The Use of Natural Fiber in Cementitious Composites
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THE USE OF NATURAL FIBER IN CEMENTITIOUS COMPOSITES Y. CHEN, C.K. PARK, M.R. SILSBEE AND D.M.ROY Materials Research Laboratory, The Pennsylvania State University, University Park, PA 16802 ABSTRACT Variations in the mechanical properties of wood fiber reinforced cementitious (WRFC) materials containing treated fiber and water soluble polymers were investigated. Flexural strength is greatly improved by the addition of polymer. The interface bonding is enhanced by the fiber pre-treatment. The mechanism responsible for the strength increase in WRFC was studied by mercury intrusion porosimetry. Experimental results indicate that the increased strength results from an enhancement in the strength of the interface and reduced porosity. INTRODUCTION Although publications refer to the use of wood fiber with cementitious materials 1 beginning with the last century, most of the interest dates from the last 10 years. Cook[ ] classified natural fibers into four classes based on their morphology, which were stem, leaf, surface and wood. Wood fibers are relatively short and inflexible, but usually strong and perform well over a long time period in the cement environment. They are potentially suitable for low cost housing applications. Reprocessed fiber from waste paper offers an attractive low cost alternative to first cycle fiber. In fiber reinforced cementitious materials (FRC), the strength of the interface is much weaker than that of the matrix. The best way to obtain higher flexural strength in FRC is to improve the strength of the interface. Coutts and Campbell [2] studied the effect of treating the cellulose pulp fiber with various coupling agents to enhance the fiber-matrix interaction. The mechanical properties of the composites could be varied to some extent by different coupling agents such as silanes and alkoxides of titanium, but the overall influence on flexural strength was not large. One of the purposes of this study is to find new agents for fiber treatment. In this paper, wood fiber reinforcement of ordinary portland cement and high alumina cement based macro defect free cements have been studied. The maximum flexural strength of wood fiber reinforced high-alumina cement (HAC) based macro-defect-free (MDF) has been found to be 126 MPa; the maximum toughness is 2.7 MPa ml/2. EXPERIMENTAL 1. Materials The wood fiber used in this study was hard wood pulp. The sugars in the wood fiber had been removed by chemical and/ or mechanical pre-treatment. The fiber was prepared according to "Laboratory processing of pulp (Beater method) T200 ts - 66". The diameter of fiber was 20-60 mm, length 0.5-3.0 mm, density about 0.30, and the tensile strength was between 125-500 MPa. The cements used in this study were Type I (Ordinary) Portland Cement (OPC), Secar 71 High Alumina Cement (HAC), Pyrament Cement (PC) and an Expansive Cement (EC). The polymers used in this study are polyacrylamide (PAM), with molecular weight more than 100,000 and poly (vinyl alcohol) (PVA) 88% mole hydrolyzed, with molecular weight 75,000. Some inorgani
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