Date of Award
2019
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Mechanical and Aerospace Engineering
Subject(s)
Cement composites., Carbon fibers.
Abstract
Cementitious composites offer design flexibility and can be tailored to a variety of applications. However, when used in unique and structurally demanding situations, consistent performance is critical. The objectives of this study are: 1) to develop a new class of lightweight cementitious composites that exhibit consistent structural performance and 2) to introduce novel methods for their construction. These, so-called Carbon Reinforced High Performance Cementitious Composites (CRHPC2), are envisioned for uses ranging from aerospace and lightweight construction to energy transfer and structural morphing. Beams are fabricated by placing lightweight (776-806 kg/m3), high-performance cementitious matrices having low flexural moduli (776-913 MPa) over two layers of relatively stiff reinforcement, each consisting of a pre-impregnated carbon fiber grid (106 GPa) backed by a fiberglass mesh (73 GPa). The matrices are reinforced with Poly(vinyl alcohol) (PVA) fibers to reduce cracking and contain silane-coated microspheres as the aggregate to facilitate chemical bonding between the cementitious constituents and fiber reinforcements. This unique combination results in matrices having average flexural strengths of 2.72-2.86 MPa, corresponding to critical strains of 2980-3670 x 10-6 m/m, and strain energy densities of 4.05-5.25 kJ/m3. As part of this study, primary reinforcement is uniformly spaced by employing a lightweight and easily contoured lattice. A novel construction approach is introduced by curing the pre-preg at 82 degrees Celsius for 16 hours after the cementitious composite is fabricated; as opposed to, curing the reinforcement separately before placing a matrix over it. Matrices are tested to determine how their performances compare with design goals; and, to identify changes due to thermal processing. Compression and flexural tests are conducted on ten-sample sets of cylinders and beams, respectively. The performances of cementitious composite beams are evaluated by conducting flexural tests. Two sets of samples are designed with a cementitious core with pre-cured and post-cured reinforcements; two others have foam cores with pre-cured and post-cured reinforcements. Each set contains ten samples. Weibull statistics are used to evaluate structural performances of cementitious matrices and cementitious composites. Comparisons are made between room-temperature-cured and thermally-processed matrices; and, composite beams containing different cores, made from either pre-cured or post-cured reinforcements.
Recommended Citation
Pinkston, Matthew, "Development of carbon reinforced high performance cementitious composites (CRHPC²) for reverse bending" (2019). Dissertations. 190.
https://louis.uah.edu/uah-dissertations/190