Post tensioning bridges is an efficient way of construction where segments of a bridge are strung together using small diameter high strength strands. The steel strands are passed through internal and/or external ducts within the concrete segments, jacked to high levels of stress, anchored using steel wedges, and then filled with a corrosion inhibiting filler. A cementitious material called grout has been widely used for over 50 years as this filler. The Federal Highway Administration design and construction manual provides recommendations in the properly filling techniques to ensure the tendons are full of grout. Despite the level of detail the manual provides, several Florida bridges that used this construction technique have seen severe corrosion related failures due to poor grout quality. Oil based products have been developed for the express purpose of reducing the corrosion rate in previously grouted tendons. Utilizing the interstitial spaces in the steel strands, low viscosity fluid is pumped through the strand which can also penetrate the surrounding grout and fill unintentional voids. However, by doing so, there is the concern that the bond strength could be compromised and increase the risk of failure. This study presents the findings of small scale grouted mono-strand tendons which determined the bond effects of defective grout, evaluated the injection capabilities of various penetrants, and determined whether or not the penetrant adversely affects bond after impregnation. No appreciable variation in bond was found.

Good bond strength between overlay and substrate is a key factor in performance of concrete repairs. This thesis was aimed at studying the evaluation of bond strength between repair material and substrate at the interface. Many factors such as surface roughness, existence of micro cracks, compaction, curing etc influence the bond strength. The quality assurance of the bond strength requires test methods that can quantify the bond strength as well as identify the failure mode. There have been numerous investigations led to development of different test methods. The forces which are applied in each test and the failure mode are important in order to choose the proper test. An interpretive study on test methods is presented. While this study can provide individually useful information on bond strength and bond characterization, it also contains discussions about each test and comparison of test methods.

OBJECTIVES: To evaluate various cements in vitro for adhesion to zirconia, light curing vs. self-curing, the effect of particle abrasion (APA) on the zirconia intaglio for maximizing retention, the effect of thermocycling, and the effect of cement space. METHODS: The tested cements included: Ceramir C&B (Doxa) Panavia F2.0 (Kuraray); Multilink Automix (Ivoclar); Theracem (Bisco); Duolink (Bisco); Bifix (Shofu); CemEZ (Zest Dental). For testing cements retention, custom made zirconia rings 12.5 mm outer diameter, 5.5 mm height and 6.147 mm inner diameter were used to emulate crowns. Round steel rods (McMaster) were manufactured to fit into the zirconia rings allowing a cement space of 50 Microns or 100 Microns. A cementing jig was used to keep the rods at the center of the zirconia rings. Cements were tested using light curing and self-curing (n=10 per each test). Groups of zirconia rings were air braded with 100 Microns aluminum oxide particles for 10 Sec. Half the specimens were stored in water for 24 hours at 37o C in dark environment or thermocycled for 5000 cycles. A ‘push-out’ test using an Instron universal machine at a crosshead speed of 0.5mm/min. Loads to failure were recorded to calculate cements retention. RESULTS: Statistical analysis was performed using JMP Pro 13 software. Data were analyzed using one way ANOVA, multiple t-test, and Tukey-Kramer HSD. For self curing method without APA, retention strength ranking for tested cements were: Ceramir C&B ≥ Theracem > Panavia F2.0 ≥ Duolink ≥ Multilink Automix ≥ Bifix. For light curing method without APA, retention strength ranking for tested cements were: CemEZ ≥ Theracem ≥ Multilink Automix ≥ Duolink ≥ Bifix ≥ Panavia F2.0. There was a significant influence in retention strength for light cured cements compared to self-curing method except for Theracem and Panavia F2.0. For the self-curing method with APA, retention strength ranking for tested cements were: Theracem > Duolink ≥ Panavia F2.0 ≥ Multilink Automix ≥ Bifix > Ceramir C&B. For the light curing method with APA, retention strength ranking for tested cements were: Theracem ≥ Multilink Automix ≥ CemEZ ≥ Duolink ≥ Panavia F.0 ≥ Bifix. A significant increase in retention strength with APA compared to self-curing method with APA. There was no significant effect of thermocycling treatment on retention strength of the cements tested. There was no significant effect of different cement spaces on retention strength except for Ceramir C&B without APA and Multilink Automix with and without APA (P < 0.0001). CONCLUSIONS: 1- There was a significant difference in retention strength to zirconia among tested cements in self and light curing methods. 2- Light curing resin cements influenced retention strength to zirconia for the tested cements. 3- APA influenced the retention strength to zirconia for tested cements except for Ceramir C&B. 4- Increasing the cement space from 50μm to 100μm had no significant difference in retention strength to zirconia except for Ceramir C&B without APA and Multilink Automix with and without APA. 5- Thermocycling had no significant effect of on retention strength to zirconia for the tested cements. / 2020-07-30T00:00:00Z

Introduction: An optimal orthodontic bonding system must minimize damage to the enamel during conditioning, have enough bond strength to prevent bracket de-bonding during treatment, and allow bracket removal at treatment completion, such that minimal damage is inflicted to the tooth.1 Pumice followed by acid etching has been the standard for many years; however, Groman Inc. (Margate, FL, USA) has stated that using their air-abrasion product will result in a tripling of bond strength. This method claims a three-fold increase in bond strength compared to traditional acid etching techniques by substituting air-abrasion using the EtchMaster® (Groman Inc., Margate, FL) 50 μm aluminum oxide in place of pumice prophy prior to acid etching. The purpose of this study is to see if this combination does in fact triple shear bond strength, and if so, what impact it has on the residual enamel surface after bracket removal, or de-bonding. Methods: Ninety recently extracted bovine incisors were randomly divided into three groups. Each of the three groups underwent different conditioning methods prior to bracket bonding. Group A: pumice + acid etch (N=30), Group B: air-abrasion + acid etch (N=30), and Group C: air-abrasion only (N=30). Enamel surface conditions were characterized using a Quanta 200 Scanning Electron Microscope (SEM) (FEI, Hillsboro, OR) and a SZX7 Stereomicroscope System (Olympus, Center Valley, PA). American Orthodontics Master Series System twin MBT mandibular incisor brackets (Sheboygan, WI, USA) were then bonded to each tooth. Following bonding, teeth were stored for twenty-four hours in water at 37°C +/- 2°C. All groups then underwent thermocycling of five hundred cycles in water baths set at five and fifty-five degrees Celsius. Next, the samples were mounted in dental stone and brackets de-bonded using a universal testing machine (Instron, Canton, MA) to obtain shear bond strength (SBS) values. SEM and optical stereomicroscopy were again utilized to evaluate the enamel surface and determine the adhesive remnant index (ARI) was score of each specimen. Results: The mean of Group A (pumice + acid etch) was 21.52 MPa with a standard deviation of 4.97 MPa. The mean of Group B (air-abrasion + acid etch) was 21.83 MPa with a standard deviation of 7.55 Mpa. The mean of Group C (air-abrasion only) was 8.12 MPa with a standard deviation of 3.05 MPa. Analysis of variance showed a main effect of Group on MPa, F(2, 87) = 60.66, p < 0.001, ηp2= 0.58. Post-hoc analyses using Tukey’s HSD indicated that SBS values were higher for teeth in Group A than for those in Group C (p < 0.001), teeth in Group B had higher SBS values than those in Group C (p < 0.001), but no difference was found for SBS between teeth in Group A and Group B (p =0.981). Results from the Fisher’s Exact test, where we controlled the Type I error using a Bonferroni correction, reveals that ARI scores differed by group (p < 0.001). Stereomicroscope images at 38.75x magnification obtained following enamel conditioning show Groups A (P+AE) and B (AA+AE) are almost indistinguishable; however, Group C (AA) has visual differences. Group C had a speckled reflective property that appeared to be residual aluminum oxide particles. Following de-bond, stereomicroscopic and SEM images showed no enamel defects on the tooth. Conclusions: SBS was not significantly different between Group A (pumice + acid etch) and Group B (air-abrasion + acid etch). SBS was significantly different between Groups A and B, and Group C (air-abrasion only). This means there is not a three-fold increase in SBS when using air-abrasion and acid etch, when compared to pumice and acid etch, as claimed by the manufacturer of the air-abrasion unit used in this study. Additionally, the air-abrasion only group displayed a significantly lower SBS than Group A and B. Air-abrasion only is not a suitable enamel preparation method for orthodontic bonding. Images obtained from the stereomicroscope and SEM reveal no observational damage to the enamel surface topography after de-bonding for any group.

Introduction: The stabilization of dentinal collagen fibers against enzymatic degradation by the use of biocompatible cross-linker agents is of clinical importance for effective dentin bonding to surpass the test of time. Objective: The present study aims to evaluate and compare the effect of the application of two versions of a desensitizer solution to sound coronal dentin, on the microtensile bond strength (μTBS) of the resin-sound coronal dentin using 4th and 6th generation dentin bonding systems. Materials and Methods: Extracted human third molars were collected from an unidentified bank of teeth followed by IRB approval. A flat surface of all 12 teeth was prepared utilizing a water-cooled high-speed diamond disc, leaving an entire hard sound dentinal area for testing. Subsequently, according to the assigned group, specimens followed specific manufacturer’s instructions for application of dentin bonding systems: specimens were subdivided into 6 groups (n=20). Group 1 (G1) First positive control group. Specimens received an application of a 4th generation dentin bonding system (DBS). Group 2 (G2) Second positive control group. Specimens received an application of a 6th generation DBS. Group 3 (G3) Specimens were exposed to Gluma Desensitizer agent, blot-dried and followed by application of a 4th generation DBS. Group 4 (G4) Specimens were exposed to Gluma Desensitizer agent, blot-dried and followed by application of a 6th generation DBS. Group 5 (G5) Specimens were exposed to Gluma Desensitizer PowerGel agent, blot-dried and followed by application of a 4th generation DBS. Group 6 (G6) Specimens were be exposed to Gluma Desensitizer PowerGel agent, blot-dried and received an application of a 6th generation DBS. After application of the adhesive systems, all specimens were restored using a microhybrid resin composite. The root portion was sectioned 1mm below the CEJ, and discarded. All specimens were thermocycled at 5-55 Cº for 7000 cycles on distilled water. Then each restored tooth was sectioned perpendicular to the bonding interface into 1mm x 1mm x 8mm beams with a slow speed diamond wafering blade under thorough irrigation. Then specimens were subjected to μTBS testing at a crosshead speed of 1mm/min. Subsequently; specimens were subjected to fracture analysis and SEM evaluation of the different failure’s mode of the involved surfaces. Statistical analysis was performed by usingone- way ANOVA, two-way ANOVA and Fisher’s PLSD test (p<0.05). Results: For the first aim of the study and after obtaining the μTBS in MPa: Group G1: 15.50 ± 6.28, Group G2: 13.06 ± 11.53, Group G3: 19.20 ± 9.43, Group G4: 12.76 ± 4.61, Group G5: 14.38 ± 5.95, Group G6: 18.54 ± 9.49. Statistical analysis showed that there is no significant influence of variables on the μTBS (Welch ANOVA [F (5,114) =2.21, p=0.057]). Treatment with Gluma desensitizing agent and Gluma desensitizing PowerGel has no significant influence on the bond strength. For the second aim of the study and to analyze group differences for type of fracture data was first recoded into two groups: (1) Adhesive failure and (2) Cohesive failure. Group differences were analyzed by type of fracture using a Fisher’s exact test. No difference was found between the groups by type offracture (5, N = 120) = 8.62, p = 0.090 Conclusion: Within the limitations of this in vitro study it can be concluded that Gluma desensitizing agent and Gluma desensitizing PowerGel did not significantly affect the μTBS of both 4th and 6th generation bonding system using extracted human teeth.

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Yes / Bond between substrate and overlay concretes is a key factor for the success of the repair method and significantly influences the structural performance of the repaired element. This study investigated the effect of fly ash and the surface preparation method on the bond strength of repaired concrete after exposure to high temperatures, that has not been comprehensively studied in the literature. For this purpose, overlay concretes containing 0, 5, 10, 15, and 20% fly ash as a replacement by weight of cement were cast on the original concrete surface prepared by four methods namely, as-cast, wire brushed, grooved and grooved-wire brushed. The bond strength of the interface between concrete substrate and overlay concrete was evaluated after exposure to 23, 200, 400, and 600oC temperatures for 1 hour. The results showed that partial replacement of cement by fly ash in the overlay concrete increased the bond strength of repaired concrete by up to 71%, depending on the amount of fly ash used, surface preparation method, and the temperature to which the sample was exposed. The maximum increase of bond strength was recorded for concrete containing 20% fly ash when the wire brushed preparation method was adopted at temperature of 200oC. However, surface preparation was the most influential parameter, achieving a bond strength gradual increase in order from as-cast, wire brushed, grooved to grooved-wire brushed methods. The results also showed that for most of the samples having similar surface preparation and the same percentage of fly ash, bond strength decreased with the increase of exposure to temperature; for example, for overlay concretes without fly ash, in as-cast and wire brushed surface preparation methods at temperatures of 400 and 600 oC, the bond strength has reached zero. On the other hand, for grooved and grooved-wire brushed surface preparation methods, the bond strength reduction was about 63%, when temperature increased from 23 to 600oC. / The full-text of this article will be released for public view at the end of the publisher embargo, 12 month from first publication.

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No / This study investigates the interfacial characteristics between aggregates and cement paste matrix in nanofillers modified concrete. A three-point bend test on the specimens composed of two pieces of aggregates bonded with a thin layer of cement pastes with/without nanofillers was carried out to characterize the interfacial bond strength of the composites. The scanning electron microscope observations and energy dispersive x-ray spectrometry analysis were also performed to characterize the interfacial microstructures and compositions of the composites. The experimental results indicated that the nanocomposites have higher interfacial bond strength and narrower interfacial transition zone thickness as well as more optimized intrinsic compositions and microstructures than that of composites without nanofillers. Specifically, the interfacial bond strength of nanocomposites can reach 7.67 MPa, which is 3.03 MPa/65.3% higher than that of composites without nanofillers. The interfacial transition zone thickness of nanocomposites ranges from 9 μm to 12 μm, while that of composites without nanofillers is about 18 μm. The ratio of CaO to SiO2 in the interface of composites without nanofillers is 0.69, and that of nanocomposites increases to 0.75–1.12. Meanwhile, the nanofiller content in nanocomposite interface is 1.65–1.98 times more than that in the bulk matrix. The interfacial microstructures of nanocomposites are more compact and the content and crystal size of calcium hydroxide were significantly reduced compared with that of composites without nanofillers. / National Science Foundation of China (51978127 and 51908103), and the China Postdoctoral Science Foundation (2019M651116).