Thermodynamic‐based model for coupling temperature‐dependent viscoelastic,viscoplastic, and viscodamage constitutive behavior of asphalt mixtures

Based on the continuum damage mechanics, a general and comprehensive thermodynamic‐based framework for coupling the temperature‐dependent viscoelastic, viscoplastic, and viscodamage behaviors of bituminous materials is presented. This general framework derives systematically Schapery‐type nonlinear viscoelasticity, Perzyna‐type viscoplasticity, and a viscodamage model analogous to the Perzyna‐type viscoplasticity. The resulting constitutive equations are implemented in the well‐known finite element code Abaqus via the user material subroutine UMAT. A systematic procedure for identifying the model parameters is discussed. Finally, the model is validated by comparing the model predictions with a comprehensive set of experimental data on hot mix asphalt that include creep‐recovery, creep, uniaxial constant strain rate, and repeated creep‐recovery tests in both tension and compression over a range of temperatures, stress levels, and strain rates. Comparisons between model predictions and experimental measurements show that the presented constitutive model is capable of predicting the nonlinear behavior of asphaltic mixes under different loading conditions. Copyright © 2011 John Wiley & Sons, Ltd.     

Ficus benjamina leaves as indicator of atmospheric pollution: a reconaissance study

We present a diagnostic study to evaluate the suitability of Ficus benjamina tree leaves as a captor of heavy metal particles from atmospheric dusts in urban areas. Leaf samples were taken at 16 localities within three areas in Morelia, state of Michoacán (Mexico??s medium size city, 830000 inhabitants). Measurements of magnetic susceptibility were conducted to determine the magnetic enhancement using samples from green, relatively unpolluted area, as a reference. The samples collected at areas with heavy traffic (main avenues) yielded values almost ten times higher than the values obtained for the unpolluted reference. Isothermal Remanent Magnetization curves are proportional to the degree of pollution. Associations of almost pure magnetite with heavy metals were revealed by scanning electron microscope.     

Goodness-of-fit tests for the spatial spectral density

Detection and modeling the spatial correlation is an important issue in spatial data analysis. We extend in this work two different goodness-of-fit testing techniques for the spatial spectral density. The first approach is based on a smoothed version of the ratio between the periodogram and a parametric estimator of the spectral density. The second one is a generalized likelihood ratio test statistic, based on the log-periodogram representation as the response variable in a regression model. As a particular case, we provide tests for independence. Asymptotic normal distribution of both statistics is obtained, under the null hypothesis. For the application in practice, a resampling procedure for calibrating these tests is also given. The performance of the method is checked by a simulation study. Application to real data is also provided.     

Thermal expansion on volcanic tuff rocks used as building stones: examples from Mexico

Three cities in the center of Mexico, declared as cultural heritage, were erected mainly of volcanic tuffs as main construction element. Many of the historic buildings of these cities show significant damage and deterioration. One of the causes of these damages can be attributed to a phenomenon poorly studied in volcanic tuffs, the thermal expansion. To understand the response of volcanic tuffs to thermal expansion, as well as to know their thermal expansion coefficient, thermal expansion test was performed on 12 representative tuffs of these localities. In the same way and to know which of their petrographic, petrophysical, mineralogical, and geochemical properties influence this phenomenon, several laboratory studies were carried out to determine which of these plays an important role in the expansion. The results of our tests showed that volcanic tuffs rocks have very varied thermal expansion values, ranging from 0.7 mm/m at their maximum expansion to even contraction in the order of ??0.5 mm/m. Equally varied were the thermal expansion coefficient values ranging from 10.1 to ??7.2 10^?6/K. The most dominant behavior type is the “anisotropic no residual strain behavior”. In general, the behavior of the tuffs in practically all the tests carried out showed a very important heterogeneity in the rocks; however, in spite of the non-homogeneous behavior of the tuffs, three main factors could be identified that play an important role in the thermal expansion of the studied rocks, the chemical composition, e.g., acid volcanic tuff rocks (rhyolitic composition) had greater expansions, while the more basic rocks (basaltic composition) expanded less, the textural and fabrics homogeneity, e.g., the most homogeneous rocks texturally have higher expansion values and the degree of crystallinity, and, e.g., the tuff rocks with the largest amount of glass showed smaller thermal expansions than the tuffs composed of microcrystals.     

GIS-based DRASTIC model for groundwater vulnerability and pollution risk assessment in the Peshawar District,Pakistan

Groundwater is the most economic natural source of drinking in urban and rural areas which are degraded due to high population growth and increased industrial development. We applied a GIS-based DRASTIC model in a populated urban area of Pakistan (Peshawar) to assess groundwater vulnerability to pollution. Six input parameters—depth to phreatic/groundwater level, groundwater recharge, aquifer material, soil type, slope, and hydraulic conductivity—were used in the model to generate the groundwater vulnerable zones. Each parameter was divided into different ranges or media types, and ratings R?=?1?–?10 were assigned to each factor where 1 represented the very low impact on pollution potential and 10 represented very high impact. Weight multipliers W?=?1?–?5 were also used to balance and enhance the importance of each factor. The DRASTIC model scores obtained varied from 47 to 147, which were divided into three different zones: low, moderate, and high vulnerability to pollution. The final results indicate that about 31.22, 39.50, and 29.27% of the total area are under low, moderate, and high vulnerable zones, respectively. Our method presents a very simple and robust way to assess groundwater vulnerability to pollution and helps the decision-makers to select appropriate landfill sites for waste disposals, and manage groundwater pollution problems efficiently.     

Meteorite impacts in the ocean: the danger of tsunamis on the coast of Buenos Aires Province,Argentina

Natural Hazards - Comets, meteorites, or asteroids impacting against the Earth are not unusual events. Such impacts on the ocean could produce tsunamis which can reach coastal areas. This paper...