Research on The Effect of Geotextile Based on MMLS3 Equipment in Preventing Reflection Crack
Abstract: The MMLS3 equipment is used to accelerate the loading test of the 1/3-scale pavement structure model, simulate the bending-shear composite effect caused by vehicle load, and track and monitor the strain and crack propagation. The study is between the surface layer and the base layer. The effect of laying wholesale polyester nonwoven geotextile to prevent reflection cracks is obtained. The results show that the loading times of the cloth group in the initial crack and the crack penetration are 3.55 times and 3.25 times respectively of the clothless group. Before the initial cracking, the high quality filament nonwoven geotextile is weakened by the layer. The inter-bonding makes the total strain and elastic strain of the surface layer larger than that of the non-cloth group, but the surface fracture can be delayed by increasing the composite fracture energy combined with the asphalt layer; after the initial cracking, the wholesale filament nonwoven geotextile is gradually stretched to withstand greater pulling. Stretching force, assisting the surface layer to resist bending and shearing, so that the total strain and elastic strain of the cloth group are gradually reduced; after the penetration, the filament nonwoven geotextile for sale can still maintain the joint of the two sides of the crack, inhibiting crack widening and structural displacement, so that the total strain and elastic strain are stabilized at 180×10-6 and 9×10-6, while the no-cloth group continues to widen due to cracks, and the total strain and elastic strain exceed 600×10-6 and 8×10-6 and continue. increase.
Keywords: road engineering; reflective crack; accelerated loading test; filament nonwoven geotextile manufacturers; semi-rigid base
The prevention of reflective cracks in semi-rigid base asphalt pavements (hereinafter referred to as anti-reverse) has always been a major problem in the engineering field. It is an economical and practical method to prevent polypropylene nonwoven geotextile manufacturers between asphalt surface and water-stable base. The causes of reflection cracks are mainly vehicle load and temperature changes. Vehicle loads cause bending and shearing on the asphalt layer, while temperature changes mainly cause tension. According to the conclusions of domestic and foreign research, high quality filament nonwoven geotextile is used to prevent tension-type reflections. The crack effect is good, but the researchers have not reached a consensus on the effect of preventing shear-type reflective cracks. Hu Changshun passed the full-scale fatigue test and thought that the high quality polypropylene nonwoven geotextile could not prevent the occurrence of shear-type reflective cracks, but could delay its expansion; Li Shuming Through finite element simulation analysis, it is considered that laying wholesale filament nonwoven geotextile does not reduce the maximum shear stress of the asphalt layer, so it has little effect on delaying shear-type reflection crack.
In the experimental research on the anti-counterfeit problem of wholesale polypropylene nonwoven geotextile at home and abroad, the majority of simulated vehicle loads are used. These studies usually use the fixed point vertical loading to simulate the bending or shearing effect of the vehicle load alone or use the wheel to reciprocate at a shorter distance. Rolling load simulates the effect of moving loads on the pavement structure. However, these two loading methods have insufficiencies compared to the actual conditions of the road. The former cannot simultaneously simulate the bending-shearing effect caused by wheel rolling, and the latter is at the loading distance. It is limited by the small loading instrument, and the reciprocating loading mode is inconsistent with the one-way driving of the vehicle in the actual road. The MMLS3 (1/3modelmobileloadsimulator) accelerating loading device developed in South Africa uses the unidirectional rolling wheel to simulate the vehicle load bending-shearing interaction. The loading length is 130cm, which can avoid the shortcomings of the above two methods, and can simulate the horizontal force on the road surface and the rutting process under the repeated action of the vehicle load. Pirmohammad pointed out that the combined bending and shearing will be significantly accelerated. The cracking of the road surface, so it is more practical to study the crack resistance effect of the filament nonwoven geotextile for sale under this condition. Righteousness.
To this end, this paper uses MMLS3 to carry out indoor fatigue test, simulates the repeated action of one-way moving load, to study the effect of polypropylene nonwoven geotextile factory price under the action of vehicle load bending and shearing to prevent reflection cracks, and to study the feasibility of using MMLS3 to study the reflection crack problem. Sex and validity are judged.
1. Test method
1.1 Pavement structure model design
The test structure model is designed based on the actual situation of the expressway from Lhasa to Gongbujiangda section. The pavement structure combination is shown in Table 1. The diameter of the MMLS3 test tire is 300mm and the width is 80mm, which is about 1/3 of the standard tire size. The pressure is 2.7MPa, which is equivalent to 1/9 of the standard axle load BZZ-100. Su Zhixiang pointed out through theoretical analysis and finite element simulation that in order to ensure that the test model has similar material and mechanical properties to the actual pavement, the material of the test model must be maintained. The actuality is the same, and the thickness is scaled to 1/3 of the actual pavement structure. Under this scaling ratio, the tensile stress and tensile strain of the test layer under the maximum wheel pressure and the actual pavement under the standard axle load BZZ-100 The corresponding values are the same.
In order to make the structural model after the thickness reduction easy, the upper, middle and lower layers of the original road are combined into one structural layer. The base asphalt of No. 90 is selected with reference to the actual road, and the ratio of oil to stone is 4%. The grading is selected according to the lower layer. AC25. Asphalt The size of the surface layer needs to be considered in consideration of the actual loading area size, crack observation and sensor layout requirements of the MMLS3. The base layer needs to consider the need for fixing the test socket and the convenience of the surface layer construction. To allow the vertical direction of the base layer during loading. Displacement and displacement, to simulate the deformation of the pavement structure under the vehicle load bending-shearing, the soil foundation is set under the pavement structure, the size is consistent with the test slot. The dimensions of each structural layer are shown in Table 1 and Figure 1.
The test polyester nonwoven geotextile for sale is a polypropylene non-woven fabric (150g·m-2). After infiltrating the emulsified asphalt, a wide strip tensile test is carried out, and the longitudinal tensile properties are measured in Table 2.
In order to crack the crack at the specified position for observation and data acquisition, the base layer is pre-sewed. There is a prefabricated crack in each of the cloth group and the non-cloth group. The width is 0.5cm according to the domestic and foreign research experience, and the length of the three base layers after cutting. 50cm, 80cm and 50cm.
In order to observe the strain at the crack, a fiber grating strain sensor is embedded in the surface layer near the bottom of the layer. There is one cloth group and one cloth group, and the direction is perpendicular to the prefabricated crack, as shown in Fig. 1a. Sensor measurement and surface The relationship between the bottom strain of the layer is shown in Fig. 2. Before the surface layer is cracked, the measured value of the sensor S1 is equal to the strain E1 of the asphalt layer. After the surface layer is cracked, the measured value of the sensor S2 is the strain E2 of the asphalt layer and the reflection crack. The sum of the opening widths ΔS of the positions. For the convenience of comparative analysis in the development of reflective cracks, the sensor measurements before and after the cracking of the surface layer are collectively referred to as a total strain.
1.2 Pavement structure model making and loading
After the soil base and the base layer are sequentially prepared and the health is completed, the prefabricated cracks are sawed on the base layer. The prefabricated cracks and the surrounding of the base layer are temporarily restrained to avoid displacement during the construction. After the base layer is arranged, the cloth set is placed on the top surface of the base layer. Spread the 1.4kg·m-2 emulsified asphalt, lay a polypropylene nonwoven geotextile for sale on top of it, and then spread 1.2kg·m-2 emulsified asphalt adhesive oil and stone chips on the surface of the wholesale filament nonwoven geotextile. For the clothless group, directly spread the cloth. Emulsified asphalt of kg·m-2. The sensor is buried at the same time as the asphalt pavement is paved. After paving, it is compacted with a small roller.
After the surface layer is rehabilitated, the mold is removed and the temporary restraint of the base layer is removed, and the MMLS3 is erected on the pavement structure model. After the bracket and the test slot are fixed and leveled, the height of the instrument is adjusted so that the wheel pressure of the loaded wheel reaches a preset value. Apply lime to the side of the surface above the crack to visually observe the crack development. After the erection is completed, as shown in Figure 1b.
The MMLS3 is started to start loading, and the circular orbit with four wheels is rotated by the transmission device so that the test model is loaded in one-way and even intervals, and the loading speed is 3600 times·h-1 (1 Hz). The simulated vehicle load bending – The principle of sharing is shown in Figure 3. When the wheel is on the side of the pre-saw, the shearing action is applied to the pavement structure. When the wheel is directly above the pre-sewed seam, the bending action is applied. The wheel drives through the pre-saw. After the seam, the shearing action is applied again.
A total of 540,000 loadings were carried out in the test, of which the first 330,000 were uninterrupted loading. During the two test groups, the reflection cracks penetrated through the surface layer. After that, due to the obvious rutting of the surface layer, the MMLS3 loaded the wheel to the road surface. The pressure of the structure is reduced. Therefore, the loading wheel is lowered and the shape of the crack is further observed. When the load is 540,000 times, the crack shape has become stable, and the test is over. The development of the side crack of the surface layer is recorded during the whole test.
2. Surface layer bottom strain analysis
After loading 330,000 times, the sensor was damaged due to a large number of repeated loadings, so only the strain data of the first 330,000 loads were analyzed.
The total strain at the bottom of the surface layer recorded by the sensor is shown in Fig. 4. The black dot in the figure is the total crack corresponding to the initial crack of the reflective crack and the penetration through the surface layer. Calculate the difference between the peaks and valleys in the strain waveform generated by each loading. That is, the elastic strain is plotted as shown in Fig. 5. The fluctuation of the bottom layer strain during the repeated loading process is investigated. The number of loadings corresponding to the crack initiation and penetration is judged by the naked eye observation and the strain data. According to the development stage of the reflection crack, The specific analysis is as follows.
2.1 Before the surface layer is cracked
Before the surface layer cracking, the total strain and elastic strain of the two test groups gradually increased with the loading process. The total strain and elastic strain of the cloth group were larger than those of the clothless group. This is because the structural deformation is small at this stage, and the high quality polyester nonwoven geotextile has not yet been produced. Sufficient tensile deformation to assist the surface layer to withstand the tensile force and the laying of the wholesale filament nonwoven geotextile will weaken the interlayer adhesion between the surface layer and the base layer, resulting in a large total strain and elastic strain.
2.2 Surface cracking
The clothless group and the cloth group were cracked when loading 0.9 million times and 32,000 times, as shown in Figures 4a and 5a. The loading times of the cloth group in the initial cracking of the surface layer were 3.55 times that of the clothless group, and the initial The total strain and elastic strain at the time of cracking are larger than those without cloth.
According to the research of Liu Yanyan and Zhang Haiwei, the composite structure with an anti-cracking interlayer between the base layer and the surface layer has greater fracture energy. In the case of the same external load, the total strain at the initial cracking of the cloth group is larger than that of the clothless group. The corresponding fracture energy is also larger. Therefore, although laying the filament nonwoven geotextile for sale will increase the bottom strain of the asphalt layer, it can still delay the cracking of the surface layer.
2.3 Reflection crack expansion
After the initial cracking of the reflective crack, the total strain growth rate of the two test groups was higher than that before the initial cracking. The non-cloth group had a faster growth rate than the cloth group, and the total strain exceeded the cloth group and gradually widened the gap. After the cracking, the overall strength of the structure gradually decreases, and the deformation and crack propagation under each loading become larger and larger. When the cloth group has cracked at the bottom of the surface layer, the wholesale filament nonwoven geotextile assists the surface layer by its own tensile deformation. The role of the deformation is gradually reflected, so that the deformation growth rate is reduced compared with the no-cloth group, delaying the expansion of the crack.
The elastic strain of the two test groups experienced a process of first decreasing and then increasing after self-cracking. The difference was that the clothless group increased slightly and then exceeded the elastic strain value at the time of cracking, and the cloth group decreased. It is maintained at a low level for a long time and does not start to increase again until the reflection crack approaches the penetration, and is always smaller than the corresponding value at the initial crack. Sangpetgnam points out that the expansion of the crack is a process in which the strain energy gradually accumulates, and the strain energy is repeatedly loaded. When accumulating to a certain threshold, the crack extends a certain length and accumulates energy again with the new crack tip. Therefore, the elastic strain will fluctuate several times with the crack propagation during the test.
The structural stress state of the reflective crack in the surface layer can be divided into the following stages: as shown in Fig. 6a, when the reflective crack is just cracked, the asphalt layer on both sides of the crack is weakened due to the fact that the bottom surface of the surface layer is no longer continuous. Therefore, the elastic deformation amounts L1 and L3 decrease; while the reflection crack just cracked, the crack width L2 is small, and the opening and closing under the load are not obvious. Therefore, the elastic strain of both test groups decreases after the initial crack.
As the crack continues to expand, the stress transmission range of the clothless group and the cloth group is as shown in Fig. 6b and Fig. 6c. Since the clothless group is only subjected to the force of the crack tip region, the sheer effect causes the vertical fault on both sides of the crack. The movement becomes larger and larger, so the elastic strain increases rapidly and exceeds the corresponding value of the initial crack. In addition to the force of the crack tip, the polyester nonwoven geotextile manufacturers still maintain the joint of the bottom surface of the two sides of the crack and transmit the stress to the two. The side layer of the side, and inhibits the displacement caused by the shearing action. In addition, as shown in Table 2, the greater the tensile deformation of the high quality filament nonwoven geotextile, the greater the tensile force that can be withstood, and thus the suppression of the displacement becomes stronger and stronger. The elastic strain of the cloth group is continuously reduced.
When the reflection crack approaches the through-layer, the force of the cloth group is as shown in Fig. 6d and the un-cracked area of the surface layer above the crack gradually decrease to form a weak area, thus causing vertical displacement under the load shear effect of the vehicle. The resistance is weakened so that the elastic strain of the cloth group increases again.
2.4 crack through
The reflection cracks of the clothless group and the cloth group penetrated the surface layer in sequence when loading 60,000 times and 195,000 times, and the loading times of the cloth group when the reflection crack penetrated were 3.25 times of the clothless group, as shown in Fig. 4b and Fig. 5b. As shown. When the crack penetrates, the total strain values of the two test groups are basically equal, both are about 200×10-6. The elastic strain of the cloth group is 11×10-6, which is still larger than the 8×10-6 of the clothless group. At this time, the total strain and elastic strain of both test groups reached a peak.
The analysis shows that the filament nonwoven geotextile for sale is delayed by the assisted surface layer, which significantly delays the penetration of the reflective crack. The total strain value is equivalent, indicating that the crack opening width of the two test groups at the bottom of the surface layer is similar. The reason why the elastic strain is still large is the same as the cracking stage.
2.5 After the crack runs through
After the reflection crack penetrated, the total strain and elastic strain of the two test groups experienced a period of reduction. After that, the total strain and elastic strain of the non-cloth group began to increase, exceeding 600×10-6 and 8×10-6. And there is no convergence trend; while the total strain and elastic strain of the cloth group are basically stable at 180×10-6 and 9×10-6.
There are two main reasons for the decrease of total strain and elastic strain in the two test groups: 1 After the reflective crack penetrates, the surface layers on both sides of the crack are separated from each other, and the sensor position is almost unaffected by bending, only shearing exists; As the loading progresses, the ruth of the asphalt layer gradually deepens, so that the external load is reduced before the crack penetrates.
Under continuous loading, the no-cloth group has been separated due to the surface layers on both sides of the crack. The vertical displacement under the load-sharing effect of the vehicle is stronger and the longitudinal displacement is stronger under the action of the horizontal force, and the crack width is further increased. Both strain and elastic strain increase. It can be seen from Table 2 that the filament nonwoven geotextile manufacturers can withstand large tensile deformation. The elongation of the polyester nonwoven geotextile factory price after the crack penetrates is far less than the elongation under its maximum load, so there is cloth. The surface layers on both sides of the group of cracks are still connected by high quality filament nonwoven geotextile and subjected to bending and shearing caused by vehicle loads so that the total strain and elastic strain tend to be stable.
3. Analysis of crack development status
Figure 7 is a comparison of the vertical expansion length of the reflective crack in the asphalt surface layer. It can be seen from the figure that the vertical expansion length of the crack increases with the number of loadings, but the expansion speed has similar fluctuations with the strain. Compared with the clothless group, filament nonwoven geotextile manufacturers significantly delays the vertical expansion speed of cracks, and its effect becomes more and more obvious with the increase of crack length.
Figure 8 and Figure 9 show the crack development status of the clothless group and the cloth group at different stages of loading, respectively. The reflection cracks are marked in white. Since the cracks of the two test groups are small before the penetration layer, The loading process did not change much, so the analysis started from the cracks of the two test groups.
It can be seen that when the reflection crack penetrates the surface layer (Fig. 8a, Fig. 9a), the crack width of both the cloth group and the clothless group is small. When the loading continues to 330,000 times (Fig. 8b, 9b), there is no cloth. The crack width of the group increases significantly, and when the main crack is widened, a number of thin cracks are formed in the upper part of the crack, and the top surface of the surface layer is extended at different positions. The side of the surface layer has a tendency to crack, and the top surface of the surface layer is also cracked. The expansion and the shearing effect caused by the vertical displacement of the pavement structure on both sides of the crack become no longer horizontal. Compared with this, the variation of the crack width of the cloth group is small, and the side of the surface layer still has good integrity; Except for one main crack, there are few micro-cracks at other locations. When loading continues to 540,000 times (Fig. 8c, Fig. 9c), the crack width of the non-cloth group increases greatly, the surface layer is almost completely broken, and the crack width of the cloth group The overall integrity of the surface layer is not much changed when it is loaded 330,000 times.
It can be seen from the variation of the crack width that the filament nonwoven geotextile for sale still maintains the joint of the two sides, which significantly inhibits the lateral expansion of the crack, and makes the structure appear “cracked and continuous”, which is beneficial to extend the pavement structure. The service life. However, the cloth-free group will be separated because the cracks are separated on both sides of the back layer, which causes the crack to gradually widen under the shearing displacement and horizontal displacement caused by the vehicle load, and accelerate the destruction of the pavement structure.
4. Conclusion
Accelerated loading test was carried out on the pavement structure model using MMLS3 equipment. The crack resistance performance of the wholesale filament nonwoven geotextile pavement structure was compared and the following conclusions were obtained:
(1) Accelerated loading test using MMLS3 equipment can simulate the bending-shear composite effect caused by actual road vehicle load, as well as the horizontal shifting effect and rutting formation process during repeated loading, and the high quality filament nonwoven geotextile can be studied here. The effect of preventing reflection cracks under the circumstances.
(2) Laying filament nonwoven geotextile manufacturers can significantly delay the initial cracking and penetration of tension-shear composite reflective cracks. In the test, the loading times of the cloth group in the initial cracking of the reflective crack are 3.55 times that of the non-cloth group, and the reflection crack runs through. The number of loadings is 3.25 times that of the clothless group.
(3) At the initial stage of loading, the total strain at the bottom of the fabric layer is larger than that of the non-cloth group. After the filament nonwoven geotextile manufacturers have a certain tensile deformation with the structure, the effect of assisting the surface layer is gradually exerted so that the total strain of the cloth group is obtained. The growth rate is slower, and the total strain is gradually smaller than the corresponding value of the clothless group. After the reflection crack penetrates the surface layer, the total strain of the cloth group is stable at 180×10-6, and the total strain of the clothless group will continue to increase, exceeding 600. ×10-6 and no convergence trend.
(4) Due to the weakening of the interlayer bond between the filament nonwoven geotextile for sale, the elastic strain of the cloth group is always larger than that of the non-cloth group. However, as the tensile deformation of the high quality filament nonwoven geotextile increases, the suppression of the vehicle load bending and shearing is gradually enhanced. Therefore, the elastic strain of the cloth group is reduced and stabilized at 9×10-6 after the reflection crack penetrates. The elastic strain of the clothless group continues to increase after the crack penetrates due to the gradually increasing shear and horizontal force. More than 8 × 10-6 and no convergence trend.
(5) filament nonwoven geotextile manufacturers have different effects at different stages of loading: before the surface layer is cracked, the composite fracture energy after the combination with the asphalt layer is increased, and the surface layer cracking is delayed; in the process of the expansion of the reflection crack, the tension is increased by itself. The tensile force can withstand the surface layer to resist the external force and delay the crack propagation; after the crack penetrates, relying on the large allowable elongation, the joint of the two sides of the crack is still maintained, and the crack continues to widen and structure. Dislocation, delaying further damage to the pavement structure.