Hot-mix Asphalt Layer Research Articles

The Influence of Asphalt Concrete Underlayment on Slope Stability of the Ballasted High-speed Railways

In recent years, a hot mix asphalt layer, known as an underlayment, has been replacing granular sub-ballast in high-speed and heavy haul tracks, aiming to overcome the limitations of traditional ballasted railways. However, there is a lack of literature regarding the impact of this layer on the slope stability of railway embankments. Ensuring the safety of trains and track availability requires a thorough understanding of embankment slope stability. Hence, this study examined the influence of the underlayment. layer on slope stability in ballasted high-speed railway embankments. Using Slope/W software, twelve embankment models with 2H:1V and 1.5H:1V slopes were analyzed. Half the number of the models were traditional ballasted, while the others incorporated the underlayment layer. Different heights (3, 6, and 8m) were simulated to evaluate the effect on slope stability for both slope levels and track cross-sections. The analysis focused on gravitational force and neglected the increase in pore water pressure. Safety factors for slope slipping surface were used to quantify stability. The findings revealed that the underlayment layer enhances slope stability by 8% to 31% in high-speed railway embankments. However, the degree of improvement decreases with increasing embankment height, and steeper slopes benefit more from the underlayment layer compared to gentler slopes. While these results are promising, further research is needed to investigate the impact of varying pore water pressure on asphaltic tracks.

Rutting performance of cement-treated base and hot mix asphalt layer in flexible pavements containing recycled concrete aggregates

ABSTRACT Cement Treated Base (CTB), when used in base course, has shown better performance against rutting than conventional base materials. This study focuses on the use of recycled coarse aggregates (RCA) as partial replacement of natural coarse aggregates (NCA) in CTB and hot mix asphalt (HMA) layers of flexible pavements. 30% NCA were replaced with RCA to study the rutting performance of flexible pavements by using 100 mm thick rutting samples prepared with 50 mm thick layers of CTB and HMA each. Four types of specimens with 100% NCA, 30% RCA and 70% NCA in CTB only, 30% RCA and 70% NCA in HMA only, and 30% RCA and 70% NCA in both CTB and HMA were used. Specimens were tested at 40°C, 50°C, and 60°C at a constant number of 10,000 passes (5,000 load cycles). It was concluded that the CTB has a significant impact on the overall rutting performance of the samples due to its rigidity. Use of 30% RCA as a replacement of NCA was found to be acceptable, except for pavements with RCA in both layers. A statistical model was also developed and predicted responses from the proposed relationship were in close agreement with the experimental results.

Performance evaluation of a HMA pavement longitudinal joint containing a void reducing asphalt membrane (VRAM)

Longitudinal joint cracking in Hot Mix Asphalt (HMA) pavements is a major issue that occurs because high density (low air voids) is not easily achieved during construction as compared to the mat away from the joints. High air voids allow water infiltration, which results in moisture-induced damage to the pavement and reduced pavement service life. The use of a Void Reducing Asphalt Membrane (VRAM) has been recommended and used at longitudinal joints of asphalt pavements as a preventative treatment to achieve good performance and increase density/reduce air void content at the longitudinal joint. The Void Reducing Asphalt Membrane material is sprayed on top of a tack coat at the longitudinal joint, 9 inches on each side of the joint below the Hot Mix Asphalt surface overlay, and is expected to migrate upward into the Hot Mix Asphalt overlay, filling 50%–70% of the air voids. This study evaluated and compared the performance of longitudinal joints constructed with Void Reducing Asphalt Membrane to that of a joint without Void Reducing Asphalt Membrane (control). Field cores were collected from 1) a section containing Void Reducing Asphalt Membrane and 2) a section without Void Reducing Asphalt Membrane that was paved for this research. Falling head permeability was carried out to determine the permeability coefficient of the specimen. Disk Compact Tension (DCT) and Semi-Circular Bend (SCB) tests were used to evaluate the cracking performance at low temperatures. A push-pull test was used to evaluate the improvement in adhesion between the top and bottom Hot Mix Asphalt layers at the intermediate temperature. The VRAM-containing samples show high values of fracture energy (Gf) and surface and joint bond energies as compared to the control sections. High surface and joint bond energies indicate that longitudinal cracking at the joints will be delayed as more energy is required to initiate cracks. Additionally, the VRAM-containing samples have a lower permeability coefficient compared to the control section. This indicates that the Void Reducing Asphalt Membrane reduces the possibility of water infiltration. The elastomeric polymer in the Void Reducing Asphalt Membrane increases the cohesion in the mixture, which increases the resistance to deformation and improves the bond strength of the joint Additionally, the Void Reducing Asphalt Membrane enhances the elasticity of the binder, thus increasing the cracking resistance of the joint.

Full-Scale Evaluation of Geosynthetic-Reinforced Hot Mix Asphalt

This study aims to evaluate the potential of using geosynthetics to reinforce flexible pavements and improve their resistance to reflective cracking. To achieve the goals, three full-scale test strips (control, geogrid, and geotextile) were constructed at Rowan University, each being 30 ft long by 15 ft wide. The pavement structure of each test strip included two hot mix asphalt (HMA) layers with a total thickness of 3.0 in., and five intentional cracks (with widths of 0.2 in.) were introduced to the first HMA layer. After sealing the cracks and applying the tack coat layer, the geosynthetic interlayer was added, and the top HMA layer was constructed. Asphalt strain gauges and thermocouples were embedded in each section to measure critical strains. All sections were also loaded using a heavy vehicle simulator (HVS) with dual-tire configurations while the temperature around the test strips was maintained at 50°F. In addition, each test strip’s deflection and rutting were measured before and after HVS loading using a heavy weight deflectometer and a laser profiler, respectively. The HVS loading results found that the geogrid-reinforced test strip had a better strain response than the geotextile-reinforced layer, and the geotextile-reinforced layer showed slightly higher bonding (lower delamination). It is noted that the results of this study are in line with a former laboratory study with respect to crack reflection and delamination. Rut profiler data recorded a 25% reduction in rut depth for reinforced sections compared to the control. Moreover, the geosynthetic interlayer was able to mitigate reflective cracking propagation. Both interlayers improved fatigue performance.

Towards a better consideration of the interface bonding conditions in the design of bonded concrete overlays

This study investigates the effect of the interface bonding conditions between a concrete overlay and the existing hot mix asphalt layer on the design life of bonded concrete overlays. Most of the current design approaches assume a full bonding between the layers and ignore the proposed models in the literature for the description of the interlayer behaviour. A reason for that is that these models are very extensive and require big computation effort. To overcome this limitation, this paper analyses temperature-dependent experimental data, that describes the bond behaviour in normal and tangential direction and involves this data in different 3D finite element (FE) models for the evaluation of the impact of the interface bonding conditions on the pavement response. Further, the effect of applying different interface modelling approaches (full bonding model, friction model and the cohesive zone model (CZM)) in a commercial FE-software on the resulting design life has been demonstrated. One of the most significant findings to emerge from this study is that the implementation of temperature-dependent empirical data to describe the interface bonding conditions leads to more realistic design results.

Comparative evaluation of dynamic responses of RCC composite pavement under different moving axles

Roller-compacted composite pavement is considered as an alternative for traditional pavements that provides the desired benefits of both rigid and flexible pavements in a cost-effective manner. To evaluate the performance of roller-compacted concrete (RCC) composite pavement under moving loads, a three-dimensional finite element model (FEM) was developed. A realistic dynamic moving load was applied to the surface of the pavement via DLOAD subroutines developed by FORTRAN. The dynamic response of the pavement at critical locations induced by single, tandem, and tridem axles at speeds of 8 and 80 km/h was determined using the developed FEM model and utilized to estimate pavement performance. Sensitivity analysis of design factors considering variations of hot mix asphalt (HMA) and RCC thicknesses, RCC elastic modulus, axle configurations, and moving speed was conducted to evaluate their impact on fatigue life and rutting development of RCC composite pavement. The results show that the performance of the pavement is significantly affected by axle configurations and moving speed. Among different axle configurations, the tandem axle creates the highest tensile stress and shear stress in the RCC base and HMA layer, respectively. The fatigue life of the pavement prolongs by increasing in the speed of moving loads, so it is expected that the pavement withstands higher load repetition when it is subjected to higher speed traffic. Moreover, increasing layer thicknesses and stiffness of the RCC layer improve fatigue life and rutting performance of the pavement. Even though increasing the thickness of the HMA layer enhances the fatigue life of pavement, increasing it to over 15 cm increases the potential of rutting.

Performance based design of bonded whitetopping overlays

This paper proposes a new performance based design method for bonded concrete overlays of existing asphalt pavements. Important input parameters such as the residual bearing capacity of the hot mix asphalt (HMA) layer and its thickness, the temperature-dependent interface bonding properties between the existing HMA and the new concrete layer, the climatic conditions and the traffic loads are being characterised. The implementation of temperature-dependent elastic modulus of the HMA and interface bonding properties in the design model allows for a more realistic determination of the overlay thickness and the design life. Further, a design catalogue was derived based on the results from a number of pavement structure analysis with varying parameters. For a given expected number of heavy goods vehicles (HGV) passes, the thickness of the existing HMA and its residual bearing capacity it is possible to determine the required concrete overlay thickness.

Fatigue damage calculation of cold recycled asphalt pavement considering measured temperature field and traffic volume distribution

<abstract> <p>A finite element simulation method for fatigue damage calculation and life prediction of pavement structures under the influence of temperature and traffic distribution factors was proposed in this study. Relying on the test cold recycled asphalt pavement structure, the existing distress, pavement structure forms, field monitored temperature and strain were first introduced and analyzed. Then, in constructing the numerical model, the viscoelastic constitutive model was introduced to characterize the effect of temperature and loading conditions on the mechanical response of the hot mix asphalt (HMA) layers and the emulsified asphalt cold recycled (EACR) layer. The damage variables are defined by fatigue equations, and the damage accumulation can be determined by Miner's linear fatigue accumulation theory. To reflect the distribution of traffic volume, the total traffic volume of a year was divided into 144 axle load groups according to the monthly and hourly distribution conditions. Accordingly, based on the monthly maximum and minimum temperature, 12 representative days were selected to represent the climate characteristics of 12 months, respectively. Then, each representative day's measured structural temperature data were extracted every 2 hours and linearly interpolated to obtain 144 representative temperature fields corresponding to 144 axle load groups. Through the above method, simulation calculations were performed for cold recycled asphalt pavement structures with different cement-stabilized aggregate (CSA) base stiffnesses. The results show that the fatigue damage accumulation of the EACR layers reaches its highest value in winter and midday hours, owing to the temperature variation and traffic distribution. Due to the weak fatigue resistance of EACR mixtures, it is not recommended to be paved EACR layers directly on top of the CSA base with poor bearing capacity. Otherwise, fatigue cracking is likely to occur first. For this reason, recommendations for ensuring the durability of the cold recycled pavement structure were also proposed in the study.</p> </abstract>

Evaluation the Usage of Local Materials in HMA Surface Layer

The importance of roads and all the facilities related to the mobility of people, goods, and vehicles in the world exceed the social and economic significance but play a main role in politics and government decisions. As a result of the increasing population in Iraq and the dramatical growth in heavy vehicles twenty years ago and due to the rising percentage of new construction projects in the country, the need appeared to assess and improve the hot mix asphalt layers used in the construction of flexible pavements. In this research, a hot mix asphalt surface layer was used with a 12.5 mm nominal maximum aggregate size from one aggregate source (Al Nibaie quarry) and one penetration grade type of asphalt binder (40 -50), also in this research work has been added one type of polymers by several percentages namely, Crumb Rubber Modifier (CRM) to enhance the properties of asphalt binder which in turn improves HMA. The evaluation process included the preparation of two types of mixtures (unmodified and modified mixtures) by using the Superpave mix design method and to estimate the ability of mixtures to resist the three main types of failure that may be flexible pavement exposed to, Wheel track test was used to simulate the permanent deformation resistance of mixtures, flexural beam fatigue test to determine the fatigue cracking resistance of mixtures and indirect Tensile Strength test was used to determine the strength to moisture damage for prepared mixtures. Results demonstrated that adding modified waste polymer to the asphalt cement with different percentages significantly improved mechanical and durability properties.

Investigation of Cold Recycling of Bituminous Surface Treatment with Foam Bitumen

The course of turned of bituminous pavement layers into hot mix asphalt (HMA) layers has been increasing day by day all over the world. Bituminous surface treatment that contains consirable amount of aggregate and bitumen, is an important source of recycling that offers a great amount of pavement materials intead of virgin material usage on pavement consruction. In the study, it was aimed to investigate the usability of bituminous surface layer treatment in the base layers of the HMA roads by mixing with foam bitumen and active filler materials in order to eliminate the potential performance degradation that will be encountered when it is recycled due to the low bitumen percentage compared to hot mix asphalt and the wear of the aggregate due to climatic conditions and traffic loads over time. The study conducted that intends to technically evaluate the cold recycling of bituminous surface treatment of roads with foam bitumen and active filler materials; for 70/100 bitumen grade, 5 different bitumen mixes were prepared and ideal bitumen percentage was investigated for this bitumen grade. The effect of bitumen percentage on mixture performance was evaluated with 50/70-100/150-160/220 bitumen grades and mixtures were prepared in single bitumen ratio (2.5%). It was investigated that active fillers will give suitable results for foam bituminous mixtures by preparing mixtures for three different active fillers; cement, hydrated lime and fly ash. To evaluate all these productions, ITS, unconfined compressive strenght, triaxial resilient modulus and asphalt permanent deformation tests were performed. The results obtained showed that production made using 2% foam bitumen and 1% was found suitable for moisture sensitivity and structural stability. Recycling of bituminous surface treatment using foam bitumen and cement is an environmentally and economically beneficial method by reducing both waste and raw material consumption.

The Quest for Renewable Energy—Effects of Different Asphalt Mixes and Laboratory Loading on Piezoelectric Energy Harvesters

In furtherance of the quest for green renewable and sustainable energy, an effort was made in this laboratory study to generate and harvest electric power from hot-mix asphalt (HMA); a viscoelastic material that is widely used for road construction. The underlying hypothesis is that the mechanical vibrations and strain energy induced by vehicle loading on the road (pavement) can be harnessed and converted into usable electric power by embedding piezoelectric sensors within the HMA layers of the pavement structure. To investigate the effects of HMA mix type on the generated energy, four commonly used Texas mix types, namely Type B (coarse-graded), Type C (dense-graded), Type D (dense-to-fine graded), and Type F (fine-graded), with up to seven different HMA mix-design volumetric characteristics were comparatively evaluated in the laboratory. In the study, the effects of loading, namely load magnitude and loading frequency, were investigated by simulating the traffic loading in the laboratory through comparative testing with the Hamburg wheel-tracking tester (HWTT) and the universal testing machine (UTM), respectively, at different temperature conditions. A prototype highway sensing and energy conversion (HiSEC) module with piezoelectric sensors was utilized for converting the applied stress on the HMA into harvestable electric energy during HWTT and UTM laboratory testing, respectively. The generated electric current, voltage, and power were measured and quantified using a multipurpose power meter. Overall, the study demonstrated that there is promising potential to harvest energy from HMA when subjected to transient loading under different temperature conditions. However, further refinement of the HiSEC module and piezoelectric sensors is still warranted to optimize the power generation and harvesting capacity, both in terms of efficiency and power output.

Integrated and comparative Structural-LCA analysis of unbound and cement-stabilized construction and demolition waste aggregate for subbase road pavement layers formation

A more extensive use of recycled aggregate in road construction is key to meeting the ambitious targets of the EU circular economy action plan. However, scepticism among designers, contractors and road agencies remains a bottleneck. This integrated structural-environmental study demonstrates the advantages of using recycled construction and demolition waste aggregate (CDW-RA) in substitution of primary natural aggregate (NA) for the formation of subbase layers in both flexible and semi-rigid road pavements. The structural responses of different pavements with a 0.30 m subbase layer made up of four materials, i.e., two unbound and two cement-stabilized obtained including NA and CDW-RA, were compared. The environmental-related impacts were also assessed by means of a life cycle assessment (LCA).Laboratory tests and structural design led to pavement structures with the same thickness for the upper hot-mix asphalt layers, i.e., 0.26 and 0.28 m for the two unbound and the two cement-stabilized subbase materials respectively. The pavement with unbound CDW-RA subbase showed the best LCA outcomes because of the more favourable environmental performance of CDW-RA compared to NA. Although the stabilization of NA and CDW-RA reduces the thickness of the top hot-mix asphalt layers by 0.02 m, the environmental benefits are outweighed by the impact associated with the usage of cement. This study encourages the use of CDW-RA in road subbase layers with similar characteristics to those investigated here. The LCA results also support the use of alternative and more environmentally friendly binders that can enhance the environmental sustainability of stabilized materials in road construction.

Improvement shear properties of HMA using crumb rubber with different filler

Rutting is one of the big problems in hot-mix asphalt (HMA) pavements. The primary mechanism of HMA rutting is shear deformation, often caused by high stress in HMA layers during traffic loading, especially at high temperatures. Current HMA rutting tests are not necessarily designed to capture HMA shear properties such as shear strength, shear strain, and shear module. The present work explores the behavior of the shear strength properties of HMA modified with Crumb Tire Rubber (CTR) and two types of filler (brick and lime dust in comparison with passing sieving No.200 as control filler) by developing a Simple Punching Shear Test (SPST) under control of temperature and loading rate. A series of laboratory sample tests to formulate and set up the SPST protocol and the related test parameters, derive the SPST results from the analysis sample to capture the HMA shear parameters from the results, and comparatively evaluate the shear properties of HMA mixes. Results have shown that the SPST is relatively receptive to the form of modifier and filler. Using limestone dust as with (5%) CTR content increased higher shear strength, the rate of increase was about (44.44%) and (51.38%). Also 5% to 7% CTR content with lime dust filler lowering shear strain more than for brick dust filler.

Improvement the Shear strength of Asphalt Mixture by using crumb tire Rubber

Rutting is one of the big problems in hot-mix asphalt (HMA) pavements. The primary mechanism of HMA rutting is shear deformation, often caused by high stress in HMA layers during traffic loading, especially at high temperatures. Current HMA rutting tests are not necessarily designed to capture HMA shear properties such as shear strength, shear strain, and shear module. The present work explores the behavior of the shear strength properties of HMA modified with Crumb Tire Rubber (CTR) and two types of filler (brick and lime dust in comparison with passing sieving No.200 as control filler) by developing a Simple Punching Shear Test (SPST) under control of temperature and loading rate. A series of laboratory sample tests to formulate and set up the SPST protocol and the related test parameters, derive the SPST results analysis sample to capture the HMA shear parameters from the results and comparatively evaluate the shear properties of HMA mixes. Results have shown that the SPST is relatively receptive to the form of modifier and filler. Using limestone dust as with (5%) CTR content increased higher shear strength, the rate of increase was about (44.44%) and (51.38%). Also 5% to 7% CTR content with lime dust filler lowering shear strain more than for brick dust filler.

Utilization of Cold Central Plant Recycled Asphalt in Long-Life Flexible Pavements

Long-life flexible pavements are well documented and used widely across the U.S. Found in every climate zone and traffic classification, long-life pavements do not experience deep structural distresses such as bottom-up fatigue cracking or substructure rutting. Full-scale test sections, built in 2003 at the National Center for Asphalt Technology (NCAT) Test Track, provided the basis for an optimized design approach that utilizes strain distributions for long-life thickness design. These sections, containing only virgin materials, were subjected to 30 million standard axle loadings with excellent performance in terms of rutting, cracking, and roughness. In 2012, three new sections were built at the Test Track using cold central plant recycled asphalt materials as the base layer. These layers, made from nearly 100% reclaimed asphalt pavement (RAP), supported hot mix asphalt layers that also included RAP with one section featuring in-place stabilization of the existing aggregate base. This paper provides a direct comparison between the sets of sections to compare and contrast their performance histories and structural characterization, and consider their economic and environmental impacts. None of the recycled sections are exhibiting any surface deterioration, despite heavy trafficking, and the section with a stabilized base is exhibiting lower strains than established long-life pavement thresholds. The economic analysis suggested that the recycled sections can deliver similar performance at a lower average structure normalized section cost than the non-recycled sections. Furthermore, the section with the stabilized base and 76% recycled material is likely a long-life pavement and can potentially outperform the sections with no recycled content.

Heterogeneity effect on fracture parameters of a multilayer asphalt pavement structure containing a top‐down crack and subjected to moving traffic loading

AbstractA part of the multilayer pavement structure containing top‐down crack in the hot mix asphalt (HMA) layer and subjected to loading of a moving vehicle is simulated using the finite element method. Aggregate distribution and packing algorithm was used for modeling the HMA layer around the top‐down crack as a heterogeneous two‐phase (aggregate/fine aggregate matrix [FAM]) medium. By considering the heterogeneity aspects of the asphalt mixture, the influence of traffic loading location, aggregate distribution, crack length, thickness layer, and mechanical properties of layers and components were investigated on the fracture parameters. The results showed that for different locations of vehicle wheels relative to the top‐down crack, the magnitude and sign of the fracture parameters in heterogeneous modeling were significantly different from the similar values of the homogeneous simulation. The stress intensity factors and especially the T‐stress were significantly sensitive to the crack tip location that can be placed either inside the stiffer aggregate or the softer FAM part.

Parametric optimization of Ground Penetrating Radar approach for assessing asphalt pavement surface layers compaction

In this study, a parametric analysis was performed and an optimized approach based on Ground Penetrating Radar (GPR) was developed for assessing accurately the compaction of surface layers of hot mix asphalt (HMA) pavements. This approach consists of data acquisition with a 2-Ghz air coupled antenna for determining the dielectric constant of asphalt, and utilization of the capabilities of ALL (Al-Qadi, Lahouar and Leng) and PANK (Päällystealan Neuvottelukunta) models in terms of data analysis supplemented with 3 cores to estimate the relative calibration factors. Field studies were performed to illustrate the validity and effectiveness of the proposed approach, in relation with the typical coring method. The results demonstrated that the estimates of compaction degree (mean values) are statistically identical to that of field cores. Moreover, by using the proposed approach the distributions of estimates are postulated to be more realistic in terms of compaction (non) uniformity of pavement mat appear in the field.

Correlating the asphalt-binder high-temperature properties (DSR) to HMA permanent deformation (RLPD) and field rutting: A laboratory-field study

Asphalt-binders are part of the key material constituents affecting the performance of hot-mix asphalt (HMA), and ultimately, the field performance of flexible pavement structures. Quite often, it is desired/useful to predict the HMA permanent deformation (viscoelastic) properties and field rutting from the asphalt-binder properties. Using the Texas flexible pavements and overlays database, namely the Texas Data Storage System (DSS), as the data source, this laboratory-field study was conducted to correlate the asphalt-binder properties to HMA permanent deformation (viscoelastic) properties and field HMA-layer rutting performance of in-service highway sections. Data extracted from the Texas DSS included asphalt-binder high-temperature rheological properties measured using the dynamic shear Rheometer (DSR) test, HMA permanent deformation (PD) and viscoelastic properties from the repeated load permanent deformation (RLPD) test, and field rut depth (RD) data for the HMA layers of in-service highway test sections. Two Texas asphalt-binder types, four HMA mixes, and four in-service field highway sections were used in the study. For some parametric comparisons, the corresponding results indicated good statistical correlations among the asphalt-binders, HMA mixes, and field rutting performance, with a coefficient of determination (R2) over 60%. Overall, the study findings indicated that the HMA PD properties and field HMA-layer rutting can be predicted from the asphalt-binder high-temperature rheological properties, with a linear or logarithmic model, to an accuracy exceeding 60%.

Laboratory evaluation of grid-reinforced HMA beams using the flexural bending-beam fatigue (FBBF) test in load-controlled mode

ABSTRACT Interlayer grid-reinforcement is one of the maintenance and rehabilitation (M&R) strategies often used to mitigate reflective cracking in hot-mix asphalt (HMA) overlays. However, there is no standardised laboratory test methodology for screening and selecting grid materials during the HMA overlay design stage. This laboratory study was conducted to comparatively evaluate, characterize, and quantify the crack resistance potential of grid-reinforced HMA using the flexural bending beam fatigue (FBBF) test based on the AASHTO T 321 concept. Two grid materials, denoted as FA-30 and FA-75, were comparatively evaluated against Control (unreinforced) HMA beam samples as the reference datum. The study findings indicated that the FBBF test setup, in a load-controlled mode based on the AASHTO T 321 concept, has promising potential as a test method for evaluating and screening grid materials in the laboratory. Overall, the grid-reinforcements used in the study exhibited over 4.0 times superiority in terms of laboratory flexural cracking-resistance performance improvement with the potential of over 25% reduction in the HMA layer thickness. The average laboratory interlayer crack performance benefit factor (ICPF), computed based on the indicative mirroring of the AASHTO R 50-09 concept, was 10.60 for FA-75 versus 5.14 for FA-30 with respective to laboratory performance.

Laboratory evaluation of gap graded rubber modified warm mix asphalt

Crumb Rubber (CR), if used in Gap-graded Hot Mix Asphalt (HMA), forms an excellent splash-&-spray resistant, durable and fatigue resistant HMA layer. The only drawback is the higher asphalt production temperature due to addition of CR. The higher production temperature can be reduced by using Warm Mix Additives with only concern being its effect on the performance. The paper contemplates the use of 1.5% Sasobit® with a view to achieve similar or better performance properties at lower mixing temperature. The results indicate an overall improvement in performance (in terms of rutting and fatigue) in light of the laboratory tests performed. The paper concludes with Gap-graded Warm Mix Asphalt (WMA) as a feasible solution when 1.5% Sasobit® is used as an additive.