Mechanics and Rheological Characterization of Construction Materials
Pelot, David D.
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This work deals with mechanical behavior and rheological characterization of construction materials. In particular, it describes self-healing fibers, characterization techniques, and two apparatuses, all of which serve to improve on already developed construction materials. Self-healing core-shell nanofibers are created using emulsion electrospinning, coelectrospinning, and emulsion solution blowing. Fiber crush test and interlayer pull out test are conducted to verify the expulsion of the core material under stress. The mechanical properties of foams with different surfactant concentrations, air contents, and the addition of PEO are measured using free drainage in a gravity settler. It was found that an increase in concentration and the addition of PEO both reduce drainage rates of the foam, making it more stable, and the air content only effects the total liquid volume in the foam. Constant volume squeeze flow of soft solids, modeled under the assumption that normal stresses are dominant, relates the axisymmetrical spreading rate to the force applied divided by the viscosity of the fluid. Also, the material’s yield stress is calculated. Then, an experimental apparatus was constructed in concert with the theory and the known rheological parameters of bentonite and Carbopol were used to validate the squeezing apparatus. Furthermore, the squeezing apparatus can measure the rheological properties of abrasive joint compounds and correlates component variation to changes in viscosity and yield stress. The same squeezing apparatus was modified in order to vary the applied force in time and identifies a transition of bentonite dispersions when squeezed from liquid-like (flowing) to solid-like (cracking) behavior. The stress required for bentonite dispersions to crack was investigated for concentrations of 11 wt% to 13 wt% and an aging time of 0 hours to 72 hours. The spreading of thick dispersions by a knife or trowel was simulated by spreading Carbopol solution with seeding particles to reveal an experimental velocity profile under a wedge at three angles and two heights using a moving plate pulled at two velocities. The experimental velocity profile is compared to the one-dimensional analytical result for a Newtonian fluid in the lubrication approximation and with the Bingham fluid model.