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This article is a continuation of work on the use of plastic waste (such as PP, PS, LDPE, HDPE, and their mixtures) processed in the proprietary pyrolysis process as asphalt additives. The article carried out detailed tests of the mixes of selected additives with pen-graded bitumen 50/70, taking into account, among others, the influence of impurities and the ratio of PE to PP in the additives as well as short- (RTFOT) and long-term (RTFOT + PAV) ageing. An extensive research program was carried out, including functional and rheological tests in a wide range of temperatures. First, tests of stability and adhesion to various types of aggregates were carried out, demonstrating the usefulness of the proposed additives. Then, the elastic recovery and the impact of technological ageing on penetration, Fraass breaking temperature, and plasticity range were assessed. The same binder mixes were subjected to rheological tests in a wide range of technological and operational temperatures, assessing, among others, viscosity, the norm of the complex shear modulus, elastic recovery and compliance in the MSCR test, and stiffness in the bending beam rheometer. This entire class of tests was carried out for clean samples and those containing impurities, indicating their impact on individual material parameters. [ABSTRACT FROM AUTHOR]

Stiffness modulus represents one of the most important parameters for the mechanical characterization of asphalt mixtures (AMs). At the same time, it is a crucial input parameter in the process of designing flexible pavements. In the present study, two selected mixtures were thoroughly investigated in an experimental trial carried out by means of a four-point bending test (4PBT) apparatus. The mixtures were prepared using spilite aggregate, a conventional 50/70 penetration grade bitumen, and limestone filler. Their stiffness moduli (SM) were determined while samples were exposed to 11 loading frequencies (from 0.1 to 50 Hz) and 4 testing temperatures (from 0 to 30 °C). The SM values ranged from 1222 to 24,133 MPa. Observations were recorded and used to develop a machine learning (ML) model. The main scope was the prediction of the stiffness moduli based on the volumetric properties and testing conditions of the corresponding mixtures, which would provide the advantage of reducing the laboratory efforts required to determine them. Two of the main soft computing techniques were investigated to accomplish this task, namely decision trees with the Categorical Boosting algorithm and artificial neural networks. The outcomes suggest that both ML methodologies achieved very good results, with Categorical Boosting showing better performance (MAPE = 3.41% and R2 = 0.9968) and resulting in more accurate and reliable predictions in terms of the six goodness-of-fit metrics that were implemented. [ABSTRACT FROM AUTHOR]

This paper presents the results of a research study and analysis conducted to determine the degree of anisotropy of asphalt concrete in terms of its initial elastic properties. The analysis of asphalt concrete was focused on determining the effective constrained stiffness modulus in three mutually perpendicular directions based on the finite element method. The internal structure of the asphalt concrete was divided into the mortar phase and the mineral aggregate phase. Static creep tests using the Bending Beam Rheometer were conducted for the mortar phase to fit the rheological model. The aggregate arrangement and orientation were analysed using an image analytical technique for the mineral phase. The Finite Element Method (FEM) meshes were prepared based on grey images with an assumption of plane strain in 2D formulation. Using the FEM model, the tension/compression tests using selected characteristic directions were conducted, and the effective constrained stiffness moduli were estimated. This study showed a dominant horizontal direction for all coarse aggregates resulting from the normal force of the road roller and paving machines during laying and compaction on a road site. Depending on the values of the mortar's mechanical parameters and the load direction, the effective stiffness modulus might differ by ±20%. Based on the FEM analysis, this result was proven and commented on through an effective directional modulus evaluation and a presentation of internal stress distribution. Depending on the shape and orientation of the aggregates, it was possible to observe local "stress bridging" (transferring stresses from aggregate to aggregate when contacting). Moreover, the rheological properties of the mortar were considered by assuming two limiting situations (instantaneous and relaxed moduli), determining the bands of all possible solutions. In the performed FEM analysis, the influence of the Poisson ratio was also considered. The analysed asphalt concrete tends to be isotropic when the Poisson's mortar ratio is close to the value of 0.5, which agrees with the physical expectations. The obtained results are limited to particular asphalt concrete and should not be extrapolated to other asphalt mixture types without prior analysis. [ABSTRACT FROM AUTHOR]

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• Asphalt binder resistance to permanent deformation is a key issue in road engineering. • Universal test for assessing resistance to permanent deformation in case of all types of binders. • Changing the MSCR parameters may lead to extend its range of applicability for all types of binders. • The proposition of MSCLR test is an attempt to find the procedure to asses all asphalt binder types. The main goal of introducing the MSCR test was to estimate the rheological properties of pen grade and modified binders using the same measure. The conditions for this test were chosen at random (the length of creep and recovery period, the stress levels, as well as the test temperature). In most applications, the test temperature value was equal to 64 or even 70°Celsius. It is clear that for such high temperature values for softer binders the test interpretation is not always possible or burdened with a significant statistical error. Some time ago authors of this paper proposed a certain very similar test, but with different test parameters and with different interpretation of the test results. The test may be called a multiple shear creep long recovery (MSCLR) test and the main differences are the test temperature assumed as 10°Celsius and duration of creep and recovery period. In the first part of test, 10 cycles of creep-recovery periods are applied in the stress shearing mode on an asphalt binder sample. This part of the test ends with a long-term recovery period. The test is interpreted through the permanent deformation ratio determined on the basis of the maximum shearing strain observed during the test and the strain value after the long recovery period. In the paper the MSCR and MSCLR tests are conducted on highly-modified binders currently produced in Polish market. The obtained results are statistically analyzed, compared with each other and correlation functions between the results from MSCR and MSCLR tests are determined. Selected results are then presented in relation to results of modified and pen binders produced 8 years before (or some archival binders used for analysis in the paper [1]). Based on the analysis of the results, it is possible to observe some advantages of MSCLR test over MSCR test. One of them is a higher test sensitivity in distinguishing resistance to permanent deformations of individual binders and another one is the simplicity of interpretation of the test data. [ABSTRACT FROM AUTHOR]