Ali Topal

Porous asphalt (PA) is a type of pavement with an open-graded aggregate that contains higher air voids than the conventional asphalt pavements after compaction, which allows precipitation waters to infiltrate from the pavement surface to the lower layers. The particle loss in the wear layer causes surface deterioration, which affects pavement performance. In addition, the porosity nature of porous asphalt leaves the pavement under the effect of air and water continuously, which accelerates the oxidation rate and affects the surface properties of the pavement. Moreover, these factors can affect the bitumen-aggregate bond strength and cause cohesion degradation within the asphalt film, causing the bitumen to peel from aggregate. The performance of porous asphalt, particularly strength and durability, is greatly affected by compaction temperature. Higher compaction temperatures can reduce the air voids of the mix, so the required mix densities may not be achieved. In this study, the particle loss of porous asphalt samples prepared at 3 different compaction temperatures by using unmodified bitumen, SBS®, Elvaloy®, and Sasobit® modified bitumen was investigated and the optimum mixing and compaction temperature was determined.

The scope of this study was to assess the predicted impact of design factors (voids percentage (V_a), effective binder content (V_be) and aggregate gradation) in each asphalt concrete (AC) layer on pavement performance for conditions in Izmir, Turkey. Research was conducted on three flexible pavement structures for three traffic levels and three subgrade types using AashtoWare Pavement ME Design software. The results indicated that increasing V_be (from 8% to 15%) and V_a (from 3% to 5%) in the wearing course resulted in, respectively, almost 1.0 mm and 0.2 mm increases in AC rutting depth, 17 m/km and 145 m/km reductions in thermal cracking length and a 55.8 m/km decrease and 85 m/km increase in top-down cracking length. For the binder course, an increase in V_be (from 7% to 14%) and V_a (from 4% to 6%) led to, respectively, nearly 1.0 mm and 0.3 mm increases in AC rutting depth and a 35 m/km increase in top-down cracking length. For the AC base course, an increase in V_be (from 6% to 12%) and V_a (from 5% to 6%) resulted in a 26.3% reduction and 14.2% increase in alligator cracking area, respectively. An increase in the fine aggregate percentage and a decrease in the coarse aggregate gradation in the hot-mix asphalt mixture led to improved performance.

Bu çalışma kapsamında İzmir’de yer alan 4 ışıksız kavşaktan toplanan verilerden yararlanarak, farklı manevralar için bağıntılar geliştirilmeye çalışılmıştır. Çalışmada, kritik aralık kabul değerinin, düşük ana yol hacim değerleri altında önemli oranda değişkenlik gösterdiği; ancak ana yol trafik akımı yüksek değerlere ulaştığında sürücülerin daha kısa aralıkları kabul ettikleri görülmüştür. Aralık kabul değerinin belirlenmesinde, kavşağa giriş yapacak sürücünün manevrasından daha çok; uygun aralık bulmaya çalıştığı manevranın daha etkin olduğu görülmüştür. Çalışmanın bir diğer çıktısı da, özellikle düşük ana yol trafik akımı etkisi altında sürücü davranışlarının daha etkili olduğu ve davranış farklılıklarının modele katılmasıyla sahada gözlemlenen değerlere daha sağlıklı biçimde ulaşılabileceği anlaşılmıştır.

Asphalt pavements are amongst the most recycled materials in the contemporary world depending on the environmental and financial advantages. The introduction of Recycled Asphalt Pavement (RAP) on newly produced asphalt pavement is possible by the utilization of rejuvenating agents, which should contain oily fractions. For this purpose, within the scope of this study, three types of agents with optimum amounts (by weight of bitumen) were utilized 5.4% Waste Engine Oil (WEO), 5.1% Waste Vegetable Oil (WVO), and 6.8% Commercial Rejuvenating Agent (CRA). The highest applicable RAP content in mixtures depends on the rejuvenator type determined by Marshall Mix Design tests (air voids, flow, and stability). Rejuvenation facilitated the use of 50 to 60% of additional RAP material in the mixtures depending on the rejuvenator type. Indirect Tensile Strength (ITS) test results declared that RAP mixtures, when subjected to the rejuvenation process, resulted in relatively less brittleness and enhanced durability properties compared to the unmodified ones. Additionally, cost comparison analyses demonstrated encouraging results as the cost-benefit ratio exceeded up to 55% for mixtures involving high percentages of rejuvenated RAP. As a final analysis, Return on Investment (ROI) values were calculated for each rejuvenator type by the cost of upgrading the facility to handle RAP and the profit of RAP usage. Consequently, ROI was calculated as a return time in months, which unveils an extremely profitable opportunity in the industry.

The response of asphalt material depends on the rate of loading and varies from elastic to plastic. Therefore, the behaviour of flexible pavement would also be different along the entire length of a road because of truck speed changes due to the existence of police checkpoints, bus stations, speed bumps, intersections, horizontal and vertical curves, and climbing lanes. The objective of this study is to investigate the effect of truck speed on the performance of flexible pavement. Thus, analyses were conducted for various truck speeds (1–75 km/hr) on three different pavement structures and three traffic levels using AASHTOWare Pavement ME Design 2.5.5 for the local conditions of Izmir, Turkey. The analysis results of the study manifested that a reduction in traffic speed (75–1 km/hr) on a road resulted in higher pavement distress. According to the results, reducing truck speed from 25 to 1 km/hr resulted in a rapid increase in AC rutting, alligator cracking and top-down cracking by 13.3 mm, 10.6% and 1473.8 m/km, respectively. It is expected that the outcomes of this study would promote the local calibration of the mechanistic-empirical pavement design guide (MEPDG) and pavement design in Turkey and the region.

In recent years, studies on porous asphalt have gained more importance and countries are conducting various studies in order to improve the engineering properties of this type of pavement. As a result of these studies, each country developed its own standard and therefore different optimum bitumen content (OBC) determination methods emerged. This paper investigates the determination of the optimum bitumen content of porous asphalt samples prepared by using different aggregate types and polymers by the methods implemented in Turkey and in other countries. The results have shown that the application of each method yielded different bitumen content.

In this study, halloysite and sepiolite nanoclays were used to reinforce SBS modified bitumens. The nanoclays used are different from the materials in the literature and have properties such as easy to find, economical and available from local sources. The mixing parameters were determined before production process. The polymer additive SBS was added into base bitumen at 3% and 5%, the nanoclay additives were added into polymer modified bitumen at 2% and 4% ratios. The morphological structures were investigated under fluorescence microscope. Physical and rheological properties of the samples were compared. The phase separation cases were investigated by storage stability test. Furthermore, rutting performance of samples was measured with zero shear viscosity (ZSV) and multi stress creep recovery (MSCR) test methods.

Developing countries like Turkey are trying to implement the Mechanistic-Empirical Pavement Design Guide (MEPDG). The implementation of this method requires comprehensive local data collection, evaluation, and, if necessary, a local calibration. The objective of this study is to prepare local data such as climate, traffic, and materials for evaluation and local calibration of MEPDG for Izmir City. For this purpose, the climate and traffic data were obtained, analysed, and converted to the MEPDG format. Besides, the bound and unbound pavement material properties were determined. Since some of the obtained local data like climate, vehicle classification, traffic growth factor, and axle load distribution cannot be directly used as design inputs, they were developed and converted to a suitable format to be used in the MEPDG. The output of this study can be used as design inputs for the evaluation and local calibration the MEPDG in Izmir and serves as a guide for data preparation for other parts of the country.

The determination of mixing and compaction temperatures through the Equiviscous method has been defined as the standard method and it is designed for the base bitumen (unmodified bitumen) based on the viscosity measurements. The implementation of the Equiviscous method for the modified bitumen resulted in high mixing and compaction temperatures which may not be required during the construction of the asphalt mixtures. This study aims to investigate several alternative methods proposed in the literature named as high shear rate method, zero shear viscosity method, steady shear flow method, and phase angle method. Besides, the obtained mixing and compaction temperatures results are compared with the standard (equiviscous) method. For this purpose, 50/70 penetration grade bitumen modified with 5 % elastomeric type – Styrene Butadiene Styrene (SBS), and 1.5 % Reactive Elastomeric Terpolymer type – Elvaloy (RET) has been used. The study also aims to measure the applicability of the proposed alternative methods for the warm mix asphalt involving organic and chemical additives. The results have shown that for the polymer modified bitumen, the application of all proposed methods in the literature resulted in lower mixing and compaction temperatures compared to the Equiviscous method. While for the warm mix asphalt, the implementation of the steady shear flow method resulted in lesser temperatures compared to the Equiviscous method.