Investigation of the Fatigue Performance of Sustainable Asphalt Pavement

Selecting suitable materials for sustainable asphalt pavement construction can be a challenging task, particularly due to the significant issue of fatigue damage in flexible pavement. The fatigue performance of gap-graded asphalt mixes (GGCP) was assessed through four-point bending beam fatigue testing, examining the impact of incorporating 6% Calcium carbonate (CaCO3) and 2% treated palm oil fuel ash (TPOFA) on fatigue cracking. The testing was conducted at various stress levels (800, 1000, and 1200 kPa) and a temperature of 5°C. Additionally, the asphalt mixtures underwent acceleration ageing and moisture conditions, which varied during the study. The experimental findings indicated that higher stress levels resulted in a decrease in the fatigue life of asphalt mixtures due to ageing effects. Moreover, moisture conditioning was found to diminish the fatigue life of the asphalt mixture. Comparatively, the fatigue model incorporating a plateau value and fatigue life demonstrated greater accuracy when compared to previous regression models.


Introduction
ehT Fatigue cracking poses a significant challenge in maintaining the longevity of flexible pavements.The fatigue life of an asphalt pavement is greatly influenced by environmental factors and the increasing number of repetitions from heavy axle loads.To mitigate premature cracking and ensure optimal pavement performance, several factors must be carefully considered during pavement planning and material selection.These factors include temperature variations, loading rates, pavement age, and the specific type of testing conducted [1,2].Fatigue failure in flexible pavement occurs when the asphaltbound layer undergoes flexing and develops cracks.In recent years, nanotechnology has played a significant role in improving the thermomechanical properties of bitumen and enhancing its resistance to fatigue cracking and rutting in flexible pavement [3].Additionally, substantial research efforts have been devoted to developing models for predicting fatigue failure in bitumen materials [4].These models utilize three distinct criteria: stiffness reduction (Nf50), dissipated

68
energy ratio (DER), and the ratio of dissipated energy change (RDEC) to calculate the fatigue life.Statistical analysis indicates that these methods yield comparable results for fatigue and healing tests [5].
Various testing methods can be developed using the same analysis technique, such as the ASTM D7460 cyclic haversine test.AASHTO T-321 specifies that the specimen should be returned to its initial position after each load pulse through continuous sinusoidal loading within a frequency range of 5 to 10 Hz [6].When nanomaterials like fly ash and silica fumes are added to asphalt binder, they can reduce the stiffness modulus, with the reduction being more pronounced at higher quantities of fly ash [7].Stone mastic asphalt, on the other hand, has shown potential for enhancing fatigue life by mitigating structural distress caused by increased traffic loading.It strengthens the resistance to cracking and permanent deformation, particularly at higher stress levels [8].In Malaysia, the use of unconventional filler materials in Gap-graded Asphalt Mixtures (GGAM) is still in the experimental phase.Palm Oil Fuel Ash (POFA) has shown promising potential as a filler material in asphalt mixtures, although its usage has been predominantly explored in concrete materials rather than pavement materials [9].Previous studies have demonstrated that incorporating 5% POFA as a filler in asphalt mixes can enhance their properties [10].It has been observed that a strong linear relationship exists between the fatigue life of asphalt mixtures and the requirement for 50% stiffness reduction, as reported by Cheng et al. (2022) [11].However, for the dissipated energy criterion, fatigue failure occurs with a stiffness reduction of only 30% instead of 50%.The choice of fatigue failure criteria is also influenced by the type of asphalt mixture.
Polymer-modified asphalt mixtures, for instance, may not meet the 50% stiffness reduction criterion due to difficulties in achieving such a level of reduction even with high loading cycles, as highlighted by Huang et al. (2016) [12].In a study by Ameri et al. (2017), a strong correlation was found between the fatigue lives of different asphalt mixtures using the dissipated energy technique [13].The primary objectives of this study are to investigate the impact of incorporating 6% CaCO3 and 2% TPOFA on the fatigue life of GGCP, as well as to assess the combined effects of stress levels, long-term ageing, and moisture conditioning on the fatigue response of GGCP.

Materials and Methods Asphalt Binder
Table 1 summaries properties of the base binder [13].

Ageing Condition Property Values
Un-aged

Filler
Two filler combinations, 6% CaCO3 and 2% TPOFA, were utilized in the study.The specific gravity of these fillers was determined following the guidelines outlined in AASHTO T 133, and the corresponding results are presented in Table 4.To acquire the TPOFA, various procedures were carried out in the Concrete Lab at USM, as illustrated in Figure 1.

Methodology of Study Asphalt Mixture Preparation
The Shear Box Compactor (SBC) was developed in order to simulate real construction compaction in the field.As shown in Figure 2, a uniform block of asphaltic concrete was produced utilizing the SBC for the flexural beam fatigue test (4PBT).The compaction parameters are shown in Table 5.The autosaw was also used for accurate cutting of beams for the fourpoint bending beam test.As shown in Figure 3

Ageing Procedures
Following the AASHTO R30 guidelines, the trays containing the samples were mixed and placed in a draft oven at 135°C for 4 hours to simulate short-term ageing (STA) [15].Subsequently, the samples underwent exposure to UV light (UV) at 85°C for five days to simulate long-term ageing (LTA), which is equivalent to approximately 7 to 10 years of service life [14].

Moisture Conditioning
In the flexural beam fatigue test, each beam specimen underwent additional partial saturation in distilled water using an accelerated laboratory vacuum saturator.This process lasted for 30 minutes at room temperature.To facilitate this procedure, a specially designed vacuum chamber was constructed at the School of Materials and Mineral Resources Engineering, USM, as depicted in Figure 4 The beam specimen was subjected to two symmetrical stresses on the testing apparatus employed in this study.For 4PBT, the specimen's dimensions were 50 x 57 x 400 mm.Table 6 lists the testing schedule.
The dissipated energy of the outcomes was examined.

Impact of Stress Level on Dissipated Energy
Table 7 illustrates the typical response of the GGCP dissipated energy under various ageing and moisture techniques.Regardless of the training techniques, the amount of energy lost rises as the level of stress increases.It might be explained by the possibility that increased loading accumulation will cause early cracking or discomfort.On the other side, such behaviour can result from the asphalt binder's increased viscosity and stiffness at a low testing temperature (5°C).Low temperatures have little of an impact on the mixture's robust quality, and the viscous-elastic reaction of the asphalt is negligible.Lower fatigue life and higher dissipated energy have been the results of the mixture being damaged by moisture.Figure 1 summarises the effects of different stress levels on the dissipated energy; it demonstrates that for the GGCP subjected to LTA at implemented testing temperatures of 5°C, as the stress level increases, the fatigue life reduces and the dissipated energy increases.

Fig 1: Impact of Stress Level on Dissipated Energy of GGCP
During the initial stage of loading, the relationship between logarithmic load cycles and dissipated energy exhibits a straight-line trend, with minimal variation in the dissipated energy.However, after approximately 10 to 100 loading cycles, nonlinearity becomes apparent in the trend line.This nonlinearity indicates a change in behavior and is associated with the initiation of possible fatigue cracks in the binder [16].This point is often referred to as the crack initiation point.Beyond this point, the variation in dissipated energy becomes more significant, and this variation is influenced by the three stress levels considered in the analysis.

Impact of Stress Level on Cumulative Dissipated Energy
The concept of the ratio of dissipated energy change is developed to characterize fatigue damage in asphalt mixtures.The cumulative dissipated energy (CDE) initially exhibits an unstable period but eventually reaches a plateau, followed by a sharp increase, indicating a significant fatigue failure.This behavior is often represented by the cumulative dissipated energy versus loading cycles damage curve.The consistent value of CDE during the plateau stage is crucial for assessing the fatigue behavior of Hot Mix Asphalt (HMA) because it represents the period when a relatively constant proportion of input energy is converted to damage.
To determine the best-fit equation for the data, including the failure point and cumulative dissipated energy (CDE), a modified curvefitting approach is employed.Typically, a power law relationship is used to achieve a strong curve fit, characterized by a high R2 value and an accurate curve trend [17].Equation 1 describes the relationship between the total energy lost and the fatigue life [18].After 10,000 load repetitions, the relationship's trend shifted from being linear to non-linear, and the variety in cumulative lost energy became more noticeable.The fatigue life of a dense mixture is determined by the number of cycles required to dissipate a cumulative energy equivalent to 1x108 J/m 3 .However, when comparing different stress levels, it is observed that the effect of stress level on fatigue life under 1200 kPa shows an extreme value of cumulative dissipated energy at 1.3x108 J/m 3 [19].The data presented in Table 8 indicates that an increase in stress levels has a significant impact on fatigue.It is evident that regardless of the stress level, fatigue life decreases as the cumulative dissipated energy increases.Furthermore, when comparing the fatigue life of GGCP under maximum tensile stress levels (800, 1000, and 1200 kPa) to unaged samples evaluated at 5°C, a reduction of 26.9%, 15.5%, and 26.2% is observed, respectively.This reduction in fatigue life can be attributed to the combination of hardening and fracturing, although the specimen did not show signs of failure until the very end of the test.the fatigue life significantly decreases.Notably, GGCP exhibits a 31% longer fatigue life at 1200 kPa compared to lower stress levels.When considering prolonged ageing, the fatigue levels decrease with higher stress levels.These findings align with the conclusions of Sarsam's study from 2016 [20].The study findings demonstrate that incorporating a combination of 6% CaCO3 and 2% TPOFA as green filler enhances the performance of GGCP.The mixture exhibits excellent performance in the fatigue resistance test, as indicated by the results from all samples.A power model proved to be the most suitable in describing the relationship between applied stress and the number of fatigue load cycles before failure.Additionally, it was observed that GGCP beams subjected to long-term ageing (LTA) have a shorter fatigue life compared to unaged beams.A lower rigidity modulus is associated with a longer fatigue life.Moisture damage also affects the stiffness of the mix, as samples subjected to ageing and various moisture conditioning experienced rapid stiffness loss during initial load repetitions.The utilization of CaCO3 and TPOFA, whenever available, is recommended as a solution to the environmental issue of solid waste disposal.In future studies, the cumulative dissipated energy approach is likely to be employed to enhance the mechanistic-empirical (ME) pavement design process.By incorporating these advantages, they can be fully integrated into the design of pavement construction.

onkc tnemeedekw
The crushed granite geometrically cubical aggregate (GCA) supplied by Kuad Quarry Sdn.Bhd., Penang was used.The basic properties of the aggregate as well as the gradation used which was developed by OPUS International are shown in Tables 2-3 respectively[14].

3 :
(a), the block samples were trimmed from all sides to achieve a smooth outer surface.Then, the block was cut into six beams.The final specimen geometry (50W*57H*400L) mm is shown in Figure3(b).a) Block Samples Were Trimmed b) Specimens Geometry Figure Beam Samples were Cut and Trimmed

2 :
Figures 2 illustrate the behaviour of GGCP subjected to LTA at testing temperature, approximately 5°C.The impact of stress level on the fatigue life and accumulative dissipated energy is very well pronounced.

Figure 3
Figure3depicts the impact of stress levels on the fatigue life of unaged GGCP.It is evident that as the maximum tensile stress level increases,

Fig 3 :
Fig 3: The Relationship Between Stress Level and Fatigue Life for GGCP ConclusionThe study findings demonstrate that incorporating a combination of 6% CaCO3 and 2% TPOFA as green filler enhances the performance of GGCP.The mixture exhibits excellent performance in the fatigue resistance test, as indicated by the results from all samples.A power model proved to be the most suitable in describing the relationship between applied stress and the number of fatigue load cycles before failure.Additionally, it was observed that GGCP beams subjected to long-term ageing (LTA) have a shorter fatigue life compared to unaged beams.A lower rigidity modulus is associated with a longer fatigue life.Moisture damage also affects the stiffness of the mix, as samples subjected to ageing and various moisture conditioning experienced rapid stiffness loss during initial load repetitions.The utilization of CaCO3 and TPOFA, whenever available, is recommended as a solution to the environmental issue of solid waste disposal.In future studies, the cumulative dissipated energy approach is likely to be employed to enhance the mechanistic-empirical (ME) pavement design process.By incorporating these advantages, they can be fully integrated into the design of pavement construction.

Table 8 :
The Relationship between CDE and Fatigue Life