No abstract

No abstract

Some of the newly constructed highway pavements in the Kingdom of Saudi Arabia have shown premature failures with consequential negative impacts on both roadway safety and economy. A major type of these failures is permanent deformation (rutting). Fillers were suspected to be major contributors to rutting susceptibility. The effect of filler type and content on the rutting potential of asphalt concrete as well as other mixes properties was investigated. The wheel tracking test (LCPC) was employed to investigate susceptibility of these mixes to rutting. The mechanical properties of mixes were studied using tests such as resilient modulus, indirect tensile strength, Hveem stability and Marshall criteria. Results of this study indicate that partial replacement of limestone dust by hydrated lime or portland cement aggravates resistance of the mixes to rutting. Furthermore, an analytical model was developed for predicting rutting potential based on various mixes properties.

Polymer modification is extensively used in the Kingdom of Saudi Arabia (KSA) because the available asphalt cement does not satisfy the high-temperature requirements. It was widely used in KSA for more than two decades, and there is little information regarding the differences in the performance of different polymers approved for binder modification. Pavement engineers require performance comparisons among various polymers to select the best polymer for modification rather than make their selection based on satisfying binder specifications. Furthermore, the mechanical properties can help select polymer type, producing mixes of better resistance to specific pavement distresses. The study objective was to compare the mechanical properties of the various polymer-modified asphalt (PMA) mixtures that are widely used in the Riyadh region. Control mix and five other mixes with different polymers (Lucolast 7010, Anglomak 2144, Pavflex140, SBS KTR 401, and EE-2) were prepared. PMA mixtures were evaluated through different mechanical tests, including dynamic modulus, flow number, Hamburg wheel tracking, and indirect tensile strength. The results show an improvement in mechanical properties for all PMA mixtures relative to the control mixture. Based on the overall comparison, the asphalt mixture with polymer Anglomk2144 was ranked the best performing mixture, followed by Paveflex140 and EE-2.

This paper presents a systematic approach for the synthesis, selection, design, and optimization of methanol plants. A metaheuristic optimization approach is proposed to reconcile the economic and environmental objectives of the process while incorporating simulation tools for the reliable modeling of the generated alternatives. In addition to shale/natural gas as the primary feedstock, CO 2 utilization is considered. Nine different configurations were synthesized, analyzed, and optimized. The optimization variables included the structural configurations as well as design and operating variables such as flowrates, temperatures, and pressures. The model is a multiobjective problem involving economic and environmental objectives. The economic objective function consists of maximizing the net profit. The environmental objective function is aimed at minimizing the total annual CO 2 emissions. To perform the optimization of this problem, process data were obtained from the chemical process simulation software Aspen HYSYS. The used stochastic optimization algorithm was an improved multiobjective differential evolution. A client−server interface based on Component Object Module technology using Excel-Visual Basic for Applications scripts was developed to call the Aspen HYSYS simulator repetitively for various sets of input variables. The results offer attractive options for both the economic and the environmental objectives.