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Various tests are used to characterise the strength and resilience of granular materials used in the subbase of a pavement system, but there is a limited understanding of how particle properties relate to the bulk material response under various test conditions. Here, we use discrete element method (DEM) simulations with a mechanistically based contact model to explore influences of the material properties of the particle on the results of two such tests: the dynamic cone penetrometer (DCP) and the resilient modulus tests. We find that the measured resilient modulus increases linearly with the particle elastic modulus, whereas the DCP test results are relatively insensitive to particle elastic modulus. The DCP test results are also relatively insensitive to inter-particle friction coefficient but strongly dependent on the particle shape. We discuss strengths and weaknesses of our modelling approach and include suggestions for future improvements. [ABSTRACT FROM PUBLISHER]

Ultrasonic tomography is an emerging method of nondestructive concrete pavement diagnostics which can be used for improved quality assurance/quality control during concrete pavement construction and assist in rehabilitation decision making. Detection of flaws using ultrasonic tomography requires significant effort and user expertise. To address these limitations, a quantitative method for determining the presence of defects in concrete pavements was developed. The proposed method is an adaptation of the recently developed impact-echo signature analysis method (IESA), which is used for comparison of impact-echo signals. The proposed two-dimensional ultrasonic tomography signature analysis (2D-UTSA) method was used to compare two-dimensional B-scans obtained using a commercial test system in field trials at the Minnesota Rd. Research Facility and the Federal Aviation Administration's National Airport Pavement Test Facility. Analysis of the results showed that the 2D-UTSA method is capable of identifying subsurface defects. [ABSTRACT FROM AUTHOR]

Pavement design optimisation is an active area of research. Due to a large number of parameters, such as thickness of layers, material properties, climatic conditions, affecting pavement performance, it is usually not feasible to determine an optimal design using a trial and error approach. In order to make the design calculation computationally tractable, the process can be posed as an optimisation problem. Previous investigations in this vein have suffered from the limitations of a specific pavement analysis tool, specific design goals and specific optimisation algorithms. This paper presents a general computational framework, combining Mechanistic-Empirical Pavement Design Guide and Design Analysis Kit for Optimisation and Terascale Applications, to overcome these shortcomings. The framework's promise is demonstrated through its application to a minimum cost pavement design problem using both direct and surrogate-based (SBO) optimisation approaches. The SBO formulation is shown to achieve significant savings in required computational time with a minimal loss of accuracy in the determined optimal design. [ABSTRACT FROM AUTHOR]

Dowels are inserted at the mid-depth of joints in jointed concrete pavements that are exposed to heavy loading to provide load transfer and reduce pumping and faulting. Dowel alignment tolerances in North America have traditionally been strict, although not based on substantial performance data. In this paper, new laboratory testing methods are proposed for evaluation of the effects of dowel misalignment on concrete joint behavior. In these tests, dowels with various levels of rotations and translations were subjected to pullout and shear loading. It was found that dowel misalignment does not have a significant effect on pullout and shear forces for certain ranges of misalignments, which far exceed the tolerances recommended by the Federal Highway Administration. At the same time, it was found that extreme cases and combinations of misalignment resulted in a significant decrease in initial stiffness and shear capacity. Therefore, there is a need for the establishment of rational alignment tolerances. The results of this study provide important information for the development of such tolerances. [ABSTRACT FROM AUTHOR]

The Cohesive Zone Model (CZM) has been used to model the propagation of cracks through beams and slabs, which is of practical application in a variety of fields. CZMs have been successfully incorporated into Finite Element (FE) models however, this involves significant pre-processing effort to develop a sufficiently fine mesh around cohesive elements, which also increases the required computational effort. To overcome this limitation, a self-contained'crack element,' consisting of cohesive elements surrounded by pre-meshed bilinear bulk elements, was developed. A linear interpolation scheme to connect this crack element to adjoining beam elements, as well as a solution procedure using static condensation to solve crack propagation in beams was developed and implemented. Bilinear and non-linear CZMs were implemented to model the behavior of the cohesive elements. Under simple Mode I tension and flexure problems, the results were in-line with the expected behavior. It was found that the crack element was convergent with increasing mesh resolution, and needed to be only as long as its thickness, with the remainder of the beam being modeled by beam elements with just a handful of DOFs, reducing the size of the problem substantially. The element was also used to verify a theoretical model for the variation of modulus of rupture of a beam with its thickness, as well as a mixed-mode problem. In both those cases, the crack element showed good results. • An element to model crack propagation in beams was developed. • An interpolation scheme connected the element to beam elements. • Size effect in beams was demonstrated using the element. • The element was used to solve mixed-mode problems. [ABSTRACT FROM AUTHOR]

• We modified the imaging condition of reverse time migration to reduce the artifacts. • We introduced a new normalization factor to consider more precisely the spreading attenuation in imaging condition. • We introduced a modification factor to the imaging condition to consider scattering attenuation in concrete members. • We showed that using the proposed approaches one can image the entire boundary of a cavity located in a concrete medium. Cross-correlation imaging condition of reverse time migration generates high-amplitude artifacts in the reconstructed images. In addition, due to geometrical spreading and scattering attenuations, this imaging condition assigns amplitudes to the points of the reconstructed image that are not a true representative of the reflection coefficient of the scanned medium at those points. These all can lead to a reduction in quality and misinterpretation of the reconstructed images. In this paper, we proposed new imaging conditions to mitigate high-amplitude artifacts and to assign more accurate amplitudes to an RTM image by considering geometrical spreading and scattering attenuation in concrete members when horizontal shear waves are used for imaging. We used data obtained by transmitting horizontal shear waves to 3D synthetic homogeneous and concrete specimens and demonstrated the effectiveness of the new imaging conditions. [ABSTRACT FROM AUTHOR]

It is commonly recognized that non-uniformity of as-constructed Portland Cement Concrete (PCC) pavement may negatively affect long-term pavement performance. Conventional wisdom states that PCC thickness deficiency is the most important factor causing premature pavement failures. To address it, transportation agencies often impose strict penalties for not meeting the designed slab thickness requirements, thus contractors build slightly thicker slabs to avoid fines. However, other aspects of construction variability on pavement performance are mostly ignored by studies because conventional methods for construction uniformity assessment fail to provide sufficient information to quantify their effect. This study utilized a non-destructive ultrasonic test to evaluate in-situ pavement construction variability. To investigate the correlation between construction variability and surface distresses, a combination of non-destructive ultrasonic thickness measurements and visual distress surveys were performed in highways prior to rehabilitation. PCC slab thicknesses and shear wave velocities were computed from recorded ultrasound signals. An in-depth statistical analysis was performed to investigate possible relations between thickness or shear wave velocity and distresses using various pavement performance parameters. The main results of this analysis illustrate the importance of material quality and uniformity control during construction, since alterations in material properties significantly influence the presence of distresses. Shear wave velocity variations significantly correlate to cracked and broken slab panels in two sections, and, more importantly, to any type of distress in all tested pavement sections. [ABSTRACT FROM AUTHOR]

Improving early-age concrete strength measurement is an important step toward opening new pavements to traffic quickly without risking long-term performance due to early age damage. The maturity method is well established as an appropriate estimation of strength; however, it contains certain unavoidable limitations. Non-destructive ultrasonic testing using shear wave velocity can be used as a complementary testing. An in-situ comparison of these strength estimation methods was performed on a 200-mm thick concrete pavement for two weeks after placement. Both methods predicted reasonable concrete strength gain trends for in-situ pavement. The linear array ultrasonic method was found to have major advantages regarding portability, strength-gain variation and testing speed. [ABSTRACT FROM AUTHOR]

Creating multifunctional concrete materials with advanced functionalities and mechanical tunability is a critical step toward reimagining the traditional civil infrastructure systems. Here, the concept of nanogenerator-integrated mechanical metamaterial concrete is presented to design lightweight and mechanically tunable concrete systems with energy harvesting and sensing functionalities. The proposed metamaterial concrete systems are created via integrating the mechanical metamaterial and nano-energy-harvesting paradigms. These advanced materials are composed of reinforcement auxetic polymer lattices with snap-through buckling behavior fully embedded inside a conductive cement matrix. We rationally design their composite structures to induce contact-electrification between the layers under mechanical excitations/triggering. The conductive cement enhanced with graphite powder serves as the electrode in the proposed systems, while providing the desired mechanical performance. Experimental studies are conducted to investigate the mechanical and electrical properties of the designed prototypes. The metamaterial concrete systems are tuned to achieve up to 15% compressibility under cycling loading. The power output of the nanogenerator-integrated metamaterial concrete prototypes reaches 330 µW. Furthermore, the self-powered sensing functionality of the nanogenerator concrete systems for distributed health monitoring of large-scale concrete structures is demonstrated. The metamaterial concrete paradigm can possibly enable the design of smart civil infrastructure systems with a broad range of advanced functionalities., (© 2023 Wiley-VCH GmbH.)

Elevated air temperatures in urban neighborhoods due to the Urban Heat Island effect is a form of heat pollution that causes thermal discomfort, higher energy consumption, and deteriorating public health. Mitigation measures can be expensive, with the need to maximize benefits from limited resources. Here we show that significant mitigation can be achieved through a limited application of reflective surfaces. We use a Computational Fluid Dynamics model to resolve the air temperature within a prototypical neighborhood for different wind directions, building configurations, and partial application of reflective surfaces. While reflective surfaces mitigate heat pollution, their effectiveness relative to cost varies with spatial distribution. Although downstream parts experience the highest heat pollution, applying reflective surfaces to the upstream part has a disproportionately higher benefit relative to cost than applying them downstream.

Although ultrasonic transducers that emit horizontal shear waves are widely used in practice, no investigation has been conducted to study the attenuation of shear waves in concrete due to scattering by aggregates and air voids. Horizontal shear waves preserve more energy in comparison with longitudinal waves when propagating in concrete in low frequencies. However, the lower wavelength of shear waves increases the potential of their scattering attenuation in concrete. In this paper, we developed a 3D numerical tool and used it to study the scattering attenuation of horizontal shear waves in concrete in the 20-150 kHz frequency range. We showed that the scattering attenuation in this frequency range strongly depends on the size and material properties of aggregates. The shape of the aggregates and the presence of air voids slightly affected the scattering attenuation., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The emergence of ultrasonic dry point contact (DPC) transducers that emit horizontal shear waves has enabled efficient collection of high-quality data in the context of a nondestructive evaluation of concrete structures. This offers an opportunity to improve the quality of evaluation by adapting advanced imaging techniques. Reverse time migration (RTM) is a simulation-based reconstruction technique that offers advantages over conventional methods, such as the synthetic aperture focusing technique. RTM is capable of imaging boundaries and interfaces with steep slopes and the bottom boundaries of inclusions and defects. However, this imaging technique requires a massive amount of memory and its computation cost is high. In this study, both bottlenecks of the RTM are resolved when shear transducers are used for data acquisition. An analytical approach was developed to obtain the source and receiver wavefields needed for imaging using reverse time migration. It is shown that the proposed analytical approach not only eliminates the high memory demand, but also drastically reduces the computation time from days to minutes., (Copyright © 2018 Elsevier B.V. All rights reserved.)