Cement-bonded composite boards made from poplar strands Alireza Ashori a,⇑ , Taghi Tabarsa b , Sima Sepahvand b a Department of Chemical Technologies, Iranian Research Organization for Science and Technology (IROST), Tehran, Iran b Department of Wood and Paper Technology, Gorgan University of Agricultural Sciences & Natural Resources (GUASNR), Gorgan, Iran article info Article history: Received 2 March 2011 Received in revised form 25 May 2011 Accepted 2 June 2011 Available online 22 June 2011 Keywords: Cement-bonded composite Building material Calcium chloride Inhibitory index abstract This study was carried out to explore the possibility of making cement-bonded wood composite building products using poplar (Populus deltoides) chopped strands. The experimental design consisted of two treatments namely wood strand and calcium chloride contents. Boards measuring 450 Â 450 Â 15 mm 3 were manufactured using wood/cement ratios of 40:60, 60:40 and 70:30 by weight and 3% and 7% of an accelerator (CaCl 2 ÁH 2 O). At least four replications were fabricated for each treatment, and the mechanical properties and water absorption of the boards were evaluated according to DIN 68763. The mechanical properties in terms of modulus of rupture, modulus of elasticity, internal bond and impact strength were investigated and compared to the neat cement controls. Test results showed that addition of CaCl 2 tends to enhance both the mechanical and water-resistance of wood–cement compos- ites. The bending and impact strengths of the wood–cement specimens increased with an increase in the wood content, and the maximum values were obtained at wood loading of 60% by weight. The negative influence of wood content on the internal bond can be explained by the reduced bonding ability because of weaker wood strands compared to cement. Water absorption and internal bonding were inversely pro- portional to the increase of cement mixture ratio, and their values increased proportional to the increase of wood ratio in the mixture. In addition, all properties of the boards were improved when the CaCl 2 con- tent was increased from 3% to 7%. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Cement-bonded wood composites (CBWCs) have the potential to provide a wide range of products for building applications by using a wide variety of wood based materials. During the last two decades, the application of woody materials in CBWCs have been gaining momentum and woody materials have been applied to enhance the properties of the construction materials [1,2]. CBWC is made of strands, particles or fibers of wood mixed with Portland cement and small amounts of additives manufactured into panels, bricks, tiles and other products used in the construc- tion industry. Wood is the aggregate and the reinforcing agent, cement is the binder, water is the reactant, and the additives are the catalysts [3,4]. A number of factors contribute to the properties of CBWC prod- ucts such as the presence of cement inhibitors in woody materials. Although a wide variety of wood species has been used in the man- ufacture of CBWCs, only a few of them are classified as low inhibi- tion. Papadopoulos [5] reported that poplar has the least inhibition index (highest compatibility) on cement hydration (Tables 1 and 2). The compatibility term refers to the degree of cement setting after mixing with water and with a given wood in fragmented form. Generally, if the chemical process of cement hardening is undisturbed by the presence of wood, it is considered that cement and wood are compatible. On the other hand, if cement hardening is impaired by the presence of wood, then cement and wood are re- ferred to as incompatible [6]. As described by Hachmi and Moslemi [7], wood–cement compatibility generally decreases as the extrac- tive content increases. These extractives are generally composed of terpenes, fatty acids, tannins, carbohydrates, and inorganic materi- als [8]. It has been reported that the water-soluble extractives of wood retard and sometimes inhibit the normal setting and strength development properties of cement during the production of CBWCs [3,4]. According to a previous study by Olorunnisola [9] on the behav- ior of husk–cement systems showed that the inhibitory effects could be minimized with the use of calcium chloride (CaCl 2 ) as an accelerator. However, other previous studies have also shown that CaCl 2 tends to have some effects on the bending elasticity, compressive strength and sorption properties of CBWC products [4,10]. More information on the strength, stiffness and sorption of CBWCs is needed to extend their acceptance and use, in the out- door and indoor structural applications. The first step in assessing the suitability of different wood species for use in CBWCs involves 0950-0618/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2011.06.001 ⇑ Corresponding author. Tel./fax: +98 228 2276629. E-mail address: ashori@irost.org (A. Ashori). Construction and Building Materials 26 (2012) 131–134 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat