Indiana University-Purdue University Indianapolis (IUPUI) / Statement of problem: Yttria-partially stabilized tetragonal zirconia polycrystal (Y-TZP) all-ceramic restorations have been reported to suffer from chipping or cracking of the veneering porcelain (VP) as the most common complication. There is little information in the literature regarding the influence of surface treatment on VP shear bond strength to Y-TZP after cyclic loading. Purpose of this study: The goals of this study were (1) to investigate the influence of zirconia surface treatments on veneering porcelain shear bond strength and (2) to investigate the influence of cyclic loading on the shear bond strength between VP and Y-TZP. Materials and Methods: 48 cylinder–shaped specimens (6mm in diameter and 4mm in height) were divided into 4 groups containing 12 specimens each according to the surface treatment. As a control group (C), no further treatment was applied to the specimens after grinding. Group H was heat-treated as a pretreatment according to the manufacturer’s recommendations. Group S was airborne-particle abraded with 50 µm alumina (Al2O3) particles under a pressure of 0.4 MPa for 10 seconds. In the group SH, the heat-treatment was performed after the airborne-particle abrasion. A VP cylinder (2.4 mm in diameter and 2 mm in height) was applied and fired on the prepared Y-TZP specimens. The shear bond strength was tested using a universal testing machine. Six specimens from each group were subjected to fatigue (10,000cycles, 1.5Hz, 10N load) before testing. Results: The 3-way ANOVA showed no statistically significant effect of surface treatment and cyclic loading on shear bond strength. The highest mean shear bond strength was recorded for the air-particle abrasion group without cyclic loading (34.1 + 10 MPa). The lowest mean shear bond strength was the air-particle abrasion group with cyclic loading (10.7 ± 15.4 MPa). Sidak multiple comparisons procedure demonstrated cyclic loading specimens had significantly lower shear bond strength than non-cyclic loading specimens after air-particle abrasion without heat treatment (p=0.0126) Conclusion: Within the limitations of this study, (1) Shear bond strength between Y-TZP and VP is not affected statistically by surface treatment using heat treatment, airborne-particle abrasion, and heat treatment after airborne-particle abrasion. (2) There is significant difference in shear bond strength with air-particle abrasion between with and without cyclic loading groups. This difference suggested that air-particle abrasion should be avoided in clinical situations as a surface treatment without heat treatment.

Indiana University-Purdue University Indianapolis (IUPUI) / In adhesive dentistry, obtaining a good bond is a fundamental goal. It has been suggested that filler addition to the adhesives would increase the bonding strength of the adhesive layer. Halloysite aluminosilicate nanotubes (HNTs) are biocompatible, hydrophilic, durable, and have high mechanical strength. These advantages make them good candidates to be used as reinforcing agents for improving the properties of dental adhesives. The objective of this study was to evaluate the effect of incorporating HNTs into a commercial two-step etch-and-rinse adhesive system or one-step self-etch adhesive system on dentin shear bond strength. HNTs were incorporated into the two commercial adhesive systems in 0 wt%, 5 wt%, 10 wt%, and 20 wt%. The commercial control adhesives and the experimental adhesives were used to bond occlusal dentin of 120 extracted human molar teeth and then tested for shear bond strength by a universal testing machine with a semi-circular edge at a crosshead speed of 1.0 mm/min. Debonded specimens were examined under light microscopy to evaluate the fracture pattern. Resin-dentin interface were evaluated under scanning electron microscopy (SEM) after bonding dentin slabs using commercial control adhesives and experimental adhesive that showed numerically highest shear bond strength from each adhesive system. Two-way ANOVA was used to evaluate the effects of adhesive system and nanofiller content on shear bond strength. Pair-wise comparisons between groups were made using Fisher's (LSD) (p < 0.05). For the self-etch adhesive system, only incorporation of 5 wt% showed a significant increase in shear bond strength to dentin compared with the commercial control group. For the etch-and-rinse adhesive system, there was no significant difference in shear bond strength between HNTs filled adhesives groups and the commercial control group. Resin-dentin interface SEM evaluation showed nanotubes infiltrated into dentinal tubules. In conclusion, incorporating the self-etch adhesive system with 5 wt% HNTs increased the bond strength to dentin. Incorporation of up to 10 wt% filler concentration into both the self-etch and the etch-and-rinse adhesive systems did not adversely affect the bond strength to dentin or the handling properties. HNTs can penetrate along with resin tags into dentinal tubules, which could expand the use of their unique properties.

Indiana University-Purdue University Indianapolis (IUPUI) / Introduction: Some intracanal medicaments used in regenerative endodontics may compromise the bond strength of root cements and lead to tooth discoloration. Objectives: To evaluate the effects of 1) low concentrations of TAP and DAP (1 mg/mL) on push-out bond strength of various root cements, and 2) low concentrations of TAP and DAP (1 mg/mL and 10 mg/mL) on crown discoloration. Materials and Methods: Single rooted human teeth (n = 144) were horizontally decoronated and instrumented according to standardized protocol. The samples were randomized into six experimental groups (Ca(OH)2, 1000 mg/mL TAP and DAP, 1 mg/mL TAP and DAP, and no medicament control group. After four weeks, the medicaments were removed and each group was divided into three subgroups to receive MTA cement, Biodentine cement, or Endosequence Bioceramic putty cement for two weeks. Then, two root cylinders were obtained from each root and push-out bond strength testing was performed. For the crown discoloration experiment, 160 crowns were obtained from intact human molars and randomized into experimental groups as described earlier with the addition of two groups (10 mg/mL TAP and DAP). The pulp chambers in half of the samples from each group were coated with an adhesive bonding agent before receiving the assigned intracanal medicament. Color changes (ΔE) were detected by spectrophotometer at 1 day, 1 week, and 4 weeks after application, as well as after thermocycling. Results: In the push-out bond strength experiment, 1 mg/mL DAP generally demonstrated significantly higher bond strength of root cements compared with the other treatment groups. For the crown discoloration experiment, when an adhesive bonding agent was used prior to (10 mg/mL or 1000 mg/mL) TAP, the crowns had significantly less discoloration than those without adhesive. DAP 10 mg/mL had the least significant color change at all time points regardless of whether adhesive was used. Conclusion: 1) 1 mg/mL DAP and Ca(OH)2 did not have significant negative effect on the bond strength of calcium-silicate-based cement to radicular dentin. 2) 1 mg/mL and 10 mg/mL of DAP and Ca(OH)2 had significantly less effect on the color change of the human tooth crown than all intracanal medicaments used in this study. / 2020-08-13

This doctoral thesis deals with design of three variants of ultra lightweight concrete (ULC) and their mechanical properties. The ULC usually has the dry density of 900-1200 kg/m3 and it is possible to use it for load bearing structures. Low density of ULC is achieved by replacing heavy aggregate for lightweight aggregate. The lightweight aggregate is known under the trade name Liapor in the Czech Republic. To achieve density below 1000 kg/m3, an aeration of the paste has to be done. An exchange of heavy aggregate for lightweight aggregate results in a very fragile behavior of ULC. A great attention is paid to bond strength between concrete and reinforcing steel in the thesis. In addition to the standard test of bond strength testing by pull-out, a modified pull-out test is designed, which includes the effect of minimum reinforcement cover. The mentioned test more precisely simulates a real behaviour of the structure exposed to bending moment. The doctoral thesis tries to point out on different parameters between measured data and the applicable standard for the design of load-bearing structures.

Indiana University-Purdue University Indianapolis (IUPUI) / Traditional resin luting agents generally have mechanical properties that are superior to the newer so-called “universal” self-etching/self-adhesive resin luting agents. However, recent reports indicate that some properties of these new luting agents have been improved, approaching those of the traditional etch and rinse resin luting agents. The objective of this study was to test some mechanical properties of four of these self-etching/self-adhesive resin luting agents [Maxcem Elite (ME), Multilink Automix (MA), RelyX Unicem (RU), SmartCem 2 (SC)] and compare them to a traditional etch and rinse resin luting agent [RelyX ARC (RA)] and a resin-modified glass ionomer luting cement [Fuji Plus (FP)], both of which have much longer histories of clinical success. By comparing the properties of the newer cements to the standards, it may be possible to determine how clinically successful the newer cements may be. The mechanical properties tested were flexural strength (FS) and shear bond strength (SBS). The FS test included making beams of each material, storing them in water for periods of time (24 hours and 90 days) and then performing a three-point bending test on a universal testing machine. The 90 day groups were thermocycled. The SBS test involved preparing human molar specimens, making flat dentin surfaces. Composite cylinders were fabricated, luted to the dentin surfaces with each of the materials tested, stored in water for periods of time (24 hours or 90 days), and then a knife edge shear test was performed on a universal testing machine. The 90 day groups were thermocycled. A Weibull-distribution survival analysis was performed. The results revealed significant differences in the FS of all materials tested at 24 hours. After 90 days and thermocycling, only SC and RA were not significantly different. At both time periods, FP had the lowest and MA the highest FS. The SBS results showed MA, RA, and RU to have the highest bond strengths; SC and ME the lowest at 24 hours. After 90 days and thermocycling, RA had significantly higher bond strength than all other groups; ME, FP and SC had the lowest. The self-etching/self-adhesive resin luting agents all performed at least as well as FP, with the exception of SC (SBS 24 hour). They did not all perform as well as RA, with the exception of SC (FS 90 day), MA (SBS 24 hour, FS 24 hour and 90 day), and RU (SBS 24 hour). The newer luting agents should expect to have clinical success, regarding flexural strength and shear bond strength, at least as good as resin-modified glass ionomer luting cements and approach the level of traditional etch and rinse resin luting agents.

Indiana University-Purdue University Indianapolis (IUPUI) / Background: A silorane based resin composite, Filtek LS restorative, has been introduced to overcome the polymerization shrinkage of the methacrylate based resin composite. The repair of resin composite may hold clinical advantages. Currently, there is no available information regarding the repair potential of silorane resin composite with either silorane or methacrylate based resin composite. Objectives: The purpose of this study was to compare the repaired microtensile bond strength of aged silorane resin composite using different surface treatments and either silorane or methacrylate based resin composite. Methods: One hundred and eight silorane resin composite blocks (Filtek LS) were fabricated and aged by thermocycling between 8oC and 48oC (5000 cycles). A control (solid resin composite) and four surface treatment groups (no treatment, acid treatment, aluminum oxide sandblasting and diamond bur abrasion) were tested. Each treatment group was randomly divided in half and repaired with either silorane resin composite (LS adhesive) or methacrylate based resin composite (Filtek Z250/Single Bond Plus). Specimens were 12 blocks and 108 beams per group. After 24 hours in 37oC distilled water, microtensile bond strength testing was performed using a non-trimming technique. Fracture surfaces were examined using an optical microscopy (20X) to determine failure mode. Data was analyzed using Weibull-distribution survival analysis. Results: Aluminum oxide sandblasting followed by silorane or methacrylate based resin composite and acid treatment with methacrylate based resin composite provided insignificant differences from the control (p>0.05). All other groups were significantly lower than the control. Failure was primarily adhesive in all groups. Conclusion: Aluminum oxide sandblasting produced comparable microtensile bond strength compared to the cohesive strength of silorane resin composite. After aluminum oxide sandblasting, aged silorane resin composite can be repaired with either silorane resin composite with LS system adhesive or methacrylate based resin composite with methacrylate based dentin adhesive.

M.Tech. (Department of Civil Engineering, Faculty of Engineering and Technology), Vaal University of Technology / This research investigated the structural bond strength of GFRP rebars in concrete beams under dynamic loading with the aim to characterize the structural bond behaviour and evaluate the limitations of the GFRP rebars under dynamic loading. The dynamic loading in this study was set at 500 repeating cycles to simulate a more realistic dynamic loading scenario such as earthquake since most dynamic loading studies are carried under ten repeating cycles. The experimental work was divided into 2 main tests which were firstly, the tensile tests of the GFRP rebars in order to evaluate the tensile strength of the rebars and characterize their properties. Secondly, the flexural tests of GFRP and steel reinforced concrete beams in order to evaluate the bond strength of GFRP and steel rebars, to characterize the average bond strength of GFRP and steel reinforced concrete beams under dynamic loading and finally to compare the average bond strength of GFRP rebars to Steel rebars in both dynamic and static loadings. The tensile tests were carried out using a Universal Testing Machine (UTM) and the results of the tensile tests of the GFRP rebars showed that the average experimental tensile strength of GFRP rebars was only 56.65% of the nominal tensile strength provided on the supplier data sheet. As for flexural tests, they were carried out through a four-point bending test using a UTM in conjunction with a universal dynamic shaker to create the dynamic loading set up. Steel reinforced concrete beams were used as control beams during the tests and factors such as the tensile strength of the GFRP rebars, the slip of the rebars, the load-deflection relationship and the stress-strain relationship were investigated. The results of the tests showed that the tensile strength of the GFRP rebar is strongly proportional to the maximum beam load bearing capacity and the maximum stresses of GFRP reinforced concrete beams. The results also showed that the average bond strength of GFRP rebars in static loading (8.44 MPa) was only 80% of the average bond strength in dynamic loading (10.95 MPa). Moreover, the experimental work showed that the failure of GFRP reinforced concrete beams depicted large deflections (19 mm) and slips (5 mm to 12.5 mm) when compared to steel reinforced concrete beams (for which the maximum deflection was 9.66 mm at failure and slippage values of 2 mm to 10 mm). Based on that it could be stipulated that the tensile strength of GFRP rebars is one determinant factor to the bond strength behaviour of GFRP rebars in concrete. Hence, the structural bond behaviour of GFRP rebars could be well-defined if more studies were done on the bond behaviour of GFRP rebars in concrete beams under dynamic loading using another type of GFRP rebars that would consist of a relatively high tensile strength as compared to the ones used in this study and different surface texture.

The current research project mainly aims to investigate the corrosion resistance and bond performance of steel reinforced recycled aggregate concrete incorporating nano-silica under both normal and corrosive environmental conditions. The experimental part includes testing of 180 pull-out specimens prepared from 12 different mixtures. The main parameters studied were the amount of recycled aggregate (RCA) (i.e. 0%, 25%, 50% and 100%), nano silica (1.5% and 3%), steel embedment length as well as steel bar diameter (12 and 20mm). Different levels of corrosion were electrochemically induced by applying impressed voltage technique for 2, 5, 10 and 15 days. The experimental observations mainly focused on the corrosion level in addition to the ultimate bond, failure modes and slips occurred. Experimental results showed that the bond performance between un-corroded steel and recycled aggregate concrete slightly reduced, while a significant degradation was observed after being exposed to corrosive conditions, in comparison to normal concrete. On the other hand, the use of nano silica (NS) showed a reasonable bond enhancement with both normal and RCA concretes under normal conditions. However, much better influence in terms of bond and corrosion resistance was observed under advancing levels of corrosion exposure, reflecting the improvement in corrosion resistance. Therefore, NS was superbly effective in recovering the poor performance in bond for RCA concretes. More efficiency was reported with RCA concretes compared to the conventional concrete. The bond resistance slightly with a small amount of corrosion (almost 2% weight loss), then a significant bond degradation occurs with further corrosion. The influence of specific surface area and amount of nano silica on the performance of concrete with different water/binder (w/b) ratios has been also studied, using 63 different mixtures produced with three different types of colloidal NS having various surface areas and particle sizes. The results showed that the performance of concrete is heavily influenced by changing the surface area of nano silica. Amongst the three used types of nano silica, NS with SSA of 250 m2 /g achieved the highest enhancement rate in terms of compressive strength, water absorption and microstructure analysis, followed by NS with SSA of 500 m2/g, whilst NS with SSA of 51.4 m2 /g was less advantageous for all mixtures. The optimum nano silica ratio in concrete is affected by its particle size as well as water to binder ratio. The feasibility of the impact-echo method for identifying the corrosion was evaluated and compared to the corrosion obtained by mass loss method. The results showed that the impact echo testing can be effectively used to qualitatively detect the damage caused by corrosion in reinforced concrete structures. A significant difference in the dominant frequencies response was observed after exposure to the high and moderate levels of corrosion, whilst no clear trend was observed at the initial stage of corrosion. Artificial neural network models were also developed to predict bond strength for corroded/uncorroded steel bars in concrete using the main influencing parameters (i.e., concrete strength, concrete cover, bar diameter, embedment length and corrosion rate). The developed models were able to predict the bond strength with a high level of accuracy, which was confirmed by conducting a parametric study. / Higher Education Institute of the Libyan Government

The current research project mainly aims to investigate the corrosion resistance and bond performance of steel reinforced recycled aggregate concrete incorporating nano-silica under both normal and corrosive environmental conditions. The experimental part includes testing of 180 pull-out specimens prepared from 12 different mixtures. The main parameters studied were the amount of recycled aggregate (RCA) (i.e. 0%, 25%, 50% and 100%), nano silica (1.5% and 3%), steel embedment length as well as steel bar diameter (12 and 20mm). Different levels of corrosion were electrochemically induced by applying impressed voltage technique for 2, 5, 10 and 15 days. The experimental observations mainly focused on the corrosion level in addition to the ultimate bond, failure modes and slips occurred. Experimental results showed that the bond performance between un-corroded steel and recycled aggregate concrete slightly reduced, while a significant degradation was observed after being exposed to corrosive conditions, in comparison to normal concrete. On the other hand, the use of nano silica (NS) showed a reasonable bond enhancement with both normal and RCA concretes under normal conditions. However, much better influence in terms of bond and corrosion resistance was observed under advancing levels of corrosion exposure, reflecting the improvement in corrosion resistance. Therefore, NS was superbly effective in recovering the poor performance in bond for RCA concretes. More efficiency was reported with RCA concretes compared to the conventional concrete. The bond resistance slightly with a small amount of corrosion (almost 2% weight loss), then a significant bond degradation occurs with further corrosion. The influence of specific surface area and amount of nano silica on the performance of concrete with different water/binder (w/b) ratios has been also studied, using 63 different mixtures produced with three different types of colloidal NS having various surface areas and particle sizes. The results showed that the performance of concrete is heavily influenced by changing the surface area of nano silica. Amongst the three used types of nano silica, NS with SSA of 250 m2 /g achieved the highest enhancement rate in terms of compressive strength, water absorption and microstructure analysis, followed by NS with SSA of 500 m2/g, whilst NS with SSA of 51.4 m2 /g was less advantageous for all mixtures. The optimum nano silica ratio in concrete is affected by its particle size as well as water to binder ratio. The feasibility of the impact-echo method for identifying the corrosion was evaluated and compared to the corrosion obtained by mass loss method. The results showed that the impact-echo testing can be effectively used to qualitatively detect the damage caused by corrosion in reinforced concrete structures. A significant difference in the dominant frequencies response was observed after exposure to the high and moderate levels of corrosion, whilst no clear trend was observed at the initial stage of corrosion. Artificial neural network models were also developed to predict bond strength for corroded/uncorroded steel bars in concrete using the main influencing parameters (i.e., concrete strength, concrete cover, bar diameter, embedment length and corrosion rate). The developed models were able to predict the bond strength with a high level of accuracy, which was confirmed by conducting a parametric study. / Higher Education Institute in the Libyan Government MONE BROS Company in Leeds (UK) for providing recycled aggregates BASF and Akzonobel Companies for providing nano silica NS, Hanson Ltd, UK, for suppling cement

Fiber-metal laminates (FML) are the advanced materials that are developed to improve the high performance of lightweight structures that are rapidly becoming a superior substitute for metal structures. The reasons behind their emerging usage are the mechanical properties without a compromise in weight other than the traditional metals. The bond remains a concern. This thesis reviews the effect of pre-treatments, say heat, P2 etch and laser treatments on the substrate which modifies the surface composition/roughness to impact the bond strength. The constituents that make up the FMLs in our present study are the Aluminum 2024 alloy as the substrate and the carbon fiber prepregs are the fibers. These composite samples are manufactured in a compression molding process after each pre-treatment and are then subjected to different tests to investigate its properties in tension, compression, flexural and lap shear strength. The results indicate that heat treatment adversely affects properties of the metal and the joint while laser treatments provide the best bond and joint strength.