Materials and Structures最新文献

This study systematically investigates the effects of BF and NS on the mechanical performance of concrete at ambient temperature, as well as its impact resistance and microstructural evolution following exposure to elevated temperatures. Compressive, flexural, and splitting tensile strengths of NS–BF hybrid concrete were measured under ambient conditions. Specimens were then subjected to thermal exposure from 20 °C to 800 °C to evaluate residual mass, surface integrity, impact performance, and microstructural characteristics. A two-parameter Weibull distribution model was applied to statistically analyze the number of impact blows under both ambient and elevated temperature conditions. The results show that NS–BF synergy markedly enhanced the mechanical and impact properties of concrete. The mix with 0.15% BF and 1.0% NS exhibited optimal static mechanical properties, while BF0.15NS1.5 achieved significant gains in initial cracking energy (W₁) and final cracking energy (W₂), increasing by 29.06% and 33.19% at 20 °C, and by 30.08% and 35.65% at 200 °C, respectively, compared to normal concrete. Impact resistance, however, deteriorated significantly above 400 °C due to severe thermal damage. The impact energy degradation index displayed a U-shaped trend with temperature, indicating a critical damage threshold around 400 °C. Additionally, this study develops an impact energy prediction model for different failure probabilities and elevated temperature conditions (20–400 °C), providing a robust theoretical foundation and practical guidance for the engineering design and application of NS–BF composite concrete under combined elevated temperature and impact loading.

Gaining a deeper insight into stress vs crack opening curve of concrete is essential, especially when crack stability governs the durability and the capacity of a structure. Despite its rationality, the direct-tension test faces the challenges entailed by strain-softening materials, namely axial and flexural instability. To address these issues, an innovative frameless testing apparatus—nicknamed 3action—was developed. The system employs three symmetrically arranged electromechanical actuators that directly apply tensile force to short, notched cylindrical specimens. The samples are first bonded to thick steel platens and then bolted to the machine’s base and moving head. The actuators, optimised for stiffness and responsiveness, operate through three parallel control loops that ensure uniform crack opening, monitored by three LVDTs positioned astride the notch. Following each tension test, the two halves of the fractured specimen were used to perform the splitting (Brazilian) tests. This paper presents and analyses results obtained from a highly brittle high-performance concrete mix, investigating the influence of polypropylene fibres and thermal exposure up to 250 °C. Finite element modelling is also employed to validate the reliability of the direct tension test in capturing the constitutive response of the material without resorting to inverse analysis. The study demonstrates the potential of transforming advanced experimental setups into standardised testing methods, offering valuable insights into the fracture behaviour of concrete under diverse mechanical and thermal conditions.

Polymer-modified cementitious systems (PMMs) are widely used in civil engineering applications for repair and waterproofing due to their specific characteristics. However, manufacturer guidelines often do not cover all real-world conditions, particularly regarding curing protocols and environmental sensitivity. This study investigates the influence of curing duration and accelerated weathering on the performance of PMMs to support the development of performance-based application guidelines. Mortars incorporating conventional polymers—styrene-butadiene rubber (SBR) and polyacrylic ester (PAE), as well as a novel silane-based emulsion (SIL), were compared with unmodified cementitious mortar (UCM). Specimens were cured for 1, 7 and 28 days, followed by exposure to alternating UV radiation and wetting cycles to simulate accelerated weathering. The mortar performance was evaluated in terms of fresh properties, pore structure, mechanical strength and durability. The results show that the performance with PMM varied significantly with curing duration and environmental exposure. The SBR and PAE systems were more sensitive to curing time, with only the 28-day curing condition ensuring strength retention after weathering. SBR-modified mortars exhibited the lowest drying shrinkage under minimal curing (1 day) but were more permeable under these conditions. In contrast, SIL-modified mortars showed better resistance to weathering, with improvement in both strength and permeability attributed to the UV stability of Si–O-Si bonds and a refined pore structure, evidenced by a 11% reduction in total porosity, compared with UCM. The SIL systems also exhibited minimal sensitivity to curing duration, and further performance gains with increased polymer dosage, which has an optimal level of 1%. These findings highlight the critical importance of aligning polymer selection and curing strategies with the environmental exposure and underscore the potential of SIL-based systems in conditions, especially where optimal curing cannot be assured or weathering could occur.

The prevention of intermediate crack-induced (IC) debonding failure in reinforced concrete (RC) members strengthened with fiber-reinforced polymer (FRP) materials is a key challenge in structural strengthening applications. This study examines the effectiveness of FRP spike anchors in mitigating IC debonding failures, focusing on variables such as anchor placement, dowel diameter, and fan length. An experimental program involving thirteen beams strengthened with externally bonded FRP sheets and secured with FRP spike anchors of varying diameters (3, 5, 6.5, 8, and 10 mm) is presented. Anchors were positioned either across the entire span, within the shear span, or concentrated at the ends of the FRP sheets. The findings are reported in terms of load capacity for each configuration and the utilization of FRP strain prior to failure. Load–deflection behavior and the analysis of failure modes are discussed for all samples, revealing a maximum load increase of 9.4% compared to unanchored beams. Anchors placed solely in the shear span demonstrated superior performance over those distributed across the span, producing more uniform FRP strain distributions in peak moment areas. Further, anchors located at the ends of the sheets improved peak displacements at failure by 40%.

To address the poor chemical stability of organic anti-aging agents in asphalt binder and the incompatibility of inorganic ones, this study developed a novel anti-aging agent IZrP (IPPD- intercalated zirconium phosphate) by intercalating the hindered amine antioxidant IPPD into zirconium phosphate (ZrP). The effects of ZrP, IZrP, IPPD and the conventional antioxidant pentaerythritol tetrakis [3-(3',5'-di-tert-butyl-4'-hydroxyphenyl) propionate] (BHPM) on the physical, rheological and anti-aging properties of asphalt binder were systematically studied. Results demonstrates that IPPD organic intercalation expands ZrP interlayer spacing from 0.76 to 1.87 nm, significantly enhancing hydrophobicity. Thermogravimetric analysis reveals increased decomposition temperatures for intercalated IPPD, confirming ZrP’s protective role in improving thermal stability. IZrP improves the low-temperature, fatigue, and storage stability of asphalt binder compared to ZrP. In thermal-oxidative aging tests, ZrP and IZrP exhibit superior performance in enhancing the aging resistance of asphalt binder compared to organic agents (BHPM, IPPD), maintaining stable long-term performance. And IZrP demonstrates the best performance, extending the asphalt binder's service life by 38.8%. These findings establish a novel strategy for developing high-efficacy, high-stability asphalt binder anti-aging agents, advancing the development of long-life asphalt pavements.

The accelerated mortar bar test (AMBT) is among the most widely used tests for evaluating the susceptibility of aggregates to alkali-silica reaction (ASR), as well as the ability of supplementary cementitious materials (SCMs) in mitigating this expansive reaction. A literature gap was identified regarding the influence of inert fillers, such as limestone and quartz, on the AMBT-induced expansion, which has not yet been thoroughly assessed. This research aims to evaluate the effects of replacing 20% of Portland cement by limestone or quartz and elucidate the physicochemical interactions that govern ASR on AMBT. The results reveal that limestone does not affect ASR expansion, whereas quartz mitigates the reaction. The retrograde solubility behavior of limestone impairs hydration and inhibits the alkali-binding capacity of C–S–H by increasing its Ca/Si ratio. In contrast, quartz undergoes AMBT-induced pozzolanic reaction, which enhances the formation of C–S–H, and increases the concentration of silicon in the pore solution, both of which promote alkali-binding. This study highlights that the commonly assumed dilution effect (i.e., 20% reduction in expansion) cannot be considered a general rule when replacing cement with inert fillers. This key methodological aspect should be factored in when interpreting the influence of prospective SCMs on AMBT-induced ASR expansion.

Rammed earth is a traditional earthen construction material widely used in the Auvergne-Rhône-Alpes region of France. It acts as a thermal and hygroscopic buffer; however, its relatively high thermal conductivity limits its compliance with current energy performance regulations. To meet these standards, additional insulation is often required. Nevertheless, due to the strong hydro-mechanical coupling inherent to rammed earth, particular attention must be paid to the choice of insulation system. The assembly must maintain a proper moisture balance to ensure the long-term durability and mechanical integrity of the structure. The objective of this study is to identify suitable insulation solutions for rammed earth walls, based on scientific literature and professional practice, while considering moisture- related risks, thermal performance, and environmental impacts. The analysis is carried out at two steps: first, by examining the intrinsic properties of rammed earth and potential insulation materials individually; and second, by evaluating their performance within assembled rammed earth-insulation systems, taking into account additional factors such as implementation, material interface and surfaces finishes. Despite numerous studies, knowledge gaps remain regarding, interface behaviour, selection of hygroscopic and capillary insulation materials and real-scale behaviour.

Salt ion erosion, which occurs during winter maintenancer or in coastal areas and near saline lakes is a key factor affecting the long-term performance of asphalt pavement. However, the underlying molecular mechanisms of asphalt eroded by salt ions remain unclear. Thus, this study aims to investigate the erosion behavior and mechanism of asphalt and asphalt-aggregate interface exposed to NaCl, CaCl_2, Na₂SO₄, and CaSO₄ solutions. For this purpose, models of asphalt, asphalt-aggregate and salt ions were established using molecular dynamics (MD) simulation. The chemical composition and conventional binder properties of asphalt were examined by SARA fraction and physical tests. MD results showed that salt ions significantly deteriorated the performance of asphalt and asphalt-aggregate interface, as evidenced by increased cohesive energy density (CED), solubility of asphalt and diffusion capability of asphalt at the aggregate surface, reduced cohesive energy density of the van der Waals (CED_vdW), the viscosity of asphalt and the interfacial adhesion of the asphalt-aggregate interface, as well as the altered distribution of asphalt components on aggregate surface. The results of SARA fraction analysis, conventional binder properties tests and adhesion pull-off tests indicated that salt ion erosion led to decreased aromatics, saturates and resins content, penetration and ductility, the pull-off test strength, as well as increased asphaltenes content, which are consistent with the MD simulation and thermal oxidative aging results. Both MD and laboratory results demonstrated that Na⁺ and Cl⁻ exhibited the strongest erosion effects on asphalt and asphalt-aggregate interface due to their small ionic radii and great diffusivity. In contrast, Ca²⁺ and SO₄²⁻ exerted weaker effects due to their large size and strong hydration. The findings of the study provide a theoretical foundation for the development of corrosion-resistant asphalt materials under salty conditions.

Graphical abstract

The mechanical integrity of cement sheaths in oil and gas well production has garnered considerable attention due to global incidents of oil and gas leaks. However, limited instances have explored the correlation between bonding strength and the microstructure of the interfacial transition zone (ITZ) at casing-cement and formation-cement interfaces under high temperatures. This study employs a back-scattered electron scanning electron microscope and digital image processing to quantify the porosity of the bulk paste and the ITZ thickness at the cement-casing and cement-formation interfaces. To reveal the underlying mechanism of temperature and silica flour dosage on the compressive strength of hardened well cement paste and the bonding strength at the cement-casing and cement-formation interfaces, the relationship between the mechanical properties and the microstructure results of bulk paste, casing-cement interface, and formation-cement interface is analyzed across various silica flour dosages and temperatures. The results indicate that the addition of silica flour leads to an initial increase, followed by a decline, and finally an increase in the ITZ thickness at the cement-casing and cement-formation interfaces at 150 °C. When the silica flour dosage is fixed at 0 wt.% or 50 wt.%, the ITZ thickness between the casing/formation and cement pastes increases with rising temperature. Furthermore, the bonding strength of the cement-casing and cement-formation interfaces decreases as the ITZ thickness increases.

3D concrete printing technologies enhance design freedom while reducing material use and costs without the need for formwork. Thereby, structural build-up is the key property governing stability and early strength evolution of 3D printed concrete after placement. Structural build-up is influenced by various factors, i.e., environmental conditions such as temperature. In this paper, the influence of ambient temperature on structural build-up was investigated through experimental and numerical approaches. Three experimental setups (small amplitude oscillatory shear, constant shear rate, and small amplitude oscillatory extensional tests) were applied to materials of increasing complexity under varying temperature conditions. A common modeling framework based on the maturity approach was developed to capture the time and temperature evolution. A stochastic framework was employed to estimate the unknown model parameters using experimental data. Experimental results demonstrate a significant temperature influence on structural build-up, consistent across all test setups and materials. The calibrated models successfully predict the structural build-up under different temperatures, confirming the applicability of the maturity approach to rheological parameters at early age. Furthermore, the stochastic parameter estimation allows a correct quantification of the uncertainties, enhancing model reliability. The comparison of two time evolution formulations indicates that a model with an additional linear stage is required for predicting the increase of the storage moduli (({G}{prime}), ({E}{prime})). In conclusion, the study demonstrates that temperature significantly affects the structural build-up, and that the proposed modeling approach allows to predict this behavior.