Residual Bond Research Articles

Carbohydrate Structure Database oligosaccharide conformation tool.

Population analysis in terms of glycosidic torsion angles is frequently used to reveal preferred conformers of glycans. However, due to high structural diversity and flexibility of carbohydrates, conformational characterization of complex glycans can be a challenging task. Herein, we present a conformation module of oligosaccharide fragments occurring in natural glycan structures developed on the platform of the Carbohydrate Structure Database. Currently, this module deposits free energy surface and conformer abundance maps plotted as a function of glycosidic torsions for 194 "inter"residue bonds. Data are automatically and continuously derived from explicit-solvent molecular dynamics (MD) simulations. The module was also supplemented with high-temperature MD data of saccharides (2,403 maps) provided by GlycoMapsDB (hosted by GLYCOSCIENCES.de project). Conformational data defined by up to 4 torsional degrees of freedom can be freely explored using a web interface of the module available at http://csdb.glycoscience.ru/database/core/search_conf.html.

Characterization, antioxidant and anticoagulant properties of exopolysaccharide from marine microalgae

The sulfated exopolysaccharide extracted from marine microalgae attracted considerable attention from both the nutraceutical and pharmaceutical industries. In the present study biomass of five marine microalgae were screened to find strains with high capacity for the production of sulfated exopolysaccharides. The anticoagulant and antioxidant activities of extracted sulfated polysaccharides were evaluated using activated partial thromboplastin time (aPTT), prothrombin time (PT), DPPH and ABTS assays, respectively. The sulfated polysaccharides extracted from Picochlorum sp. showed a strong DPPH scavenging effect with 85% antioxidant activity. The sulfated polysaccharides of Chlorella sorokiniana, Chlorella sp. (L2) and Chlorella sp. (D1) scavenged more than 90% of the ABTS radicals. However, the sulfated polysaccharide extracted from Chlorella sorokiniana, and Chlorella sp. (N4) showed anticoagulant properties. The dual anticoagulant-antioxidant activities in Chlorella sorokiniana could be explained by the combination of various factors including sulfate content and their binding site, monosaccharide residue and glycoside bond which are involved in the polysaccharide’s bioactivity.

Mixture optimisation for cement-soil mixtures with embedded GFRP tendons

The glass fiber-reinforced polymer (GFRP) rebar reinforced cemented soil is widely employed to solve the weak foundation problem led by sludge particularly. The robustness of this structure is highly dependent on the interface bond strength between the GFRP tendon and cemented soils. However, its application is obstructed owing to the deficient studies on the influence factors. Therefore, this study investigates the effects of water content (Cw: 50%–90%), cement proportion (Cc: 6%–30%), and curing period (Tc: 28–90 days) on peak and residual interface bond strengths (Tp and Tt), as well as the unconfined compression strength (UCS). Results indicated that mechanical properties were positively responded to Tc and Cc, while negatively correlated to Cw. Besides, Random Forest (RF), one of the machine learning (ML) models, was developed with its hyperparameters tuned by the firefly algorithm (FA) based on the experimental dataset. The pullout strength was predicted by the ML model for the first time. High correlation coefficients and low root-mean-square errors verified the accuracy of established RF-FA models in this study. Subsequently, a coFA-based multi-objective optimisation firefly algorithm (MOFA) was introduced to optimise tri-objectives between UCS, Tp (or Tt), and cost. The Pareto fronts were successfully acquired for optimal mixture designs, which contributes to the application of GFRP tendon reinforced cemented soil in practice. In addition, the sensitivity of input variables was evaluated and ranked.

Set of Cytochrome P450s Cooperatively Catalyzes the Synthesis of a Highly Oxidized and Rearranged Diterpene-Class Sordarinane Architecture.

Cytochrome P450s are one of the most versatile oxidases that catalyze significant and unique chemical transformations for the construction of complex structural frameworks during natural product biosynthesis. Here, we discovered a set of P450s, including SdnB, SdnH, SdnF, and SdnE, that cooperatively catalyzes the reshaping of the inert cycloaraneosene framework to form a highly oxidized and rearranged sordarinane architecture. Among them, SdnB is confirmed to be the first P450 (or oxidase) that cleaves the C-C bond of the epoxy residue to yield formyl groups in pairs. SdnF selectively oxidizes one generated formyl group to a carboxyl group and accelerates the final Diels-Alder cyclization to furnish the sordarinane architecture. Our work greatly enriches the enzyme functions of the P450 superfamily, supplies the missing skills of the P450 synthetic toolbox, and supports them as biocatalysts in further applications toward the synthesis of new chemical entities.

Mesoscale modelling of bond performance between deformed steel bar and concrete subjected to dynamic loads

The good bond property is the base for rebar and concrete to work together, influencing the mechanical behaviour of reinforced concrete structures. To investigate the bond-slip performance between deformed steel bars and concrete under dynamic loadings, a three-dimensional meso-scale numerical model was established, considering the inherent heterogeneity of concrete and explicitly modelling the surface characteristics of the rebar. The interaction between the rebar and concrete was implemented by the surface-to-surface contact strategy. The strain rate effect of materials was also taken into account. The rationality and accuracy of the proposed model were verified by the good consistency between the simulation and available test results in terms of failure pattern and bond stress-slip curves. With the help of the meso-scale model, the bond-slip behaviour under various loading rates was simulated and analysed. Finally, a simplified model to describe the dynamic bond stress-slip relationship was developed. It has been found that due to the propagation of stress waves, the cracking process of the specimen varies with the strain rate while the final failure pattern is similar, exhibiting splitting type failure. Thus, a considerable part of pull-out loading was resisted by the inertia of the system at the initial stage. With the increase of strain rate, the shape of the dynamic bond stress-slip curves is similar with a significantly increased bond strength and reduced slip, especially at high strain rates. The ratio between the residual and peak bond stress is approximately constant, irrespective of strain rate. The proposed simplified model is able to effectively characterize the dynamic bond stress-slip relationship between the deformed rebar and concrete.

Effect of high temperature on bond strength of concrete reinforced with 180° hooked bars

As far as the authors know, this is a novel study. Pull-out prism specimens were used to test the residual bond strength with compressive strength (30 MPa). The variables are the diameter of hooked bar (10 mm and 12 mm), and the temperature levels (200°C, 400°C and 600°C) in addition to room temperature. Ratio of stress of steel to concrete at failure (fs / fc′) is considered as an indication to the residual bond strength. The results showed that the stress ratio (fs / fc′) for the concrete with Φ10 mm bars is greater than Φ12 mm bars, also the results showed that the decrease in bond strength after exposing to high temperature for concrete with Φ10 mm bars is more than it for concrete with Φ12 mm bars. Up to 200°C, the decrease in bond strength is small, but the decrease for higher temperatures is significant. When the temperature was elevated to 400°C, the decrease is 18% and 11% for concrete reinforced by bars of Φ10 mm and Φ12 mm, respectively, while decrease is 27% and 15% when the temperature is elevated to 600°C.

Experimental Investigation of the TRM-to-Masonry Bond after Exposure to Elevated Temperatures: Cementitious and Alkali-Activated Matrices of Various Densities.

Limited research has focused on the effect of high temperatures on the textile-reinforced mortar (TRM)-to-masonry bond. In this study, masonry prisms that were furnished with double-layered TRM strips were tested under shear bond conditions after their exposure to 200 °C and 400 °C for 1 h using the single-lap/single-prism setup. A total of four TRM systems were applied sharing the same type of textile –a dry AR glass fiber one– and different matrices: two cementitious matrices, namely a normal-weight (TRCNM) and a lightweight (TRCLM) one, and two counterpart alkali-activated matrices (TRAANM and TRAALM) based on metakaolin and fly ash. Specimens’ exposure to elevated temperatures did not alter their failure mode which was due to the sleeve fibers’ rupture along with core fibers’ slippage from the mortar. The residual bond capacity of the TRM systems decreases almost linearly with increasing exposure temperature. The alkali-activated textile reinforced mortars outperformed their cement-based counterparts in terms of bond strength at every temperature. All systems retained close to 50% of their original shear bond strength after heating at 400 °C. Per the type of binder, lightweight matrices resulted in either comparable (cement-based systems) or better (alkali-activated systems) heat protection at the TRM/masonry interface.

On-Demand Photopolymerization of Fiber-Reinforced Polymers Exhibiting the Shape Memory Effect.

Fiber-reinforced polymers exhibiting the shape memory effect were created on the basis of a one-pot three-step chemical process. The first step is a Michael addition, which creates linear polymer chains. The second step is free radical photopolymerization, which increases the degree of curing of polymers. The last step is post-consolidation due to the reaction of previously formed secondary amines on the residual double bonds. By employing such chemistry to impregnate glass fibers, the final composite exhibits a convincing shape memory effect, as shown by cyclic thermomechanical tests.

Bond of Ribbed Steel Bar in High-Performance Steel Fiber Reinforced Expanded-Shale Lightweight Concrete

For the structural application of high-performance Steel Fiber Reinforced Expanded-shale Lightweight Concrete (SFRELC), a reliable bond of ribbed steel bar should be ensured. In this paper, an experimental study was carried out on the bond properties of ribbed steel bar embedded in SFRELC by the direct pull-out test. The SFRELC was produced with a strength grade of 35 MPa and a volume fraction of steel fiber as 0%, 0.8%, 1.2%, 1.6% and 2.0%, respectively. Fifteen groups of specimens were made with a central placed steel bar with diameter of 14 mm, 20 mm and 28 mm, respectively. Complete bond stress-slip curves were determined for each group of specimens, and the characteristic values of bond-stress and slip at key points of the curves were ascertained. Results show that the bond strength, peak-slip and residual bond strength increased with the increase of the volume fraction of steel fiber. With the increase of steel bar diameter, bond strength decreased while the peak-slip increased, and the descending curves became sharp with a decreased residual bond strength. Formulas for calculating the bond strength and peak-slip were proposed. The relationships were determined for the splitting bond strength, residual bond strength with the bond strength, the splitting bond slip and residual bond slip with the peak-slip. Combined with rational fitting analyses of bond strength and slip, a constitutive model was selected for predicting the bond stress-slip of ribbed steel bar in SFRELC.

(Invited) Impact of Boron Doping and H2 Annealing on Light Emission from Ge/Si Core-Shell Quantum Dots

We have fabricated Si-QDs with boron-doped Ge core with an areal density as high as ~1011 cm-2 on ultrathin SiO2 and characterized their room temperature photoluminescence (PL) properties. With B doping to the Ge core, stable PL observed in the energy range of 0.62 - 0.85 eV was increased by a factor of ~1.5. Note that a new relatively-narrow component peaked at ~0.64 eV emerges in addition to four components derived from the spectral deconvolution of the PL spectrum of undoped QDs and is attributable to radiative recombination between the first quantized state in the conduction band of the Si clad and the B-acceptor level in the Ge core. With H2 post-anneal at 100°C, the integrated PL intensity of the B-doped QDs was reduced by ~35% and the 0.64 eV component disappeared. With increasing H2 post-anneal temperature up to 350°C, the PL intensity was increased to ~1.4 times the initial intensity before post-annealing, and the 0.64 eV component was recovered. The observed PL changes with post-anneal are attributable to hydrogen-induced passivation of B acceptors at 100°C and thermal dissociation of B-H complex at higher temperatures up to 350°C accompanied with hydrogen passivation of residual dangling bond defects as seen in the undoped case.

Application of Superabsorbent Polymer as Self-Healing Agent in Self-Consolidating Concrete for Mitigating Precracking Phenomenon at the Rebar–Concrete Interface

Improved autogenous healing capacity of concrete using superabsorbent polymers (SAPs) was used as an efficient approach for mitigating damage between steel rebar and self-consolidating concrete (SCC). The results for normal concrete (NC) and those for SCC mixtures were compared. Two SAPs with different particle sizes and chemical compositions were used in the experimental program. Results showed that despite the greater reduction effect of SAP with a smaller particle size on compressive strength, SCC containing this type of SAP had the highest bond strength in uncracked specimens, compared with SAP with larger particle sizes, for SAP-modified NC and SCC mixtures. Moreover, results showed that SCC and NC containing SAP had considerably greater healing improvement factors for large crack widths (w≥0.30 mm) compared with mixtures without polymers; almost 46%, 30%, and 24% healing improvement factors were obtained for average bond stress, bond strength, and residual bond stress of SAP-containing concrete mixtures, respectively. Furthermore, complete strength recovery (100% healing improvement factor) was obtained for SCC mixture with w=0.10 mm after a 28-day healing period.

Residual TRM-to-Concrete Bond after Freeze-Thaw Cycles.

In the present work, the effect of various freeze–thaw cycles (namely, 0, 10, 30, 50, 60, and 70) on the residual bond characteristics of textile reinforced mortar (TRM)-to-concrete was experimentally examined. The TRM consisted of a carbon dry fiber textile embedded in a cement-based matrix. Two mortar types were used as the matrix: a normal-weight and a lightweight one sharing the same hydraulic powders but different aggregates (limestone and pumice sand, respectively). The single-lap/single-prism set up was applied after the specimens underwent hygro-thermal treatment (according to ASTM C 666-Procedure B). Failure was due to the sleeve fibers rupturing the load aligned yarns or textile slippage from the mortar for an exposure period ranging between 0 and 60 cycles and to TRM debonding from the substrate for 70 cycles. Increasing cycles resulted in the intensification of partial interlaminar debonding phenomena and the weakening of the textile-to-matrix bond, with lightweight mortar being more prone to these effects. In the absence of a commonly accepted standardized method for the assessment of the freeze–thaw resistance of cement-based composites, the criterion for the termination of the freeze–thaw sequence was the number of cycles inferring a shift in failure mode (from fiber rupture/fiber slippage to TRM debonding from the substrate).

Experimental research on the mechanical behavior of grouted sleeves with fiber-reinforced grouting material under cyclic loading

The normal grouting material which has been widely used in traditional grouted sleeve connections has high brittleness and it often burst when broken. Moreover, these grouted sleeve connections required larger anchorage length and exhibited a worse cyclic load capacity than the steel bar. In this research, three kinds of fibers, including polypropylene fiber, polyvinyl alcohol fiber and basalt fiber, were selected as mixing materials in the grouting material. Their performance was tested in three areas: basic mechanical properties, toughness, and the optimal content and length of each fiber. Then, a total of 120 grouted sleeve connections with three selected optimal fiber grouting materials and five different anchorage lengths were manufactured. The mechanical performance of the grouted sleeves connections was tested under two loading schemes: cyclic loading at high stress (CH) and cyclic loading at large strain (CL). The compression test results of grouting materials demonstrated that fiber was an ideal material for improving the toughness of the grouting material. The optimal content of each fiber in grouting material was 0.5% (PP), 0.3% (BF) and 0.1% (PVA) and the optimal length was 9 mm (PP), 3 mm (BF) and 3 mm (PVA), respectively. Meanwhile, the minimum anchorage length of rebar in the grouted sleeves could be reduced by at least 1 d (d: diameter of rebar) when the fiber reinforced grouting material was adopted. According to the load–deflection curves under cyclic loading, the fiber reinforced grouted sleeve connections exhibited better residual deformation and stiffness degradation. Test results demonstrated that the fiber could clearly enhance the residual bond strength and ductility of the reinforced section, and the residual bond strength of the connections with the fiber grouting material could be increased by 3.8% ~ 22.8% when the steel bar was pulled out.

Formation of the Metal-Binding Core of the ZRT/IRT-like Protein (ZIP) Family Zinc Transporter.

Zinc homeostasis in mammals is constantly and precisely maintained by sophisticated regulatory proteins. Among them, the Zrt/Irt-like protein (ZIP) regulates the influx of zinc into the cytoplasm. In this work, we have employed all-atom molecular dynamics simulations to investigate the Zn2+ transport mechanism in prokaryotic ZIP obtained from Bordetella bronchiseptica (BbZIP) in a membrane bilayer. Additionally, the structural and dynamical transformations of BbZIP during this process have been analyzed. This study allowed us to develop a hypothesis for the zinc influx mechanism and formation of the metal-binding site. We have created a model for the outward-facing form of BbZIP (experimentally only the inward-facing form has been characterized) that has allowed us, for the first time, to observe the Zn2+ ion entering the channel and binding to the negatively charged M2 site. It is thought that the M2 site is less favored than the M1 site, which then leads to metal ion egress; however, we have not observed the M1 site being occupied in our simulations. Furthermore, removing both Zn2+ ions from this complex resulted in the collapse of the metal-binding site, illustrating the "structural role" of metal ions in maintaining the binding site and holding the proteins together. Finally, due to the long Cd2+-residue bond distances observed in the X-ray structures, we have proposed the existence of an H3O+ ion at the M2 site that plays an important role in protein stability in the absence of the metal ion.

Multi-layer casting of self-consolidating concrete: Influence of mortar rheology and casting parameters on the inter-layer bond strength

Inter-layer bond strength is a critical factor to achieve structurally sound monolithic concrete structures. This paper discusses the effects of the cementitious paste volume (CP%vol), structural build-up of mortar (Athixm), and their interactions with casting parameters (i.e., free fall height (HFF), and delay time) on the residual bond strength of multi-layer self-consolidating concrete. It is found that the residual bond strength can be improved by increasing the CP%vol and HFF, or by reducing the delay time and Athixm. Out of the factors investigated, Athixm has the largest effect on both the residual bond strength and the critical delay time.

Bond behaviors between nano-engineered concrete and steel bars

This paper investigated the bond characteristics between eight types of nanofillers modified reactive powder concrete (RPC) and plain steel bars, aiming to explore the modifying mechanisms and establish a bond-slip relationship model for nanofillers modified RPC and steel bar interface. The experimental results indicated that the incorporation of nanofillers can increase the bond strength and reduce the slip between RPC and plain steel bars. It was shown that a 2.15 MPa/20.5% of absolute/relative increase in cracking bond strength, a 1.25 MPa/10.3% of absolute/relative increase in ultimate bond strength, a 2.35 MPa/22.4% of absolute/relative increase in residual bond strength, a 0.592 mm/56.5% of absolute/relative reduction in ultimate bond slip, and a 1.779 mm/52.1% of absolute/relative reduction in residual bond slip were the best achieved due to the addition of various nanofillers. The enhancement of nanofillers on RPC-steel bar interface has been mainly attributed to RPC microstructure improvement, optimization of intrinsic compositions, and elimination of defects in the interface, especially the underside near steel bar, due to the nano-core effect of nanofillers enriched in the interface. In addition, the bond-slip relationship of nanofillers modified RPC-steel bar interface can be accurately described by the proposed model considering an initial branch.

Bond behavior of plain round bar embedded in high ductile concrete under monotonic and cyclic loading

AbstractBond behavior is the basis of combined action of steel bar and high ductile concrete (HDC), which has an important effect on the mechanical performance of reinforced HDC structures. In this paper, nine groups of pullout specimens were tested to investigate the bond behavior and degradation mechanism of plain round bar embedded in HDC under monotonic and cyclic loading. The design parameters included HDC compressive strength, HDC flexural toughness and anchorage length. Experimental results indicated that only a small free end slip occurred for specimens with plain round bar when the maximum bond stress was reached. Bond strength of polyethylene fiber specimens was 1.67 times that of polyvinyl alcohol fiber specimens. Compared with the monotonic specimens, the cyclic specimens exhibited an obvious degradation in bond strength and residual bond strength, and the degradation degree of former was more serious than that of latter. Besides, it also should be noted that the HDC compressive strength had a great influence on the energy dissipation capacity of cyclic specimens. Based on the test results, a calculating formula of bond strength was built. Then this paper proposed a bond stress‐slip relationship model for the plain round bar embedded in HDC under monotonic loading.

Influence of matrix-modification and fiber-hybridization on high-temperature residual mechanical performance of strain-hardening cementitious composites

This research experimentally examines the influence of matrix-modification and fiber-hybridization on the residual mechanical properties and bond behavior (with steel reinforcement) of Strain-Hardening Cementitious Composites (SHCC) after exposure to high temperatures. The matrix-modification entailed replacing fly ash and silica sand used in conventional SHCC matrix with slag and calcium carbonate (CC) powder for improving the thermal stability of the matrix. Furthermore, a combination of steel and polyvinyl alcohol (PVA) fibers was used to prevent brittle failure of SHCC after the melting of PVA fibers around 230 °C. Four SHCC materials (including conventional SHCC), corresponding to the four possible combinations of the aforementioned modifications, were subjected to temperatures of up to 800 °C. Residual mechanical properties and bond behavior of all the materials were experimentally determined after exposure to high temperatures. The improvement in the thermal stability of the cementitious matrix and fiber-hybridization resulted in significant enhancement of the residual mechanical properties and bond behavior of SHCC exposed to temperatures of up to 600 °C.

A mechanical bond model for reinforcing bar in concrete subjected to monotonic and reversed cyclic loading

The reinforcing bar with diameters of 10 mm and 12 mm are widely used in shear walls, whose bond-slip performance has great influence on the seismic performance of the shear walls. Besides, the bond stress-slip model plays an important role in the theoretical analysis of the seismic performance of shear walls. Therefore, an analytical solution for the maximum bond stress was carried out and modified based on the thick-walled cylinder model and the tensile stress-strain model of concrete. The bond-slip tests of reinforcing bars in concrete were conducted on 48 specimens under monotonic and reversed cyclic loading. The effects of concrete strength, diameter of bar and bonding length on the bond-slip performance were examined and analyzed. The test results showed both the maximum bond stress and residual bond stress increased with increasing concrete strength, but decreased with increasing diameter of bar or bonding length. The reversed cyclic loading can cause the degeneration of the maximum bond stress and the bond stiffness. According to the bond-slip performance, the bond stress-slip model was established based on the analytical solution for the maximum bond stress, which is suitable for calculating both monotonic and reversed cyclic loading. A good agreement was observed by comparing the proposed models with the test curves in the study.

Residual bond strengths of epoxy and cement-bonded CFRP reinforcements to concrete interfaces after elevated temperature exposure

This paper presents the results from a comparative study on the residual bond performance of epoxy and cement-bonded carbon fiber-reinforced polymer (CFRP) reinforcement to concrete interfaces that experienced different levels of elevated temperature exposure. In total twelve groups of concrete beams strengthened with CFRP sheet and grids of the same tensile stiffness, through epoxy and cement-based adhesive bonding, respectively, were carefully prepared and exposed to different test temperature levels from 20 °C to 600 °C. Both polymer cement mortar (PCM) and ductile engineered cementitious composite (ECC) were adopted as the cement binder. The strengthened beams were tested under three-point monotonic bending after different levels of elevated temperature exposure. It was found that with increasing the exposure temperature, the failure modes of the strengthened beams shifted from debonding in a thin layer of concrete substrate to debonding near the fiber-adhesive interface and tearing off of CFRP grids from the ECC matrix. The peak loads of concrete beams strengthened with cement-bonded CFRP grids are at least 50% higher than their counterparts strengthened with epoxy-bonded CFRP sheets given the same temperature exposure.