Interface bond strength performance of overlap joints within the corrugated pipes used in prefabricated bridges

This paper presents an experimental study of a novel composite structure used in prefabricated bridges. Corrugated pipes were used to improve the interface bond performance of the structure because of their excellent stiffening effect on the grouting material. Interface bond performance of overlap joints within corrugated pipes was explored by the load-displacement curve and load-strain curves. Ultra-High Performance Concrete (UHPC) and high-strength mortar were used as grouting materials. The diameter of steel bars, UHPC, high-strength mortar, strength grades of surrounded concrete, anchorage length, the diameter of the corrugated pipe, and lap length was taken as influential factors. Twenty specimens were designed for the pull-out test by using a larger cover thickness. The failure modes and the influence of different influential factors on the interface bond strength of each specimen were analyzed. The results show that the bond performance between UHPC and reinforcement was better than that of high-strength mortar and normal concrete, which can effectively improve the bond strength and reduce the basic anchorage length of reinforcement besides the design size of prefabricated members. In addition, the differences in anchorage length and lap length between the corrugated pipe grouting reinforcement were compared to the different specifications and prefabricated concrete members. Combined with the test phenomenon and analysis results, it is suggested that the anchorage length and lap length of connecting reinforcement should be reconsidered. Furthermore, the grouting effect under different diameters of corrugated pipe and reinforcement were compared. It is recommended that the corrugated pipe diameter should be four times that of the overlapping grouting reinforcement.

Comparison of insertion time, pull-out strength, and screw-media interface area of customized pedicle screw with different core and thread design against commercial pedicle screw: a pilot study on Indonesian Population

Objective This research aimed to developing customized pedicle screw based on Indonesian vertebral anatomy and compare the insertion time, pull-out strength, and screw-media interface area of different screw design. We have developed 3 different types of pedicle screws (v-thread cylinder-core, square-thread cylinder-core and square-thread conical-core). The thread diameter was calculated from pedicle width of Indonesian population (6 mm). We used commercially available pedicle screw as control group (6.2 mm). Result The insertion time were significantly difference between v-thread cylinder-core pedicle screw (22.94 s) with commercially available pedicle screw (15.86 s) (p < 0.05). The pull-out strength was significantly difference between commercially available pedicle screw (408.60 N) with square-thread conical pedicle screw (836.60 N) (p < 0.05). The square-thread conical-core group have the highest interface area (1486.21 mm2). The data comparison showed that the square-thread conical-core customized pedicle screw group has comparable insertion time and has better pull-out strength than commercially available pedicle screw.

Thermal conductivity and bending strength of SiC composites reinforced by pitch-based carbon fibers

In this work, pitch-based carbon fibers were utilized to reinforce silicon carbide (SiC) composites via reaction melting infiltration (RMI) method by controlling the reaction temperature and resin carbon content. Thermal conductivities and bending strengths of composites obtained under different preparation conditions were characterized by various analytical methods. Results showed the formation of SiC whiskers (SiCw) during RMI process according to vapor—solid (VS) mechanism. SiCw played an important role in toughening the Cpf/SiC composites due to crack bridging, crack deflection, and SiCw pull-out. Increase in reaction temperature during RMI process led to an initial increase in thermal conductivity along in-plane and thickness directions of composites, followed by a decline. At reaction temperature of 1600 °C, thermal conductivities along the in-plane and thickness directions were estimated to be 203.00 and 39.59 W/(m·K), respectively. Under these conditions, bending strength was recorded as 186.15±3.95 MPa. Increase in resin carbon content before RMI process led to the generation of more SiC matrix. Thermal conductivities along in-plane and thickness directions remained stable with desirable values of 175.79 and 38.86 W/(m·K), respectively. By comparison, optimal bending strength improved to 244.62±3.07 MPa. In sum, these findings look promising for future application of pitch-based carbon fibers for reinforcement of SiC ceramic composites.

Numerical Study of the Bond Strength Evolution of Corroded Reinforcement in Concrete in Pull-Out Tests

The corrosion of rebars in reinforced concrete structures impacts their geometry (diameter and ribs) and mass, damages the concrete at the interface between the two materials, deteriorates the bond strength, and causes the cracking of the concrete cover. In the following study, a 2D numerical model of the pull-out test is presented in order to study the impact of corrosion on the bond strength. Several parameters are investigated: the embedment depth, the rebar’s diameter, and the width of the concrete cover. The model reproduces the slip of the rebar and the failure through the splitting of concrete. It integrates an interface between the two materials and a concrete damage model that simulate the deterioration of concrete in compression and tension. The results obtained are validated with experimental data from the literature. Moreover, a parametric study is carried out to determine the impact of the embedment depth, the diameter of the rebar, and the concrete cover on the bond strength. The present study confirms that a greater embedment depth increases the pulling load. The study also confirms that the rebar’s diameter impacts highly the loss of bond between the rebar and the concrete cover. Lastly, the final main result of this paper is that the width of the concrete cover slows the loss of bond strength between the two materials.

Photodynamic Therapy (PDT) in Prosthodontics: Disinfection of Human Teeth Exposed to Streptococcus mutans and the Effect on the Adhesion of Full Ceramic Veneers, Crowns, and Inlays: An In Vitro Study

The use of PDT in prosthodontics as a disinfection protocol can eradicate bacteria from tooth surfaces by causing the death of the microorganisms to which the photosensitizer binds, absorbing the energy of laser light during irradiation. The aim of the study was to investigate the capacity of PDT to increase the bond strength of full ceramic restorations. In this study, 45 extracted human teeth were prepared for veneers, crowns, and inlays and contaminated with Streptococcus mutans. Tooth surfaces decontamination was performed using a diode laser and methylene blue as a photosensitizer. The disinfection effect and the impact on tensile bond strength were evaluated by scanning electron microscopy (SEM) and pull-out tests of the cemented ceramic prosthesis. Results show that the number of bacteria was reduced from colonized prepared tooth surfaces, and the bond strength was increased when PDT was used. In conclusion, the present study indicates that using PDT as a protocol before the final adhesive cementation of ceramic restorations could be a promising approach, with outstanding advantages over conventional methods.

Effects of plate contouring quality on the biomechanical performance of high tibial osteotomy fixation: A parametric finite element study

Locking plates have threaded holes, in which threaded-head screws are affixed. Hence, they do not need to be in intimate contact with underlying bone to provide fixation. There are, however, reports that a large distance between the plate and the bone might cause clinical complications such as delayed union or nonunion, screw pull out, and screw and plate breakage. Considering the diversity in the capabilities and costs of different plate customization techniques, the purpose of this study was to investigate the effect of the plate contouring quality on the biomechanical performance of high tibial osteotomy (HTO) fixation. A finite element model of proximal tibia was developed in Abaqus, using the QCT data of a cadaver. The model was then subjected to open-wedge HTO (correction angle 12°) with TomoFix plate fixation. The sagittal curvature of the plate was changed parametrically to provide certain levels of geometrical fit, and the biomechanical performance parameters of fixation were assessed. Results indicated 5%, 9% and 38% increase in the stiffness of the construct, and the von Mises stress in the plate and locking screw just above the osteotomy site, respectively, when the level of fit of plate changed from 0% (initial non-contoured initial shape) to 100% (fully adapted shape). The same change decreased the pressure at the lateral hinge of the osteotomy by 61%, and the mean of the tensile stress on the screw shaft by 12%. It was concluded that the level of fit has conflicting effects on the biomechanical parameters of the HTO fixation system, that is, the structural stiffness, the pressure at the lateral hinge, the stresses in the plate and screws, and the pull out resistance of the screws. In particular, for HTO patients with high quality bone, the optimal level of fit should provide a tradeoff between these parameters.

Two antagonistic effects of flow/mixing on reactive polymer blending

Reactive polymer blending is basically a flow/mixing-driven process of interfacial generation, interfacial reaction for copolymer formation and morphology development. This work shows two antagonistic effects of mixing on this process: while mixing promotes copolymer formation by creating interfaces and enhancing collisions between reactive groups at the interfaces, excessive mixing may pull the in-situ formed copolymer out of the interfaces to one of the two polymer components of the blend, especially when the copolymer becomes highly asymmetrical. As such, the copolymer may loss its compatibilization efficiency. The mixing-driven copolymer pull-out from the interfaces is a catastrophic process (less than a minute), despite the high viscosity of the polymer blend. It depends on the molecular architecture of the reactive compatibilizer, polymer blend composition, mixing intensity and annealing. These findings are obtained using the concept of reactive tracer-compatibilizer and a model reactive polymer blend.