Relationship between Aggregate Packing Characteristics and Compactability of Hot-Mix Asphalt Mixes (original) (raw)
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Estimating Optimum Compaction Level for Dense-Graded Hot-Mix Asphalt Mixtures
Journal of Engineering Research
A critical step in the design of asphalt mixtures is laboratory compaction. Laboratory compaction should reflect field compaction and should produce mixtures that are economical and possess high structural stability. During the compaction process, asphalt mixtures are subjected to certain amount of compaction energy in order to achieve the required density. The Superpave volumetric mix design is based on compacting HMA mixtures to a specified compaction level described by the number of gyrations from the Superpave gyratory compactor (SGC). This level is termed Ndes and represents the required energy (based on the traffic level expected) to densify the mixture to a 4% air voids level. This paper re-examines the Superpave compaction requirements through extensive laboratory investigation of the response of a number of asphalt mixtures to the applied compaction energy. It also presents an alternative method to estimate the number of gyrations at which a mixture first reaches an optimum...
Powder Technology, 2020
In this study, the effect of coarse aggregate shape characteristics on the compactability and microstructural properties of asphalt mixtures was virtually investigated using a discreet element method (DEM). Results reveal there is a statistically significant correlation between coarse aggregate flatness, elongation, roundness, and sphericity as shape descriptors and initial asphalt mixture density, as a compaction parameter. Analyses indicate 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, the compaction slope decreases. Additionally, flatness and elongation values greater than 0.75 result in lower average coordination number values compared to those values less than 0.75. Results also indicate that although the probability density function (PDF) of low contact force highly depends on flatness, elongation and sphericity of particles, the PDF of high and very high contact forces is independent of the particle shape.
Properties of dense-graded asphalt mixture compacted at different temperatures
IOP Conference Series: Earth and Environmental Science, 2019
Poor compaction work is one of the identified causes of road failure and has always been a concern to the asphalt industry. The use of compaction machinery, compaction temperature, weather factor and the type of mixture used could potentially affect the asphalt pavement performance. This study measures the properties of hot mix asphalt (dense-graded AC10) prepared at different compaction temperatures. Various compaction temperatures were selected for the laboratory slab samples preparation i.e. 152°C, 142°C, 132°C and 122°C. A 60/70 pen bitumen was used to prepare the slab with the size of 305mm x 305mm x 50mm. Thermocouple was used to monitor the temperature of the mix. The slab samples were then cored for cylindrical samples at the approximate size of 100mm diameter for mechanical tests. The core samples were tested for volumetric properties, degree of compaction (DOC), Marshall stability and resilient modulus. It was found that low compaction temperature increases the air void in the total mix (VTM) and decreases the air void filled with bitumen (VFB) due to the increase in bitumen viscosity. In other words, reduction in compaction temperature resists the compactibility of the loose mix and resulted in low final DOC and low modulus.
Aggregate Packing Characteristics of Asphalt Mixtures
2019
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. 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 mecha...
Evaluation of the effects of gyratory and field compaction on asphalt mix internal structure
Materials and Structures, 2015
This study investigates the effect of gyratory and field compaction on the internal structure of asphalt mixtures. For this purpose, three new fullscale pavement test sections with different HMA mixes were selected for sampling loose material and field cores. Loose material was compacted using the gyratory compactor and adjusting several parameters, namely the gyration angle, compaction temperature and specimen geometry. Internal structure of the gyratory and field compacted specimens was quantified in terms of the aggregate contact points, orientation and segregation by means of 2-D image analysis. From the laboratory investigation it was demonstrated that the gyration angle and specimen geometry significantly affected the internal structure. The results also indicated that the field compaction produced similar internal structure in asphalt pavements and, especially, compaction with gyration angle of 1.45 o best simulated the internal structure of field cores.
Typical strength of asphalt mixtures compacted by gyratory compactor
Journal of the Mechanical Behavior of Materials
Design of asphalt mixes and quality testing is influenced by the laboratory compaction procedure. Laboratory specimens must be manufactured in a way that suitably resembles field compaction for a performance test to give reliable mechanical properties. The internal structure of the mixture, which is referred to in this article as the spread of aggregate and air voids, provides the basis for the simulation. Gyratory compaction uses a kneading effort to produce cylindrical specimens. The goal of the present article is to determine the required strength for asphalt mix compaction of 40–50 per surface. This look was achieved with three distinct types of filler material and two kinds of sand. The asphalt mixture’s compressibility was tested. By adding the cumulative energy expended during gyratory specimen compaction to the compression data, the force applied to the sample during gyrations may be calculated. The relation between the number of gyrations and forces demonstrates pressure re...
2013
Abstract—During the process of compaction in Hot-Mix Asphalt (HMA) mixtures, the distance between aggregate particles decreases as they come together and eliminate air-voids. By measuring the inter-particle distances in a cut-section of a HMA sample the degree of compaction can be estimated. For this, a calibration curve is generated by computer simulation technique when the gradation and asphalt content of the HMA mixture are known. A two-dimensional cross section of HMA specimen was simulated using the mixture design information (gradation, asphalt content and air-void content). Nearest neighbor distance methods such as Delaunay triangulation were used to study the changes in inter-particle distance and area distribution during the process of compaction in HMA. Such computer simulations would enable making several hundreds of repetitions in a short period of time without the necessity to compact and analyze laboratory specimens in order to obtain good statistics on the parameters ...
An overview of asphalt mix designs using various compactors
IOP conference series, 2019
Generally, road network is a well-thought-out vital transportation medium that is in place throughout the world. As, such, utmost care is taken in providing the best possible safe and comfortable and yet cost-effective road transportation system. One of the areas that scrutinized is the performance of asphalt mixtures in the flexible pavements. Traditionally, laboratory asphalt mixture designs are based on Marshall Method whereby the asphalt mixtures are compacted using a 4.5kg drop weight hammer. Although the volumetric properties are reasonably accepted, the actual achievement of the roller compacted volumetric properties at the site is still farfetched. This is because the laboratory mix designs developed using a Marshall Drop weight compactor and in the field, the asphalt layer is compacted using a heavyduty roller. In recent years, the Superpave Gyratory Compactor (SGC) have come into play with a static load and kneading approach. This objective of this paper is to look into the existing methods and processes carrying out the asphalt mix designs and review to see if there is or are any mismatch as compared with field compaction protocol.
Effect of Compaction Methods on the Morphology of Aggregates in Hot Mix Asphalt
IOP Conference Series: Materials Science and Engineering
Hot mix asphalt plays a very important function in determining a pavement's capacity with regard to major failures, such as fatigue, permanent deformation, and thermal-associated cracking. Hot mix asphalt's behaviour is affected by the mechanistic attributes and shape of its constituent aggregates, alongside the geometric properties of those aggregates such as position and orientation. This paper focused on characterising the aggregates used in producing hot mix asphalt and their allocation within such asphalt mixes using digital image processing (DIP) methods. Additional laboratory tests were also performed in order to match compaction methods used in the laboratory with those occurring in the field. The results provided evidence that this methodology offers simpler and faster ways to provide a full indication of the behaviour of aggregates during compaction and to determine their tendency to randomise throughout the compaction process. ImageJ Fiji software was found to be competent to characterise aggregates' constituent forms and orientations; randomness, represented by vector magnitude, is determined in an aggregate directional array as an orientation factor (∆) and used as a reference for better interlocking where heavy compaction is used. This factor ranges from 0 to 100%, where 0% indicates completely random particles and 100% indicates that particles are exactly within a single array. Mixes compacted with a Superpave gyratory compactor (SGC) and roller compactor had aggregate particles with relatively higher numbers of contact points and randomness than those mixes compacted using a Marshall Hammer. The results also showed that vector magnitude is an approach to determining field compaction, with results of 82.6, 67.43, and 90.7% for SGC, Marshall Hammer, and roller compacter compaction, respectively. This makes it clear that SGC and roller compaction are the nearest types of compaction to those used the field. DIP also showed that the percentage of contact points in various types of compaction were 63.6 and 92.9% for Marshall and roller compacters, respectively, while field core was found to have 88.4% contact points when produced by SGC.
Analysing the Gyratory Compaction Design Level for a Dense Mixture and a Stone Mastic Asphalt
The achievement of a desired level of bituminous mixtures’ performance is an important issue to increase the durability of pavements and to reduce maintenance costs as well as its impacts. A decisive stage is the mixture design process, in particular the choice of bitumen content to be used. This parameter can affect all the major performance properties of the mixtures. In Portugal, the Marshall method is used for bituminous mixtures design. This is an empirical method which has some drawbacks in the design of non-traditional mixtures as well as some limitations to represent in-service conditions (for example the compaction of the mixtures). Many countries have been using a volumetric design method to overcome these drawbacks. The adoption of a more efficient design methodology can improve the durability of pavements, leading to important costs saving and environmental impact reduction throughout the pavement’s life cycle. However, there is a great experience with the use of the current mix design methods and the mixture’s in-service performance is thought to be generally adequate in most cases. Therefore, the compositions obtained with the current methods are regarded as a reference in the analysis of the volumetric design method. In this project a Portuguese typical dense graded bituminous mixture used in base and binder layers as well as a Stone Mastic Asphalt (SMA) mixture were formulated by the Marshall method and by the volumetric design method. The mixture’s volumetric properties were evaluated and compared with threshold values from available standards and other specifications. The results of the design processes are compared regarding the volumetric properties of the mixtures.