Experimental investigation of bond performance between BFRP and different strength recycled-aggregate concrete

In recent years, there has been a large number of studies on recycled-aggregate concrete as a potential solution to the problem of a scarcity natural resources. This study investigated the bonding performance of a new reinforcement material employed in medium and high-strength recycled aggregate concrete. The pull-out test was carried out by employing basalt fiber-reinforced polymer (BFRP) bars with different diameters (12, 14, and 20 mm) in medium and high-strength concrete with different ratios of recycled coarse aggregate replacement (0, 25, 50, 75, and 100%). Based on the concrete bond damage, the failure modes were identified, the corresponding bond mechanism was analyzed and the bond stress–slip characteristics were summarized. The effect of each parameter on the failure mode, bond strength, and the bond-slip curve between recycled-aggregate concrete and BFRP bars was evaluated. Results indicated that as the diameter of the BFRP bar increased, the failure mode was shifted, the uneven distribution of bond stress became more pronounced, and the bond strength showed a decreasing trend. Two distinct situations of medium to high-strength concrete with very different relative bond strengths at different replacement ratios were found. The relative bond strength of medium-strength concrete increased at first and then decreased with the increase of the replacement ratio of recycled coarse aggregate. A non-linear relationship between the bond strength of recycled concrete and its compressive strength was found. The two-stage model was proposed to describe the bonding behaviour more accurately between BFRP bar and medium to high-strength recycled aggregate concrete.</p

Study on the bond properties between basalt fiber-reinforced spontaneous combustion coal gangue concrete and BFRP bars

Microstructural characterization of spontaneous combustion coal gangue (SCCG), the hydration products and mechanism of spontaneous combustion coal gangue concrete (SCCGC) were discerned through microscopic analysis. The bond performance was assessed employing a central pull-out test on samples variably substituted with SCCG (0%, 25%, 50%, 75%, and 100%) and augmented with basalt fiber (BF) (0%, 0.1%, 0.15%, and 0.2%). The failure mode and bonding mechanism were also revealed by this test. The bond-slip curves were fitted by various bond-slip constitutive models and a suitable model was found for each section. As indicated by the results, SCCGC possessed a lower carbon content and higher Al and Si element contents. These elements would undergo secondary hydration reactions with CH, which could enhance the strength of the ITZ and the compactness of the bond interface between BFRP bars and concrete. The failure modes were splitting and pull-out. An inverse correlation was observed between bond strength and the increment in SCCG aggregate substitution, ranging from a decline of 2.6% to 23.1%. As the BF content increased, the bond strength and peak slip increased by 3.9% ∼ 19.7% and 4.0% ∼ 14.6%, respectively. Furthermore, the reinforcing effect of BF on bond strength increased from 3.9% ∼ 10.3% to 8.8% ∼ 19.7% as the SCCG replacement rate increased, which was noticeable. The Malvar model and the Continuous Curve model were the best fitting models for the ascending and descending sections of bond-slip curves, respectively, while the residual stage was well fitted by the Hao Qingduo model.</p

Uncovering the Effect of A‑Site Cations on Localized Excitons Photoluminescence of Manganese-Doped Zinc Chloride Nanocrystals

Elucidating the key factors that affect the localized excitons (LEs) photoluminescence (PL) in lead-free metal halide nanocrystals (NCs) is important for their optoelectronic applications. However, the effect of A-site cations on LEs based PL is not well understood. Herein, we varied the A-site cation ratio (Rb/Cs) to investigate the influence on LEs based PL in manganese-doped zinc chloride NCs. Through time-resolved photoluminescence (TR-PL) spectra and density functional theory (DFT) calculations, we discovered that Cl vacancy is energetically more favorable in Mn2+-doped Rb3ZnCl5 NCs compared to Mn2+-doped Cs3ZnCl5 NCs. The higher concentration of Cl vacancy increases the nonradiative recombination process in Rb3ZnCl5:Mn2+ NCs, ultimately determining the PL efficiency. This research enhances the understanding of the A-site cation effect on LEs-based PL in lead-free metal halide NCs

Molecular Engineering of Highly Fluorinated Carbon Dots: Tailoring Li⁺ Dynamics and Interfacial Fluorination for Stable Solid Lithium Batteries

Fluorinated carbon dots (FCDs) have garnered interest owing to their distinct physicochemical properties. Nevertheless, intricate synthesis procedures and quite low fluorine doping levels limit its development and application. Herein, we propose a facile approach based on the Claisen–Schmidt reaction to realize gram-scale synthesis of highly fluorinated carbon dots (up to 20.79 at. %) at room temperature and atmospheric pressure, and a comprehensive exploration of the specific reaction mechanism is conducted. Furthermore, in consideration of the high fluorine content, good dispersibility, and compatibility with polymer electrolyte, the synthesized FCDs are utilized as an additive for PEO-based solid electrolytes of a Li battery to improve its ionic conductivity, interface stability, and mechanical properties. The introduction of FCDs can not only reduce the crystallinity of PEO and enhance the interaction of polymer chains, but also facilitate the establishment of uninterrupted pathways and in situ fluorination at the interface, which is substantiated by both theoretical calculations and experimental findings. As a result, the lithium symmetrical battery can operate stably for 1000 h at a current density of 0.4 mA cm–2. Simultaneously, the LiFePO4/Li battery utilizing the composite electrolyte exhibits a capacity of 130.3 mAh g–1 over 300 cycles while maintaining a capacity retention rate of 95.10%. This study develops a strategy for synthesizing highly fluorinated carbon dots, which demonstrate a useful influence on PEO electrolytes, thus boosting the advancement of FCDs and solid-state batteries