Master of Science / Department of Civil Engineering / Mustaque Hossain / A recent study at Kansas State University has shown that asphalt producers in Kansas are producing hot-mix asphalt (HMA) mixtures with lower asphalt contents than those in the job-mix formula. These drier mixtures are thought to be susceptible to moisture. This project evaluated the effect of asphalt content on rutting and moisture resistance of HMA. Two different mixtures and four varying asphalt contents, optimum and lower, were selected. Another large-size mixture with four varying asphalt contents was also studied. The Hamburg Wheel Tracking Device (HWTD)test (TEX-242-F) and the Kansas Standard Test-56 (KT-56), or modified Lottman test, were used to predict moisture damage and rutting potential of these mixes. All specimens tested were prepared with the Superpave gyratory compacter. Results of this study showed the drier mixtures performed better in rutting and were less susceptible to moisture.Asphalt content significantly affects the number of wheel passes in the HWTD test. The study also revealed a weak correlation between asphalt film thickness and performance test results. Thus, the effect of varying asphalt content is nonconclusive from a durability point of view. However, performance simulations using a theoretical model show that very dry mixes in asphalt pavements are likely to have shorter performance lives.

Asphalt mix design includes the determination of a gradation, asphalt content, other volumetric properties, the evaluation of mechanical properties and moisture damage potentials. In this study, a computational method is developed to aid mix design. Discrete element method (DEM) was used to simulate the formation of skeleton and voids structures of asphalt concrete of different gradations of aggregates. The optimum gradation could be determined by manipulating the particle locations and orientations and placing smaller particles in the voids among larger particles. This method aims at an optimum gradation, which has been achieved through experimental methods. However, this method takes the mechanical properties or performance of the mixture into consideration, such as inter-aggregate contacts and local stability. A simple visco-elastic model was applied to model the contacts between asphalt binder and aggregates. The surface texture of an aggregate particle can be taken into consideration in the inter-particle contact model. The void content before compactions was used to judge the relative merits of a gradation. Once a gradation is selected, the Voids in Mineral Aggregate (VMA) can be determined. For a certain air void content, the mastics volume or the binder volume or the asphalt content can be determined via a digital compression test. The surface area of all the aggregates and the film thickness can be then calculated. The asphalt content can also be determined using an alternative approach that is based on modeling the inter-particle contact with an asphalt binder layer. In this study, considering the necessity of preservation of the compaction temperature, the effect of various temperatures on Hot Mix Asphalt (HMA) samples properties has been evaluated. As well, to evaluate the effect of this parameter on different grading, two different grading have been used and samples were compacted at various temperatures. Air voids also influence pore water pressure and shrinkage of asphalt binder and mixture significantly. The shrinkage is measured on a digital model that represents beams in a steel mold and is defined as the linear autogenous deformation at horizontal direction. / Ph. D.

In the world there are adverse climates, climates that hinder the good construction and paving of roads, generating insecurity among the locals and visitors. This over time affects the economy of a country, as a road boosts tourism, transport and commerce. Therefore, a mixture was designed to mitigate a problem in the placement of hot asphalt mixture at temperatures below zero degrees Celsius. That is, a conventional mix design was proposed, but with different types of filler (lime, Portland cement type I and silica) tested with the Marshall and Lottman method which are governed according to the EG-2013 standards [1] and parameters established in the Asphalt Institute [2]. To find the optimum, it was tested with 5.0%, 5.5% 6.0% and 6.5% asphalt cement. Then with the results obtained a comparative analysis was performed. Finally, specimens without any additives were made, the specimens once prepared at 140°C were subjected to freezing, resulting in the three types of filler, that the hot asphalt mixture with incorporation of Portland cement type I to a 5, 90% of asphalt cement is the optimum since, subject to extreme temperatures below 0°C they comply with the parameters required in the standards.