Browsing by Author "Rueda, Eduardo J."

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    Homogenization of rammed earth walls under changing environmental conditions
    (2024) Villacreses, Juan P.; Caicedo, Bernardo; Rueda, Eduardo J.; Ibagón, Laura; Acosta, Johana
    Construction with rammed earth walls is a technique used for the construction of structures that has been increasing and by its nature requires in-depth knowledge due to the exposure of its materials (soil) to environmental factors, such as precipitation and solar radiation. This causes its structural elements to experience humidity fluctuations that affect the soil that constitutes them, resulting in a structure built with a material with heterogeneous properties, a fact that makes it difficult to understand its behaviour. The use of simulations in numerical models has helped to understand the internal dynamics of these elements. However, these procedures can present challenges in model construction and can also be computationally expensive, depending on the complexity of the model. In this context, the present research focuses on examining the behaviour of rammed earth walls against seismic action, when despite being made up of a single material, its composition is considered heterogeneous due to the humidity variations inherent to its exposure. Next, these models were subjected to a homogenization process of its properties using the Hashin and Shtrikman homogenization bounding theory. The objective is to find equivalent properties that facilitate the analysis of structural behaviour, assuming the homogeneity of the material. This homogenization process was extended to all parameters defined within the Pressure Independent Multi-yield material model employed in OpenSees, encompassing shear modulus, bulk modulus and density. As a result, applying Hashin and Shtrikman's upper bound to homogenize rammed earth walls produces remarkably similar results to those obtained using simulations of heterogeneous walls. This research provides valuable insights to understand rammed earth wall homogenization techniques and their behaviour, with important implications for their design and analysis.
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    Influence of wetting-drying cycles on the linear viscoelastic properties of asphalt ixtures
    (2023) Rueda, Eduardo J.; Caro, Silvia; Caicedo, Bernardo
    The top asphalt layers of pavement structures are subjected to loading demands and multiple environmental factors. Even though existing studies on moisture damage in asphalt mixtures have demonstrated the deleterious effects of water on different mechanical properties of these materials, the impact caused by changes in the partial saturation during the application of wetting–drying cycles on the linear viscoelastic properties of the mixture is an unexplored field. This study quantifies, for the first time, the changes in these properties (i.e., dynamic modulus, |E*|, and phase angle, ϕ) of a conventional asphalt mixture subjected to multiple wetting–drying moisture vapour cycles. The testing specimens were conditioned at five different relative humidity (RH) environments that were increased (wet path) or reduced (dry path) gradually, causing different saturation levels within their microstructures. The magnitude of |E*| and ϕ of the specimens was measured after reaching a steady state condition at each individual RH environment. In total, the specimens were subjected to five wetting–drying cycles and to a total of 41 dynamic modulus tests. The results corroborate that the degree of saturation impacts the linear viscoelastic properties of the mixture and show the irreversible effect of wetting–drying cycles on these properties. Since the dynamic modulus is an input parameter in the design of flexible pavements, the results also suggest that the degradation of this property due to changes in the partial saturation under field conditions could be included as part of existing mechanistic-empirical design methodologies.
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    Temperature effect of asphalt production on the thermo-chemical properties of Kraft lignin
    (2024) Marquez, J. Waldo; Fuentes, Valentina; Rueda, Eduardo J.; Tundidor-Camba, Alain; Escalona, Nestor; Norambuena-Contreras, Jose; Gonzalez, Alvaro
    Global warming has triggered a series of strategies and efforts to reduce greenhouse gas emissions and increase the reuse and recycling into asphalt pavements. One of these, is the reduction of production temperatures of asphalt mixtures, and the other is using sustainable antioxidants, such as Kraft lignin, with high phenolic content. Kraft lignin is usually mixed at high temperatures without considering the effect of temperature on its antioxidant properties. This research aimed to study the impact of the production temperatures of asphalt mixtures on the thermo-chemical properties of Kraft lignin and its antioxidant capacity. To evaluate these properties, thermogravimetry, infrared spectroscopy, and DPPH tests were done. To validate the results, bitumen-lignin blends were prepared considering representative temperatures for Hot-Mix-Asphalt (HMA), 160 degrees C, and for Warm-Mix-Asphalt (WMA), 135 degrees C. Bitumen-lignin blends were prepared considering 0% and 20% Kraft lignin by total weight bitumen. The blended samples, unaged and aged. were evaluated considering mechanical, rheological, and chemical properties. The main conclusion of the study demonstrated that although Kraft lignin can be used in HMA, using it in mixtures with lower temperatures conserve its properties. WMA production temperatures preserve Kraft lignin's chemical properties, increasing the durability and resilience of bitumen throughout its service life.