The Microstructure of Wood Fiber Reinforced Cementitious Composites
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X. LIN, M.R. SILSBEE, D.M. ROY, The Pennsylvania State University, Intercollege Materials Research Laboratory, University Park, PA 16802.
ABSTRACT Wood fiber reinforcing of cement matrices is an economic and an efficient approach to producing high performance cementitious composites. In this study, wood fiber reinforced cementitious composites (WFRCs) were made by using both conventional and novel processing styles. Wood fibers exhibited a considerable ability to improve the flexural strength and the toughness of WFRC when an adequate content of the fibers was used. The morphologies of various type of wood fibers and fracture surface of WFRC were examined by scanning electron microscope (SEM) and an environmental scanning electron microscope (ESEM). The microstructures of wood fiber and WFRC were correlated with their mechanical properties. Results indicate a significant interfacial bonding between the cement matrix and the wood fibers. INTRODUCTION Plain cement, a widely used traditional construction material, is stiff, durable, has adequate compressive strength, but is weak in flexural and impact strengths due to its brittleness and low strain capacity, which have greatly limited its application in may aspects. Using fibers to strengthen brittle cement matrices is an old concept. Ancient Egyptians used straw to reinforce adobe bricks. Now a wide range of fiber types has been employed in reinforcing cement matrices. The type of fiber materials have included steel, polymer, ceramic and natural products which are well documented by Bentur et al. [1]. Wood fiber, one type of natural fiber was proposed as a reinforcement in cement-based building materials almost 100 years ago, while cellulose has been used as an economic substitution for asbestos for nearly 50 years [2]. The development and production of WFRCs have attracted increasing attention in the last 10-20 years [3]. It was reported that wood fiber reinforced cement and concrete panels have served as both non-structural and structural, and as both internal and external building materials in Finland, Indonesia, Malaysia, New Zealand and Australia [4,5]. The forms of wood used in cement have been wood chips, flakes, excelsiorthin ribbon-like strands and fibers. In Europe, South America, and Asia, cement has been used as a bonding agent for wood excelsior boards, particleboard, fiberboard, and wood-cement composite products for nearly 50 years. In the United States, manufacturing cement-bonded wood composite products has been limited to excelsior board made from a mixture of southern pine and portland cement [6]. WFRC can be used as wall sections, masonry blocks and precast units etc. In this study, wood fibers were employed in both ordinary portland cement and macrodefect-free (MDF) cement systems using paddle mixer and high shear mixer, respectively. This study was focused on the microstructure of various wood fibers and WFRC samples in order to understand the mechanism of WFRC's performance in the aspects of mechanical, physical and chemical properties.
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