in units of ; The mass of dried flaking material generated 2 hours before the end of a single freeze-thaw cycle of a coupled cycle, expressed in grams; The mass of flaking material after drying produced in one coupled-cycle wheel-type accelerated loading polishing test is expressed in grams; A is the surface area of the test surface of a single specimen. The other steps are the same as those in Specific Implementation Methods One through Seven.
[0046] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that: in step five, when comparing the salt-freezing resistance of different concretes, the concrete specimens that underwent more coupled cycle tests exhibited superior salt-freezing resistance; in step five, when comparing the salt-freezing resistance of different concretes, under the same number of coupled cycle tests, the smaller the total composite spalling mass per unit area of the specimen after N coupled cycle tests, the superior the salt-freezing resistance of the concrete specimen. Other steps are the same as in Specific Implementation Methods One to Eight.
[0047] Specific Implementation Method Ten: The difference between this implementation method and Specific Implementation Methods One through Nine is that: after completing nine coupled cycle tests in step five, the surface spalling level is divided into four grades: Grade 1, Grade 2, Grade 3, and Grade 4, corresponding to the concrete specimen's salt freeze resistance performance as excellent, good, qualified, and unqualified; among them, Grade 1 is defined as the total composite spalling mass per unit area of the concrete specimen ≤ 500g / m² after completing nine coupled cycle tests. 2 Level 2 is defined as a concrete specimen with a total composite spalling mass per unit area greater than 500 g / m² after completing 9 coupled-cycle tests. 2And ≤1000g / m 2 Level 3 is defined as a concrete specimen with a total composite spalling mass per unit area greater than 1000 g / m² after completing 9 coupled-cycle tests. 2 And ≤1500g / m 2 Level 4 is defined as a concrete specimen with a total composite spalling mass per unit area greater than 1500 g / m² after completing 9 coupled-cycle tests. 2 The other steps are the same as those in Specific Implementation Methods One through Nine.
[0048] The beneficial effects of the present invention are verified using the following embodiments:
[0049] Example 1: A method for evaluating the salt-frost resistance of cement concrete for airport pavements, comprising the following steps:
[0050] I. Preparation of concrete specimens with strength grade C40:
[0051] Concrete was prepared using water, P·O42.5 cement, river sand with a fineness modulus of 2.3, natural crushed stone with a particle size of 5-30 mm, and a naphthalene-based water-reducing agent with a water reduction rate of 20% as raw materials. The amounts of water, cement, river sand, natural crushed stone, and naphthalene-based water-reducing agent per cubic meter of concrete were 139 kg, 330 kg, 711 kg, 1320 kg, and 4.95 kg, respectively. The concrete was then molded into concrete specimens.
[0052] The type of naphthalene-based water-reducing agent mentioned in step one is: Naphthalene-based high-efficiency water-reducing agent, purchased from Jiangsu Subote New Material Co., Ltd.
[0053] The concrete specimen mentioned in step one has dimensions of 300mm × 300mm × 50mm;
[0054] II. Specimen curing: The concrete specimens were cured to 28 days and then sealed to obtain the concrete specimens to be tested.
[0055] The method for curing the concrete specimen to 28 days and sealing it in step two is as follows: the concrete specimen is cured in water at 18℃~22℃ for 7 days, then placed in an environment with a temperature of 20℃ and a relative humidity of 60% to dry for 24 days, and then the other four surfaces except the two opposite test surfaces are sealed with epoxy resin and dried for another 28 days.
[0056] III. Pre-absorption treatment: The molded surface of the concrete specimen to be tested is used as the test surface. The test surface is placed face down in contact with the pad strip. The test liquid is added and the liquid level is maintained at 10 mm. One test surface is immersed in the test liquid. The surface area of the test surface is A. The specimen is pre-absorbed with water for 7 days to obtain the concrete specimen to be tested after water absorption.
[0057] The test liquids mentioned in step three are respectively selected from: 3.5% sodium chloride solution (NaCl), 4% potassium acetate solution (KAc), and 12.5% ethylene glycol solution (EG).
[0058] IV. Coupled Cyclic Test:
[0059] Take out the concrete specimens to be tested and mark them on the top surface of the specimens. Record the mass of each specimen. The concrete specimens soaked in each test liquid are divided into freeze-thaw group and abrasion group, with 2 parallel specimens in each group.
[0060] A coupled-cycle test was conducted on the concrete specimens after water absorption. The spalling material was collected, dried, and the specimen quality was recorded.
[0061] Quantity; A single coupled cycle test includes two sequential single-sided freeze-thaw cycles and one wheel-type accelerated loading polishing test;
[0062] The procedure for one single-sided freeze-thaw cycle in step four is as follows: freeze at -20°C for 17 hours, then thaw at 20°C for 7 hours;
[0063] Step four, the single wheel-type accelerated loading polishing test, includes the following steps:
[0064] (1) Two hours before the end of a single freeze-thaw cycle, collect and dry (dry at 110°C for 24 hours) the exfoliated material generated during the freeze-thaw cycle. Record the quality of the test specimens;
[0065] (2) Fix the test specimen with the test surface facing up in the groove of the wheel grinder, so that the tire contacts the test surface, apply pressure to 200 kg, rotate at 25 r / min for 10 min, collect the peeling material generated during the grinding process, and then rotate the test specimen counterclockwise 90°.
[0066] (3) Repeat step (2) three times, and collect and dry the waste (dry at 110℃ for 24 hours) using a wheel.
[0067] Peeling material produced by accelerated grinding test Record the quality of the test specimens;
[0068] 5. Repeat step 3 until 9 coupled cycle tests are achieved. Calculate the total composite spalling mass per unit area of the specimen after N (N=9) coupled cycle tests, as shown in the following formula:
[0069] ;
[0070] In the formula: The total composite spalling mass per unit area of the specimen after N coupled cycle tests, in units of ; The mass of dried flaking material generated 2 hours before the end of a single freeze-thaw cycle of a coupled cycle, expressed in grams; The mass of flaking material after drying produced in one coupled-cycle wheel-type accelerated loading polishing test is expressed in grams; A is the surface area of the test surface of a single specimen. );
[0071] VI. Performance Evaluation: The surface spalling grade after completing 9 coupled cycle tests was used to characterize the salt freeze resistance of the concrete, as shown in Table 1.
[0072] After completing 9 coupled-cycle tests in step six, the surface spalling grade is divided into four levels: Level 1, Level 2, Level 3, and Level 4, corresponding to the excellent, good, qualified, and unqualified salt freeze resistance of the concrete specimens. Level 1 is defined as a total composite spalling mass per unit area of the concrete specimen ≤ 500 g / m² after completing 9 coupled-cycle tests. 2 Level 2 is defined as a concrete specimen with a total composite spalling mass per unit area greater than 500 g / m² after completing 9 coupled-cycle tests. 2 And ≤1000g / m 2 Level 3 is defined as a concrete specimen with a total composite spalling mass per unit area greater than 1000 g / m² after completing 9 coupled-cycle tests. 2 And ≤1500g / m 2 Level 4 is defined as a concrete specimen with a total composite spalling mass per unit area greater than 1500 g / m² after completing 9 coupled-cycle tests. 2 .
[0073] Table 1. Surface spalling grade and salt freeze resistance of specimens immersed in different test liquids.
[0074]
[0075] According to Table 1, the surface spalling grade of the concrete specimens was "Level 4" when the test liquid (freeze-thaw medium) was 3.5% sodium chloride solution, indicating unqualified frost resistance; the surface spalling grade was "Level 3" when the test liquid (freeze-thaw medium) was 4% potassium acetate solution, indicating qualified frost resistance; and the surface spalling grade was "Level 2" when the test liquid (freeze-thaw medium) was 12.5% ethylene glycol solution, indicating good frost resistance.
[0076] Example 2: The difference between this example and Example 1 is that in step five, after N coupled cycle tests, the total mass of composite peeling per unit area of the specimen is greater than 1500 g / m². 2The test was stopped at the designated time; the specimen was deemed damaged, and the number of freeze-thaw cycles at this point was recorded; in step six, the number of freeze-thaw cycles endured was used to characterize the concrete's resistance to salt freezing, with the freeze-thaw group undergoing only a single-sided freeze-thaw test, and the wear group undergoing both a single-sided freeze-thaw test and a wheel-type accelerated loading polishing test; the results are shown in Table 2 and... Figure 1 The other steps and parameters are the same as in Example 1.
[0077] Table 2 Number of freeze-thaw cycles when specimens reach the failure criterion
[0078]
[0079] According to Table 2, the total composite spalling mass per unit area of the specimen is greater than 1500 g / m². 2 As a cause of concrete failure
[0080] The number of freeze-thaw cycles experienced by the concrete specimens in the wear group was significantly lower than that under the single-sided freeze-thaw test conditions, only 60% to 70% of that in the freeze-thaw group. The test time of the wear group was also significantly lower than the 50 cycles (50 days) specified in standards such as GB / T 50082, MH / T 6083, and ASTM C672, or even more.
Claims
1. A method for evaluating the salt-frost resistance of cement concrete pavement for airports, characterized in that... The method includes the following steps: I. Specimen curing: The concrete specimens were cured to an age of 28 days and then sealed to obtain the concrete specimens to be tested; 2. Pre-absorption treatment: The molded surface of the concrete specimen to be tested is used as the test surface. The test surface is immersed in the test liquid. The surface area of the test surface is A. The specimen is pre-absorbed with water to obtain the concrete specimen to be tested after water absorption. III. Coupled Cycle Test: A coupled cycle test was conducted on the concrete specimens after water absorption, and the samples were collected and dried. Exfoliated material and specimen quality were recorded; a single coupled cycle test included two consecutive single-sided freeze-thaw cycles and one wheel-type accelerated loading polishing test. IV. Repeat the loop: Repeat step three until the stopping condition is met; In step four, the stopping condition includes any of the following situations: (1) Achieve 9 consecutive coupling cycle tests; (2) After N coupled cycle tests, the total mass of composite spalling per unit area of the specimen is greater than 1500 g / m². 2 ; (3) After completing 9 coupled cycle tests, the surface peeling level reached level 4; V. Performance Evaluation: When the stopping conditions are met, the concrete’s salt-freezing resistance is characterized by at least one of the following evaluation methods: the number of coupled cycle tests, the total composite spalling mass per unit area of the specimen after N coupled cycle tests, and the surface spalling grade after 9 coupled cycle tests.
2. The method for evaluating the salt-frost resistance of airport pavement cement concrete according to claim 1, characterized in that... The concrete specimen mentioned in step one has dimensions of 300mm × 300mm × 50mm.
3. The method for evaluating the salt-frost resistance of airport pavement cement concrete according to claim 1, characterized in that... The method for curing the concrete specimen to 28 days and sealing it in step one is as follows: the concrete specimen is cured in water at 18℃~22℃ for 7 days, then placed in an environment with a temperature of 18℃~22℃ and a relative humidity of 55%~65% to dry for 24 days. Then, epoxy resin is used to seal the other four surfaces except for the two opposite test surfaces, and drying continues until 28 days.
4. The method for evaluating the salt-frost resistance of airport pavement cement concrete according to claim 1, characterized in that... The test liquid mentioned in step two is selected from: a sodium chloride solution with a mass fraction of 3.5%, a potassium acetate solution with a mass fraction of 4%, or an ethylene glycol solution with a volume fraction of 12.5%.
5. The method for evaluating the salt-frost resistance of airport pavement cement concrete according to claim 1, characterized in that... The pre-absorption time mentioned in step two is 7 days.
6. The method for evaluating the salt-frost resistance of airport pavement cement concrete according to claim 1, characterized in that... The procedure for one single-sided freeze-thaw cycle in step three is as follows: freeze at -20℃ for 16 to 18 hours, and then thaw at 20℃ for 6 to 8 hours.
7. The method for evaluating the salt-frost resistance of airport pavement cement concrete according to claim 1, characterized in that... Step 3, the single wheel-type accelerated loading polishing test, includes the following steps: (1) Two hours before the end of a single freeze-thaw cycle, collect and dry the exfoliated material generated during the freeze-thaw cycle. Record the quality of the test specimens; (2) Fix the test specimen with the test surface facing up in the groove of the wheel grinder, so that the tire contacts the test surface, apply pressure to 200 kg, rotate at 23 r / min to 27 r / min for 10 min, collect the peeling material generated during the grinding process, and then rotate the test specimen counterclockwise 90°. (3) Repeat step (2) three times. After the test, collect and dry the slough produced by the wheel-type accelerated loading polishing test. , Record the quality of the test specimens.
8. The method for evaluating the salt-frost resistance of airport pavement cement concrete according to claim 1, characterized in that... The formula for calculating the total composite spalling mass per unit area of the specimen after N coupled cycle tests mentioned in step (2) is as follows: ； In the formula: The total composite spalling mass per unit area of the specimen after N coupled cycle tests, in units of ; The mass of dried flaking material generated 2 hours before the end of a single freeze-thaw cycle of a coupled cycle, expressed in grams; The mass of the dried flaking material produced in one coupled-cycle wheel-type accelerated loading polishing test is expressed in grams. A is the surface area of the test surface of a single specimen. ).
9. The method for evaluating the salt-frost resistance of airport pavement cement concrete according to claim 1, characterized in that... In step five, when comparing the salt-freezing resistance of different concretes, the concrete specimens that underwent more coupled cycle tests showed superior salt-freezing resistance. In step five, when comparing the salt-freezing resistance of different concretes, under the same number of coupled cycle tests, the smaller the total composite spalling mass per unit area of the specimen after N coupled cycle tests, the better the salt-freezing resistance of the concrete specimen.
10. The method for evaluating the salt-frost resistance of airport pavement cement concrete according to claim 1, characterized in that... After completing 9 coupled-cycle tests in step five, the surface spalling grade is divided into four levels: Level 1, Level 2, Level 3, and Level 4, corresponding to the concrete specimen's salt freeze resistance performance as excellent, good, qualified, and unqualified, respectively. Level 1 is defined as a total composite spalling mass per unit area of the concrete specimen ≤ 500 g / m² after completing 9 coupled-cycle tests. 2 Level 2 is defined as a concrete specimen with a total composite spalling mass per unit area greater than 500 g / m² after completing 9 coupled-cycle tests. 2 And ≤1000g / m 2 ; Level 3 is defined as a concrete specimen with a total composite spalling mass per unit area greater than 1000 g / m² after completing 9 coupled-cycle tests. 2 And ≤1500g / m 2 ; Level 4 is defined as a concrete specimen with a total composite spalling mass per unit area greater than 1500 g / m² after completing 9 coupled-cycle tests. 2 .