Hot Mix Asphalt Samples Research Articles

Effects of different bitumen modifiers on the rutting and cracking resistance of hot mix asphalts

ABSTRACTIn this study, four different additives (Styrene–butadiene–styrene (SBS), Trinidad Lake Asphalt (TLA), Iranian Gilsonite (IG) and American Gilsonite (AG)) were used in bitumen modification. The rheological properties of bitumen were improved with the additive usage, and the desired performance grade (PG 70-34) was achieved by using additives in pure bitumen (PG 58-34) at the indicated ratios. Wheel tracking tests and semi-circular bending tests were applied for hot mix asphalt (HMA) samples. The main results showed that all the additives increased resistance to permanent deformation of HMAs, and that TLA was the most effective additive. In addition, it was found from the semi-circular bending tests that deformation values of mixtures prepared with modified bitumens and subjected to long-term ageing decreased. As a result, long-term aged and modified bitumen mixtures exhibited more brittle behaviour. The increase in maximum load values led to an increase in the area under the load-strain curves. Thus, crack propagation resistance of mixtures prepared with modified binders was increased.

Back analysis of the multilayer cylindrical HMA samples – height reduction method

ABSTRACTAlthough the complex modulus is one of the most basic properties used in pavement analysis and design, its accurate measurement for existing pavement layers has always been a challenging task. When samples cut out from the pavement asphalt layers are used for the hot mix asphalt (HMA) complex modulus tests, they are performed separately for each layer. This paper describes an original method for determining the complex moduli of individual asphalt layers. The new idea is tested by applying uniaxial loading–unloading cycle tests to the HMA specimens combined of multiple layers. It was observed that changing the thickness ratios in samples' layers, allows obtaining the sets of load and displacement values (F, u), which effectively enlarge the database needed for the back analysis. For now, the conducted analysis presented in the paper focused on numerical modelling of HMA specimens. The simulated numerical testing conditions were based on viscoelastic parameters of asphalt concrete samples whose values were determined in real laboratory tests. In the case of noisy results of laboratory test simulations with a stochastic Gaussian process, by applying multiple cuts and changing sample's height, the determined values of stiffness moduli of the individual layers do not vary from the reference values by more than 10%.

Performance analysis of nano modified bitumen and hot mix asphalt

The aim of the research was to evaluate the performance of Hot Mix Asphalt (HMA) and bitumen by modifying bitumen with nano materials according to Superpave™ mix design procedure. In this research, bitumen was modified by Multi-Walled Carbon Nanotube (MWCNT) and Carbon Nanotubes Doped with 50 wt% SiO2 Nanopowder (SiO2dopedCNT). Nano materials were mixed with base bitumen at contents of 1, 3 and 5% by weight. Rutting and fatigue performance of bitumen was determined. HMA is prepared with nano modified bitumen at optimum binder content (OBC). Moisture susceptibility of modified hot mix asphalt was evaluated according to Modified Lottman test procedure. Nano modified bitumens were also evaluated by scanning electron microscopy whether the modification was uniform or not.As a result, better performance was obtained by SiO2dopedCNT modification. Performance Grade (PG) of all modified bitumen was determined as PG 64-22 except MWCNT modified bitumen at the content of 1% (which was PG 58-22). OBCs were decreased by modification. All nano modified hot mix asphalt samples were determined as high resistive to moisture compared to reference sample except samples modified with SiO2dopedCNT at the content of 5%. Homogenous mixture was obtained according to scanning electron microscopy results. It was found that the agglomeration of nano materials is mostly lower than 4 μm in the mixtures.

GERİ KAZANILMIŞ ASFALT BETONU MALZEMESİNİN AŞINMA TABAKASINDA KULLANILABİLİRLİĞİNİN ARAŞTIRILMASI

In this study, Reclaimed Asphalt Pavement (RAP) were used in Hot Mix Asphalt (HMA) samples, stability and flow resistance and Indirect Tensile Strength Test (IDT) of HMA samples were investigated. Initially, optimum bitumen content of wearing course was determined by Marshall Stability test method and then RAP, 5 to 50 % in terms of total asphalt concrete samples weight was added to HMA samples at the predefined optimum bitumen content. Besides, control samples were performed and compared with the RAP added samples. Test results show that Reclaimed Asphalt Pavement (RAP) can be used in wearing course as an additive in accordance with Turkey General Directorate of Highways (GDH) specification limits. This paper demonstrates that the asphalt mixtures containing RAP performed at least like, or better than, that of conventional asphalt materials.

Performance of WMA additives under freeze–thaw action

Warm mix asphalt (WMA) is an energy-saving and environmental-friendly technology with a broad prospect for application in highway construction. When compared with hot mix asphalt (HMA), WMA reduces the mixing and compaction temperatures (by 25–30°C) and hence reduction in energy consumption and emissions of harmful gases while maintaining the workability of HMA. In this study, three different additives, namely, Sasobit (organic wax additive), Evotherm (emulsion-based chemical additive) and Zycotherm (anti-stripping chemical additive) were evaluated for their laboratory performance under repeated weathering actions. HMA and WMA laboratory samples for Marshall stability, indirect tensile strength and tensile strength ratio were cast and subjected to 0, 2, 4, 6 and 8 freeze and thaw cycles (F&T cycles) in numbers and then tested. A comparative study was performed among HMA and three WMA mixes (control and weathered), that is, Sasobit-WMA (S-WMA), Evotherm-WMA (E-WMA) and Zycotherm-WMA (Z-WMA) to analyse the trend of variation in strength and properties with varying F&T cycles. Aggregate coating and compactibility were also analysed.

Moisture sensitivity and mechanical performance assessment of warm mix asphalt containing by-product steel slag

Warm Mix Asphalt (WMA) has recently become an attractive alternative in pavement engineering due to its potential for significant reduction in energy consumption and carbon footprint of asphalt industry; however, concerns have been raised regarding durability of material and potential to moisture damage due to lower mixing and compaction temperatures. Furthermore, steel slag which is mostly disposed in landfills as waste material could be an appealing option as substitute of natural aggregates for asphalt concrete (AC) production because of its adequate affinity with asphalt binder. The aim of this study is therefore, to assess whether the integration of basic oxygen furnace (BOF) steel slag into Sasobit WMA technology would indicate satisfactory performance in terms of moisture susceptibility. This paper also examines if BOF slag WMA mixture can provide acceptable mechanical performance to be used as a more sustainable approach for pavement construction.To capture short-term moisture damage resistance of BOF slag WMA, specimens prepared with two Sasobit dosages were subjected to two different testing methods. Modified Lottman test and boiling water test using an image analysis technique were performed to compare moisture susceptibility and stripping resistance of BOF slag WMA and HMA (hot mix asphalt) samples with conventional mixtures. Dynamic creep test, Hamburg wheel-track device and resilient modulus test were then conducted on specimens to evaluate mechanical behavior of BOF slag WMA in comparison with BOF slag HMA and another type of WMA mixture prepared with natural aggregates.Findings showed that BOF slag WMA provided significant resistance to short-term moisture damage and therefore, could be considered as durable bituminous mixture when compared to conventional asphalt mixtures. Furthermore, BOF steel slag HMA/WMA exhibited superior mechanical behaviors compared to limestone HMA/WMA mixtures, implying that steel slag could be an effective alternative as pavement material.

Examination of hot mix asphalt and binder performance modified with nano silica

The aim of the study is to evaluate the performance of Hot Mix Asphalt (HMA) and bitumen by modifying bitumen with nano materials according to Superpave™ mix design procedure. In this study, bitumen is modified by silica nanopowder (SiO2NP). Nano powders are mixed with base bitumen at contents of 0.1, 0.3 and 0.5% by weight. Rutting and fatigue performance of bitumens are determined. HMA is prepared with nano modified bitumens at optimum binder content (OBC). Moisture susceptibility of modified HMA is evaluated according to Modified Lottman test procedure. Nano modified bitumens are also evaluated by scanning electron microscopy (SEM) whether the modification is uniform or not. As a result, better performance is obtained by SiO2NP at a content of 0.3% modification. Performance Grades (PG) of all modified bitumens are determined as PG 64-22. OBCs are decreased by modification. HMA sample modified by SiO2NP at a content of 0.3% is determined 26.25% higher resistive to moisture compared to reference sample. Homogenous mixture is obtained according to SEM results. It is found that the agglomeration of nano materials is mostly lower than 4μm in the mixtures. As a result, SiO2NP 0.3% shows satisfying results.

Rutting behavior of hot mix asphalt modified by polyvinyl chloride powder

ABSTRACTIn this experiment, at first, waste polyvinyl chloride was used as an additive in an attempt to improve the performance of bitumen and hot mix asphalt (HMA) in order to minimize the amount of rutting. To further these aims, conventional and rheological tests were conducted on bitumen and all HMA specimens were tested by Marshall stability, flow, and repeated load axial tests. After investigating rutting resistance of HMA samples, the results demonstrated that this waste material could improve the rheological properties of bitumen, and the HMA samples, manufactured by this particular type of bitumen, are more resistant to rutting.

Effect of sample setting time on experimental evaluation of hot mix asphalt

Hot mix asphalt (HMA) samples tested randomly after molding might lead to misleading performance prediction of asphalt mixture in laboratory. This paper aims to investigate how the sample setting time affects the laboratory evaluation results for HMA mixes. Nine kinds of test procedures were employed to analyze the performance evolution of asphalt mixture AC-13 for varying sample setting times ranging from 1day to 90days. Test results showed that oxidative aging and emission behavior of volatile organic compounds from asphalt might be the causes for stiffness effect of lab-molded samples, and consequently leads to test results change. With the setting time prolonging, permanent deformation resistance of asphalt mixture was improved, while the anti-cracking and fatigue properties were degraded. Noticeable variation of test results occurred during the initial week after HMA sample molded in laboratory. Moreover, sample setting time effect on result evolution of different test methods were relatively diverse due to their particular test procedures and objectives. In consideration of field performance of asphalt mixture, more laboratory test procedures and HMA mixes are recommended to specify the reasonable sample setting time for different test methods.

Mechanisms of asphalt mixture rutting in the dry Hamburg Wheel Tracking test and the potential to be alternative test in measuring rutting resistance

Rutting is one of the most important failures occurring in hot mix asphalt (HMA) especially in the summer season and slow moving traffic areas. Rutting is a pavement surface failure compromising the safety and ride comfort of traveling and thus needs to be accurately evaluated in a laboratory. Although the flow number (FN) test is commonly used for evaluating the rutting resistance of HMA in a laboratory, there are some shortcomings in using FN test such as the costly and complicated equipment. Another potential test that is likely to be more advantageous than the FN test for evaluating the rutting resistance is the Hamburg Wheel Tracking (HWT) test, however, it is typically conducted in wet condition, and inadequate results in dry condition have been reported. The objective in this study is to optimize the HWT test subject to dry condition to be one potential method in measuring rutting resistance in a laboratory. Two rutting mechanisms (densification and shear failure) of HMA samples conducted in the HWT device were determined by Image Processing and Analysis version 2 (IPAS2). Results indicate that HMA samples under the dry HWT test can exhibit both rutting mechanisms in which typically occur in the field. Also, the dry HWT test shows a very good R2 for a relation of creep slope with the confined and unconfined FN test. As a result, the dry HWT can be an effective tool of quantifying rutting potential with better simulating to field behavior, lower cost of equipment, and less complicated geometry that can also accommodate field cores.

Degradation of hot mix asphalt samples subjected to freeze-thaw cycles and partially saturated with water or brine

In the province of Quebec, during winter and spring, hot mix asphalt (HMA) is subjected to freeze-thaw cycles (FTCs). This paper presents a part of a general research programme which aims to characterise damage generated on HMA samples by FTCs, under dry and partially saturated (PS) conditions, with water (PSW) or brine (PSB). The samples were subjected to complex modulus (E*) test after different number of FTCs, which allowed us to assess the evolution of the damage due to freeze-thaw sequences. Rheological model, 2S2P1D, was used to simulate the behaviour of the HMAs. The 2S2P1D model well simulates the linear viscoelastic behaviour of the HMAs. Over the FTCs, damage is observed for all samples. But is seen to be much higher for the PSW sample. For PS samples, the time–temperature superposition principle (TTSP) is less valid over the FTCs. A different shift factor evolution could be observed below and above the ice formation temperature. Damage due to FTCs seems to have a greater impact at high temperatures and low frequencies.

Application of nano-silica and styrene-butadiene-styrene to improve asphalt mixture self healing

ABSTRACTNanoparticles, due to their physical and chemical characteristics, present an inherent potential to improve the performance of bituminous materials. Presently, the technology of producing nanosized particles is evolving, and their application in various aspects of pavement engineering is becoming more cost-effective. Nanosilica, due to its spherical shape, high specific area, very tiny size and higher density compared to bitumen, presents an inherent potential to accelerate molecular randomisation movements, promote bitumen binder flow into microcracks and evolve healing index (HI) of hot mix asphalt (HMA). Moreover, it has been proved that Styrene–Butadiene–Styrene polymer (SBS) promotes fatigue life of HMA and decreases its temperature sensitivity. It would be interesting to know if the addition of nanosilica to modified binder with SBS will promote the total HI and lead to an enhanced HMA life cycle. In this study, the effects of four parameters, most importantly, the effect of the combination of nanosilica particles and SBS polymer to improve the self-healing of asphalt mixture was investigated using the Taguchi design of experiment (DOE) method. Experiments performed with the Superpave indirect tensile test included repeated loadings (fracture) and healing phases. These experiments showed that the combination of nanosilica and SBS promoted the self-healing of HMA, significantly. Moreover, the optimum condition to attain maximum HI and effect factor of each parameter, based on Taguchi DOE method, was obtained. Furthermore, scanning electron microscope images of fatigued, under healing and healed HMA samples were captured to investigate HMA self-healing mechanism.

Effect of Sugarcane Bagasse Ash as Filler in Hot Mix Asphalt

Hot Mix Asphalt (HMA) is a combination of asphalt and aggregates that will give durable road surface for pavement and is widely used in Malaysia. However, due to damages caused by excessive traffic loadings, the HMA pavement normally required frequently maintenance and rehabilitation works. Therefore in recent years, research on modification of HMA has tremendously increased in highway construction field using natural sources and recycling products such as rubber, plastic, anti-stripping agents, waste materials and etc. This study was conducted to evaluate the effect of sugarcane bagasse ash (SCBA) used as filler in HMA. Experimental laboratory were done to compare the properties of normal HMA sample with modified HMA sample using SCBA. Result obtained for both sample were compared to Malaysian Public Works Department (MPWD) specification. The laboratory result reveals that SCBA are effective in increasing the Marshall stability, flow and Resilient Modulus of normal HMA. The SCBA increases Marshall stability by 0.6%, flow 4.9% and Resilient Modulus 17.4% respectively of ordinary HMA and all test and analysis parameters for asphaltic concrete of SCBA sample comply with MPWD requirements. Therefore, SCBA has potential in modifying normal HMA.

The Hamburg rutting test – Effects of HMA sample sitting time and test temperature variation

The Hamburg Wheel Tracking Test (HWTT) is a widely used routine laboratory test with a proven history of successfully identifying and screening hot-mix asphalt (HMA) mixes that are prone to rutting and/or susceptible to moisture damage (stripping). Based on Texas specification Tex-242-F, the HWTT is typically conducted at a single test temperature of 50°C (122°F) with 12.5mm rut depth as the standard HMA pass-fail screening criteria. However, with the record high summer temperatures of the recent years in Texas, several premature field rutting failures have occurred with some HMA mixes that had passed the HWTT screening criteria in the laboratory. This laboratory study was thus initiated to review and evaluate if the current Texas HWTT protocol and its associated Texas test specification (Tex-242-F) are simulative of the current summer field conditions for routine HMA mix-design and screening to optimize rutting resistance performance. Specifically, two key aspects were evaluated, namely the HMA sample sitting time and test temperature. The corresponding laboratory test results indicated that a maximum sample sitting time of five days should be consistently adapted, i.e., lab-molded samples should be tested within five days of fabrication, particularly for HMA mix-design screening purposes. For HMA mixes to be used in high temperature/stress environments, the study findings suggested that higher (>50°C), and/or multiple HWTT test temperatures should be considered.

Utility of polyparaphenylene terephtalamide fiber in hot mix asphalt as a fiber

In this study, utility of polyparaphenylene terephtalamide (PT) was investigated in hot mix asphalt as a fiber. For this aim samples were prepared with limestone aggregate at different proportions. Marshall Stability test was applied and optimum bitumen content was determined. In the second stage of the study, new samples were prepared using different polyparaphenylene terephtalamide fiber (PTF) rates of 0.25%, 0.50%, 0.75%, 1.00%, 1.50%, 2.00% based on optimum bitumen content. When examining test results, samples which prepared using 0.25% PTF rate gave highest Marshall Stability result. At the final stage of the study, different bitumen contents (4.15%, 4.65% and 5.15%) were conducted for the best fiber rate (0.25%) and close to this result (0.50% and 0.75%). Thus, the effect of bitumen content on determined fiber rate at the second stage of the study was investigated. Also Indirect Tensile (IDT) Strength Test was performed on hot mix asphalt (HMA) samples preparing at 0.25%, 0.50% and 0.75% fiber rates and moisture sensitivities were determined. All results showed that, the best fiber rate was 0.25% and determined optimum bitumen content remain constant with the fiber additive for the reference samples. Besides, some sample groups which prepared using different PTF rates proved the specification limits and it was said that; PTF can be used in asphalt concrete as a fiber additive.

Use of leaching tests to quantify trace element release from waste to energy bottom ash amended pavements

A series of roadway tests strips were paved on-site at a landfill in Florida, U.S. Waste to energy (WTE) bottom ash was used as a partial course aggregate replacement in a hot mix asphalt (HMA) and a Portland cement concrete (PCC) pavement, along with control HMA and PCC sections. This allowed for a comparison of the relative degree of leaching between both materials (HMA and PCC) as well as between the ash-amended and control pavements. Batch and monolithic tank leaching tests were conducted on the pavements. Testing of the PCC samples demonstrated that Mo and Al were elevated above regulatory thresholds for both the control and ash amended samples. Further leach testing demonstrated that the release of Mo was likely from the PCC and not a result of the inclusion of the BA into pavement. Batch leach testing of ash-amended HMA samples revealed Sb as a constituent of potential concern. The results of the monolith leaching test displayed leaching of Sb within the same order of magnitude as the regulatory threshold. Calculation of the leachability index (LI) for Sb found that it would have limited mobility when incorporated in the HMA matrix.

Characterizing the cracking and fracture properties of geosynthetic interlayer reinforced HMA samples using the Overlay Tester (OT)

Reflective cracking is one of the undesirable distresses occurring in hot-mix asphalt (HMA) overlays; costing highway agencies millions of tax payer dollars in maintenance and rehabilitation activities. To mitigate this distress, crack-impeding interlayer materials such as geosynthetic interlayers are specified to protect the HMA overlays as part of maintenance and rehabilitation strategies. Currently however, there is no universally standardized laboratory crack test method to aid in the selection of the most appropriate geosynthetic interlayer material for maximum crack resistance and performance. This study was undertaken to evaluate the laboratory cracking-resistance and fracture performance of different geosynthetic interlayer materials embedded in HMA samples. As a means to investigate its applicability for testing interlayer materials, the Overlay Tester (OT), in a monotonic tensile loading mode (3.375mm/min) at 0°C, was explored as the study test method. Eight different geosynthetic interlayer products with different properties were compared to a ‘control specimen’ using a dense-graded HMA mix. Although field validation is still warranted, the study results indicated a substantial improvement (over 20%) in the laboratory crack and fracture performance of the geosynthetic interlayer reinforced samples over the Control samples; suggesting that use of these interlayer materials may be beneficial in mitigating reflective cracking in HMA overlays. For the test conditions considered, the OT test in monotonic tensile-loading mode also exhibited promising potential as a rapid crack test method for testing geosynthetic interlayer materials. The sample crack failure mode, test repeatability, and statistical variability in the test data were generally within reasonable expectations.

Relationship between fatigue life of asphalt concrete and polypropylene/polyester fibers using artificial neural network and genetic algorithm

While various kinds of fibers are used to improve the hot mix asphalt (HMA) performance, a few works have been undertaken on the hybrid fiber-reinforced HMA. Therefore, the fatigue life of modified HMA samples using polypropylene and polyester fibers was evaluated and two models namely regression and artificial neural network (ANN) were used to predict the fatigue life based on the fibers parameters. As ANN contains many parameters such as the number of hidden layers which directly influence the prediction accuracy, genetic algorithm (GA) was used to solve optimization problem for ANN. Moreover, the trial and error method was used to optimize the GA parameters such as the population size. The comparison of the results obtained from regression and optimized ANN with GA shows that the two-hidden-layer ANN with two and five neurons in the first and second hidden layers, respectively, can predict the fatigue life of fiber-reinforced HMA with high accuracy (correlation coefficient of 0.96).

Investigating the effects of using nanomaterials on moisture damage of HMA

In the past few years, several studies have been conducted focusing on the use of nanomaterials as additives in asphalt mixtures. Nevertheless, the effects of these additives on the moisture susceptibility of asphalt mixtures have not been studied. In this study, the effects of using nano-CaCO3 as an antistrip additive on moisture susceptibility of asphalt mixtures have been assessed using the surface free energy (SFE) method and modified Lottman test. Hot mix asphalt (HMA) samples were made with asphalt binders containing 0, 2, 4 and 6% of nano-CaCO3 and two sources of aggregate, namely limestone and granite. One, three and five freeze–thaw cycles were applied to HMA samples in a modified Lottman test to explore the effect of nanomaterials, clearly. The results of the modified Lottman test show that the wet/dry ratio values of indirect tensile strength (ITS) for mixtures containing nanomaterials were higher than those of control samples. In addition, the results of the SFE method indicate that nano-CaCO3 increases the wettability of the asphalt binder on the aggregate and promotes the adhesion between the asphalt binder and aggregate. Adding nanomaterials leads to the decrease of the acid component of SFE and increases the basic component of SFE of the asphalt binder that leads to an increase of adhesion between the asphalt binder and sensitive aggregate against moisture damage.

Investigating the effect of nanoparticles on the rutting behaviour of hot-mix asphalt

Rutting is considered as one of the major damages in asphalt mixtures. In this study, different types of nanoparticles such as TiO2, Al2O3, Fe2O3 and ZnO in different percentages were added to the base asphalt binder in order to decrease the rutting potential of hot-mix asphalt (HMA). In the first step, asphalt binder tests for characteristics such as penetration grade, ductility, softening point and viscosity were performed on the asphalt binder modified by the nanoparticles. Then, after preparing HMA samples, the static creep test was done at two stress levels at a specific temperature. Results of this study showed that using the nanoparticles improved the behavioural properties of the asphalt binder and decreased rutting in asphalt mix samples. Furthermore, scanning electron microscope images taken from the asphalt binder samples modified by the nanoparticles demonstrated that these nanoparticles were properly distributed in the asphalt binder space and had a positive effect on the rutting performance of the asphalt mixes.