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Cementing is one of the most crucial operations in an oil well since it fixes the casing and prevents fluid migration across permeable zones. However, the material used in this process, Class G cement, faces exposure to various agents during and after its curing process, particularly at greater depths where temperatures and pressures are elevated. Exposure of this cement to elements like brine, H2S gas, and CO2gas tends to compromise the material's durability and the well's integrity. Consequently, exposure to these agents leads to modifications in the cement paste's physical, chemical, and mechanical properties. Thus, investigations into the influence of these agents are crucial to ensure the integrity of the cement sheath. In this study, Class G cement pastes were exposed for three months in an autoclave under elevated pressure (20 MPa) and temperature (88 °C) in a brine-saturated environment with either H2S or CO2at different stages. The research investigated mechanical behavior through uniaxial and triaxial compression tests, physical properties through porosity and micro-computerized tomography tests, and chemical properties through X-ray diffraction and pH tests. The study demonstrates that confining pressure significantly affects the deformation of samples exposed to brine+H2S and brine+CO2, causing plastic deformations at confining pressures above 20 MPa even before applying deviatoric stresses. Exposure to acidic gases also leads to a 27% reduction in compressive strength for brine+H2S and a 45% reduction for brine+CO2, affecting the elastic moduli due to potential micro-defects originating from the curing process and chemical reactions induced by the presence of the acidic gases.

Several fiber treatments can be applied to mitigate the high water absorption of vegetal fibers. Wetting and drying cycles are usually performed in the industry of paper and cellulose to reduce the volume variation of the natural fibers. This procedure stiffens the polymeric structure of the fiber-cells (process known as hornification) resulting in a higher dimensional stability. The aim of this study is to determine the effect of the hornification on the interface of natural fibers. For this purpose, cycles of wet and drying was applied on Sisal, Curaua and Jute fibers. Fiber pull-out tests were performed in embedment lengths of 25mm. Furthermore, the influence of the hornification in the fibers mechanical (under tensile loading) and microstructural (surface modifications of the fiber and changes in the fiber-cell structure) behavior were investigated. The results indicate changes on the tensile strength and strain capacity of the studied fibers, showing that morphology and chemical composition play an important role on the efficiency rate of hornification.

In the present work a natural textile reinforced concrete (TRC) was developed and mechanically characterized. A fabric made of jute, a natural occurring fiber, was used as reinforcement in a fine grained cementitious matrix with a low content of calcium hydroxide. Tensile tests were performed on TRC reinforced with 3 and 5 layers of jute fabric. The mechanical tensile tests were coupled with image analysis in order to measure the crack spacing and the results were correlated with the applied tensile strain. Various stages of loading corresponding to initiation, propagation, distribution, opening, and localization of a crack system in the specimen are discussed. In order to improve the fiber-matrix interface the jute fabric was treated with a polymer based coating.

In the present work the morphology of natural fibers was correlated with their mechanical properties via image analysis. Jute, sisal, curaua, coir and piassava fibers were tested under direct tension in a universal testing machine and the cross-sectional areas of the fibers were calculated using images obtained in a scanning electron microscopy. For the jute fiber the tests were performed for several gage lengths in order to investigate its influence on the tensile strength and to compute the machine compliance. For sisal, jute and curaua fibers the amount of fiber-cells, the size of the cell walls and the real area of the fibers were measured and their correlation with the tensile strength addressed. The curaua fiber presented the highest mechanical performance with tensile strength and Young's modulus of 543MPa and 63.7GPa, respectively. Weibull statistical analysis was used to quantify the variability of fiber strength. The sisal fibers presented the highest Weibull modulus (3.70), whereas the curaua presented the lowest one (m=2.2), which means that the sisal had the lowest variability and curaua the highest.

The Cuiabá mine is an underground gold operation located in Sabará (Minas Gerais, Brazil), which began to use fiber reinforced shotcrete as rock support since 2012. In order to carry on a mechanical analysis and to design the steel and polypropylene fiber reinforced shotcrete linings, the work in hand presents an experimental investigation on the mechanical behavior of the applied composite material inside the Cuiabá mine. Through standardized panel tests, the paper evaluates the toughness performance levels for each studied fiber reinforced shotcrete and applies the current design guidelines for mining works. Based on the rock mass classification of the analyzed mine slopes, while the use of 4.2 kg/m3of polypropylene fiber volume fractions seems to be suitable where fair rock quality is observed, the addition of 25 kg/m3of steel fibers is more indicated where severe ground movement is expected. On the other hand, a mismatch between the standardized panel tests (ASTM C1550 and EN 14488-5) on the shotcrete design guidelines was also assessed in the present research. The analyzed fiber reinforced shotcrete received different classifications depending on the used standardized panel test, resulting on an overestimation of the PP fiber reinforced shotcrete for the square panel tests. Safety factors can be applied in order to mitigate the possible mismatch between square and round panel tests.

This article presents the results of an experimental investigation on the mechanical behavior of hybrid fiber reinforced Strain Hardening Cementitious Composites (SHCC) subjected to monotonic and cyclic loadings. For the study, PVA, ultra-high molecular weight polyethylene (UHMWPE) and steel fibers were used in a constant volume fraction of 2.0%. To study the synergetic effects between the fibers, hybrid compositions were also produced by replacing PVA and polyethylene by steel fibers in 0.5% and 1.0% volume fractions. The mechanical response was measured under direct tension tests, four-point bending tests on plates and three-point bending tests on notched specimens while the crack pattern was investigated using optical microscopy. To study the mechanical performance of the materials when subjected to loading/unloading cycles, cyclic three-point bending tests were also carried on. The partial replacement of PVA and polyethylene fibers by steel fibers increased the strength and post-cracking stiffness but reduced the ductility of the composites. The hybrid SHCCs presented a good mechanical performance when subjected to cyclic loadings, since the load bearing capacity and the multiple cracking behavior were maintained even for high crack opening values. The stiffness degradation and the dissipated energy over the loading/unloading cycles varied when different fibers combinations were used.