Effects of Hydrothermal Treatment on the Phase Transformation, Surface Roughness, and Mechanical Properties of Monolithic Translucent Zirconia

SUMMARY Objectives: This study aimed to investigate the effects of hydrothermal treatment on four types of monolithic, translucent, yttria-stabilized, tetragonal zirconia polycrystals (Y-TZPs). Methods and Materials: Two commercially available Y-TZP brands—SuperfectZir High Translucency (Aidite Technology Co, China) and Katana HT (Kuraray Noritake Dental, Japan) were assessed. For each brand of Y-TZP, materials of four coloring types, including noncolored (NC), colored by staining (CS), precolored (PC), and multilayered (ML) specimens were investigated after hydrothermal aging in an autoclave at 134°C/0.2 MPa for 0 (control group), 5, 10, and 20 hours. The tetragonal-to-monoclinic phase transformation, surface roughness, flexural strength, and structural reliability (Weibull analysis) were measured and statistically analyzed (α=0.05). The subsurface microstructure was analyzed with scanning electron microscopy. Results: The group ML exhibited the lowest flexural strength and Weibull characteristic strength among the four coloring types (p<0.05). Slight increases in the monoclinic phase volume, flexural strength, and Weibull characteristic strength were observed after hydrothermal aging (pall<0.05). Regardless of coloring type, no significant effects of aging on the Weibull modulus or surface roughness were found for the tested materials. Compared with the Katana HT cross-sections, the SuperfectZir High Translucency cross-sections exhibited a similar but thicker transformation zone. Conclusions: The coloring procedure and material type were found to affect the mechanical properties and aging resistance of translucent monolithic Y-TZP ceramics. Regardless of the aging time, the surface roughness of the tested Y-TZP ceramics remained unchanged.

Size Effect of the Number of Parallel Joints on Uniaxial Compressive Strength and Characteristic Strength

The number of parallel joints has an impact on the size effect of the uniaxial compressive strength and characteristic strength of a rock; however, the relationships between them are yet to be derived. We studied the influence of the number of joints and rock size on the uniaxial compressive strength of the rock. This study established ten numerical simulation programs using numerical simulations and the RFPA software. Stress–strain curves of different numbers of parallel joints and sizes of rocks were analyzed. Relationships between the uniaxial compressive strength and number of parallel joints and rock size were proposed, and their special functions were obtained. Mathematical models between rock characteristic size, rock characteristic strength and the number of parallel joints were established. Simulations of the verification program confirmed that these relationships are still applicable after the angle of parallel joints changes.

Estimation of Present-Day Strength of Concrete for a 40-year-old Building from Non-destructive Tests: A Case Study "

Assessment of the present health of existing concrete structures is necessary, particularly for enhancing the life of the infrastructure facilities reaching the end of their design life. The codes stipulate establishment of site-specific correlation expressions to estimate the compressive strength of concrete from indirect non-destructive tests (NDT) such as rebound hammer or ultrasonic pulse velocity tests. However, in certain circumstances, requisite number of partially destructive (core) tests required for establishing the site-specific equations might not be feasible. In such scenario, selection of a suitable correlation expression from literature has to be performed in a rational way, as discussed in this article with a case study of a 40-year-old concrete building. From the study, it has been ob-served that for the limited number of direct tests, the Indian code stipulation resulted in higher characteristic strength of concrete as compared to the parametric estimation, which can be attributed to the assumption of Normal distribution and code stipulated (conservative) standard deviation value. In case of the indirect estimation cases, the parametric characteristic strength was pretty close to the corresponding non-parametric values indicat-ing that the fitted distributions represented the strength values very well. Recommendations for the suitable cor-relation expression from literature applicable for estimation of equivalent strength from NDT for the structure, recommendation for characteristic compressive strength of concrete and the suggestions for accounting for the inaccuracies in estimated strength in subsequent structural re-analysis have been provided from the results of the study.

Structural Behavior of Nanocoated Oil Palm Shell as Coarse Aggregate in Lightweight Concrete

Oil palm shells (OPS) are mechanical waste that is utilized as coarse aggregates in lightweight concrete. These OPS have shape and strength like conventional aggregates yet the substantial made with these OPS invigorates a limit of 18 MPa. The characteristic strength which must be utilized in structures is seen to be around 25 MPa to 30 MPa. Considering the strength as one of the boundaries for design to be sturdy, the OPS are surface-covered with nanosilane compound. This nanosilane covering goes about as infill on the outside of the aggregates and holds the concrete paste as traditional cement. Operations are permeable in nature; their inner construction has permeable design which makes the aggregates frail. Nanosilane coatings go about as holding between the concrete stage and aggregate stage and hold the substantial solid. In the present examination, mechanical and underlying conduct of nanocovered oil palm shell lightweight concrete is contrasted with that of regular cement. Nanocovered oil palm shell lightweight substantial shows comparative strength as customary cement and decrease in nonsustainable wellspring of energy in oil palm shell lightweight concrete. Supplanting of customary cement with oil palm shell concrete addresses the modern waste which can be utilized for making concrete solid and solid. Morphology and material portrayal of oil palm shell and ordinary aggregates are investigated.

Characteristic strength and acoustic emission properties of weakly cemented sandstone at different depths under uniaxial compression

As coal mining is extended from shallow to deep areas along the western coalfield, it is of great significance to study weakly cemented sandstone at different depths for underground mining engineering. Sandstones from depths of 101.5, 203.2, 317.3, 406.9, 509.9 and 589.8 m at the Buertai Coal Mine were collected. The characteristic strength, acoustic emission (AE), and energy evolution of sandstone during uniaxial compression tests were analyzed. The results show that the intermediate frequency (125–275 kHz) of shallow rock mainly occurs in the postpeak stage, while deep rock occurs in the prepeak stage. The initiation strength and damage strength of the sandstone at different depths range from 0.23 to 0.50 and 0.63 to 0.84 of peak strength (σc), respectively, decrease exponentially and are a power function with depth. The precursor strength ranges from 0.88σc to 0.99σc, increases with depth before reaching a depth of 300 m, and tends to stabilize after 300 m. The ratio of the initiation strength to the damage strength (k) ranges from 0.25 to 0.62 and decreases exponentially with depth. The failure modes of sandstone at different depths are tension-dominated mixed tensile-shear failure. Shear failure mainly occurs at the unstable crack propagation stage. The count of the shear failure bands before the peak strength increases gradually, and increases first and then decreases after the peak strength with burial depth. The cumulative input energy, released elastic energy and dissipated energy increase with depth. The elastic release rate ranges from 0.46 × 10–3 to 198.57 × 10–3 J/(cm3 s) and increases exponentially with depth.

The Evaluation of Mechanical Properties of Concrete Due to The Use of Glass Waste as Partial Substitution of Fine Aggregate

Increasing human awareness of the importance of protecting the environment and conserving natural resources requires concrete innovation as an environmentally friendly and sustainable material. Accumulated of solid waste begins to be processed and reused, one of which is as a constituent of concrete. Among the various types of solid waste, glass waste is considered as an alternative that can be used as a substitute for fine aggregate (sand), coarse aggregate (split stone) and cement. This study investigated the use of mix coloured glass waste consisting of clear, green, and brown as partial substitution of sand in concrete. Although the glass colors were mixed, the proportion of each color had been determined in this study, namely 25%, 25%, and 50%. The purpose of determining these proportions is to find out which type of color glass has the most effect on concrete mix. The target characteristic strength of 25 MPa was produced by replacing sand with 20% of mix coloured waste glass. Three combinations of concrete mixes were prepared for this study. Compression tests were conducted at 7, 14, and 28 days. Workability of fresh concrete, density, compressive strength, and failure mode were investigated in this study. Results showed that the use of waste glass was able to increase the workability of fresh concrete. K1, K 2, and K3 obtained slump values which were 4%, 6,7%, and 1,3% higher than normal concrete. Normal concrete and all combinations exhibited similar density values. Only normal concrete achieved the characteristic strength of 25,7 MPa at 28 days. Meanwhile K1, K2, and K3 achieved strengths of 22,4 MPa, 22,1 MPa, and 24,7 MPa, respectively. It was evident that as workability values increased, the compressive strengths were noticed to reduce.

Factors Affecting the Dependency of Shear Strain of LRB and SHDR: Experimental Study

In this research we conducted a sensitivity experimental study where we explored the dependency of the shear strain on the seismic properties of bearings, namely lead rubber bearing (LRB) and super high damping rubber bearing (SHDR). The factors studied were vertical pressure, temperature, shear modulus of the inner rubber (G value), loading frequency, and loading sequence. Six specimens were adopted, i.e., three LRBs and three SHDR bearings. A series of test plans were designed. The seismic characteristics of the bearings were captured through a cyclic loading test, which included post-yield stiffness, characteristic strength, area of a single cycle of the hysteretic loop, equivalent stiffness, and equivalent damping ratio. A whole analysis of variances was then conducted. At the same time, to explore certain phenomena caused by the factors, an extended discussion was carried out. Test results showed that the temperature is the most dominant feature, whereas the G value is the least contributing factor, with the effect of the loading frequency and the loading sequence found between these two. The increment of the post-yielded stiffness for LRB from 100% to 25% is a significant reduction from a low temperature to high one. The slope of the characteristic strength versus the shear strain for LRB under high temperature is larger than the one under low temperature.

Resin Composite Materials for Chairside CAD/CAM Restorations: A Comparison of Selected Mechanical Properties

Objective. The aim was to evaluate the flexural strength, flexural modulus, microhardness, Weibull modulus, and characteristic strength of six resin composite blocks (Grandio Blocs-GR, Tetric CAD-TE, Brilliant Crios-CR, Katana Avencia-AV, Cerasmart-CS, and Shofu Block HC-HC). Methods. Flexural strength and flexural modulus were measured using a three-point bending test and microhardness using the Vickers method. Weibull analysis was also performed. Results. The materials showed flexural strength ranging from 120.38 (HC) to 186.02 MPa (GR), flexural modulus from 8.26 (HC) to 16.95 GPa (GR), and microhardness from 70.85 (AV) to 140.43 (GR). Weibull modulus and characteristic strength ranged from 16.35 (CS) to 34.98 (TE) and from 123.45 MPa (HC) to 190.3 MPa (GR), respectively. Conclusions. GR, TE, and CR presented significantly higher flexural strength, modulus, Weibull modulus, and characteristic strength than the others.