Keywords

1 Introduction

With the rapid advancement of the transportation industry, steel bridge decks play a crucial role in modern bridge structures and have a direct impact on driving safety and the service life of bridges. Modified asphalt concrete, recognized as high-performance pavement materials, have garnered widespread attention in steel bridge deck pavement due to their exceptional crack resistance, durability, and high-temperature stability. Previous studies by Hao et al. [1], Liu et al. [2], and others have explored the application of high-elasticity modified asphalt concrete in steel bridge deck pavement, demonstrating significant improvements in temperature stability and fatigue performance. Additionally, Zhang et al. [3] investigated the influence of basalt fiber on epoxy asphalt concrete in cold regions, revealing that the addition of basalt fiber effectively enhanced flexibility and deformation characteristics of the epoxy asphalt concrete. However, the focus of research on modified asphalt concretes has primarily been on road performance, with relatively limited attention given to the compaction characteristics of construction. Additionally, there are technical challenges and difficulties associated with the application of steel bridge deck pavement.

Compaction plays a critical role in the construction process of modified asphalt concrete, and its effectiveness directly impacts the smoothness and density of the pavement [4], which ultimately determines the performance of the pavement. Modified asphalt concrete with added fibers exhibit significantly different compaction characteristics compared to regular asphalt concrete due to their unique composition and properties [5]. Therefore, conducting a comprehensive study on the compaction characteristics of composite modified asphalt concrete is highly significant for optimizing construction techniques and enhancing pavement quality.

Compared with Marcel compaction, the rotary compactor can better simulate the compaction process of pavement construction site by kneading, and obtain the density of asphalt concrete by controlling the compaction parameters. Jiu-peng Z et al. [6] studied the warm mix SBS asphalt concrete specimens through gyratory compaction and established the optimal compaction temperature. Zhang et al. [7] studied the relationship between the compaction characteristic parameters of the concrete and the composition of the asphalt concrete (gradation, asphalt content) and the molding temperature. The study showed that the medium gradation was easier to compact, and with the increase of the asphalt-aggregate ratio, the compactability increased linearly. Alexandros M et al. [8] studied the effect of compaction temperature on the compaction curve of the concrete.

This article aims to investigate the compaction characteristics of low-void modified asphalt concrete with added PE modifiers and polymer fibers through gyration compaction testing technology. It considers two factors: gradation type and asphalt-aggregate ratio. The experimental research and theoretical analysis aim to provide technical reference for improving the quality of modified asphalt concrete steel bridge deck pavement.

2 Materials and Test Methods

2.1 Materials

PG-76 Modified Asphalt

Based on previous research regarding the performance of pavement materials, The asphalt used in this study is PG-76 modified asphalt produced by Guangdong Xinyue Jiafu Asphalt Co., Ltd., and its performance indicators are shown in Table 1.

Table 1. Technical Indicators of PG-76 Modified Asphalt
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Aggregate

The test aggregate is divided into three sizes: 0–3 mm, 3–5 mm, and 5–10 mm. We used aggregate produced by Zhongshan Aggregate Plant, with limestone powder from the same plant. Performance indicators can be found in Table 2.

Table 2. Technical Indicators for Coarse Aggregates
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Modifier

In this study, we used PE-type modifiers and polymer fibers as modifiers.

2.2 Gradation

The concrete comprises three types of asphalt concrete: low void asphalt concrete LA-10 (with a 0.075 mm passing rate of 15%), SMA-10, and AC-10. The synthetic gradation of the concrete can be found in Table 3.

Table 3. Gradation in this study
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2.3 Research Plan

Modifier addition: Based on results from rut tests, beam bending tests, pull-out tests, etc., we found that adding a composite modifier with 10% asphalt mass fraction and 0.3% polymer fiber mass fraction to the concrete resulted in better road performance. The modifier addition method used in this test is dry addition.

To study the compaction of low void composite modified asphalt concrete, we selected LA-10, SMA-10, and AC-10 gradations as mentioned in 2.2. Road performance tests of the modified asphalt concrete showed that when the oil-stone ratio is 8.0, the concrete still has good high-temperature stability. Therefore, concrete with oil-stone ratios of 7.5%, 8.0%, and 8.5% were chosen, with a mixing temperature of 185 ℃ and a specimen preparation temperature of 185 ℃.

2.4 Specimen Preparation

The gyratory compactor primarily simulates on-site compaction to form asphalt concrete. The PINE-AFG1 type of gyratory compactor was utilized in this experiment, following the standards AASHTO T312, ASTMD 6925-08, and EN 12697-31. The parameters set for this test include a vertical loading pressure of 600 kPa, a rotation speed of 3030r/min, and a rotation area inclination of 1.25°.

The gyratory compactor is capable of accurately recording the height changes of each compaction, thus obtaining the compaction curve of the asphalt concrete and understanding the compaction process of the specimen [9]. The compaction process generally consists of two stages: initial compaction during construction to achieve the design void ratio, and subsequent compaction under traffic load after open traffic to reach the limit void ratio and above. Therefore, the resulting compaction curve can reflect changes in compactness during both construction and operation.

When evaluating the compaction characteristics of asphalt concrete, two main indicators are relied upon: the Compaction Energy Index (CEI) during construction and Traffic Density Index (TDI) during traffic. CEI focuses on measuring the area under the compaction curve from initial compaction to reaching 92% density. A lower CEI value indicates easier workability during construction. It should be noted that when void ratio is less than 2%, it is considered close to its limit [10].

Through these indicators, a more comprehensive understanding can be gained regarding the compaction characteristics of asphalt concrete during both construction and use, ensuring quality and safety in road construction.3Test Results and Analysis.

3 Test Results and Analysis

3.1 Analysis of Modified Asphalt Concrete Void Ratio

As shown in Fig. 1, after 160 compaction cycles, the void ratios of the nine kinds of asphalt concrete were measured and all maintained relatively low levels.

It is noteworthy that for the LA-10 concrete, when the asphalt-aggregate ratio increased from 7.5% to 8.0%, the void ratio decreased by 16.8%, but this change was not significant. However, when the asphalt-aggregate ratio further increased to 8.5%, the void ratio remained almost unchanged. In contrast, the void ratio of the AC-10 concrete exhibited a different trend with changes in the asphalt-aggregate ratio. From 7.5% to 8.0%, the void ratio of AC-10 rapidly decreased by 42%, and then the decrease narrowed to 19% when the asphalt-aggregate ratio increased to 8.5%. Additionally, for the SMA-10 concrete, as the asphalt-aggregate ratio increased from 7.5% to 8.5%, the decrease in void ratio first dropped from 25% to 8.6%, indicating that the rate of decrease in void ratio gradually slowed down with increasing asphalt content.

For all three kinds of concretes, the void ratios showed relatively significant decreases when the asphalt-aggregate ratio increased to 8.0%, but the decreases became gradually smaller. Therefore, under the same compaction conditions, all three kinds of concrete exhibited relatively ideal compaction effects when the asphalt-aggregate ratio was 8.0%. Additionally, a comparison at the same asphalt-aggregate ratio revealed a trend of SMA-10 > AC-10 > LA-10 in terms of void ratio. When the asphalt-aggregate ratio exceeded 8.0%, the difference in void ratio between LA-10 and AC-10 gradually decreased, indicating similar performance characteristics.

Fig. 1.
figure 1

The compaction void ratio of 9 types of concrete

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3.2 Compaction Curves of Three Asphalt Concretes with Different Asphalt-Aggregate Ratios

The asphalt-aggregate ratio is a critical factor affecting the compaction performance of asphalt concrete. As the asphalt-aggregate ratio increases, the compaction rate of asphalt concrete typically accelerates, enabling them to reach the desired void ratio or compaction density faster. However, it is noteworthy that not all types of concrete exhibit significant improvements in compaction rate with increasing asphalt-aggregate ratios.

Fig. 2.
figure 2

Compaction curves of concrete with different oil stone ratios

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As shown in Fig. 2, compaction curves for three different graded concrete at asphalt-aggregate ratios of 7.5%, 8.0%, and 8.5% are presented. It can be clearly observed that as the asphalt-aggregate ratio gradually increases, the compaction performance of the asphalt concrete also improves. Further analysis of compaction curves for different graded concrete reveals the following:

For LA-10 grade, the compaction curves for the three asphalt-aggregate ratios are relatively close. Notably, when the asphalt-aggregate ratio exceeds 7.5%, there is no significant improvement in the compaction performance of the concrete, indicating that further increases in the asphalt-aggregate ratio have limited contributions to the compaction process.

For AC-10 grade, when the asphalt-aggregate ratio increases from 7.5% to 8.0%, the compaction rate of the concrete shows a noticeable improvement. However, when the asphalt-aggregate ratio further increases to 8.0% and 8.5%, the compaction curves become similar, and the increase in compaction rate is not significant, indicating that the compaction performance of the concrete has stabilized under these two asphalt-aggregate ratios.

Similarly, SMA-10 grade exhibits a similar trend to AC-10. During the increase of asphalt-aggregate ratio from 7.5% to 8.0%, the compaction rate increases slightly. However, when the asphalt-aggregate ratio exceeds 8.0%, the compaction curves become similar, indicating that the growth of compaction rate has leveled off.

Based on the above information, there are significant differences in the compaction performance of asphalt concrete with different graded types and asphalt-aggregate ratios. Comparing Fig. 1 with Fig. 2, it can be seen that for the same graded concrete, as the asphalt-aggregate ratio increases, the trend of increasing compaction rate is similar to the decreasing trend of void ratio. Therefore, there is a clear correlation between the void ratio and compaction curve. When selecting an appropriate asphalt-aggregate ratio, it is necessary to consider the graded type of the concrete and the compaction target to achieve the best compaction performance.

3.3 Compaction Characteristics of Asphalt Concrete with Different Grades

Based on the influence of asphalt-aggregate ratio on the void ratio and compaction characteristics of asphalt concrete discussed earlier, it is found that when the asphalt-aggregate ratio is 8.0%, the asphalt concrete can meet the requirement of a low void ratio while providing good construction ease. Therefore, this study compares the compaction curves of three graded mixtures with an asphalt-aggregate ratio of 8.0% to the commonly used epoxy asphalt concrete EA-10 for steel bridge deck pavement.

Figure 3 shows the compaction curves and their fitting curves for the four graded concrete. The compaction curves in the figure are relatively distinct, indicating significant differences in compaction characteristics among different graded concrete. It can be clearly seen from the figure that the compaction energy index (CEI) follows the order: SMA-10 > AC-10 > LA-10 > EA-10. Calculations reveal that the traffic density index (TDI98) is highest for AC-10 (172), followed by LA-10 (170), SMA-10 (164), and EA-10(28).

Fig. 3.
figure 3

Compaction curves of the four gradations

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In summary, the LA-10 concrete has a CEI close to EA-10 and a low void ratio. Considering its high-temperature stability and other pavement performance characteristics, it is suitable for application in the lower layer of steel bridge deck pavement. On the other hand, SMA-10 has a higher CEI, making it difficult to compact during construction. However, it has a higher TDI98 and exhibits good high-temperature performance, making it suitable for the upper layer of steel bridge deck pavement.

4 Conclusion

In this study, the influence of three grading types of asphalt concrete (LA-10, AC-10, and SMA-10) on the compaction performance of asphalt concrete at oil-stone ratios of 7.5%, 8.0%, and 8.5% was investigated through gyratory compaction tests. The results showed that:

  1. 1)

    Both the grading and oil-stone ratio significantly impact the compaction performance of asphalt concrete, with a close relationship between void content and compaction curves.

  2. 2)

    For LA-10 graded concrete, little change in void content and similar compaction curves were observed when the oil-stone ratio exceeded 7.5%. Similarly, for AC-10 and SMA-10 graded concrete, changes in void content and compaction curves were not significant when the oil-stone ratio exceeded 8.0%.

  3. 3)

    The dense energy index ranking is as follows: SMA-10 > AC-10 > LA-10 > EA-10. During construction compaction, LA-10 exhibits similarities to epoxy asphalt concrete EA-10.

The comprehensive test results indicate that the low-void composite modified asphalt concrete designed in this study can achieve target voids under conventional construction conditions. However, this paper only tested specific gradations and oil stone ratios. Future studies can further expand the scope of tests to more fully understand the effects of gradations and oil stone ratios on the compaction properties of asphalt concretes.