Interlayer Bond Research Articles

Study of vacancy defect in 2D/3D semiconductor heterostructure based on monolayer WSe2 and GaN

2D/3D heterostructure have attracted considerable attention within the scientific community due to their superior electronic properties and extensive spectral absorption capabilities. However, structural defect is inevitably introduced during the synthesis of 2D materials, which can significantly alter their intrinsic physical properties. Hence, 2D/3D semiconductor heterostructure composed of monolayers of WSe2 and GaN are constructed using first-principles calculations in this study. The impact of vacancy defect on the geometrical, electronic, and optical properties of the WSe2/GaN heterostructure is then systematically explored. The electronic property reveals that the introduction of impurity levels by vacancy defect, as well as interlayer surface-suspended bonds, results in a reduced band gap. This modification enhances the transfer ability of electrons from the valence band to the conduction band. Optical characterization demonstrates that the heterostructure formed by WSe2 and GaN exhibits a broad absorption spectrum, spanning from the visible to ultraviolet region, indicating a dual-wavelength photoresponse. Furthermore, regarding absorption coefficient and reflectivity, the heterostructure containing vacancy defect displays superior optical performance compared to the pristine heterostructure across both the visible and ultraviolet regions. The electronic and optical properties of the heterostructure can be tuned through the introduction of vacancy defects. These theoretical findings are anticipated to offer a foundational framework for the design of ultraviolet photodetectors utilizing WSe2/GaN heterostructure.

Nano-SiO2/polyurethane modified unsaturated polyester resin mortar for thin layer repairing on airport pavement

This paper introduces a novel toughened polymer mortar designed for runway repair, featuring outstanding impact resistance, high strength, and cost-effectiveness. To augment the toughness of unsaturated polyester (UP) polymer mortar, nano-SiO2 and polyurethane (PU) were incorporated. Firstly, the optimal dosages of nano-SiO2 and PU were determined through tensile test and impact test. Then, the modification mechanism of nano-SiO2/PU on UP resin was explored by microscopic image technology. In addition, the compression, flexural, fluidity, flexural bond strength and construction time tests were carried out to determine the optimal formula of nano-SiO2/PU modified UP resin mortar. Finally, the durability, impact resistance, impermeability resistance, skid resistance, and interlayer bond strength of modified UP resin mortar were studied and compared with those of pure UP resin mortar and epoxy (EP) resin mortar. Results show that the optimum proportion by mass for nano-SiO2/polyurethane modified UP resin is, UP resin: PU: dibutyltin dilaurate: nano-SiO2: initiator: accelerator: diluent: plasticizer = 1: 0.1: 0.002: 0.01: 0.01: 0.01:0.15:0.01. Furthermore, the mass proportion of modified UP resin to aggregate is 1: 1.2. In nano-SiO2/PU modification of UP resin, the -NCO groups of PU have been involved in chemical interaction with the -OH group of UP, while nano-SiO2 and UP resin are blended physically only. Compared with pure UP resin mortar, the nano-SiO2/PU modified UP resin mortar exhibited a 44% reduction in shrinkage rate, approximately 20% less corrosion loss, a 32% decrease in freeze-thaw loss, a 37% improvement in impact resistance, and increased shear bonding strength, flexural bonding strength, and tensile bonding strength by 44%, 33%, and 47%, respectively. Although the modified UP resin mortar demonstrated slightly lower performance in terms of dry shrinkage, corrosion resistance, skid resistance, and tensile bond strength compared to EP resin mortar, its freeze-thaw durability, impact resistance, flexural bond strength, and shear bond strength surpassed those of EP resin mortar. All three materials exhibited excellent impermeability. Leveraging the advantages of PU and nano-SiO2, the modified UP resin presents a promising repair material for airport pavement with enhanced toughness, high stability, and reduced cost.

Effect of absorption kinetics of superabsorbent polymers on printability and interlayer bond of 3D printing concrete

This study examines the effect of the material characteristics of superabsorbent polymers (SAPs) on the printability and interlayer bond strength of 3D printing concrete. Three types of SAP, including two acrylamide-co-acrylic polymers with coarse and fine particle sizes (S1 and S2) and an acrylic copolymer (S3), were employed. The investigated mortar mixtures had a fixed initial mini-slump flow of 195 ± 10 mm and yield stress of 290 ± 25 Pa. The fluidity of SAP-incorporated mortars was maintained by either adjusting the superplasticizer dosage or increasing the water content. Test results indicate that particle flocculation is dependent on SAP absorption kinetics shortly after the end of mixing. The use of S1 and S2 SAPs exhibiting high retention ability enhanced thixotropy, whereas the S3 SAP with rapid desorption reduced thixotropy. The S2 SAP improved the bridging effect of nucleation at early age due to its finer size, leading to a significant increase in the structuration rate at 30 min. Pull-out strength test and splitting tensile strength test were used to investigate the interlayer bond strength. The S1 SAP was the most significant in maintaining a higher internal relative humidity (IRH), thus resulting in higher 28-d interlayer bond strength, while the S2 SAP exhibited an intermediate ability to maintain elevated IRH, thus resulting in higher increase in 7-d interlayer bond strength.

Preparation of Structure-Function Integrated Layered CNT/Mg Composites.

Magnesium (Mg)-matrix composites have excellent damping and electromagnetic shielding properties. However, the mismatch between their strength and toughness limits their wide application. The aim of this work is to overcome the strength-toughness mismatch by constructing micro- and nanostructures while maintaining the good functional properties of Mg-matrix composites. Electrophoretic deposition (EPD) was used to spread carbon nanotubes (CNTs) out evenly on a Mg foil matrix. After spark plasma sintering (SPS), the grain organisation was refined, and the interlayer bonding was strengthened by hot rolling deformation. Finally, the microstructure, mechanical properties, damping properties, and electromagnetic shielding properties of the composites were analysed. Compared with the pure Mg laminates, the tensile strength and elongation of the CNT/Mg laminates were increased by 6.4% and 108.4%, respectively, with the significant improvement in toughness resulting from the increase in energy required for crack propagation due to the laminate structure. When the total rolling deflection reaches 80%, the interlayer bond strength of the material is significantly increased, the grain is further refined, and the strength and elongation of the composite material reaches the optimum, with the tensile strength reaching 241.70 MPa and the elongation reaching 6.90%. The interlayer interface and grain refinement also affected the damping Mg and electromagnetic shielding effect of the composites. This work provides an experimental idea for the preparation of high-performance structure-function integrated Mg-based materials.

Fused granulate fabrication of injection molding inserts from high-performance ULTEM 9085™ thermoplastic for cosmetic packaging industry

RTIM refers to the integration of rapid tooling (RT) using additive manufacturing (AM) with injection molding (IM). Due to the use of raw material (pellet), screw extrusion, fused granulate fabrication (FGF) allows for a cost-effective and versatile production of RTIM inserts especially compared to other material extrusion (MEX) AM processes, such as fused filament fabrication (FFF). This study 3D printed RTIM inserts out of high-performance thermoplastic polyetherimide (PEI) (ULTEM 9085) in granular form, using an in-house developed FGF system. A cosmetic compact was used as a case study part with a simplified design. A dynamic mechanical analysis (DMA) conducted on FGF ULTEM 9085 demonstrated that the strength of the inserts is sustained up to 140 °C, which suits injection molding using polypropylene (PP). Optical profilometry of the FGF 3D printed RTIM inserts demonstrated that when using a 0.4 mm nozzle, the flat surfaces produced had microscopic gaps larger than 10–1 mm. These gaps are sufficiently large so that melt of low viscosity polymer is able to flow through, which leads to undesired part flash. The IM experiments confirmed that the inserts were capable of producing PP parts but with the predicted flash. Simulated part deflection differed both on geometry and magnitude from the actual deflection measured by optical profilometry. A total of 36 prototype parts were produced before the inserts failed due to poor inter-layer bond strength. FGF RTIM using ULTEM 9085 is deemed suitable for prototype part production. Improving the inter-layer bond strength and decreasing part complexity could increase the number of parts produced.

Geometric Complexity Control in Topology Optimization of 3D-Printed Fiber Composites for Performance Enhancement.

This paper investigates the impact of varying the part geometric complexity and 3D printing process setup on the resulting structural load bearing capacity of fiber composites. Three levels of geometric complexity are developed through 2.5D topology optimization, 3D topology optimization, and 3D topology optimization with directional material removal. The 3D topology optimization is performed with the SIMP method and accelerated by high-performance computing. The directional material removal is realized by incorporating the advection-diffusion partial differential equation-based filter to prevent interior void or undercut in certain directions. A set of 3D printing and mechanical performance tests are performed. It is interestingly found that, the printing direction affects significantly on the result performance and if subject to the uni direction, the load-bearing capacity increases from the 2.5D samples to the 3D samples with the increased complexity, but the load-bearing capacity further increases for the 3D simplified samples due to directional material removal. Hence, it is concluded that a restricted structural complexity is suitable for topology optimization of 3D-printed fiber composites, since large area cross-sections give more degrees of design freedom to the fiber path layout and also makes the inter-layer bond of the filaments firmer.

Design and Application of Rich Bottom Layer Mixtures

This study aims to summarize design indexes for rich bottom layer mixtures (RBLMs) and design asphalt mixtures with superior performance to reduce reflective cracks and fatigue cracking resulting from semi-rigid base cracking in the asphalt layer. First, this study synthesizes the research results about RBLMs and introduces the related design indexes. After that, using ABAQUS 6.13, finite element analysis was performed to analyze the change in bottom stress when the base cracked and the interlayer bond weakened. SBS-modified asphalt mixtures (SMMs) and composite-modified asphalt mixtures (CMMs) were subsequently developed as RBLMs utilizing the Marshall test method and applied on a test road. The research findings reveal that design indexes for RBLMs include a volume of air voids (VVs) within the range of 2.0–3.0%, a maximum flexural strain exceeding 3500με, and a dynamic stability surpassing 1000 cycles/mm. Both mixtures satisfy the design requirements, with the CMM demonstrating superior performance and offering promising application prospects. Future research endeavors will concentrate on prolonged monitoring of the test section to authenticate the effectiveness of an RBL in practical road applications.

Magnetism and Superconductivity in the t–J Model of La3Ni2O7 Under Multiband Gutzwiller Approximation

The recent discovery of possible high temperature superconductivity in single crystals of La3Ni2O7 under pressure renews the interest in research on nickelates. The density functional theory calculations reveal that both d z 2 and d x 2–y 2 orbitals are active, which suggests a minimal two-orbital model to capture the low-energy physics of this system. In this work, we study a bilayer two-orbital t–J model within multiband Gutzwiller approximation, and discuss the magnetism as well as the superconductivity over a wide range of the hole doping. Owing to the inter-orbital super-exchange process between d z 2 and d x 2–y 2 orbitals, the induced ferromagnetic coupling within layers competes with the conventional antiferromagnetic coupling, and leads to complicated hole doping dependence for the magnetic properties in the system. With increasing hole doping, the system transfers to A-type antiferromagnetic state from the starting G-type antiferromagnetic (G-AFM) state. We also find the inter-layer superconducting pairing of d x 2–y 2 orbitals dominates due to the large hopping parameter of d z 2 along the vertical inter-layer bonds and significant Hund’s coupling between d z 2 and d x 2–y 2 orbitals. Meanwhile, the G-AFM state and superconductivity state can coexist in the low hole doping regime. To take account of the pressure, we also analyze the impacts of inter-layer hopping amplitude on the system properties.

B63: The Most Stable Bilayer Structure with Dual Aromaticity.

The emergence of a bilayer B48 cluster, which has been both theoretically predicted and experimentally observed, as well as the recent experimental synthesis of bilayer borophene sheets on Ag and Cu surfaces, has generated tremendous curiosity in the bilayer structures of boron clusters. However, the connection between bilayer boron cluster and bilayer borophene remains unknown. By combining a genetic algorithm and density functional theory calculations, a global search for the low-energy structures of the B63 cluster was conducted, revealing that the Cs bilayer structure with three interlayer B-B bonds is the most stable bilayer structure. This structure was further examined in terms of its structural stability, chemical bonding, and aromaticity. Interestingly, the interlayer bonds induce strong electronegativity and robust aromaticity. Furthermore, the dual aromaticity stems from diatropic currents originating from virtual translational transitions for both σ and π electrons. This unprecedent bilayer boron cluster is anticipated to enrich the concept of dual aromaticity and serve as a potential precursor for bilayer borophene.

Effect of Interlayer Bonding on Superlubric Sliding of Graphene Contacts: A Machine-Learning Potential Study.

Surface defects and their mutual interactions are anticipated to affect the superlubric sliding of incommensurate layered material interfaces. Atomistic understanding of this phenomenon is limited due to the high computational cost of ab initio simulations and the absence of reliable classical force-fields for molecular dynamics simulations of defected systems. To address this, we present a machine-learning potential (MLP) for bilayer defected graphene, utilizing state-of-the-art graph neural networks trained against many-body dispersion corrected density functional theory calculations under iterative configuration space exploration. The developed MLP is utilized to study the impact of interlayer bonding on the friction of bilayer defected graphene interfaces. While a mild effect on the sliding dynamics of aligned graphene interfaces is observed, the friction coefficients of incommensurate graphene interfaces are found to significantly increase due to interlayer bonding, nearly pushing the system out of the superlubric regime. The methodology utilized herein is of general nature and can be adapted to describe other homogeneous and heterogeneous defected layered material interfaces.

FEATURES OF MAGNETIC OSCILLATIONS IN A TWO-LAYER STRUCTURE WITH EXCHANGE COUPLING

Graphs of time and frequency dependences of the components of magnetic oscillations of the layers of a planar two-layer structure and their portraits of oscillations were constructed. The excitation of the structure layers for different interlayer coupling coefficients was carried out by a microwave magnetic field of circular polarization. The interlayer bond is characterized by an additional local energy minimum, the spatial position of which depends on the coupling coefficient.

Microscopic understanding of the in-plane thermal transport properties of 2H transition metal dichalcogenides

Transition metal dichalcogenides (TMDs) are a class of layered materials that hold great promise for a wide range of applications. Their practical use can be limited by their thermal transport properties, which have proven challenging to determine accurately, both from a theoretical and experimental perspective. We have conducted a thorough theoretical investigation of the thermal conductivity of four common TMDs, MoSe2, WSe2, MoS2, and WS2, at room temperature, to determine the key factors that influence their thermal behavior. We analyze these materials using calculations performed with the program, anharmonic lattice dynamics and the Boltzmann transport equation formalism, as implemented in the temperature-dependent effective potentials method. Within this framework, we analyze the microscopic parameters influencing the thermal conductivity, such as the phonon dispersion and the phonon lifetimes. The aim is to precisely identify the origin of differences in thermal conductivity among these canonical TMD materials. We compare their in-plane thermal properties in monolayer and bulk form, and we analyze how the thickness and the chemical composition affect the thermal transport behavior. We showcase how bonding and the crystal structure influence the thermal properties by comparing the TMDs with silicon, reporting the cases of bulk silicon and monolayer silicene. We find that the interlayer bond type (covalent vs. van der Waals) involved in the structure is crucial in the heat transport. In two-dimensional silicene, we observe a reduction by a factor ∼15 compared to the Si bulk thermal conductivity due to the smaller group velocities and shorter phonon lifetimes. In the TMDs, where the group velocities and the phonon bands do not vary significantly passing from the bulk to the monolayer limit, we do not see as strong a decrease in the thermal conductivity: only a factor 2–3. Moreover, our analysis reveals that differences in the thermal conductivity arise from variations in atomic species, bond strengths, and phonon lifetimes. These factors are closely interconnected and collectively impact the overall thermal conductivity. We inspect each of them separately and explain how they influence the heat transport. We also study artificial TMDs with modified masses, in order to assess how the chemistry of the compounds modifies the microscopic quantities and thus the thermal conductivity. Published by the American Physical Society 2024

Optimization of fiber reinforced lightweight rubber concrete mix design for 3D printing

A novel lightweight insulation concrete for 3D concrete printing is developed in this study, which incorporates crumb rubber (R) as a modifier to achieve low density, exceptional thermal insulation properties, and high ductility. The mechanical properties and fiber reinforcement mechanism of lightweight rubber aggregate concrete (CR) are investigated under varying R substitution rates, encompassing compressive strength, flexural strength, tensile strength, and tensile strain of CR. The thermal conductivity test offers insights into the thermal insulation mechanism of CR. The study investigates the compatibility between the material properties of fiber reinforced rubber concrete and the parameter matching of concrete printing equipment, as well as explores the relationship between interlayer bond strength and material composition. The optimal water-binder ratio for 3D printed fiber-reinforced lightweight rubber concrete compatible with printer equipment is determined through fluidity experiments and buildability tests. The findings indicate a statistically significant decrease in CR density by 16.5% when the replacement rate reaches 30%. Although the mechanical strength of CR decrease with the increasing substitution rate of R, the tensile strain showe an increasing trend. The addition of glass fiber reinforcement resulted in a notable enhancement of the mechanical properties and a significant increase in tensile strain for CR. In addition, CR thermal conductivity is reduced by 20.65%, with the excellent thermal insulation performance. This study is of great significance to promote the rational utilization of rubber resources, promote the development of circular economy, and build a conservation-oriented and environment-friendly society.

The effect of interlayer adhesion on stress distribution in 3D printed beam elements

Interlayer adhesion is one of the most pivotal aspects related to mechanical performance and durability of 3D printed concrete. However, due to continuous printing of multi-layered structures, large-scale buildings require long time intervals between layer deposition, with interlayer bond strength decreasing as time intervals between printed layers increase. This study evaluates comprehensively the effects of time intervals between layers: 1 h, 1.5 h, 2 h, 3 h, and 4.5 h as well as two different height to span ratios (hb/s). In order to assess the properties of interlayer regions microstructural examinations using techniques such as X-ray micro-computed tomography (micro-CT), scanning electron microscopy (SEM) were applied. In addition destructive testing of compressive, splitting tensile and flexural strengths along with crack opening analysis using the Digital Image Correlation (DIC) method was performed and supported with FEM analysis. The results show that interlayer adhesion strength decreased significantly for time intervals of up to 2 h, with a linearly decreasing trend. The reduction in strength the interlayer bond for a 2-h interval was 56.6%, compared to the reference specimen. Afterwards, the decrease in strength was minimal (up to 68.5% after 4.5 h time interval). However, microstructural investigations revealed that specimens with printing interval beyond 2 h exhibited noticeable continuous cracking in interfacial zone with widths reaching of up to 100 μm (SEM). At the same time micro-CT analysis confirmed creation of longitudinal pores which in turn was reflected in different cracking phenomena of specimens with longer printing intervals (>2 h). This phenomenon was further explained through FEM modeling. As an outcome it was proven through DIC that that increasing the time interval between the deposit of successive layers not only affects the strength of the entire beam, but also affects its cracking mode. The discontinuities in the interlayer contact zone leads to destruction characteristic of composite structures, thus the structure comes to be destroyed layer by layer, resulting from insufficient interlayer adhesion. The presented study is the first to fully evaluate the failure behavior of 3D printed specimens with long time intervals.

Orthotropic mechanical properties of PLA materials fabricated by fused deposition modeling

Polylactic Acid (PLA) sample manufactured by fused deposition modeling (FDM) technique is typically assumed to be transversely isotropic without a thorough examination of its orthotropy in three-dimensional space. This study investigated the mechanical orthotropy of PLA samples with two air gap levels (0 mm and -0.05 mm) and various loading directions. Tensile strength and elastic modulus were experimentally measured and the Hill48 yield model and orthotropic elastic model were calibrated. Results revealed that the anisotropy induced by interlayer bond was more pronounced than that within layer. Introducing a -0.05 mm air gap remarkably reduced voids in printed samples, enhancing the stiffness and strength of tensile samples. It also delayed the transition of fracture modes in intra-layer samples as the filament angle increased from 0° to 90°, which shifted from filament breakage to combined fracture mode and subsequently to interface failure. Despite these improvements, the inherent anisotropy of FDM printed PLA materials remained due to the oriented molecular chains and insufficient chain diffusion. The study emphasizes the importance of orthotropic mechanical models, demonstrating their reliability through calibration with acceptable accuracy.

Exfoliation of Metal-Organic Frameworks to Give 2D MOF Nanosheets for the Electrocatalytic Oxygen Evolution Reaction.

The structure and properties of materials are determined by a diverse range of chemical bond formation and breaking mechanisms, which greatly motivates the development of selectively controlling the chemical bonds in order to achieve materials with specific characteristics. Here, an orientational intervening bond-breaking strategy is demonstrated for synthesizing ultrathin metal-organic framework (MOF) nanosheets through balancing the process of thermal decomposition and liquid nitrogen exfoliation. In such approach, proper thermal treatment can weaken the interlayer bond while maintaining the stability of the intralayer bond in the layered MOFs. And the following liquid nitrogen treatment results in significant deformation and stress in the layered MOFs' structure due to the instant temperature drop and drastic expansion of liquid N2, leading to the curling, detachment, and separation of the MOF layers. The produced MOF nanosheets with five cycles of treatment are primarily composed of nanosheets that are less than 10 nm in thickness. The MOF nanosheets exhibit enhanced catalytic performance in oxygen evolution reactions owing to the ultrathin thickness without capping agents which provide improved charge transfer efficiency and dense exposed active sites. This strategy underscores the significance of orientational intervention in chemical bonds to engineer innovative materials.

Exfoliation of Metal–Organic Frameworks to Give 2D MOF Nanosheets for the Electrocatalytic Oxygen Evolution Reaction

AbstractThe structure and properties of materials are determined by a diverse range of chemical bond formation and breaking mechanisms, which greatly motivates the development of selectively controlling the chemical bonds in order to achieve materials with specific characteristics. Here, an orientational intervening bond‐breaking strategy is demonstrated for synthesizing ultrathin metal–organic framework (MOF) nanosheets through balancing the process of thermal decomposition and liquid nitrogen exfoliation. In such approach, proper thermal treatment can weaken the interlayer bond while maintaining the stability of the intralayer bond in the layered MOFs. And the following liquid nitrogen treatment results in significant deformation and stress in the layered MOFs’ structure due to the instant temperature drop and drastic expansion of liquid N2, leading to the curling, detachment, and separation of the MOF layers. The produced MOF nanosheets with five cycles of treatment are primarily composed of nanosheets that are less than 10 nm in thickness. The MOF nanosheets exhibit enhanced catalytic performance in oxygen evolution reactions owing to the ultrathin thickness without capping agents which provide improved charge transfer efficiency and dense exposed active sites. This strategy underscores the significance of orientational intervention in chemical bonds to engineer innovative materials.

Laboratory cracking and interlayer bond strength performance characterization of full-scale accelerated geosynthetic reinforced asphalt concrete

This study was conducted to evaluate the performance of geosynthetic reinforced asphalt pavements through full-scale and laboratory testing. The study also investigated the field cracking performance of geosynthetic test sections under accelerated loading and validated with the laboratory cracking performance results. Three sections were constructed including: control, geogrid and geosynthetic reinforced AC. After applying the accelerated loading, cores and slabs were extracted from the wheel path (W) and outside of the wheel path (OW) to evaluate the impact of accelerated loading on cracking performance of AC. The laboratory cracking performance and shear bond strength were assessed using Indirect Tension Asphalt Cracking Test (IDEAL-CT), Interlayer Shear bond Strength (ISS), Bending beam Fatigue (BBF), and Texas overlay tests. Additionally, strain response on top of pre-existing notch was also analyzed from the accelerated test sections to monitor field cracking potential of reinforced AC and to validate it with laboratory cracking performance. According to the BFF, OT and ISS results, the W AC showed degraded performance compared to OW AC, however, IDEAL-CT test results mentioned that W AC showed better cracking performance compared to OW AC. Overall, geosynthetic reinforced AC showed better laboratory cracking performance and lower shear bond strength. At full-scale section, higher tensile strains were registered indicating that geosynthetic reinforcement can undergo potentially larger displacement without failing in the pre-existing crack area. Both laboratory and field test results compliment the findings of each other.

Post-fire properties of lightweight 3D printed concrete containing expanded perlite

There has been an increase in construction with three-dimensional (3D) printing technology but 3D printed (3DP) structures also require weight reduction similar to conventional reinforced concrete structures. In addition, the behaviour of this type of structure against fire needs to be investigated. The number of printed layers and the time gap between layers for the 3DP specimens were among the variables examined. The test results demonstrate that as the replacement percentage of natural sand (NS) with expanded perlite (EP) increased, at 25% volume of replacement, the interlayer bond strength increased on average by 18.6%, while at the highest replacement level, of 75%, the strength decreased on average by 5.8%. Additionally, by incorporating EP, the compressive and flexural strengths of 3DP specimens declined on average from 9% to 29.7%, and from 39.3% to 49.3%, respectively. As the replacement level of NS increased, residual compressive and flexural strengths increased after exposure to 800°C. Furthermore, it was demonstrated that exposure to high temperature had the least effect on interlayer bond strength, whereas it significantly reduced the compressive and flexural strength. The results show that increasing the time gap between layers reduced interlayer bond strength and flexural strength while negligibly affecting compressive strength.

An in-situ method to evaluate the interlayer bond between hot-mix asphalt and portland cement concrete surface

Proper bonding between different layers of a composite pavement is a major factor in ensuring that the entire structure acts as a monolithic layer under load. This paper studies the bonding between hot mix asphalt (HMA) overlay and Portland cement concrete (PCC) pavement using tack coats. An in-situ pull-off test method was developed for use on project sites on a routine basis to screen and test the quality of bond between asphalt layer and concrete layer. This test replaces the arduous process of coring through often times very thick concrete layer with steel rebars, transporting the core to a lab, trimming the concrete side of the core to fit the shear jig, and finally conducting a shear test. Results show that the in-situ pull-off test method developed in this study is strongly correlated to the laboratory based direct shear test. Limits were also suggested to indicate an adequate bond strength in the PCC–HMA interlayer on the basis of laboratory and field testing. This study also evaluates the influence of various factors on the performance of the interlayer bond in laboratory. These factors include the type of tack coat, application rate, the texture of the concrete pavement surface, the surface cleanliness and the surface moisture. Results indicate that sandblasting and hydro-demolition textures offer the best interlayer bond strength, the influence of application rate is not significant on the interlayer bond strength and the influence of surface moisture and cleanliness are dependent on the type PCC surface texture.