Effect of bitumen characteristics obtained according to EN and Superpave specifications on asphalt mixture performance in low-temperature laboratory tests
The paper aims to identify those characteristics of bitumen which have the greatest impact on asphalt mixture low-temperature performance. It was observed that stiffness and m-value of bitumen from BBR test were moderately related to stiffness and m-value of asphalt mixture obtained from 3 PB test. Simultaneously those rheological properties significantly impact on cryogenic stresses induced during TSRST test. The multiple regression model was developed and it implied that mixture failure temperature depends both on rheological properties, brittle fracture and content of bitumen, what means that only comprehensive assessment of bitumen properties enables reasonable assessment of its low-temperature performance.
The influence of combination of binding agents on fatigue properties of deep cold in-place recycled mixtures in Indirect Tensile Fatigue Test (ITFT)
The publication presents fatigue properties of cold recycled mixtures for eight combinations of binding agents (cement and bituminous emulsion). Cold recycled mixtures were evaluated in Indirect Tensile Fatigue Test (ITFT) at the temperature of 20 C in controlled stress mode. As a function of horizontal stress, fatigue life is strongly influenced by combination of the binding agents. When fatigue life is analyzed as a function of initial horizontal strain, the difference between different combinations decreases. In all cases, the influence of a specific binding agent is more visible for combinations with lower total amounts of the two agents.
The phenomenon of vehicle overloading—illegal exceeding of maximum legal weight of vehicles, is a serious problem both in developing and developed countries around the world. Overloaded vehicles occur less frequently in comparison to properly loaded vehicles but due to their greater potential to cause damage they significantly contribute to distress of pavement structure. As studies show, the number of overloaded vehicles increases when the control of traffic is insufficient. Weigh in Motion (WIM) systems significantly improve control level and contribute to decrease in the number of overloaded vehicles. Data delivered from WIM were used to perform statistical analysis of vehicle overloading in Poland. The average percentage of overloaded vehicles (OV) in Poland varies from 5% for roads with high enforcement level to 23% for roads where control is poor. Every weighed vehicle was considered in terms of exceeding maximum legal gross weight and maximum legal axle load. For each vehicle separately truck equivalency factors were calculated. Subsequently the relationship between average values of truck equivalency factors and percentages of overloaded vehicles was found. This relationship was used as a basis to determine the impact of overloaded vehicles on decrease in fatigue life of pavement structure (DFL) and increase factor IF, which expresses the extension of service period. It was proved that reduction of overloaded vehicles from 23 to 5% will contribute to increase in service period of pavement structures by factor 1.5. The life cycle cost analysis (LCCA) was performed for two levels of overloading OV = 23% and OV = 5%. The paper revealed that improvement of vehicle control and reduction of the percentage of overloaded vehicles from 23 to 5% will cause the reduction of whole life cost borne by road authority by 11%. 1 Introduction
Asphalt concrete subjected to long-time loading at low temperatures – Deviations from the time-temperature superposition principle
The article presents the observed deviations from the time-temperature superposition principle of asphalt concretes, tested in the bending beam creep test at low temperatures for a long time of loading. In almost all tested asphalt concretes, deviations appeared after 500 s of loading at the temperature of -10 C. Some types of bitumen presented deviations at other temperatures – usually the harder the grade of the bitumen, the higher was the temperature of appearance of deviation. The article investigates also the impact of the following factors on the described deviations: type of bitumen, assumed time of loading and level of loading.
The statistical impact of experimental result scatter of asphalt mixtures on their numerical modelling
The paper presents selected test results of asphalt mixture conducted in low temperatures. The obtained parameters are highly diverse. It concerns ultimate breaking loads, stiffness parameters related to Young's modulus but also the fracture course. Statistical analysis upon the results makes it possible to relevantly estimate the material-defining parameter values. Such a random approach leads to the mean values of breaking and fracture-triggering loads, dealing with their dispersion too. The estimated parameters allow to form appropriate numerical models of asphalt mixture specimens. This type of analysis supports the laboratory tests. The paper presents the authors' simplified model considering non-uniform material features. The results reflect the scatter of real laboratory test outcomes. In order to do so an algorithm to calibrate the numerical model parameters was created.