Performance Evaluation of Steel Slag on Hot Mix Asphalt Mixture

Researchers have been actively exploring alternative substances to modify asphalt mixtures and improve their qualities. While asphalt has been the traditional binder used in road construction due to its excellent adhesive and waterproofing properties. In this investigation, an assessment is conducted in a laboratory environment to evaluate the effectiveness of incorporating recycled steel slag as an addition in hot mix asphalt. The utilization of the Superpave mix design methodology was employed in this study to modify fine steel slag with a particle size of 300 m. Various percentages of steel slag modifier, namely 5%, 10%, 15%, and 20% of the total weight of the fine aggregate, were incorporated. The outcomes of this investigation revealed that the mixtures containing steel slag exhibited superior performance compared to those without any slag addition, serving as the control sample (0% (slag. The inclusion of steel slag in the asphalt mixes has demonstrated a significant enhancement in stability while concurrently reducing the levels of permanent deformation. The outcomes derived from the study indicate that asphalt mixtures containing steel slag additives at varying proportions (5%, 10%, 15%, and 20% by weight of the fine aggregates) exhibited superior performance in terms of the indirect tensile modulus test, static creep test, and dynamic creep test when compared to the control sample. Notably, the results highlight that the incorporation of 15% steel slag yielded the most favorable overall performance values among the tested asphalt mixes.


INTRODUCTION
The government allocates substantial funds to construct new roads and invests even more in their maintenance to ensure their usability.However, those who utilize these roads, particularly highways, may readily observe the significant deterioration caused by the increased loads carried by trucks transporting goods between cities.This is especially noticeable on the designated truck lanes, which are subjected to damage as trucks veer from their designated paths onto the central lanes.As a result, this creates numerous problems for private vehicles and poses challenges to overall road functionality.Hence, there is a global trend of escalating traffic loading on road networks, leading to accelerated deterioration of transportation infrastructure in many countries.This phenomenon is widespread and has been observed across various nations, highlighting the urgent need for comprehensive strategies to address the challenges posed by the increased strain on road systems (1).Steel slag exhibits commendable mechanical properties and possesses a visually appealing surface topography, making it a desirable choice as an aggregate.However, the primary concerns associated with its utilization lie in its high water absorption capacity and the subsequent expansion in volume that it undergoes.These factors necessitate careful consideration and appropriate management strategies when incorporating steel slag in construction applications (2).The production of steel results in the generation of steel slag, which is considered as a byproduct.However, the steelmaking industry's rapid expansion and low utilization rate of total slag have led to concerns regarding the accumulation of steel slag, its impact on land occupation, and environmental pollution.Concurrently, the rapid development of the economy and transportation sector has resulted in a significant increase in road construction and the subsequent demand for high-quality natural aggregates.This surge in demand has presented challenges in meeting the escalating requirements for road construction materials (3).On the other hand, in an electric arc furnace, the oxidation of steel pellets results in the production of steel slag, which contributes to 15-20% of the iron output (4).In the modern era, the construction and maintenance of pavements have embraced the principles of sustainable development.This approach aims to minimize reliance on resources and reduce energy consumption.By incorporating sustainable practices into pavement projects, we can contribute to the preservation of our natural resources and mitigate the environmental impact of infrastructure development.This shift towards sustainability ensures that our road networks are built and maintained in a manner that aligns with long-term environmental goals (5).Every year, Iran's steel factories produce substantial amounts of steel slag as a byproduct.Despite the fact that it can be utilized as a synthetic source of aggregates, it is disposed of in landfills (6).For technical, monetary, and environmental grounds, using steel slag in industrial projects is a good strategy.Steel slag aggregates have a rough surface and a form that is extremely angular.Moreover, the hot mixed asphalt known as Stone Matrix Asphalt (SMA) was created in Germany in the late 1960s.SMA has been used for more than 20 years in other European nations to increase rutting resistance and reduce tire wear from studded wheels (7).In the same way, steel slag has the potential to replace natural aggregate because it is an industrial solid waste and shares many of the same physical and mechanical characteristics as natural stone (8).Steel slag use is encouraged by a lack of natural stone and the expensive cost of obtaining high-quality aggregate (9).The physical and chemical interactions between aggregate and asphalt are intricate, and the chemical characteristics of the aggregate greatly influence the mechanical and physical characteristics of asphalt pavement.The use of low-grade minerals and solid waste is encouraged by a lack of natural stone supplies and severe environmental degradation.So, instead of using traditional aggregates to build asphalt pavement, steel slag and granite might be employed (10).
Highway pavement is frequently built and rebuilt using asphalt mixture, which is the primary form of road construction material.It is generally true that filler, aggregate, and asphalt binder are used to make asphalt mixture.The volume of aggregate in the asphalt mixture ranges from 92% to 96%; the remainder is primarily made up of asphalt binder and filler (11).Reusing steel slag as aggregate for induction heating has become a significant asphalt paving topic (12).
A type of solid waste called steel slag has been extensively used in civil engineering, and both the environment and the entire sector have benefited from this use.Researchers also discovered that steel slag can be utilized as an induction heating material (13) (14).Recent years have seen demand on the HMA sector to include a variety of waste materials in HMA pavements (15).A by-product of the steel-making process is steel slag.Three tons of stainless steel are produced, leaving behind around one tone of slag (16).A surface water isolation structure was suggested using three surface treatment techniques to prevent steel slag's volume expansion and enhance the performance of the steel slag asphalt mixture on the pavement (17).The primary solid waste in the steelmaking sector is steel slag.In China, 100 million tons of steel slag were produced in 2016 (18).In comparison to limestone asphalt mixture, steel slag asphalt mixture is more moisture and crack resistant (19).The growth of the national economy depends heavily on the efficiency of the road transportation system.Every year, China builds and reconstructs a significant number of highways, placing strain on the availability of natural resources (20).In a well compacted pavement, permanent deformation is a shearing mechanism leading to flow of the mixture away from the loaded area.Permanent deformation causes rutting, shoving and distortion in pavement surfaces (21).Although this problem can be tackled by improved mix design, the binder role is important.Therefore, the asphalt properties need to be developed to reduce the problem (22).It is a problem in environments where large temperature changes occur, including the incidence of very low temperatures.Failure occurs when the thermally induced tensile stress exceeds the tensile strength (23).Moisture damage involves the displacement of the asphalt film from the aggregate surface in the presence of water.This can result in a decrease in bond at the surface leading to raveling or to stripping of asphalt from the aggregate in the pavement leading to mechanical failure by cracking and rutting (24).

MATERIALS Asphalt Binder
In this research, the asphalt binder employed was of the 80/100 penetration grade.To ensure the preservation of its properties and prevent frequent heating during the preparation and blending process for binder testing, the asphalt was carefully placed in small containers with a capacity of ‫العلوم‬ ‫األسمرية:‬ ‫الجامعة‬ ‫مجلة‬ ‫التطبيقية‬ Journal of Alasmarya University: Applied Sciences approximately one liter.Additionally, the specific gravity of the asphalt binder was measured to be 1.03.

Aggregate
The study materials for this investigation will include aggregate, binder, and modified steel slag.It is imperative to adhere to the standard specifications outlined by the American Society for Testing and Materials (ASTM) in the preparation of these materials.Table 1 provides the Superpave Compactor effort based on Equivalent Single Axle Loads (ESALs).Furthermore, the study incorporates filler, coarse aggregate, and fine aggregate.Fine aggregate is defined as material that passes through a sieve size of 4.75 mm and remains retained on a sieve size of 75 mm.Conversely, coarse aggregate refers to material that is retained on a sieve size of 4.75 mm, as depicted in Table 1.

Steel Slag Modifier
In this particular study, steel slag in powdered form, with a particle size of 300 m, was introduced.The quantities of the steel slag modifier added to the mixes were denoted by the percentages of the weight of the aggregate with a screen size of 300 m.The various percentages considered in the study were 0%, 5%, 10%, 15%, and 20%.As illustrated in Figure 1, the size of the steel slag used in this investigation falls under the classification of fine steel slag with a particle size of 300 m.

Indirect Tensile Modulus Test
To assess the stiffness modulus of Hot Mix Asphalt (HMA), an indirect tensile modulus test was conducted following the procedure outlined in ASTM D4123.Specimens were placed in the MATTA machine at a temperature of 40°C and maintained at a constant temperature of 0.5°C for a minimum of four hours.Subsequently, the pressure was adjusted to a value of 75 kPa to ensure standardized testing conditions.A direct compressive load is applied to the specimens using loading strips that are 12 mm wide and span across the vertical diameter.The resulting indirect tensile stress and strain along the horizontal diameter of the specimens are measured using linear variable differential transducers (LVDTs).This allows for accurate and precise quantification of the mechanical response of the specimens during the indirect tensile modulus test, Prior to the commencement of the actual test, a conditioning period was implemented to ensure optimal test conditions.During this period, five load pulses were applied to the specimens, with a three-second interval between each pulse.This served two purposes: first, to assess the strength of the specimens and determine the appropriate load to be applied during the subsequent test period, ensuring sufficient horizontal deformation without causing damage to the specimens.Second, the load pulses aided in promoting proper adherence of the loading strips to the samples, ensuring reliable and consistent test results.The rise time, which is the amount of time between the beginning of application and the peak load, was arbitrary set at 100 milliseconds.The test conditions, as outlined previously, were rigorously maintained throughout the duration of the test, as they directly influenced the elastic stiffness of the specimens, as presented in Table 2.The elastic stiffness for each load pulse was calculated based on the peak vertical load, horizontal stress, horizontal deformation, and rise time.These parameters were carefully monitored and recorded to ensure accurate assessment of the specimens' elastic response and to establish a comprehensive understanding of their mechanical behavior.To ensure accuracy and reliability, the mean elastic stiffness for each test was determined by calculating the average of the five values obtained from multiple applications of five load pulses.This approach allowed for a more representative evaluation of the specimens' elastic behavior.Additionally, to account for any potential directional effects, the test was repeated for each specimen after rotating it approximately 90°.This rotation ‫العلوم‬ ‫األسمرية:‬ ‫الجامعة‬ ‫مجلة‬ ‫التطبيقية‬ Journal of Alasmarya University: Applied Sciences helped to capture any variations in the specimens' response to the applied loads, providing a comprehensive understanding of their elastic properties.

Static Creep Test
In this particular test, a sample undergoes a static load under controlled conditions of time and temperature, while the resulting deformation of the sample is measured.To ensure standardized test conditions, the prescribed procedures were diligently followed.The specimens were placed in the MATTA machine and maintained at a temperature of 40±0.5˚C for a minimum duration of four hours.During the test, the skin and core temperatures of the specimen were carefully monitored using two thermo-couples.These thermo-couples were inserted into a dummy specimen and positioned near the specimen under test, enabling accurate temperature monitoring throughout the test duration.Subsequently, the specimen was carefully positioned between hardened and polished circular platens.Axial stress of 70 kPa was then repeatedly applied to the specimen using a steel ball, which was seated in a conical recess in the upper platen.The stress pulse was assumed to have a square waveform, with a loading period of one second.LVDTs probes, mounted on slide rods and in contact with the upper platen, were used to measure the resulting axial strain.The test was terminated after a total of 1000 stress pulses, during which intervals of axial strain corresponding to the number of stress pulses were recorded and plotted.These intervals are detailed in Table 3, providing a comprehensive representation of the specimen's mechanical response over the course of the test.

Dynamic Creep Test
The Dynamic Creep Test involves repeatedly applying unaxial stress pulses to an asphalt material and employing linear variable deferential transducers (LVDTs) to quantify the consequent deformations in the same direction as presented in Table 4.The test conditions were summarize as following; the specimens are kept in the MATTA machine at temperature 40±0.5˚C for at least four hours.Then, the test was performed at 40ºC, and sample's skin and core temperatures during the test were monitored by two thermo-couples which were inserted in a dummy samples and located near the specimen under test.The duration of each pulse width is set at 100 ms, followed by a rest period of 900 ms before the next pulse is applied.To prevent the vertical loading shaft from lifting off the test specimen during the rest interval, a contact stress of 9 kPa is applied.The deviator stress for each loading pulse is maintained at 207kPa.The test is conducted for a total of 10,000 cycles, or until the maximum axial strain limit is reached, whichever occurs first.This comprehensive testing protocol ensures that the specimen's mechanical behavior is thoroughly evaluated under controlled conditions.

RESULTS AND DISCUSSIONS
The laboratory test results were carefully analyzed to assess and compare the properties of Hot Mix Asphalt (HMA) using two types of aggregates: normal aggregate and modified aggregate with steel slag.All the mixes were prepared following the Superpave mix design method.The density of the compacted samples was observed at the optimum bitumen content.The comparison of the properties of the hot mix asphalt mixtures was conducted in terms of density, indirect tensile modulus, static creep, and dynamic creep.These parameters provide valuable insights into the performance and characteristics of the different mixtures, aiding in the evaluation and selection of suitable asphalt mixes for specific applications.

Aggregate
The aggregates used in the study underwent an initial sieving process and were divided into the required sizes following the guidelines specified in ASTM D3515-96 (D-4).To ensure uniformity and consistency, the total weight of aggregates used for each sample was set at 1200g.This standardized approach in aggregate preparation ensures reliable and comparable results throughout the study.

Sieve analysis and aggregates distribution
In this study, aggregate was separated based on sieve size using a sieve analysis.According to the standards for hot mix asphalt mixtures, aggregate particles must fall within a certain size range and must be distributed according to a specific ratio.The aggregates were mixed and sieved in accordance with ASTM D 3515-96 (D-4) as shown in Table 5 and Figure 2. Based on the percentage of samples passing through each sieve size, aggregates were batched.

Indirect Tensile Modulus Test
The test involves subjecting the specimen to repetitive vertical forces at varying frequencies and intensities.By measuring the resulting horizontal (indirect) deformations, the stiffness of the specimen can be determined.This test serves multiple purposes, including failure analysis and quality control assessment.However, its primary application lies in providing a rapid technique for quality control.The resilient modulus, a crucial factor in the mechanical design of pavement structures, is of paramount importance.It enables the evaluation of how the pavement will respond to dynamic stresses and corresponding strains.In this study, two samples were tested for each steel slag content using the diametric resilient modulus test at a temperature of 40°C. Figure 3 presents a summary of the results obtained from the resilient modulus test for all steel slag ratios, providing a comprehensive overview of the material's performance.The analysis of the test results revealed a significant increase in the average resilient modulus when steel slag was incorporated into the mixtures.Specifically, the resilient modulus increased from 1535 MPa for mixes containing 5% steel slag to 3805 MPa for mixes containing 20% steel slag, as documented in Table This finding clearly demonstrates that the addition of steel slag positively impacts the resilient modulus of the modified mixes.This improvement in resilient modulus signifies the enhanced performance and structural integrity of the asphalt mixes when steel slag is utilized as a supplementary material.

Static Creep Test
To assess the resistance of bituminous mixes to permanent deformation under field conditions, a static creep test was conducted.This test involved applying a static load to a specimen at the Optimum Bitumen Content (OBC) and measuring the resulting permanent deformation after unloading.Its purpose was to evaluate the potential for regular and modified asphalt mixtures to experience permanent distortion.By correlating the observed persistent deformation with the rutting potential of the asphalt mixtures, valuable insights into their performance were obtained.
The test parameters and sample dimensions were standardized to ensure consistency and comparability.The rate of creep permanent deformation of a cylindrical specimen, under an axial static load, was measured over a specified time period.Figure 4 and Table 6 present a summary of the results obtained from the static creep test for all steel slag mix specimens with OBC.Notably, the results indicate that the modified mix containing 20% steel slag exhibited superior performance compared to other mixtures.Furthermore, this modified mix also outperformed the control mix, highlighting the beneficial effects of incorporating steel slag in enhancing the resistance to permanent deformation of the asphalt mixture.

Dynamic Creep Test
The dynamic creep test can be used to measure the resistance of bituminous mixes to plastic deformation.The load is applied repeatedly until the samples distorted using the same testing apparatus as the static creep test.The results indicate that the 15% steel slag modified mix shows higher performance compare to other mixes including control mix.Figures 5 and Table 7 shows the repeated dynamic creep curves and results for all mixes.The search for the optimum value of permanent deformation for the different mixes was conducted, and a graph illustrating this relationship was generated (Figure 6).According to the graph, the optimum permanent deformation was found to be 0.0848 mm, specifically at a steel slag content of 17.25% in the mixtures.This finding suggests that the mixtures containing 17.25% steel slag exhibit the most desirable level of permanent deformation, indicating improved resistance to rutting and deformation under field conditions.It is important to note that this optimal value provides valuable guidance for selecting the appropriate steel slag content in asphalt mixtures to achieve optimal performance and durability.

SUMMARY
Based on the test results presented in this chapter, it is evident that the inclusion of steel slag as a modifier in hot mix asphalt has yielded positive effects.The sample mixtures incorporating steel slag displayed superior performance compared to the control sample.Notably, the addition of steel slag has enhanced the resistance of the asphalt concrete to creep deformation.This improvement implies that the modified asphalt mixtures are less prone to permanent deformation under applied loads.The findings highlight the beneficial effects of steel slag in enhancing the overall performance and durability of hot mix asphalt.These results contribute to a better understanding of the impact of steel slag on asphalt mixtures and support its utilization as a viable modifier in the construction of durable and resilient pavement structures.
In the indirect tensile modulus test, the results demonstrate that the inclusion of steel slag in hot mix asphalt leads to an improvement in performance.The addition of steel slag enhances the tensile modulus of the asphalt mixture, indicating increased resistance to cracking and improved structural integrity.This improvement in performance is attributed to the beneficial properties and characteristics of steel slag, which contribute to the overall durability and longevity of the hot mix asphalt.Therefore, the utilization of steel slag as a modifier in hot mix asphalt has proven to be effective in enhancing its performance and ensuring its suitability for various applications.
According to the results obtained from the static creep test, it may be concluded that the mix containing 20% steel slag modifier outperforms the other categories.This particular mix demonstrates superior performance in terms of axial strain, indicating enhanced resistance to permanent deformation.The inclusion of 20% steel slag in the mix effectively improves the overall performance and durability of the hot mix asphalt, making it more resilient to long-term deformations.Therefore, based on these findings, the mix with a 20% steel slag modifier can be considered as the optimal choice for achieving the best performance in terms of permanent deformation resistance.
It could be concluded that the mix containing 15% steel slag modifier exhibits the best performance in terms of resisting plastic deformation strength under axial strain.This particular mix demonstrates superior performance in terms of its ability to withstand and resist the development of plastic deformation.The inclusion of 15% steel slag in the mix enhances its overall strength and durability, making it more resistant to deformation under dynamic loading conditions.Therefore, based on these findings, the mix with a 15% steel slag modifier can be considered as the optimal choice for achieving the best performance in terms of resisting plastic deformation strength under axial strain in the dynamic creep test.
Based on the analysis of the curve, it can be determined that the mix containing 17.25% steel slag modifier exhibits the best performance in terms of resisting plastic deformation strength under axial strain.This specific mix demonstrates superior performance in its ability to withstand and resist the development of plastic deformation.The inclusion of 17.25% steel slag in the mix enhances its overall strength and durability, making it highly effective in resisting plastic deformation under applied axial strain.Therefore, based on the findings derived from the curve

Figure 3 :
Figure 3: Resilient Modulus Results For Steel Slag Mixes

Figure 4 :
Figure 4: Static Creep Behavior For Steel Slag Mixes

Table 2 :
The Parameters For Resilient Modulus.

Table 3 :
The Parameters for Static Creep Test

Table 4 :
The Parameters For Dynamic Creep Test

Table 5 :
Average Resilient Modulus for Steel Slag

Table 6 :
Static Creep Results for Steel Slag

Table 7 :
Dynamic Creep Results For Steel Slag Mixes