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Large-scale triaxial tests are popular for evaluating the mechanical properties of railroad ballast. The literature shows that different compaction methods have been used to prepare the samples. This research investigates the potential variation caused by different compaction methods, even when the samples are compacted to the same density. A series of triaxial tests are conducted, and the results confirm that the way in which ballast is compacted significantly affects its stiffness, but not its peak strength, as long as the density is consistent. Discrete-element method simulations are performed to explore this phenomenon and discover that stiffness variations are caused by different ways in which particles interlock and arrange themselves during compaction. Based on the findings from this study, it is recommended to consider the influence of compaction methods when conducting large-scale triaxial testing on railroad ballast or when evaluating the test results. [ABSTRACT FROM AUTHOR]

The object of this study is the compaction methods of asphalt mixtures under laboratory conditions. The experience of determining the physical properties of coarse-grained asphalt concretes taken from the layers of the road pavement structure shows that their values do not correspond to those of the samples obtained by laboratory compaction using the pressing method. In 90 % of cases, the density of cores exceeds the density of laboratory samples while the indicators of void content and water saturation are significantly lower than for laboratory samples. The compressive strength indicators of asphalt concrete are almost independent of compaction methods and are not very informative. All of the above leads to the conclusion that the methods of laboratory compaction by pressing do not meet modern requirements. Low values of water saturation and void content of cores and laboratory samples compacted with a gyrator allow us to argue about outdated approaches to the design of grain compositions of asphalt concrete. Low-informative indicators of compressive strength indicate the need to use other mechanical characteristics that will make it possible to predict the properties of asphalt concrete in the pavement, for example, rutting resistance. As a summary, template solutions in the design of asphalt concrete warehouses and physical and mechanical characteristics are necessary only to establish compliance with the requirements of regulatory documents. The current work shows that it is almost impossible to predict the properties of asphalt concrete based on laboratory samples obtained by pressing. All this leads to the need to change the regulatory framework, which is possible by using regulatory documents of the countries in the European Union and the United States of America [ABSTRACT FROM AUTHOR]

[Objective] This paper focuses on the development of a bidirectional consolidated soil sample-making apparatus. The aim is to compare samples made by this apparatus with those created using compaction and static pressure methods and to analyze and verify the feasibility of the bidirectional properties. [Methods] In this paper, three types of test equipment were used to prepare consolidated soil samples of specified age. Several comparative tests were conducted, such as the unconfined compressive strength (UCS) test, the industrial electron microscopy test, the scanning electron microscopy test, and the mercury-in-pressure porosimetry test. These tests helped analyze and verify the feasibility of the bidirectional consolidated soil sample maker. They also enabled us to study the macro/fine/micro characteristics of the samples produced by the three test equipment from various angles, such as UCS and its destructive form, apparent porosity of the sample, microscopic porosity and filling of the curing product, microscopic pore volume, and pore size distribution. [Results] The results show that in terms of macro UCS of consolidated soil samples, the bidirectional sample has the highest UCS, followed by the static pressure sample and then the compaction sample. In terms of sample formation and destruction form, the bidirectional sample is uniform in color and has a stable destruction form (all are shear destruction). The static pressure sample is denser at the top and looser at the bottom, with destruction mostly in the weaker and lower parts. The compaction sample, however, shows distinct layering with varying shades and multiple forms of damage. Thus, the uniformity of the bidirectional sample is superior to that of the compacted and static compaction samples. Upon fine analysis, we found that compared with the static compaction sample (which has an apparent porosity that gradually increases from top to bottom) and the compaction sample (where the apparent porosity gradually decreases from top to bottom), the bidirectional sample has the smallest and most uniformly distributed apparent porosity. At the microscopic level, the bidirectional sample has the highest amount of curing products that can effectively fill the pores, making its internal microstructure the densest. It also has the least amount of mercury intake and is dominated by interparticle pores with smaller diameters. This is followed by the static pressure sample, while the compaction sample has the least amount of curing products, larger pores, the highest amount of mercury intake, and pores mainly distributed in the interparticle pores with larger diameters and the intragranular pores. [Conclusions] Therefore, the multiscale comparative study shows that the self-developed bidirectional sample-making instrument is better than that of the static pressure instrument outperforms both the static pressure and the three-segment mold (or double membrane) in terms of sample making. Not only does it deliver superior results, but it also exhibits a smaller margin of errors in tests. Consequently, this makes it a viable option for widespread adoption and application in geotechnical tests. [ABSTRACT FROM AUTHOR]

Pavement structures must guarantee safety, trafficability and comfort to highways users during its service life. The quality of these parameters is related to distresses that may occur as surface distortions, that might be caused by mechanical behaviour problems and to surface texture, which also affect highway safety. The surface texture is evaluated by parameters such as microtexture and macrotexture, related to aggregate rugosity and mixture characteristics, respectively. Both mechanical behaviour and surface texture can be affected by the compaction method of the mixture, as it affects the internal structure and the internal friction between aggregate particles, resulting in alterations in the permanent deformation resistance and surface aspects of the mixture. Hence, this paper proposed a new laboratory compaction method, using roller compaction with vibration, considering three aggregate gradations. This study evaluated the effect of the laboratory compaction method in the permanent deformation resistance and the surface texture of samples, comparing to field mixtures. The proposed compaction method presented efficiency for dense-graded mixture. The mixture's performance regarding mechanical behaviour and surface texture according to the compaction method variation was also dependent on the aggregate gradation. Mixtures with a discontinuity on the gradation presented a negative impact due to the vibration process. [ABSTRACT FROM AUTHOR]

This research aims to assess the microscopic differences in void characteristics of porous asphalt mixtures and their effect on mechanical and functional performance when prepared using different compaction methods. Marshall compaction (MC) and Superpave Gyratory Compactor (SGC) methods were employed to prepare the specimens, and digital image processing techniques were used to analyze the differences in void size, shape and complexity of the mixtures. Through bending, fatigue, drainage and noise reduction tests, the mechanical and functional performances of the mixture specimens under two compaction methods were compared and analyzed. The results revealed that the compaction method had a substantial effect on the specimens' drainage and noise reduction performance. Moreover, the correlation results between the meso-structure and macro performances of the mixtures indicate that SGC exhibits greater responsiveness to the overall performance of the mixtures. These findings facilitate the understanding of the compaction mechanism, thereby improving the design and compaction procedures, and providing insights into the relationship between microstructure and macroscopic performance of asphalt mixtures. • The effects of compaction methods on void characteristics and macro performances. • Analyzed the microstructural differences in void characteristics during compaction. • The SGC method strongly correlates with mixture's mechanics, while MC with functionality. • Established scale correlation between compaction methods, void parameters, and mixture performances. [ABSTRACT FROM AUTHOR]

New methods for compacting graphite fiber powder composites developed by the authors are described. These methods help to remove considerable amounts of gases and liquid vapors from powder loaded into the punch-and-die set and from the compact prior to the main compacting operation. [ABSTRACT FROM AUTHOR]

Marshall and Superpave mixture designs are based mainly on volumetric parameters. Despite this similarity, the definition of the optimum asphalt binder content is highly influenced by the laboratory compaction method. The main objective of this study is to evaluate the effect of the compaction method on the air void content and the mechanical properties of compacted asphalt mixtures. The experimental procedure included the Marshall and Superpave mixture design methods (the second one uses SGC – Superpave Gyratory Compactor, with two mold sizes), the French gyratory shear compactor (PCG), and also the LCPC French roller compactor. The effect of the compaction method, mold size and the number of gyrations on the air void content (and, consequently, on the optimum asphalt binder content), mechanical properties, permanent deformation, and fatigue behavior were evaluated. The main contribution of this study is the recommendation of the Superpave Gyratory Compactor with mold size of 100 mm diameter (Nominal Maximum Aggregate Size NMS ≤ 12.5 mm) for medium and high traffic. The use of 150 mm molds in the SGC is recommended only if the number of gyrations is smaller than the one used in this study (100 gyrations). [ABSTRACT FROM AUTHOR]

• The internal meso structure of AC compacted using six different compaction methods was analyzed. • The distribution characteristics of asphalt binder and aggregate of compacted AC by six different compaction methods were obtained. • The relationship between aggregate contact points, aggregate freedom degree and mechanical performance of AC was established. • The AC compacted by roller and SGC in the laboratory could effectively simulate the compaction state on site. The difference between asphalt concrete (AC) compacted in the laboratory and the field significantly influences its gradation design and performance evaluation accuracy. In this research, the effect of the laboratory compaction and field compaction on AC characteristics were compared using the characteristic indexes of surface texture, internal structure, asphalt binder distribution, aggregate distribution, compressive resilience modulus, and the crack resistance index (CRI). Six different compaction methods for AC specimens were studied, and five different types of laboratory compaction equipment were used, namely the Marshall compactor, Steel segmented roller compactor (SSRC), Superpave gyratory compactor (SGC), shear box compactor (SBC), and roller. The results showed that a uniform texture of AC surface was created with vibration and kneading. The aggregate contact distribution of specimens compacted by SGC, SBC, and roller was similar to field compaction as an inverse "bathtub" shape. The aggregate rotation angle of AC compacted by SGC, SBC, and roller showed higher randomness. The coarse aggregate of specimens degraded after Marshall compaction. The fine aggregate coated with more asphalt binder being moved towards the middle height of the specimen, resulting in higher asphalt binder content in the middle layer during the compaction of SGC and SBC. The specimens compacted with SGC and SBC had better mechanical properties, especially in the middle layer of the specimen. The increase of aggregate contact points improved the mechanical properties of the mixture. The free movement of aggregates was helpful for slippage of aggregates and promoted the filling of voids with asphalt mastic to make the skeleton structure more compact. Correlation analysis showed that SGC and the roller could better reproduce the field compaction state. [ABSTRACT FROM AUTHOR]

• Dynamic responses of the Smart Aggregate in aggregate mixture were studied under different compaction methods. • Compaction process was discussed at meso -scale by analyzing particle movement and number of contact points. • Effects of material factors on dynamic responses of the Smart Aggregate were discussed. Knowing compaction process of pavement at meso -scale is of great significance for improving the material design and construction quality. This study aims to investigate dynamic responses of particle in aggregate mixture during compaction by using a Smart Aggregate. As the compaction method and material composition have significant influence on dynamic responses of the particle in compaction process, various compaction methods, including impact, vibration, static and gyratory compaction, were first conducted on lubricated mixtures in the laboratory. Then, number of contact points and movements of the Smart Aggregate in mixture were analyzed in different stages of gyratory compaction process. Additionally, effects of critical influencing material factors, including lubrication effect, particle size, aggregates packing and gradation on the particle movement in mixture were discussed. Results indicate that the dynamic responses (i.e. acceleration, rotation and contact force) of the Smart Aggregate exhibited significant relation to the loading mode of compaction efforts. Regarding to gyratory compaction, drastic particle movement and sharp increase in number of contact points mainly occurred in the first stage in which the reduced height of specimen was more than 1 mm. Although lubrication had a marked impact on compaction of aggregates system, its influence on movement could be negligible for the Smart Aggregate. Those adjacent aggregates with particle size less than 4.75 mm performed well in terms of restricting the movement of the Smart Aggregate. After filling fine aggregates with particle size less than 2.36 mm into packed aggregates, the deviation of change in acceleration amplitude and relative rotation was reduced to a low level. Compaction methods, adjacent particles' size and aggregates packing had significant influences on the dynamic responses of the Smart Aggregate. [ABSTRACT FROM AUTHOR]

With the increasing application of cold in-place recycling (CIR) techniques, many performance studies have been done, but they rarely focus on the internal structure of CIR mixture. The objective of this study is to investigate the characteristics of air voids in CIR mixtures with the X-ray computed tomography (CT) and digital image processing (DIP) methods. The volume, size, and number of air voids in CIR specimens were statistically analyzed considering different aggregate gradations and compaction methods. The two-parameter Weibull function was used to model the air void gradation of CIR mixtures. Especially, the differences in air voids between CIR and hot mix asphalt (HMA) mixtures were fully quantified. According to the results of this study, with coarser aggregate gradation, the CIR mixture tends to have larger size and less number of air voids. Comparing with the Superpave gyratory compactor (SGC) method, the Static Load compaction produces relatively small air voids. The distributions of air void number in specimen depths for the three compaction methods are different. The scale and shape parameters in Weibull function are both sensitive to the changes in aggregate gradation and compaction method. The substantial difference of air voids between CIR and HMA mixtures is in the aspect of the air void number rather than the air void size. Overall, this study provides a solid foundation for future research in exploring the internal structure and mix design of CIR mixtures. [ABSTRACT FROM AUTHOR]

Abstract: A wide variety of recycled waste has been successfully used in the production of concrete paving blocks. It is known that the mechanical properties of these concrete products tend to be inconsistent, which is understandable in view of the range of mix designs as well as the variety of materials and compaction methods that were adopted in the production. In this study, recycled waste tyre (crumb rubber) was used to replace sand by volume at the level of 0%, 10%, 20% and 30% in order to investigate how the soft rubber particles behave under plant-machine compaction method during the production of rubberized concrete paving blocks (RCPB). In the hardened stage, the physical properties as well as mechanical properties of RCPB including density, compressive strength, bending strength and skid resistance were studied. The results showed that as a small proportion (∼10%) of soft rubber particles was included in the mixture, the particles easily distorted and filled the voids between the solid particles. This filling mechanism reduced the porosity of concrete mixtures and effectively developed an adequate adhesion between the particles, resulting in higher gain in strengths. On the contrary, as the rubber ratio increased more than 10%, which the deformability is more predominant than the filling mechanism, this results in higher total stress concentrations and rebound stress of rubber particles, thus, increasing the porosity and micro-cracks, resulting in loss in strengths. Nevertheless, the presence of rubber in concrete did not demonstrate brittle failure, but rather a ductile which had an ability to withstand post-failure loads. In comparison, the mechanical properties of plant-made RCPB performed better than that of corresponding manually-made RCPB. Therefore, plant-compaction method is recommended for future RCPB production and crumb rubber content used to replace sand by volume should be kept at or less than 10%. [Copyright &y& Elsevier]

Australian practice is moving towards the utilisation of gyratory compacted samples tested by indirect diametrical tensile testing for determination of both modulus and fatigue life of cementitiously stabilised pavement materials. At the same time, conformance testing is expected to remain an unconfined compressive strength and density based assessment. The influence of material density on the strength and modulus of these materials is important as differing densities are achieved in the laboratory and the field. The effect of compaction method, where different test methods are used for characterisation and conformance testing, is also important. An investigation was undertaken to determine the influence of both dry density and compaction method on the strength and modulus of reclaimed pavement material stabilised with a slag-lime binder. As a prelude, the influence of compaction method and the addition of binder to the host material on the optimum moisture content and maximum dry density were also determined. The gyratory compactor protocol required to achieve densities equivalent to Standard Proctor compaction was determined and the influence of the addition of binder to a host material was found to be material specific. Whilst the compaction method (at the same dry density) had no significant influence on the strength and modulus of these materials, the density had a significant impact on both strength and modulus. [ABSTRACT FROM AUTHOR]

• Aggregate degradation of field and six laboratory compaction methods was analyzed. • Void characteristics of field and six laboratory compaction methods were obtained. • Mathematical models of the void gradation were established. • Similarity of laboratory specimens to field specimens was evaluated. Asphalt mixtures compacted in the field and in a laboratory show obvious differences in their internal structures, and this affects the evaluation of pavement performance. Hence, in this study, to find a laboratory compaction method most similar to the field method, the effect of the field method and multiple laboratory compaction methods on the internal structure of asphalt mixture specimens was investigated. First, based on the principle of keeping the same compaction degree, specimens cored from field specimens were prepared with six laboratory methods. Then X-ray computed tomography (X-ray CT) and digital image processing (DIP) technologies were used to analyze the internal structure of the specimens, including the spatial distribution and particle size of the voids, as well as the aggregate degradation. Finally, the similarity of the laboratory specimens to the field specimens was evaluated. The results indicated that the spatial distribution of the voids was affected by the compaction methods. The edge effect was different in specimens with different heights. The symmetry of the distribution curve of the air voids was affected by the distribution of the compaction effort. The void particles in a certain size range occupied most of the volume, and the size distribution of the void particles inside the specimens was affected by the compaction methods. In the compaction process of the static load method, the aggregates were constrained and seriously broken, while the dynamic load and the kneading action could protect aggregates from being broken. In general, the partial specimens compacted using a Superpave gyratory compactor (SGC) and a shear box compactor (SBC) were more similar to the field specimens than other laboratory specimens. This study offers a reliable basis for studying the internal structure of asphalt mixture specimens compacted using different methods and for guiding laboratory compaction based on the field method. [ABSTRACT FROM AUTHOR]

Aggregate skeleton is a significant factor that determines load transfer paths in asphalt concrete. This study prepared asphalt mixtures with different aggregate morphologies, gradations and compaction methods. Digital image processing technique was used to quantify aggregate skeleton structures including orientation, distribution and contact properties of aggregate. Indirect tensile strength and fatigue tests were conducted to explore the relationship between skeleton indexes with mechanical properties. The results show that gradation types have a significant impact on average contact number and internal structure index of asphalt mixtures. In a certain gradation and abrasion times, the average contact number of samples manufactured by roller compactor are larger than that of Marshall compactor samples. Moreover, the abrasion has a negative effect on average contact number as the loss of aggregate morphologies would adversely impact aggregate interlocking. The results of indirect tensile strength and fatigue test are basically consistent with the results of average contact number and internal structure index, which shows that the short-term and long-term mechanical properties of asphalt mixtures are directly affected by aggregate contact characteristics. [ABSTRACT FROM AUTHOR]