A method for testing and evaluating the segregation degree of mortar

Abstract

The present application relates to a kind of mortar segregation degree test and evaluation method, the test and evaluation method includes the following steps: mortar mix is loaded into test cylinder, then knock, first shear test is carried out using indoor vane shear instrument, and first shear strength τ1 is obtained;Mortar mix is loaded into test cylinder, then knock, after standing, second shear test is carried out using indoor vane shear instrument, and second shear strength τ2 is obtained;The indoor vane shear instrument is returned to original position, then indoor vane shear instrument is pressed into test cylinder, and third shear test is carried out, and third shear strength τ3 is obtained;According to τ1-τ3, segregation degree SI and segregation coefficient SC are calculated and evaluated.The evaluation method uses shear strength to evaluate segregation degree SI and segregation coefficient SC, and the range of the mortar segregation condition it reflects is wider than mortar stratification degree and other indicators.

Description

Technical Field

[0001] This invention belongs to the field of civil engineering technology, and in particular relates to a method for testing and evaluating the degree of mortar segregation. Background Technology

[0002] Mortar is a commonly used binding material in bricklaying. It is made by mixing sand and binders (cement, lime paste, clay, etc.) with water in a certain proportion, and is also called mortar. Freshly mixed mortar refers to mortar in its plastic state before it sets and hardens.

[0003] The properties of mortar or concrete mainly fall into three categories: workability, strength, and durability. Workability refers to the ability of freshly mixed mortar to be used in a given project or component; it is also known as workability. Workability directly determines the difficulty of transporting and pouring the freshly mixed mortar or concrete, as well as the quality of the final product. It significantly affects important indicators such as the pore structure, bleeding, and density of mortar or concrete products, and therefore also has a significant impact on strength and durability.

[0004] Workability mainly includes three aspects: fluidity, cohesiveness, and water retention. Cohesiveness is the ability of mortar to ensure that the cement paste coats the aggregate and prevents them from separating. Mortar with poor cohesiveness gradually exhibits obvious segregation and stratification over time, which may be accompanied by significant bleeding. However, there is no absolute correlation between the two. The intensity of mortar segregation and stratification, the main time period of occurrence, and the relationship between the initial setting time significantly affect the smooth progress of mortar transportation and pouring. The most common method for evaluating mortar segregation is the mortar segregation degree test in the "Standard for Test Methods of Basic Performance of Building Mortar" (JGJ / T70-2009). This test requires approximately 5.3L of mixed sample, a 30-minute settling time, and the removal of the previous mortar. It can only be performed once, and the sample is discarded after the test and cannot be recycled. Furthermore, the above segregation degree is calculated based on mortar consistency testing, which itself has certain range limitations. Its effective testing range is smaller than the consistency range (0-14.5cm).

[0005] CN102749439A discloses a device for testing and evaluating segregation in freshly mixed concrete, comprising a vibrating component and a test component. The vibrating component includes a base with a counterweight chamber mounted on it; an engine chamber is fixed to the upper end of the counterweight chamber, and an engine is mounted inside the engine chamber; a vibrating table connected to the engine is mounted on the upper part of the engine chamber; the test component is fixed on the vibrating table; the test component includes an upper and lower material-holding chamber that are interconnected, with a disc positioned between the upper and lower material-holding chambers, and the upper and lower material-holding chambers are connected by a rotating shaft; the disc has circular holes. This device is relatively complex, and its segregation rate is measured by testing the density of the upper and lower layers. Density characteristics cannot reflect the shear behavior of the slurry in the pipe, and the testing method does not actually simulate segregation but uses vibration.

[0006] Therefore, for current engineering applications of mortar, providing a testing and evaluation method that can effectively simulate the segregation behavior of mortar and fully reflect the uniformity changes in the shear characteristics of the mortar is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a method for testing and evaluating the degree of mortar segregation. This method is simple to operate, requires minimal mortar, and allows for multiple retests. It uses shear strength to evaluate the degree of segregation (SI) and the segregation coefficient (SC), providing precise guidance and construction basis for controlling the time of each stage during application, such as transportation, pouring, and molding. This reduces delays caused by pipe blockage and excessive local stress, ensuring the performance and quality of the hardened mortar.

[0008] To achieve the above-mentioned technical effects, the present invention adopts the following technical solution:

[0009] This invention provides a method for testing and evaluating the degree of mortar segregation, the method comprising the following steps:

[0010] (1) The mortar mixture was loaded into the test cylinder and then struck. The first shear test was performed using an indoor vane shear tester to obtain the first shear strength τ1.

[0011] (2) The mortar mixture was loaded into the test cylinder, and then it was tapped and left to stand. The second shear test was then performed using an indoor vane shear tester to obtain the second shear strength τ2.

[0012] (3) Return the indoor vane shearing device described in step (2) to its original position, then press the indoor vane shearing device into the test cylinder and perform the third shearing test to obtain the third shear strength τ3.

[0013] (4) Calculate and evaluate the segregation degree SI and segregation coefficient SC based on the shear strength obtained from steps (1) to (3).

[0014] In this invention, the mortar mixture is freshly mixed mortar. Based on the approximate shear strength range of the mortar mixture, the range of the vane blade length and width of the indoor vane shear tester, as well as the range of the test cylinder diameter, are determined.

[0015] In this invention, the indoor vane shear tester can select multiple test points on the same test surface to conduct tests, avoiding the influence of accidental factors. Moreover, the test is fast and does not require drainage, which meets the test requirements. Therefore, the indoor vane shear tester is selected for shear testing of mortar mixtures.

[0016] It is worth noting that the test method is simple to operate, requires little mortar, and is easy to mix. The same test cylinder sample can be tested multiple times under the condition that the distance between the edge and the measuring point is met. The shearing process used in the test method is similar to the mortar pumping process in the pipeline. Pumping is the most mainstream transportation method for large quantities of mortar in engineering. Using the parameters of the shearing process is more suitable for calculating and characterizing the segregation of mortar. The evaluation method uses shear strength to evaluate the degree of segregation SI and the segregation coefficient SC, which reflects the segregation of the slurry in a wider range than indicators such as the degree of mortar stratification.

[0017] As a preferred technical solution of the present invention, the tapping specifically involves using a wooden hammer to tap the mortar mixture 5-8 times at four different locations at equal distances from the test cylinder, so that the surface of the mortar mixture is smooth, free of air bubbles, and begins to rise.

[0018] In this invention, the number of taps is 5-8 times, for example, 5 times, 6 times, 7 times or 8 times, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] Preferably, the tapping time is ≤2 minutes, for example, it can be 1 minute, 1.2 minutes, 1.5 minutes, 1.7 minutes or 2 minutes, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0020] As a preferred technical solution of the present invention, the blade length of the indoor vane shearing device is 4.8-5.2cm, for example, it can be 4.8cm, 4.9cm, 5cm, 5.1cm or 5.2cm, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] Preferably, the width of the vane blade of the indoor vane shearing device is 2-3cm, for example, it can be 2cm, 2.2cm, 2.4cm, 2.6cm, 2.8cm or 3cm, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] The indoor vane shearing apparatus described in this invention is an automatic testing device, and related operations are performed according to SL 237.

[0023] Preferably, the diameter of the test tube is ≥8cm, for example, it can be 8cm, 9cm, 10cm, 12cm, 14cm or 16cm, etc., but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] In this invention, the diameter of the test cylinder is preferably not less than 4 times the width of the cross blade.

[0025] As a preferred technical solution of the present invention, the filling height of the mortar mixture in step (1) is ≥9.6cm, for example, it can be 9.6cm, 10cm, 10.4cm, 10.8cm, 11cm or 12cm, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] In this invention, the filling height of the mortar mixture in step (1) is preferably not less than 2 times the length of the cross blade.

[0027] Preferably, the indentation depth of the indoor vane shear in step (1) is such that the upper surface of the indoor vane shear is covered by the surface of the mortar mixture.

[0028] As a preferred technical solution of the present invention, the shear rate of the first shear test in step (1) is (9-20)° / min, for example, it can be 9° / min, 10° / min, 12° / min, 14° / min, 18° / min or 20° / min, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, the shear rates of the second shear test in step (2) and the third shear test in step (3) are the same as the shear rate in step (1).

[0030] In this invention, the same shear rate is used in the three shear tests, and the allowable error is no more than ±0.2° / min.

[0031] In this invention, the distance between the test point and the test cylinder wall in the first shear test in step (1) is ≥2cm. If the test point is too close to the cylinder wall, the measured value will be too large.

[0032] As a preferred technical solution of the present invention, the filling height of the mortar mixture in step (2) is 25.8-26.2cm, for example, it can be 25.8cm, 25.9cm, 26cm, 26.1cm or 26.2cm, etc., but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Preferably, the settling time in step (2) is 20-40 minutes, for example, it can be 20 minutes, 24 minutes, 28 minutes, 30 minutes, 34 minutes, 38 minutes or 40 minutes, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] In this invention, for mortars with large differences in initial setting time, the settling time can be adjusted as needed.

[0035] As a preferred technical solution of the present invention, the indentation depth of the indoor vane shear in step (2) is such that the upper surface of the indoor vane shear is covered by the surface of the mortar mixture.

[0036] In this invention, the surface of the mortar mixture in step (2) does not include the uppermost layer of exuded water after the mortar has settled.

[0037] Preferably, the distance between the test point and the test cylinder wall in the second shear test in step (2) is ≥2cm, for example, it can be 2cm, 2.4cm, 2.8cm, 3cm or 3.5cm, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] In this invention, the distance between the edge of the test point selected for the second shear test and the test cylinder wall is not less than the width of the cross blade.

[0039] As a preferred technical solution of the present invention, the pressing depth in step (3) is 10-30cm, for example, it can be 10cm, 12cm, 14cm, 16cm, 18cm, 20cm, 22cm, 24cm, 26cm, 28cm or 30cm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0040] In this invention, the pressing depth is controlled by the stud, scale, or electronic display of the shearing device; for mortars with large differences in cohesiveness, the pressing depth can be adjusted as needed.

[0041] In this invention, step (3) of returning the indoor vane shear to its original position means rotating the indoor vane shear back to 0°.

[0042] As a preferred technical solution of the present invention, the segregation degree SI in step (4) is calculated and evaluated using formula (1):

[0043] SI=τ3-τ1 (1)

[0044] Preferably, the evaluation criteria for the segregation degree SI are: SI < 0.8, no segregation and sedimentation occurs; SI ≥ 0.8, segregation and sedimentation occur.

[0045] In this invention, the evaluation of segregation degree SI changes with the time of the slurry. The higher the value of segregation degree SI, the more likely segregation and sedimentation will occur.

[0046] As a preferred technical solution of the present invention, the segregation coefficient SC in step (4) is calculated and evaluated using formula (2):

[0047]

[0048] Preferably, the evaluation criteria for the segregation coefficient SC are as follows: SC≤1.1, no segregation has occurred, and the homogeneity is excellent; 1.1<SC≤1.3, the degree of segregation is relatively mild, and the homogeneity is qualified; SC≥1.3, the degree of segregation is strong, and the homogeneity is unqualified.

[0049] In this invention, the segregation coefficient SC can evaluate the homogeneity and severity of segregation after slurry segregation. The larger the value of the segregation coefficient SC, the more severe the slurry segregation and the worse the homogeneity.

[0050] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] (1) The test method provided by the present invention is simple to operate, requires less mortar, and is easy to mix. The same test cylinder sample can be retested multiple times under the condition that the edge and measuring point distance are satisfied. The shearing process used in the test method is similar to the mortar pumping process in the pipeline. Pumping is the most mainstream transportation method for a large amount of mortar in engineering. Using the parameters of the shearing process is more suitable for calculating and characterizing the segregation of mortar.

[0053] (2) The evaluation method provided by the present invention uses shear strength to evaluate the degree of segregation SI and the segregation coefficient SC, which reflects the segregation of the slurry in a wider range than indicators such as the degree of slurry segregation. Detailed Implementation

[0054] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0055] In this embodiment of the invention, the blade length of the indoor vane shearing instrument is 5cm, the blade width is 2.5cm, and the diameter of the test cylinder is 12cm.

[0056] Example 1

[0057] This embodiment provides a method for testing and evaluating the degree of mortar segregation, the method comprising the following steps:

[0058] (1) The mortar mixture is filled into the test cylinder to a height of 11cm. The mortar mixture is tapped 6 times at four different positions at equal distances from the test cylinder with a wooden hammer to make the surface of the mortar mixture smooth, free of air bubbles and start to rise. The tapping process takes 1 minute. Then, the first shear test is performed using an indoor vane shear tester at 12° / min. The indentation depth is determined by the upper surface of the vane blade being just covered by the mortar surface. The first shear strength τ1 is obtained.

[0059] (2) The mortar mixture was loaded into the test cylinder to a height of 26m. At four different locations at equal distances from the test cylinder, the mixture was tapped 6 times with a wooden hammer to make the surface of the mortar mixture smooth, free of air bubbles and start to rise. The tapping process took 1 minute. After standing for 30 minutes, the second shear test was performed using an indoor vane shear tester at 12° / min. The depth of penetration was determined by the upper surface of the vane blade being just covered by the slurry surface. The distance between the edge of the test point and the wall of the test cylinder was 3cm. The second shear strength τ2 was obtained.

[0060] (3) Return the indoor vane shearing device described in step (2) to its original position, and then press the indoor vane shearing device into the test cylinder to a depth of 20cm. Perform the third shearing test at 12° / min to obtain the third shear strength τ3.

[0061] (4) Formulas (1) and (2) are used to calculate and evaluate the degree of segregation SI and the segregation coefficient SC, respectively;

[0062] SI=τ3-τ1 (1)

[0063]

[0064] Example 2-3

[0065] This embodiment provides a method for testing and evaluating the degree of mortar segregation. Except for the composition of the mortar mixture, which is different from that in Embodiment 1, all other conditions are the same as in Embodiment 1.

[0066] Example 4

[0067] This embodiment provides a method for testing and evaluating the degree of mortar segregation. Except for the shear rate of 14° / min in step (2), all other conditions are the same as in embodiment 1.

[0068] Example 5

[0069] This embodiment provides a method for testing and evaluating the degree of mortar segregation. Except for the shear rate of 14° / min in step (3), all other conditions are the same as in embodiment 1.

[0070] Example 6

[0071] This embodiment provides a method for testing and evaluating the degree of mortar segregation. Except for the shear rate of 14° / min in steps (2) and (3), the other conditions are the same as in embodiment 1.

[0072] Example 7

[0073] This embodiment provides a method for testing and evaluating the degree of mortar segregation. Except that the shear rate in steps (1) to (3) is 6° / min, all other conditions are the same as in embodiment 1.

[0074] Example 8

[0075] This embodiment provides a method for testing and evaluating the degree of mortar segregation. Except for the shear rate of 24° / min in steps (1) to (3), the other conditions are the same as in embodiment 1.

[0076] Example 9

[0077] This embodiment provides a method for testing and evaluating the degree of mortar segregation. Except for the tapping time of 4 minutes in steps (1) and (2), all other conditions are the same as in embodiment 1.

[0078] Example 10

[0079] This embodiment provides a method for testing and evaluating the degree of mortar segregation. Except for the filling height of 9cm in step (1), all other conditions are the same as in embodiment 1.

[0080] Example 11

[0081] This embodiment provides a method for testing and evaluating the degree of mortar segregation. Except for the filling height of 24cm in step (2), all other conditions are the same as in embodiment 1.

[0082] Example 12

[0083] This embodiment provides a method for testing and evaluating the degree of mortar segregation. Except for the filling height of 28cm in step (2), all other conditions are the same as in embodiment 1.

[0084] Comparative Example 1

[0085] This comparative example provides a method for testing and evaluating the degree of mortar segregation, using the JGJ / T70-2009 standard for basic performance test methods of building mortar for analysis and testing.

[0086] The test method involves letting the mortar stand for 30 minutes, then removing the top 200mm section of mortar. The remaining 100mm of mortar is poured out and mixed in a mixing pot for 2 minutes. The consistency is then measured according to the consistency test method. The difference between the measured consistency and the unmeasured consistency is the segregation value of the mortar. After the test, the sample is discarded and cannot be recycled. Furthermore, its effective test range is less than the consistency range (0-14.5cm).

[0087] The specific composition and related properties of the mortar mixtures in Examples 1-3 are shown in Table 1.

[0088] Table 1

[0089]

[0090] The test results of the first shear strength τ1, the second shear strength τ2, and the third shear strength τ3 in the above embodiments are shown in Table 2.

[0091] Table 2

[0092] <![CDATA[τ1 / kPa]]> <![CDATA[τ2 / kPa]]> <![CDATA[τ3 / kPa]]> Example 1 6.13 5.31 6.79 Example 2 4.33 3.90 6.09 Example 3 2.05 1.83 3.08 Example 4 6.12 5.54 6.79 Example 5 6.13 5.32 6.88 Example 6 6.13 5.45 6.90 Example 7 5.89 5.10 6.45 Example 8 6.58 5.59 7.15 Example 9 6.02 5.18 6.88 Example 10 6.13 5.44 6.54 Example 11 6.14 5.19 6.83 Example 12 6.12 5.11 6.89

[0093] The shear strength of the above embodiments was calculated and evaluated using formulas (1) and (2) respectively. The results of the segregation degree SI, segregation coefficient SC and evaluation are shown in Table 3.

[0094] Table 3

[0095]

[0096] The following points can be drawn from Tables 2 and 3:

[0097] (1) The test methods provided in Examples 1-3 of this invention can be used to evaluate the degree of segregation of freshly mixed mortar with different consistency;

[0098] (2) Based on Examples 1 and 4-6, it can be seen that when the same shear rate is not maintained during the test, the calculated segregation degree changes; based on Examples 1 and 7-8, it can be seen that when the shear rate is too low during the test, the shear strength test value is too low; when the shear rate is too high during the test, the shear strength test value is too high.

[0099] (3) As can be seen from Examples 1 and 9, when the tapping process takes too long, it leads to increased segregation, and the degree of segregation and the segregation coefficient increase.

[0100] (4) As can be seen from Examples 1 and 10-12, when the packing height is too low in the first shear test, the segregation degree and segregation coefficient are significantly reduced, and the test is inaccurate; when the packing height is too low or too high in the second and third shear tests, the segregation is reduced or aggravated, and the segregation degree and segregation coefficient are increased accordingly.

[0101] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for testing and evaluating the degree of mortar segregation, characterized in that, The testing and evaluation method includes the following steps: (1) The mortar mixture is loaded into the test cylinder and then struck. The first shear test is performed using an indoor vane shear tester to obtain the first shear strength τ1; the filling height of the mortar mixture is ≥9.6cm; In step (1), the indentation depth of the indoor vane shear is such that the upper surface of the indoor vane shear is covered by the surface of the mortar mixture. (2) The mortar mixture is loaded into the test cylinder, then tapped and left to stand. A second shear test is then performed using an indoor vane shear tester to obtain the second shear strength τ2. The loading height of the mortar mixture is 25.8-26.2 cm. In step (2), the indentation depth of the indoor vane shear is such that the upper surface of the indoor vane shear is covered by the surface of the mortar mixture. (3) Return the indoor vane shearing device described in step (2) to its original position, and then press the indoor vane shearing device into the test cylinder to perform the third shearing test and obtain the third shear strength τ3. The pressing depth in step (3) is 10-30cm; (4) Calculate and evaluate the segregation degree SI and segregation coefficient SC based on the shear strength obtained from steps (1) to (3); The degree of segregation SI is expressed by the formula: Perform calculations and evaluations; The segregation coefficient SC is calculated using the formula... Perform calculations and evaluations; The shear rate of the first shear test is (9-20)° / min; Among them, the shear rate of the second shear test in step (2) and the third shear test in step (3) are the same as the shear rate in step (1); The tapping time is ≤2 minutes.

2. The testing and evaluation method according to claim 1, characterized in that, The tapping specifically involves using a wooden hammer to gently tap the mortar mixture 5-8 times at four different locations at equal distances from the test cylinder, until the surface of the mortar mixture is smooth, free of air bubbles, and begins to rise.

3. The testing and evaluation method according to claim 1, characterized in that, The blade length of the indoor vane shearing machine is 4.8-5.2 cm.

4. The testing and evaluation method according to claim 1, characterized in that, The width of the vane blades in the indoor vane shearing machine is 2-3 cm.

5. The testing and evaluation method according to claim 1, characterized in that, The diameter of the test tube is ≥8cm.

6. The testing and evaluation method according to claim 1, characterized in that, The settling time in step (2) is 20-40 minutes.

7. The testing and evaluation method according to claim 1, characterized in that, In step (2), the distance between the test point and the test cylinder wall in the second shear test is ≥2cm.

8. The testing and evaluation method according to claim 1, characterized in that, The evaluation criteria for the degree of segregation SI are: SI < 0.8, no segregation and sedimentation occurs; SI ≥ 0.8, segregation and sedimentation occur.

9. The testing and evaluation method according to claim 1, characterized in that, The evaluation criteria for the segregation coefficient SC are: SC≤1.1, no segregation has occurred, and the homogeneity is excellent; 1.1 < SC ≤ 1.3 indicates mild segregation and moderate homogeneity; SC ≥ 1.3 indicates strong segregation and poor homogeneity.

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