Investigating the effect of nanomaterials on the Marshall properties and durability of warm mix asphalt

Abstract Warm mix asphalt (WMA) has gained significant interest recently as a more sustainable and environmentally friendly alternative to conventional hot mix asphalt (HMA). WMA is produced at lower temperatures, reducing energy consumption and greenhouse gas emissions. However, there is an ongoing need to improve the durability of WMA to satisfy the expanding demands of modern road infrastructure. Nanomaterials that possess unique characteristics of high surface area and reactivity could serve as promising additives for improving the performance of WMA. This research aims to investigate the effect of four nanomaterial types on the Marshall properties and durability of warm mix asphalt (WMA). These types are; nano silica$\left({{\rm{NS}}} \right)$NS, nano carbonate calcium $\left({{\rm{NCC}}} \right),{\rm{ }}$NCC, nano clay$\left({{\rm{NC}}} \right)$NC, and nanoplatelets $\left({{\rm{NP}}} \right)$NP. For each type of Nanomaterial, three contents are tried as follows; ${\rm{NS}}$NS(1%, 3%, and 5%), ${\rm{NCC}}$NCC(2%, 4%, and 6%), ${\rm{NC}}$NC(3%, 5%, and 7%), and ${\rm{NP }}$NP(2%, 4%, and 6%) by weight of asphalt cement. Following the Marshall mix design method, the optimum asphalt cement content is determined; thereafter the optimum dosage for each nanomaterial is obtained based on the highest Marshall stability value. The durability of the control mix (no nanomaterial) and modified mixtures have been compared based on moisture damage, resilient modulus, and permanent deformation. These properties are evaluated using indirect tensile strength$\left({{\rm{ITS}}} \right)$ITS and uniaxial repeated load tests. The findings of this research emphasize the potential of nanomaterials to improve the Marshall properties and the durability of WMA significantly. Also, the results showed that using nanomaterials to construct asphalt concrete surface course extended the service life of pavement structures. Compared to CM, modifying asphalt concrete by one of the nanomaterials, NC, NS, NCC, and NP, improved the design life by 59.6, 43.1, 24.4, and 12.2%, respectively. However, the improvement rate for each property depends on the nanomaterial dosage and type. Therefore, this work provides a basis for producing more durable and sustainable paving mixtures using nanomaterials to offer better resistance to distress.

Abstract: Warm mix asphalt (WMA) has gained significant interest recently as a more sustainable and environmentally friendly alternative to conventional hot mix asphalt (HMA).WMA is produced at lower temperatures, reducing energy consumption and greenhouse gas emissions.However, there is an ongoing need to improve the durability of WMA to satisfy the expanding demands of modern road infrastructure.Nanomaterials that possess unique characteristics of high surface area and reactivity could serve as promising additives for improving the performance of WMA.This research aims to investigate the effect of four nanomaterial types on the Marshall properties and durability of warm mix asphalt (WMA).These types are; nano silica NS ð Þ, nano carbonate calcium NCC ð Þ; nano clay NC ð Þ, and nanoplatelets NP ð Þ.For each type of Nanomaterial, three contents are tried as follows; NS(1%, 3%, and 5%), NCC(2%, 4%, and 6%), NC(3%, 5%, and 7%), and NP(2%, 4%, and 6%) by weight of asphalt cement.Following the Marshall mix design method, the optimum asphalt cement content is determined; thereafter the optimum dosage for each nanomaterial is obtained based on the highest Marshall stability value.The durability of the control mix (no nanomaterial) and modified mixtures have been compared based on moisture damage, resilient modulus, and permanent deformation.These properties are evaluated using indirect tensile strength ITS ð Þ and uniaxial repeated load tests.The findings of this research emphasize the potential of nanomaterials to improve the Marshall properties and the durability of WMA significantly.Also, the results showed that using nanomaterials to construct asphalt concrete surface course extended the service life of pavement structures.Compared to CM, modifying asphalt concrete by one of the nanomaterials, NC, NS, NCC, and NP, improved the design life by 59.6, 43.1, 24.4, and 12.2%, respectively.However, the improvement rate for each property depends on the nanomaterial dosage and type.Therefore, this work provides a basis for producing more durable and sustainable paving mixtures using nanomaterials to offer better resistance to distress.

Introduction
Recently, technical advancements which permit the production of warm-mix asphalt WMA ð Þ at temperatures lower than those required to produce hot-mix asphalt mixture are widely used.WMA is a technique for reducing energy consumption, environmental emissions, and viscosity of the asphalt binder due to lowering mixing and compaction temperatures by 15-40 °C (Albayati et al., 2018).There are typically three different techniques used to create WMA.In the first, paraffin wax material called Sasobit was added to asphalt cement in dosages ranging from 0.8 to 3 percent by weight of asphalt cement, which decreased the viscosity of the asphalt cement.The second type uses chemical additives like Evotherm, which strengthen the binding between aggregate and asphalt cement.This type of additive is added at a rate of 1 to 2 percent by the weight of asphalt cement.The third kind uses foaming agents like Aspha-min or Advera (synthetic zeolite materials).The addition rate varies from 0.2 to 0.3 percent by weight of the entire mixture, and at mixing temperature, the foaming agents are added (Albayati, 2018).
Despite WMA having received considerable attention over the past decade, its in-service durability properties still need further research and improvement (Abdel-Wahed et al., 2022;Ali, 2013;Cao et al., 2019).Nanomaterials could be one of the promising materials that can be used to improve the durability of WMA (Ali, 2013).A nanomaterial is a substance with one or more dimensions between one and one hundred nanometers.Nanomaterials differ from traditional materials due to their vast surface area and small size.They also exhibit various innovative traits and exceptional properties that make them suitable for use as an additive for asphalt concrete mixtures (Aljbouri & Albayati, 2023).
Nanomaterials are a broad category of materials often categorized based on their unique features or structures (e.g., nanoparticles, nanotubes, nanowires, nanoplatelets, nanorods, and nanoporous) (Crucho et al., 2019).Due to the enormous influence of atomic and molecular interactions on macroscopic material properties, nanotechnology involves the creation of novel molecularly-based materials and systems that make these materials extensively employed for industrial products and in various engineering fields around the world (Hornyak & Rao, 2016).The existing literature shows that the researchers tried different types of nanomaterial to be used in different asphalt concrete mixtures types, i.e., HMA(hot mix asphalt), WMA, SMA(stone mastic asphalt), as well as different concrete pavement types (Mashaan et al., 2022) By modifying the asphalt cement with NCC, Yusoff et al. (2014a) investigated the impact of NCC on the performance of asphalt concrete type HMAagainst the moisture damage mode of failure.The results demonstrated improved performance for modified asphalt concrete in comparison to the control mix (unmodified).
According to research by Albayati et al. (2022), there is a positive correlation between the performance of asphalt concrete type HMAregarding rutting and moisture damage and the fineness of the hydrated lime HL ð Þ particles.This correlation exists between three different hydrated lime(HL) sizes, ranging from nano, sub-nano, and micro-scale.The best performance is found by substituting 2% of nano HLfor traditional mineral filler.Ismael and Ismael (2019) investigated the impact of NC on the Marshall characteristics and moisture susceptibility of the asphalt concrete mixture.Two types of asphalt cement, AC(40-50) and AC(60-70), were modified using NC in 2%, 4%, and 6% by weight of asphalt cement.According to the researchers, adding 6% NCto asphalt cement increased Marshall's stability and resistance to moisture damage.Gedafa et al. (2017).investigated the modification of two different binders, PG 58-28 and PG 64-28, with 1%, 3%, and 5% NC The authors concluded that the resistance to permanent deformation of HMA increased with increasing NC dosage.The effect of the modifications in the softer binder  was stronger than in the harder binder .Ghile (2006) and van de Ven et al. (2009) studied the performance of HMA modified with 6% NC.The modified mixture showed a 12% average increase in resilient modulus at a temperature range from 5 °C to 35 °C.The modification also improved the resistance to permanent deformation (50% increase in the flow number in dynamic creep tests at a temperature of 60 °C) Zalnezhad et al. (2015) found that the WMAresistance to rutting is improved by adding NS.The addition of NS increases resistance to permanent deformation, according to the results of various rheological tests.Binders with NS modifications have good oxidative age resistance.Based on this research findings, the researcher recommended the use of 4 % by weight of asphalt cement as an optimum NS content for the WMAmodification since it has shown the best performance.Obaid, H. A. (2021) studied the effect of NS in the range of 2-5 by weight of asphalt cement for two kinds of WMA, with Polypropylene polymer PP ð Þand without PP.The results show that adding Nano-silica and Polypropylene enhances the asphalt binder.Also, the findings show that adding asphalt modifiers such as Nano-silica and polypropylene improves the performance and durability of WMA.Ghasemi et al. (2012) examined a stone matrix asphalt (SMA) modified with varying percentages of NS (0.5%, 1.0%, 1.5%, and 2.0%).The authors examined the Marshall stability, indirect tensile strength, and indirect tensile rigidity modulus of asphalt concrete mixtures.The effects observed in experiments increased proportionally with increasing NS dosage.Thus, the mixture with 2% nanosilica had the most improved mechanical behavior.Cai et al. (2018) investigated the modification of HMA with 1% NS.The authors cited the following effects: 27% increase in Marshall stability; 14% reduction in permanent deformation; improvement in retained Marshall stability from 83% to 88%; 14% increase in stiffness modulus and better fatigue life Various studies explored the performance of asphalt mixtures with different types and percentages of nanomaterials as shown in Table 1.A significant amount of work has focused on HMA.However, minimal research has dealt with adding nanomaterials to WMA.To overcome the gap in the literature, this research aims to investigate the effect of four types of nanomaterials, i.e., NS, NC, NCC, and NP, with three levels of contents for each one on the Marshall properties, resilient modulus, moisture damage, and permanent deformation.Also, the pavement performance in terms of the allowable number of load repetitions and service life using these nanomaterials at their optimum dosage is considered.

Research methodology
The sequence of the experimental work is depicted in the flow chart shown in Figure 1.

Asphalt cement
Asphalt cement with a penetration grade of 40-50 is used for this research work; its supplied by the Dora refinery (southwest of Baghdad).Various experiments are carried out to determine the physical characteristics of the net asphalt cement, and the results are shown in Table 2.

Aggregate
The aggregate used in this work was crushed quartz obtained from the Amanat Baghdad asphalt concrete mix plant located in Taji (north of Baghdad); its source is the Al-Nibaie quarry.This aggregate is widely used in Baghdad city for asphaltic mixes due to its availability.Routine tests were performed on the aggregate to assess their physical properties.The results and the specification limits set by the SCRB, R/9 (2003) are summarized in Table 3.

Selection of aggregate gradation
The coarse and fine aggregates used in this work were sieved and recombined in the proper proportions to meet the wearing course gradation with an aggregate top size of 19 mm (0.75 inches) as required by SCRB specification (2003).The gradation curve for the aggregate is shown in Figure 2.   4.

WMA additive
Aspha-min powder (Shown in Figure 3) is used to produce WMA.It is a sodium aluminum silicate that is hydrothermally crystallized and has a weight percentage of water over 21%.Its chemical composition and physical characteristics are listed in Table 5.

Nanomaterials
The four nanomaterials (NS; NC, NCC, andNP) utilized in this investigation are thoroughly mixed with asphalt cement type 40-50 after being added at various rates, speeds, and temperatures.Tables 6, 7 , 8 , and 9 display each nanomaterial's characteristics.

Testing methods
This section describes the tests performed to prepare the mix design and assess the durability of WMA.Following the Marshall method for mix design, the optimum asphalt cement is obtained for each mix type with a specific type and content of nanomaterial.After that, asphalt concrete mixes were made at their optimum asphalt content and tested to evaluate the durability properties ofWMA.An indirect tensile strength test is performed to evaluate moisture damage, and the uniaxial repeated loading tests are conducted to evaluate the resilient modulus and permanent deformation.
The addition of the nanomaterials to the net asphalt cement is carried out using different mixing temperatures, speeds, time, and content, as presented in Table 10.These methods are abstracted from the literature.Storage stability testing has been done per the procedure indicated in ASTM D 7173 to validate the effectiveness of the mixing procedures presented in Table 10.During this test,  the sample of modified asphalt cement with nanomaterial was thoroughly stirred and poured 50 ± 0.5 g into the vertically held tube.Then the tube is conditioned in the oven for 48 hrs at 163 ± 5 °Cand then for 4 hrs in the freezer at − 10 ± 10 °C.Then, the tube is cut into two parts, the upper and bottom half.The difference in softening point between the top and bottom samples extracted from the test tube, denoted as (∆T), was measured as an indication of sample homogeneity and the potential for nanomaterial sedimentation in the net asphalt cement.The conditioning tube and softening point test are exhibited in Figure 4.According to the results shown in Figure 5, the suggested mixing conditions were proven efficient since the ∆T values were below the permitted limit (less than 2.2 °C).

Marshall mix design
The Marshall test (Figure 6) was conducted following the ASTM D6926 to determine the optimum asphalt content based on the stability, flow, and volumetric properties, including total air voids (AV %), voids in mineral aggregate (VMA%), and voids filled with asphalt (VFA%).Three Marshall specimens are prepared for each percentage of asphalt cement content, and the average test result is recorded.Within this test, according to the gradation requirements shown in Figure 2, the various fractions of aggregate retained on each of the following sieves, 12,3/8,No. 4,No. 8,No. 50,No. 200, and mineral filler, were combined into a batch of 1150 g.The aggregate blend is heated to 120°C in a bowl for 6 hours.The asphalt binder (asphalt cement modified with nanomaterials) was heated separately for 2 hours at 155°C to achieve a viscosity of 170 c.St.Following that, an exact amount of asphalt binder is added to the blend in the specified percentages (4.0, 4.3, 4.6, 4.9, and 5.2% by weight of total mix), and they are thoroughly mixed for two minutes, and the temperature is controlled at 125 °C, which is 30 °C below the HMAtemperature 155 °C (as per the Aspha-Min     technical specification).The mixed mixture and the container bowl are then transferred to an oven at a controlled temperature of 115 °C for 10 minutes.After then, the mixture is poured into readily prepared molds (cylindrical specimens 101.6 mm (4 inches) in diameter and 63.5 mm (2.5 inches) in height) of the same temperature, 115 °C, and compacted with 75 blows per face using the Marshall compactor.Before testing for stability and flow properties, the compacted specimens are immersed in water for 30-45 minutes.

Moisture susceptibility test
The moisture susceptibility of asphalt concrete mixtures is evaluated using an indirect tensile strength test as outlined in ASTM D 4867.Each mix's specimens were prepared using the Marshall procedure and compacted at two ends to achieve a 7 ± 1% air void content.Each mix received six specimens.They are then divided into two groups: three as controls were tested directly at 25°C (namely, unconditioned, UC), while the other three (namely, conditioned, C) were subjected to a cycle of freezing and thawing exposure at −18 2°C for 16 hours, followed by another 24 hours at 60 1°C before the tensile test at 25°, During ITS test, a vertical load is applied in the direction parallel to and along the vertical diametrical plane through a set of 0.5 in.wide steel strips that were curved at the interface with the specimens at a rate of (50.8 mm/min) until the specimen failed by splitting along the vertical diameter.The tensile strength is calculated according to Equation (1).A tensile strength ratio TSR ð Þ, Equation (2), is defined as the tensile strength of the conditioned specimens (C.ITS) to that of the unconditioned ones (UC.ITS).Figure 7 shows the specimen in the ITS testing device.

Uniaxial repeated loading test
The pneumatic loading system is used to conduct uniaxial compressive tests, as shown in Figure 8.A repetitive load in the form of a rectangular wave with a constant frequency of 1 Hz (0.1 sec.loading time and 0.9 sec.rest time).The applied stress was 20 psi (0.137 MPa) for a specimen 4 in (101.6 mm) in diameter and 8 in (203.2 mm) in height.Two series of tests are conducted at a normal temperature of 20°C to measure resilient modulus with a loading repetition range from 50 to 150 cycles and at a controlled temperature of 40°C to measure permanent deformation with a loading repetition of 10,000 cycles or total failure in the specimen, whichever is earlier.The information on specimen preparation for the tests can be found in another paper Albayati (2006).
The permanent strain (εpÞ is calculated by applying the following equation: where εp = axial permanent microstren pd = axial permanent deformation h = Specimen height The results of the permanent deformation tests for this study are represented by the linear loglog relationship between the number of load repetitions and the permanent microstrain, as shown in Equation ( 2) below, which was first proposed by Monismith et al. (1975) and Barksdale (1972).

Results and discussion
In the first stage, the Marshall experiment results are obtained and analyzed to determine the optimum asphalt cement content (OAC) for net asphalt cement.Since the primary goal of this study was to investigate the effects of varying the type and content of nanomaterials on the durability properties of asphalt concrete mixes, it was decided to keep the same optimum asphalt content obtained for net asphalt cement rather than optimizing the mix design for each type and content of nanomaterials mixes based on the Marshall properties.The optimal percentage of nanomaterials added to bitumen cement was determined based on the highest stability value.The Marshall stability is the maximum load the specimen can withstand until failure.The effect of adding the optimal percentage of nanomaterials on the durability properties of asphalt concrete mixtures in terms of moisture damage, resilient modulus, and permanent deformation is recorded and compared to those obtained with unmodified WMAmixes with nanomaterials, i.e., control mix CM ð Þ.

Optimum asphalt cement content
A complete mix design is performed using the Marshall method as outlined in ASTM D6926 to determine the OACfor asphalt concrete mixes with varying percentages of asphalt cement.The OACis calculated by averaging the three asphalt cement contents to achieve the highest stability, unit weight, and 4% air voids (AI, 1981).The relationship between asphalt cement content and its stability, flow, unit weight, and volumetric properties, including %AV, %VMA, and %VFA, is depicted in Figure 9.The obtained OACwas 4.9% as a result of averaging the asphalt cement content for the three properties mentioned above.Other properties at the OACwere within the (SCRB, R/9 2003) specification limit.Flow, VMA, and VFApercentages were 3.75 mm, 16.2, and 76.6, respectively.The specification's corresponding limits are (2-4 mm), more than 14%, and (70-85%).

Optimum nanomaterials content
Marshall stability and flow tests are performed on specimens made with three percentages of each nanomaterial at a 4.9%OAC.These are NS(1%, 3%, and 5%), NCC(2%, 4%, and 6%), NC(3%, 5%, and 7%), and NP(2%, 4%, and 6%).The CM's stability and flow values were 9.43 kN and 3.75 mm, respectively.The plots in Figure 10 show that adding nanomaterials at a specific dosage improved the stability values compared to the CM.Based on the highest Marshall stability value, the optimal contents for nanomaterials are 4% for NCC, 5% for NS, 7% for NC, and 6% for NP.In the case of the NP and NCC plots, the peak in the stability curve is prominent.However, for the other types of nanomaterials, as their content increased, so did the stability; thus, the highest nanomaterial content is chosen as the optimal content.Regarding the flow values shown in Figure 11, they generally decreased as the nanomaterials contents increased; this could be attributed to the highest surface area of these tinny materials, the matter which enhanced their capability to infiltrate into the aggregate skeleton pores and thereby increase the stiffness of the mixture therefore, reduce their flow value.

The effect of optimum nanomaterial content on Marshall properties
The influence of nanomaterial types on Marshall properties at their optimum contents is depicted graphically in Figure 12.Marshall's stability improved when nanomaterials were used in comparison to CM. NShad the highest improvement rate (16.69 %), while NCC, NC, and NPhad 12.36%, 11.37%, and 12.19%, respectively.The most significant improvement associated with the use of NScould be explained using density and VMA plots.However, this type of mix had lower density as compared to other types of mixes as well as comparatively higher VMA value in the matter, which collectively indicate higher pores in the aggregate skeleton; therefore, the higher stability could be attributed to the stiffer asphalt mastic (modified asphalt cement and filler).Compared to the specification limit for SCRB ( 2003), all the mixes satisfy the stability requirement, even the CM.Marshall flow values revealed improved asphalt cement stiffening and, as a result, lower flow values when nanomaterials were incorporated.Since the Marshall flow specification limit is 2-4 mm, the flow values were almost always within the specification limit.In interest, NChad slightly more effect on lowering the flow value than other nanomaterial types; this could be attributed to NC having the highest surface area compared to other nanomaterial types, as shown in Table 7.
The density (unit mass) of the mixes modified with nanomaterials is lower than that of CM, revealing the low-density nature of these materials since they have low mass/volume due to their tinny nature.The high density of the CM mixes resulted in lower AV values than the other mix types.Despite that, the modified mixes with nanomaterials have % AV values that satisfy the specification limit (3-5 percent).The VMA, which indicates the efficiency of compaction effort since measures the volume of voids in the mixture, reveals that the mixes with NShave the highest VMAvalue (16.99 percent) s compared to other mix types.Therefore more compaction is needed for this mix consisting of very high viscosity and stiff binder, which is gained from the use of NS that have a higher surface area in comparison with other nanomaterial types, so the highest capability to stiffen the binder.Based on the VFA results, which is the volume filled with asphalt per the volume of due to the enrichment of binder viscosity and stiffness incorporated with the use of this nanomaterial, therefore it's challenging to infiltrate the tiny pores as compared to the net asphalt cement with low viscosity.Thus the VFA values are reduced due to the use of nanomaterial addition.The most significant reduction associated with using NP compared to CM was about 4.3%, while NCC, NS, and NC resulted in reductions of 3.4%, 3.1%, and 0.75%, respectively.Nevertheless, all the VFA values are within the specification limit of 70 to 85 percent.

Effect of nanomaterials on moisture susceptibility
According to the results shown in Figure 13, the mixes with nanomaterials had better resistance to indirect tensile stress for unconditioned samples than the CM.The highest   improvement in splitting unconditioned tensile strength belonged to mixes containing NP, which was approximately 40.7% higher than CM, while the corresponding improvement for mixes containing NS, NC, and NCC were 23.25%, 11.63%, and 2.32%, respectively.Furthermore, as shown in Figures 13 and 14 together, the unconditioned indirect tensile stress for WMA is less sensitive to nanomaterial types than conditioned indirect tensile strength since the variability of TSR is higher than that of unconditioned tensile strength stress.The CM and NCC nanomaterial mixes had the slightest difference in TSR, while the NS had the most remarkable difference.The highest improvement due to using NS could be attributed to the enhanced stiffness of the asphalt binder that mobilizes the cohesion and improves the bond between asphalt and aggregate, thereby increasing the resistance to the diametral splitting force.Given that the minimum acceptable limit for TSR is 80%, the mixes containing nanomaterials met the specification requirement for this type of damage, as opposed to CM, which did not (TSR, 79%).

%VMA
In general, these findings demonstrated nanomaterials' ability to improve the resistance of asphalt concrete mixes to moisture damage.

Effect of nanomaterials on permanent deformation
Figure 15 shows the test result of the permanent deformation measured in the microstrain with the number of load repetitions in the log-log scale.The power fitting for the data of each mix resulted in a linear trend.These lines are defined in two parameters, intercept, and slope.The slope is the rate of permanent deformation accumulation, and the intercept is the permanent strain at N = 1.The less the two parameters value, the better the mix resistance to rutting.
Examinations of the presented data in (Table 11) for these two parameters generally show there is an improvement in permanent deformation resistance when nanomaterials are used in WMA in comparison to CM, Specifically, when compared to CM, adding NC at its optimal content (7%) reduced the slope coefficient of permanent deformation by about 32.5%.This was primarily due to NC having the largest surface area compared with other nanomaterial types, resulting in a dense mass with high resistance to shear flow, which is the main reason for the permanent deformation besides the densification.The slope values for NCC, NP, and NS mixes were by 2.3%, 12%, and 24.7%, respectively, compared to CM.As a result, as the surface area of nanomaterials increases, the slope parameter decreases, resulting in better resistance to permanent deformation.
The values for the intercept coefficient of permanent deformation were somewhat irreconcilable with the slope values.The intercept values for the mixes containing NS, NC, and NP were 17.6%, 31.9%, and 2.5% higher than that for CM, respectively.The NCC mix, on the other hand, had a 26.05% lower intercept value.
Based on the contradictionctory in the slope and intercept results, it's decided to consider the permanent strain value at the 10,000th load repetition for the best simulation of the permanent deformation of mixes, which combines the effect of intercept and slope.The presented values in Table 11 could serve in descending ordering the mixes based on their resistance of permanent deformation as follows, NC, NS, NP, NCC, and CM.These results revealed that the mixes with NC have had the best resistance to permanent deformation; it accounts for 63.4% higher than the CM.Whereas.The average improvement in the permanent strain endured at 10000 load repetitions compared with CM was approximately 25.6%, 54.6%, and 31.9 % for the NCC, NS, and NP mixes,  respectively.These findings confirmed that introducing nanomaterials into WMA can significantly reduce the rutting mode of failure for asphalt concrete pavement, which is exacerbated by hot summer temperatures under increased traffic volume and loadings.

Effect of nanomaterials on resilient modulus
Figure 16 exhibits the Mr tests result for mixes with various nanomaterials types at their optimum contents and CM.In general, as nanomaterials are used, there is an improvement in the elastic properties of WMA.The highest improvement belongs to the mixes with NC.Compared to the CM, the improvement rates for mixes with NC, NS, NP, and NCC are 58.6,43.7, 12.9, and 25.4 percent, respectively.The high Mr for these mixes could be attributed to the tinny nature of these particles, which resulted in a high surface area, allowing them to fill the pores in the aggregate skeleton while also increasing the stiffness of the asphalt binder; the above findings are consistent with the fundamentals of material strength and asphalt rheology phenomena.During the test, tensile stress develops in the transverse direction at the mid-height of the specimens under axial compressive loading.Because aggregate particles cannot withstand tensile force, the strength of asphalt concrete primarily depends on the asphalt cement's cohesion.The ultra-fine nanomaterial particles improve the cohesion and stiffness of the asphalt matrix.Thereby effectively increasing the resilient modulus.

Durability analysis of pavement
In this section, a simplified procedure for determining the durability of the pavement structure is followed using the KENLAYER software.The pavement system is assumed to be an elastic multilayer system in this software, with each layer being isotropic, homogeneous, and having a specified resilient modulus and Poisson ratio.Except for the bottom layer, each layer extends to infinity in the horizontal direction and has a finite thickness.The solution for a multi-layer elastic system (up to 19 layers) under a circularly loaded area and the determination of the pavement response (stress, strain, and deflection) at predetermined points within the pavement structure is the backbone of the KENPAVE software Huang (2004).The pavement section considered for this analysis consists of three layers; the first upper layer is an asphalt concrete surface layer type WMA with a thickness of 100 mm (4 in.) laid on a granular subbase layer with a total thickness of 300 mm (12), the roadbed is compacted subgrade soil with infinity in thickness.Each layer is characterized using Mr and Poisson ratio.The resilient modulus is obtained from test results in a single tire with a circular tire imprint area having a radius of 107.4 mm (4.23 in.) and tire inflation pressure of 552 kPa (80 psi) which simulates the AASHTO standard axle tire configuration; the repetition of this wheel load is 100,000 applications per year.In order to calculate the critical responses, i.e., critical tensile strain at the bottom of the asphalt concrete layer and the compressive strain at the top of the subgrade, the former caused fatigue cracking in the asphalt concrete layer and the latter caused rutting if they exceed the allowable limits.Since single wheel load is considered in the analysis, the critical response in terms of strains occurs in the center of the wheel load.The pavement structure, as well as the wheel load configuration, are shown in Figure 17.
The critical strains for tension and compression are determined using Equations 6 and 7, respectively.
Where Nf = allowable number of load repetitions to control fatigue cracking εt = horizontal tensile strain at the bottom of the asphalt concrete layer E = resilient modulus of the WMA.
Where Nd = the allowable number of load repetitions to control permanent deformation ɛc = vertical compressive strain at the top of the subgrade.
Figures 18 and 19 exhibit the responses of the pavement structure to traffic loading in terms of critical tensile and critical compressive strains, allowable load repetitions, and design life obtained from the runs of KENPAVE software.It's evident that using nanomaterials in the WMA of asphalt concrete surface course results in the reduction of the tensile strain and compressive strain compared to CM.The reduction related to the use of NC, NS, NCC, and NP is 23 %, 18.4%, 11.7%, and 6.4% for tensile strain, respectively.At the same time, the corresponding reduction in compressive strain is 11.8%, 9.2%, 5.7%, and 3.1%.This reduction in the strain consequently increases the allowable number of load repetitions, thereby increasing the pavement structure service life.As shown in Figure 19, the use of NC in the WMA for the construction of asphalt concrete surface course raises the design life by 59.6 % compared to the CM.Whereas the NS, NCC, and NP increased design life by 43.1%, 24.4%, and 12.2%.These results agree with those reported by Aljbouri and Albayati (2023), who investigated the effect of using nanomaterials in the performance of HMA.Furthermore, the findings reflect the possibility of producing asphalt concrete surface course using WMA modified with nanomaterials with longer design life and better durability than CM.

Conclusions
WMA is an asphalt concrete type produced and compacted at a lower temperature than traditional hot mix asphalt, reducing energy consumption and emissions and providing cost savings.Recently, there has been growing interest in using nanomaterials to improve the performance of asphalt concrete since they have various innovative traits and exceptional properties.This research aimed to investigate the effect of type and content of nanomaterial on the Marshall as well as the durability properties of WMA.The investigated nanomaterials were as follows, NS (1%, 3%, and 5%), NCC (2%, 4%, and 6%), NC (3%, 5%, and 7%), and NP (2%, 4%, and 6%).The Marshal mix design was adopted to determine the optimum asphalt cement content (OAC) for the mixes.After that, mixes are prepared at OAC; the optimum nanomaterial content was selected based on the highest Marshall stability.The durability properties include moisture damage, resilient modulus, and permanent deformation.Also, durability analysis of pavement structure is conducted to obtain the critical strains, the allowable number of load repetitions, and design life.Based on the findings, the following conclusions can be drawn from the results.
(1) Based on the highest Marshall stability, the optimum content for the investigated nanomaterials is 4% for NCC, 5% for NS, 7% for NC, and 6% for NP.
(2) Compared to CM (WMA without nanomaterial), NS at their optimum content had the highest improvement rate (16.69 %) in Marshall stability, while NCC, NC, and NP rates of 12.36%, 11.37, and 12.19%, respectively.Also, it shows the superior ability to enhance the resistance of WMA to moisture damage since the mixes modified with NS have the highest TSR value, 91 percent.
(3) Better performance is noticed for the WMA modified with NC at their optimum content in the uniaxial repeated load test.The permanent deformation results revealed that the mixes with NC have the best resistance to permanent deformation; it accounts for 63.4% higher resistance than the CM.Also, the corresponding improvement in Mr value was 58.6 percent.
(4) Using nanomaterials to construct asphalt concrete surface course extended the service life of pavement structures.Compared to CM, modifying asphalt concrete by one of the nanomaterials, NC, NS, NCC, and NP, improved the design life by 59.6, 43.1, 24.4, and 12.2%, respectively.
Local ordinary Portland cement, which is compatible with the requirements of SCRB specification SCRB/R9 (2003), was used for this research work.The physical properties of Portland cement, a non-plastic material passing through sieve No. 200 (0.075 mm), are presented in Table

Figure 1 .
Figure 1.Flow chart of experimental work.

Figure
Figure 4. Tests for softening point, conditioning tube, and storage stability.

Figure
Figure 6.The specimen during Marshall test.

Figure
Figure 7. Specimen during indirect tensile strength test.
Figure 9.The relation between the asphalt content and Marshall properties.
Figure 10.Effect of nanomaterials on stability.
Figure 12.The Effect of optimal nanomaterials on Marshall properties.
Figure 14.Effect of nanomaterials content on TSR.
Figure 15.Effect of nanomaterials on permanent deformation.

Figure
Figure 17.Pavement structure with load configuration.

Figure 19 .
Figure 18.Effect of nanomaterials on pavement critical strains.

Table 11 . Effect of nanomaterials on permanent deformation coefficients
*Control Mix failed at N=7950.