Pavement Damage Due to Different Tire and Loading Configurations on Secondary Roads
Due to the large percentage of goods moved by commercial trucks and its ever-growing freight industry, the U.S. needs innovative technologies to improve the efficiency of trucking operations and ensure continuous growth of the economy. One example of such a technology is the introduction of wide-base single tires to replace conventional dual tire systems. After more than two decades of research powered mainly by the tire industry, a new generation of wide-base tire was recently introduced. Compared to the first generation of wide-base tires, these new tires offer safety and cost-savings characteristics. Despite the significant advancements achieved through previous research projects on the impact of wide-base tires on pavements, past investigations have not evaluated the damage wide-base tires cause to low-volume secondary roads. This pavement class is widely encountered in many trucking applications, although for short distances, but the impact of the new generation of wide-base tires on these pavement structures is unclear. In addition, the static uniform loading assumption used in conventional flexible pavement design methods is inconsistent with realistic tire loading conditions and may result in erroneous pavement response and damage predictions. To address these shortcomings, this research project uses a developed three-dimensional (3-D) finite element model to predict pavement responses to loading applied by various tire configurations on secondary road pavements. This model incorporates the measured 3-D tire-pavement contact stresses, hot-mix asphalt (HMA) linear viscoelasticity, continuous moving load, and utilizes implicit dynamic analysis. The impact of wide-base tires on secondary road pavement damage was analyzed using available damage models, and the results were compared to the damage from conventional dual-tire assemblies. Findings of the study suggest that due to the different contact stress distributions at tire-pavement interface, the impact of the new generation of wide-base tire (455/55R22.5) on secondary road pavements varies when compared to the impact of the conventional dual-tire assembly.
Dynamic Analysis and in Situ Validation of Perpetual Pavement Response to Vehicular Loading
A three-dimensional (3-D) finite element (FE) model was developed to predict pavement responses to vehicular loading. The model incorporates measured tire-pavement contact stresses, continuous moving wheel loading, and hot-mix asphalt (HMA) viscoelastic characteristics. The model was fine-tuned using implicit-dynamic analysis and validated using pavement response from accelerated loading. Two tire configurations (dual-tire assembly and wide-base 455 tire) and three full-depth flexible pavement designs (HMA 152 mm, 254 mm, and 420 mm) were used in both FE modeling and accelerated loading tests. The predicted and calculated strain responses at the bottom of HMA were in agreement. Most important, the study shows that vertical shear strain in the upper 76 to 100 mm of the pavement surface is critical for thick pavement and is influenced by the 3-D tire-pavement contact stresses under each tire rib. However, the tensile strain at the bottom of HMA is affected mainly by the total wheel load. The vertical shear strain is responsible for near-surface fatigue cracking as well as HMA primary rutting. Top-down cracking could result from the local vertical shear strain in the upper 25 mm of the HMA where the effect of tire-pavement tangential stresses are the highest. In addition, the study concluded that wide-base tires cause higher longitudinal tensile strain at the bottom of HMA and compressive strain at the top of subgrade, where those responses are highly affected by the total wheel load. However, wide-base tires were found to cause less vertical shear strains near the surface than dual-tire assembly loading regardless of HMA thicknesses.
Heavy metal adsorption from industrial wastewater by PAMAM/TiO2 nanohybrid: Preparation, characterization and adsorption studies
Abstract This study investigates the removal of heavy metals from industrial wastewater using TiO 2 nanoparticles modified with poly-amidoamine dendrimer (PAMAM, G 4 ). The metal ions Cu 2 + , Pb 2 + , and Cd 2 + were selected as model pollutants. FTIR, SEM, BET surface area and Zeta potential measurements, and Dispersion Observing methods have been employed for characterizing the synthetic nanohybrid and these techniques indicated that the PAMAM loaded on to TiO 2 have been favorably synthesized. The effects of several parameters including initial metal ion concentration, temperature, pH solution, the nanohybrid dosage and contact time were studied. The experimental data were analyzed using equilibrium isotherm and kinetics models. The adsorption process was studied using isotherm, kinetics, and thermodynamics models. The analysis shows that the Langmuir isotherm and pseudo-second-order kinetics are appropriate models for the adsorption process. The thermodynamic parameters illustrate that the absorption is endothermic and spontaneous. The findings suggest that the nanohybrid is a good super absorbent for the removal of heavy metals from industrial effluents.