Orientador: Marco Antonio Bottino / Banca: Luiz Felipe Valandro Soares / Banca: Eduardo Miyashita / Banca: Paulo Francisco Cesar / Banca: Carlos Augusto Pavanelli / Resumo: Este estudo avaliou o efeito de diferentes protocolos de jateamento na resistência à flexão biaxial e na estabilidade estrutural de uma cerâmica de Y-TZP. Para tanto, duzentos e dezesseis discos sinterizados de Y-TZP (Lava, 3M ESPE) (ISO 6872, diâmetro: 15 mm, espessura: 2 mm) foram confeccionados pelo fabricante. Para o ensaio de resistência à flexão, 180 discos (n=10) foram divididos entre 18 grupos de acordo com os fatores "tipo de partícula (Al2O3- 50 e 110μm; SiO2- 30 e 110 μm)", "pressão (2,5 e 3,5 bar)" e "ciclagem mecânica (CM) (com e sem)". O jateamento foi realizado a uma distância de 10 mm e com duração de 20 s: Gr1- Controle - (sem tratamento de superfície); Gr2- Al2O3 50 μm/2,5 bar; Gr3- Al2O3 50 μm/3,5 bar; Gr4- Al2O3 110 μm/2,5 bar; Gr5- Al2O3 110 μm/3,5 bar; Gr6- SiO2 30 μm/2,5 bar; Gr7- SiO2 30 μm/3,5 bar; Gr8- SiO2 110 μm/2,5 bar; Gr9- SiO2 110 μm /3,5 bar. Os grupos Gr10 a Gr18 são respectivamente os grupos anteriores submetidos à CM (100.000 ciclos, 50 N, 4 Hz, água 370C. Em seguida todas as amostras foram submetidas ao ensaio de resistência à flexão biaxial (ISO 6872) em máquina de ensaio universal (EMIC, 1 mm/min). Após ensaio de flexão, os dados obtidos (MPa) foram submetidos ao teste de Dunnett (5%) e à Análise de Variância (3 fatores). Para determinar a quantidade e profundidade de possíveis transformações de fase da zircônia (t→m) induzida pelo jateamento e/ou pela ciclagem mecânica, foi realizada a análise de difração de Raios-X em vinte amostras (n=2) dos grupos Gr1 ao Gr9 e Gr18, antes e após tratamento térmico (ciclo de queima da VM9/Vita). Os resultados demonstraram que todos os protocolos de jateamento promoveram um aumento significativo da resistência à flexão da cerâmica de Y-TZP em relação... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This study evaluated the effect of different air-particle-abrasion protocols on the biaxial flexural strength and on the structural stability of Y-TZP ceramic. Disc shaped (ISO 6872, Ø: 15 mm, thick: 2 mm) sintered zirconia specimens (N=216) were obtained from the manufacturer (Lava, 3M ESPE). To the flexure test 180 discs (n=10) were divided among the groups according to the factors "particle (Al2O3 50 and 110μm; SiO2 30 and 110 μm)", "pressure (2.5 and 3.5 bar)" and "mechanical cycling (MC)(with and without)". The air-particle-abrasion protocols were performed with 10 mm of distance and duration of 20 s: Gr1- Control - (without air-particle-abrasion); Gr2- Al2O3 50 μm/2,5 bar; Gr3- Al2O3 50 μm/3,5 bar; Gr4- Al2O3 110 μm/2,5 bar; Gr5- Al2O3 110 μm/3,5 bar; Gr6- SiO2 30 μm/2,5 bar; Gr7- SiO2 30 μm/3,5 bar; Gr8- SiO2 110 μm/2,5 bar; Gr9- SiO2 110 μm /3,5 bar. The groups Gr10 to Gr18 are those groups before submitted to MC, respectively (100.000 cycles; 50 N, 4 Hz, water 370C). After, all specimens were tested for biaxial flexural strength (ISO 6872) in a universal testing machine (EMIC). After, all specimens were tested for biaxial flexural strength (ISO 6872) in a universal testing machine (EMIC). The data were submitted to statistical tests ANOVA and Dunnett (5%). To determine the percentage and deep of possible zirconia transformations (te mo) after the air-particle-abrasion protocols and/or MC, the X-Ray diffraction was performed on 20 samples (n=2) from the groups Gr1 to Gr9 and Gr18, before and after thermal treatment (VM9/Vita firing cycle). The results showed that all air-particle-abrasion protocols increased significantly the flexure strength of the Y-TZP ceramic compared to the negative Control... (Complete abstract click electronic access below) / Doutor

Made available in DSpace on 2014-06-11T19:35:03Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-08-13Bitstream added on 2014-06-13T19:05:09Z : No. of bitstreams: 1 souza_roa_dr_sjc.pdf: 6581184 bytes, checksum: 4f86438bdc1d92ecc5aaf0fbfa8a4c53 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Este estudo avaliou o efeito de diferentes protocolos de jateamento na resistência à flexão biaxial e na estabilidade estrutural de uma cerâmica de Y-TZP. Para tanto, duzentos e dezesseis discos sinterizados de Y-TZP (Lava, 3M ESPE) (ISO 6872, diâmetro: 15 mm, espessura: 2 mm) foram confeccionados pelo fabricante. Para o ensaio de resistência à flexão, 180 discos (n=10) foram divididos entre 18 grupos de acordo com os fatores “tipo de partícula (Al2O3- 50 e 110μm; SiO2- 30 e 110 μm)”, “pressão (2,5 e 3,5 bar)” e “ciclagem mecânica (CM) (com e sem)”. O jateamento foi realizado a uma distância de 10 mm e com duração de 20 s: Gr1- Controle – (sem tratamento de superfície); Gr2- Al2O3 50 μm/2,5 bar; Gr3- Al2O3 50 μm/3,5 bar; Gr4- Al2O3 110 μm/2,5 bar; Gr5- Al2O3 110 μm/3,5 bar; Gr6- SiO2 30 μm/2,5 bar; Gr7- SiO2 30 μm/3,5 bar; Gr8- SiO2 110 μm/2,5 bar; Gr9- SiO2 110 μm /3,5 bar. Os grupos Gr10 a Gr18 são respectivamente os grupos anteriores submetidos à CM (100.000 ciclos, 50 N, 4 Hz, água 370C. Em seguida todas as amostras foram submetidas ao ensaio de resistência à flexão biaxial (ISO 6872) em máquina de ensaio universal (EMIC, 1 mm/min). Após ensaio de flexão, os dados obtidos (MPa) foram submetidos ao teste de Dunnett (5%) e à Análise de Variância (3 fatores). Para determinar a quantidade e profundidade de possíveis transformações de fase da zircônia (t→m) induzida pelo jateamento e/ou pela ciclagem mecânica, foi realizada a análise de difração de Raios-X em vinte amostras (n=2) dos grupos Gr1 ao Gr9 e Gr18, antes e após tratamento térmico (ciclo de queima da VM9/Vita). Os resultados demonstraram que todos os protocolos de jateamento promoveram um aumento significativo da resistência à flexão da cerâmica de Y-TZP em relação... / This study evaluated the effect of different air-particle-abrasion protocols on the biaxial flexural strength and on the structural stability of Y-TZP ceramic. Disc shaped (ISO 6872, Ø: 15 mm, thick: 2 mm) sintered zirconia specimens (N=216) were obtained from the manufacturer (Lava, 3M ESPE). To the flexure test 180 discs (n=10) were divided among the groups according to the factors “particle (Al2O3 50 and 110μm; SiO2 30 and 110 μm)”, “pressure (2.5 and 3.5 bar)” and “mechanical cycling (MC)(with and without)”. The air-particle-abrasion protocols were performed with 10 mm of distance and duration of 20 s: Gr1- Control – (without air-particle-abrasion); Gr2- Al2O3 50 μm/2,5 bar; Gr3- Al2O3 50 μm/3,5 bar; Gr4- Al2O3 110 μm/2,5 bar; Gr5- Al2O3 110 μm/3,5 bar; Gr6- SiO2 30 μm/2,5 bar; Gr7- SiO2 30 μm/3,5 bar; Gr8- SiO2 110 μm/2,5 bar; Gr9- SiO2 110 μm /3,5 bar. The groups Gr10 to Gr18 are those groups before submitted to MC, respectively (100.000 cycles; 50 N, 4 Hz, water 370C). After, all specimens were tested for biaxial flexural strength (ISO 6872) in a universal testing machine (EMIC). After, all specimens were tested for biaxial flexural strength (ISO 6872) in a universal testing machine (EMIC). The data were submitted to statistical tests ANOVA and Dunnett (5%). To determine the percentage and deep of possible zirconia transformations (te mo) after the air-particle-abrasion protocols and/or MC, the X-Ray diffraction was performed on 20 samples (n=2) from the groups Gr1 to Gr9 and Gr18, before and after thermal treatment (VM9/Vita firing cycle). The results showed that all air-particle-abrasion protocols increased significantly the flexure strength of the Y-TZP ceramic compared to the negative Control... (Complete abstract click electronic access below)

For roughly fifteen years the military has sought to use the properties of ceramics for armor applications. Current high-performance ceramics have extremely high compressive strengths and low densities. One ceramic that has been shown to be highly resistant under ballistic impact is silicon carbide (SiC). It has been found that even within the silicon carbides, those manufactured by certain methods and those with certain microstructural properties have advantages over others. In order to understand the microstructural reasons behind variations in ballistic properties, plate impact tests were conducted on two sintered silicon carbides with slightly different microstructures. Two variations of a silicon carbide with the trade name Hexoloy SA were obtained through Saint Gobain. Regular Hexoloy (RH) and Enhanced Hexoloy (EH) are pressureless sintered products having exactly the same chemistries. EH went through additional powder processing prior to sintering, producing a final product with a slightly different morphology than RH. Samples of each were characterized microstructurally including morphology, density, elastic wavespeeds, microhardness, fracture toughness, and flexure strength. The characterization revealed differences in porosity distribution and flexure strength. It was determined that the porosity distribution in EH had fewer large pores leading to an 18% increase in flexural strength over that for RH. The focus of the mechanics of materials community concerning dynamic material behavior is to pin down what exactly is happening microstructurally during ballistic events. Several studies have been conducted where material properties of one ceramic type are varied and the dynamic behavior is tested and analyzed. Usually, from one variation to the next, several properties are different making it hard to isolate the effect of each. For this study, the only difference in the materials was porosity distribution. Plate impact experiments were conducted at the Army Research Laboratory (ARL) using the gas gun facilities within the Impact Physics Branch. A VISAR was utilized to measure free surface velocities. Tests were performed on each material to determine the Hugoniot Elastic Limit (HEL) and spall strength. Spall strength was measured as a function of impact stress, and pulse duration.

Orientador: Fábio Luiz Camargo Villela Berbert / Resumo: Objetivo: O objetivo desse estudo foi avaliar protocolos de agitação do EDTA aplicando dois diferentes tipos lasers de diodo de alta potência, comparando-os com os métodos de agitação convencional e com o ultrassom, quanto à extrusão apical, alteração de temperatura, resistência à fratura radicular e análise de pH na dentina radicular. Material e Métodos: Essa pesquisa experimental ex-vivo, utilizou 120 pré-molares inferiores, unirradiculados, com ráizes retas, com rizogênses completa e com tamanho radicular superior a 16mm, pré-selecionados por meio de radiografia digital. Suas coroas foram removidas, padronizando as raízes em 16 mm, seguido do preparo com a lima K#15 K#20 e o sistema reciproc R25, R40 e R50, 1 mm aquém do comprimento real do dente, com irrigação durante o preparo com NaOCl a 2,5%. Os espécimes foram distribuídos aleatoriamente em 6 grupos segundo protocolos de irrigação final: AD- água destilada (controle), CV- inundação com EDTA 17% e agitação com lima K #50, PUI- inundação com EDTA 17% agitado com ultrassom (Passive ultrasonic irrigation-PUI), PUI/CUI- inundação com EDTA 17% agitado com ultrassom (PUI) e irrigação com água destilada, agitada com ultrassom (Continuous ultrasonic irrigation-CUI), TL- inundação com EDTA 17% agitado com laser diodo Thera Lase Surgery, e GE- EDTA 17% agitado com laser diodo Gemini. Após irrigação final, todos os dentes foram irrigados com água destilada para remoção do EDTA. Resultados: Na avaliação da extrusão apical foi real... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Objective: The objective of this study was to evaluate EDTA agitation protocols by applying two different types of high-power diode lasers, comparing them with conventional agitation methods and with ultrasound, in relation to apical extrusion, temperature change, fracture resistance root and pH analysis in root dentin. Material and Methods: This ex-vivo experimental research used 120 lower premolars, uniradicular, with straight roots, with complete rhizogenesis and with root size greater than 16mm, pre-selected by means of digital radiography. Their crowns were removed, standardizing the roots by 16 mm, followed by preparation with the K # 15 K # 20 file and the reciproc system R25, R40 and R50, 1 mm below the actual length of the tooth, with irrigation during preparation with NaOCl to 2.5%. The specimens were randomly distributed into 6 groups according to final irrigation protocols: AD- distilled water (control), CV- flood with 17% EDTA and agitation with K # 50 file, PUI- flood with 17% EDTA agitated with ultrasound (Passive ultrasonic irrigation-PUI), PUI / CUI- flooding with 17% EDTA stirred with ultrasound (PUI) and irrigation with distilled water, stirred with ultrasound (Continuous ultrasonic irrigation-CUI), TL- flooding with 17% EDTA stirred with laser diode Thera Lase Surgery, and GE-EDTA 17% stirred with Gemini diode laser. After final irrigation, all teeth were irrigated with distilled water to remove EDTA. Results: In the evaluation of the apical extrusion, the... (Complete abstract click electronic access below) / Mestre

Preplaced aggregate concrete (PAC) is produced by grouting high workability cement based grouts among the voids of compacted coarse aggregate mass. Because of its low shrinkage, PAC has been used for many repair jobs like; tunnel lines, dams and bridge piers. Moreover, it has been used for underwater construction. Grout has a major effect on the properties of produced PAC and well defined grout controls the properties of resulted PAC. The effect of types and amount of powder materials, admixtures, sand and water content on the properties of fresh and hardened grout for the production of PAC have been investigated. Tests on hardened grout and PAC properties have also been carried out to investigate the most important effects. A correlation between hardened properties of grout and PAC has also been analyzed. Grout rheology using four different gradation sands at two different cement-sand and at different w/c ratios ratios has been identified experimentally; no added chemical admixtures or mineral additives had first employed, then superplasticizer (SP) was added at 2% and 1%, and finally a combination of 1% SP and pulverized fuel ash (Pfa) at 20% of the cement weight was employed for all mixes. Grout tests have included two point workability tests by the Viskomat NT, flow time funnel test, Colcrete flow meter test, and water bleeding test. After that, eighteen grout mixes with high workability were produced using three different sands at three w/c ratios and two c/s ratios with 1% SP and Pfa at 20% of the cement weight were designed. Eighteen hardened grout and PAC then produced and their compressive strength and sorptivity were tested. Grout rheology can be defined by the rheology of cement paste employed and the internal distance between sand particles. The effect of sand surface texture on grout rheology is important at very low internal distances. Fresh grout yield stress is the most important property which gives the same degree of sensitivity for all grouts regardless the material type and content used in the mix. There are strong relations between compressive strength of grout and PAC, but less correlation between them in sorptivity test because of the effect high quantity of coarse aggregate of PAC. Sorptivity of PAC is low comparing with different kinds of concrete suggesting its advantage for underwater construction.

The mechanical properties of boron carbide (B4C) with 10 and 20 vol% particulate inclusions of commercially available nano-sized alpha-phase silicon carbide (a-SiC) or micron-sized titanium diboride (TiB2) were investigated so as to produce a fine-grained material with high hardness, toughness, and overall strength in order to increase the effectiveness of B4C as a structural ceramic, whose use in the field has been limited because of the extreme brittle nature of the material. Full density sintering of the ceramics (≥99% theoretical) was completed using the novel Plasma Pressure Compaction (P²C®) technique, which limited grain growth due to a reduced processing temperature and a significantly reduced consolidation time. The reinforced ceramic composites had particulate grains homogeneously distributed within the B4C matrix. X-ray diffraction patterns confirmed that the constituents did not interdiffuse. The four-point flexure strength for the monolithic B4C ceramic was found to be significantly larger than any recorded value found in scientific literature, and was most likely attributed to the fine-grained microstructure resulting from the P²C® processing. The mechanical properties of the nano-sized a-SiC-B4C ceramics showed a slight increase in the Chevron-notched four-point bend fracture toughness due to the crack deflection toughening mechanism. A slight decrease in the Vickers microhardness and the static elastic modulus values were also observed. A significant increase in the fracture toughness as well as a slight increase in the microhardness and elastic modulus of the micron-sized TiB2-B4C materials was found. The toughening mechanism of this composite was attributed to the slight chemical bond between the B4C matrix and the ultra-small, ultra-tough TiB2 particulates, which forced a propagating crack to completely rip apart the TiB2 reinforcing particles. This cleaving nature resulted in significant amounts of energy being absorbed by the micron-sized particulates. It was concluded that the composite with 20 vol% TiB2 allowed for the largest gain in toughness because it possessed the largest number of ultra small, ultra tough particulate-cracktip interactions.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This study evaluated the effect of different surface treatments on the biaxial flexure strength and reliability of a ceramic Y-TZP by using Weibull analysis. In addition, the influence of these methods on the bond strength of a resin cement and ceramic Y-TZP were studied. The surface treatments analyzed were the following: air-borne particle abrasion with silica-coated aluminum oxide particles for 10 s with 10 mm distance (TBS); application of a ceramic overglaze on the surface and etching with 10% hydrofluoric acid gel (HF) for 1 min (GLZ1), 5 min (GLZ5), 10 min (GLZ10), and 15 min (GLZ15); and deposition of 5 nm thick SiO2 nanofilm by physical vapor deposition (PVD) (SNF). This last treatment was performed only to study the biaxial flexural strength. Regarding the biaxial flexural strength and reliability of the material, 210 discs (15mm × 1.2mm) of Y-TZP were made following the ISO 6872-1999 and then sintered according to the manufacturer`s instructions. The discs (n=30) were divided according to the different surface treatments applied (6 groups), apart from the control group which did not receive any treatment. Using the flexural strength data, a Weibull statistical analysis was performed to describe the reliability of the ceramic material. To evaluate the bond strength, 75 Y-TZP (In-Ceram YZ, Vita) blocks (5×5×4 mm) were assigned into five groups (n=15) according to the different surface treatments. Specimens of composite resin (diameter=3.25mm; height=3mm) were cemented to the Y-TZP blocks using resin cement (Relyx ARC). All the specimens were subjected to aging (10,000 thermal cycles and storage for 90 days), tested in shear, analyzed under a stereomicroscope and under a scanning electron microscope (SEM), and measured by phase transformation analysis (XRD). In relation to the biaxial flexure, the TBS group statistically presented the highest strength values, and the groups with glaze application followed by etching with hydrofluoric acid (GLZx) showed the lowest values, independent of the HF treatment time. However, no surface treatment negatively influenced the reliability of the material when compared with the control group with no surface treatment, according to the Weibull analysis results. With respect to adhesion, the TBS groups showed the highest bond strength values. It may be concluded that treatment with blasting (TBS group) confers the best bond strength to ceramics out of all the tested methods, without negatively influencing the strength of the material. / Este estudo avaliou o efeito de diferentes tratamentos de superfície na resistência à flexão biaxial e confiabilidade da cerâmica Y-TZP usando a análise de Weibull. Além disso, a influência desses métodos na resistência de união entre um cimento resinoso e a cerâmica Y-TZP foi estuda. Os tratamentos de superfície analisados foram: jateamento com partículas de óxido de alumínio revestidas por Sílica por 10 segundos e com 10 mm de distância (TBS); aplicação de glaze na superfície da cerâmica e condicionamento com ácido fluorídrico gel 10% (HF) por 1 min (GLZ1), 5 min (GLZ5), 10 min (GLZ10) e 15 min (GLZ15) e deposição de nanofilme de SiO2 com 5 nm de espessura através da deposição física de vapor (PVD) (SNF). Este último tratamento foi utilizado apenas no trabalho referente a resistência à flexão biaxial. Para a resistência à flexão biaxial e confiabilidade do material 210 discos (15mm x 1.2mm) de Y-TZP foram confeccionados seguindo a ISO 6872-1999 e sinterizados de acordo com instruções do fabricante. Os discos foram divididos (n=30) de acordo com o tratamento de superfície aplicado (6 grupos) além do grupo controle o qual não recebeu tratamento. Através dos dados de resistência à flexão, foi realizada também a análise estatística de Weibull, a qual é utilizada para descrever a confiabilidade de materiais cerâmicos. Para avaliar a resistência de união, 75 blocos de Y-TZP (In-Ceram YZ, Vita) (5×5×4 mm) foram divididos em cinco grupos (n=15) de acordo com o tratamento de superfície. Espécimes de resina composta (diâmetro=3.25mm; altura=3mm) foram cimentados nos blocos de Y-TZP usando um cimento resinoso (Relyx ARC). Todos os espécimes foram submetidos ao envelhecimento (10,000 ciclos e armazenamento por 90 dias), ao teste de cisalhamento, analisados no estereomicroscópio, no microscópio eletrônico de varredura (MEV) e submetidos a análise de transformação de fase (XRD). Com relação à flexão biaxial, pode-se notar que o grupo TBS apresentou o maior valor de resistência e os grupos com aplicação do glaze seguido de condicionamento com ácido fluorídrico mostraram os menores valores independente do tempo de condicionamento. Entretanto nenhum tratamento influenciou de maneira negativa a confiabilidade do material quando comparado com o grupo controle. Para os resultados de adesão, o grupo TBS obteve os maiores valores de resistência de união. É possível concluir que o tratamento com jateamento (grupo TBS) confere uma melhor resistência de união na cerâmica não influenciando de forma negativa na resistência flexural desse material.

Fundação de Amparo a Pesquisa no Estado do Rio Grande do Sul / The aim of this study was to investigate the effect of heat treatments on the flexural strength, surface roughness and crystalline structure of a leucite reinforced glass ceramic (IPS Empress CAD, Ivoclar Vivadent, Liechtenstein). A hundred fifty (150) discs were machined by CEREC inLab MC XL (Sirona, Alemanha) and distributed into five groups, n=30: C (control, no heat treatment), A-575 (annealed at 575°C during 15 min, followed by slow cooling and furnace opening at 200°C), A-790 (annealed at 790°C during 15 min, followed by slow cooling and furnace opening at 200°C), G (glazed at 790°C during 1,5 min, followed by fast cooling - immediate furnace opening) and GM (modified glaze, at 790°C during 1,5 min, followed by slow cooling and furnace opening at 200°C). Biaxial flexural strength was determined by the piston-on-three ball test (ISO 6872/2008). Weibull modulus (m) and characteristic strength (σ0) were calculated from the results. The surface roughness (Ra and Rz) was measured before and after the treatments. One specimen from each group was used for X-ray diffraction. A-790 produced the highest values of fracture strength (211.7 MPa). The values of σ0 obtained for the other tested regimens (A-575: 167.9 MPa, GM: 157.7 MPa and G: 153.7 MPa) were lower than those from the control group (187.7 MPa). The value of m was statistically similar between the groups. All heat treatments were able to reduce the mean roughness (Ra) of the specimens. The mean amplitude (Rz), showed a significant reduction only for the groups submitted to the annealing treatments (A-575 e A-790). The X-ray diffraction analysis revealed no changes in the crystalline phase (tetragonal leucite) of the material after the different heat treatments. Variations in the size of the leucite crystallites after thermal cycles were not significant. Thus, high values of fracture strength and decreased surface roughness for a leucite reinforced glass ceramic are achieved by annealing above the glass transition (Tg=625 ± 20ºC) after machining. This regimen (A-790) was capable to produce favorable structural reorganization of the material, without modifying its original crystalline structure. Annealing bellow the glass transition (A- 575) and thermal cycle for glazing (G and GM) significantly reduced the strength of the material. / A proposição deste estudo foi investigar o efeito de tratamentos térmicos na resistência flexural biaxial, na rugosidade superficial e na estrutura cristalina de uma vitrocerâmica reforçada por leucita (IPS Empress CAD, Ivoclar Vivadent, Liechtenstein). Para tanto, 150 discos foram obtidos por usinagem em equipamento CEREC inLab MC XL (Sirona, Alemanha) e distribuídos em cinco grupos, de n=30: C (controle, sem tratamento térmico), A-575 (annealing à 575°C por 15 min, seguido de resfriamento lento com abertura do forno em 200°C), A-790 (annealing à 790°C por 15 min, seguido de resfriamento lento com abertura do forno em 200°C), G (glazeamento à 790°C por 1,5 min, seguido de resfriamento rápido com abertura imediata do forno) e GM (glazeamento modificado à 790°C por 1,5 min, seguido de resfriamento lento com abertura do forno em 200°C). A resistência flexural dos discos foi determinada pelo teste piston-on-three ball, conforme normas da ISO 6872/2008 e os dados submetidos à análise de Weibull para cálculo do módulo de Weibull (m) e da resistência característica (σ0). A rugosidade superficial (Ra e Rz) antes e após os tratamentos foi mensurada. Um espécime de cada grupo foi utilizado para difração de raios-X. O regime A-790 produziu os maiores valores de resistência à fratura (211,7 MPa). Os valores de σ0 promovidos pelos demais ciclos testados (A-575: 167,9 MPa, GM: 157,7 MPa e G: 153,7 MPa) foram inferiores aos do grupo controle (187,7 MPa). O valor de m não diferiu significativamente entre os grupos. Todos os tratamentos térmicos foram capazes de reduzir a rugosidade média (Ra) dos espécimes. Já os valores de amplitude média do perfil (Rz), apresentaram redução significativa apenas para os grupos submetidos à annealing (A-575 e A-790). A análise de difração de raios-x revelou não ter havido mudanças de fase cristalina (leucita tetragonal) do material após os tratamentos térmicos. As alterações no tamanho dos cristalitos de leucita após a realização dos ciclos térmicos não foram expressivas. Sendo assim, maiores valores de resistência à fratura e diminuição da rugosidade superficial para uma vitrocerâmica reforçada por leucita puderam ser conseguidos através de annealing acima da transição vítrea (Tg=625 ± 20ºC) após a usinagem. Tal regime (A-790) foi capaz de produzir reorganização estrutural favorável do material, sem contudo modificar sua estrutura cristalina original. Annealing abaixo da transição vítrea (A-575) e regimes de glazeamento (G e GM) reduziram significativamente a resistência do material.

Preplaced aggregate concrete (PAC) is produced by grouting high workability cement based grouts among the voids of compacted coarse aggregate mass. Because of its low shrinkage, PAC has been used for many repair jobs like; tunnel lines, dams and bridge piers. Moreover, it has been used for underwater construction. Grout has a major effect on the properties of produced PAC and well defined grout controls the properties of resulted PAC. The effect of types and amount of powder materials, admixtures, sand and water content on the properties of fresh and hardened grout for the production of PAC have been investigated. Tests on hardened grout and PAC properties have also been carried out to investigate the most important effects. A correlation between hardened properties of grout and PAC has also been analyzed. Grout rheology using four different gradation sands at two different cement-sand and at different w/c ratios ratios has been identified experimentally; no added chemical admixtures or mineral additives had first employed, then superplasticizer (SP) was added at 2% and 1%, and finally a combination of 1% SP and pulverized fuel ash (Pfa) at 20% of the cement weight was employed for all mixes. Grout tests have included two point workability tests by the Viskomat NT, flow time funnel test, Colcrete flow meter test, and water bleeding test. After that, eighteen grout mixes with high workability were produced using three different sands at three w/c ratios and two c/s ratios with 1% SP and Pfa at 20% of the cement weight were designed. Eighteen hardened grout and PAC then produced and their compressive strength and sorptivity were tested. Grout rheology can be defined by the rheology of cement paste employed and the internal distance between sand particles. The effect of sand surface texture on grout rheology is important at very low internal distances. Fresh grout yield stress is the most important property which gives the same degree of sensitivity for all grouts regardless the material type and content used in the mix. There are strong relations between compressive strength of grout and PAC, but less correlation between them in sorptivity test because of the effect high quantity of coarse aggregate of PAC. Sorptivity of PAC is low comparing with different kinds of concrete suggesting its advantage for underwater construction. / Libyan High Education Ministry