A full life cycle test method for dynamic performance of ballastless track embedded structural concrete

Abstract

The present invention discloses a full-lifecycle dynamic performance test method for embedded concrete structures of ballastless track. The method comprises the following steps: 1) preparing embedded concrete specimens in proportion to the actual dimensions of the bi-block ballastless track; 2) subjecting the specimens to static loading and measuring their ultimate strength; 3) developing fatigue or impact dynamic tests to determine the dynamic failure life and dynamic shear cracking life of the specimens; 4) determining a repair system based on the life ratio of the dynamic shear cracking life to the dynamic failure life; and 5) performing grouting repairs after shear cracking of the specimens, followed by fatigue or impact dynamic tests to estimate the life attenuation rate and service life of the bi-block ballastless track structure. The present invention employs specimens that accurately reflect the embedded structure of the bi-block ballastless track and develops a dynamic test system that is more consistent with actual service conditions, providing a method for evaluating the service life of ballastless track, determining a repair system, and selecting repair materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of testing building materials, and specifically relates to a full-life cycle dynamic performance test method for embedded structural concrete of ballastless track. The method is suitable for embedded structural concrete performance testing, and is particularly suitable for dynamic performance testing of double-block ballastless track on high-speed railways. Background Art

[0002] Ballastless tracks, with concrete as the main engineering material, have been widely used in high-speed railways around the world. Currently, the main types of ballastless tracks are CRTSI and CRTSII double-block ballastless tracks. During their service, ballastless tracks are mainly subjected to high-frequency fatigue loads caused by the operation of high-speed trains. High-frequency fatigue loads will significantly accelerate the initiation of microcracks and the expansion of existing microcracks in concrete with high brittleness and insufficient toughness, resulting in a decrease in the service performance of the concrete structure, which makes the concrete more susceptible to damage. Although the service life of ballastless track structures is still relatively short, defects such as cracking of the roadbed slab and failure of the bonding between the sleepers and cast-in-place parts have already affected the durability of the ballastless track structure and the safety of driving. Therefore, it is necessary to propose a test method for the dynamic performance of concrete in double-block ballastless track structures throughout their entire life cycle to provide technical support for the service life evaluation and service performance improvement of double-block ballastless track structures.

[0003] Because railway structures are subject to typical cyclic loading, the dynamic performance of concrete is a key concern for the railway industry. Chinese standards such as "Fatigue Test Methods for Prestressed Concrete Sleepers" (TB / T1878-2002), "Concrete Track Slabs for CRTS II Twin-Block Ballastless Track" (TB / T3399-2015), and "Bending Fatigue Test Methods for Prestressed Concrete Simply Supported Beams" (TB / T2326-1992) already specify fatigue test methods for various structures. However, there are no specific standards for the dynamic performance of twin-block ballastless track. The "Standard for Test Methods for Long-Term Properties and Durability of Ordinary Concrete" (GB / T50082-2009) also addresses fatigue performance of concrete materials, but only for loading frequencies of 4Hz to 8Hz. Twin-block ballastless track structures are subject to complex stress patterns, with fatigue load frequencies generally exceeding 20 Hz. When high-speed trains operate at speeds of 300-350 km / h, the maximum load frequency can reach around 40 Hz. Furthermore, high-stress impact loads caused by random defects and structural deformations under high-frequency fatigue loads accelerate fatigue failure. This leads to significant discrepancies between the relevant standards and the fatigue loads actually experienced by ballastless track structures.

[0004] Bi-block ballastless track is cast on-site, with bi-block sleepers embedded in cast-in-place concrete to form the trackbed slab, which together with the cast-in-place supporting layer form the track structure. Sleepers possess the highest strength and directly bear the train loads. However, due to differences in the dynamic properties of different concrete types and complex load transfer, dynamic bond failure and damage are common at the interface between the new and old concrete in embedded structures. Relevant standards analyze only a single material and fail to reflect the complex stress transfer and damage processes within the embedded structure of bi-block ballastless track. In order to realize the rapid detection of the performance of the concrete embedded structure, the double-block ballastless track unit structure can be simplified into an embedded structure. However, patents such as "A Double-Block Concrete Sleeper" (CN109537374A), "A Steel Tube Concrete Double-Block Sleeper Integral Roadbed Construction Structure" (CN217399278U), and "A Double-Block Ballastless Track Slab and Its Preparation Method" (CN107574725A) all study the overall structural performance of the double-block ballastless track. At present, there is a lack of research on embedded structural concrete structures.

[0005] The current dynamic test of twin-block ballastless track concrete has the following problems:

[0006] (1) The existing concrete specimens are mainly made of a single material, which is inconsistent with the embedded structural characteristics of the twin-block ballastless track;

[0007] (2) The loading frequency of the fatigue test is too low, which is significantly different from the dynamic loads of high-frequency fatigue and impact that the ballastless track concrete is subjected to, and cannot accurately reflect the actual service conditions of the ballastless track embedded structure;

[0008] (3) The test evaluation method is single and cannot provide guidance for the repair system of the double-block ballastless track structure. There is also a lack of analysis methods for the full life cycle performance of the ballastless track structure. Summary of the Invention

[0009] In response to the current situation of lack of a full-life cycle test method for the dynamic performance of embedded structural concrete in ballastless track, the present invention invents a test method for the dynamic performance of embedded structural concrete that conforms to the fatigue load characteristics of high-speed railway structures, so as to achieve accurate evaluation of the full-life cycle dynamic performance of double-block ballastless track concrete.

[0010] The technical solution of the present invention:

[0011] A full life cycle test method for the dynamic performance of ballastless track embedded structural concrete, the test steps of this method are as follows:

[0012] 1) Prepare embedded structural concrete specimens in proportion to the actual size of the bi-block ballastless track;

[0013] 2) Static loading of embedded structural concrete specimens to measure their ultimate strength;

[0014] 3) Formulate a fatigue or impact dynamic test system based on the ultimate strength of embedded structural concrete specimens and conduct tests to determine the dynamic failure life and dynamic shear cracking life of the specimens;

[0015] 4) Determine the repair system for the entire life cycle of the twin-block ballastless track structure based on the life ratio of dynamic shear cracking life to dynamic failure life;

[0016] 5) When shear cracking occurs, select materials for grouting repair, and then conduct fatigue or impact dynamic tests to estimate the life attenuation rate and service life of the twin-block ballastless track structure.

[0017] Furthermore, the preparation method of the embedded structural concrete specimen is:

[0018] 11) The preparation dimensions of the embedded structural concrete specimens are designed according to the principle of equal proportions. First, the inner layer of concrete is prepared and poured into the inner layer steel mold;

[0019] 12) Remove the mold after one day of pouring and place it in a standard curing room for 14 days;

[0020] 13) After preparing the outer layer of concrete and placing it in the outer steel mold for casting, place the inner layer of concrete with the molded surface facing upwards on the outer layer of concrete and continue pouring to fill the mold;

[0021] 14) After pouring for 1 day, the mold is removed and the specimen is cured in a standard curing room. The overall curing time of the specimen is not less than 28 days;

[0022] 15) Before the test, the uneven parts of the specimen surface should be smoothed with sandpaper, and there should be no holes with a diameter exceeding 5mm and a depth exceeding 2mm near the loading area.

[0023] Furthermore, the static loading in step 2) is performed on a press, with each group of test pieces being no less than 3 and a loading speed of 0.08 MPa / s to 0.10 MPa / s.

[0024] Furthermore, when the test part is located in the position of the line that mainly bears fatigue load, the dynamic test method is selected as fatigue dynamic test, the fatigue loading stress upper limit S = 0.6 times the ultimate strength, the stress ratio is 0.1, the loading mode is bending fatigue, the loading waveform is a sine wave, the loading frequency f ≥ 20 Hz, and the maximum number of loading times is 2×10 6 Each test group shall have no less than 3 test specimens. The vertical displacement of the inner and outer layers of concrete shall be measured and recorded during the test. Fatigue life shall be less than 2×10 6 times, record the dynamic failure life and take the average value N1. If the load is 2×10 6 If the specimen is still not damaged, the 6The dynamic failure life N1 of the concrete specimen is recorded as the time of displacement. When the displacement suddenly changes, the displacement difference between the two layers of concrete exceeds 20%, or the displacement is opposite, it is considered that the bonding between the embedded structure concrete layers has failed, and the embedded structure should be repaired. The dynamic shear cracking life N2 of the bonding part at this time is recorded.

[0025] When the test location is at the position where the switch sleeper or track unevenness mainly bears the impact load, the dynamic test method is selected as the bending drop hammer impact dynamic test. The drop hammer mass is 5kg, the drop hammer height is 500mm~1500mm, and the span of the bending fixture is 300mm. Before the test, the specimen is adjusted so that the impact point is located at the center of the specimen. Each group of test specimens is no less than 3 pieces. During the test, the vertical displacement of the inner and outer layers of concrete is measured and recorded, and the dynamic damage life caused by the impact is recorded and the average value N1 is taken; when the displacement suddenly changes, the displacement difference between the two layers of concrete exceeds 20% or the displacement is opposite, it is considered that the bonding between the concrete layers of the embedded structure has failed, the embedded structure should be repaired, and the dynamic shear cracking life N2 of the bonding part at this time is recorded.

[0026] Furthermore, the method for determining the repair system in step 4) is: based on the life ratio of dynamic shear cracking life to dynamic failure life, the repair system of the bi-block ballastless track structure within the 60-year life cycle is analyzed:

[0027]

[0028] Where: N is the repair interval of the bi-block ballastless track structure, N1 is the dynamic failure life of the embedded structure concrete, and N2 is the dynamic shear cracking life of the bonding part of the embedded structure concrete.

[0029] Furthermore, the life attenuation rate calculation method of the bi-block ballastless track structure is as follows: when the performance of the repaired specimen needs to be analyzed, the dynamic test is stopped when the specimen reaches the bonding failure or separation state, and the repair is carried out by pressure grouting. The dynamic test is continued after the grouting material hardens for 7 days; the dynamic shear cracking life of the repaired specimen is recorded and the average value N3 and the separation life N4 are taken. According to formula (1), the repair interval of the repaired ballastless track structure can be calculated, and the life attenuation rate after repair is evaluated according to formula (2):

[0030]

[0031] Where x is the life attenuation rate of the bi-block ballastless track structure, N2 is the dynamic shear cracking life of the embedded structural concrete specimen before repair, and N4 is the dynamic shear cracking life of the bonding part of the embedded structural concrete after repair.

[0032] The service life calculation method of the ballastless track structure is as follows: after repeated repairs, when x reaches 40%, the dynamic performance of the specimen is determined to be failed, and the damage life N before x reaches 40% is recorded. 2n-2 According to formula (3), the service life N of ballastless track after n repairs is estimated n :

[0033] N n =N2+N4+...+N 2n-2 +60 (3).

[0034] The mechanism of the present invention: As a typical feature of train operation, dynamic loads can easily cause damage to concrete with poor tensile properties and continue to accumulate, eventually leading to diseases in the ballastless track structure. At the same time, the bonding area between the inner and outer layers of concrete of the embedded dual-block ballastless track is a weak area of ​​the structure, and the initial damage within the interface may become the starting point for the development of fatigue damage. Under repeated dynamic loads, the deformation difference of the concrete will eventually lead to shear failure at the interface. Based on this feature, by analyzing the deformation difference of the concrete before and after loading, its dynamic performance can be evaluated. At the same time, the fatigue life at different stages also provides a reference for the repair system of the dual-block ballastless track structure.

[0035] Advantages of the present invention:

[0036] (1) The innovative embedded structural specimen with the same structure as the double-block ballastless track can more accurately evaluate the dynamic performance of the ballastless track;

[0037] (2) A dynamic test system that is closer to the actual service conditions of high-speed railways has been developed, which can better reflect the dynamic load characteristics of the twin-block ballastless track structure;

[0038] (3) The repair system and the experimental analysis method of the life cycle performance of the embedded structure of ballastless track have been enriched, and the life prediction of the ballastless track structure has been realized. The prediction results are consistent with the actual service conditions of the double-block ballastless track structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Attached photos Figure 1 Schematic diagram of the embedded structural concrete specimen of the present invention.

[0040] In the picture: 1-C60 sleeper, 2-cast-in-place concrete. DETAILED DESCRIPTION

[0041] The technical solution of the present invention is further described in detail below through embodiments and in conjunction with the accompanying drawings.

[0042] Example 1: An embedded structure concrete specimen was prepared according to the actual size of the embedded structure of the CRTSⅠ type sleeper, and the preparation requirements were as follows: 1) the total height of the inner and outer layers was 110 mm, and an inner layer of C60 concrete was prepared and poured into a steel mold with a size of 200 mm × 60 mm × 60 mm; 2) the mold was removed after 1 day of pouring, and the specimen was placed in a standard curing room for curing for 14 days; 3) the outer layer of C40 concrete was prepared and poured into a steel mold with a size of 400 mm × 100 mm × 100 mm, with a casting height of 50 mm. The inner layer concrete was placed with the formed surface facing up on the outer layer concrete and the mold was continued to be filled. The inner layer concrete was 10 mm higher than the outer layer; 4) the mold was removed after 1 day of pouring and the specimen was placed in a standard curing room for curing. The overall curing time of the specimen was not less than 28 days; 5) before the test, the uneven parts of the specimen surface should be smoothed with sandpaper, and there should be no holes with a diameter of more than 5 mm and a depth of more than 2 mm near the loading part.

[0043] Three embedded structural concrete specimens were statically loaded on a press, with three specimens in each group. The loading speed was 0.10 MPa / s, and the average ultimate load was measured to be 23.2 kN.

[0044] Three embedded concrete specimens were subjected to dynamic fatigue testing. The fatigue stress limit, S, was 13.92 kN, the stress ratio was 0.1, and the loading method was flexural fatigue. The loading waveform was a sinusoidal wave at a loading frequency of f = 20 Hz. During the test, cracking of the outer concrete layer and displacement of the bonded joint were measured and recorded. Bond failure between the concrete layers was considered to occur when there was a sudden change in displacement, a displacement difference of more than 20% between the two concrete layers, or when the displacements were opposite. The fatigue failure lives of the three specimens were 784,000, 882,000, and 1.28 million cycles, with an average fatigue failure life of 982,000 cycles. The bond failure lives of the three specimens were 152,000, 390,000, and 448,000 cycles, respectively, with an average bond failure life of 330,000 cycles.

[0045]

[0046] Based on the ratio of fatigue failure life to dynamic shear cracking life when the bonding parts of embedded structural concrete specimens are damaged, it is concluded that within the 60-year service life, the twin-block ballastless track structure should be inspected and repaired approximately 33.6 years.

[0047] The embedded structural concrete specimens were repaired by pressure grouting, and fatigue dynamic tests were continued after the grouting material hardened for 7 days. The dynamic failure life after repair was obtained and the average value was 842,000 times. The dynamic shear cracking life of the bonding part after repair was 284,000 times.

[0048]

[0049] The life attenuation rate after repair is 13.9%, which is less than 40%, and the specimen has not reached the state of dynamic performance failure.

[0050] N2=20.2+60=80.2

[0051] Based on the separation life and dynamic damage life before and after repair, it is estimated that the service life of the ballastless track after repair is about 80.2 years.

[0052] Example 2:

[0053] Embedded structure concrete specimens were prepared according to the actual dimensions of the embedded structure of the CRTS I type sleeper. The preparation requirements were as follows: 1) The total height of the inner and outer layers was 110 mm. The inner layer of C60 concrete was prepared and poured into a steel mold with dimensions of 200 mm × 60 mm × 60 mm. 2) The mold was removed after 1 day of pouring and the specimen was placed in a standard curing room for curing for 14 days. 3) The outer layer of C40 concrete was prepared and poured into a steel mold with dimensions of 400 mm × 100 mm × 100 mm. The casting height was 50 mm. The inner layer of concrete was placed with the formed surface facing up on the outer layer of concrete and the mold was continued to be filled. The inner layer of concrete was 10 mm higher than the outer layer. 4) The mold was removed after 1 day of pouring and the specimen was placed in a standard curing room for curing. The overall curing time of the specimen was not less than 28 days. 5) Before the test, the uneven parts of the specimen surface should be smoothed with sandpaper. There should be no holes with a diameter of more than 5 mm and a depth of more than 2 mm near the loading part.

[0054] Three embedded concrete specimens were subjected to dynamic drop-hammer impact testing. The drop weight was 5 kg, the drop height was 1000 mm, and the span of the bending fixture was 300 mm. During the test, the cracking of the outer concrete layer and the displacement of the bonding area were measured and recorded. Bond failure between the concrete layers was considered to occur when there was a sudden change in displacement, a difference of more than 20% in displacement between the two concrete layers, or when the displacements were opposite. The impact failure life of the three specimens was 26, 30, and 43 times, with an average impact failure life of 33 times. The dynamic shear cracking life of the three specimens was 11, 15, and 26 times, respectively, for a total of 17.3 times.

[0055]

[0056] Based on the ratio of the impact failure life to the dynamic shear cracking life when the bonding parts of the embedded structural concrete specimens are damaged, it is concluded that within the 60-year service life, the twin-block ballastless track structure should be inspected and repaired approximately 30.2 years.

[0057] The embedded structural concrete specimens were repaired by pressure grouting. After the grouting material hardened for 7 days, a drop hammer impact dynamic test was carried out. The dynamic failure life after repair was obtained and the average value was 28 times. The dynamic shear cracking life of the bonding part after repair was 11 times.

[0058]

[0059] The life attenuation rate after repair is 36.4%, which is less than 40%, and the specimen has not reached the state of dynamic performance failure.

[0060] N2=31.9+60=91.9

[0061] Based on the separation life and dynamic damage life before and after repair, it is estimated that the service life of the ballastless track after repair is about 91.9 years.

[0062] The above description of the embodiments is intended to facilitate understanding and application of the present invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring creative effort. Therefore, the present invention is not limited to the embodiments described herein, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention should fall within the scope of protection of the present invention.

Claims

1. A full life cycle ballastless track embedded structure concrete dynamic performance test method, characterized in that: The test steps of this method are: 1) Prepare embedded structural concrete specimens in proportion to the actual size of the bi-block ballastless track; 2) Static loading of embedded structural concrete specimens to measure their ultimate strength; 3) Formulate a fatigue or impact dynamic test system based on the ultimate strength of embedded structural concrete specimens and conduct tests to determine the dynamic failure life and dynamic shear cracking life of the specimens; 4) Determine the repair system for the entire life cycle of the twin-block ballastless track structure based on the life ratio of dynamic shear cracking life to dynamic failure life; 5) When shear cracking occurs, select materials for grouting repair, and then conduct fatigue or impact dynamic tests to estimate the life attenuation rate and service life of the twin-block ballastless track structure; When the test part is located in the position of the line that mainly bears fatigue load, the dynamic test method is fatigue dynamic test, the fatigue loading stress upper limit S = 0.6 times the ultimate strength, the stress ratio is 0.1, the loading method is bending fatigue, the loading waveform is a sine wave, the loading frequency f ≥ 20 Hz, and the maximum number of loading times is 2×10 6 Each test group shall have no less than 3 test specimens. The vertical displacement of the inner and outer layers of concrete shall be measured and recorded during the test. Fatigue life shall be less than 2×10 6 times, record the dynamic failure life and take the average value N1. If the load is 2×10 6 If the specimen is still not damaged, the 6 times as the dynamic failure life N1 of the concrete specimen; When the displacement suddenly changes, the displacement difference between the two layers of concrete exceeds 20%, or the displacement is opposite, it is considered that the bonding between the embedded structure concrete layers has failed, and the embedded structure should be repaired. The dynamic shear cracking life N2 of the bonding part at this time should be recorded; When the test location is at the position where the switch sleeper or track irregularity mainly bears the impact load, the dynamic test method is the bending drop hammer impact dynamic test. The drop hammer mass is 5kg, the drop hammer height is 500mm~1500mm, and the span of the bending fixture is 300mm. Before the test, the specimen is adjusted so that the impact point is located at the center of the specimen. Each group of test specimens is no less than 3 pieces. During the test, the vertical displacement of the inner and outer layers of concrete is measured and recorded, and the dynamic damage life caused by the impact is recorded and the average value N1 is taken; when the displacement suddenly appears, the displacement difference between the two layers of concrete exceeds 20% or the displacement is opposite, it is considered that the bonding between the concrete layers of the embedded structure has failed, the embedded structure should be repaired, and the dynamic shear cracking life N2 of the bonding part at this time is recorded.

2. The method for testing the dynamic performance of ballastless track embedded concrete during the entire life cycle according to claim 1 is characterized in that: The preparation method of the embedded structural concrete specimen is as follows: 11) The preparation dimensions of the embedded structural concrete specimens are designed according to the principle of equal proportions. First, the inner layer of concrete is prepared and poured into the inner layer steel mold; 12) Remove the mold after one day of pouring and place it in a standard curing room for 14 days; 13) After preparing the outer layer of concrete and placing it in the outer steel mold for casting, place the inner layer of concrete with the molded surface facing upwards on the outer layer of concrete and continue pouring to fill the mold; 14) After pouring for 1 day, the mold is removed and the specimen is cured in a standard curing room. The overall curing time of the specimen is not less than 28 days; 15) Before the test, the uneven parts of the specimen surface should be smoothed with sandpaper, and there should be no holes with a diameter exceeding 5mm and a depth exceeding 2mm near the loading area.

3. The method for testing the dynamic performance of ballastless track embedded concrete during the entire life cycle according to claim 1 is characterized in that: The static loading in step 2) is performed on a press, with each group of test pieces being no less than 3 and a loading speed of 0.08 MPa / s to 0.10 MPa / s.

4. A full life cycle ballastless track embedded structure concrete dynamic performance test method according to any one of claims 1 to 3, characterized in that: The method for determining the repair system in step 4) is: based on the life ratio of dynamic shear cracking life to dynamic failure life, analyze the repair system of the bi-block ballastless track structure within the 60-year life cycle: Where: N is the repair interval of the bi-block ballastless track structure, N1 is the dynamic failure life of the embedded structure concrete, and N2 is the dynamic shear cracking life of the bonding part of the embedded structure concrete.

5. The full life cycle ballastless track embedded structure concrete dynamic performance test method according to claim 4 is characterized in that: The life attenuation rate calculation method of the bi-block ballastless track structure is as follows: when the performance of the repaired specimen needs to be analyzed, the dynamic test is stopped when the specimen reaches the bonding failure or crack separation state, and the repair is carried out by pressure grouting. The dynamic test is continued after the grouting material hardens for 7 days; the dynamic shear cracking life of the repaired specimen is recorded and the average value N3 and the crack separation life N4 are taken. The repair interval of the repaired ballastless track structure can be calculated according to formula (1), and the life attenuation rate after repair is evaluated according to formula (2): Where x is the life attenuation rate of the bi-block ballastless track structure, N2 is the dynamic shear cracking life of the embedded structural concrete specimen before repair, and N4 is the dynamic shear cracking life of the bonding part of the embedded structural concrete after repair. The service life calculation method of the ballastless track structure is as follows: after repeated repairs, when x reaches 40%, the dynamic performance of the specimen is determined to be failed, and the damage life N before x reaches 40% is recorded. 2n-2 According to formula (3), the service life N of ballastless track after n repairs is estimated n : A n =N2+N4+...+N 2n-2 +60 (3).

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