Evaluation of moisture damage for warm mix asphalt (WMA) containing reclaimed asphalt pavement (RAP)

1 Introduction

Building environmentally friendly and sustainable transportation infrastructure saves natural resources, protects the environment, and uses less energy [1,2]. Additionally, in today’s world, it is crucial to restrict carbon emissions, reduce dangerous gasses, and save fuel. For these reasons, the pavement sectors are searching for different techniques to lower the temperature at which asphalt concrete is produced [3]. When warm mix asphalt (WMA) was first deployed, green construction was recognized by the Federal Highway Administration (FHWA) in a 2007 study. In Europe, WMA technologies have been in use for about a decade, with positive outcomes. According to Yee and Hamzah [4], warm mixes can be made more workable by heating them to a lower temperature. Numerous investigations were conducted on a wide range of WMA combinations with various properties, both in the lab and in real-world settings, evaluating their efficacy against traditional hot mix asphalt (HMA) mixtures.

A new WMA technology, beginning to transition from the theoretical to the practical field, is investigated. Despite the first experiments at WMA that began in America in 2004, the technology was investigated in Europe between 1999 and 2001 [5,6]. Currently, WMA makes up roughly 30% of all asphalt concrete mixes produced locally in the United States [7]. Based on the kind of additives used to create WMA, the mixing and compaction temperatures of this form of asphalt concrete are typically less than the temperatures for HMA concrete by 15–40°C. This means that the manufacturing processes for these two types of asphalt concrete are different. The decrease in fuel expenses for heating the raw materials, along with the reduced carbon dioxide emissions, led to both economic and environmental benefits. While WMA has been produced in millions of tons globally since the late 1990s and is widely utilized for paving projects, Iraq has not yet employed this kind of mix. In 2006, Barthel et al. [8] first reported on the creation of WMA with the utilization of zeolite in 2004 [7]. As temperature increases beyond 100°C, the synthetic zeolite, known as Aspha-min or Advera will be a compound consisting of sodium aluminum silicate and 21% of its mass is crystallized water. This results in a foaming effect and increases the workability of the mix since the binder viscosity is lowered [9]. Aspha-min is normally added to the mixture either before or along with the binder, at a rate of 0.3% by weight of the entire mixture. The two primary issues with the use of WMA have been an increased risk of moisture damage and rutting. Moisture damage was described as “the progressive functional deterioration of a pavement mixture by loss of the adhesive bond between the asphalt cement and the aggregate surface and/or loss of the cohesive resistance within the asphalt cement principally from the action of water” by Kiggundu and Roberts (1988, p. 3) [10,11] The presence of both water and traffic significantly induces moisture damage in the field. [12,13,14,15]. Moisture damage is frequently a gradual process of failure and can sometimes result in rapid irreversible deformation, either before or without the loss of adhesion [13].

Multiple researchers have documented that the partially dehydrated aggregates at lower mixing temperatures in WMA can form a weak connection with the asphalt binder, making it susceptible to degradation when exposed to water [16,17,18,19,20]. Prior research has demonstrated varying levels of moisture damage susceptibility in WMA mixtures, based upon the specific technologies and procedures employed. For instance, the Sasobit^® modified WMA mix and HMA mix showed comparable tensile strength ratio (TSR) values, according to Goh and You [21]. The moisture damage performance of Evotherm^® and Sasobit^® WMA and HMA mixes, which were utilized to build field test sections, was also examined by Hurley et al. [22], who found that both mixes functioned similarly well.

The impact of the utilization of Aspha-min on the associated performance parameters of WMA was examined by Hurley and Prowell [23]. The temperatures at which mixes were compacted were 149, 129, 110, and 88°C. The blending temperature was approximately 19°C above the compacting temperature. According to their findings, the moisture-induced damage, as measured by the ratio of tensile force, had decreased in WMA in comparison to HMA. In 2008, Bhusal [24] carried out laboratory research to assess the possibility of moisture damage, ruts characteristics, and the dynamic modulus for WMA employing both kinds of additions (Sasobit and Aspha-min). When these outcomes were contrasted with an HMA reference, it became clear that neither the WMA nor the Control HMA met the required TSR criterion of 80%; instead, the Sasobit produced the greatest TSR and conditioned indirect tensile strength (ITS) values. The findings of the Hamburg wheel tracking show that, as compared to the control HMA and the WMA with Aspha-min, a WMA containing Sasobit has the best level of rut challenge. In the year 2010, Zhang [25] produced WMA using three different types of additives and compared its performance with HMA, which also included the same additives: Advera (synthetic zeolite), Evotherm, and Sasobit. The author carried out several laboratory studies to assess the rutting potential, moisture susceptibility, and dynamic modulus. After evaluating the moisture damage using the TSR, it was discovered that every blend generated TSR values that were lower than the 80% failing criteria. The TSR index for the WMA containing Sasobit is greater than the TSR value of Advera or Evotherm. The results for the dynamic modulus were found to be very similar for all the mixtures. The efficacy of WMA generated with both kinds of additions (Aspha-min^® and Sasobit^®) was investigated by Al-Jumaili and Al-Jameel [26].

The WMA samples were made at 120–125°C for compaction and 125–135°C for mixing, The researchers found that the WMA exhibited a decreased ITS in comparison to the HMA. Additionally, they determined that the WMA created with Sasobit achieved superior performance compared to the WMA generated with Aspha-min. Furthermore, one of the most popular methods for improving asphalt pavements’ resistance to moisture damage is the application of antistripping chemicals [27]. In this research, Zycotherm, WETMUL-950, GRIPPER L, Evonik, and TeraGrip are the five types of antistripping additives whose effects on asphalt pavements’ moisture resistance were assessed and contrasted with one another. The laboratory evaluation findings demonstrated that every ingredient utilized in this study enhanced the adhesion and cohesiveness qualities and raised the asphalt mixes’ resistance to moisture susceptibility. Another study by Amirkhani et al. [28], assessed how the use of fly ash, calcium carbonate, and Portland cement type II as filler affects the performance of WMAs manufactured with the Kaowax addition. The findings showed that the fly ash filler containing WMA samples exhibited good moisture susceptibility. Also, increased rutting resistance was the outcome of using cement filler in the WMA. Ameri et al. [29] examined how zeolite, a WMA addition, affects combinations of HMA and recycled asphalt (RA). The impact of these modifiers on the characteristics of binders and asphalt mixes was investigated using a variety of tests, including rotating viscosity, dynamic creep, resilient modulus, indirect tensile fatigue, and moisture susceptibility (TSR and RMR). The results show that adding zeolite and CR enhanced the mechanical characteristics. Furthermore, zeolite improved the long-term performance and ability of HMA and RA mixes, but the addition of CR to mixtures not having zeolite lowered the TSR, RMR, and workability of the mixtures. The outcomes of the cost-effective study also showed that when zeolite and CR are used properly, not only is the energy consumption reduced, but so is the cost of manufacturing the modified asphalt mixture.

On the other hand, many different countries have made it a priority in recent decades to move toward ecologically sustainable economic development. Reusing materials from construction is an additional technique to help the environment. Recycling aggregates to replace natural aggregates is a common practice in pavement construction [30]. In this way, it is feasible to protect natural resources and mitigate the effects of resource exploitation, leading to financial and energy savings as well as a reduction in greenhouse gas emissions [31,32,33].

The benefits of RAP for the environment and economy have led to a fast growth in its use in asphalt mixtures [34]. The presence of a binder in RAP decreases the quantity of new binder required for the production of asphalt mixtures. Moreover, the aggregates included in the RAP are utilized again to reduce the original expenses of construction and save natural resources [34,35]. This way of thinking applies to the utilization of reclaimed asphalt pavement (RAP). Indeed, the utilization of reclaimed asphalt pavement (RAP) in asphalt mixture can yield favorable mechanical characteristics when employed appropriately [36,37].

The performance of asphalt mixes was examined by Zhao et al. [38] concerning the kind of WMA technology (foaming process and Evotherm) and the RAP concentration (0–40%). Regardless of the WMA technology employed, the results of the WMA study indicated that mixtures with greater RAP percentages exhibited better fatigue performance compared to both high and low RAP content in HMA. Nevertheless, WMA that has been mixed with larger proportions of Reclaimed Asphalt Pavement (RAP) exhibited reduced susceptibility to moisture and rutting in comparison to HMA with a greater proportion of RAP, but superior to WMA with a reduced RAP percentage. As to Schreck’s research [39], utilizing RAP at rates ranging from 10 to 40% enables cost reductions of 9 and 36% in the production, respectively.

Furthermore, according to Vidal et al. [40], RAP in HMA and WMA (with synthetic zeolite) decreases the ecological effects related to the asphalt mixture’s life cycle analysis. Although the use of RAP in asphalt mixes has presented several difficulties, the enhanced adhesion between the aggregate and binder for RAP might potentially mitigate the risk of damage caused by the presence of moisture caused by foaming WMA [41,42,43]. In 2020, Goli and Latifi [44] conducted an investigation on how moisture impacts the performance of mixtures by experimental methods such as resilient modulus, ITS, semi-circular bending, and dynamic creep tests. In general, the findings showed that even with water-loving and moisture-sensitive aggregates as well as aged binder, the WMA mixes including RAP performed suitably in terms of moisture resistance. As a result, this type of mixture might be advised for areas where there is a risk of moisture damage, environmental issues, and limited natural resources. Another study carried out by Valdes-Vidal et al. [45] conducted a testing investigation to analyze the physical properties of WMA mixes made using zeolite from Chile and varying quantities of reclaimed asphalt pavement (RAP) for eco-friendly pavement development. The findings indicated that WMA mixes including zeolite could be produced at a certain temperature of 20°C lower than the standard HMA [46], while still meeting the design requirements. An investigation conducted by Joni and Alkhafaji [47] examined the utilization of WMA-RAP and its effects on the efficiency of the asphalt mix. The study involved adding four different percentages of RAP (0, 20, 30, and 40%) to both HMA and WMA that contained 4% Sasobit. There was a little reduction in the ability of both HMA and WMA incorporating RAP to resist moisture compared to control mixtures of Asphalt. This was indicated by a fall in the TSR. However, the TSR values remain much higher than the minimum requirement of 80%. Another research [48] assessed the influence of including Sasobit on the susceptibility of mixtures to permanent distortion and moisture. The results show that the rut depth of the WMA, which underwent testing in the Hamburg wheel tracking device, exhibited a reduction in comparison to the control HMA, and the use of Sasobit resulted in a drop in moisture resistance compared to traditional HMA, as seen by a reduction in TSR. However, the moisture resistance remained over the lowest limit of 80%.

In addition to this, RA mixes with high-performance characteristics may be created at a lower temperature utilizing natural zeolite for environmentally friendly pavement building. In 2021, Rahman et al. [49] assessed the foamed WMA with RAP’s laboratory performance, specifically its susceptibility to deterioration from rutting and moisture, and compared with that of HMA with an equivalent quantity of RAP. Due to the use of cyclic load settings, it is shown that MIST conditioning more accurately replicates moisture-induced damage and can capture the inclination of asphalt mixtures to moisture damage than the AASHTO T283 technique [50]. Due to lower mixing and compaction temperatures, the foamed WMA showed increased susceptibility to rutting and moisture-induced damage compared to HMA. Increasing the RAP concentration was discovered to decrease rutting and susceptibility to moisture-induced damage in WMA. Numerous studies suggest that there is a problem with moisture sensitivity in warm mixes, The potential for damage caused by moisture in warmed blends has a clear relationship to their manufacturing process. A study by Kadhim et al. [6] examined and evaluated organic additive techniques. Based on the results, the majority of warm combinations met the minimal requirement for TSR set by the AASHTO (80%). However, certain mixtures did not meet this criterion, suggesting that moisture resistance is an issue in warm mixes. In the same approach, Asmael et al. [51] conducted a comprehensive investigation to evaluate the performance of WMA combinations using locally sourced components. According to the findings, the rut depth of surface mixtures increases in direct proportion to the concentration of WMA additives. Increasing the amount of Asphaltan A^® results in a greater rut depth, whereas increasing the amount of Asphaltan B^® leads to a reduction in rut depth. Both WMA and HMA combinations meet the acceptable standards for all mixes.WMA is created by employing the foaming technique or reducing viscosity additions in the binder to improve its rheological characteristics. A study with two rates of Aspha- mean (0.3 and 0.5%) was used [52]. The outcomes point out that the WMA exhibits significant resistance to rutting, comparable to that of the HMA mix. For organic additive techniques [53], the research conducted has shown that the inclusion of organic additives has a beneficial effect on the performance of warmed blends, namely, in terms of enhancing their fatigue resistance.

In the field of asphalt pavement, the demand for ecologically friendly roadway development and building is of utmost importance. The study by Ugla and Ismael [54] examined the impact of using alumina waste, namely, secondary aluminum dross (SAD), with asphalt-compressed samples that include recycled concrete aggregate (RCA) to be the coarse aggregate. Based on the results, by substituting 20% of the traditional filler with SAD in the blend that includes RCA at various proportions, the criteria for TSR and IRS are met. Another research [55] investigated the impact of various fillers, such as coconut peat and bagasse, on the efficiency of asphalt mixtures and their susceptibility to moisture damage. The results indicated a positive correlation between Rigden voids and pore size, as well as a negative correlation between Rigden voids and surface area, The moisture damage testing revealed that all mixes, including both dense and porous ones, exhibited good ability to resist damage caused by moisture.

The moisture sensitivity in warm mixes is an issue and therefore needs to be monitored and quantified. In this research, before adopting WMA technology, it is necessary to investigate the feasibility of using locally accessible materials for this technology. Therefore, locally reclaimed asphalt taken from one of the affected streets will be used and the effect of moisture on WMA will be evaluated using different proportions of this reclaimed asphalt. In addition, three types of mineral filler materials, which are available locally will be used.

2 Materials

A warm asphalt mixture was created using local aggregates and asphalt as the primary components of the pavement. The sections that follow describe the necessary attributes.

2.4 Aspha-min

The utilization of Aspha-min powder served as an addition to the manufacturing process of WMA. It is finely powdered sodium aluminosilicate that has been hydrothermally crystallized. Aspha-min, which has a water content of roughly 21% by weight, was included in the mixture at a concentration of 0.3% by weight. The physical properties of the Aspha-min are shown in Table 4, and Figure 1 illustrates this material.

Table 4

Physical properties of additive (Aspha-min)

Property	Result
Color	White
Specific gravity	2.03
Bulk density	568 kg/m3
Solubility in water	Insoluble
pH value	11.6
Odor	Odorless

Figure 1

Aspha-min.

2.5 RAP

The RAP employed in the mixtures in this investigation was sourced via surface milling of Al-Shaab Stadium – Intersection in Baghdad – Iraq, also it was examined to ascertain the proportion of asphalt binder material by the ASTM D6307 – 10 standard. “Asphalt content by Ignition Furnace,” illustrates the RAP’s mean asphalt concentration of 4.79%. A test of this RAP’s particle size distribution was conducted as shown in Table 5. Figure 2 illustrates this material.

Table 5

Gradation of RAP

Sieve size	Iraqi specification (SCRB R9, 2003) surface layer type IIIA (% passing)			RAP specification
Standard sieves (mm)	English sieves	Min.	Max.	Passing %
19	3/4″	—	100	100
12.5	1/2″	90	100	97
9.5	3/8″	76	90	91
4.75	#4	44	74	65
2.36	#8	28	58	46
0.3	#50	5	21	25
0.075	#200	4	10	8.2

Figure 2

RAP material.

3 Production of mixtures

Marshall’s mix design process was the mix design technique used in this study to produce both warm and hot mixes. There are three different kinds of asphalt mixtures: warm mixes, hot mixes, and warm mixes with RAP. Asphalt cement, fine and coarse aggregates, three kinds of mineral fillers, a warm additive (Aspha-min), and a waste additive (RAP) make these mixtures. The zeolite was utilized (0.3 % of the total weight of the mixture) to produce the WMA. The aggregate is graded using wearing layer aggregate grade, which has a nominal maximum aggregate sieve size of 12.5 mm.

3.1 Preparation of specimens without RAP

Marshall specimen dimensions were used to create cylindrical samples for HMA and WMA specimens, which are 101.3 mm (diameter) × 63.5 mm (height), The samples were compacted using the Marshall compaction apparatus. According to ASTM D2493, the viscosity of the asphalt binder was measured at 135 and 165°C using the Equiviscous technique to determine the temperature ranges for mixing and compacting HMA samples. The asphalt binder’s mixing and compacting temperature for viscosities ranges 0.17 ± 0.02 Pa s and 0.28 ± 0.03 Pa s is 155 and 145°C, respectively.

In this study, homogeneity was maintained by compacting a mixture of WMA at 120°C after blending at 135°C. These temperatures were selected based on the literature, professional opinions, and suitable recommendations from the manufacturers of WMA technologies [57,58,59,60,61,62,63]. This procedure adheres to the WMA design methodology described in NCHRP Report 714 [52,64]. The bitumen becomes less viscous as a result of this temperature reduction. Following the process of crystallization, the bitumen transforms increased rigidity, resulting in enhanced resistance of the asphalt to deformation.

The volumetric characteristics of the WMA mixes are used to calculate the optimum contents of asphalt binder. This will decrease the impact of aging and boost the effectiveness of the warm mix components [58,65,66]. Figure 3 presents the prepared samples without RAP.

Figure 3

WMA samples prepared without RAP.

3.2 WMA with RAP

RAP is utilized as a proportion of the aggregate. The content of the asphalt binder and the crushed RAP aggregates in the recycled mixture must be ascertained. The proportions of the amount of RAP in the blends were 10, 20, and 30% of the mix’s whole weight (for this mixture, the overall amount of asphalt was maintained steady). The Marshall mix design approach was utilized in the laboratory to produce and compress all of the WMA mixes. Figure 4 presents the prepared samples with RAP.

Figure 4

Samples prepared with RAP.

3.2.1 Moisture susceptibility test

The method used to assess WMA and HMA samples’ sensitivity to moisture is ASTM D 4867 [67]. A range of 6–8% air void level was achieved by compacting six specimens of each mix type using the Marshall compaction technique. Three specimens from one subset of the specimens (the unconditioned specimens) were evaluated using an indirect tension test at a temperature of 25°C. When the other group (conditioned specimens) was evaluated, it was initially exposed to a single cycle of freezing and thawing (16 h at −18 ± 2°C and another 24 h at 60 ± 1°C). By loading the specimen along its diameter, the indirect tension test records the applied load (as shown in Figure 5). Below is the calculation of the test parameters:

(1) ITS = 2,000 P π Dh ,

where P is the applied load, h is the height of specimen (thickness), and D is the diameter of specimen.

Figure 5

Indirect tension test.

To assess the moisture susceptibility of all mixes, the TSR, which is the ratio of the ITS of a wet specimen to the ITS of a dry specimen, was determined. Equation (2) was utilized to get the TSR value for every mixture. According to ASTM D4867M 09, adequate resistance to moisture damage is often defined as having a TSR value higher than or equal to 80%. Figures 6 and 7 show some of the samples prepared and tested.

(2) TSR = C . ITS UC . ITS × 100% ,

where TSR is the tensile strength ratio, %, C.ITS is the average tensile strength of the wet condition, kPa (conditioned case), and UC.ITS is the average tensile strength of the dry condition, kPa (unconditioned case).

Figure 6

Some samples at 25°C.

Figure 7

Some samples test.

4 Results and discussion

The mixes were put to the test in both wet and dry environments. Asphalt mixes based on AASHTO T283 requirements were used for the TSR test.

4.1 ITS

For both the conditioned (wet) sample and the unconditioned (dry) sample, the asphalt mixture’s ITS is shown in Figures 8 and 9, and Table 6. Based on these results, for WMA mixtures without including RAP in their mix, it is noticeable that WMA mixtures are more sensitive to moisture degradation than HMA mixes. For all samples, when comparing the WMA mixes with the HMA mixes, the average tensile strength (ITS) is lower. Higher value of ITS was found for samples containing cement as a filler but comparing with the HMA it is lower by about 22.8%, and 20.6% for two cases conditioned and unconditioned, respectively. While the samples with fillers limestone and hydrated lime showed lower values than the cement filler, as shown in Figure 8, which is approximately 58% conditioned, 30.5% unconditioned for limestone, and 73.1% conditioned, 58.6% unconditioned for hydrated lime, respectively lower than the HMA.

Table 6

Moisture susceptibility values

Mix type	ITS, kPa (psi)		TSR, %
	Cond.	Uncond.
HMA	1,490	1,581	94
WMA C 0% RAP	1,150	1,255	91.6
WMA C 10% RAP	1,090	1,106	98.5
WMA C 20% RAP	1,361	1,493	91
WMA C 30% RAP	1,379	1,440	95.7
WMA L 0% RAP	625	1,098	57
WMA L 10% RAP	1,019	1,480	68.8
WMA L 20% RAP	1,242	1,480	84
WMA L 30% RAP	1,004	1,621	62
WMA H 0% RAP	400	654	61
WMA H 10% RAP	1,321	1,389	95
WMA H 20% RAP	1,479	1,510	99
WMA H 30% RAP	758	828	91.5

Figure 8

ITS results without RAP.

On the other hand, For the WMA mixtures, the average tensile strength (ITS) increased, when the amount of RAP in WMA mixes increased with different percentages (10, 20, and 30%) as shown in Figure 9. In both dry and wet situations, greater ITS values are achieved with three types of fillers for all mixtures comparable with mixes without RAP in their continents. The results show that the utilization of RAP could enhance the resistance to moisture damage. In addition, a higher value for TS was found for samples containing cement as a filler.

Figure 9

ITS results with RAP.

As presented in Figure 9, for 10% RAP, it is clear that mixes containing hydrated lime as a filler have a higher ITS value for the conditioned state than other fillers by 17.5 and 22.9% for cement and limestone filler respectively, whereas limestone filler shows a higher value of ITS for the unconditioned state than other fillers by 25.2 and 6.1% for cement and hydrated lime, respectively. For 20% of RAP, mixes containing hydrated lime as a filler have a higher ITS value for the conditioned state than other fillers by 8 and 16% for cement and limestone filler, and by 1.1 and 2% for cement and limestone filler for the unconditioned state, respectively. For 30% of RAP, mixes containing cement as a filler have a higher ITS value for the conditioned state than other fillers by 27 and 45% for limestone and hydrated lime filler, whereas for the unconditioned state, limestone filler shows a higher value than other fillers by 11.2 and 49% for cement and hydrated lime, respectively.

4.2 TSR

The susceptibility of the mixes to moisture was calculated using the TSR. A minimum requirement of 80% for the indirect TSR is recommended to distinguish between moisture-resistant and moisture-susceptible combinations (ASTM D4867M-09, 2014) and (AASHTO, T283 - 07, 2007). Figure 10 exhibits the TSR for control hot mix, and WMA mixes with and without RAP.

Figure 10

TSR results.

As presented in the figure, for mixes without RAP, the maximum percentage of TSR is (94%) for the traditional HMA. For the WMA mixture (content 0.3% synthetic Zeolite with 0% RAP), the ratio decreased to 91.6% for the WMA mixture with cement as filler, it is about 2.5% lower than the HMA. However, it satisfied the required minimum value (80%) for TSR, and then the ratio dropped to 61%, and 57% for the WMA mixes that contain hydrated lime and limestone as a filler, respectively. All WMA mixes have TSR values that are lower than those of the traditional HMA mixture without adding the RAP material. This shows that the possibility of moisture damage was raised by the use of synthetic zeolite. Previous investigations [19,57,68] have also reported similar findings.

Because of the possibility of inadequate drying of aggregates caused by lower mixing and compaction temperatures, zeolite WMA mixes may be more susceptible to moisture degradation. Increased moisture sensitivity may be caused by the water that is trapped in the coated aggregate as a result.

As seen in Figure 10, the TSR values of the WMA mixtures with different percentages of RAP (0, 10, 20, and 30%) containing cement as a filler material, met the requirement of a minimum limit of 80% for indirect TSR. It can be concluded that 10% RAP is the optimum value for mixes having cement as a filler material, which has an ITS ratio of 98.5%.

For WMA mixtures that have hydrated lime as a filler, as can be seen in the figure, the TSR values with different percentages of RAP (10, 20, and 30%) met the requirement of a minimum limit of 80% for indirect TSR and the optimum value of the RAP is 20% with ITS ratio of 99%. The enhancement in moisture resistance can be attributed to the intricate surface textures of hydrated lime, which can result in a rise in the asphalt covering the aggregate. This, in turn, can impact the resistance of mixtures to stripping. Consequently, this indicates that the addition of RAP with hydrated lime as a filler in a mixture leads to increased resistance to moisture damage.

Mixtures that contain limestone as a filler show that only 20% RAP met the requirement of a minimum limit of 80% for an indirect TSR value of 84% as presented in Figure 10.

The increase in the amount of RAP needs a higher temperature to be mixed and avoid a weak bond between the aggregate and binder. This indicates that when the proportion of RAP increases, it might lead to a potential decrease in the TSR values and lower resistance to moisture damage.

5 Conclusion

Based on the work presented in this study, considering the constraints of the experiment, and the materials employed, the potential for damage caused by moisture on WMA was assessed and contrasted with that of reference HMA that had the same gradations and RAP content. The following points were concluded from this study:

1. The WMA mixtures are more sensitive to moisture degradation than the HMA and have a lower average TSR than the HMA mixtures.

2. The WMA mixture with cement filler (0% RAP) was the only filler type that met the moisture damage standard criterion of a minimum TSR of 80%. However, it is still 2.5% lower than the HMA.

3. Adding the RAP component to the WMA mixtures enhanced the average tensile strength (ITS) value. The ITS ratio for WMA mixtures having cement, hydrated lime, and limestone filler is 98.5, 99, and 84% respectively, for the optimum percent of RAP for each type of filler.

4. Higher ITS values are achieved in dry and wet cases using three types of filler for all mixes, comparable to blends without RAP in their compositions.

5. Utilizing RAP with WMA was shown to decrease the risk of damage caused by moisture. All WMA with 10, 20, and 30% RAP have passed the TSR min. requirement (80%) except 10 and 30% RAP for limestone filler. As a result, the impacts of the RAP and foamed WMA process may balance each other.

6. The utilization of RAP with hydrated lime as a filler in WMA improves the resistance to moisture damage.

7. The optimum RAP content for WMA mixtures for cement filler is 10%, and for hydrated lime, and limestone filler is 20%.

8. It is recommended to use other filler types to evaluate the moisture damage of the WMA and try to use polymers to enhance the resistivity of the WMA mixtures to moisture damage.