4 research outputs found
Structural evolution and impact on the compressive strength of fly ash-based geopolymers
Abstract
This paper concentrates on valorization of the fly ash originating from thermal power plant by alkaline activation. Structural and textural characterization of raw material and prepared geopolymers was carried out. The used raw material belonged to Class F according to ASTM C618–05 and it was mainly composed of quartz, mullite, hematite and calcite, that coexisted with hydroxy-sodalite in final geopolymers. The proportion of the hydroxy-sodalite phase increased with the concentration of the activating agent. During geopolymerization, structural changes appeared including the incorporation of aluminum into the silicate network leading to their crosslinking. Textural characterization showed that the material became more compact during the geopolymerization process, which in agreement with the increase of hydroxy-sodalite phase. These changes lead to an increase of mechanical strength of geopolymers
Effects of dynamic sitting interventions on tissue oxygenation in individuals with spinal cord disorders
Study Design: An explorative cross-sectional study. Objectives: The objective of this study was to investigate the possibility of imposing dynamic sitting behavior on individuals with spinal cord disorders by using the Dynasit chair and to investigate its effect on the (sub-)cutaneous tissue oxygenation. Setting: Rehabilitation Centre het Roessingh, Enschede, the Netherlands. Subjects: Ten male subjects with a spinal cord disorder. Methods: The Dynasit chair, an experimental simulator chair, containing mechanical concepts for postural adjustments, regulation of tuberal load and pelvic rotation, was developed to allow individuals with a spinal cord disorder to sit in a dynamic way. An experiment was carried out in which a dynamic sitting pattern was imposed. The sitting pattern consisted of series of actuated changes in posture, tuberal load and pelvic orientation. Effects of these changes on (sub-)cutaneous buttock tissue oxygenation were investigated by transcutaneous measurement of tissue oxygenation. Results: Nonparametric statistical analyses were carried out on nine subjects that completed the study. Results showed significant positive effects (P<0.05) of actuated changes in tuberal load on the cutaneous and subcutaneous tissue oxygenation. Conclusion: The Dynasit chair is effective in imposing dynamic sitting behavior in individuals with a spinal cord disorder and consequently might reduce the chance of tissue degradatio