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Building products development using extrusion technique

Authors Liu, Chun Pong
Issue Date 2001
Summary Recent studies have shown that the characteristics of the Fiber-Reinforced Cementitious composite (FRCC) depend largely on the methods of processing. The fibre-reinforced cement based composites manufactured by extrusion show a great improvement in strength, toughness, ductility, and durability as compared to the traditional casting method. The extrudate showed a superior workability for nailing, sawing and drilling. The advantages of the extrusion technique include: mass-production capability, product manufacture flexibility, the ability to produce complicated and varied shapes, and the capability of improving the material properties. This property improvement can be attributed to the achievement of low porosity and good interfacial bond under high shear and compressive stress during the extrusion process. Various kinds of building product, such as cylinder, sheet, pipe, channel and honeycomb wall panel by incorporating various mineral admixtures and polymers have been manufactured by the extrusion technique. Two kinds of short fiber, ductile polyvinyl alcohol (PVA) fibers and stronger but less ductile glass fibers, were used as the reinforcement in the products. A number of extruded plates were exposed to repeated cycles of freezing and thawing in accordance with ASTM C666 (Procedure B) after the 28-days curing period in the presence of 3% sodium chloride solution. Variables investigated were the matrix content, fiber volume ratio, type of fiber, w/c ratio and addition of polymer and color pigment. After three hundred cycles of freezing and thawing, flexural tests were conducted in order to compare the strength and the global response of both reference and freeze-thaw specimens. Also, deicer salts scaling resistance was evaluated by means of mass change measurements after 300 cycles. The primary concern of glass fiber-reinforced cementitious composites (GFRC) is the durability of glass fibers in the alkaline environment of cement. Despite the use of improved alkaline-resistant glass fibers (AR-glass) and pozzolanic materials such as silica fume and fly ash, durability concerns still exist. In AR-GFRC, growth of hydration products around the filaments plays a dominant role in inducing embrittlement of the fibers and loss of toughness of the composites. The improvement of the matrix is obtained by using polymers to optimize the nature of the hydrates in the interface between the fibers and the matrix. One of the purposes of this thesis is to present an experimental investigation on the effects of polyvinyl alcohol (PVA) powder on GFRC properties under different severe environments. In order to evaluate the efficiency of the polymer on the durability of GFRC, flexural tests were performed on specimens exposed to both short period of normal curing condition and long term of high temperature condition. The final part of this thesis introduces two types of laminates, double-layer reformed bamboo (Cross-ply) laminate and unidirectional FRC plate-reformed bamboo laminate. The latter is made of reformed bamboo and extruded Fibre-Reinforced Cementitious (FRC) plates. The reformed bamboo is ductile and tough, and has high tensile strength while the FRC plate has a higher compressive strength but poor in toughness. The FRC plate-reformed bamboo laminate developed fully utilizes the advantages of each component to achieve superior mechanical properties. A series of flexural, impact, and Compression After Impact (CAI) tests have been conducted to evaluate the performance of the laminate. It is found that the newly developed laminate has high flexural strength (I00MPa), excellent impact resistance, good ductility, and outstanding toughness. Hence, it has a good potential in engineering applications.
Note Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2001
Language English
Format Thesis
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