The Effect of Using Various Types of Mineral Fillers on Moisture Damage of Hot Mix Asphalt

In general, asphalt additives are designed to improve the performance of asphalt mixtures by increasing their durability and resistance to cracking, and other forms of damage. Asphalt additives can be made from natural or synthetic materials, and some are biodegradable. Natural asphalt additives such as steel slag powder and silica fume are generally more sustainable than synthetic ones. The use of sustainable asphalt additives can help reduce the environmental impact of asphalt mixtures while improving their performance. This study aims to evaluate the effects of various fillers on the performance of the asphalt mixture and its tolerance to moisture damage, including steel slag powder, silica fume, and ordinary Portland cement. The research involves establishing a standard reference mix for comparison as well as several asphalt mixtures with varying amounts of mineral fillers (0, 25, 50, and 75% SSP and 3, 6, and 9% SF & OPC). The Marshall stability tests and the indirect tensile strength test were among the tests used to evaluate the mechanical properties, and the results showed that the optimal value for using steel slag powder is (25%) and for silica fume is (9%).


Introduction
One of the causes of early failure in the asphalt concrete mixture is moisture degradation.For several years, moisture damage was considered as a main concern for asphalt technology specialists.Studies have been looking for a test that distinguishes between good and poor performing asphalt mixtures from stripping potential since 1920 [1].Developing asphalt mixes with different types of additives enhances road efficiency.Pavement usually shows excessive problems and discomfort in the initial stages of the pavement due to (and high traffic volume, and climatic conditions represented by temperature and humidity) due to their ability to affect the hardness and deterioration of pavement materials, these elements have long been taken into account in road design [2].Under challenging climatic conditions and traffic loads, such as the impact of the summer-winter temperature difference, the intensity of the load, etc., asphalt concrete pavement does not always meet the acceptable quality criteria.These elements all play a role in the declining pavement service life.Due to their benefits, such as increased smoothness, decreased traffic noise, simplicity of maintenance, and speed of construction, asphalt concrete mixtures are frequently employed in the building of pavement.Paving material made of asphalt binder and mineral aggregate is called asphalt concrete [3].The characteristics of the asphalt binder are significantly influenced by its temperature.Asphalt cement binder gets viscous at high temperatures.Rutting, one of the most frequent asphalt surfaces distresses, may be a result of this behaviour in hot weather.In extremely freezing temperatures, asphalt binder becomes incredibly rigid and behaves like an elastic solid.Any generated elastic deformation is fully restored.Asphalt mixtures are intricate composites that have a weight percentage of (90-95) % mineral particles.The performance of mixtures is significantly impacted by the physical and chemical characteristics of aggregates.The finest mineral aggregates are called fillers, and they have a significant impact on how mechanically sound asphalt mixtures behave.the mineralogical makeup and shape of filler elements can change how asphalt mixes behave the filler component of aggregates significantly affects moisture damage.Numerous studies have demonstrated that the characteristics of mineral fillers (particles passing a 0.075-mm screen) significantly affect the performance of asphalt concrete pavements [4].Hot mix asphalt (HMA) ingredient improvement, mixed design, analytical techniques, and pavement design all require more study.This increases the pavement's useful life and, as a result, reduces the costs associated with repairing failed pavement.Consequently, engineers and researchers are constantly working to enhance the performance of asphalt pavement [5], [6].The rutting and fatigue life of asphalt pavements are also influenced by the type of mineral filler.These roads often fail due to the strain on the asphalt pavement caused by the distresses that develop in the pavement.As a result, numerous efforts are made to enhance the characteristics of asphalt materials to improve the performance of pavement [7].Mineral fillers are composed of minerals with tiny granules of materials such as steel slag powder, hydraulic cement, silica fume, rock dust, hydrated lime, or other suitable mineral materials, Filler is used in mixtures as an inert substance to fill the spaces between aggregated particles.[8].SSP which is a by-product of the steel-making process, poses a significant hazard to the environment [9], [10].Researchers have used treated SSP as a road engineering material to successfully overcome the aforementioned issues and have implemented these materials in real-world engineering, particularly in pavement [11], [12].They discovered that an asphalt blend including SSP as filler had improved (water stability, high-temperature deformation resistance, and low-temperature) fracture resistance when compared to an asphalt blend containing limestone filler.The researchers also discovered that using steel powder as a filler might enhance the anti-rutting capabilities of asphalt binder while somewhat lowering the crack resistance of asphalt mastic [13].A substantial percentage of road pavements are rutted and cracked, according to practical experience with highway systems.To avoid a reduction in useful life and an increase in maintenance costs, engineers must look for materials that can withstand these deformities.This issue has frequently occurred because the asphalt mix's attributes and the prerequisite qualities for the ideal design mix of either (binder/asphalt mix) were lacking.In this work, the behaviour of HMA is investigated concerning the use of silica fume (SF) as a filler aggregate substitute.For a number of years, asphalt technology experts' top concern was moisture damage.Since 1920, research has sought a test to discriminate between asphalt mixtures with high and low stripping potential.Asphalt concrete moisture damage is defined as a loss of stability and strength brought on by moisture that is actually present., there are two main mechanisms that contribute to the spread of moisture damage (loss of adhesion & cohesion).Adhesion loss occurs between (the surrounding binder and the aggregate), whereas loss of cohesion occurs within binder itself [14].The presence of water has unfavourable result on the performance of the pavement.Therefore, researchers must identify the problem and find solutions to it.There are several sources of water or moisture inside the pavement, the most important of which is the entry of water from cracks in the pavement or from the ground due to the high groundwater level or from the sides [15].The factors that affect the amount of damage resulting from the presence of moisture in HMA are (a defect in the design of HMA consisting of bitumen and aggregates, environmental factors represented by temperature, rain, etc., in addition to traffic and other factors) [14].The purpose of studying the effect of moisture on hot asphalt mixture is to better understand how moisture affects the performance and durability of asphalt pavement.By understanding how moisture affects the properties of asphalt, researchers can develop more effective and durable asphalt mixtures that are better able to withstand the effects of moisture.This research can also help inform decisions about when and where to use different types of asphalt mixtures in order to maximize their performance and longevity.

Materials
To ascertain their efficacy in enhancing road performance, this study used locally-made materials that are frequently used in Iraqi road pavement.

2-1 Asphalt Cement
Traditional asphalt cement was outfitted with a penetration grade (40-50) The necessary laboratory tests for this binder were carried out in line with the relevant standards.Table (1) & figure (1) show these tests with results.

2-3-1-Ordinary Portland Cement (OPC)
Cement is a binding agent used in construction projects to set, harden, and bond the Portland concrete cement components.The chemical and physical properties of cement, as shown in Tables ( 4) and ( 5) respectively.The term 'silica' refers to both amorphous and crystalline forms of silicon dioxide (SiO2) containing materials.The extremely fine non-crystalline silica produced in electric arc furnaces as a by-product of producing silicon elements or silicon alloys according to the Institute of American Concrete is what is meant by silica fume [16].The chemical and physical properties of SF, as shown in table (6).

2-3-3-Steel Slag Powder (SSP)
A by-product of the steel-making process is steel slag.It is produced in the furnaces used for manufacturing steel when molten steel is segregated from impurities.After cooling, the silicate and oxide in the slag combine to form a complicated liquid that solidifies as a molten liquid [17].Adding steel slag powder to the hot asphalt mix can provide several benefits, including:  Increased durability and strength of the asphalt mix.Steel slag powder is a by-product of steel production and is composed of hard, angular particles that can help improve the strength and durability of the asphalt mix. Improved resistance to cracking and rutting.The hard particles in steel slag powder help to fill in any voids in the asphalt mix, providing additional support and reducing the risk of cracking or rutting over time. Reduced costs associated with asphalt production.Steel slag powder is a cost-effective alternative to other materials used in asphalt production, such as limestone or fly ash, which can help reduce overall costs associated with asphalt production.The chemical properties of SSP, as shown in Table (7).

3-Mix design and testing procedure 3-1-Design of the Marshall mix
The main goal of the bituminous mix design is to do several trial mixes to find an affordable mix that can resist significant loads of traffic under challenging conditions.In routine pavement testing procedures, bituminous paving mixes are designed and evaluated using the Marshall Test method.According to the ASTM D6926 protocol, the samples are created (ASTM, 2010).The optimal asphalt content (OAC) is determined as 4.8% (by wt. of total mix) for the control mix.To determine the OAC, three samples were prepared for five various asphalt binder contents (4, 4.5, 5, 5.5, and 6) percent by total mixed weight.three types of mixtures were prepared.

3-1-1-Control mixtures:
This mixture was designed as a benchmark for comparison with other mixtures designed for this project.The design of this mixture employed only pure asphalt binder (40-50) and no fillers.
3-1-2-Asphalt mixture with SSP Three percentages of SSP were used to replace the mineral filler in HMA to demonstrate the impact of utilizing SSP (25%, 50%, and 75%).At this time, research is being done to determine how SSP will affect how well HMA performs and how well it can reduce moisture damage when using a pure binder.

3-1-3-Asphalt mixture with SF
Three percentages of SF6 replacing mineral fillers in HMA were used to illustrate the effect of using SF6 (3%, 6%, and 9%).At this time, research is being conducted to determine how SF affects how well HMA performs and how well it can reduce moisture damage when a pure binder is used.

3-2-Experimental Plan
This study used a variety of methods to evaluate the volumetric, mechanical, and durability characteristics of HMA in the surface layer.

3-2-1-Mechanical Characteristics
Before using HMA in a transportation facility, performance testing of HMA mixes is carried out to assess novel materials and design strategies to improve the performance of HMA pavements.The sections that follow will go into greater detail on that.

3-2-1-1-Marshall Stability and Flow
To ascertain the stability and flow of the conventional mixture, a Marshall test was conducted.The ASTM D6927 [18] guide was used to prepare the asphalt mixtures, three samples are prepared for five proportions of asphalt mortar(4,4.5,5,5.5,6%)by the weight of the total asphalt mixture with a different type of additives (100% OPC) [19], OAC was found (4.8%).Numerous specimens were created using various filler percentages, including (25, 50, and 75%) SSP and (3,6, and 9%) SF with OPC.Tensile Strength Ratio (TSR), which is calculated using Eq. ( 2) below is used to determine the compacted samples' moisture susceptibility.

S tm
S tc Where; S tm: average moisture-conditioned sample tensile strength, S tc: average of the control sample's tensile strength.Placed in a water bath for 20 min at 25°C

3-2-1-3-Vacuum Saturation Equipment
According to AASHTO T283, specimen conditioning was done using this approach by submerging the samples in water and subjecting them to a vacuum for varying treatment times to reach saturation levels between 70% and 80%.The specimens used in this study were conditioned using the following method:  In the vacuum container, place the specimen on the perforated spacer.
 Pour enough potable, room-temperature water into the vacuum container to cover the specimen with at least 1 inch (25 millimeters) of water. Delay stopping the vacuum pump until the gauge pressure exceeds 25 in Hg (check the vacuum gauge).Close the pressure release valve on the lid after opening it gradually to the partial pressure of 20 in Hg.For five minutes, maintain this pressure. Open the pressure release valve to gradually release the suction. Submerge the specimen in water for an additional five minutes. After the partial vacuum saturation, remove the cover and measure the mass of the saturated, surface-dry specimen.Samples are conditioned once again in the vacuum chamber by adjusting either the duration or the pressure until the appropriate saturation level is obtained if they are unable to reach saturation levels between 70% and 80%.However, samples are eliminated if they reach a saturation level of more than 80%.Before the IDT test, the vacuumconditioned samples were incubated for two hours at 60 °C in a water bath [20].The vacuum conditioning equipment utilized in this work is depicted in

4-1-Marshall stability test (MST)
The marshal method is an important method for hot asphalt mix because it provides a reliable and consistent way to measure the properties of asphalt mixes.The method is used to determine the stability, flow, and voids in mineral aggregate (VMA) of asphalt mixtures.This information is essential for determining the performance characteristics of asphalt mixes and ensuring that they meet the requirements of the project.The Marshall Method also helps to identify potential problems with asphalt mixes before they are placed in service, which can save time and money in the long run.‫الترجمة‬ ‫حفظ‬ A constant percentage of filler minerals (100% OPC) was used.The optimum bitumen content (OBC) was calculated as 4.8 % for 100% OPC as a filler and the largest stability value (13.5 kN) and flow value (3) were obtained.Table (10) displays the characteristics of reference blends using 100% OPC.Table (11) & Figure (4) show the characteristics of mixes with SSP and OPC.The replacement ratios for SSP were calculated using OPC and 25%, 50%, and 75% SSP.Adding steel slag powder to the hot asphalt mix can provide some benefits like increased durability and strength of the asphalt mix, and improved resistance to cracking and rutting.The hard particles in steel slag powder help to fill in any voids in the asphalt mix, providing additional support and reducing the risk of cracking or rutting over time.According to test results, mixes with 25% SSP and 75% OPC of filler rate exhibited the highest Marshall stability (14.47kN) when compared to mixtures with other replacement percentages and control mix.The addition of steel slag powder in proportions (25% and 50%) to the asphalt mixture can improve the resistance to stripping, but large quantities of steel slag powder can negatively affect the mixture by reducing the adhesion between the asphalt and aggregates, and also that iron and slag oxides can negatively affect the Adhesion When immersed in water or during wetting, the active particles in steel slag powder react with water [21].Figure (5) shows the characteristics of mixes containing SF and OPC.The replacement ratios for SF were calculated using OPC at 3%, 6%, and 9%.When added to hot asphalt mix, it increases the strength and durability of the asphalt.It also improves resistance to water damage, fatigue cracking, and raveling.Silica fume also helps reduce permeability and shrinkage cracking.In addition, it improves the adhesion between asphalt layers and aggregate particles, making it an ideal choice for roads with heavy traffic or in areas with extreme weather conditions [22].According to the results, the combinations with (6%, 9%) SF and OPC of filler rate showed the best Marshall stability (14.7,14.9kN)when compared to mixtures with different replacement percentages and control mix.

4-2-Indirect Tensile Strength (ITS)Test
ITS is a measure of the maximum stress that a material can withstand before it fails in tension.It is determined by testing a sample of the material in an indirect tensile test, which involves applying a force to the sample and measuring the resulting deformation.The ITS is calculated from the maximum force applied and the cross-sectional area of the sample.ITS test was carried out to evaluate the impact of two additives on the specimens (moisture resistance and tensile strength).Higher ITS and TSR levels in mixes improve moisture resistance [19].Results in Figures ( 6)& (8) showed that mixes containing 25% SSP and 75% OPC as filler had higher ITS values than the control combination.By examining the relationship between moisture damage resistance and the adhesion of asphalt mortar with aggregate, it may be discovered that the outcomes of a water immersion test for asphalt mixtures with various fillers essentially mirror the outcomes of moisture damage resistance.Usually, loose mixes with low stripping rates are more resistant to moisture damage.The difference is that excessive steel slag powder (such as a substitution of 75% or 100%) will result in lesser adhesion than the control group and that steel slag powder is advantageous to the mixture's water stability regardless of the level of substitution [21].Using different proportions of silica fume (3, 6, 9% depending on the filler weight).The results indicated in Figures (7)& (9), that the ITS and TSR values of the mixtures containing 9% SF as a filler had a good moisture damage resistance compared to the original mixture.The ITS values decline as SF percentages are raised since doing so may increase the binder's absorption, which would then result in less coating on the aggregate particles and more voids, which would lower the ITS values.

Figure 1 .
Figure 1.Some tests on asphalt binder.2-2-Aggregate The aggregate used in this work was obtained from local sources.Dense-graded surface course type A with (12.5 mm) mid-graduation, according to the State Corporation for Roads & Bridges (SCRB, 2003 This type of aggregate is commonly and locally used in the asphalt paving industry.The gradation and physical properties of the coarse and fine aggregates were tested experimentally in the laboratories of Engineering College -University of Al-Qadisiyah and the results are illustrated in Table (2) and (3) respectively.

Table 2 .
Gradation of aggregate for surface course type A Table (2) and (3) respectively.

Table 3 .
The physical properties of course & fine aggregates 2-3 -Mineral FillerIs a passing sieve No. 200 (0.075mm) non-plastic material that is used to fill the gaps in paving mixtures and enhance mixture qualities.In this work, a variety of mineral fillers (MF) are employed, including Common Portland Cement (OPC).

Table 4 .
The physical characteristics of Ordinary Portland cement (OPC)

Table 6 .
The Physical & Chemical characteristics of silica fume (SF)

Table 7 .
Chemical composition of steel slag powder (SSP)

Table 9 .
According to ASTM D4867 (Indirect tensile strength test conditions)

Table 10 .
Summary of test results of the conventional mix design

Table 11 .
Properties of mixtures with different ratios of SSP and SF