Evaluating the Effects of Using Recycled Asphalt Pavements on Fatigue Properties of Warm Mix Asphalt

This paper presented an experimental study to characterize thestiffness modulus and fatigue life of warm mix asphalt mixturecontaining recycled asphalt pavements (RAP) with and withouta rejuvenating agent. For this purpose, warm mix asphaltswere produced using Sasobit and Asphamin as two of the mostcommon additive materials. The following five mixes were preparedand tested: a mix with 30% RAP, two mixes with 30%RAP plus warm mix asphalt additives, and two mixes with 30%RAP plus warm mix asphalt additives and a rejuvenating agent.The results indicated no significant difference in the stiffnessmodulus of warm mix asphalt mixtures containing RAP andconventional mixtures including recycled asphalt pavement.However, the indirect tensile fatigue test results showed thatthe addition of the warm mix asphalt additives and rejuvenatingagent improved the fatigue life of the mixtures at differenttemperatures

R-curve behavior and crack propagation properties of asphalt concrete at low temperatures

Fracture properties and crack propagation characteristics of asphalt concrete mixtures were studied by obtaining fracture resistance curves using three point single edge SE(B) notched beam specimens. Elastic-plastic approach is used in the calculation of the J-integral since the fracture process zone size is large enough to not use a linear elastic approach. Crack length measurements were obtained directly from high resolution images taken during the tests. A rising R-curve was observed in all the specimens which indicates ductility and a toughening mechanism in the ductile to quasi-brittle fracture of the mixture. Mixtures developed by limestone and siliceous aggregates with 4%, 4.5% and 5% binder contents were tested at temperatures ranging from +5ºC to –20ºC. Mixtures with 5% binder content showed greater crack resistant behavior at each temperature. Crack lengths at which crack propagation instability occurred were decreased by the reduction of temperature. A significant drop of this critical crack length is observed in temperatures below –15ºC. As well, the elastic-plastic fracture toughness is increased by the reduction of temperature up to –15ºC and starts to diminish thereafter

Studying Non-coaxiality in Non-lane-based Car-following Behavior

In this paper, in order to study non-lane-based car-following, the non-coaxiality concept is defined, where there is a significant lateral difference between the leader and follower vehicle. Two main reasons for non-coaxiality were addressed by drivers in the interview: providing more visible distances beyond leader vehicle and increasing the possibility of escaping in sudden brakes to avoid rear-end collision. Results showed that non-lane-based behavior was due to the effect of the existence of other cars in the traffic flow. By reducing speed or increasing density, vehicles more affect each other.  But this trend will continue up until vehicles fill the free spaces. In other words, vehicles make others stick to the leader’s path in high-density flow. Studying the relationship between lateral distance and time headway demonstrated that time headway threshold for initiation of car-following behavior in Iranian drivers can be approximately 2 seconds. In this study, Overtaking was defined as a part or continuation of the non-lane-based driving behavior. For overtaking on the left, steering angle, the final lateral distance and the lateral speed difference between the follower and leader were 33%, 28% and 15% less than overtaking on the right

A study on following behavior based on the time headway

While time headway (TH) is a relatively simple variable and has been well researched, it has been less explored in non-lane-based traffic. The main aim of this paper is considering lateral distance in studying TH in a non-lane-based traffic flow. In this study driving behavior, speed-TH relationship, and the following threshold by using only TH in a non-lane-based flow were investigated. In a novel approach, THs were segmented into five intervals in a step by step manner from smallest to largest THs. Considering lateral distance led to divide driving behavior into intervals (based on the average TH), including: Unsafe (0-0.7 sec), non-lane-based car-following (0.9 sec), lane-based car-following (1.0 sec), overtaking TH (1.3 sec), and free driving (larger than 2.5 sec). It was founded that the TH of starting overtaking maneuver can be a good criterion to distinguish between following and free driving behavior. Also, in lane-based car-following behavior, when lateral distance between the following and preceding vehicles was not considerable, the smallest THs were seen. It has happened around the average speed of the flow as the driver may adopt lower THs because of the tendency to overtaking. Linear relationship was found between TH and lateral distance in non-lane-based car-following conditions. TH of non-lane-based behavior is less than lane-based and smaller THs would force drivers to apply lateral distance or vice versa

The effects of using recycled concrete on fatigue behavior of hot mix asphalt

Fatigue cracking is the main form of structural damage in flexible pavements. Under the action of repeated vehicular loading, deterioration of the asphalt concrete materials in pavements caused by the accumulation and growth of the micro and macro cracks gradually takes place. The results of a laboratory study evaluating the fatigue properties of hot-mix asphalt (HMA) mixtures using indirect tensile fatigue test (ITFT) were investigated in this paper. The HMA mixtures containing 0%, 35%, 70%, and 100% of recycling concrete aggregate (RCA) were plant prepared with one source of aggregate, limestone, and one type of binder, 60/70-penetration grade. In this paper, it is shown that the use of recycled concrete produced by crushing demolished concrete elements can increase the efficiency of asphalt mixes, reduce primary production costs and prevent much fullness of the recycled materials in the environment. It was found that replacing up to 100% of the virgin aggregate by RCA improved the fatigue properties of the asphalt mixtures

A new method to determine maintenance and repair activities at network-level pavement management using falling weight deflectometer

Pavement condition assessment at network level requires structural evaluation that can be achieved using Falling Weight Deflectometer (FWD). Upon analysing FWD data, appropriate maintenance and repair methods (preser­vation, rehabilitation or reconstruction) could be assigned to various pavement sections. In this study, Structural Condi­tion Index (SCI), defined as the ratio of Effective Structural Number (SNeff) to Required Structural Number (SNreq), was used to determine if a pavement requires preservation or rehabilitation works (i.e. preservation SCI > 1, rehabilitation SCI < 1). In addition to FWD deflection data, SCI calculation requires pavement layer thicknesses that is obtained using GPR with elaborated and time consuming works. In order to reduce field data collection and analysis time at network-level pavement management, SCI values were calculated without having knowledge of pavement layer thicknesses. Two regression models were developed based on several thousand FWD deflection data to calculate SNeff of pavements and resilient modulus (MR) of their subgrades. Subgrades MR values together with traffic data were then used to calculate SNreq. Statistical analysis of deflection data indicated that Area under Pavement Profile (AUPP) and the deflection at distance of 60 cm from load center (D60) parameters showed to have strong correlation with SNeff and MR respectively. The determination coefficients of the two developed models were greater than those of previous models reported in the literature. The significant result of this study was to calculate SNeff and MR using the same deflection data. Finally, imple­mentation of the developed method was described in determining appropriate Maintenance and Repair (M&R) method at network level pavement management system

Rheological properties of bitumen modified with a combination of FT paraffin wax (sasobit®) and other additives

Fischer–Tropsch paraffin Sasobit® is a popular Warm Mix Asphalt (WMA) modifier applied to improve physi­cal and rheological properties of bitumen. Although there are a number of studies investigating the effects of sasobit on bitumen properties, little has been carried out on evaluation of bitumen modified by sasobit along with other additives. In this study, sasobit modified bitumen is used as the base condition and four common modifiers namely anti-stripping agent, Crumb Rubber (CR), Styrene–Butadiene–Styrene (SBS) and Polyphosphoric Acid (PPA) are added separately to the FT – Wax modified bitumen to evaluate the compatibility of these additives with sasobit. Morphological, rheological and physical properties of modified binders are studied using Fourier Transform Infrared Spectroscopy (FT-IR), Scan­ning Electron Microscopy (SEM), Dynamic Mechanical Analysis (DMA), Bending Beam Rheometer (BBR) alongside with conventional tests. Results show that although anti-stripping agent reduce bitumen viscosity and mixing/compac­tion temperatures of asphalt mixtures, it has significantly increased the stiffness of sasobit modified bitumen at low temperatures. Among all, sasobit and crumb rubber combination exhibited the best performance, especially at low and intermediate temperatures

Characterization of permanent deformation resistance of precipitated calcium carbonate modified asphalt mixture

Rutting in asphalt pavements that appears as an indentation in the longitudinal direction continues to create problems for pavement agencies. This paper presents the results of the laboratory study on rutting susceptibility of asphalt mixtures containing Precipitated Calcium Carbonate (PCC) coated by a thin layer of a polymeric compound. To assess the impact of PCC on rutting properties of HMA, control mixtures (without PCC) and mixtures containing PCC were tested using dynamic creep and indirect tensile stiffness modulus tests. The HMA mixtures containing 0%, 5%, 10%, and 15% of PCC were prepared. In this paper, it is shown that the use of PCC can decrease the rutting potential of asphalt mixes. According to the results obtained in this study; using a 5% PCC in HMA is acceptable for heavy traffic volume roads especially in tropical regions

Studying the effect of fatigue and sleepiness of long-haul truck drivers on road accidents by adopting structural equation models analysis

The significant increase in transportation and heavy vehicle traffic has caused freeway routes with heavy traffic to face a decrease in safety levels. Furthermore, fatigue and sleepiness are proven to be two of the main reasons of road accidents, and therefore focus on these issues is crucial. Factors such as “use of engineering (safety) technology for road transport”, “informing the drivers on various educational methods”, “controlling the drivers’ work hours”, “use of different routes (alignment inconsistency)” and “observing the drivers’ mental health” should be approached to reduce the accidents caused by fatigue and sleepiness. Given the complex interrelationships between these variables and the number of road accidents, structural equation modelling has been used in this study to estimate the effect and relationships between multiple variables. Data were collected during a 5-month period by interviewing heavy vehicle drivers (2765 filled-out questionnaires). The Confirmatory Factor Analysis (CFA) has also been used to ascertain the validity of the questionnaires. The mentioned factors affecting the drivers’ fatigue were analyzed using SPSS 24.0 package, which allowed ascertaining that the drivers’ mental health is the factor of greater influence on road accidents caused by fatigue and drowsiness. Therefore, actions to improve the drivers’ mental and emotional health (by improving the currently used engineering (safety) technology and alignment inconsistency) should be enhanced rather than excessive controls on the drivers’ work hours by using GPS, work papers and inspections