Stone matrix asphalt (SMA) mixtures rely on stone-on-stone contacts among particles to resist applied forces and permanent deformation. Aggregates in SMA should resist degradation (fracture and abrasion) under high stresses at the contact points. This study utilizes conventional techniques as well as advanced imaging techniques to evaluate aggregate characteristics and their resistance to degradation. Aggregates from different sources and types with various shape characteristics were used in this study. The Micro-Deval test was used to measure aggregate resistance to abrasion. The aggregate imaging system (AIMS) was then used to examine the changes in aggregate characteristics caused by abrasion forces in the Micro-Deval. The resistance of aggregates to degradation in SMA was evaluated through the analysis of aggregate gradation before and after compaction using conventional mechanical sieve analysis and nondestructive X-ray computed tomography (CT). The findings of this study led to the development of an approach for the evaluation of aggregate resistance to degradation in SMA. This approach measures aggregate degradation in terms of abrasion, breakage, and loss of texture.

In this study, relationships between aggregate shape parameters and compressive strength of concrete were investigated using digital image processing and analysis methods. The study was conducted based on three mix design parameters, gradation type, aggregate type and maximum aggregate size, at two levels. A total of 40 cubic concrete specimens were prepared at a constant water-cement ratio. After the compressive strength tests were performed, each specimen was cut into 4 equal pieces in order to obtain the digital images of cross sections using a digital flatbed scanner. A number of aggregate shape parameters were then determined from the digital image of the cross sections to investigate their relationships with the compressive strength. The results indicted that even though the aggregate type was found to give strong correlation with the compressive strength, weak correlations, however, exist between the compressive strength and the aggregate shape parameters. The study suggested that the analyses of relationships should be further investigated by including the effects of aggregate distribution within the specimen cross sections.

<p><a>Voids in the mineral aggregate (VMA), as a main volumetric design parameter in the Superpave mixture design method, is an important factor to ensure asphalt mixture durability and rutting performance. Moreover, an asphalt mixture’s aggregate skeleton, related to VMA, is another important factor that affects critical asphalt mixture properties such as durability, workability, permeability, rutting, and cracking resistance. The objective of this study is to evaluate the effects of aggregate size distribution and shape parameters on aggregate packing characteristics (volumetric and compaction properties) of asphalt mixtures. Three tasks were undertaken to reach this goal. </a></p> <p>The first task was to propose an analytical approach for estimating changes in voids in the mineral aggregate (VMA) due to gradation variation and determining the relevant aggregate skeleton characteristics of asphalt mixtures using the linear-mixture packing model, an analytical packing model that considers the mechanisms of particle packing, filling and occupation. Application of the linear-mixture packing model to estimate the VMA of asphalt mixtures showed there is a high correlation between laboratory measured and model estimated values. Additionally, the model defined a new variable, the central particle size of asphalt mixtures that characterized an asphalt mixture’s aggregate skeleton. Finally, the proposed analytical model showed a significant potential to be used in the early stages of asphalt mixture design to determine the effect of aggregate gradation changes on VMA and to predict mixture rutting performance.</p> <p>As the second task, a framework to define and understand the aggregate structure of asphalt mixtures was proposed. To develop this framework, an analytical model for binary mixtures was proposed. The model considers the effect of size ratio and air volume between the particles on the aggregate structure and packing density of binary mixtures. Based on this model, four aggregate structures, namely coarse pack (CP), coarse-dense pack (CDP), fine-dense pack (FDP) and fine pack (FP), were defined. The model was validated using a series of 3D discrete element simulation. Furthermore, the simulation of multi-sized aggregate blends using two representative sizes for fine and coarse stockpiles was carried out to apply the proposed analytical model to actual aggregate blends. The numerical simulations verified the proposed analytical model could satisfactorily determine the particle structure of binary and multi-sized asphalt mixture gradations and could, therefore, be used to better design asphalt mixtures for improved performance. </p> <p>The third task virtually investigated the effect of shape characteristics of coarse aggregates on the compactability of asphalt mixtures using a discreet element method (DEM). The 3D particles were constructed using a method based on discrete random fields’ theory and spherical harmonic and their size distribution in the container was controlled by applying a constrained Voronoi tessellation (CVT) method. The effect of fine aggregates and asphalt binder was considered by constitutive Burger’s interaction model between coarse particles. Five aggregate shape descriptors including flatness, elongation, roundness, sphericity and regularity and, two Superpave gyratory compactor (SGC) parameters (initial density at N_ini and compaction slope) were selected for investigation and statistical analyses. Results revealed that there is a statistically significant correlation between flatness, elongation, roundness, and sphericity as shape descriptors and initial density as compaction parameter. Also, the results showed that the maximum percentage of change in initial density is 5% and 18% for crushed and natural sands, respectively. The results of analysis discovered that among all particle shape descriptors, only roundness and regularity had a statistically significant relation with compaction slope, and as the amount of roundness and regularity increase (low angularity), the compaction slope decreases. Additionally, the effect of flat and elongated (F&E) particles percentage in a mixture using a set of simulations with five types of F&E particles (dimensional ratios 1:2, 1:3, 1:4 and 1:5) and ten different percentage (0, 5, 10, 15, 20, 30, 40, 50, 80 and 100) with respect to a reference mixture containing particles with flatness and elongation equal to 0.88 was conducted. Results indicated that increase of F&E particles in a mixture (more than 15%) results in a significant reduction in the initial density of the mixture especially for lower dimensional ratio (1:4 and 1:5). <b><i></i></b></p> <br> <p> </p>

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.

Pavement layers are constructed using a combination of materials, of which rock aggregates constitute a larger proportion. Current understanding is that the performance of pavements is dependent on the aggregate shape properties which include form, angularity and surface texture. However, direct and accurate measurements of aggregate shape properties remain a challenge. The current standard test methods used to evaluate aggregate shape properties cannot measure these properties accurately. Among the reasons contributing to the difficulties in the determination of aggregate shape properties is irregular shapes of aggregate particles. Therefore, current research efforts focus on developing accurate, reliable and innovative techniques for evaluation of aggregate shape properties. The work presented in this dissertation contributes to the current innovative research at the Council for Scientific and Industrial Research (CSIR) in South Africa, to automate the measurement of aggregate shape properties. The CSIR’s present research is aimed at improving pavement performance through better materials characterisation, using laser scanning and advanced modelling techniques. The objective of this study was to investigate improved techniques for the determination of aggregate shape properties using analytical and laser scanning techniques. A three-dimensional (3-D) laser scanning device was used for scanning six types of aggregate samples commonly used for construction of pavements in South Africa. The laser scan data were processed to reconstruct 3-D models of the aggregate particles. The models were further analysed to determine the shape properties of the aggregates. Two analysis approaches were used in this study. The first approach used the aggregate’s physical properties (surface area, volume and orthogonal dimensions) measured by using laser scanning technique to compute three different indices to describe the form of aggregates. The computed indices were the sphericity computed by using surface area and volume of an aggregate particle, the sphericity computed by using orthogonal dimensions of an aggregate particle, and the flat and elongated ratio computed by using longest and smallest dimensions of an aggregate particle. The second approach employed a spherical harmonic analysis technique to analyse the aggregate laser scan data to determine aggregate form, angularity and surface texture indices. A MATLABTM code was developed for analysis of laser scan data, using the spherical harmonic analysis technique. The analyses contained in this dissertation indicate that the laser-based aggregate shape indices were able to describe the shape properties of the aggregates studied. Furthermore, good correlations were observed between the spherical harmonic form indices and the form indices determined by using the aggregate’s physical properties. This shows that aggregate laser scanning is a versatile technique for the determination of various indices to describe aggregate shape properties. Further validation of the laser-based technique was achieved by correlating the laser-based aggregate form indices with the results from two current standard tests; the flakiness index and the flat and elongated particles ratio tests. The laser-based form indices correlated linearly with both, the flakiness index and the flat and elongated particles ratio test results. The observed correlations provide an indication of the validity of laser-based aggregate shape indices. It is concluded that the laser based scanning technique could be employed for direct and accurate determination of aggregate shape properties. / Dissertation (MEng)--University of Pretoria, 2013. / gm2013 / Civil Engineering / Unrestricted

Because of a very variable geological composition of the Czech Republic, there is a various scale of all genetic types of rocks that are used for the production of crushed stone. The most often used group of rocks are effusive magmatic rocks, which represent about 34 % of crushed stone marketed (Starý et al. 2010). These rocks are used for all kinds of construction purposes including roads. The experimental material of crushed stone used in this thesis was sampled from 40 active quarries in the Czech Republic. The studied volcanic rocks originated from Neoproterozoic and Paleozoic complexes of Barrandien, Carboniferous and Permian of Krkonose Piedmont Basin, Carboniferous and Permian of Intrasudetic basin, area of ordovician Železné Hory, from the main volcanic center of Bohemian Massif in the north-west Bohemia (České středohoří Mts. and Doupov Mts.), Neovolcanic area of Czech Cretaceous basin and area of Neovolcanic East and West Sudeten. Petrographic study was carried out in a form of standard petrographic analysis of thin sections and chemical analysis, which helped inclusion of rocks to a classified systems. The whole suite of volcanic rocks was separated to five petrographic-technologic subgroups defined as: (1) rhyolites / porphyres, (2) phonolites, (3) basalts s.l., (4) spilites and (5)...