Method for determining frost resistance of concrete

Abstract

The invention belongs to the technical field of concrete performance detection, and particularly discloses a concrete anti-freezing performance determination method, which comprises the following steps: pre-determining a first anti-freezing relationship among a mass loss rate, a water-binder ratio and a gas content and a second anti-freezing relationship among a relative dynamic elastic modulus, the water-binder ratio and the gas content according to a freeze-thaw test; inputting the actual water-binder ratio and the actual gas content of the concrete mixture into the first anti-freezing relation to obtain the actual mass loss rate; inputting the actual water-binder ratio and the actual gas content of the concrete mixture into the second anti-freezing relation to obtain the actual relative dynamic elastic modulus; and determining the anti-freezing grade of the concrete corresponding to the concrete mixture according to the actual mass loss rate and the actual relative dynamic elastic modulus. According to the concrete anti-freezing performance determination method, the anti-freezing performance of the concrete can be rapidly determined in the concrete mixture stage, so that the construction mix proportion is adjusted in time, and concrete quality control is facilitated.

Description

Technical Field

[0001] The invention discloses a method for determining the antifreeze performance of concrete, and belongs to the technical field of concrete performance detection. Background Art

[0002] Hydraulic concrete is often used in extremely cold regions. Freeze-thaw damage is an important factor affecting the durability of its structure. Therefore, the frost resistance grade is a very important evaluation indicator of hydraulic concrete.

[0003] At present, there are two main test methods for the frost resistance of concrete: slow freezing method and quick freezing method. The slow freezing method is suitable for determining the frost resistance of concrete specimens under repeated freeze-thaw cycles of "air freezing and water thawing", while the quick freezing method is suitable for determining the frost resistance of concrete specimens under repeated freeze-thaw cycles of "water freezing and water thawing". Compared with the slow freezing method, the quick freezing method has a shorter test cycle and is more suitable for the use conditions of hydraulic concrete. Therefore, the commonly used specifications for water conservancy and hydropower engineering SL / T 352 and DL / T 5150 recommend the use of the quick freezing method to test the frost resistance of concrete.

[0004] The quick freezing method is to measure the mass loss rate and relative dynamic modulus of hardened concrete specimens after a specified number of freeze-thaw cycles. When the relative dynamic modulus drops to a preset value or the mass loss reaches a preset value, the specimen is considered to have reached failure, and the corresponding number of freeze-thaw cycles is used as the frost resistance grade of the concrete (expressed as F). This test method has the following disadvantages: First, the test cycle is too long. Taking the 90d-old F200 frost resistance grade concrete as an example, it takes at least 130 days from concrete molding to the completion of the frost resistance test. This makes it impossible to adjust the mix ratio parameters in time according to the frost resistance performance during concrete quality control. Especially for the construction site, if the frost resistance performance of the concrete cannot be accurately grasped in time, it is not conducive to concrete quality control and construction progress; second, the quick freezing method test requires the use of professional equipment such as rapid freeze-thaw testing machines and dynamic modulus measuring instruments, and the test steps are more and the test personnel have higher operating requirements. For general on-site construction site laboratories, the investment in personnel and equipment is large. Summary of the invention

[0005] The purpose of the present invention is to provide a method for determining the frost resistance of concrete, so as to solve the technical problems of poor timeliness, high operating requirements for test personnel and high cost in the existing method for determining the frost resistance grade of concrete.

[0006] The present invention provides a method for determining the frost resistance of concrete, comprising:

[0007] Step 1: Determine the first antifreeze relationship between mass loss rate, water-binder ratio and air content and the second antifreeze relationship between relative dynamic elastic modulus, water-binder ratio and air content according to freeze-thaw tests.

[0008] Step 2: Input the actual water-binder ratio and the actual air content of the concrete mixture into the first antifreeze relationship to obtain the actual mass loss rate; input the actual water-binder ratio and the actual air content of the concrete mixture into the second antifreeze relationship to obtain the actual relative dynamic modulus.

[0009] Step 3: Determine the frost resistance grade of the concrete corresponding to the concrete mixture according to the actual mass loss rate and the actual relative dynamic elastic modulus.

[0010] Preferably, the step 1 specifically includes:

[0011] Step 1.1, construct a corresponding relationship group between the water-binder ratio of each test and the air content of a plurality of different tests that increase in sequence.

[0012] Step 1.2, determining the mass loss rate and relative dynamic modulus of each relationship group under a plurality of freeze-thaw cycle numbers increasing in sequence.

[0013] Step 1.3, determine the fitting relationship between the mass loss rate of the test under each number of freeze-thaw cycles and the water-binder ratio and the air content of the corresponding test, which is recorded as the first antifreeze relationship; determine the fitting relationship between the relative dynamic modulus of the test under each number of freeze-thaw cycles and the water-binder ratio and the air content of the corresponding test, which is recorded as the second antifreeze relationship.

[0014] Preferably, the gas content of the test ranges from 2.0% to 7.0%.

[0015] Preferably, the gas content in the test is increased in increments of 0.8% to 1.2%.

[0016] Preferably, the number of freeze-thaw cycles is 50 to 300 times.

[0017] Preferably, the increment of the number of freeze-thaw cycles is 25 or 50 times.

[0018] Preferably, the step 3 specifically includes:

[0019] The current number of freeze-thaw cycles corresponding to when the actual mass loss rate is greater than the first preset value or the actual relative dynamic modulus is less than the second preset value is obtained; and the number of freeze-thaw cycles before the current number of freeze-thaw cycles is recorded as the frost resistance grade of the concrete.

[0020] Preferably, the first preset value is 5%.

[0021] Preferably, the second preset value is 60%.

[0022] Compared with the prior art, the method for determining the frost resistance of concrete of the present invention has the following beneficial effects:

[0023] Compared with the traditional quick freezing method, the method for determining the antifreeze performance of concrete of the present invention can greatly shorten the test cycle, and its antifreeze performance can be calculated in the concrete mixing stage. The traditional quick freezing method for testing the antifreeze performance requires that the concrete specimens be cured to a specified age before the test can begin, and it takes about 10 days for every 100 cycles. In actual construction, if the concrete has been poured and the antifreeze performance is unqualified in the later stage, the rework cost is very high or even impossible to rework. The method provided by the present invention can grasp the antifreeze performance of the concrete before pouring, which is convenient for timely adjusting the construction mix ratio, and is therefore more conducive to concrete quality control.

[0024] For construction site laboratories, the method for determining the antifreeze performance of concrete proposed by the present invention is simple to operate and can effectively improve the detection efficiency while reducing the investment in personnel and equipment, and has good economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The flowchart of the method for determining the frost resistance of concrete in an embodiment of the present invention is shown in FIG. DETAILED DESCRIPTION

[0026] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present invention.

[0027] The embodiment of the present invention provides a method for determining the frost resistance of concrete. Figure 1 As shown, including:

[0028] Step 1: Determine the first antifreeze relationship between mass loss rate, water-binder ratio and air content and the second antifreeze relationship between relative dynamic elastic modulus, water-binder ratio and air content according to freeze-thaw tests.

[0029] The above step 1 of the embodiment of the present invention specifically includes:

[0030] Step 1.1, construct a corresponding relationship group between the water-binder ratio of each test and the air content of a plurality of different tests that increase in sequence.

[0031] In the embodiment of the present invention, at least 4 groups of water-cement ratios meeting the design requirements are selected according to the concrete design frost resistance grade by the relevant test method of DL / T 5330. The strength range corresponding to the water-cement ratio of each group of tests should be able to include the corresponding preparation strength of concrete of each design grade.

[0032] In the same test of the embodiment of the present invention, under the premise that the slump of the concrete mixture remains unchanged, the water-cement ratio is increased by increasing the amount of air-entraining agent so that the air content of the concrete mixture is increased in the range of 2.0% to 7.0%, and the increment is 0.8% to 1.2%. Exemplarily, the increment may be 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, etc., preferably 1.0%.

[0033] To ensure the accuracy of the first antifreeze relationship and the second antifreeze relationship finally obtained, the water-cement ratio of the same test in the embodiment of the present invention corresponds to no less than 6 groups of concrete mixtures with different air contents in the tests. Taking 6 groups with an increment of 1.0% as an example, the water-cement ratio of the same test can produce 6 relationship groups, and the air contents of the tests in each relationship group are 2.0%, 3.0%, 4.0%, 5.0%, 6.0%, and 7.0%, respectively.

[0034] After obtaining the concrete mixtures of the above multiple relationship groups, the embodiments of the present invention are molded respectively according to the requirements of the quick freezing method in DL / T 5150. The prismatic concrete specimens are then placed in a standard curing room for curing to the specified age.

[0035] Step 1.2, determine the mass loss rate and relative dynamic modulus of each relationship group under a plurality of freeze-thaw cycle numbers increasing in sequence.

[0036] In the embodiment of the present invention, the number of freeze-thaw cycles is 50 to 300 times; the increment of the number of freeze-thaw cycles is 25 times or 50 times.

[0037] The number of freeze-thaw cycles in the embodiment of the present invention can be 2 to 12 types. For example, taking the increment of 50 times as an example, 6 types of freeze-thaw cycles can be generated, specifically 50 times, 100 times, 150 times, 200 times, 250 times, and 300 times.

[0038] Exemplarily, the test method of step 1.2 of the embodiment of the present invention is:

[0039] The concrete specimens corresponding to each relationship group and cured to the age were used to measure the mass loss rate and relative dynamic modulus of the tests under various freeze-thaw cycles according to the relevant test steps of the quick freezing method in DL / T 5150.

[0040] Step 1.3, determine the fitting relationship between the mass loss rate of the test under each number of freeze-thaw cycles and the water-binder ratio and the air content of the corresponding test, which is recorded as the first antifreeze relationship; determine the fitting relationship between the relative dynamic modulus of the test under each number of freeze-thaw cycles and the water-binder ratio and the air content of the corresponding test, which is recorded as the second antifreeze relationship.

[0041] The water-binder ratio, air content and mass loss rate of each freeze-thaw cycle were fitted according to formula (1):

[0042] (1)

[0043] In the formula, For concrete specimens Mass loss rate of the test after freeze-thaw cycles (%); The amount of cementitious material (kg / m 3 ); is the water consumption (kg / m 3 ),but is the water-binder ratio of the test; is the test air content of concrete mixture (%); is the coefficient to be determined.

[0044] The water-binder ratio, air content and relative dynamic modulus of each freeze-thaw cycle are fitted according to formula (2):

[0045] (2)

[0046] In the formula, For concrete specimens Relative dynamic modulus of the test after freeze-thaw cycles (%); The amount of cementitious material (kg / m 3 ); is the water consumption (kg / m 3 ),but is the water-binder ratio of the test; is the test air content of concrete mixture (%); is the coefficient to be determined.

[0047] Step 2: Input the actual water-cement ratio and the actual air content of the concrete mixture into the first antifreeze relationship to obtain the actual mass loss rate; input the actual water-cement ratio and the actual air content of the concrete mixture into the second antifreeze relationship to obtain the actual relative dynamic modulus.

[0048] After obtaining the first antifreeze relationship and the second antifreeze relationship, the embodiment of the present invention substitutes the actual water-binder ratio and the actual air content into formula (1) to obtain the actual mass loss rate of concrete corresponding to each number of freeze-thaw cycles under multiple numbers of freeze-thaw cycles that increase in sequence; and substitutes the actual water-binder ratio and the actual air content into formula (2) to obtain the actual relative dynamic modulus of concrete corresponding to each number of freeze-thaw cycles under multiple numbers of freeze-thaw cycles that increase in sequence.

[0049] Step 3: Determine the frost resistance grade of the concrete mixture corresponding to the concrete according to the actual mass loss rate and the actual relative dynamic elastic modulus, specifically including:

[0050] Step 3.1, obtaining the current number of freeze-thaw cycles corresponding to when the actual mass loss rate is greater than the first preset value or the actual relative dynamic elastic modulus is less than the second preset value, wherein the first preset value is 5% and the second preset value is 60%.

[0051] Step 3.2: The number of freeze-thaw cycles before the current number of freeze-thaw cycles is recorded as the frost resistance grade of the concrete.

[0052] when Greater than the first preset value or When it is less than the second preset value, it is judged that the concrete has reached destruction. Therefore, in the embodiment of the present invention, the number of previous freeze-thaw cycles is used as the freeze-thaw resistance grade of the concrete to be tested, which is represented by F.

[0053] The method for determining the antifreeze performance of concrete of the present invention will be described in detail below with more specific embodiments.

[0054] Example 1

[0055] For hydraulic normal concrete with a maximum designed frost resistance grade of F200, four water-cement ratios of 0.35, 0.40, 0.45 and 0.50 were initially selected for mixing concrete. The water-cement ratio of each test was adjusted by adjusting the amount of air entraining agent so that the air content of the test increased from the benchmark (without air entraining agent) by about 1% to about 7.0%, and there were no less than 6 groups. The air content of each group of concrete mixtures was measured respectively. The test results are shown in Table 1.

[0056] Table 1 Antifreeze factor values

[0057]

[0058] A group of concrete mixtures with different air contents corresponding to the water-binder ratio of each test are formed separately. The prismatic concrete specimens were cured in a standard curing room until 90 days old. According to the requirements of the quick freezing method in DL / T 5150, the present invention measured the , , the results are shown in Table 2.

[0059] Table 2 Antifreeze Grade Index Values

[0060]

[0061] Formula (1) and formula (2) were used to fit Table 1 and Table 2 to obtain the following results for each freeze-thaw cycle: , The equation for the variation of water-binder ratio and air content of the test.

[0062] 50 freeze-thaw cycles are:

[0063] (3)

[0064] (4)

[0065] 100 freeze-thaw cycles:

[0066] (5)

[0067] (6)

[0068] 150 freeze-thaw cycles:

[0069] (7)

[0070] (8)

[0071] 200 freeze-thaw cycles:

[0072] (9)

[0073] (10)

[0074] For design level C 90 25W6F100, C 90 The actual water-binder ratios of the two groups of 30W6F200 hydraulic concrete were 0.46 and 0.40 respectively, and the actual air contents measured during concrete mixing were 4.2% and 5.3% respectively. The results calculated using the above method and the test results measured by the quick freezing method after curing to 90 days are compared in Table 3.

[0075] Table 3 Comparison of results

[0076]

[0077] It can be seen from Table 3 that the test results obtained by the method of the present invention are not much different from the test results of the traditional quick freezing method, which shows that the method of the present invention can quickly and accurately detect the antifreeze performance of hydraulic concrete.

[0078] Example 2

[0079] The maximum frost resistance grade of hydraulic concrete is F300. , The fitting method of the equation for changes in the water-binder ratio and the air content of the test is the same as in Example 1.

[0080] Cast in place C 90 20W6F100, C 90 For 35W8F300 hydraulic concrete, the actual water-binder ratios are 0.48 and 0.34 respectively, and the actual air contents of the mixtures are 3.6% and 5.0% respectively. The calculation results of the corresponding freeze-thaw cycle fitting equations are shown in Table 4.

[0081] Table 4 Results of antifreeze grade index

[0082]

[0083] From Table 4 we can see that C 90 20W6F100 meets the design antifreeze requirements after 100 freeze-thaw cycles; C 90 After 300 freeze-thaw cycles, the mass loss rate of 35W8F300 was greater than 5%, which did not meet the design antifreeze requirements. The results showed that C 90 The actual frost resistance grade of 35W8F300 is F250. By adjusting the mix ratio, the actual water-binder ratio is adjusted to 0.32, and the amount of air-entraining agent is increased to make the actual air content reach 5.5%. 90 35W8F300-2 meets the design antifreeze requirements.

[0084] The present invention uses the theory that the antifreeze performance of concrete is positively correlated with the glue-water ratio and the air content (air content within a certain range) under the premise of the same raw materials, and proposes a method for determining the antifreeze performance of concrete. Compared with the traditional quick freezing method, it can greatly shorten the test cycle and infer its antifreeze performance during the concrete mixing stage. The traditional quick freezing method for testing the antifreeze performance requires that the concrete specimens be cured to a specified age before the test can begin, and it takes about 10 days for every 100 cycles. In actual construction, if the concrete has been poured and the antifreeze performance is unqualified in the later stage, the rework cost is very high or even impossible to rework. The method provided by the present invention can grasp the antifreeze performance of the concrete before pouring, which is convenient for timely adjustment of the construction mix ratio, and is therefore more conducive to concrete quality control.

[0085] For construction site laboratories, the method for determining the antifreeze performance of concrete proposed by the present invention is simple to operate and can effectively improve the detection efficiency while reducing the investment in personnel and equipment, and has good economy.

[0086] The above are only several embodiments of the present invention and are not intended to limit the present invention in any form. Although the present invention is disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with the profession, without departing from the scope of the technical solution of the present invention, using the above disclosed technical content to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for determining the frost resistance of concrete, characterized in that: include: Step 1: Determine the first antifreeze relationship between mass loss rate, water-binder ratio and air content and the second antifreeze relationship between relative dynamic elastic modulus, water-binder ratio and air content according to freeze-thaw tests; Step 2: Inputting the actual water-binder ratio and the actual air content of the concrete mixture into the first antifreeze relationship to obtain the actual mass loss rate; inputting the actual water-binder ratio and the actual air content of the concrete mixture into the second antifreeze relationship to obtain the actual relative dynamic elastic modulus; Step 3: Determine the frost resistance grade of the concrete corresponding to the concrete mixture according to the actual mass loss rate and the actual relative dynamic elastic modulus.

2. The method for determining the frost resistance of concrete according to claim 1, characterized in that: The step 1 specifically includes: Step 1.1, constructing a corresponding relationship group between the water-binder ratio of each test and the gas content of a plurality of different tests that increase in sequence; Step 1.2, determining the mass loss rate and relative dynamic modulus of each relationship group under a plurality of freeze-thaw cycle numbers increasing in sequence; Step 1.3, determine the fitting relationship between the mass loss rate of the test under each number of freeze-thaw cycles and the water-binder ratio and air content of the corresponding test, and record it as the first antifreeze relationship; Determine the fitting relationship between the relative dynamic elastic modulus of the test under each number of freeze-thaw cycles and the water-binder ratio and air content of the corresponding test, which is recorded as the second antifreeze relationship.

3. The method for determining the frost resistance of concrete according to claim 2, characterized in that: The gas content of the test ranges from 2.0% to 7.0%.

4. The method for determining the frost resistance of concrete according to claim 3, characterized in that: The gas content of the test was increased in increments of 0.8% to 1.2%.

5. The method for determining the frost resistance of concrete according to claim 2, characterized in that: The number of freeze-thaw cycles is 50 to 300 times.

6. The method for determining the frost resistance of concrete according to claim 5, characterized in that: The increment of the number of freeze-thaw cycles is 25 or 50 times.

7. The method for determining the frost resistance of concrete according to any one of claims 2 to 6, characterized in that: The step 3 specifically includes: Obtaining the current number of freeze-thaw cycles corresponding to when the actual mass loss rate is greater than the first preset value or the actual relative dynamic elastic modulus is less than the second preset value; The number of freeze-thaw cycles before the current number of freeze-thaw cycles is recorded as the frost resistance grade of the concrete.

8. The method for determining the frost resistance of concrete according to claim 7, characterized in that: The first preset value is 5%.

9. The method for determining the frost resistance of concrete according to claim 7, characterized in that: The second preset value is 60%.

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