Indirect Tensile Resilient Modulus Research Articles

Strength and resilient modulus characteristics of emulsion-stabilised demolition wastes in pavement structures

The use of bitumen emulsion has commonly been limited to pavement surface treatments or stabilising virgin aggregates. There is a lack of experimental evidence about the resilient modulus responses of bitumen emulsion-stabilised recycled demolition wastes in pavement applications. The aim of this study is to evaluate the effect of bitumen emulsion on the tensile strength and resilient modulus responses of recycled crushed concrete aggregate and crushed brick for pavement base/subbase course applications. A type of slow-set anionic bitumen emulsion was used at different contents of 0, 1, 2, and 3 % by dry weight of aggregates to prepare compacted specimens. The specimens were dried back to 70 and 90 % of the compaction moisture content to simulate the field conditions. Specimens were next investigated through a comprehensive testing program, including indirect tensile strength, indirect tensile modulus, and repeated triaxial loading tests. Results showed that the tensile strength of the mixtures generally increased as the emulsion content increased. The inclusion of 2 % and 3 % bitumen emulsion to RCC and CB provided the highest indirect tensile resilient modulus (ITMr) at 359 and 310 MPa, respectively, for those samples cured for 3 h. The highest ITMr results were obtained from samples cured for 3 days at 40 °C in a dry state with the inclusion of 2 % emulsion. For CB and RCC specimens, the results were 2808 and 3361 MPa, respectively. However, specimens of CB and RCC with 3 % emulsion that were cured for 3 days at 40 °C and then soaked in water at 25 °C exhibited the highest ITMr at 1981 and 2900 MPa, respectively. The resilient modulus in the majority of the specimens peaked at 2 % emulsion content, which was recommended as the optimum emulsion content. Results also indicated an enhanced resistance to moisture damage in demolition wastes through emulsion stabilisation. This study proposes, validates and promotes the sustainable approach of emulsion stabilisation of recycled aggregates used in the construction of pavement structures.

Stiffness, rutting, and fatigue performance evaluation of cement-natural rubber latex stabilized recycled concrete aggregate

ABSTRACT The stiffness, rutting, and fatigue performance of cement-natural rubber latex (NRL) stabilized recycled concrete aggregate (RCA) were evaluated under cyclic loading. The RCA was stabilized with 3% cement content and dry rubber content to cement (r/c) ratios at 5%, 10% and 15%. The performance evaluation was carried out through advanced experiments, including indirect tensile resilient modulus test, indirect tensile fatigue test, and rutting susceptibility test using a Hamburg wheel tracking device. The results indicated that the r/c ratio of 10% was optimum for cement-NRL stabilized RCA (3C10R-RCA), which exhibited the optimum performance in terms of permanent deformation, fatigue cracking, and rutting susceptibility. The indirect tensile fatigue life of 3C10R-RCA was found to be 79.3% greater than that of the 3% cement stabilized RCA (3C-RCA), while the rut depth of 3C10R-RCA was 8% lower. Although the resilient modulus value of 3C10R-RCA was slightly lower than that of 3C-RCA, the tensile permanent deformation was found to be lower, which is associated with the lower rut depth. As a result of the significant improvement in fatigue life and rutting performance, the resistance to fatigue cracking and premature failure of cement-NRL stabilized RCA were improved.

Modification and Enhancing Contribution of Fiber to Asphalt Binders and Their Corresponding Mixtures: A Study of Viscoelastic Properties.

The performance of asphalt binders and asphalt mixtures can be enhanced by the inclusion of fiber. The viscoelastic characteristics of fiber-reinforced asphalt binders and their corresponding mixtures were characterized in this study. To generate fiber-reinforced asphalt samples for dynamic shear rheometer (DSR) tests, polypropylene fibers (PPFs), polyester fibers (PFs), and lignin fibers (LFs) were added into modified asphalt with a ratio of 5wt%. Indirect tensile resilience tests were conducted on the fiber-reinforced asphalt mixture with Marshall samples, which was prepared with a 6.4% of bitumen/aggregate ratio. The addition of fiber can increase the anti-rutting performance of asphalt binders, and also reduce the anti-fatigue performance of asphalt binders to varying degrees. Viscoelastic properties of the fiber-reinforced asphalt binders are highly dependent on the shape of the used fiber. The resistance of the fiber-reinforced asphalt binders to rutting at high temperatures increases with the roughness degree of the fiber's surface morphology. PPF-reinforced asphalt binders surpass the others in terms of anti-rutting capabilities. The high-temperature deformation resistance of the PPF-reinforced asphalt mixture is stronger, whereas the low-temperature crack resistance of the PF-reinforced asphalt mixture is stronger, which can be observed from the master curve of indirect tensile resilient modulus.

Hemp Fiber-Modified Asphalt Concretes with Reclaimed Asphalt Pavement for Low-Traffic Roads

Reclaimed asphalt pavement (RAP) contributes substantially to the volume of recycled waste in the world. This research aims to evaluate the mechanistic performance of asphalt concrete with 100% RAP (RAP-AC) modified with natural hemp fiber (HF) reinforcement. The effects of HF lengths and HF contents on the mechanistic performance were investigated. The static tests included Marshall stability, strength index (SI), and indirect tensile strength (ITS), whilst the cyclic tests included indirect tensile resilient modulus (IT Mr), indirect tensile fatigue life (ITFL), and rutting resistance tests. The microstructural analysis revealed that HF could absorb more asphalt cement and function as a reinforcement. The 0.05% HF with a 24 mm HF length was suggested as the best ingredient. For various stress levels, the higher resilience properties—due to the addition of HF—contribute to higher levels of ITFL and rutting resistance. Based on a critical analysis of the cyclic test data, the distress model for HF-RAP-AC was developed for mechanistic pavement design. The outcome of this research promotes the usage of HF-RAP-AC as a greener material for low-traffic roads, which account for over 70% of the total roads worldwide.

Improved Fatigue Performance and Cost-Effectiveness of Natural Rubber Latex–Modified Cement-Stabilized Pavement Base at Raised Temperatures

The increased temperature at the early state of curing affects the fatigue properties of pavement base materials. The fatigue properties of stabilized pavement bases and subbases govern the performance and service life of pavement structures. This research study utilized natural rubber latex (NRL) to enhance the tensile fatigue properties of cement-stabilized base materials at various temperatures. The effects of influence factors such as cement content (3%, 5%, and 7%), NRL replacement ratio (0%, 10%, 15%, 20%, 25%, and 30%), and temperature (25°C, 40°C, and 60°C) on indirect tensile strength (ITS), indirect tensile resilient modulus (IT Mr), and indirect tensile fatigue life (ITFL) were studied in this research. NRL replacement was found to improve the UCS, ITS, IT Mr, and ITFL of cement (C)-stabilized soil up to the highest values at the optimum NRL replacement ratios, which were 20%, 15%, and 10% for cement contents of 3%, 5%, and 7%, respectively. The cement-NRL (C-NRL)-stabilized samples were found to have superior ITS, IT Mr, and ITFL values compared with C-stabilized samples for the same cement content but had the same rate of reduction in ITS due to the raised temperature. For the NRL replacement ratio on the dry side of optimum, the C-NRL-stabilized samples had lower rate of IT Mr reduction than the C-stabilized samples, although they had the same ITS due to the higher toughness. Therefore, the rate of ITFL reduction of C-NRL-stabilized samples was lower than that of the C-stabilized samples. It was proven in this research that the NRL replacement could reduce the thickness (superior IT Mr) of a cement-NRL-stabilized base course for a given traffic volume and service life, and therefore the construction (material and operation) cost by 17.26% benchmarked to a C-stabilized base course. Finally, the cost-effective design method for C-NRL-stabilized bases course was proposed, which will promote the use of NRL as an alternative green additive instead of synthetic polymer.

Improved fatigue properties of cement-stabilized recycled materials – Lateritic soil using natural rubber latex for sustainable pavement applications

This research project investigates the role of a new recycled pavement material and natural rubber latex (NRL), in improving the resilient and fatigue performances of cement-stabilized recycled materials and lateritic soil (LS) blends under traffic loads. Two types of recycled materials, being steel slag (SS) and recycled concrete aggregate (RCA) and 5% cement content by weight were studied in this research. The dry rubber content in NRL to cement (r/c) ratios of 0%, 3%, 5%, 10%, and 15% were designed as the influence factor. The results indicated that mechanical strength properties namely unconfined compressive strength (UCS) and indirect tensile test (ITS), as well as fatigue properties namely indirect tensile resilient modulus (IT Mr) and indirect tensile fatigue (ITF) were enhanced with the NRL additive. Beyond the optimum r/c ratio, the excessive amount of NRL generated thick NRL films and retarded the cement hydration products, resulting in low strength and performance improvement. The r/c ratios of 3% and 5% were found to be the optimum r/c ratios for cement-NRL stabilized SS:LS and RCA:LS blends, respectively. The brittleness and permanent deformation of cement-stabilized SS/RCA:LS blends were significantly improved by the NRL additive. The superior mechanical and physical properties of SS and RCA were also attributed to the enhancement of fatigue characteristics of the cement-NRL stabilized blends. Finally, the mechanistic and fatigue models of cement- and cement-NRL stabilized soil with recycled material replacements were proposed, which are important for pavement designers and engineers when using a mechanistic-empirical pavement design approach.

Investigation of the Usability of Foamed Bituminous Mixtures as Bituminous Base Course

Materials recycled with foam bitumen are promising materials for pavements economically and environmentally. However, there are different opinions in the literature about how these materials are positioned in the pavement. It is clear that their performances will not be suitable for the wearing course, but that they are used for the plant mixture base course because they contain bitumen, and that these materials will be neglected in the evaluation of these materials. In the study, 4 different foam bituminous mixes prepared with a recycled pavement material and a standard bituminous base course mix were compared in terms of the resilient modulus obtained from the uniaxial indirect tensile resilient modulus test. Gradation is the same for three of the mixtures, two of them use cement as a mineral binder, but 70/100 grade bitumen in one of these two productions and 50/70 grade bitumen in the other. In the third mixture, 70/100 grade bitumen and hydrated lime (HL)+fly ash (FA) were used. In the final mixture, 70/100 grade bitumen and cement were used as mineral binders, but gradation was changed. In addition, permanent deformation control for the final production was carried out with a triaxial cyclic compression test. It was concluded that all these variables affect the results, but the resilience modulus values obtained for all were quite close to those obtained from the bituminous base sample. Considering that the foamed bituminous mixtures will be thicker than the bituminous base course in practice, it is considered structurally appropriate to use this layer instead of the bituminous base course.

Improved Performance of Asphalt Concretes using Bottom Ash as an Alternative Aggregate

Road networks are major infrastructures that support the economic development in both developed and developing countries. Bottom ash (BA) is a by-product from coal-fired powerplants, which is composed of a lipophilic molecule with effective reactivity to bituminous binder. BA was adopted in this research, as a green fine aggregate, to improve the mechanistic performance of asphalt concretes in this research. The effect of BA-replacement ratio (0%, 10%, 15%, 20% and 25%, by total weight of natural fine aggregate) on the Marshall stability and flow, indirect tensile strength (ITS), and mechanistic performance of BA-asphalt concrete, were examined. The mechanistic performance tests included the indirect-tensile condition (indirect tensile resilient modulus (IT Mr), indirect tensile fatigue life (ITFL)) and compressive condition (permanent deformation (PD), rut depth, and skid resistance). BA replacement improves the Marshall stability and flow, strength index, and ITS, up to the optimum BA-replacement ratio, of 5%. The change in IT Mr was found to be linearly proportional to the change in ITS, for all BA-replacement ratios. The ITFL is dependent upon the repeated stress level and can be estimated in terms of IT Mr. For the compressive condition, the PD, rutting, and skid resistances were found to be improved by the BA replacement. The lowest PD and rut depth as well as the highest skid resistance, for IT Mr and ITFL, were found at the optimum BA-replacement ratio, of 5%. The outcome of this research will promote the usage of BA as a cleaner additive in asphalt concrete pavement, which is useful in terms of engineering and environmental perspectives.

Image Analysis and Mechanical Properties of Asphalt Mixture with Waste Plastic

Cracking is a typical problem that deteriorates the strength and longevity of a pavement structure. Waste plastic in pavement construction is cost-effective and environmentally friendly. The use of waste plastic has been growing in recent years. Adding waste plastics to the asphalt mixture would improve its physical and mechanical characteristics. As a result, it is a sustainable and long-term solution that helps to reduce plastic waste and preserve the environment. This research aims to develop the image analysis and assess the characteristic of modifying bitumen with different percentages of plastic wastes (0%, 4%, 6%, and 8%). Using blending processes, modified bitumen was prepared. The binder used in this study is penetration grade PEN 60/70. Marshall Test, Indirect Tensile Strength, Resilient Modulus and Dynamic Creep Modulus test were carried out to determine the optimum percentage of waste plastic in asphalt mixture. The modified binders can be used in high-performance asphalt mixtures, as well as to use a well-developed image analysis technique using ImageJ software to characterize asphalt pavement surfaces. The result shows that the modified asphalt mixture is more efficient than the conventional asphalt mixture. Addition of the waste plastic proved sufficient to increase the performance of the asphalt pavement as modified asphalt mixture performance is more stable than conventional mixture.

Influence of Gradation on the Mechanical Properties of Aged Hot-Mix Asphalts

When a hot-mix asphalt (HMA) ages, its mechanical properties, resistance, and durability change. Several studies have been conducted throughout the world to evaluate the effects of aging in HMAs. However, few studies have analyzed the influence of gradation. The main objective of this study was to evaluate the influence of gradation on the mechanical properties of aged HMA mixes. For such purposes, three HMA mixes with different gradations were manufactured (named HMA-10, HMA-19, and HMA-25), which were conditioned in STOA (short-term oven aging) and LTOA (long-term oven aging) by following the guidelines established by the AASHTO R30 specification. Marshall, Indirect Tensile Strength (ITS), resilient modulus, permanent deformation, fatigue (under controlled-stress condition), and Cantabro tests were performed. These tests were carried out to evaluate resistance under monotonic and cyclic load as well as the resistance to moisture damage and abrasion. The best performing mix in the test was HMA-19. There is no clear trend about the influence of gradation over the susceptibility of mixes for aging. This susceptibility changes depending on the test performed and the property measured. Furthermore, in resilient modulus tests, it is observed that the influence of gradation on aging susceptibility changes depending on the test temperature.

Evaluation of durability against wetting and drying cycles of cement-natural rubber latex stabilised unpaved road under cyclic tensile loading

ABSTRACT Cement stabilised unpaved roads have been implemented worldwide in both developed and developing countries. In this research project, natural rubber latex (NRL) was used to improve the durability against wetting and drying (w-d) cycles of cement stabilised soil, under cyclic tensile loads. The influences of NRL replacement ratio on the indirect tensile strength (ITS), indirect tensile resilient modulus (IT Mr), and indirect tensile fatigue life (ITFL) prior to and after w-d cycles were studied. Cement-NRL stabilised soil was found to have superior resilient properties to minimise the plastic deformation and prevent sudden damage against the repetitive tensile stresses. The NRL replacement could improve the durability against w-d cycles of cement stabilised soil whereby the highest ITS, IT Mr, and ITFL were found at the optimum NRL replacement ratio of 20% for all number of w-d cycles tested. NRL was found to enhance the service life of cement stabilized soil as an unpaved material against fatigue cracking failure. The outcome of this research will promote the usage of NRL, which is available in plentiful supply in Thailand and other Southeast Asian and South American countries, as a sustainable additive in pavement applications.

Performance improvement of asphalt concretes using fiber reinforcement

This study reports on the laboratory performance, field performance and cost analysis of fiber-reinforced asphalt concrete (FR-AC) pavement using AC60/70 and polymer modified asphalt (PMA) as binders. The performance testing included indirect tensile resilient modulus, indirect tensile strength modulus, indirect tensile fatigue life, dynamic creep and wheel-tracker tests. Field trials of AC60/70 and PMA mixtures, were undertaken with and without fibers and the International Roughness Index, texture depth, and rutting of the mixtures were measured over time. The PMA + Fiber mixture exhibited the best performance among the materials tested. The performance of AC60/70 + Fiber mixture were comparable to PMA mixture. The improvement of both fatigue cracking and rutting were similar for AC60/70 + Fiber mixtures while the improvement of fatigue cracking was higher than rutting for the PMA mixtures. Since the performance of FR-AC was similar for both laboratory and plant mixed specimens, the laboratory mix design results can be used to interpret the field performance. The fiber reinforced AC60/70 mixture was found to be the most economical. The outcome of this research can be used as a guide, for establishing the specification of FR-AC pavement in Thailand and other countries using similar mix design.

Use of Steel Slag as an Alternative to Aggregate and Filler in Road Pavements.

Today the use of Construction and Demolition Materials (CDM) can be considered as a suitable solution for the construction or the rehabilitation of road pavements. In this context, it is central to minimizing waste production, favoring the reuse through new production cycles to replace virgin natural raw materials. As illustrated in this study, steel slag has mechanical properties that justify its use as aggregate in the manufacture of bituminous mixes. In road construction, their use is focused on the substitution of fine aggregate and filler in bituminous mixtures. Mechanical characterizations, Marshall stability and indirect tensile resilient modulus (ITSM) tests were used to evaluate the laboratory performance of the mixtures. The research aims are to provide the use of these materials for the construction of the entire road pavement structure; in this study authors used these materials both in the characterization of cementitious layers and in those with bituminous conglomerate. In both cases, the use of steel slag has favored an increase of stiffness in the mixtures.

Experimental and numerical investigations of non-standardised semi-circular bending test for asphalt concrete mixtures

ABSTRACT Fracture due to mechanical loads is one of the main distresses of asphalt concrete (AC) pavement. Characterisation of fracture properties of AC is thus vital. The semi-circular bending (SCB) test is recognised as a simple but robust test to evaluate the fracture resistance of AC. Current SCB test standards adopt a fixed sample geometry of 150 mm diameter, while the 100 mm diameter sample has not standardised yet. However, in specifications for AC design and quality control purposes, such as indirect tensile test and resilient modulus, cylindrical samples with either 100 or 150 mm diameter obtained from existing pavements or fabricated in laboratories are used in parallel. This raises the question of whether the 100 mm diameter SCB sample is applicable. The literature review shows the limited investigation into the applicability of SCB test on 100 mm diameter. It also shows no clear justification for why standardised geometry is preferred compared to 100 mm one. For these reasons, this study attempts to investigate the applicability of the SCB test with a non-standardised 100 mm diameter samples using a combined experimental and numerical approach. The numerical approach is based on the discrete element method combining with an enriched cohesive damage-plasticity contact model suitable for AC. The predictive capability of the numerical model is first assessed against the experimental data. Subsequently, the validated numerical model is applied to investigate the effects of notch length and sample thickness on the fracture properties of AC. The study demonstrated that the proposed non-standardised sample geometry of SCB test can provide reliable results with high repeatability. Furthermore, with an appropriate notch length and sample thickness, the non-standardised test can produce a similar value of fracture toughness as the standardised test. These results suggest that the non-standardised test can be used to characterise the fracture properties of AC mixes.

Laboratory evaluation of the performance of asphalt mixtures containing biomass fillers

Asphalt mixtures performance is influenced by its components. Mastic properties and interaction between of filler and bitumen control viscoelastic properties of asphalt mixture. In this research, asphalt mixtures performance containing biomass fillers (Rice Husk Ash (RHA) and Wood Saw Ash (SA)) was evaluated. For this purpose, Marshall stability, Indirect tensile strength, Moisture sensitivity and resilient modulus tests were used. To study more about biomass particles and to have a better analysis of the results of tests, the biomass fillers were photographed by X-ray diffraction. The results of tests show that the combination of 75 per cent RHA and 25 per cent limestone (LS) caused greater Marshall Stability and lower moisture sensitivity compared to the sample containing 100% LS filler, and the combination of 25 per cent SA and 75 per cent LS shows the best tensile performance. Therefore, it is expected that replacing the biomass fillers not only protect the environment and natural resources but also can achieve mixtures with better performance.

Performance evaluation of polyamine anti-stripping additives

Polyamine anti-stripping additives in asphalt mixes are chemical chains that bond chemically with an acidic siliceous aggregate at one end and an asphalt binder at the other. They help to prevent the hydro-oxide of siliceous aggregates from reacting with water molecules, which can lead to a breakdown of the asphalt mix. The effect of two proprietary polyamine-based anti-strippers, Wetfix and Tackamin-200, on moisture susceptibility, the resilient modulus and rutting performance were evaluated at percentages from 3 to 6% with increments of 0·1%. Wet and dry indirect tensile strength, the indirect tensile resilient modulus and dynamic creep tests were used to assess the moisture susceptibility, structural response and rutting resistance of treated asphalt mixes. The results indicated that 0·5% was the optimum dosage for both additives with respect to all performed tests, with Wetfix being more efficient. Overall, it was found that the impact of the anti-stripping agents on moisture susceptibility was significant.

Evaluation of the double coated recycled concrete aggregates for hot mix asphalt

The use of recycled concrete aggregates (RCAs) in pavement industry can mitigate natural aggregates shortage, promote sustainable practices and reduce construction cost. However, the engineering properties of RCAs are usually inferior to those of natural aggregates. In this investigation, a new state of the art coating technique, namely, double coating technique (DCT), is developed to improve strength and durability of the RCAs. The RCAs were firstly coated with a layer of cement slag paste (CSP) to reinforce its weak particles. Then, a second layer of Sika Tite-BE (here called ABE) was applied to reduce its water/bitumen absorption and enhance the durability. Marshall tests, indirect tensile test, indirect tensile ratio test and indirect tensile resilient modulus test were performed to evaluate intermediate AC14 mixtures made with 0%, 20%, 40% and 60% of double coated recycled concrete aggregates (DCRCAs). The results indicated that the DCT decreases the water absorption of the DCRCAs by 12.3% and 26.1% compared to uncoated RCAs and RCAs coated with CSP respectively. Also, the DCT effectively enhances moisture resistance and produces stiffness higher than 4000 MPa proposed for AC14 intermediate mix according to Australian practices.

Effect of fines on the drying crack resistance of composite soil stabiliser-stabilised gravel soil

The objective of this research was to investigate the effect of fines on the drying crack resistance of composite soil stabiliser-stabilised gravel soil (CSSSGS) using the following laboratory tests: indirect tensile strength (ITS), indirect tensile resilient modulus (ITRM), and drying shrinkage (DS). The indirect tensile failure strain (ITFS), which was calculated according to the ITS and ITRM, was used to replace the direct tensile failure strain (DTFS). The DS energy anti-cracking coefficient (DSEAC) and the ratio of ITFS to DS strain (RID) were used to estimate the crack resistance of CSSSGS with varying fines contents. This study showed that the values of these two indices decreased with the increase in fines content and water loss time, indicating that fines content and water loss adversely affect the crack resistance of CSSSGS.

Measuring the effects of styrene butadiene copolymer latex-Portland cement additives on properties of stabilized soil-aggregate base

The fundamental objective of this research is to study the behavior and properties of the traditional and non-traditional additives and to characterize the cementitious stabilized base layer. This research presents experimental results on the improvement of short-term road base performance by the addition of carboxylated styrene butadiene emulsion (Tylac® 4190); Portland cement and Tylac® 4190-Portland cement mixture. To evaluate the short-term performance, the specimens were molded, cured for 7, 28, and 60 days, and subjected to different stress sequences to study the unconfined compressive strength (UCS), indirect tensile strength (ITS), indirect tensile resilient modulus (ITRM), flexural strength (FS) and un-soaked California bearing ratio (U-CBR). The results indicate that the additives improved the strength and the stiffness of the specimens, which has been found to be an important quality indicator of mechanical properties of road base. The flexural strength tests showed that the addition of a 4% Portland cement–8% Tylac® 4190 mixture resulted in improvement of 81.5% of modulus of rupture as compared to the sample with 4% cement. Therefore, this research nominates a new polymer additive having outstanding engineering properties.

Evaluation of mechanical properties and aging index of 10-year field aged asphalt materials

Ten years’ field aged asphalt specimens have collected and being detailed studied. The aging index, viscoelastic behavior of aged binder recovered from the cored specimens, indirect tensile strength and residual fatigue life of the top layer and underneath layer were studied. Saturates, Aromatics, Resins and Asphaltenes (SARA) analysis and Fourier Transform Infrared Analysis (FTIR), viscoelastic analysis, Indirect Tensile (IDT) resilient modulus and fatigue test were performed.Both SARA, FTIR and viscoelastic analysis indicates that traffic loading does have positive degradation influence on asphalt binder. FTIR shows that traffic loading has limited influence on the chemic changes of SO compounds, while has positive contribution on degrading the CC bonds and hence promotes the oxidize aging. Although surface layer can protect underneath asphalt layer from aging, 10-year field aging would introduce significant deterioration onto the underneath layer. The effective aging depth can go as deep as to the second layer. Fatigue tests illustrate that 10-year service has resulted in very weak asphalt pavement surface. Its fatigue life is very sensitive to traffic loading.