No description available.

Concrete is an integral material in modern infrastructural requirements worldwide. The production of Portland cement is however expensive, energy intensive, and results in globally significant greenhouse gas emissions. Natural pozzolans such as pumice can be used as a partial replacement for Portland cement in concrete, which can reduce production costs and greenhouse gas emissions, and improve concrete performance. A fluvial pumice deposit which may be suited for use as a natural pozzolan has been identified on the floodplains of the Waikato River. A sample was milled in Germany, and returned to New Zealand in two subsamples. These were tested in concrete, with tests divided into four rounds. The first two rounds established baseline concrete strengths at water/binder (w/b) ratios of 0.6 and 0.5, with pumice replacing cement at 5, 10, 15 and 30%. Round Three assessed the use of high pH mix water (pH=12.9), and Round Four assessed the use of a polycarboxylate superplasticiser, both with 10% pumice. Pumice is known to retard early concrete strength, however through optimisation of mix design, improvements in concrete strength and durability can be made. Indeed, all 28 day concrete strengths in this research were below Ultracem, however half of these achieved or exceeded Ultracem strengths at 91 days. The use of superplasticiser achieved the best 28 day concrete strengths, and dosage optimisation is expected to yield further improvements. Concrete durability was tested at w/b=0.5, with 10% and 30% pumice. After prolonged curing (231 days), composite concrete showed substantial improvements in electrical resistivity and resistance to chloride attack, most notably with 30% pumice. Concrete porosity was essentially unaffected. This pumice has shown significant promise as a partial cement replacement. Further mix optimisation is likely to yield greater improvements in concrete strength and durability, and will provide a more economically and environmentally sustainable product for the New Zealand concrete market.

by Chan Shun Hang. / Chinese title in romanization: Gu tao ci he fu shi zhi ruo shi guang jian ding you duan dai fa di yan jiu. / Thesis (M.Ph.)--Chinese University of Hong Kong, 1987. / Bibliography: leaves 120-122.

Thesis (M.S.)--Oregon State University, 1985. / One map folded in pocket. Typescript (photocopy). Includes bibliographical references (leaves 85-90). Also available online.

Tez (Yüksek Lisans) - Süleyman Demirel Üniversitesi, Fen Bilimleri Enstitüsü, İnşaat Mühendisliği Anabilim Dalı, 2008. / Kaynakça var.

Yes / With the technological advances in the field of building materials, there has been an increasing focus on the research of lightweight concrete made with coated aggregates for improving the durability of concrete. In this study, pumice aggregates were coated with cast-based polyester to obtain polymer-coated pumice aggregates (PCPA). Lightweight concretes were produced with different cement dosages (200, 250 and 300) and PCPAs at different ratios (0%, 50% and 100%). Physical properties, mechanical strength, thermal properties and internal structure analysis (SEM-EDS) of the produced concrete samples were performed. According to the RILEM functional classification of lightweight concrete, the test results showed that REF D300 and REF D250 dosage series are in the semi-load-bearing lightweight concrete class, and the other all series are in the insulation concrete class, and the produced concretes can be classified as lightweight insulation materials. It can also be used in non-load-bearing walls or as an alternative lightweight insulation material. / The first author wish to thank the support of Scientific and Technical Research Council (TUBITAK) BIDEB-2219 Postdoctoral Research (Project Number: 1059B192100644) and the second author also thank to the Düzce University. / The full-text of this article will be released for public view at the end of the publisher embargo on 20 June 2024.

No description available.

“Xeno-pumice” describes a pumice-like material, high in silica content and vesiculation, found as a xenolith in a more mafic rock. A xeno-pumice is an indicator of magma-crust interaction; however, the origin, nature, and processes behind this xenolith are still debated. Xeno-pumice has been described in a few places worldwide, including the Canary Islands in Spain, Indonesia, Iceland, the USA, Chile and Mexico. This thesis, for the first time, presents and analyzes the mineralogy, textural features, whole-rock geochemistry (major and trace element), and oxygen isotopes of xeno-pumice samples found in Harrat Rahat, Saudi Arabia. Harrat Rahat is a volcanic field whose last eruption was in 1256A.D. and reached the outskirts of Madinah, one of the main cities in Saudi Arabia. Harrat Rahat is characterized by a wide range of volcanic products: from basalts to trachyte. Previous studies suggested that this chemical variation has its source in the mantle and minor crustal contamination; however, the xeno-pumice samples found indicate magma-crust interaction. Thus, in this thesis, the crust-melt interaction hypothesis is addressed as a process that could modify the composition of the melt and thus the resulting volcanic products and eruptive style of the volcanic field. Indeed, the chemistry and oxygen isotope values of the studied volcanic rocks show a variation in composition, which is suggested to be the consequence of crust-melt interaction. The petrology, chemistry and oxygen isotope values suggest that the melt interacted with either the metamorphosed plutonic portion of the upper Arabian crust or with (meta-) sediments below Harrat Rahat. Finally, this thesis proved that magma-crust interaction occurred at Harrat Rahat, which has important implications for interpreting eruption mechanisms and mantle sources.

Submitted in fulfillment of requirements of the degree of Master in Health Sciences: Dental Technology, Durban University of Technology, Durban, South Africa, 2016. / Pumice is used in the polishing of dental appliances to remove surface irregularities. It is usually used in a slurry form that is pumice powder mixed with water. In Nigeria, the increased cost of pumice as a result of its limited supply into the country has encouraged dental technicians to re-use pumice slurry for longer periods than advocated when polishing acrylic dentures, whether new or old dentures which have been worn in the mouth. Consequently, this is likely to increase cross-infection of communicable diseases in the dental technology laboratory. Although materials such as white sand, black sand and porcelnite can be used, literature documents that these materials are less effective in the polishing of acrylic dentures (Areeg 2011). The focus of this study was to use eggshells, a natural waste product, to develop and test the quality of an alternative material to reduce the surface roughness of heat-cured acrylic resins. A quantitative research paradigm and an experimental research strategy were adopted. The research design included two phases. In phase one of this study, different characterisation techniques such as Brunnae-Emmer Teller (BET); Fourier Transform Infrared Spectroscopy (FTIR); X-ray Diffraction (XRD); Energy Dispersive X-ray Spectroscopy (EDX) and Scanning Electron Microscope (SEM); Transmission Electron Microscopy (TEM); Laser Scattering Particle Size Distribution Analyser (PSA); Thermo-Gravimetric Analysis (TGA); and Induction-Coupling-Optical Emission Spectroscopy (ICP-OES) were used to assess the suitability of the new abrasive material (NAM). In addition, the level of microbial contamination of the NAM was assessed in line with the specified microbial limits for cosmetic products. In contrast, phase two investigated the product-based quality of the NAM as an abrasive material for removable dental appliances. There were two sample groups, that is, the NAM (test group) and Pumice (control), and each sample group had 50 PMMA acrylic specimens. The surface roughness (Ra) was measured using a Talysurf profilometer. An Independent Tukey test was used to analyse the Ra values (p=0.05). A Scanning Electron Microscope (SEM) and Optical Microscope (OEM) were further used to support the results of the profilometer in terms of the quality of surface finish and polish. Validity of the study was achieved following the ISO 20795-1 (2013) methods of preparation and fabrication of the acrylic specimens. The reliability was determined via reproducibility and repeatability of tests. The BET analysis showed that the NAM is predominantly a mesoporous powder. The FTIR and XRD analyses confirmed that the NAM is pure calcite with unique water absorbing characteristics, and is free of bacteria. The EDX and ICP-OES analyses revealed calcium, oxygen and carbon as the major elemental composition of the NAM. The SEM and TEM images revealed irregular shaped particles in the NAM. The PSA analysis of the particle distribution showed the NAM to be superfine (50nm to 0.3µm) and medium (44µm powder), respectively. The TGA analysis revealed a high-grade carbonate product in the NAM (>66.0 mass% of calcium carbonates). In addition, and in terms of in the qualities of the NAM in reducing the surface roughness of PMMA resins, the test group and the control group produced Ra values that were significant different (p<0.0001). The SEM and OEM analyses further confirmed the differences in the surfaces between the polished sample groups at different magnifications. Overall, the control showed the highest mean average (0.1056±0.03688µm), whereas the test group had the lowest Ra values (0.0476±0.01379). The lowest Ra values measured with the test group indicated that the NAM improves the surface smoothness of PMMA acrylic specimens. Notably, this study conclusively showed that the NAM effectively reduces the surface roughness to below the threshold limit value of 0.2µm. Significantly, and in associating the Ra values to the threshold limit value of 0.2µm, the NAM produced better results than pumice. Hence the use of the NAM as a polishing material for acrylic dentures is highly recommended. Finally and in line the NAM being a suitable alternative to pumice as it effectively reduces the surface roughness of PMMA specimens, future investigation into the use of eggshell nanoparticles to develop dental prophylaxes will be encouraged. / M

Self-etching primers (SEP) have recently simplified the orthodontic bonding process and questions have arisen regarding their reliability and efficiency. The goal of this study was to assess the importance of a pumice prophylaxis prior to bonding with SEP (Transbond Plus, 3M Unitek, Monrovia, CA) in reducing bond failures. Thirty orthodontic patients volunteered to participate in this split-mouth prospective clinical trial. A pumice prophylaxis experimental group and a non-pumice control group of teeth were randomly assigned in a contralateral quadrant pattern within each patient. A total of 508 teeth were bonded and monitored over 3 months for bond failures. There were 35 total failures (6.9%) with 6 (2.4%) in the pumice group and 29 (11.4%) in the non-pumice group. Bond failures were compared as a total number between groups and also as the number of patients who experienced bond failures with each method using Chi-square analysis. There were statistically significant differences both in the total number of bond failures (P < .001) and in the number of patients with bond failures between groups (P < .01). A significantly lower and clinically acceptable bond failure rate was demonstrated when using Transbond Plus SEP after pumice prophylaxis. This study produced strong evidence to suggest the need for pumice prophylaxis in orthodontic bonding when using SEP.