Open-graded Friction Course Mixtures Research Articles

Effect of High Polymer, Crumb Rubber, and Epoxy-Modified Asphalt Binders on Laboratory Performance of Open-Graded Friction Course Mixtures

Open-graded friction course (OGFC) is a thin asphalt mixture surface layer. It is gap-graded with a high percentage of coarse aggregates that are nearly uniform in size, resulting in a high percentage of interconnected air voids and asphalt binder, which provides improved skid resistance, visibility, and decreased pavement–tire noise. However, construction personnel at the Louisiana Department of Transportation and Development reported that conventional OGFC mixtures have durability issues and shorter service life, compared with thin asphalt mixture lifts. Hence, effects of different asphalt binder types on the performance of OGFC mixtures were evaluated. Five types of asphalt binder were utilized: conventional styrene-butadiene-styrene (SBS) asphalt binder PG 76-22M; high SBS content asphalt binder PG 88-28; diluted epoxy asphalt (EA) binder with two different dosages (25% and 50%); and a hybrid modified asphalt binder prepared with SBS and crumb rubber modifier PG 76-22G. The optimal aggregate structures were determined based on minimum required air voids and voids in coarse aggregate. Physical and mechanical tests were conducted to assess the performance of OGFC mixtures, including draindown, permeability, loaded wheel track, and Cantabro abrasion loss. Results indicate that OGFC mixtures incorporating diluted EA binder exhibited lower draindown values than mixtures containing PG 76-22M and PG 88-28. Moreover, mixtures with PG 88-28 and 50% EA binders demonstrated improved resistance to rutting. Mixtures with 50% EA and PG 88-28 binders demonstrated improved durability, compared with mixtures with PG 76-22M for unaged and aged conditioning, as measured by Cantabro abrasion loss values.

A multi-gradient analysis of microscopic void characteristics' influence on the mechanical properties of open-graded friction course bituminous pavement

The mechanical properties of the open-graded friction course (OGFC) bituminous pavement are tied to its microscopic void structure, but multiple void parameters influence void formation and distribution. Solely using air voids as an indicator of pavement stability is challenging. Thus, a multi-gradient analysis of void structure factors is vital for advancing OGFC pavement's mechanical property research. This study used computerized tomography (CT) and digital image processing (DIP) to gather data on void structure distribution, size, and complexity in OGFC bituminous mixtures. Mechanical experiments assessed high-temperature deformation, low-temperature cracking, and water damage resistance. Analysis of void parameters' influence led to a predictive model for mechanical property in OGFC mixtures. The study found that as air voids increase within the 18 %–24 % range, both equivalent void diameter and void fractal dimension increase, while void count decreases. Conversely, coarser gradation and a larger nominal maximum aggregate size (NMAS) lead to increased equivalent void diameter but decreased void fractal dimension, reducing void complexity. The mechanical properties of OGFC mixtures decline with rising air voids but improve with coarser gradation and larger NMAS. The predictive model highlights the void fractal dimension and NMAS as critical indicators, with other factors showing weaker influence or multicollinearity issues that are unfit for model fitting. The findings could provide useful references for the structural design, property evaluation, and quality control of OGFC bituminous pavements in actual road construction.

Study on induction healing properties of OGFC asphalt mixture with high elasticity and high viscosity modifier

Induction healing is a promising preventive maintenance method of asphalt pavement, but the healing properties of Open-Graded Friction Course (OGFC) asphalt mixture with high elasticity and high viscosity modifier (HEV) were not clear. OGFC asphalt mixture used for induction heating was prepared by adding steel wool fibers and HEV. The effects of HEV and steel wool on the properties of OGFC mixture were studied. The particle loss resistance, water stability, porosity, induction heating and self-healing properties of OGFC-13 asphalt mixture with different steel wool contents were measured. The results showed that HEV slightly improved the properties of resistance to particle loss, fracture strength and water stability of OGFC-13 asphalt mixture, had little effect on the induction heating rate and porosity, but reduced the healing rate by 10%. The addition of steel wool to OGFC-13 can enhance the particle loss resistance, heating rate and healing effect, and the optimal dosage is 8% of the volume fraction of bituminous binder. The healing rate rose steadily as the heating temperature increased. At the optimal healing temperature of 110 ℃, healing depth ratios of the mixtures without and with HEV were 56.3% and 43%, respectively, and the fracture energy healing rates were 72.4% and 63.1%, both at a high healing level. The incorporation of steel fibers and HEV reduced the porosity and water permeability of OGFC very slightly, and the porosity and water permeability of OGFC did not change significantly after induction heating. It is concluded that induction heating has a potential to heal the cracks within OGFC mixture with HEV to prevent surface raveling which is the primary damage of OGFC.

Sustainable Open-Graded Friction Course asphalt mixes with steel slag aggregates

A permeable mixture called Open-Graded Friction Course (OGFC) is used to lessen the effects of climate change, especially during periods of heavy rain. It is made up of open gradation, mostly coarse aggregates, and fewer fines. The advantages of an OGFC mixture include the removal of surface water from the pavement, noise absorption, increased frictional resistance and more. Steel slag is a waste product left over from the Iron and Steel industry that can be utilized as aggregates in OGFC mixes. The primary goal of this work is to assess the usage of steel slag aggregates in place of conventional aggregates to produce the OGFC mix for getting improved mixture properties. Five percentage substitutions were employed to examine the design and quality of the OGFC mix, namely, 0% (control mix), 25, 50, 75, and 100% of steel slag aggregates in place of conventional aggregates. Tests for air voids, binder draindown, unaged and aged Cantabro abrasion loss, and Indirect Tensile Strength (ITS) test were conducted to evaluate the performance of OGFC mixes containing different percentages of steel slag. The test results show that the performance of the mix was improved by the addition of various percentages of steel slag. The results of the physical properties tests on steel aggregates were better than that of conventional aggregates. The mix with steel slag aggregates exhibits a slight improvement in the drainage property when compared to the conventional aggregate mix, according to the test results of the draindown test. When compared to the conventional mix, the mix with 100% replacement at 5.75% bitumen content produced better raveling resistance, and the mix with 50% steel slag replacement indicated improved resistance to moisture susceptibility with good Tensile Strength Ratio. The test results showed 100% replacement mix performed better in terms of abrasion loss, binder draindown, and air voids content, while a 50% replacement mix performed better in terms of moisture susceptibility along with other parameters. Overall, it can be concluded that using steel slag aggregates in the OGFC mix can be advantageous and increase sustainability with utilization of steel slag as an industrial marginal material in construction of pavements.

Investigation on the Short-Term Aging Scheme for High Viscosity Modified Bitumen.

Due to the highly viscous characteristics of high viscosity modified bitumen (HVMB), the commonly used short-term aging schemes are not suitable for it. As such, the objective of this study is to introduce a suitable short-term aging scheme for HVMB by increasing the aging period and temperature. For this purpose, two kinds of commercial HVMB were aged via rolling thin-film oven test (RTFOT) and thin-film oven test (TFOT) at different aging periods and temperatures. At the same time, open-graded friction course (OGFC) mixtures prepared using HVMB were also aged via two aging schemes to simulate the short-term aging of bitumen at the mixing plant. With the aid of temperature sweep, frequency sweep, and multiple stress creep recovery tests, the rheological properties of short-term aged bitumen and the extracted bitumen were tested. By comparing the rheological properties of TFOT- and RTFOT-aged bitumen with those of extracted bitumen, suitable laboratory short-term aging schemes for HVMB were determined. Comparative results showed that aging the OGFC mixture in a 175 °C forced-draft oven for 2 h is suitable to simulate the short-term aging process of bitumen at the mixing plant. Compared with RTOFT, TFOT was more preferable for HVMB. Additionally, the recommended aging period and temperature for TFOT was 5 h and 178 °C, respectively.

Laboratory Investigation of Draindown Behavior of Open-Graded Friction-Course Mixtures Containing Banana and Sugarcane Bagasse Natural Fibers

Open-graded friction courses (OGFCs) are asphalt paving mixes with a higher number of interconnecting air voids to provide advantages with respect to improved drainage, increased dry/wet surface friction resistance, decreased splash and spray, and reduced aquaplaning. However, binder draindown has been a recurring issue during the manufacture, storage, transportation, and service life of OGFC mixtures. The addition of stabilizers in the form of fiber is often used with OGFC mixes to counteract the draindown. Increasing environmental awareness, the depletion of fossil resources, and the rise of global waste problems have necessitated the use of locally accessible natural fibers as an alternative to expensive synthetic fibers. In this study, the banana fiber obtained from the waste pseudo-stem of the banana plant post-harvesting and the sugarcane bagasse fiber obtained from the post-residual after sugar extraction is explored along with a commercial cellulose fiber to evaluate the draindown characteristics of OGFC mixtures. A cone penetration test and fiber absorption test was performed on the fiber-mixed asphalt binder. The draindown characteristics of 168 combinations of OGFC mixes were evaluated considering various parameters, viz. fiber parameters (types, lengths, dosages), binder dosage, binder types (unmodified binder and polymer-modified binder), and time period. Finally, a statistical analysis was conducted to determine the efficacy of different influencing factors. The best performance was exhibited by banana fiber, which had a dosage of 0.45% and a length of 9 mm, followed by sugarcane bagasse and cellulose fiber. All the input factors were found to be statistically significant.

Freeze–Thaw damage characteristics of composite modified open graded friction course

To reasonably describe the damage characteristics of composite modified open graded friction course (OGFC) after multiple freeze-thaw cycles, based on the Able viscoelastic constitutive equation, a viscoelastic model of freeze-thaw damage was constructed and analyzed using the Weibull distribution function, damage mechanics, and fractional derivative theory. Under the conditions of composite modified OGFC mixtures with different mixing ratios (12%, 0%), (12%, 1%), and (12%, 2%), and multiple freeze-thaw cycles (0–16), low-temperature bending and creep tests of the mixtures were carried out. The stress-strain curve data obtained were fitted to analyze the physical significance of the model parameters. The results show that the model is suitable for characterizing the viscoelastic stage of composite modified OGFC under 10 freeze-thaw cycles. The freeze-thaw damage model parameters of three types of composite modified OGFC with different mixing ratios were compared and analyzed. The order of the fractional derivative of the composite modified OGFC model (12%, 1%) was 0.2223, the maximum damage threshold was 1.108, and the maximum viscosity coefficient was 371.84. This composite modified OGFC had the best low-temperature crack resistance.

Evaluate Pavement Skid Resistance Performance Based on Bayesian-LightGBM Using 3D Surface Macrotexture Data.

The lack of skid resistance performance is a crucial factor leading to road traffic accidents. The pavement surface friction is an essential indicator for measuring the skid resistance. The surface texture structure significantly affects the friction between the tire and the pavement, determining the pavement skid resistance. To deeply study the relationship between surface texture structure and pavement skid resistance performance, two types of asphalt mixture specimens, asphalt concrete (AC) and open-graded friction course (OGFC), are prepared for the skid resistance performance test. Firstly, a high-precision 3D smart sensor Gocator 3110 is used to collect the 3D point cloud data of the asphalt mixture surface texture. The British pendulum tester is used to measure the friction. Secondly, ten feature parameters are extracted to describe the 3D macrotexture characteristics. A data set containing 10 features and 200 groups of texture and friction data was also constructed. Meanwhile, the influence of macro-texture features on the skid resistance performance is discussed. Finally, an optimized Bayesian-LightGBM model is trained based on the constructed dataset. Compared with LightGBM, XGBoost, RF, and SVR algorithms, the Bayesian-LightGBM model can evaluate skid resistance more accurately. The R2 value of the proposed model is 92.83%. The research results prove that ten macrotexture features contribute to the evaluation of skid resistance to varying degrees. Furthermore, compared with AC mixture specimen, the texture surface of OGFC mixture specimen has more obvious height characteristics and higher roughness. The skid resistance of OGFC mixture specimens is better than that of AC.

Laboratory Study and Simulation Analysis on Anticrack Properties of Open-Graded Friction Course Based on Creep Tests

Cracking is a common early disease of asphalt pavements. To evaluate the temperature shrinkage cracking resistance of an open-graded friction course (OGFC), the viscoelastic parameters of an OGFC mixture at different temperatures were obtained by uniaxial compression creep tests. According to the viscoelastic parameters, numerical models of the creep, relaxation, and temperature shrinkage cracking of an OGFC were established. Subsequently, the reliability of the numerical model was verified based on the creep test results and the extensive Maxwell model. The crack initiation temperature of the OGFC mixture at different cooling rates was analyzed by combining indirect tensile strength and temperature shrinkage stress. The results showed that the simulation results were close to the model results, and the average errors of the simulation results for creep compliance and relaxation modulus did not exceed 7.18% and 1.83%, respectively. The faster the cooling was, the greater the temperature shrinkage stress and the higher the crack initiation temperature were. The crack initiation temperature of the OGFC at a cooling rate of 20°C/h was about −3.5°C. This research provides a reference for quickly obtaining the crack initiation temperature of asphalt mixtures at different cooling rates.

A semi-empirical model for top-down cracking depth evolution in thick asphalt pavements with open-graded friction courses

Thick asphalt pavements with open-graded friction course (OGFC) are exposed to top-down cracking (TDC), a distress consisting of longitudinal cracks that initiate on the pavement surface close to the wheel path and propagate downwards. The main objective of this study is to develop a semi-empirical model for the prediction of TDC depth evolution for such pavements. For this purpose, a series of cores were taken from different Italian motorway pavements affected by TDC and analyzed in the laboratory. Cracked cores taken from the wheel path area were analyzed to determine TDC depth, whereas intact cores taken from the middle of the lane (not affected by traffic loadings) were tested to obtain the volumetric and mechanical properties of the OGFC mixture. The proposed model, developed on the basis of the results already available in literature and on the findings of the laboratory investigation, predicts the evolution of TDC depth as a function of the applied traffic loadings (in terms of 12-ton fatigue equivalent single axle loads, i.e., ESALs). The model is sigmoidal with a maximum TDC depth assumed equal to 150 mm. The shape parameter of the sigmoidal function depends on the indirect tensile strength (ITS) of the OGFC mixtures (which takes into account indirectly also the volumetrics and stiffness of the OGFC), whereas the evolutive translation factor depends on the age of the OGFC mixture. After excluding some outliers, the model was able to predict the measured TDC depth very well. Moreover, in-situ observations allowed a preliminary validation of the proposed model. This model can be used in pavement management systems (PMSs) to plan surface repairs due to TDC in a timely manner, thus minimizing pavement damage and maintenance costs. • The semi-empirical model predicts TDC depth as a function of the traffic loads. • The model is sigmoidal with a maximum TDC depth assumed equal to 150 mm. • The model parameters depend on the properties and the age of the OGFC. • In-situ observations provide a preliminary validation of the model. • The model can be used in a PMS to identify pavement areas where TDC is critical.

Pavement and Noise Reduction Performance of Open‐Graded Asphalt Friction Course Improved by Waste Tire Crumb Rubber

To further reveal the road performance and noise reduction performance of open‐graded friction course (OGFC), the crumb rubber prepared by adding waste tires were considered, and the performance requirements of the material were put forward. To avoid the influence of rubber particle swelling on aggregate, the special gradation and mix proportion of OGFC mixture were designed, and the particle size of 4.75 mm was proposed as the control size. The test results show that the aggregate forms a good embedded structure. The resilient modulus, deformation performance, and fatigue performance of R‐OGFC asphalt mixture with different crumb rubber contents were studied. According to the test results, the rubber particle content under the best road performance and noise reduction effect was proposed. The results show that, after adding a certain amount of crumb rubber, the performance of asphalt mixture has been greatly improved, especially the dynamic stability has been improved by 84%. Although the resilient modulus has decreased by 10%, the creep performance has decreased by 37%, and the fatigue life has decreased by 31% (2% rubber content), the noise reduction can reach 3.6–8.6 dB, and the noise reduction performance is significant. This shows that the best content of rubber particles is between 1.5% and 2%, and the R‐OGFC mixture modified by rubber has a good application prospect.

Durability assessment of open-graded friction course using a sustainable polymer

Open-graded friction course (OGFC) asphalt mixture, usually used to construct porous pavements, represents one of the materials supporting low-impact development (LID) philosophy due to its use of coarse aggregate gradation. Using such mixtures brings several benefits related to safety, environment and economy. Alas, coarse, open-graded skeleton of OGFC mixtures is prone to failure, particularly raveling and stripping. Continuous traffic loading and the environmental impacts give hand in hand to further increase the potential for failure, hence higher pavement maintenance and rehabilitation costs. Application of different types of modifiers has proved effective in mitigating failure potential. The most common modifiers are polymers, fibers and anti-stripping agents. Aiming at minimizing the costs and maximizing the lifespan while considering sustainability, the study was to investigate the effect of using a recycled stabilizing material as an asphalt modifier on the performance of OGFC asphalt mixtures. Recycled Low-Density Polyethylene (R-LDP) was adopted in this investigation. Changes in mixture air void, porosity, draindown, permeability, rut depth, moisture damage and abrasion loss were observed to evaluate the effect. Compared with unmodified asphalt samples, R-LDP modification increased mixture air void, porosity and permeability by 15%, 10% and at least 40%, respectively. Also, it noticeably contributed to reducing rut depth, moisture damage and abrasion loss (both unaged and aged) by 31%, 20% and at least 40%, respectively. More significantly, it almost eliminated the draindown problem. Incorporating R-LDP proved effective in upgrading OGFC mixture properties to an acceptable level required by most specifications.

Influence of high-surface-area hydrated lime on cracking performance of open-graded asphalt mixtures

Hydrated lime has been used in hot mix asphalt (HMA) to reduce moisture sensitivity and stripping since 1910 in the United States. During the past 40 years, researchers from all over the world have focused on this topic finding that hydrated lime can actually provide many other benefits to asphalt mixtures. In this paper, the use of a high surface area (HSA) hydrated lime as a filler in asphalt mixtures was investigated to assess the influence of lime microstructure on mixtures cracking behaviour. Two different open-graded friction course (OGFC) asphalt mixtures were prepared using different types of filler (calcium carbonate, calcium carbonate + hydrated lime and calcium carbonate + HSA hydrated lime) and tested using the SuperPave indirect tensile test protocol. The cracking behaviour of the mixtures was evaluated according to the HMA fracture mechanics approach developed at the University of Florida. The results show that HSA hydrated lime is able to improve the fracture performance of OGFC mixtures, even more significant than the traditional one.

Evaluating four typical fibers used for OGFC mixture modification regarding drainage, raveling, rutting and fatigue resistance

Fiber is an essential additive used in asphalt mixture due to its asphalt absorption and reinforcement characteristics, especially for Open-Graded Friction Course (OGFC) mixture. However researches about the influence of varying fibers types on OGFC mixture are not adequate. In this study, 4 typical fibers, namely lignin fiber, basalt fiber, polyester fiber, and polyacrylonitrile fiber were evaluated. Their raw material sources, appearance and physical properties were compared. Also, resultant mixture drainage property, raveling resistance, rutting resistance, stiffness and fatigue life were evaluated using Schellenberg binder drainage test, Cantabro test, Hamburger Wheel Tracking test, and Four-Point-Bending test, respectively. Different fiber contents (0.15%, 0.3% and 0.45%) were considered. Results show that fiber modification improves the mixture overall performance, but the improvement notably differs between fiber types. Lignin fiber has a small density, which renders it the best improvement on mixture drainage property. But lignin fiber has little tensile strength and shows the least improvement on OGFC mixture mechanical properties. The other three fibers are strong filaments that can physically crosslink with each other and demonstrate better performance than lignin fiber. Polyester fiber exhibits the best improvement and thus is recommended. Increasing the fiber content does not necessarily facilitate the improvement due to the agglomeration issue during mixing. An optimal fiber content exists for each fiber type, which is 0.3%, 0.15%, 0.3%, and 0.15% for lignin fiber, basalt fiber, polyester fiber, and polyacrylonitrile fiber, respectively.

Laboratory Evaluation on the Performance Comparison between OGFC Asphalt Reinforcement with Fibers and Modified with Nanosilica

Abstract Open-graded friction course (OGFC) is a mixture with gap-graded aggregate that is used in pavement surfacing. This research proposes methods to improve the durability and structural contribution of OGFC mixtures through laboratory performance testing. A draindown test, a Cantabro test, a permeability test, and an indirect tensile strength test were used to evaluate the performance of OGFC mixtures. The main parameters of this research specify optimum bitumen and desirable air voids, maximum reduction of draindown and abrasion loss, and retained tensile strength ratio. It was observed that the effect of fiber in both states on bitumen percentage caused increased sensitivity to oxidation of the asphalt mixture; however, the effect of nanosilica on the reduction of sensitivity to oxidation was considerable. The effect of glass fiber in enhancing tensile strength was far higher than that of basalt fiber. In both states, nanosilica caused improved tensile strength of the mixture. Additionally, the moisture sensitivity of the OGFC mixtures with glass fiber was far better than that of the basalt fiber, and addition of nanosilica caused further improvement. The results showed a negative effect of the addition of basalt fiber alone in the asphalt mixture with a higher between percentage, necessitating the addition of nanosilica in conjunction with basalt fiber.

Nanoscaled Characteristics of Recovered Asphalt Binders from Weathered Asphalt Mixtures

Abstract The nanoscaled properties including morphology and mechanics of recovered asphalt binders from open-graded friction course (OGFC) asphalt mixtures weathered in a laboratory were measured by atomic force microscopy. In addition, specific functional groups and molecular size distributions of the recovered binders were tested by Fourier infrared spectroscopy and gel permeation chromatography (GPC), respectively. The OGFC mixtures were weathered in an accelerated weathering machine for various durations of 0, 1,000, 2,000, and 3,000 h. The results showed that (1) as the weathering degree increased, the root mean square of morphology increased, and both the number of the “bee-structures” and the adhesion decreased; (2) as the weathering degree increased, the carbonyl and sulfoxide indexes increased, whereas the butadiene-based index decreased; and (3) the large molecular size groups from GPC tests increased, whereas the small molecular size groups decreased, as the weathering time increased. The changes of the molecular size groups had fairly good linear correlations with the weathering time.

Moisture Susceptibility of Open-Graded Friction Course Mixes with EAF Steel Slag and Modified Binders

Abstract Open-graded friction course (OGFC) mixtures are sensitive to the moisture damage because of their high air void content and longer exposure to water. In the present study, moisture susceptibility characteristics of OGFC mixes in terms of tensile strength characteristics, aggregate-binder bond strength, and the raveling potential of OGFC mixtures were studied. The experimental design for this study included OGFC mixes with two different types of aggregates (natural aggregates as a main source and electric arc furnace (EAF) steel slag as a secondary source), two different types of modified binders (polymer-modified bituminous binder and crumb rubber–modified bituminous binder), and one cellulose fiber as an additive. OGFC mixes were designed with five different percentages (0, 25, 50, 75, and 100 %) of secondary aggregates as a partial replacement of main aggregates. OGFC mixes were then evaluated for moisture susceptibility through four different test methods, viz. the indirect tensile strength (ITS) or tensile strength ratio (TSR) method, wet abrasion loss (WAL) method, static immersion test method, and modified boiling test method. OGFC mixes with EAF steel slag showed higher ITS values under both dry and wet conditions compared with the control mixes with natural aggregates alone. Steel slag content, binder type, and freeze-thaw cycles had statistically significant effects on the ITS, TSR, and WAL values. Modified boiling test results showed a good correlation with the modified Lottman and WAL test results.

Experimental study on the effect of basalt and glass fibers on behavior of open-graded friction course asphalt modified with nano-silica

• The sample which has the largest permeability, had the minimum value of draindown. • The effect of glass fiber in reducing the permeability is far greater than that of the basalt. • The tensile strength of asphalt mixtures increases by adding fiber. • The effect of nano-silica in reducing abrasion and reduction of sensitivity to oxidation is considerable. Open-graded friction course (OGFC) is a mixture having gap graded aggregate which is used in pavement surfacing. Asphalt mixtures were modified by Nano silica, polymer, basalt fiber and glass fiber. A draindown test, Cantabro test, permeability test and an indirect tensile strength test and moisture susceptibility were used to evaluate the performance of OGFC mixtures. Test results revealed optimum compounds for 0.2% basalt fiber with 2% nano-silica and 4.5% Styrene-Butadiene Styrene (SBS) Polymer. The minimum air voids content of fiber-reinforced OGFC mixtures modified with nanomaterial should be 13% for 6% bitumen. The results showed the effect of nano-silica in reducing abrasion and reduction of sensitivity to oxidation is considerable and the effect of basalt fiber per 0.2% in the asphalt mixture to be greater than that of glass fiber in reducing the draindown phenomenon; and for controlling the level of draindown phenomenon, nano-silica compound should also be used with basalt fiber. It was also found that although the use of basalt fiber is more effective in decreasing draindown in comparison with glass fiber, the effect of glass fiber in reducing the permeability of the asphalt mixture is far greater than basalt fiber.

Evaluation of Crumb Rubber Modification on Specification Compliance of Asphalt Mixtures

Since 2008, the Louisiana Department of Transportation and Development (LaDOTD) has allowed the use of crumb rubber modification (CRM) as per the specifications. However, the introduction of CRM has presented unique challenges during design and production. LaDOTD districts have reported early cracking for dense-graded mixtures. Adhesion and stability issues have been reported for open-graded friction course (OGFC) and stone matrix asphalt (SMA) mixtures. Currently, LaDOTD specifications allow the contractor to switch asphalt cement supplies without redesigning the mixture. This study evaluated several CRM-modified mixture designs to address design and performance concerns; it also evaluated the volumetric and mechanistic properties of dense, SMA, and OGFC mixtures designed with unmodified asphalt cement, styrene-butadiene-styrene-modified asphalt cement and five crumb rubber sources. SuperPave volumetric parameters were evaluated to ascertain the impact of CRM on the design of these mixtures. Rutting and intermediate temperature cracking susceptibility were determined using the Hamburg Loaded Wheel Tracker (LWT) and semi-circular bend test (SCB), respectively. Solvent extraction and the ignition furnace were used to determine the asphalt content of the modified mixtures. The results showed that CRM improved the laboratory rutting resistance of the mixtures. However, the laboratory cracking resistance was decreased for the CRM-modified mixtures. Based on statistical analysis, additional asphalt content, reduced CRM dosage, and the use of polymer additives may mitigate the reduced laboratory cracking performance of the CRM-modified mixtures. The volumetric parameters were also affected by CRMs. The mixtures should be re-designed if the contractor anticipates using a CRM-modified asphalt cement.

Examining relationships between properties of weathered asphalt mixtures and nano-sized morphology of their recovered binders

The objective of this study was to examine the relationship between the properties of weathered asphalt mixtures and the nano-scaled morphology of their recovered asphalt binders. Firstly, asphalt mixtures of open-graded friction course (OGFC) were weathered in an accelerated weathering machine (AWM) and then tested for selected properties. Secondly, the asphalt binders were recovered using an Abson method and investigated for their nano-scaled morphology by an atomic force microscopy (AFM). Finally, the relationships between the selected properties of the weathered mixtures and the nano-scaled morphology of their asphalt binders were established. The results revealed that (1) the increasing height roughness and wrinkle degree of the nano-morphology of the recovered asphalt binder could be well exhibited by the increasing AFM indexes: image surface area difference (ISAD), height root-mean-square (R q) and the difference between maximum and minimum height (R max), a clear demonstration of how asphalt binder surfaces stiffen with age; (2) the cracking-resistance at low temperature, the rutting resistance and the splitting strength of the weathered OGFC mixtures decreased, while the AFM indexes of the nano-sized morphology increased as the weathering time increased; (3) There was a linear relationship between the properties of the weathered mixtures and the three AFM indexes.