Materials and Structures最新文献

The bonding performance between fiber-reinforced polymer (FRP) bars and high-strength thermal insulation mortar (FRP-HIM) is crucial for its application in masonry structure thermal insulation and the reinforcement of integrated renovation projects. This paper studies the bonding performance of FRP-HIM through pull-out tests. The analysis considers factors such as the type of FRP bar, the diameter of the FRP bar, the anchoring length of the FRP bar, and the cover thickness by evaluating their impact on the bonding performance and failure mode. The test results demonstrate that carbon fiber-reinforced polymer (CFRP) bar specimens with smaller rib heights exhibited pull-out failure, while both basalt fiber-reinforced polymer (BFRP) bars and (glass fiber-reinforced polymer) GFRP bar specimens displayed splitting failure. Simultaneously, the bond performance of FRP-HIM specimens gradually increased with higher FRP bar rib heights. When rib heights were identical, specimens with higher elastic modulus FRP bars exhibited smaller ultimate slip values during pull-out tests. The average bond strength and slip of FRP-HIM specimens increased progressively with greater cover thickness of the HIM, but decreased gradually with larger FRP bar diameters and longer anchorage lengths. By employing the principles of thick-walled cylinders in elastic mechanics, a theoretical model for the bond strength of FRP-HIM is established through a fitting analysis of the test data. The calculated values from this model showed good agreement with the test values when compared to the experimental results.

Determining the yield stress of cementitious materials is crucial for casting and concrete mix design. Fresh concrete possesses yield stress, behaving as a solid with viscoelastic properties below this threshold. When the yield stress is exceeded, concrete flows with a steady-state behavior commonly described by the Bingham or Herschel-Bulkley models. As the construction industry increasingly consumes more and more scarce raw materials, there is a growing need to develop and explore alternative construction materials to replace traditional ones while valorizing waste. Raw Crushed Wind Turbine Blade (RCWTB) has demonstrated interesting results when included in cementitious mixtures. However, a full characterization of rheology including the yield stress of mixtures containing RCWTB is still missing and would be of great practical interest. In this paper, the yield stress of cementitious pastes and mortars containing RCWTB with two different water/cement ratios is measured. Results demonstrate higher yield stress for higher RCWTB inclusion, this is mainly due to the bridge effect of the Glass Fiber Reinforced Polymer (GFRP) contained in the RCWTB. Finally, a physical model is applied for RCWTB to predict GFRP fibers maximum packing fraction based on their geometry, elastic properties, and the rheology of the surrounding cement-based material. This model is then validated with experimental yield stress of cement pastes and mortars.

The behavior of 3D-printed concrete (3DPC) differs significantly from conventional concrete, as 3DPC is printed in layers, leading to interface formation that impacts its hardened state mechanical strength. These interface layers are of different types according to the stacking nature, namely deposition interface (with self-weight aided cohesion due to vertical stacking of layers) and transition interface (without self-weight aided cohesion due to horizontal translation of layers). Thus, investigating the anisotropic mechanical properties of hardened 3DPC and studying the behavior of interfaces is crucial for ensuring its safe application in structural design. This research focuses on the anisotropic mechanical behavior of hardened 3DPC under compression and tension, considering directional properties owing to the interfaces. The study further investigates the shear behavior of interfaces. The study uses experimental tests such as the axial compression test for compression, split tension test for tension and couplet test for interface behavior under shear. The study compares the strength and deformation characteristics of hardened 3DPC and the bond strength between layers of different types of interfaces, through displacement-controlled monotonic static loading and quantifying the frictional properties such as cohesion and the internal angle of friction of the interfaces. The study observes a decrement of 18% for the transition interface compared to the deposition interface in terms of cohesive parameters. The study confirms that the deposition interfaces show higher resistance than transition interfaces, highlighting the latter’s weakness in achieving proper bonds between the layers and affecting the structural performance, which should be a concern for structural design.

The retardation and depression mechanisms induced by two differently charged styrene acrylate copolymer latexes on OPC hydration, adsorption and complexation, were investigated. The used latexes were dialysed latexes where the constituents beside the polymer particles were removed and a high polymer/cement ratio was used to ensure that complexation might occur. For the first time ion complexation by polymer particles was observed directly by measuring ions in unfiltered pore solutions. The results were compared with the filtered pore solution composition, total organic carbon content, in-situ X-ray analysis and heat flow calorimetry. It is found that complexation occurs, but the effect on the hydration is limited compared to the adsorption of polymer particles. The adsorption process, dependent on the surface charge of the polymer particles, determines the strength of the negative influence on the early OPC hydration.

Utilizing seawater and sea sand for construction engineering represents a significant approach to achieving efficient exploitation and utilization of marine resources. The incorporation of supplementary cementitious materials (SCMs) into seawater–sea sand cementitious materials can effectively improve their performance, provide a favorable service environment for steel reinforcement, and promote the sustainable development of these materials. This study examines the effects of several typical SCMs on the properties of seawater-sea sand mortars (SSSMs), including strength, hydration, microstructure, and chloride binding. The results show that the particle size and pozzolanic reactivity of SCMs are the primary factors influencing strength development. The unique solution environment created by seawater and sea sand significantly enhances the early hydration of SCMs and accelerates the formation of microstructure. The highly reactive Al₂O₃ present in SCMs can interact with chloride provided by seawater and sea sand to form Friedel’s salt, thereby reducing the chloride content in SSSMs. The binding capacity of SCMs for free chlorides is influenced by both chemical binding and physical adsorption capabilities. The incorporation of GGBS, FA, and MK reduce the free chloride content in SSSC from 3.91 mg g⁻¹ to 1.95–2.30 mg g⁻¹, 2.09–2.66 mg g⁻¹, and 0.92–1.70 mg g⁻¹, respectively. This study comprehensively compares the effects of several typical SCMs on the performance of SSSMs, and provides substantial experimental data to elucidate their influence mechanisms. These findings offer experimental validation for utilizing SCMs in seawater–sea sand cementitious systems.

When used as crack repairing material, epoxy asphalt lacks the required flexibility, and styrene–butadiene–styrene (SBS) modified asphalt (SA) is prone to aging, impairing durability. To overcome these issues, an epoxy resin prepolymer (ERP) and SBS composite modified asphalt (SECA) was prepared. The properties of SECA were systematically evaluated after aging simulated by rotating film oven test (RTFOT), pressure aging vessel (PAV) and ultraviolet aging chamber methods. The optimum dosages of ERP and SBS were determined by the evolution of basic performance of SECA. The effects of polymer degradation on high-temperature rheology were investigated through temperature sweep, multiple stress creep (MSCR), and master curve modeling. Fourier transform infrared (FTIR) analysis was used to analyze the chemical changes during aging, while fluorescence microscopy (FM) revealed the distribution of ERP and SBS. Results indicate that the optimal aging resistance of SECA is achieved with 4% SBS and 30% ERP. The aging-induced deterioration of SECA is mainly due to asphalt oxidative hardening combined with polymer bond breakdown and reorganization. SECA exhibits superior aging resistance over SA, mainly because the formed interpenetrating polymer network structures (IPNs) that delays structural degradation. These findings provide a valuable reference for selecting anti-aging crack repairing materials in high temperature regions.

Cold recycling techniques have gained increasing attention over the past few decades as sustainable and cost-effective solutions for pavement rehabilitation. However, the design of cold recycled asphalt mixtures (CRMs) remains challenging, mainly due to the limited understanding of how active fillers influence binder dispersion, cohesion development, and long-term mechanical performance. In particular, the lack of clear criteria for selecting the optimal filler type and dosage hinders consistent field application and performance prediction. This study investigates the influence of active fillers on the mechanical behavior of CRMs through a comparative experimental program. CRM specimens were prepared using either foamed bitumen or bitumen emulsion and incorporating two commonly used active fillers, cement and lime, at different dosages. Two mechanical tests were conducted to evaluate mechanical properties: the indirect tensile strength (ITS) test and the monotonic triaxial shear strength (TSS) test. Additionally, a shear stress to strength ratio analysis was performed to comparatively evaluate the rutting potential under traffic loading. Results indicate that both filler type and amount significantly affect mechanical response. ITS was more sensitive to early binder-aggregate interaction, while TSS better reflected the long-term effects of filler-binder interaction. Cement contents slightly above the commonly recommended 1% threshold may improve the mechanical response, increasing stiffening without clear evidence of brittle behavior. In contrast, lime was effective only at 2% or higher, with 1% proving insufficient for enhancing cohesion or activating pozzolanic reactions. These findings provide preliminary but meaningful insights into the role of active fillers, and their relative influence on the mechanical behavior of cold recycled mixtures.

The split-joint is the weak link of the segmental prefabricated concrete cap beam. In order to study its shear bearing capacity, this paper conducted shear performance tests and finite element simulation analysis on the key epoxy joint of the cap beam. The shear load-slip curve and the cracking failure pattern obtained by the simulation are in good agreement with the test results. The effects of lateral compressive stress, concrete strength, reinforcement ratio, number of teeth, depth and angle of teeth on the shear strength of the epoxy joint were discussed by using the verified finite element model. The results show that the failure mode of the epoxy joint under direct shear load is brittle failure. The shear capacity of the epoxy joint increases with the increase of lateral compressive stress, concrete strength and reinforcement ratio. When the lateral compressive stress increases from 1 to 9 MPa, the shear capacity increases by about 71%. When the concrete strength grade is increased from C40 to C80, the shear capacity increases by about 22%. When the internal reinforcement ratio of key increases from 0.5 to 2.6%, the shear capacity increases by 14.8%. The number, depth and inclination of key have a great impact on the shear strength of the epoxy joint. It is recommended that the number of key should not exceed 3, the depth should not exceed 105 mm, and the inclination should not exceed 45° in the actual project. Based on the Gopal formula, a practical calculation formula for the shear strength of the epoxy joints was established. The calculation results of the formula are in good agreement with the test and finite element analysis results, and can be used to calculate the shear strength of the epoxy joints.

Digital fabrication offers the opportunity to reintroduce force-flow-aligned reinforcement as a material-efficient solution in concrete construction. Nevertheless, it raises new questions regarding the structural design and performance of such elements.

The current paper discusses design and structural performance of full-scale reinforced concrete beams of two types, with the same external dimensions but different reinforcement layout reflecting fabrication methods. One type was traditionally cast, and features modern orthogonal reinforcement composed of longitudinal bars and stirrups. The other type was digitally fabricated with Shotcrete 3D Printing (SC3DP) additive manufacturing method, and with force-flow aligned reinforcement in form of bent-up steel reinforcement bars. Both types were tested under three- and four-point bending, to investigate their response under shear force and bending moment respectively.

The structural testing results prove that the two types of beams can be considered as equivalent under the bending moment at Ultimate and Serviceability Limit States, while the SC3DP beam contains only around half of steel reinforcement mass compared to the cast one. Furthermore, the challenges in calculation and verification of reinforced concrete beams with non-orthogonal reinforcement are discussed. Additionally, it is demonstrated that the same cementitious material exhibits higher mechanical performance when processed with SC3DP compared to casting in formwork, with similar or lower scatter. Finally, it is concluded that the reinforced SC3DP elements follow the same structural principles as the cast concrete ones, and as such can be designed using existing methods while respecting the reinforcement detailing as required per complex layouts.

Grouting materials play a critical role in road engineering applications. However, traditional cementitious or polymer-based grouting materials have defects such as limited adjustability of fluidity and mechanical strength high energy consumption, and serious environmental pollution. To address these challenges and promote resource recovery, this study utilized industrial solid wastes—slag (SL), fly ash (FA), and anhydrite (AH)—whose disposal poses environmental risks. These materials were combined with citric acid (CA) and anhydrous borax (AB) to develop a semi-flexible pavement grout based on a geopolymer matrix. The resultant material demonstrates tunability in both curing time (30–120 min) and compressive strength (10–60 MPa), achieved through systematic composition optimization. Through mechanical property testing and microstructural analysis, the curing mechanism of the material was elucidated. Furthermore, based on the requirements of pavement engineering applications, the high-temperature stability, low-temperature crack resistance, moisture stability, and fatigue characteristics of semi-flexible pavement asphalt materials were systematically evaluated, demonstrating their excellent and practical road performance.. This study provides theoretical foundations and technical support for enhancing pavement material performance and promoting energy-saving and environmentally friendly road construction.