Analyzing the Mechanical and Durability Characteristics of Steel Slag-Infused Asphalt Concrete in Roadway Construction
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Institute of Industrial Economy and Innovation Management, Nanjing Institute of Technology, Nanjing 211167, China
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School of Civil Engineering and Architecture, Nanjing Institute of Technology, Nanjing 211167, China
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Author to whom correspondence should be addressed.
Buildings 2024, 14(3), 679; https://doi.org/10.3390/buildings14030679
Submission received: 20 December 2023
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Revised: 11 January 2024
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Accepted: 31 January 2024
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Published: 4 March 2024
(This article belongs to the Special Issue Innovation in Pavement Materials: 2nd Edition)
Abstract
:Steel slag is a solid byproduct of the steelmaking process, widely generated in the metallurgical industry. Due to its alkaline nature and excellent adhesive properties with asphalt, it represents a potential road construction material with outstanding road performance, making it well-suited for utilization in highway construction. This paper conducts a systematic analysis of the physical and chemical properties of steel slag, specifically South Steel Electric Furnace slag, and compares it with natural basalt and limestone aggregates. The aim is to establish a foundation for the application of steel slag in asphalt mixtures. Building upon this foundation, we carry out proportioning design for AC-13C and SMA-13 steel slag asphalt mixtures, followed by a comprehensive study of their high-temperature stability, low-temperature stability, water stability, and fatigue performance. Our research reveals variations in the chemical composition of different steel slags, with CaO, SiO2, and Fe2O3 being the primary components. The content of harmful elements varies depending on the steelmaking raw materials and additives used. Notably, the optimum asphalt-to-aggregate ratios for AC-13C and SMA-13 significantly surpass the specified requirements. The freeze–thaw splitting strength ratio and residual stability of steel slag AC-13C and SMA-13 asphalt mixtures exceed the specified requirements, with AC-13C demonstrating the highest water stability, boasting a freeze–thaw splitting strength ratio of 94.07%, and a residual stability of 93.8%. In terms of fatigue characteristics, SMA-13 exhibits a longer fatigue life than AC-13C, indicating superior fatigue performance for steel slag SMA-13. Steel slag enhances the abrasion resistance and rutting resistance of asphalt pavement surface layers, fully meeting the performance requirements for high-grade road surface layers.
1. Introduction
Steel slag is a solid by-product produced during the steelmaking process and represents a significant waste product in the metallurgical industry. It primarily consists of oxides formed when various elements in the metallic charge are oxidized, as well as impurities brought in by the metallic charge, refractory lining materials, and additives intentionally introduced to modify slag properties, such as limestone, dolomite, and iron ore [1]. Steel slag exhibits excellent physical and mechanical properties, including high density, hardness, strength, high polishing value, well-graded particle size distribution, and low shrinkage, surpassing traditional aggregates like limestone and basalt [2]. Being an alkaline aggregate, steel slag has good adhesion with asphalt, making it a promising material for road construction with superior performance. Consequently, researchers have begun to explore its potential as a substitute for natural aggregates in asphalt pavement construction [3].
The production of steel slag is substantial, accounting for approximately 10% to 15% of crude steel production. Initially, steel slag was considered waste and discarded, leading to massive slag piles that occupied large areas of industrial and agricultural land and caused significant environmental pollution. This challenging situation prompted countries to place unprecedented emphasis on the environmentally friendly disposal and resource utilization of steel slag [4]. Developed countries have achieved nearly 100% utilization rates of steel slag, taking into account its application potential, steelmaking process characteristics, and its ability to enhance steel production capacity [5].
Taking cues from the experiences of developed countries in steel slag utilization, road engineering, including cement and asphalt concrete, is a primary avenue for the resource utilization of steel slag [6]. For instance, in Germany, Japan, and the United Kingdom, 90% of steel slag is used in asphalt and cement concrete. Scholars widely recognize that steel slag exhibits superior mechanical properties compared to crushed stone; it is not only wear-resistant and has well-graded particle size distribution but also exhibits excellent adhesion with asphalt. The utilization of steel slag also effectively addresses the shortage of high-quality aggregates. With the rapid development of China’s highway industry, the supply gap for high-quality natural aggregates is expected to widen. Utilizing steel slag as an aggregate in asphalt pavements is an excellent solution to counteract the scarcity of natural aggregates [7,8].
Europe, America, and Japan have accumulated a wealth of experience in the use of steel slag for road engineering construction and have achieved significant results. The United States and Japan have formulated their own construction specifications and technical standards for steel slag road materials. Steel slag aggregates exhibit superior mechanical properties, such as natural gradation, abrasion resistance, and suitable particle shapes, making them ideal aggregates for asphalt concrete pavements [9].
In 1970, the American Iron and Steel Institute proposed that the use of various steel slags as alkaline aggregates in construction should be increased. While blast furnace slag can be recycled in steelmaking, steel slag may not have the same significant potential for steel production. However, steel slag has unique advantages, such as its suitability for road construction due to its excellent abrasion resistance. In 1998, the U.S. Congress passed the Transportation Equity Act, allocating USD 205 billion to promote the reuse of steel slag. In 2001, the United States produced approximately 845,000 tons of steel slag throughout the year, much of which was reused or exported [10,11].
Germany also places great emphasis on the comprehensive utilization of steel slag and the circular economy. New technologies and equipment continue to emerge. Currently, the primary utilization of steel slag in Germany is as a construction material, extensively used in road engineering for subgrades, base layers, subbase layers, and asphalt surface layers. Germany discards only about 10% of steel slag each year due to quality reasons, while another 5% is temporarily stored in yards for various reasons. This indicates that Germany has ample experience in metallurgical slag treatment. Surveys show that Germany has established a series of well-implemented processing systems for the recycling of steel slag, supported by corresponding policies and regulations [12,13].
Japan has undertaken significant work in steel resource utilization. In 1976, the Steel Slag Resource Utilization Committee was established within the Japan Iron and Steel Federation to gain in-depth knowledge of the basic characteristics of steel slag, develop basic technologies for utilization and production, and aim for Japanese Industrial Standards as a research and development goal. Starting in 1979, the Ministry of Construction, the Civil Engineering Research Institute, and the Steel Slag Association of the Japan Iron and Steel Federation conducted joint research on the application of steel slag in road engineering [14]. In 1988, the “Guidelines for Asphalt Pavement Construction” were revised to confirm the use of steel slag. Sumitomo Metal Industries conducted indoor tests and on-site tests in three plants in Kitakyushu, Kashima, and Wakayama to study the use of steel slag as an upper-layer roadbed material. After two years of tracking investigations, it was confirmed that there were no abnormal phenomena in road surface quality due to steel slag expansion [15]. By 2010, Japan’s steel slag utilization rate had exceeded 95%, with over 20% being used in road engineering. In some regions, the utilization rate reached 40%. Steel slag applications in Japan are mainly concentrated in civil engineering, road engineering, and the return to metallurgical recycling. Japan has provided valuable reference and insights for countries worldwide in the comprehensive recycling of industrial waste resources and the development of a circular economy model [16,17].
The use of steel slag in road engineering in China dates back to the 1970s. The Tianjin Port Second Road was the first road to use steel slag as a fill material for its roadbed, with a total length of 2.42 km, and it was opened to traffic in 1980 [18]. According to survey data from 2005, the cement road surface of this section remained intact, except for some damage at expansion joints. Wuhan Iron and Steel Metal Resources Co., Ltd. collaborated with Wuhan University of Technology to construct an experimental road section using steel slag asphalt concrete internally within the company. The surface layer was made of AC-20Ⅰ-type steel slag asphalt concrete, while the upper layer used AC-20Ⅰ-type steel slag asphalt concrete [19]. Shanghai Tongji University and the Beijing Municipal Research Institute conducted experimental research on the treatment of steel slag from Baosteel and Shougang. Their research primarily focused on the use of steel slag as a road surface base material and as a high-activity additive admixture in cement concrete [20,21].
Through research, the physical and chemical properties of steel slag were analyzed to a certain extent. Steel slag possesses excellent mechanical properties, such as high strength, high abrasion resistance, a low crushing value, a good particle shape, and well-balanced natural gradation, which are superior to natural crushed stone aggregates [22]. Enterprises and research institutions have conducted research and analysis on the expansion problem, which is the primary concern when using steel slag, but the depth of research is insufficient. In addition to its excellent mechanical properties, steel slag exhibits excellent adhesion with asphalt. The adhesion level between asphalt and steel slag obtained through a boiling test reached Grade 5. This is mainly due to the large porosity of steel slag, allowing asphalt and other binding materials to infiltrate various voids, resulting in stronger adhesion that rivals gravel and crushed stone [23,24].
When examining the current utilization of steel slag in road engineering both domestically and internationally, steel slag is generally applied in various structural layers such as roadbeds, road base layers, sub-base layers, and cement concrete surface layers. However, its application in the surface layer of asphalt concrete roads is still in the early exploration stage. There is a lack of relevant experience, and systematic research on the performance of steel slag, construction processes for steel slag asphalt mixtures, and quality control is needed to guide engineering practice [25,26]. This paper, taking into consideration the actual situation of national and provincial trunk roads in Wujiang District, conducts in-depth research on the design methods of steel slag asphalt mixtures, summarizes a complete set of construction and quality control technologies for steel slag asphalt mixtures, and holds significant theoretical and practical value [27,28].
Regarding the widespread application of steel slag asphalt mixtures, steel slag resources are primarily used in the form of aggregates in asphalt mixtures [29]. However, due to the differences in physical properties, water absorption, and other aspects between coarse and fine steel slag particles, it is challenging to fully utilize them. One of the important characteristics of bulk solid waste is the diversity of the forms in which resources exist. Therefore, achieving comprehensive utilization of different forms and qualities of steel slag and realizing “non-selective utilization” is an important approach to promote the efficient and rational utilization of steel slag asphalt mixtures.
This paper conducts a systematic study on the physical properties and chemical properties of steel slag aggregates, and the road performance of different types of steel slag asphalt mixtures. This research plays a crucial role in promoting the efficient utilization of steel slag in asphalt mixtures and achieving the high-added-value recycling of steel slag resources. Based on the characteristics of steel slag, this paper selects the gradation type of steel slag asphalt mixtures and designs the mixture proportions to determine the mixed design method for steel slag asphalt mixtures. Performance comparative analysis is conducted on steel slag asphalt mixtures and conventional asphalt mixtures in terms of high-temperature stability, low-temperature cracking resistance, moisture sensitivity, and fatigue resistance.
2. Raw Materials and Test Methods
2.1. Steel Slag Coarse Aggregate
2.1.1. Morphological Characteristics
Steel slag is formed at temperatures ranging from 1500 °C to 1700 °C, where it exists in a liquid state at high temperatures and transforms into a blocky shape upon slow cooling. The exterior can appear as porous blocky, less porous blocky, or non-porous blocky. For ease of study, the steel slag aggregates collected from the field were sieved and their relevant physical properties were investigated. Figure 1 presents the appearance of the electric furnace steel slag used in this study. Figure 1a–d respectively show the appearances of the 1# (9.5 mm~16.0 mm), 2# (4.75 mm~9.5 mm), 3# (2.36 mm~4.75 mm), 4# (0~2.36 mm) steel slag aggregates.
From Figure 1, the surface state of the larger particle sizes of steel slag aggregates, specifically the 9.5 mm fractions, can be observed. The surface of the steel slag is porous and rough, with generally well-formed particles, characterized by a predominance of angular and cubic shapes. For the 2.36 mm~4.75 mm fraction of steel slag aggregate, there is also a notable angularity, but due to the higher dust content on the surface, the angularity of some particles becomes less pronounced. Figure 1d shows the steel slag aggregates smaller than 2.36 mm. Compared to natural aggregates (shown in Figure 2), this fraction of steel slag aggregates exhibits poorer angularity and a higher dust content.
Due to the environmental conditions of steel slag production and its processing techniques, some dust particles are tightly bonded to the steel slag. During the cleaning process of the 9.5 mm~16.0 mm fraction aggregates, it was found that ordinary water washing and rubbing methods were ineffective in thoroughly removing dust from the surface of the steel slag aggregates. To gain a clear understanding of the surface morphology of the steel slag aggregates, this paper employed a soft-bristled steel wire brush to remove dust from the surface of randomly selected 1# steel slag aggregates. The appearance of the dust-free particles is shown in Figure 3. As observed in Figure 3, the surface of the steel slag particles is rough with pronounced porosity, which may aid in adhesion with asphalt, but it could also potentially increase asphalt absorption.
Figure 4 presents the cross-sectional morphology of the electric furnace slag selected for this study. The figure reveals that even for slag produced in the same batch using the same raw materials and equipment from the same steel mill, there are noticeable differences in the internal structure.
During the cooling process of steel slag, a critical phase transition occurs where liquid water transforms into steam. This phase change is accompanied by a significant volumetric expansion, which instantaneously creates a network of bubbles within the molten slag. As the slag solidifies, these bubbles become trapped, forming a porous structure characterized by a multitude of voids. The size, distribution, and connectivity of these pores play a pivotal role in defining the material’s microstructure.
Furthermore, under certain cooling conditions, the rapid escape of steam can lead to the formation of vesicular structures, as illustrated in Figure 4 [30]. These structures are characterized by their hollow, often spherical cavities, which are a direct result of the trapped gases expanding and then escaping from the viscous liquid slag. The presence of such vesicular formations is a key factor in the resultant mechanical properties of the slag. The porous and vesicular nature of cooled steel slag has significant implications for its mechanical behavior. These structural features can lead to a reduction in density, a decrease in mechanical strength, and an increase in brittleness. When incorporated into asphalt mixtures, the slag’s porous nature can affect the mixture’s overall density and stability. The interaction between the bitumen and the slag’s surface, which is largely governed by the slag’s porosity and surface area, can also influence the durability and moisture susceptibility of the asphalt mixture. Therefore, understanding the microstructural characteristics of steel slag is crucial for predicting and optimizing its performance in asphalt mix applications.
2.1.2. Crushing Value/Crushing Index
The aggregate crushing value is an important measure of the ability of coarse and fine aggregates to resist crushing under a gradually increasing load. It is a key indicator of the mechanical properties of stone materials and an important parameter for assessing their suitability in highway engineering projects. The three types of aggregates used in the experiment were in a non-dry state. To eliminate the influence of aggregate moisture on the crushing value results, the samples were first dried to constant weight in a 105 °C oven and then cooled to room temperature in a desiccator. Subsequently, three groups of 3 kg samples each, with particle sizes ranging from 9.5 to 13.2 mm, were tested for each type of aggregate. The test results are shown in Table 1 and Table 2.
The comparison of the crushing value of steel slag coarse aggregate with basalt and limestone aggregates is shown in Figure 5.
From the comparison results in Figure 5 regarding the crushing values of steel slag, basalt, and limestone coarse aggregates, it can be seen that the crushing value of steel slag is not superior to that of basalt or limestone aggregates. This may be attributed to the more abundant voids and vesicular structures within the steel slag aggregates. According to the ‘Technical Specifications for Construction of Highway Asphalt Pavements’ (JTG F40-2004) [31,32], the crushing value for coarse aggregates used in surface layers should be less than 26.0%. The electric furnace steel slag used in this project meets the requirements specified in these standards.
2.1.3. Asphalt
This study selected SBS-modified asphalt for use. The experiments were conducted in accordance with the Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering. The basic performance indicators and specification requirements are presented in Table 3.
2.2. Test Methods
2.2.1. High-Temperature Stability
The high-temperature performance of the steel slag asphalt mixture was evaluated using a rutting test. The specific test conditions and parameters were referenced from the ‘Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering’ (JTG E20-2011) [33]. The test temperature was set at 60 °C, with a wheel pressure of 0.7 MPa. The specimens were prepared according to the ‘Method of Making Asphalt Mixture Specimens (T0703-2011) [33]’ using the rolling method, with dimensions of 300 mm × 300 mm × 50 mm. At a temperature of 60 °C, the contact pressure between the test wheel and the specimen was maintained at 0.7 MPa ± 0.05 MPa.
2.2.2. Low-Temperature Stability
This study evaluated the low-temperature stability of steel slag asphalt mixtures using a low-temperature bending failure test. The specific test conditions and parameters follow those outlined in the ‘Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering’, particularly the ‘Asphalt Mixture Bending Test (T0715-2011)’ [33]. The test temperature was set at −10 °C. The specimens were prepared according to the ‘Method of Making Asphalt Mixture Specimens (T0703-2011)’ using the rolling method, and then cut into prismatic specimens measuring 30 mm × 35 mm × 250 mm [33]. The loading rate during the test was 50 mm/min.
2.2.3. Moisture Sensitivity
This paper investigated the moisture sensitivity of steel slag asphalt mixtures using two methods: the immersion Marshall test and the freeze–thaw splitting test. The immersion Marshall test was conducted according to the ‘Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering’ (JTG E20-2011), specifically the ‘Marshall Stability Test of Asphalt Mixture (T0709-2011)’ [33]. One group of Marshall specimens was kept at a constant temperature of 60 °C in hot water for 30 min before measuring its stability, while another group was maintained at 60 °C for 48 h before stability measurement. The cylindrical specimens, sized Φ101.6 mm × 63.5 mm, were prepared according to the ‘Method of Making Asphalt Mixture Specimens (T0703-2011)’ using the compaction method. The loading rate for the test was 50 mm/min.
The freeze–thaw test was carried out as per the ‘Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering’ (JTG E20-2011), specifically the ‘Freeze–thaw Splitting Test of Asphalt Mixture (T0729-2011)’. The curing methods for the two groups of specimens followed the requirements of T0729-2011. The cylindrical specimens, sized Φ101.6 mm × 63.5 mm, were prepared according to the ‘Method of Making Asphalt Mixture Specimens (T0702-2011)’ using the compaction method. The loading rate for this test was also set at 50 mm/min.
2.2.4. Fatigue Characteristics
This paper employed a strain-controlled approach to study the fatigue life of steel slag asphalt mixtures. The test was conducted in accordance with the ‘Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering’ (JTG E20-2011), specifically the ‘Four-Point Bending Fatigue Life Test of Asphalt Mixture (T0739-2011)’. The curing methods for the two groups of specimens followed the requirements outlined in T0739-2011. The specimens were prepared according to the ‘Method of Making Asphalt Mixture Specimens (T0703-2011)’ using the rolling method, and then cut into prismatic specimens measuring 380 mm × 65 mm × 50 mm. The loading frequency was set at 10 Hz, using a strain loading mode (150 με). The test was terminated when the bending stiffness modulus reduced to 50% of the initial bending stiffness modulus, corresponding to the number of loading cycles.
2.3. Mixed Proportion Design of Steel Slag Asphalt Mixture
This paper utilized the ‘equivalent volume replacement method’ for the mixed proportion design of steel slag asphalt mixtures. Due to the significant difference in specific gravity between steel slag and basalt, the design was conducted using the volumetric method. The volumetric percentages of each aggregate were then multiplied by the corresponding aggregate’s bulk relative density to determine the mass proportion of the mineral ingredients.
2.3.1. Selection of Gradation Ratio for AC-13C Steel Slag Asphalt Mixture
The three gradations A, B, and C, for the AC-13C steel slag asphalt mixture determined in this paper are shown in Table 4. These gradations represent the composition of the combined mineral materials for the experimental mix design.
The sieve passing rates for each of the three gradation compositions of the combined mineral materials are shown in Table 5.
The composite gradation curves of the three types of aggregates are shown in Figure 6.
Referring to the relevant requirements in the ‘Technical Specifications for Construction of Highway Asphalt Pavements’ (JTG F40-2004) [32], the estimated asphalt content was calculated to be 4.6%. Therefore, Marshall specimens were prepared with 4.6% asphalt content, and corresponding physical indicators were measured, including the bulk relative density, void ratio, voids in mineral aggregate, degree of saturation, stability, and flow value. The test results for the three types of gradations are shown in Table 6.
Based on the initial asphalt content test results for the three gradations in Table 6, it could be determined that gradation A does not meet the requirements for void ratio (VV), voids filled with asphalt (VFA), and degree of saturation (VFA). Gradation B fails to satisfy the criteria for void ratio (VV) and voids filled with asphalt (VFA). In contrast, the steel slag asphalt mixture for gradation C meets the design requirements for stability, flow value, void ratio, voids in mineral aggregate, and degree of saturation. Based on experience and comprehensive consideration, gradation C was selected as the baseline mix proportion for subsequent road performance tests.
2.3.2. Selection of Gradation Ratio for SMA-13 Steel Slag Asphalt Mixture
The three gradation compositions A, B, and C, for the SMA-13 steel slag asphalt mixture determined in this study are shown in Table 7. These gradations represent the composition of the combined mineral materials for the experimental mix design.
The sieve passing rates for each of the three gradation compositions of the combined mineral materials are shown in Table 8.
The composite gradation curves of the three minerals are shown in Figure 7.
Referring to the relevant requirements in the ‘Technical Specifications for Construction of Highway Asphalt Pavements’ (JTG F40-2004) [32], the estimated asphalt content is calculated to be 5.5%. Therefore, Marshall specimens are prepared with 5.5% asphalt content, and corresponding physical indicators are measured, including bulk relative density, void ratio, voids in mineral aggregate, degree of saturation, stability, and flow value. The test results for the three types of gradations are shown in Table 9.
Based on the initial asphalt content test results from Table 9 for the three gradations, it could be determined that gradation A does not meet the requirements for void ratio (VV) and voids in mineral aggregate (VMA). Gradation C fails to satisfy the criteria for void ratio (VV). However, the steel slag asphalt mixture for gradation B meets the design requirements for stability, flow value, void ratio, voids in mineral aggregate, and degree of saturation. Based on experience and comprehensive consideration, gradation B was selected as the baseline mix proportion for subsequent road performance tests.
2.3.3. Determination of Optimal Bitumen–Aggregate/Stone Ratio
According to the selected gradation in 2.3.2, Marshall specimens were made for AC-13C steel slag asphalt mixture at oil stone ratios of 4.3%, 4.5%, 4.8%, 5.1%, and 5.4%, respectively. Marshall specimens were made for SMA-13 steel slag asphalt mixture at oil stone ratios of 4.9%, 5.2%, 5.5%, 5.8%, and 6.1%, and corresponding physical indicators were measured. The experimental results are shown in Table 10 and Table 11.
Through the analysis of experimental results, the relationships between density, stability, flow value, void ratio, saturation, VMA (Voids in Mineral Aggregate), and the bitumen-aggregate ratio were examined. The corresponding bitumen–aggregate ratios for the maximum density, maximum stability, target void ratio, and median value of the saturation range were identified. The average of these four ratios was taken as the initial optimal bitumen–aggregate ratio (OAC1). The range of bitumen–aggregate ratios meeting the requirements for asphalt concrete (OACmin, OACmax) was determined, with the median of this range being OAC2. If the initial optimal bitumen–aggregate ratio (OAC1) falls between OACmax and OACmin, the design result is considered feasible. The median of OAC1 and OAC2 can be taken as the optimal bitumen–aggregate ratio (OAC) for the target mix design. Consequently, the optimal bitumen content was determined. The analysis revealed that within the selected range of bitumen content for the experiment, the optimal bitumen content for AC-13C was 4.84%, and for SMA-13, it was 5.8%.
3. Results and Discussion
3.1. Analysis of Adhesiveness Properties of Steel Slag Aggregates
Adhesiveness in the context of asphalt mixtures refers to the ability of an aggregate’s surface, when coated with a thin layer of asphalt, to resist water erosion, which can lead to stripping. To ensure the moisture sensitivity of asphalt mixtures, it is essential to establish requirements for the adhesion between the aggregate and asphalt. In this study, we conducted tests in accordance with the ‘Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering’ (JTG E20-2011).
Considering the morphological characteristics of steel slag aggregates, it is often observed that they often have a high dust content on their surfaces. Typically, a higher dust content can adversely affect the bond between asphalt and aggregate. To investigate the disparity in adhesiveness between original steel slag aggregates and those subjected to surface dust removal treatment, we employed a dust removal process through water washing. Subsequently, we assessed the adhesiveness of these two types of steel slag aggregates using both the boiling water method and the water immersion method, as illustrated in Figure 8, Figure 9 and Figure 10.
According to the evaluation standards for the adhesiveness level between asphalt and aggregates, the adhesiveness of both the original state steel slag and basalt aggregates reached level 5. However, for the steel slag particles treated with water washing to remove dust, the area of asphalt film stripping increased, resulting in an adhesiveness rating of level 4. Typically, to ensure good moisture sensitivity of asphalt mixtures, strict requirements are often imposed on the dust content of natural aggregates. Evidently, these conventional requirements and practices are contrary to the results of this experiment. To ensure the accuracy of the test results, the experiment was repeated, and the results remained consistent with those previously mentioned.
3.2. Chemical Properties of Steel Slag Aggregates
In order to scientifically and effectively comprehensively utilize waste steel slag in road engineering, it is necessary to comprehensively understand the chemical composition, mineral composition, surface element distribution, and harmful element evaluation of steel slag, and determine its applicability in roadbed and pavement.
3.2.1. Chemical Composition
The chemical composition of steel slag is greatly influenced by the production of raw materials and treatment processes, but generally speaking, its element content has a certain regularity. This project mainly tested the chemical composition of steel slag aggregates through X-ray fluorescence spectroscopy (XRF). Table 12 shows the chemical composition test results of the Nangang electric furnace slag used.
From Table 12, it can be seen that the main components of the electric furnace steel slag used by the research group are CaO, Fe2O3, and SiO2, with a SiO2 content of only 19.085%, indicating that the steel slag is a more alkaline aggregate. Based on existing data, there are certain differences in the content of steel slag obtained from different steel mills using different raw materials, but its main components all contain CaO and SiO2, which have certain similarities with natural aggregates.
3.2.2. Evaluation of Hazardous Elements
Due to the demand for steel performance, different chemical elements are often added during the smelting process, and steel slag, as a by-product of the steelmaking process, may also have residual chemical elements inside. During the stacking process of steel slag, the surface is directly exposed to the natural environment. Under the action of sunlight and rainwater, the harmful chemical elements contained inside may gradually leach out and immerse into groundwater resources, causing environmental pollution. Generally speaking, the main pollutants in steel slag are zinc, lead, cadmium, nickel, and chromium. These metals are easily enriched in soil and plants in the form of ions, which can cause harm to the human body. In view of this, scholars mainly use wrapping to safely handle steel slag. One method is to melt and wrap the slag, and wrapping the steel slag with asphalt is also an effective form of safe utilization of steel slag. At present, compared with foreign countries, China’s research on the impact of steel slag on the environment is not given enough attention. With the enhancement of people’s environmental awareness, while recycling steel slag, higher requirements will also be put forward for its environmental benefits.
The detection of harmful components in steel slag can be determined through leaching experiments. The method is to dry and screen the steel slag aggregate, weigh a certain mass of steel slag aggregate with a particle size between 2.36 and 4.75 mm, soak it in a polyethylene container of distilled water, seal the container, place it in a rotary shaker for vibration, filter the filtrate after vibration with glass fiber filter paper, and analyze it using an atomic absorption spectrometer. The experimental results are shown in Table 13.
The experimental results indicate that the Ca exudation concentration in steel slag is the highest, which is consistent with the main components of steel slag. On the other hand, steel slag contains a large amount of f-CaO, which reacts with water. The products generated on its surface are easily infiltrated by water and enter groundwater. Several heavy metal ions that pose significant harm to the human body have not been discovered, or their presence is negligible. But the content of Al exceeds the standard value, and when using asphalt coating, its exudate concentration meets the specification requirements. Al is a chronic toxin that can have an impact on memory and can lead to dementia in severe cases. The steel slag determined by Xie Jun is from Wuhan Iron and Steel Corporation, and its composition can be traced back to the raw materials and added components of Wuhan Iron and Steel Corporation. It can be seen that when applying steel slag to road engineering, the harmful components of steel slag should be strictly measured, and the composition of the exudate after asphalt coating should be analyzed to ensure that it does not have a negative impact on the environment. In particular, the steel slag generated during the special steel smelting process should be accurately measured for harmful elements.
In addition, research in Germany has shown that strict use of steel slag that meets standard requirements will not have a negative impact on the environment, based on its 25 years of experience in using steel slag in road engineering. In this regard, Germany’s experience is worth learning from. Based on environmental protection, the steelmaking industry considers the resource utilization of steel slag in the selection of raw materials for steelmaking. Therefore, it is advisable to select raw materials with minimal negative effects on the environment and strictly treat steel slag, truly achieving environmental protection from the source.
3.3. Road Performance Analysis
3.3.1. High-Temperature Stability
Based on the selected gradations, rutting plate specimens of AC-13C- and SMA-13-type steel slag asphalt mixtures were prepared, and dynamic stability tests were conducted in accordance with the standard requirements. The test results are presented in Table 14.
Table 14 shows that the dynamic stabilities of both AC-13C- and SMA-13-type asphalt mixtures prepared using steel slag coarse aggregates are significantly higher than the requirements specified in the standards. To accurately evaluate the high-temperature stability of the AC-13C- and SMA-13-type steel slag asphalt mixtures prepared in this study, their dynamic stability was compared with that of different types of asphalt mixtures with a maximum nominal diameter of 13.2 mm. The results of this comparison are presented in Table 15.
Based on the different types of aggregates used, namely steel slag, basalt, and limestone, as well as the variation in the types of asphalt employed, the dynamic stability of different types of asphalt mixtures is illustrated in Figure 11.
It is evident from the above comparisons that, in general, the dynamic stability of asphalt mixtures made with steel slag aggregates exceeds that of mixtures prepared with basalt and limestone aggregates. However, for steel slag asphalt mixtures, variations in the properties of steel slag raw materials, the gradation of combined mineral materials, the steel slag content, and the asphalt–aggregate ratio can lead to significant differences in dynamic stability, even within the same type of steel slag asphalt mixture. Nevertheless, the addition of steel slag clearly enhances dynamic stability when compared to the corresponding control asphalt mixtures composed of natural aggregates.
This study focused on AC-13C- and SMA-13-type steel slag asphalt mixtures. It reveals that, in comparison to the literature data and other engineering applications of AC-13C- and SMA-13-type, and asphalt mixtures with added modifiers, the dynamic stability of steel slag mixtures showed a substantial increase. When comparing SMA-13- and SUP-13-type steel slag asphalt mixtures with mixtures made from natural aggregates, it was observed that the addition of steel slag resulted in dynamic stability that matched or slightly exceeded that of mixtures using different modifiers and high-viscosity asphalts.
3.3.2. Low-Temperature Stability
Based on the selected gradation and the determined optimal asphalt–aggregate ratio, rutting plate specimens of AC-13C- and SMA-13-type steel slag asphalt mixtures were prepared. Small-beam specimens were cut from these plates, and low-temperature small-beam bending tests were conducted in accordance with the standard requirements. The test results are presented in Table 16.
Table 16 shows that the failure strain of the AC-13C-type asphalt mixture made with steel slag coarse aggregate was 3105 με, which was higher than the standard requirement of 2500 με. In comparison, the SMA-13-mixture exhibited more coarsening than the AC mixture, and there was a slight reduction in this phenomenon with the increase in asphalt content. To accurately evaluate the low-temperature stability of the AC-13C- and SMA-13-type steel slag asphalt mixtures prepared in this study, their results were compared with those of small beam bending tests of different types of asphalt mixtures with a maximum nominal diameter of 13.2 mm. The details of this comparison can be found in Table 17.
Based on the different types of aggregates used, namely steel slag and basalt, as well as the variation in the types of asphalt employed, the failure strains of different types of asphalt mixtures are illustrated in Figure 12.
Generally, under low-temperature conditions, a greater bending strain and a smaller bending stiffness modulus indicate improved crack resistance of the asphalt mixture. From the comparisons made earlier, it is evident that, overall, asphalt mixtures containing steel slag aggregates demonstrate superior low-temperature stability compared to those made with basalt aggregates.
For steel slag asphalt mixtures, variations in test materials and testing environments can lead to significant differences in failure strain, even when the type of asphalt mixture remains the same. When comparing the AC-13C- and SMA-13-type steel slag asphalt mixtures prepared in this study with the literature data, it becomes clear that their failure strains are consistent with those reported in the literature and exceeded the standard requirement of 2500 με.
3.3.3. Moisture Sensitivity
From Table 18, it can be observed that both AC-13C and SMA-13 steel slag asphalt mixtures met the requirements for freeze–thaw splitting and Marshall residual stability tests as per the specifications. These results indicate that the steel slag asphalt mixtures have good moisture sensitivity, which is essential for their performance in real-world applications.
From Table 18, it can be observed that the AC-13C and SMA-13 steel slag asphalt mixtures prepared with coarse steel slag aggregates exhibited superior performance in terms of freeze–thaw splitting strength ratio and water-soaked residual stability compared to the specified requirements. Among them, AC-13C showed the best moisture sensitivity, with a freeze–thaw splitting strength ratio of 94.07% and a water-soaked residual stability of 93.8%.
To provide an accurate assessment of the moisture sensitivity of the AC-13C and SMA-13 steel slag asphalt mixtures formulated in this study, their test results were compared with those of different types of asphalt mixtures with a maximum nominal particle size of 13.2 mm, as detailed in Table 19 and Figure 13 and Figure 14.
In accordance with the differences in steel slag aggregates, basalt aggregates, and the type of asphalt used, the freeze–thaw splitting strength ratio and water-soaked Marshall stability of different types of asphalt mixtures are presented in Figure 13 and Figure 14.
From Figure 13 and Figure 14, it is evident that various types of steel slag asphalt mixtures exhibit high levels of freeze–thaw splitting strength ratio and water-soaked Marshall stability. The moisture sensitivity of AC-13C steel slag asphalt mixtures, prepared with matrix asphalt and steel slag, surpasses that of SMA-13 asphalt mixtures made with basalt aggregates. Furthermore, the moisture sensitivity of AC-13C steel slag asphalt mixtures, prepared with SBS-modified asphalt and steel slag, is slightly better than that of SUP-13 and SMA-13 asphalt mixtures, which are also prepared with SBS-modified asphalt and basalt aggregates.
3.3.4. Fatigue Performance
Based on the selected gradations and determined optimum asphalt-to-stone ratio, AC-13C and SMA-13 steel slag asphalt mixtures were prepared using the “Asphalt Mixture Test Specimen Preparation Method (T0703-2011)” by the rolling method. Fatigue characteristics were tested using the British INSTRON fatigue testing machine at a temperature of 15 °C. The test results are presented in Table 20. It is evident from the results that SMA-13 exhibited a longer fatigue life, characterized by a greater number of load cycles until material fatigue failure, compared to AC-13C. This indicates that under these conditions, the fatigue performance of steel slag SMA-13 is superior to that of AC-13C.
4. Conclusions
Based on the selected electric furnace steel slag aggregate from Nangang, this study conducted the mix design, preparation, and road performance testing of AC-13C and SMA-13 steel slag asphalt mixtures. The main conclusions are summarized as follows:
(1) Compared to natural basalt and limestone aggregates, steel slag has a rougher surface and more angular edges. Steel slag is primarily composed of dense phases and porous, vesicular parts, with higher surface and internal porosity, which is beneficial for adhesion with asphalt. However, this may also increase the asphalt demand. The higher porosity also leads to a higher water absorption rate. The apparent relative density of steel slag aggregates is significantly higher than that of natural basalt and limestone aggregates. Due to the processing techniques used, steel slag aggregates possess higher strength, offering better performance indicators for road use.
(2) The chemical composition of steel slag varies depending on the raw materials used in steelmaking and the components added during the process, but it mainly consists of CaO, SiO2, and Fe2O3. The content of harmful elements varies with the steelmaking raw materials and additives used. Strictly using steel slag that meets standard requirements does not pose a negative environmental impact. Encapsulating steel slag in asphalt can effectively reduce the leaching of harmful elements from the slag and minimize environmental pollution.
(3) The optimum asphalt-to-aggregate ratio for AC-13C and SMA-13 significantly exceeds the specified requirements. Dynamic stability tests for AC-13C and SMA-13 resulted in rutting values of 8341 cycles/mm and 9168 cycles/mm, respectively, well above the specified requirement of 2800 cycles/mm and 3000 cycles/mm. When compared with asphalt mixtures from the literature and other engineering applications, including those with additives, the steel slag asphalt mixtures prepared in this study exhibited a substantial increase in dynamic stability. Their dynamic stability surpassed or slightly exceeded that of asphalt mixtures with different modifiers and high-viscosity asphalt.
(4) The failure strain of AC-13C asphalt mixture prepared with steel slag coarse aggregates was 3105 με, which surpassed the specified requirement of 2500 με.
(5) The freeze–thaw splitting strength ratio and residual stability of AC-13C and SMA-13 asphalt mixtures prepared with steel slag coarse aggregates surpassed the specified requirements. Among these, AC-13C exhibited the highest moisture sensitivity, with a freeze–thaw splitting strength ratio of 94.07% and a residual stability of 93.8%. The moisture sensitivity of AC-13C steel slag asphalt mixture prepared with matrix asphalt and steel slag even exceeded that of SMA-13 asphalt mixture prepared with basalt aggregates. Meanwhile, the moisture sensitivity of AC-13C steel slag asphalt mixture prepared with SBS-modified asphalt and steel slag was slightly better than that of Sup-13 and SMA-13 asphalt mixtures prepared with SBS-modified asphalt and basalt aggregates.
(6) SMA-13 demonstrated a greater fatigue life, expressed in terms of the number of loading cycles until material fatigue failure, compared to AC-13C. This suggests that under these conditions, steel slag SMA-13 exhibits superior fatigue performance.
(7) Due to limitations in experimental equipment and other factors, this article conducted routine research on the high-temperature stability and fatigue performance of steel slag asphalt mixture. It is necessary to further conduct tests on indicators such as creep, permanent deformation, and low-temperature fatigue to study the high-temperature performance and fatigue resistance of steel slag asphalt mixtures.
Author Contributions
Conceptualization, Y.Z.; methodology, Y.Z.; software, Y.Z.; validation, Y.Z.; formal analysis, Y.Z.; investigation, X.Z.; resources, Y.Z.; data curation, X.Z.; writing—original draft preparation, X.Z.; writing—review and editing, X.Z.; visualization, X.Z.; supervision, X.Z.; project administration, Y.Z.; funding acquisition, Y.Z. All authors have read and agreed to the published version of the manuscript.
Funding
This research was supported by Transportation Technology Project of Jiangsu Province (2022Y13-2, 2023Y13).
Data Availability Statement
Data is contained within the article.
Conflicts of Interest
The authors declare no conflicts of interest.
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Figure 1.
Appearance and morphology of steel slag.
Figure 2.
Appearance and morphology of natural fine aggregate.
Figure 3.
Steel slag particles (1 #) after surface dust removal treatment.
Figure 4.
Pore structure of steel slag.
Figure 5.
Crushing value of steel slag coarse aggregate.
Figure 6.
Composite grading curve of three AC-13C mineral materials.
Figure 7.
SMA-13 synthetic grading curve of three mineral materials.
Figure 8.
Raw materials used in the experiment.
Figure 9.
Water immersion test results.
Figure 10.
Water boiling method test results.
Figure 11.
Comparison of high-temperature stability of steel slag asphalt mixture and ordinary asphalt mixture. 70 #, 90 #, SBS and B are different asphalt codes.
Figure 11.
Comparison of high-temperature stability of steel slag asphalt mixture and ordinary asphalt mixture. 70 #, 90 #, SBS and B are different asphalt codes.
Figure 12.
Comparison of low-temperature stability of steel slag asphalt mixture and ordinary asphalt mixture. 70 #, B and SBS are different asphalt codes.
Figure 12.
Comparison of low-temperature stability of steel slag asphalt mixture and ordinary asphalt mixture. 70 #, B and SBS are different asphalt codes.
Figure 13.
Comparison of freeze–thaw splitting strength ratio of steel slag asphalt mixture and ordinary asphalt mixture. 70 #, 90 #, and SBS are different asphalt codes.
Figure 13.
Comparison of freeze–thaw splitting strength ratio of steel slag asphalt mixture and ordinary asphalt mixture. 70 #, 90 #, and SBS are different asphalt codes.
Figure 14.
Comparison of the stability of steel slag asphalt mixture and ordinary asphalt mixture in water. 70 #, 90 #, and SBS are different asphalt codes.
Figure 14.
Comparison of the stability of steel slag asphalt mixture and ordinary asphalt mixture in water. 70 #, 90 #, and SBS are different asphalt codes.
Table 1.
Test results of crushing value of steel slag coarse aggregate.
| Trial Number | Calibrated Quality (g) | Average Value (g) | Total Test Mass (g) | 2.36 mm Sample Mass under Sieve (g) | Crush Value Test Value (%) | Average Value (%) | Specification Requirements |
|---|---|---|---|---|---|---|---|
| 1 | 3343.5 | 3343.5 | 3344.5 | 554.5 | 16.6 | 16.6 | 26.0 |
| 2 | 3343.5 | 3342.4 | 552.5 | 16.5 | |||
| 3 | 3343.5 | 3341.2 | 553.8 | 16.6 |
Table 2.
Crushing index of steel slag fine aggregate.
| Particle Size (mm) | Drying Quality before the Experiment (g) | Residual Mass after Test (g) | Passing Mass after Test (g) | Crush Value Test Value (%) | Measured Crush Value of Single Particle Fraction (%) | Crushing Index Value (%) |
|---|---|---|---|---|---|---|
| 4.75~2.36 | 330 | 307.4 | 22.6 | 93 | 88 | 97 |
| 330 | 296.1 | 33.9 | 90 | |||
| 330 | 305.2 | 24.8 | 92 | |||
| 2.36~1.18 | 330 | 286.6 | 43.4 | 87 | 92 | |
| 330 | 292.9 | 37.1 | 89 | |||
| 330 | 290.3 | 39.7 | 88 | |||
| 1.18~0.6 | 330 | 316.6 | 13.4 | 96 | 96 | |
| 330 | 315.4 | 14.6 | 96 | |||
| 330 | 315.8 | 14.2 | 96 | |||
| 0.6~0.3 | 330 | 319.1 | 10.9 | 97 | 97 | |
| 330 | 319.0 | 11.0 | 97 | |||
| 330 | 319.2 | 10.8 | 97 |
Table 3.
Technical performance test results of SBS-modified asphalt.
| Pilot Project | Test Results | Specification Requirements |
|---|---|---|
| Penetration (25 °C, 100 g, 5 s) (0.1 mm) | 69 | 60~80 |
| Penetration Index PI (15 °C, 25 °C, 30 °C) | −0.19 | ≥−0.4 |
| ductility (5 cm/min, 5 °C) (cm) | 45 | ≥30 |
| Softening point (TR&B) (°C) | 73 | ≥55 |
| Kinematic viscosity (135 °C) (Pa·s) | 1.69 | ≤3 |
| Flash point (°C) | >300 | ≥230 |
| Relative density (25 °C) | 1.033 | Actual measurement |
| Segregation, softening of spreads (°C) | 0.9 | ≤2.5 |
| Elastic recovery (%) | 97.9 | ≥65 |
| Asphalt film heating test | ||
| Change in quality (%) | −0.162 | ≤±1.0 |
| Residual penetration ratio (25 °C) (%) | 96.6 | ≥65 |
| Residual ductility (5 °C) (cm) | 37 | ≥20 |
Table 4.
The mixture ratio of the experimental graded.
| Minerals | Graded A (%) | Graded B (%) | Graded C (%) |
|---|---|---|---|
| 1# | 25 | 31 | 36 |
| 2# | 27 | 28 | 27 |
| 3# | 13 | 11 | 11 |
| 4# | 34 | 29 | 25 |
| Mineral powder | 1 | 1 | 1 |
Table 5.
Breakdown of the pass rate of each screen hole of the three gradations.
| Aggregates | Percentage of Passing through the Sieve Hole (Square Hole Sieve, mm) (%) | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 16.0 | 13.2 | 9.5 | 4.75 | 2.36 | 1.18 | 0.6 | 0.3 | 0.15 | 0.075 | |
| 1# | 100.0 | 78.1 | 14.6 | 1.0 | 1.0 | 1.0 | 1.0 | 1.0 | 0.8 | 0.8 |
| 2# | 100.0 | 100.0 | 100.0 | 10.2 | 1.6 | 1.6 | 1.6 | 1.4 | 1.4 | 1.2 |
| 3# | 100.0 | 100.0 | 100.0 | 100.0 | 13.6 | 2.6 | 2.6 | 2.4 | 2.4 | 2.2 |
| 4# | 100.0 | 100.0 | 100.0 | 100.0 | 92.6 | 76.2 | 55.2 | 38 | 29.2 | 17.7 |
| Mineral powder | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100 | 99.8 | 91.7 |
| Synthetic Gradation A | 100.0 | 94.5 | 78.7 | 51.0 | 34.0 | 27.9 | 20.8 | 14.9 | 11.8 | 7.7 |
| Synthetic Gradation B | 100.0 | 93.2 | 73.5 | 44.2 | 29.2 | 24.1 | 18.1 | 13.0 | 10.4 | 6.9 |
| Synthetic Gradation C | 100.0 | 92.1 | 69.3 | 40.1 | 25.5 | 21.1 | 15.9 | 11.6 | 9.2 | 6.2 |
| Standardized upper | 100.0 | 100.0 | 80.0 | 53.0 | 40.0 | 30.0 | 23.0 | 18.0 | 12.0 | 8.0 |
| Standard lower limit | 100.0 | 90.0 | 60.0 | 30.0 | 20.0 | 15.0 | 10.0 | 7.0 | 5.0 | 4.0 |
| Normalized median | 100.0 | 95.0 | 70.0 | 41.5 | 30.0 | 22.5 | 16.5 | 12.5 | 8.5 | 6.0 |
Table 6.
Calculation table of physical indexes of AC-13C steel slag asphalt mixture at all levels.
| Grading Type | Oil–Stone Ratio (%) | Stability (kN) | Flow Value (0.1 mm) | Void Ratio VV (%) | Ore Clearance Rate VMA (%) | Saturation VFA (%) | Gross Volume Relative Density | Theoretical Relative Density |
|---|---|---|---|---|---|---|---|---|
| Graded A | 4.8 | 25.01 | 41.3 | 3.3 | 13.3 | 5.4 | 2.837 | 2.933 |
| Gradation B | 4.8 | 23.85 | 45.8 | 3.5 | 13.5 | 74.3 | 2.853 | 2.955 |
| Gradation C | 4.8 | 23.06 | 47.9 | 4.4 | 14.6 | 70.2 | 2.861 | 2.993 |
| Request | / | ≥8.0 | 20~50 | 4.0~6.0 | ≥14.5 | 65~75 | / | / |
Table 7.
Composition of the mixture ratio of the experimental graded ore.
| Minerals | Graded A (%) | Graded B (%) | Graded C (%) |
|---|---|---|---|
| 1# | 46 | 46 | 46 |
| 2# | 29 | 32 | 35 |
| 4# | 16 | 13 | 10 |
| Mineral powder | 9 | 9 | 9 |
| Fiber | 0.3 | 0.3 | 0.3 |
Table 8.
Breakdown of the pass rate of each sieve hole of the three gradations.
| Aggregates | Percentage of Passing through the Sieve Hole (Square Hole Sieve, mm) (%) | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 16.0 | 13.2 | 9.5 | 4.75 | 2.36 | 1.18 | 0.6 | 0.3 | 0.15 | 0.075 | |
| 1# | 100.0 | 81.5 | 16.5 | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 |
| 2# | 100.0 | 100.0 | 100.0 | 9.0 | 1.0 | 1.0 | 1.0 | 1.0 | 1.0 | 1.0 |
| 3# | 100.0 | 100.0 | 100.0 | 100.0 | 15.0 | 3.0 | 3.0 | 3.0 | 2.5 | 2.5 |
| 4# | 100.0 | 100.0 | 100.0 | 100.0 | 83.8 | 52.6 | 33.4 | 17 | 11.9 | 7.5 |
| Mineral powder | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100 | 99.8 | 91.7 |
| Synthetic Gradation A | 100.0 | 91.5 | 61.6 | 27.8 | 22.9 | 17.9 | 14.9 | 12.2 | 11.4 | 10.0 |
| Synthetic Gradation B | 100.0 | 91.5 | 61.6 | 25.1 | 20.4 | 16.4 | 13.9 | 11.8 | 11.1 | 9.8 |
| Synthetic Gradation C | 100.0 | 91.5 | 61.6 | 22.4 | 18.0 | 14.8 | 12.9 | 11.3 | 10.8 | 9.6 |
| Standardized upper | 100.0 | 100.0 | 80.0 | 53.0 | 40.0 | 30.0 | 23.0 | 18.0 | 12.0 | 8.0 |
| Standard lower limit | 100.0 | 90.0 | 60.0 | 30.0 | 20.0 | 15.0 | 10.0 | 7.0 | 5.0 | 4.0 |
| Normalized median | 100.0 | 95.0 | 70.0 | 41.5 | 30.0 | 22.5 | 16.5 | 12.5 | 8.5 | 6.0 |
Table 9.
Calculation table of physical indexes of SMA-13 steel slag asphalt mixture at all levels.
| Grading Type | Bitumen- Aggregate/Stone Ratio (%) | Stability (kN) | Flow Value (0.1 mm) | Porosity VV (%) | Ore Clearance Rate VMA (%) | Saturation VFA (%) | Coarse Aggregate Skeleton Clearance Ratio VCAmix (%) | Gross Volume Relative Density | Theory Relative Density |
|---|---|---|---|---|---|---|---|---|---|
| Graded A | 5.8 | 22.51 | 47.3 | 2.6 | 15.4 | 83.1 | 41.7 | 2.839 | 2.915 |
| Gradation B | 5.8 | 18.73 | 48.8 | 3.7 | 16.6 | 77.5 | 40.7 | 2.814 | 2.928 |
| Gradation C | 5.8 | 17.35 | 47.9 | 4.5 | 17.3 | 73.9 | 38.8 | 2.803 | 2.942 |
| Request | / | ≥6.0 | -- | 3.0~4.0 | ≥16.5 | 75~85 | ≤VCADRC | / | / |
Table 10.
Calculation table of physical indicators for various grades of AC-13C steel slag asphalt mixture.
Table 10.
Calculation table of physical indicators for various grades of AC-13C steel slag asphalt mixture.
| Grading Type | Bitumen-Aggregate/Stone Ratio (%) | Stability (kN) | Flow Value (0.1 mm) | Porosity VV (%) | Ore Clearance Rate VMA (%) | Saturation VFA (%) | Coarse Aggregate Skeleton Clearance Ratio VCAmix (%) | Gross Volume Relative Density |
|---|---|---|---|---|---|---|---|---|
| AC-13C | 4.2 | 20.01 | 36.5 | 6.7 | 15.1 | 56.0 | 2.831 | 3.032 |
| 4.5 | 23.52 | 43.4 | 5.6 | 14.9 | 62.5 | 2.847 | 3.015 | |
| 4.8 | 20.35 | 44.7 | 4.5 | 14.8 | 69.5 | 2.858 | 2.999 | |
| 5.1 | 19.46 | 47.6 | 3.9 | 14.8 | 73.4 | 2.865 | 2.982 | |
| 5.4 | 18.91 | 51.2 | 3.1 | 14.8 | 78.9 | 2.873 | 2.966 | |
| Request | / | ≥8.0 | 20~50 | 4.0~6.0 | ≥14.5 | 65~75 | / | / |
Table 11.
Calculation table for physical indicators of SMA-13 steel slag asphalt mixture at each grade.
Table 11.
Calculation table for physical indicators of SMA-13 steel slag asphalt mixture at each grade.
| Grading Type | Bitumen-Aggregate/Stone Ratio (%) | Stability (kN) | Flow Value (0.1 mm) | Porosity VV (%) | Ore Clearance Rate VMA (%) | Saturation VFA (%) | Coarse Aggregate Skeleton Clearance Ratio VCAmix (%) | Gross Volume Relative Density | Theory Relative Density |
|---|---|---|---|---|---|---|---|---|---|
| SMA-13 | 4.9 | 17.26 | 39.2 | 4.9 | 16.8 | 71.2 | 40.9 | 2.781 | 2.975 |
| 5.2 | 16.39 | 32.7 | 4.8 | 17.0 | 72.0 | 41.0 | 2.784 | 2.959 | |
| 5.5 | 19.48 | 48.6 | 4.3 | 16.8 | 74.4 | 41.1 | 2.797 | 2.943 | |
| 5.8 | 21.15 | 41.2 | 3.9 | 16.7 | 76.8 | 40.8 | 2.810 | 2.927 | |
| 6.1 | 18.12 | 50.1 | 3.2 | 16.3 | 80.5 | 40.5 | 2.830 | 2.913 | |
| Request | / | ≥6.0 | -- | 3.0~4.0 | ≥16.5 | 75~85 | ≤VCADRC | / | / |
Table 12.
Chemical composition of steel slag.
| Chemical Composition | Content/% | Chemical Composition | Content/% | ||
|---|---|---|---|---|---|
| Coarse Aggregate | Fine Aggregate | Coarse Aggregate | Fine Aggregate | ||
| CaO | 36.835 | 37.835 | K2O | 0.047 | 0.345 |
| Fe2O3 | 31.257 | 32.257 | Cl | 0.025 | 0.036 |
| SiO2 | 19.085 | 20.085 | SrO | 0.024 | 0.022 |
| Al2O3 | 4.317 | 5.317 | WO3 | 0.022 | 0.007 |
| MnO | 2.718 | 3.718 | ZrO2 | 0.020 | 0.006 |
| MgO | 1.527 | 2.527 | CuO | 0.015 | 0.024 |
| P2O5 | 1.054 | 2.054 | ZnO | 0.011 | 0.035 |
| TiO2 | 0.779 | 1.779 | Nb2O5 | 0.006 | 0.004 |
| Cr2O3 | 0.683 | 1.683 | PbO | —— | 0.006 |
| SO3 | 0.556 | 1.556 | NiO | —— | —— |
| V2O5 | 0.2287 | 1.2287 | Loss on ignition | 0.699 | 3.209 |
| BaO | 0.101 | 0.123 | —— | —— | —— |
Table 13.
Results of chemical element leaching test in steel slag (mg/L).
| Al | Ba | Ca | K | Li | Mg | Zn | |
|---|---|---|---|---|---|---|---|
| Standard requirements | 0.05 | 2.000 | - | - | - | - | 5.000 |
| Untreated | 0.315 | 0.815 | 1924 | 0.046 | 7.077 | 0.009 | 0.196 |
| Asphalt wrapping | 0.021 | 0.672 | 824.4 | 0.015 | 0.007 | 0.007 | 0.017 |
Note: “-” indicates no requirement made.
Table 14.
Results of dynamic stability test of rutting test.
| Grading Type | Gross Volume Relative Density | Dynamic Stability (Times/mm) | Coefficient of Variation (%) | Technical Standards |
|---|---|---|---|---|
| Steel slag AC-13C | 2.858 | 8341 | 17.6 | ≥2800 |
| Steel slag SMA-13 | 2.814 | 9168 | 16.1 | ≥3000 |
Table 15.
Comparison of dynamic stability of steel slag asphalt mixture and ordinary asphalt mixture.
Table 15.
Comparison of dynamic stability of steel slag asphalt mixture and ordinary asphalt mixture.
| Data Source | Type of Asphalt | Type of Asphalt Mixture | Optimal Bitumen- Aggregate/Stone Ratio (%) | Dynamic Stability (Times/mm) | Additive Type | Technology Standard | Aggregates Type |
|---|---|---|---|---|---|---|---|
| The paper | SBS modification | AC-13C | 4.8 | 8341 | not | ≥2800 | Steel slag coarse aggregate |
| SMA-13 | 5.8 | 9168 | not | ≥3000 | |||
| L1 [34] | AH-90 | AC-13C | 5.49 | 1694 | not | ≥1000 | All steel slag |
| L2 [35] | AH-70 | AC-13C | 6.63 | 2516 | not | ≥1000 | 73.9% steel slag |
| L3-1 [36] | AH-70 | AC-13C | 5.6 | 2897 | cement | ≥1000 | All steel slag |
| L3-2 [36] | AH-70 | AC-13C | 4.8 | 1478 | cement | ≥1000 | basalt |
| L4-1 [37] | SBS modification | SMA-13 | 6.1 | 6550 | not | ≥3000 | 75.0% steel slag |
| L4-2 [37] | SBS modification | SMA-13 | 5.8 | 5950 | not | ≥3000 | basalt |
| L4-3 [37] | SBS modification | SMA-13 | — | 3100 | not | ≥3000 | limestone |
| L5 [38] | I-A modification | SMA-13 | 6.4 | 9000 | not | ≥3000 | Steel slag powder |
Table 16.
Results of low-temperature trabecular test.
| Asphalt Mixture Type | Flexural Tensile Strength (MPa) | Destruction Strain (με) | Stiffness Modulus (MPa) | Technical Standards (με) |
|---|---|---|---|---|
| AC-13C | 9.102 | 3105 | 2931 | ≥2500 |
| SMA-13 | 10.47 | 4417 | 2370 | ≥2500 |
Table 17.
Comparison of low-temperature stability of steel slag asphalt mixture and ordinary asphalt mixture.
Table 17.
Comparison of low-temperature stability of steel slag asphalt mixture and ordinary asphalt mixture.
| Data Source | Bitumen Type | Type of Asphalt Mixture | Type of Additive | Aggregate Type | Bending and Pulling Strength (MPa) | Destruction Strain (με) | Stiffness Modulus (MPa) | Technology Standard (με) |
|---|---|---|---|---|---|---|---|---|
| The paper | SBS modification | AC-13C | not | Steel slag coarse aggregate | 9.102 | 3325 | 2737 | ≥2500 |
| SMA-13 | not | 10.47 | 4417 | 2370 | ≥2500 | |||
| L1 [36] | AC-13C | cement | all Steel slag | 3.179 | 3423 | 2026.0 | — | |
| L2-1 [38] | SMA-13 | Mineral powder | all Steel slag | 10.58 | 3522.5 | 3002.9 | ≥2500 | |
| L2-2 [38] | Slag powder | 12.25 | 3834.8 | 3212.3 | ≥2500 | |||
| L3-1 [39] | SMA-13 | not | 72.0% Steel slag | 9.3 | 4972.5 | 1873.1 | ≥2500 | |
| L3-2 [39] | 6.7 | 2295.0 | 2929.1 | ≥2500 | ||||
| L3-3 [39] | 9.5 | 4428.0 | 2139.8 | ≥2500 | ||||
| L3-4 [39] | 6.8 | 5775.0 | 1183.4 | ≥2500 | ||||
| L4 [35] | AH-70 | AC-13C | 73.9% Steel slag | 3.7 | 3323 | 1865 | — |
Table 18.
Moisture sensitivity test results.
| Asphalt Mixture Type | Freeze–Thaw Splitting Strength Ratio TSR (%) | Technical Standards (%) | Residual Stability of Immersion (%) | Technical Standards (%) |
|---|---|---|---|---|
| AC-13C | 94.07 | ≥80 | 93.8 | ≥85 |
| SMA-13 | 89.10 | ≥80 | 90.27 | ≥80 |
Table 19.
Comparison of moisture sensitivity of steel slag asphalt mixture and ordinary asphalt mixture.
Table 19.
Comparison of moisture sensitivity of steel slag asphalt mixture and ordinary asphalt mixture.
| Data Source | Type of Asphalt | Type of Asphalt Mixture | The Type of Aggregate | Additive Type | Freeze–Thaw Splitting Strength Ratio TSR (%). | Technology Standard (%). | Residual Stability of Immersion (%). | Technology Standard (%). |
|---|---|---|---|---|---|---|---|---|
| The paper | SBS modification | AC-13C | Steel slag coarse aggregate | not | 94.07 | ≥80 | 93.8 | ≥85 |
| SMA-13 | not | 89.10 | ≥80 | 90.27 | ≥85 | |||
| L1 [34] | AH-90 | AC-13C | All steel slag | not | 92 | ≥75 | 91.4 | ≥80 |
| L2 [35] | AH-70 | AC-13C | 73.9% Steel slag | not | 84.98 | ≥75 | 90.36 | ≥80 |
| L3-1 [36] | SBS modification | AC-13C | All steel slag | cement | 81.3 | ≥80 | 87.8 | ≥85 |
| L3-2 [36] | AH-70 | AC-13C | cement | 84.7 | ≥75 | 92.7 | ≥80 | |
| L4-1 [37] | SBS modification | SMA-13 | 75.0% Steel slag | Polyacrylonitrile | 93.7 | ≥75 | 91.0 | ≥80 |
| L4-2 [37] | SBS modification | SMA-13 | basalt | Polyacrylonitrile | 90.1 | ≥75 | 83.0 | ≥80 |
Table 20.
Fatigue performance test results.
| Type of Mixture | σf/MPa | Technical Requirements |
|---|---|---|
| AC-13C | 1.17 | - |
| SMA-13 | 1.53 | - |
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Zhao, X.; Zhang, Y. Analyzing the Mechanical and Durability Characteristics of Steel Slag-Infused Asphalt Concrete in Roadway Construction. Buildings 2024, 14, 679. https://doi.org/10.3390/buildings14030679
AMA Style
Zhao X, Zhang Y. Analyzing the Mechanical and Durability Characteristics of Steel Slag-Infused Asphalt Concrete in Roadway Construction. Buildings. 2024; 14(3):679. https://doi.org/10.3390/buildings14030679
Chicago/Turabian StyleZhao, Xijuan, and Yemao Zhang. 2024. "Analyzing the Mechanical and Durability Characteristics of Steel Slag-Infused Asphalt Concrete in Roadway Construction" Buildings 14, no. 3: 679. https://doi.org/10.3390/buildings14030679
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