Rollover is defined as a moving vehicle’s abrupt loss of the trajectory of the center of gravity. In horizontal curves, it refers to overturning by an unbalance of the lateral acceleration. The likelihood that this turnover occurs can be estimated by studying the static rollover potential, which is calculated with lateral acceleration thresholds that, when being exceeded, make the vehicle to suffer a rollover. These models consider the geometry of the vehicle, the road and operating speed, and sometimes the vehicle’s suspension system. This approach is suitable for analyzing the rollover potential of individual vehicles, but it is not very practical when analyzing vehicle fleets driving at operating speeds that follow a probability distribution according to the geometrical conditions of the environment and the type of vehicle. This work analyzes the rollover phenomenon through a probabilistic approach based on the reliability theory, which allows estimating the rollover risk considering random variables. It applies the Hasofer-Lind First-Order Reliability Method to calculate the rollover probability, based on the geometry, type of vehicle, and operating speed when taking horizontal curves. Additionally, it discusses three rollover calculation methods and presents the reliability theory concepts used herein. This paper describes the construction of limit state functions, experimental design, input data, and the failure probability curves for 4 types of vehicle and 3 input speeds. It was concluded that it is not recommendable to use a horizontal curve radius of less than 170 m, especially because heavy vehicles run the risk of suffering rollover.
Asphalt mixes with Reclaimed Asphalt Pavement (RAP) offer many advantages when reusing this material. But without the adequate treatment, these mixtures present durability problems due to the material’s loss of properties over time. The use of copper slag can reduce these problems through its physical-chemical properties, such as highly angular characteristics, lime content in its composition and low silica content, while contributing with friction and strong adhesive characteristics. On the other hand, the amount of copper slag stockpiles and their associated lixiviation are also reduced. This work presents the results obtained in asphalt mixes with RAP percentages from 0 to 40%, combined with copper slag percentages ranging from 0 to 35%. Sixteen (16) combinations of materials were used to prepare Marshall specimens in order to carry out stability and flow tests, indirect tensile strength tests and resilient modulus by diametral compression. The use of copper slag improves the performance of asphalt mixes with RAP. With 15% copper slag amounts by mass, the stability and flow values are stabilized, thereby improving the Marshall stiffness index. The values for indirect tensile strength and resilient modulus with RAP percentages over 20% are also improved, especially in mixtures with high RAP percentage (40%). These results favor the use of RAP in applications that require more demanding parameters.
In Chile, the selection of asphalt binders is based on traditional specifications. Although the Superpave specification has not been implemented yet, it was consider important to make a zoning process of the Chilean territory according to this methodology. This activity relied on the information of 94 weather stations of the Chilean Meteorological Service (DMC in Spanish) and Chile’s Water Department (DGA in Spanish), which have reliable data for a minimum of 20 years. Weather data, together with the Köppen climate classification for Chile and the topography of our territory, were used to define approximate zones where the use of each type of asphalt binder is appropriate. Zoning data indicate that most of our territory can be covered by three types of asphalt binders: for the northern and southern regions the use of PG 58-28 is recommended; the central region requires PG 64-22; and finally, the Patagonia and high mountain zones need PG 52-34. In the IX Region, there is a small area in the Andean foothills, where PG 64-34 is required, according to the available climate information and the methodology applied. Classifications PG 64-22, PG 58-28 and PG 52-34 are traditional binders, which were zoned for high-speed traffic conditions and moderate traffic volume.
For many decades, studies have addressed the development of plastic strains in flexible pavements. Currently, there are models available that allow predicting this type of failure, and it is a common practice to include them in the structural design of pavements. However, variables required for this prediction are complex and difficult to obtain on site; therefore, they are not easy to apply in the diagnostic process. The measurement of deflections is a structural evaluation method for flexible pavements, whose value may include the competence of the pavement as a whole. This research seeks to correlate deflection data on the pavement’s surface with probable plastic strains over time, and to use this prediction to calculate the pavement’s remaining service life, with the criterion of maximum rutting allowed. Real-scale data from 4 different lanes were tested by the National Laboratory of Materials and Structural Models of the University of Costa Rica. The proposed model was able to predict future rutting using as input the thickness of the pavement structure, the surface deflection measured at loads of 40 kN, and the equivalent axle repetition; a high goodness of fit was achieved. The rut level estimate should help maintenance and rehabilitation policies of the road management system to be assessed and applied at the right time.
Complex emergent and adaptive systems raise modeling challenges that cannot always be faced through mathematical modeling. The agent-based simulation is a simulation technique of socio-technical systems that allows modeling the interactions among agents, thereby offering an emergent alternative to the development of road infrastructure management systems. Road infrastructure management is a socio-technical system similar to open and adaptive systems, because there is interaction among the agents (state, private and public); it needs to consider the variability through the risk inclusion and it induces externalities that modify the system’s initial conditions. This paper discusses the agent-based simulation and how it can be used for designing road asset management systems. Therefore, a generic model is proposed, based on the existing literature, in order to characterize the types of agents involved. A plan is also discussed to include the risks in the infrastructure asset management under the agent-based simulation system. It was concluded that this modeling approach allows incorporating the effect of the agents’ decisions on maintenance planning, and the same time it has enough flexibility to include other effects, such as uncertainty and risk, considering that an asset management system is an open socio-technical system and not necessarily a closed mechanistic system.
Reducing the temperatures in the production of asphalt mixes is currently one the most important challenges in the field of road engineering. This paper studies one the latest technologies applied in the manufacture of warm mix asphalt, called super stabilized emulsion. The application of mixing and compacting procedures for hot mix asphalt to this type of warm mixes, was studied. Additionally, physical and mechanical properties of the mixes with super stabilized emulsion were compared with hot mix asphalt. It was concluded that the most appropriate manufacturing method for these warm mixes includes the use of a gyratory compactor. The properties of warm mixes were different than those of hot mixes, however, they were within adequate ranges.
PDF
(1MB)
PDF
(3MB)
HTML
(41KB)
