Investigating the role of aggregate structure in asphalt pavements (original) (raw)
Related papers
International Journal of Pavement Engineering, 2019
Aggregate size distribution is an important parameter in asphalt mixture design and performance. The main objective of this study is to develop a framework to define the aggregate structure of asphalt mixtures when fine and coarse aggregate stockpiles are blended. To develop this framework, an analytical model for binary mixtures is 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, three aggregate structures, namely coarse pack (CP), dense pack (DP) and fine pack (FP), are defined. The model is 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. In order to assess how well the model applies to asphalt mixtures, compaction parameters including compaction slope (CS), initial density (N ini), locking point and compaction energy index (CEI) were analyzed. The numerical simulations verify the proposed analytical model can satisfactorily determine the particle structure of binary and multi-sized asphalt mixture gradations and can be used to better design asphalt mixtures for improved performance. ARTICLE HISTORY
EFFECT OF AGGREGATE GRADATION ON THE STIFFNESS OF ASPHALT MIXTURES
Aggregate gradation plays an important role in the behaviour of asphalt mixtures. Packing of aggregate is a very important factor that will be affected by changing the aggregate gradation. Many researchers have investigated different ways of describing packing both theoretically and practically. Bailey ratios have recently been used to understand the volumetric properties of mixtures. In this paper, the Bailey ratios have been used, and two further ratios have also been introduced to allow the asphalt mixture gradation to be fully understood. Thirteen different aggregate gradations have been chosen within the 14 mm asphalt concrete specification to investigate the effect of particle size distribution on the stiffness of the mixture. It was found that variation in aggregate gradation has a significant effect on asphalt stiffness, even within specification limits, and a reasonable correlation between the set of ratios investigated and the Indirect Tensile Stiffness.
Aggregates for Asphalt and Concrete Mixes
2017
Paving asphalt concrete is a rather complex multiphase material, whose properties largely depend on those of bitumen. Bitumen-containing rocks are heterogeneous; i.e., are characterized by the presence of interface between different phases (solid, liquid and gas). The results of studies have demonstrated that asphalt concrete exhibits almost all the properties that are typical of elastic, viscous and plastic bodies depending on conditions and character of loads. For this very reason, it is classified as a visco-elastoplastic material; one of its main factors being viscosity of bitumen or the asphalt binding agent. The properties of asphalt concrete are variable and depend on a number of factors, such as the magnitude and nature of load, the ratio between mix components and primarily on temperature. The existence of a large number of parameters affecting the production technology makes it impossible to accurately describe the compaction process under complex loading types. In this case, most of the studies should be carried out at the experimental level in order to determine the qualitative indicators. The task of determining the deflected mode of material under punched operative parts executing a certain type of force impact. The effect of complex loading of the material being compacted on accumulation of irreversible deformations has been successfully assessed both theoretically and experimentally.
Sustainability
Optimum stiffness and linear deformation in the unloading phase are fundamental properties of asphalt mixtures required for the durability of flexible pavements. In this research, blends of six different aggregate gradations were used for two base course (BC) and four wearing course (WC) asphalt mixtures. Stability and indirect tensile strength of resulting asphalt mixtures were evaluated to relate to viscoelastic unloading deformation and resilient moduli (instantaneous (MRI) and total (MRT)) at 25 °C using a 40/50 binder for 0.1 and 0.3 s load durations. Results indicated that an increase in coarse aggregate proportion from 48 to 70% for BC has shown a 12% and 14% increase in MRT for 0.1 and 0.3 s load durations, respectively, and an increase in coarse aggregate proportion from 41 to 57.5% for WC has caused a 26% and 20% increase in MRI for 0.1 and 0.3 s load durations, respectively. The same coarse aggregate proportions showed an increase in linear viscoelastic deformation at 0.1...
International Journal of Pavement Engineering, 2013
With the increased awareness of building sustainable transportation systems, recycled materials and industrial byproducts increasingly are being used in highway construction, especially as base materials. When compared to traditional base materials, such as crushed aggregate, recycled materials and industrial byproducts often display unique properties. However, the physical properties of recycled materials and industrial byproducts have yet to be fully characterised for the purpose of pavement design. This study evaluated the mechanical properties of a full-depth reclaimed pavement material (RPM) and RPM stabilised with high carbon/high calcium fly ash, and compared these with properties of a conventional crushed aggregate. It was found that RPM exhibited higher modulus than the traditional base course material (crushed aggregates) did. However, RPM also showed higher plastic strain than crushed aggregate, indicating a higher potential for rutting in RPM base. Adding high carbon/high calcium fly ash significantly increased the California Bearing Ratio (CBR) and resilient modulus and lowered plastic strain of RPM. The strength and stiffness of field-mixed RPM stabilised with fly ash was significantly lower than that of laboratory-mixed mixtures, as indicated by different measures, i.e., CBR, resilient modulus and unconfined compressive strength (UCS). Data obtained in this study, along with other data obtained from similar studies, indicate that there are good correlations between resilient modulus and CBR (R 2 ¼ 0.96), as well as between resilient modulus and UCS (R 2 ¼ 0.94) for recycled base materials stabilised with fly ash. However, there is still a need for more testing to further verify the proposed relationships. Nonetheless, the proposed relationships constitute the first such relationship proposed and can be useful in pavement design. Additionally, it is shown that flexural strength is about 20% of UCS as it is recommended for materials stabilised with other cementitious materials.
Influence of Coarse Aggregate Shape on the Strength of Asphalt Concrete Mixtures
Journal of the Eastern Asia Society for Transportation Studies, 2005
The objectives of this paper are to evaluate aggregate characteristics including elongation, flatness, and other shape indices. The following particle shapes were selected for this study: cubical, rod, disk, and blade. The change in rotation angle of coarse aggregate was found to correlate well with the internal resistance of a HMA mix. The particle index (PI) was shown to be an adequate measure of the combined contribution of particle shape, angularity, and surface texture to the stability of an aggregate. The PI value correlated well to aggregate geometric characteristics including elongation ratio, flatness ratio, shape factor, and sphericity. Cubical particles were desirable for increased aggregate internal friction and improved rutting resistance. The more cubical the aggregate, the higher the PI value. The PI value of coarse aggregate significantly affected the engineering properties of a HMA mix. The particle shape determined how aggregate was packed into a dense configuratio...
Impact of Truck Loading on Design andAnalysis of Asphaltic Pavement Structures-Phase III
2012
This study investigated the impact of the realistic constitutive material behavior of asphalt layer (both nonlinear inelastic and fracture) for the prediction of pavement performance. To this end, this study utilized a cohesive zone model to consider the fracture behavior of asphalt mixtures at an intermediate temperature condition. The semi-circular bend (SCB) fracture test was conducted to characterize the fracture properties of asphalt mixtures. Fracture properties were then used to simulate mechanical responses of pavement structures. In addition, Schapery's nonlinear viscoelastic constitutive model was implemented into the commercial finite element software ABAQUS via a user defined subroutine (user material, or UMAT) to analyze asphalt pavement subjected to heavy truck loads. Extensive creep-recovery tests were conducted at various stress levels and multiple service temperatures to obtain the stress-and temperature-dependent viscoelastic material properties of asphalt mixtures. Utilizing the derived viscoelastic and fracture properties and the UMAT code, a typical pavement structure was modeled that simulated the effect of material nonlinearity and damage due to repeated heavy truck loads. Two-dimensional finite element simulations of the pavement structure demonstrated significant differences between the cases: linear viscoelastic and nonlinear viscoelastic modeling with and without fracture in the prediction of pavement performance. The differences between the cases were considered significant, and should be addressed during the process of performance-based pavement design. This research demonstrates the importance of accurate and more realistic characterizations of pavement materials.
A three-dimensional (3-D) finite element (FE) model was developed to investigate the dynamic responses of thin, flexible pavement under impulsive loading similar to a falling weight deflectometer test. The FE model simulated the hot-mix asphalt (HMA) surface layer as a linear viscoelastic material and considered the cross-anisotropic stress dependent modulus for the unbound base layer. Implicit dynamic analysis was used to consider the effect of inertia on pavement structural responses. Using two thinpavement structures of different HMA layer thicknesses, 76 and 127 mm, the study analyzed the effects of cross-anisotropic stress-dependent aggregate base modulus and dynamic analysis on pavement responses, including surface deflection, tensile strain at the bottom of the HMA layer, deviator stress in the base layer, and compressive strain on top of the subgrade. Results showed that use of the cross-anisotropic stress-dependent modulus for the unbound base layer resulted in greater predicted pavement responses and, hence, less estimated pavement life for rutting and fatigue cracking. It was found that as the thickness of HMA surface layer or the ratio of horizontal modulus to vertical modulus decreases, the effects of stress dependency and cross anisotropy become more significant. Analysis-predicted surface deflections were compared to field-measured values and they were in agreement when the stress dependency and cross anisotropy of the base layer and subgrade were considered.
Periodica Polytechnica Civil Engineering, 2015
Proper characterisation of the mechanical properties of unbound granular materials (UGM) is an essential issue in the analysis and design of flexible pavements. In particular, the resilient modulus of aggregates is a key input parameter in UGM characterization and prediction of pavement structural performance. In the present work, three UGM constitutive models are implemented within an axi-symmetric finite element code developed to simulate the nonlinear behaviour of pavement structures including two local aggregates of different mineralogical nature, typically used in Algerian pavements. The performance of these mechanical models is examined with regards to their capability of representing adequately, under various conditions, the granular material non-linearity in pavement analysis. In addition, deflection data collected by falling weight deflectometer (FWD) are incorporated into the analysis in order to assess the sensitivity of critical pavement design criteria and pavement design life to the three constitutive models. Finally, conclusions of engineering significance are formulated.