Experimental study on roller compacted asphalt concrete core wall considering the influence of different paving thickness

Roller compacted asphalt concrete impervious core wall is widely used in water conservancy and hydropower projects because of its excellent anti-seepage, deformation adaptation and seismic performance. The current specification stipulates that the thickness of single-layer paving is 30 cm and 25 cm after compaction, which limits the construction efficiency and economy. In order to break through this limitation, this study relies on the Hongshuihe Reservoir Project in Suzhou District of Jiuquan City to explore the feasibility of increasing the paving thickness to 38 cm and above. Through the field layered paving test, the influence of three different rolling times on the compactness, permeability and mechanical properties of asphalt concrete is studied. The density, permeability coefficient and tensile, compressive and flexural properties were measured by using non-destructive testing and core sample testing methods, and the interlayer bonding quality and construction economy were analyzed. The test shows that the physical and mechanical properties of asphalt concrete meet the requirements of design specifications under the condition of paving thickness of 38 cm. The increase of rolling times significantly optimizes the density and permeability coefficient. The tensile strength, compressive strength and bending resistance of the material can reach the standard index. The bonding quality between the layers is good, and the appearance of the core sample has no obvious delamination trace. Compared with the current 30 cm thickness scheme, the thickness of 38 cm can reduce the number of construction layers by about 69 layers, save the construction period by 35 days and reduce the construction cost by about 628,400 yuan. The research confirms that it is feasible to increase the paving thickness of asphalt concrete to 38 cm under the existing equipment and process conditions, and the construction efficiency and economy are significantly improved. The influence of different rolling times on the performance index is clear, and the optimization of the second rolling times can ensure the paving quality and engineering safety. This study provides important data support and reference for the construction technology optimization and specification revision of roller compacted asphalt concrete core wall.

1 Introduction

As the core anti-seepage structure of rockfill dam, the roller compacted asphalt concrete core wall is closely related to the safety performance of the dam (Liangshu et al., 2007; Hao et al., 2018; Lu et al., 2024). Thanks to its good adaptability to deformation, seismic performance, anti-seepage performance and erosion resistance, this material is widely used in water conservancy and hydropower projects (Zhang et al., 2012; Li et al., 2019; Deng et al., 2023). However, with the continuous expansion of the project scale and the gradual improvement of the design height (Rao et al., 2014), the traditional single-layer paving process has increasingly exposed the problems of long construction period, high cost and low efficiency under the limitation of equipment performance and construction technology, which is difficult to meet the needs of modern engineering (El Hussein et al., 1993; Li, 2003; Sheng et al., 2009).

When the asphalt concrete core wall is used as the anti-seepage of the dam, its upstream water load directly acts on the core wall. The downstream thrust generated by the water pressure causes the core wall to deform in the same direction, and its stress is complex (Jiang et al., 2016; Dang et al., 2019; Benbo et al., 2021; Li et al., 2024). Therefore, improving construction efficiency and quality and exploring thick layer paving technology have gradually become the current research hotspot (Wang et al., 2014; Liu et al., 2021). The research shows that increasing the thickness of single-layer paving can not only reduce the number of construction layers and shorten the construction period, but also significantly reduce the construction cost (Bayagoob and Bamaga, 2019; Gao et al., 2019; Zhang et al., 2020). Rao Xibao (Rao et al., 2014) put forward that optimizing the mix ratio of asphalt concrete can improve the material performance and provide guarantee for thick layer construction; (Chen et al., 2010) pointed out that the stress-strain characteristics, strength (maximum deviatoric stress and shear strength) and creep behavior of asphalt concrete are significantly affected by temperature: stress softening at low temperature (0 °C) and stress hardening at high temperature; the increase of temperature leads to the decrease of maximum deviator stress and shear strength, and the increase of creep. By analyzing the thermal parameters of various types of asphalt concrete, (Uulu et al., 2021) found that water storage asphalt can reduce the heat transfer from the asphalt surface to the lower foundation and effectively organize the heat exchange between the surface and the surrounding air. Wan et al. (2011) found that the construction quality can be guaranteed when the temperature of the joint surface is raised to 100 °C by studying the compaction performance of the asphalt concrete at different temperatures; (Kai et al., 2020) found that when the base temperature is higher than 100 °C, the compaction performance of asphalt concrete core wall will be significantly reduced; (Li et al., 2006) found that the stress-strain relationship curve of asphalt concrete in triaxial test is composed of two stages: strain hardening and softening. It is a curve with hump. When describing the mechanical properties of asphalt concrete, the Nanshui nonlinear model should be adopted. The research of Luo et al. (2011) shows that the introduction of advanced construction equipment makes it possible to pave with larger thickness, and the advantage of thick layer paving in economy is particularly significant (Liu et al., 2012; Xiang et al., 2014). However, in the construction of thick layer paving, there are still technical problems such as insufficient compactness and decreased interlayer bonding performance (Cai, 2017; Liu et al., 2017).There is a lack of systematic verification of the adaptability of existing construction specifications to thick layer paving.

Based on this, based on the Hongshuihe Reservoir Project in Suzhou District of Jiuquan City, this paper studies the technology of increasing the paving thickness of roller compacted asphalt concrete anti-seepage core wall. Through field test, the feasibility of increasing paving thickness from 30 cm to 38 cm is verified, and the influence of different rolling technology and construction parameters on the compactness, mechanical properties and economy of asphalt concrete is analyzed. It provides theoretical support for optimizing construction technology and improving engineering quality, and provides scientific basis for the optimization and improvement of relevant specifications.

2 Test scheme

2.1 Project profile

The Hongshuihe Reservoir Project in Suzhou District of Jiuquan City is one of the key water conservancy projects in Gansu Province (Figure 1). It aims to improve the flood control, irrigation and water resources allocation capabilities of the basin, and ensure regional water security and agricultural irrigation needs. The project is located in Suzhou District, Jiuquan City, Gansu Province. The planned total storage capacity is 49.1 million cubic meters, and the maximum dam height is 82.4 m. The total investment of the project is 1.095 billion yuan, the construction period is 55 months, and the construction is in accordance with the standard of medium-sized third-class project. The reservoir not only undertakes important flood control tasks, but also has multiple functions such as water resources allocation, irrigation and water supply. It is an important part of regional water conservancy infrastructure.

Figure 1

Figure 1. Suzhou location map of jiuquan city.

The core part of this project is the roller compacted asphalt concrete core wall rockfill dam. It adopts the advanced roller compacted asphalt concrete technology, which has strong anti-seepage performance and good deformation adaptability. Asphalt concrete core wall is a key component of the project, and its construction quality directly affects the stability and long-term operation safety of the dam. In order to improve the construction efficiency, reduce the construction period, and ensure the anti-seepage effect and economy, the paving thickness lifting technology is studied. The design of dam rockfill and related buildings in this project is strictly in accordance with the secondary and tertiary flood control standards (SL 514-2013). The construction of key facilities such as spillway and flood discharge tunnel ensures the safety of the reservoir.

As of December 2023, the project has completed 1.9347 million cubic meters of earth and rock excavation, and the core wall construction has completed 13,500 cubic meters of concrete filling. The design and process standards are strictly implemented to ensure that the design requirements of the core wall on key indicators such as density and permeability coefficient are met. The filling volume of the dam has reached 2.4492 million cubic meters, and the concrete pouring of the core wall base and the wing wall has been completed as planned, laying a solid foundation for the subsequent construction. The construction efficiency and quality control level are further improved by using the technology of layered paving and optimizing the number of rolling passes, which provides valuable experience for similar projects.

2.2 Experimental study on asphalt concrete core samples with different rolling times when paving thickness is 40 cm

Based on the roller compacted asphalt concrete core wall rockfill dam project of Hongshuihe Reservoir Project in Suzhou District of Jiuquan City, this study carried out the roller compacted test of asphalt concrete by using the original roller compacted test site (width 1.0 m, length 24.0 m) on the construction site. The construction mix ratio verified by experts is selected in the test. It is paved in two layers. Each layer is divided into three sections, and rolling is carried out for 10 times, 12 times and 14 times respectively. The rolling equipment used in the test is the Hummer double steel wheel vibration mill. Since asphalt concrete is a temperature sensitive material, it must be rolled in a specific temperature range to ensure its compaction effect. In the test, the initial grinding temperature and the final grinding temperature are managed according to the temperature control index recommended by the rolling test report (Ge, 2010; Ge, 2011).

After the test is completed, after the internal temperature of asphalt concrete is naturally cooled to the ambient temperature, the core sample is drilled from the second layer and the relevant test is carried out according to the design index of asphalt concrete. The main test items include: bulk density and permeability coefficient of asphalt concrete nondestructively tested after compaction. By analyzing the relationship between bulk density, porosity and rolling times under different rolling times, the influence and variation law of different rolling times on the permeability coefficient of non-destructive testing and the permeability coefficient of drilling core samples are studied. In addition, the water stability, tensile strength, uniaxial compressive strength, beam bending performance and static triaxial mechanical properties under different rolling times were tested, and whether they met the design indexes was analyzed (DL/T 5363-2006). Finally, through the analysis of the bonding quality between the core samples, the construction feasibility of asphalt concrete under the condition of loose paving thickness of 38 cm is explored. Table 1 shows the mix proportion of asphalt concrete construction. Table 2 lists the main technical parameters of asphalt concrete vibrating roller. Figure 2 is the rolling situation of asphalt concrete on site. Tables 3–5 provide the detailed technical parameters of the raw materials.

Table 1

Table 1. Asphalt concrete construction mix proportion.

Table 2

Table 2. Main technical parameters of asphalt concrete vibration mill.

Figure 2

Figure 2. Rolling test site.

Table 3

Table 3. Test result table for no. 90 (Grade A) petroleum asphalt.

Table 4

Table 4. Coarse aggregate test results table.

Table 5

Table 5. Table of test results of fine aggregate.

2.3 Experimental study on physical and mechanical deformation performance of asphalt concrete core wall

In the test site, the thickness of the layer is 40 cm, and the rolling times are 10 times, 12 times and 14 times respectively. When the internal temperature drops to the natural state, 40 core samples are drilled to test the tensile strength, uniaxial compressive strength, bending characteristics, permeability characteristics and static triaxial deformation of the core samples. It is studied whether the mechanical properties can meet the design requirements (DL/T 5363-2006) when the thickness of the layer is 38 cm, so as to guide the construction of asphalt concrete.

3 Test result

3.1 Paving thickness and settlement test of asphalt concrete

The test adopts the construction technology of manual paving. The technological process includes construction preparation, measurement lofting, formwork erection, paving of transition material, initial grinding of transition material, surface treatment, paving of asphalt concrete, initial grinding of asphalt concrete, synchronous rolling of asphalt concrete and transition material, final grinding and quality inspection.

During the test, the steel formwork with a height of 36 cm, a length of 120 cm and a thickness of 8 cm was selected for the asphalt concrete test formwork. Before the asphalt concrete is put into the warehouse, the surveyors use the total station to collect the elevation data of the base surface of the rolling area of 10 times, 12 times and 14 times, and install the artificial template and use the buckle to fix it. After the template is installed, the width is 1.0 m. When the asphalt concrete is put into the warehouse, it is transported manually with the loader, and the artificial leveling is carried out after the warehouse is put into the warehouse. After leveling, the surveyor tracks and controls the lifting height of the template according to the corresponding point data to ensure that the lifting height of the template meets the requirements of 38 cm paving thickness. After the template lifting is completed, the transition materials on both sides of the template are repaired manually with the excavator, and finally the remaining asphalt concrete is leveled.

According to the process and procedure, the artificial paving test of asphalt concrete is carried out, which is divided into 2 days and two layers. The rolling times of each layer are as follows: 2 times of static pressure and 10 times of vibration rolling. After the vibration rolling is completed, the temperature of asphalt concrete is reduced to 120 °C, and the static pressure is collected twice to form a rolling mode of 2 + 10+2 (static + dynamic + static); The static pressure is carried out twice, and the vibration rolling is carried out for 12 times. After the vibration rolling is completed, the asphalt concrete temperature is reduced to 120 °C, and the static pressure is carried out twice to collect light, forming a 2 + 12+2 (static + dynamic + static) rolling mode; The static pressure is carried out twice, and then the vibration rolling is carried out for 14 times. After the vibration rolling is completed, the asphalt concrete temperature is reduced to 120 °C, and the static pressure is carried out twice to collect light, forming a 2 + 14+ 2 (static + dynamic + static) rolling mode. Tables 6, 7 are the statistical tables of paving thickness and settlement of the first and second layers. Figure 3 show the bar chart of the change of settlement and rolling times of the first and second layers.

Table 6

Table 6. Asphalt concrete rolling mode comparison table.

Table 7

Table 7. Statistical table of the first layer paving thickness.

Figure 3

Figure 3. Bar chart of settlement and rolling times change: (a) The first layer of settlement; (b) The second layer settlement.

According to the statistical data of paving thickness in Tables 6, 8, the average paving thickness of the first layer is 41.6 cm, and the average paving thickness of the second layer is 38.9 cm, which meets the minimum paving thickness requirement of 38 cm set in this test. From the bar chart of the settlement and rolling times change in Figure 3, it can be seen that under the condition that the paving thickness of the first layer is 41.6 cm, the settlement is 4.7 cm when the rolling times are mode A; When the number of rolling passes is mode B, the settlement is 5.3 cm. When the number of rolling passes is mode C, the settlement is 6.3 cm, indicating that the number of rolling passes is proportional to the settlement. For the second layer paving thickness of 38.9 cm, the settlement is 5.85 cm when the number of rolling passes is model A; When the number of rolling passes is mode B, the settlement is 6.25 cm; When the number of rolling passes is mode C, the settlement is 6.4 cm, which also shows that there is a positive proportional relationship between the number of rolling passes and the settlement, which is consistent with the change rule that the voids between the aggregates of each component gradually decrease and the compactness gradually increases during the rolling process of asphalt concrete. In addition, through the comparative analysis of the settlement of the first layer and the second layer, it can be seen that under the same rolling times, the settlement of the second layer is generally greater than that of the first layer. The reason may be that after the paving thickness increases to 40 cm, the vibration force acting on the unit volume of asphalt concrete decreases under the existing tonnage vibration mill and excitation force, resulting in the settlement of the first layer less than that of the second layer.

Table 8

Table 8. The second layer paving thickness statistics table.

3.2 Correlation between bulk density, permeability coefficient and rolling times of asphalt concrete

After the first layer and the second layer of asphalt concrete are paved and rolled, the non-destructive testing of asphalt concrete is carried out by using the non-nuclear density meter and the gas permeability meter. The density and permeability coefficient are measured, and the variation law between the number of rolling passes and these two indexes is analyzed. From the curve of the relationship between the number of rolling passes and the density and permeability coefficient in Figure 4, it can be seen that with the increase of the number of rolling passes, the density gradually increases, the permeability coefficient gradually decreases, and the density and porosity meet the design requirements: Density ≥2.38 g/cm³, permeability coefficient ≤1 × 10 cm/s. According to the data in Tables 6, 7, the paving thickness is greater than 38.0 cm, and the average paving thickness of the first layer is 41.6 cm, which is significantly larger than the average paving thickness of the second layer of 38.9 cm. From the data analysis of Tables 9, 10, it can be seen that the permeability coefficient of the first layer of asphalt concrete is less than that of the second layer, and the density of the two layers of asphalt concrete changes little under different rolling times. Although the paving thickness of the first layer is greater than that of the second layer, the reason may be that the base surface of the first layer of asphalt concrete is hard base, while the second layer is constructed on the basis that the first layer has been paved and rolled. Due to the slow cooling rate of asphalt concrete, when the second layer is paved and rolled, the first layer of asphalt concrete has a certain viscoelasticity as the base surface, forming a similar effect of soft foundation, so the permeability coefficient of the second layer is greater than that of the first layer. According to the above data analysis, when the paving thickness of asphalt concrete is 38 cm, the density and permeability coefficient of asphalt concrete after rolling meet the design index requirements. Therefore, it is feasible to break through the limitation of the current specification on the thickness of the paving layer and increase the thickness of the paving layer.

Figure 4

Figure 4. Density and permeability coefficient under different rolling times: (a) Number of rolling passes of the first layer; (b) Number of rolling passes of the second layer.

Table 9

Table 9. The first layer rolling times and permeability coefficient, density data statistics table.

Table 10

Table 10. The second layer rolling times and permeability coefficient, density data statistics table.

3.3 Monitoring and analysis of interlayer bonding quality during construction of roller compacted asphalt concrete core wall

In the construction of roller compacted asphalt concrete core wall in water conservancy and hydropower projects, the control requirements for the temperature of the layer are strict. Usually, the temperature of the layer is controlled above 70 °C according to the specifications, and does not exceed 90 °C (SL 514-2013). When the interlayer temperature is lower than 70 °C during the construction process, the surface of asphalt concrete needs to be heated to more than 70 °C by heating equipment (such as infrared heater) to pave the upper asphalt concrete to ensure the interlayer bonding quality. However, there are security risks in the construction process of liquefied gas heating equipment, and it is difficult to ensure the uniformity of heating, resulting in local asphalt aging, so gradually abandoned. In this experiment, when the second layer is paved, the temperature of the first layer is first measured. The results show that the temperature range of the layer is 42 °C–58 °C. Under this condition, the surface of asphalt concrete is not extra heated, and the warehousing operation is carried out directly. After the second layer of paving and rolling is completed, drilling and coring are carried out, and the length of the sampled core sample is between 52 cm and 54 cm. The appearance and interlayer bonding of the core sample are shown in Figure 5. It is found that the aggregate distribution of the core sample is uniform and the compactness is good. It is difficult for the naked eye to detect the traces of interlayer bonding, indicating that the interlayer bonding quality of the core sample is good. This result is similar to the conclusion of the literature (Kai et al., 2020) on the mechanical properties of core wall asphalt concrete with different joint surface temperatures.

Figure 5

Figure 5. Bonding quality between core samples.

4 Mechanical performance index

In view of the excellent impermeability, good deformation adaptability, seismic performance and crack self-healing ability of asphalt concrete core wall, it is very important to ensure that the mechanical performance index can meet the design and specification requirements under the condition of increasing the paving thickness. Therefore, on the basis of the previous non-destructive testing, in order to further verify the mechanical performance index, it is necessary to drill the core of the asphalt concrete that has been paved and compacted, and test its mechanical properties and deformation characteristics.

4.1 Core sample permeability coefficient

The aforementioned analysis of the permeability coefficient index of non-destructive testing of asphalt concrete after each layer of test. According to the test results, the permeability coefficient under all rolling passes meets the design requirements (≤1 × 10 cm/s). In order to eliminate the detection error caused by the instrument, the permeability coefficient test is further carried out by drilling sampling, so as to more accurately reflect the permeability coefficient of compacted asphalt concrete under different rolling times. Through the core sample permeability coefficient test, the following results are obtained:When the number of rolling passes is mode A, the permeability coefficient of the core sample is 3.2 × 10 cm/s; When the number of rolling passes is mode B, the permeability coefficient of the core sample is 2.1 × 10 cm/s; When the number of rolling passes is mode C, the permeability coefficient of the core sample is 2.7 × 10 cm/s. The specific data are shown in Table 11 Statistical table of permeability coefficient test results of core samples with different rolling times. By comparing the variation law of the permeability coefficient of the non-destructive testing and the permeability coefficient of the core sample under the same rolling times of the second layer, the curve of the permeability coefficient changing with the rolling times in Figure 6 is shown. Firstly, the permeability coefficient of the core sample increases first and then decreases with the increase of the number of rolling passes. When the number of rolling passes is mode B, the permeability coefficient reaches the maximum value. At the same time, under all rolling passes, the permeability coefficient of the core sample meets the design requirements (no more than 1 × 10⁻⁸ cm/s). Secondly, the variation of the permeability coefficient of the core sample is not completely consistent with the variation of the permeability coefficient of the non-destructive testing. Specifically, the permeability coefficient of the core sample increases first and then decreases with the increase of the number of rolling passes, while the permeability coefficient of non-destructive testing continues to increase with the increase of the number of rolling passes. In addition, under the same number of rolling passes, the permeability coefficient of non-destructive testing is generally higher than that of core sample. The reason may be related to the deviation of the test results due to the operation skills of the operator and the sealing of the operating tray during the non-destructive testing of the gas permeameter. Whether it is the permeability coefficient of the core sample or the permeability coefficient of the gas permeameter, the test results are one order of magnitude lower than the design and specification requirements, but still meet the design requirements. Therefore, it is more reliable to analyze the test results based on the permeability coefficient of the core sample.

Table 11

Table 11. Statistical table of permeability coefficient test results of core samples with different rolling times.

Figure 6

Figure 6. Curve of permeability coefficient changing with rolling times.

4.2 Coefficient of water stability

Water stability test is an important index to evaluate the long-term durability of asphalt concrete under water. It reflects the adhesion of aggregate to asphalt and whether stripping occurs under the action of long-term water, and can detect the stability of its performance under water damage (Kai et al., 2020). Before the test, the specimens were processed into two groups of 6 specimens with a diameter of 100 mm ± 2 mm and a height of 100 mm ± 0.5 mm. One group of specimens were maintained in air at 20 °C ± 1 °C for no less than 48 h. The other group of specimens were immersed in 60 °C ± 1 °C water for 48 h, and then transferred to 20 °C ± 1 °C water. Finally, the water stability test was carried out by electronic universal testing machine. According to the design and specification requirements, the water stability coefficient of roller compacted asphalt concrete should be greater than or equal to 0.9. The test results are as follows: When the number of rolling passes is mode A, the water stability coefficient is 0.92; The water stability coefficient is 0.95 when the rolling times is mode B; When the number of rolling passes is C, the water stability coefficient is 0.97. (See Table 12, statistical table of water stability coefficient test results under different rolling times).

Table 12

Table 12. Statistical table of water stability coefficient test results of different rolling passes.

By analyzing the variation law of water stability coefficient under different rolling times (see Figure 7), it can be seen that the water stability coefficient of core sample increases with the increase of rolling times, and under all rolling times, the water stability coefficient meets the design requirements (≥0.9). Therefore, under the condition of increasing the paving thickness, the results of the water stability test can ensure that the design requirements are met.

Figure 7

Figure 7. Variation curve of water stability coefficient with rolling times.

4.3 Analysis of tensile and uniaxial compression results

For the asphalt concrete anti-seepage body in water conservancy and hydropower projects, the asphalt concrete and the horizontal section base concrete, the bank slope base concrete joint surface and the 1:3 joint formed due to construction interruption are all weak links of asphalt concrete. In the normal operation period of asphalt concrete core wall dam, these parts are usually in tension state. Therefore, it is of great significance to verify the tensile strength under the condition of increasing the paving thickness. In the test, the core sample taken out from the borehole was first processed into a standard specimen with a size of 220 mm × 40 mm × 40 mm, and three specimens were prepared for each group of tensile tests. The processed specimens were allowed to stand at 10 °C for 3 h, and then the specimens were installed on an automatic temperature control universal testing machine for tensile test. The strain rate of 2.2 mm/min was selected in the test, and the test results were taken as the average of the experimental results of the three specimens. The test results are as follows: The tensile strength is 1.05 MPa and the maximum tensile strain is 1.35% when the number of rolling passes is mode A; The tensile strength is 1.13 MPa and the maximum tensile strain is 1.42% when the number of rolling passes is mode B; When the number of rolling passes is mode C, the tensile strength is 1.10 MPa and the maximum tensile strain is 1.32%. (See Table 13, statistical table of tensile test results under different rolling times).

Table 13

Table 13. Statistical table of tensile test results under different rolling times.

By analyzing the variation law of tensile strength and maximum tensile strain under different rolling times (see Figure 8, the curve of tensile strength and maximum tensile strain with rolling times), it can be seen that the tensile strength and maximum tensile strain increase first and then decrease with the increase of rolling times. When the number of rolling passes is mode B, the tensile strength reaches a maximum of 1.13 MPa and the maximum tensile strain is 1.42%. At the same time, the tensile strength of the core sample is greater than 1 MPa under all different rolling passes.

Figure 8

Figure 8. Variation curves of tensile strength and maximum tensile strain with rolling times.

The above-mentioned tensile tests were carried out on the core samples under different rolling times. In order to verify its compression performance, the uniaxial compression test of the core samples was further carried out to evaluate the compressive strength limit of the core samples under different rolling times. First, the drilled core sample is processed into a standard specimen with a diameter of 100 mm and a height of 100 mm. Three specimens are prepared for each group, and the test results are averaged. The test results are as follows: When the number of rolling passes is mode A, the compressive strength is 3.15 MPa, and the strain at the maximum stress is 5.18%; When the number of rolling passes is mode B, the compressive strength is 3.71 MPa, and the strain at maximum stress is 6.12%; The compressive strength is 3.48 MPa and the strain at the maximum stress is 5.72% when the number of rolling passes is mode C (See Table 14, statistical table of uniaxial compression and strain test results at maximum stress under different rolling passes).

Table 14

Table 14. Statistical table of strain detection results under uniaxial compression and maximum stress under different rolling passes.

According to the change law of compressive strength and strain at maximum stress under different rolling times (see Figure 9, the curve of compressive strength and strain at maximum stress with rolling times), it can be seen that with the increase of rolling times, the compressive strength and strain at maximum stress increase first and then decrease. When the number of rolling passes is mode B, the compressive strength reaches the maximum value of 3.71 MPa, and the strain at the maximum stress is 6.12%. At the same time, the compressive strength of the uniaxial compression test is more than 3.0 MPa under all rolling passes.

Figure 9

Figure 9. Curves of compressive strength and strain at maximum stress changing with rolling times.

4.4 Analysis of trabecular bending results

The bending design index of this project is: bending strength (kPa)≥1,800 kPa, maximum bending strain (%)≥2.6%. After the second layer test is completed, when the temperature drops to the ambient temperature, the trabecular bending test is carried out by drilling and sampling. Before the test, the test piece was processed into a standard test piece with a size of 250 mm × 35 mm × 40 mm, and three samples were prepared for each group. The trabecular bending test was carried out using the asphalt concrete comprehensive performance test system. The test results are as follows: When the rolling pass number mode A is adopted, the bending strength is 1,890 kPa, the maximum bending tensile strain is 2.785%, the bending deformation modulus is 62.5 MPa, and the deflection span ratio is 2.1%; When the number of rolling passes is B, the bending strength is 1,935 kPa, the maximum bending strain is 2.845%, the bending deformation modulus is 69.2 MPa, and the deflection span ratio is 2.5%; When the number of rolling passes is mode C, the bending strength is 1,925 kPa, the maximum bending tensile strain is 2.815%, the bending deformation modulus is 65.5 MPa, and the deflection span ratio is 2.4% (See Table 15, statistical table of test results of trabecular bending test under different rolling passes). By analyzing the change rule of bending strength and maximum bending tensile strain under different rolling times (see Figure 10, the change curve of bending strength and maximum bending tensile strain with rolling times), it can be seen that the bending strength increases first and then decreases with the increase of rolling times, and the maximum bending tensile strain also shows a similar change rule. Under the combination of three rolling passes, the bending strength and the maximum bending strain meet the design requirements. The bending strength is greater than or equal to 1,800 kPa, and the maximum bending strain is greater than or equal to 2.6%.

Table 15

Table 15. Statistical table of test results of trabecular bending test under different rolling times.

Figure 10

Figure 10. Curves of bending strength and maximum bending strain with rolling times.

5 Conclusion

In this paper, aiming at the construction control range of 30 cm paving thickness of asphalt concrete core wall, we try to break through the limitation of single layer paving thickness stipulated in the current construction standard. Based on the paving thickness of 38 cm, the basic field test is carried out by using the existing asphalt concrete mixing equipment and compaction equipment. After the test, the conventional performance test of asphalt concrete was carried out, and the mechanical properties were tested by drilling and coring. Combined with the results of on-site non-destructive testing and core sample testing, the economic benefits of asphalt concrete core wall construction are further analyzed.

Mainly draws the following conclusions:

1. When the paving thickness is 38 cm, the general performance indexes such as density and permeability coefficient of asphalt concrete can meet the design and specification requirements through non-destructive testing under different rolling times. The mechanical properties of the drilling core samples also meet the design and specification requirements. This preliminarily proves that the existing mixing, paving and rolling equipment can ensure the quality reliability of asphalt concrete under the paving thickness of 38 cm, and the construction feasibility can be verified.

2. Through the comparative analysis of construction economy, if the paving thickness increases from 30 cm to 38 cm, based on the construction cost of asphalt concrete core wall of this project, the construction period can be saved by 38 days, and the construction cost can be reduced by 628,400 yuan. Therefore, the construction of 38 cm paving thickness is feasible, which can effectively speed up the construction progress of asphalt concrete core wall, significantly reduce the construction cost and have obvious economic benefits.

3. With the increasing application of asphalt concrete core wall dam in water conservancy and hydropower projects and the increasing design of dam height, the construction equipment is also gradually upgraded. Therefore, the research on construction technology of hydraulic asphalt concrete needs to be continuously promoted. Through the analysis of the results of this field test, it can provide valuable reference and reference for the future research of asphalt concrete core wall construction technology.

Data availability statement

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author.

Author contributions

LH: Writing – original draft. ZL: Writing – original draft. SL: Writing – original draft. WS: Writing – original draft. JG: Writing – review and editing. AH: Writing – review and editing. YY: Writing – review and editing.

Funding

The authors declare that financial support was received for the research and/or publication of this article. Natural Science Foundation of Gansu Province (Grant No. 23JRRA831); the Doctoral Research Initiation Project of Lanzhou University of and Technology (Grant No. 2022062105); the water conservancy science experimental research and technology promotion plan (Grant Nos. 24GSLK053; 24GSLK055).

Conflict of interest

Authors LH and SL were PowerChina Sinohydro Engineering Bureau 4 Co., Ltd.

The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Generative AI statement

The authors declare that no Generative AI was used in the creation of this manuscript.

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