Browsing by Author "González, Álvaro"
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Item Effect of fibres addition on the physical and mechanical properties of asphalt mixtures with crack-healing purposes by microwave radiation(2016) Norambuena-Contreras, J.; Serpell, R.; Valdés Vidal, G.; González, Álvaro; Schlangen, E.Microwave heating is regarded as a promising technique to promote crack-healing of asphalt mixtures reinforced with steel wool fibres. In addition to serving as a heat source when subject to microwave radiation, steel wool fibres are expected to affect the physical and mechanical properties of the asphalt pavements. However, it is not clear what this effect is, and what is the optimum fibre content that can provide effective crack-healing without having a negative impact on other relevant mixture properties. This paper reports a study of the steel wool fibres spatial distribution and their influence on the physical and mechanical properties of asphalt mixtures. For this purpose, five different dense asphalt mixtures, with the same aggregates gradation and bitumen content, but with five different percentages of steel wool fibres were manufactured. Then, their mechanical properties such as particle loss resistance in dry and wet conditions, and stiffness modulus and cracking resistance in Mode I of fracture at four different temperatures were evaluated. Samples of these mixtures were examined using Scanning Electron Microscopy and analysed using X-ray micro computed tomography to study the condition and distribution of fibres within the bitumen matrix. Microscopy results showed that fibres can be damaged during the mixing and compaction processes. A larger variability in the local distribution of fibres for mixtures incorporating a higher fibre content was observed in the tomography analysis, with presence of fibre clusters more than double of the average fibre content of the mixture. Although addition of fibres appears to reduce the bulk density of mixtures, according to tomography analysis differences in average porosity between samples were not statistically significant. Finally, it was confirmed that regardless of test temperature, steel wool fibres did not have a relevant influence on the improvement of particle loss resistance, stiffness modulus and cracking resistance of asphalt mixtures. (C) 2016 Elsevier Ltd. All rights reserved.Item Evaluation of additional Laboratory Test for Design of Full-Depth Reclamation Mixtures Using Foamed Bitumen(2016) González, Álvaro; Paniagua, Fernando; Thenoux, Guillermo; López, Carlosnormally fix a constant active filler content, and an indirect tensile strength (ITS) test is used to determine the optimum bitumen content. However, it has been reported in the literature that for some materials the ITS test is not sufficiently sensitive to bitumen content. This lack of sensitivity is a problem for the practitioner engineer who has to validate the bitumen content adopted in the mixture design. The main objective of this work is to examine the sensitivity to bitumen content of additional laboratory tests that could complement current design methods based on ITS. The mixtures used in the study were prepared by using three recycled blends of reclaimed asphalt pavement and aggregate that were mixed with bitumen foam contents of 1.25%, 2.5%, and 3.75%. Test results confirmed the low sensitivity of the ITS test, and it was found that the indirect tensile fatigue (ITF) test was the most sensitive among all tests. To explain the higher sensitivity of the ITF test compared with the ITS test, a stress-strain diagram and a simple unidirectional mechanical model were developed. In addition, an S-N fatigue diagram was used to illustrate that at a larger number of load cycles, the effect of the foamed bitumen content is dear, as shown in the experimental work. Overall, the laboratory program and material behavior analysis indicate that when the ITS test does not provide conclusive results, the laboratory program should be complemented with ITF tests to determine the optimum foamed bitumen content with more reliability.Item Evaluation of Portland and Pozzolanic cement on the self-healing of mortars with calcium lactate and bacteria(2020-10) González, Álvaro; Parraguez, Araceli; Corvalán, Liliana; Correa, Néstor; Castro, Javier; Stuckrath, Claudia; González, MarceloThis article studies the effect of Portland and Pozzolanic cement on the crack-healing of mortars prepared with Bacillus pseudofirmus bacteria and calcium lactate as a nutrient. Mixtures were prepared with the same content of cement, water, sand, and Light Weight Aggregate. Results showed an inverse relationship between crack width and self-healed area, with most of the healing occurring between 0 and 21 days of sample conditioning. The healing on samples with calcium lactate only and calcium lactate + bacteria was significantly higher than in control samples. Results indicate that Portland cement better promotes the self-healing of cracks compared to Pozzolanic cement.Item Probabilistic assessment of asphalt pavement design(2016) Rodríguez Moreno, M.; Thenoux, Guillermo; González, ÁlvaroIn Chile, as in many South American countries, AASHTO-93 is the current official method for the design of asphalt pavements. The method gives an estimated number of 80 kN standard axle loads (W18) that the pavement can withstand for a certain serviceability. A safety factor is then applied to W18 to take into account the confidence level and the estimated variance of the inputs used in the method, whereby the magnitude of the structure's life cycle is estimated. Normally, data used in the AASHTO-93 method are assumed to be deterministic, disregarding their random nature. This paper presents a probabilistic assessment of the AASHTO-93 pavement design method under Chilean conditions, which provides a set of probability density functions (PDFs) that allow a probabilistic estimation of the pavement life cycle in terms of the value W18. To achieve the goal, we developed a simulation model based on a sample of 13 groups of roads located throughout Chile.