The commercial use of hemp fiber in the construction industry within the United States is non-existent. This lack of use is because of State and Federal laws forbidding the growth of hemp in the United States, which has led to a lack of research. Not having an established supply chain for hemp and coupled with limited research has put the United States behind other countries in finding viable options for these renewable resources. This is a study of the performance of raw hemp fibers and processed hemp twine in a cement past mixture subjected to tensile loading. Three water/cement ratios (0.66, 0.49, 0.42) were considered. Replacement of cement with fly ash is also part of the program to see if it affects the performance of the system. A detailed description of the method of applying the tensile load to the micro/macro fibers along with the fixture setup is part of this article. The results of this investigation show the hemp twine and fibers will bond to the cement matrix and they can carry higher tensile loads at higher w/c ratios. This study shows that 30 mm embedment length is best for hemp macro fibers and 20 mm embedment for hemp micro fibers. This study also includes a comparative investigation of the performance of hemp fibers to synthetic and steel fibers added to a concrete mix. This investigation examined the compressive strength of the fiber-reinforced concrete mixes, flexural capacity, ductility, flexural toughness and the effects the fibers have on Young’s modulus of elasticity. All fibers were introduced to the same mix design (w/c = 0.49) with replacement of 25% of cement with fly ash. Hemp micro fibers at the same dosing rate a synthetic micro fibers has a slightly higher toughness and equivalent flexural strength. Hemp macro fibers at a higher dosing rate as compared to synthetic fibers will have similar toughness and equivalent flexural strength. Steel fibers performed better than the synthetic and natural fibers at 28-day compressive strength.

This research was conducted to characterize the flexural and tensile characteristics of thin, very high-strength, discontinuously reinforced concrete panels developed by the U.S. Army Engineer Research and Development Center. Panels were produced from a unique blend of cementitous material and fiberglass reinforcing fibers, achieving compressive strength and fracture toughness levels that far exceeded that of typical concrete.The research program included third-point flexural experiments, novel direct tension experiments, implementation of micromechanically based analytical models, and development of finite element numerical models. The experimental, analytical, and numerical efforts were used conjunctively to determine parameters such as elastic modulus, first-crack strength, post-crack modulus and fiber/matrix interfacial bond strength. Furthermore, analytical and numerical models implemented in the work showed potential for use as design tools in future engineered material improvements.

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The heavy use of de-icing salts in the winter to accommodate heavy traffic has been the most detrimental cause of chloride-induced corrosion in Canadian reinforced concrete (RC) bridge infrastructure. In addition, the rise of greenhouse emissions and subsequent increase in the mean surface temperature have increased the potential risk of carbonation-induced corrosion. It is believed that the synergistic effect of multiple deteriorating mechanisms will accelerate the incidence of reinforcement corrosion in Canadian infrastructure. Over time, premature deterioration of RC bridges due to reinforcement corrosion leads to concrete cover cracking and spalling, loss of bond between reinforcement and concrete, and reduction in the structural capacity and ductility of the structure. There is limited research work that has examined the effect of corrosion on the structural performance of RC columns. This research has evaluated the axial and flexural capacity of corroded RC columns exposed to different levels and patterns of reinforcement corrosion. An experimental testing campaign of ten RC columns was conducted in two stages. During the first stage, eight columns were subjected to an accelerated corrosion regime by impressing a constant current for 137 days. In the second stage, all ten columns were subjected to an axial quasi-static load until failure. Five columns were loaded concentrically, while the remaining five were loaded eccentrically. The structural performance (residual strength, ductility, resilience, stiffness, toughness and failure mode) of the columns were analyzed from load-displacement curves of the entire and mid-span length of the columns. The experimental results show that corrosion of the ties directly affects the column's post-peak response even at low corrosion levels. Columns with corroded ties had a brittle failure, and the residual ductility and toughness were significantly reduced. On the other hand, longitudinal reinforcement corrosion primarily affects the residual strength of the columns, which is prominent at a medium level of corrosion. At high levels of both longitudinal and transverse reinforcement corrosion, the residual strength, ductility, and axial stiffness are significantly reduced. This is accompanied by a significant deterioration of the cover and local buckling of the longitudinal rebars, which is attributed to a significant reduction in the confinement pressure of the core concrete. A three-dimensional non-linear finite element model (3D-NLFEM) of the columns was developed using the finite element package DIANA (v.10.4) and validated with the experimental results. The effect of reinforcement corrosion on the structural response of columns was modelled as a change in the mechanical and geometrical properties of concrete and steel materials. This was achieved by integrating constitutive and deteriorating models into the 3D-NLFEM. The model accounts for the bond-slip behaviour between longitudinal bars and concrete (for eccentrically loaded columns), the confinement of the concrete core and strength reduction of the concrete cover, and the buckling potential of longitudinal reinforcement. The validated model was used to conduct a parametric analysis to investigate the effect of several influencing variables such as damage level and patterns and to explore scenarios beyond those tested in a laboratory setting. Finally, an analytical model based on sectional analysis was developed and compared with both the experimental and FEM results. The proposed analytical approach was developed by integrating deteriorating models and incorporating data collected from field investigation. Based on this evaluation, a practical analytical approach is proposed to estimate the nominal residual capacity of corroded columns considering the reduction in confinement effects, bond loss and potential buckling. The results from the experimental, numerical, and analytical studies correlate well. This work's outcome will contribute to a better understanding of the axial and flexural performance in terms of the ultimate capacity, post peak response and failure mode of RC columns affected by the reinforcement corrosion and static loading. Moreover, it provides a simplified analytical tool for practicing engineers to predict the axial and flexural capacity of deteriorated bridges vulnerable to reinforcement corrosion and increased traffic volume.

[pt] A protensão de estruturas de concreto com cabos externos já é uma prática comum em vários países e, tem sido empregada tanto na recuperação e reforço de estruturas existentes quanto na concepção de novas estruturas. Entre algumas vantagens estão a redução do peso da estrutura,simplicidade no traçado dos cabos e melhores condições de concretagem. A protensão externa pode ser feita com cabos de aço ou com cabos sintéticos. Estes últimos são constituídos de fibras de alta resistência e excelente resistência à corrosão. O cálculo da resistência das vigas protendidas com cabos não aderentes é mais complexo do que o caso de cabos aderentes, pois a variação de tensão é função da integral das deformações da viga ao longo do traçado do cabo. Este trabalho apresenta um modelo rígido-plástico simplificado para estimar a variação da força em cabos de protensão não aderentes, para estágios de carregamento onde ocorrem deformações plásticas nos materiais, considerando que todas as rotações estejam concentradas em uma rótula plástica. O modelo leva em consideração a dependência da variação da força em cabos de protensão com o comportamento geral da estrutura, bem como a influência da resistência do concreto, da taxa de armadura na seção e dos deslizamentos que ocorrem ao longo da armadura não aderente. A eficiência deste tipo de análise é verificada por meio de uma boa concordância entre resultados analíticos e experimentais, desde que se tenha uma boa estimativa da capacidade de rotação e/ou posição relativa da linha neutra na ruptura. Apresenta-se um estudo paramétrico, sobre o comportamento à flexão de vigas protendidas com cabos externos, utilizando o modelo computacional de Campos (1993). A análise é utilizada para enfatizar as principais implicações do emprego de cabos externos de diferentes módulos de elasticidade. Estabeleceu-se também, uma relação entre a capacidade de rotação da seção e posição relativa da linha neutra, com o objetivo de facilitar a determinação da variação de força em cabos não aderentes quando o modelo rígido-plástico simplificado é empregado. Verificou-se uma boa concordância entre resultados analíticos e experimentais. / [en] Beams prestressed with external tendons have a number of attractions for engineers. They allow a reduction in weight, since concrete is not provided merely to act as cover to tendon or duct; they allow the tendons to be inspected for signs of corrosion and tendons can be replaced or retensioned if necessary. External prestressing is also an ideal application of tendons made of new materials, such as aramids; since the tendons are brittle, it is necessary to avoid the strains concentrations that occur at crack locations with bonded tendons. Since aramids fibres are non-corrodable , there is no problem about the lack of alkaline environment. The main difference in behaviour between bonded and unbonded tendons is that the deflected shape of the unbonded tendon is not the same of the beam. The force change in unbonded tendons depends on the overall geometry of the beam. This work presents a rigid plastic analysis for predicting the force in unbonded tendons , which takes into account the overall geometry of the beam, concrete strenght, reinforment index, as well as the effects of the friction at deflector points. The method is validated with a good agrement with experimental results, provided that a good aproximation of the rotational capacity of a critical section and/or the relative position of the neutral axis are known. A numerical parametrical study of the flexural resistance of concrete beams prestressed with external tendons is carried out, with particular attention paid to those beams prestressed with aramid tendons. This study used a computer program developed by Campos(1993) based on the finite element method for the analysis of concrete structures prestressed with both bonded and unbonded tendons , including external prestressing. A relationship between the rotational capacity of a critical section and the relative position of the neutral axis was stablished. The usage of this relationship together with the rigid plastic model lead to a good agreement with experimental results. Beams prestressed with external tendons have a number of attractions for engineers. They allow a reduction in weight, since concrete is not provided merely to act as cover to tendon or duct; they allow the tendons to be inspected for signs of corrosion and tendons can be replaced or retensioned if necessary. External prestressing is also an ideal application of tendons made of new materials, such as aramids; since the tendons are brittle, it is necessary to avoid the strains concentrations that occur at crack locations with bonded tendons. Since aramids fibres are non-corrodable , there is no problem about the lack of alkaline environment. The main difference in behaviour between bonded and unbonded tendons is that the deflected shape of the unbonded tendon is not the same of the beam. The force change in unbonded tendons depends on the overall geometry of the beam. This work presents a rigid plastic analysis for predicting the force in unbonded tendons , which takes into account the overall geometry of the beam, concrete strenght, reinforment index, as well as the effects of the friction at deflector points. The method is validated with a good agrement with experimental results, provided that a good aproximation of the rotational capacity of a critical section and/or the relative position of the neutral axis are known. A numerical parametrical study of the flexural resistance of concrete beams prestressed with external tendons is carried out, with particular attention paid to those beams prestressed with aramid tendons. This study used a computer program developed by Campos(1993) based on the finite element method for the analysis of concrete structures prestressed with both bonded and unbonded tendons , including external prestressing. A relationship between the rotational capacity of a critical section and the relative position of the neutral axis was stablished. The usage of this relatio / [es] La protensión de extructuras de concreto con cabos externos es ya una práctica común en varios países y, ha sido empleada tanto en la recuperación y refuerzo de extructuras existentes cuanto en la concepción de nuevas extructuras. Entre algunas ventajas están la reducción del peso de la extructura,simplicidad en el trazado de los cables y mejores condiciones para el concretaje. La protensión externa puede ser hecha con cables de acero o con cables sintéticos. Estos últimos están constituídos de fibras de alta resistencia y excelente resistencia a la corrosión. El cálculo de la resistencia de las vigas protendidas con cables no adherentes es más complejo del que el caso de cables adherentes, pués la variación de tensión es función de la integral de las deformaciones de la viga a lo largo del trazado del cable. Este trabajo presenta un modelo rígido-plástico simplificado para estimar la variación de la fuerza en cables de protensión no adherentes, para estadíos de carregamento donde ocurren deformaciones plásticas en los materiales, considerando que todas las rotaciones esten concentradas en una rótula plástica. El modelo lleva en consideración la dependencia de la variación de la fuerza en cables de protensión con el comportamiento general de la extructura, así como la influencia de la resistencia del concreto, de la tasa de armadura en la sección y de los deslizamientos que ocurren a lo largo de la armadura no adherente. La eficiencia de este tipo de análisis se verifica por meio de una buena concordancia entre resultados analíticos y experimentales, desde que se tenga uma buena estimativa de la capacidad de rotación y/o posición relativa de la línea neutra en la ruptura. Se presenta un estudio paramétrico, sobre el comportamiento a la flexión de vigas protendidas con cables externos, utilizando el modelo computacional de Campos (1993). El análisis se utiliza para enfatizar las principales implicaciones del uso de cables externos de diferentes módulos de elasticidad. Se establece también, una relación entre la capacidad de rotación de la sección y posición relativa de la línea neutra, con el objetivo de facilitar la determinación de la variación de fuerza en cables no adherentes cuando se emplea el modelo rígido-plástico simplificado. Se erificó una buena concordancia entre resultados analíticos y experimentales.

This work is made up of three parts. Part one looks to establish design values for two types of three ply access mats from the U.S. South and Midwest. The mats were subject to 3 point bending tests to determine strength and stiffness values. Values for MOE (Modulus of Elasticity) and MOR (Modulus of Rupture) are reported by region and mat design. Part two tested five species groups of hardwoods for wear resistance and hardness. These species groups include white oak, red oak, ash, sweetgum and hickory. These tests for wear were performed on a Navy-Type Wear Tester according to ASTM D2394-17. Hardness specimens were tested with the Janka method according to ASTM D143-14. The third and final part looks at the impact of thermomechanical densification on rate of wear in five species groups of hardwood. The species groups were white oak, red oak, ash, sweetgum and hickory. Samples were pressed at 1000psi at temperature of 350 degrees Fahrenheit, in order to plasticize the wood and densify it at the same time. These samples were then tested on the Navy-Type Wear Tester to determine whether densification had an impact on wear resistance.