Os materiais bioativos são materiais sintéticos que possuem superfícies ativas em que os minerais presentes em tecidos duros podem se ligar quimicamente. Há alguns estudos em Odontologia, onde partículas desses materiais foram incorporadas aos Cimentos de Ionômero de Vidro (CIVs) e Cimentos de Ionômero de Vidro modificados por resina (CIVMRs) com o objetivo de se obter bioatividade, e conseqüente remineralização dentária. O presente estudo teve como objetivo avaliar os efeitos da incorporação de nanopartículas de vitrocerâmica bioativa nas propriedades de resistência à compressão e rugosidade de CIVMRs. Fuji II LC e Vitremer foram considerados os grupos controles. Materiais experimentais foram feitos através da incorporação de 2, 5 e 10% em peso de Biosilicato nestes CIVMRs. Seis corpos-de-prova de cada material foram confeccionados para o teste de resistência à compressão, que foi realizado em máquina de ensaios universal (Emic), a uma velocidade de 1,0 mm/min, depois de mantidos por 24 horas em água destilada a 37°C. Para análise da rugosidade, foram confeccionados dois corpos-de-prova de cada material, armazenados em água destilada por sete dias, para terem suas superfícies analisadas por meio de Microscopia de Força Atômica. Os dados da resistência à compressão e rugosidade foram submetidos à análise estatística por meio da Análise de Variância (ANOVA) a dois critérios e para comparações múltiplas foi aplicado o teste de Tukey, com nível de significância de 5%. Apenas os cimentos com 2% de nanopartículas de vitrocerâmica bioativa obtiveram resistência à compressão semelhante ao grupo controle, as demais concentrações contribuíram para a diminuição dessa resistência. A incorporação de 5% de nanopartículas de vitrocerâmica bioativa aumentou a rugosidade superficial dos CIVMRs estudados. / Bioactive materials are synthetic materials that have active surfaces that are capable to chemically bond to dental structures. There are some studies where particles of these materials were incorporated in Glass-ionomer cements (GIC) and Resin-modified glass-ionomer cements (RMGIC) trying to achieve bioactivity and dental remineralization. The aim of this study was to evaluate the effects of the incorporation of bioactive glass-ceramics nanoparticles on the compressive strength and roughness of RMGIC. Fuji II LC and Vitremer were considered the control groups. Experimental materials were made adding 2, 5 and 10% (weight) of Biosilicate into these RMGIC. Six specimens of each material were made to be tested on compressive strength performed with a universal testing machine (Emic) at a crosshead speed of 1.0 mm / min, after they were stored in distilled water for 24 hour at 37°C. To roughness analysis, two specimens of each material were made and stored in distilled water for 7 days and their surfaces were analyzed with a Atomic Force Microscope. Data of compressive strength and roughness were statistically analyzed by ANOVA and Tukey test for multiple comparisons. Only the RMGICs with 2% of bioactive glass-ceramic nanoparticles obtained compressive strength similar to the control RMGICs, the other concentrations decreased their compressive strength values. The incorporation of 5% of bioactive glass-ceramic nanoparticles increased the roughness of the RMGICs.

El número de rebote es el valor resultante del ensayo de dureza superficial, que consiste en determinar el nivel de compacidad de las partículas del concreto. Esta característica lleva relación directa con el desarrollo de la resistencia a compresión, denominada f’c; ya que mientras más compactas se encuentren las partículas del concreto, mayor será la resistencia mecánica y mayor el valor del número de rebote. La relación de estos ensayos ha sido materia de estudio desde hace muchos años y se ha determinado valores altos de correlación, aunque sin cuantificar la influencia de parámetros adicionales que no resultan ajenos al ensayo de esclerometría. En la presente investigación se analizan los principales factores que afectan al valor de dureza superficial e influyen en la determinación de la resistencia mecánica del concreto. Los factores estudiados son la relación agua – cemento, condición de humedad, edad del concreto y tamaño máximo de agregado. Estos factores son analizados en muestras de concreto normalizadas (probetas diseñadas según norma de calidad vigente) y los resultados obtenidos procesados estadísticamente bajo la metodología de Red Neuronal Artificial (RNA), con el que se podrá predecir resultados de resistencia a compresión una vez determinados los factores antes mencionados. Los resultados demuestran que puede predecirse el resultado de resistencia a la compresión con margen de error aceptable y que considerar los factores de influencia en la predicción genera mayor exactitud en los resultados y reducción en el índice de correlación de Pearson estudiado entre los ensayos de dureza superficial y resistencia a compresión. / The rebound number index is a result value of surface hardness´s test. This method is based on obtain concrete particular’s level. This characteristic has a direct relationship with the development of compressive strength, called f’c. So, if concrete particulars are more compact, it will increase mechanic strength and rebound number index´s value. The relationships between these tests have been studied over the years and it has been estimated high values of correlation, although without quantifying the influence of additional parameters that are not indifferent to the sclerometer test. In this research are analyzed the principal factors which affect surface hardness´s value and influent in the determination of mechanic strength of concrete. The factors studied are the water-cement ratio, humidity condition, age of concrete and maximum size of aggregate. These factors are analyzed in standardized concrete samples and the results obtained were processed statistically by artificial neuronal network’s methodology (RNA), this tool will predict results of compressive strength when other factors, which were explained, have been determinate. The results of this research show that the result of resistance to compression can be predicted with acceptable margin of error and that considering the influence factors in the prediction generates better accuracy in the results and reduction in the Pearson correlation index studied between the test of surface hardness and compressive strength. / Tesis

The role of surface chemical effects in hydraulic fracturing of shale is studied using the results of unconfined compression tests and Brazilian tests on Mancos shale- cored at depths of 20-60 ft. The rock mineralogy, total organic carbon and cation exchange capacity were determined in order to characterize the shale. Adsorption tests to study the interaction of the shale and aqueous fluid mixture were also carried out using surface tension measurements. The uniaxial compressive strengths and tensile strengths of individual shale samples after four hours exposure to water, 2.85 x 10^-3 M cationic surfactant (dodecyltrimethylammonium bromide-DTAB) and 2.81 x 10^-3 M anionic surfactant (sodium dodecylbenzenesulfonate-SDBS) were analyzed using ANOVA and Bonferroni tests. These mechanical strengths were largely reduced on exposure to the aqueous environments studied, despite the relatively low clay and low swelling clay content of the Mancos shale. Further comparison of the uniaxial compressive strengths and tensile strengths of the shale on exposure to water, to the strengths when exposed to the surfactant solutions showed that their difference was not statistically significant indicating that exposure to water had the greatest effect on strength loss. The surface tension measurement of 2.85 x 10^-4 M DTAB and 2.81 x 10^-4 M SDBS solutions before and after equilibration with shale showed about 80% increase in surface tension in the DTAB solution and 10% increase in surface tension in the SDBS solution. The probable sorption mechanism is electrostatic attraction with negatively charged sites of the shale as shown by significant loss of the cationic surfactant (DTAB) to the shale surface, and the relatively minor adsorption capacity of the anionic surfactant (SDBS). Although these adsorption tests indicate interaction between the shale and surfactant solutions, within the number of tests carried out and the surfactant concentration used, the interaction does not translate into a significant statistical difference for impacts of surfactants on mechanical strength of this shale compared to the impact of water alone. The relevance of this work is to facilitate the understanding of how the strength of rock can be reduced by the composition of hydraulic fracturing fluids, to achieve improved fracture performance and higher recovery of natural gas from shale reservoirs.

This thesis presents the results of an investigation of factors which influence the geotechnical properties of frozen mine backfill (FMB). FMB has extensive application potential for mining in permafrost areas. The uniaxial compressive strength (UCS) of hardened backfill is often used to evaluate mine backfill stability. However, the deformation behaviour and stiffness of the FMB are also key design properties of interest. In this thesis, uniaxial compressive tests were conducted on FTB and FCPB samples. Information about the geotechnical properties of FMB is obtained. The effects of FMB mix components and vertical compression pressure on the geotechnical properties of FMB are discussed and summarized. An optimum total water content of 25%-35% is found in which the strength and the modulus of elasticity of the FTB are 1.4-3.2 MPa and 35-58 MPa, respectively. It is observed that a small amount (3-6%) of cement can significantly change the geotechnical properties of FTB.

Microtruss cellular materials have large internal surface areas and small cross-sectional strut dimensions, permitting surface modification to substantially enhance their mechanical performance. For instance, a ~400% increase in compressive strength with virtually no weight penalty can be induced by a hard anodized Al2O3 ceramic coating of only ~50 µm thickness. The present study seeks the optimal architecture of these composites by exploring three research challenges: architecture and degree of forming are interdependent due to stretch-forming, architecture and the material properties are interdependent due to work-hardening, and ceramic structural coatings add design complexity. Theoretical predictions and architectural optimizations demonstrated a potential weight reduction of ~3% to ~60% through the increase of internal truss angle for both annealed and work-hardened microtruss cores. While further validation is needed, experimental evidence in this study suggested the collapse in ceramic-aluminum microtruss composites could be considered as a mixture of composite strut global buckling and oxide local shell buckling mechanisms.

Microtruss cellular materials have large internal surface areas and small cross-sectional strut dimensions, permitting surface modification to substantially enhance their mechanical performance. For instance, a ~400% increase in compressive strength with virtually no weight penalty can be induced by a hard anodized Al2O3 ceramic coating of only ~50 µm thickness. The present study seeks the optimal architecture of these composites by exploring three research challenges: architecture and degree of forming are interdependent due to stretch-forming, architecture and the material properties are interdependent due to work-hardening, and ceramic structural coatings add design complexity. Theoretical predictions and architectural optimizations demonstrated a potential weight reduction of ~3% to ~60% through the increase of internal truss angle for both annealed and work-hardened microtruss cores. While further validation is needed, experimental evidence in this study suggested the collapse in ceramic-aluminum microtruss composites could be considered as a mixture of composite strut global buckling and oxide local shell buckling mechanisms.

This thesis presents the results of an investigation of factors which influence the geotechnical properties of frozen mine backfill (FMB). FMB has extensive application potential for mining in permafrost areas. The uniaxial compressive strength (UCS) of hardened backfill is often used to evaluate mine backfill stability. However, the deformation behaviour and stiffness of the FMB are also key design properties of interest. In this thesis, uniaxial compressive tests were conducted on FTB and FCPB samples. Information about the geotechnical properties of FMB is obtained. The effects of FMB mix components and vertical compression pressure on the geotechnical properties of FMB are discussed and summarized. An optimum total water content of 25%-35% is found in which the strength and the modulus of elasticity of the FTB are 1.4-3.2 MPa and 35-58 MPa, respectively. It is observed that a small amount (3-6%) of cement can significantly change the geotechnical properties of FTB.

Roller Compacted Concrete (RCC) is new technology gaining popularity in the recent years due to its low cost, rapid construction, and using opportunity of by-products. RCC is widely used in the world. However, the use of RCC has been restricted to construction of few cofferdams, and limited to local use in dam construction up to date. In this thesis, two types of cement, two types of natural pozzolan, aggregates with varying gradations, and a type of water reducing chemical admixture were used. Prior to carrying out the tests, the chemical and physical properties of materials were determined. Additionally, steam curing was applied to the test specimens in order to get long term compressive strength at early ages. Differences between steam cured specimens and normal cured specimens have been discussed in the discussion part. In the study, the results indicate that usage of water reducing chemical admixture improves compressive strength of RCC. Moreover, it is revealed that usage of fine material is essential to obtain desired results since the amount of cementitious materials is considerably low in RCC. Steam curing is known as its property of providing long term compressive strength at early ages. It was observed that application of steam curing in CEM I type cement used RCC mixtures generated expected results. However, in CEM IV type cement used RCC mixtures compressive strength results did not behave in the same manner.

The aim of this thesis is to twofold, in order to demonstrate the variabilities that can be faced within the compressive strength of blended cements, one blended cement namely CEM IV / B (P-V) 32.5N is selected and the 28-day compressive strength is obtained by 16 different laboratories following TS EN 196-1 standard. Later, to show the variabilities that could be faced by different standards, three different cement types were selected and their compressive strengths are determined following two procedures first with TS EN 196-1, later with similar procedure described in ASTM. The strength of cement is determined by TS EN 196-1 in Turkey that is the same for all types of cements. However, American cement producers use different standards for testing the strength of Portland cement and blended cements. The main difference is the amount of water utilized in producing the cement mortar. It was observed that for Portland and Portland composite cements / there is not any significant difference in between the compressive strength results of cement mortars prepared by both methods. However, for pozzolanic cements, there is much deviance in the compressive strength results of cement mortars prepared by TS EN 196-1.

This thesis describes improvements on newly-discovered high-strength pozzolan-based materials fabricated via a low-cost chemical reaction that takes place between 90 and 115 ℃ for 3 to 24 hours. The reported results focus on pozzolan constituents acquired from Coal Combustion Products (CCPs) such as cenospheres, fly ash C and F, as well as bottom ash. The thesis reports on various types of these materials with specific gravity ranging from 0.5 to 1.6; compressive strength ranging from 300 to 3600 psi, and compressive modulus ranging from 50 to 240 ksi. In addition to their good mechanical properties under compression that are attractive for the building and construction industries, the materials further exhibit great potential for applications as energy absorption cores in sandwich construction that could extend their value in other industries including the automotive and aerospace industries. For example, the load-displacement curve exhibits a short elastic zone followed by a long load-plateau; while the materials crush through a controlled vertical cracking process. Additionally, an attempt was made to further decrease the manufacturing cost of the material by investigating incorporation of chemicals that accelerates dehydration of the mixture. One such successful chemical reported in this thesis is aluminum phosphate; while it is not conclusive how the chemical improves any major property.