New insights into wood and cement interaction

Alexandre Govin, Arnaud Peschard, Emmanuel Fredon, René Guyonnet
2005 Holzforschung  
This work deals with the influence of poplar extractives and poplar alkaline degradation products on the hydration of cement. The wood chemical composition was characterized to determine the impact of soft alkaline conditions on wood-fiber. Some of the constituents are hydrolyzed and converted into carboxylic acids which are identified and quantified. The monitoring by electrical conductivity clearly showed that wood extractives are less effective than wood alkaline degradation products to
more » ... on products to inhibit the hydration of cement. the mechanism of the wood-cement interaction is not yet fully understood. The present study aims at the investigation of the effect of wood components on the hydration of cement and the behavior of wood in such systems. Precisely, the effect of cement and a soft alkaline medium was studied on poplar wood by quantifying the content of sugar, lignin and extractives in the leaching and analyzing the degradation products by gas chromatography (GC). The influence of extractives and alkaline degradation products on the hydration of cement was explored by means of electrical conductivity. Materials and Methods Raw materials A gray Portland cement CPA CEM I 52.5 was used in this study. The designation follows the French standard NF P 15-301. Chemical composition and mineralogical phases of the cement were calculated by the Bogue approximation (Taylor 1990 ) and these are listed in Table 1 . Poplar (Populus hybrid I214) powder was prepared by milling wood and screening through a 150 and a 200 µm mesh. The powder between the two screens was used as wood sample and was stored at 20 °C and 60 % of relative humidity. Each experiment was conducted in triplicate. Wood soaks preparation The soaks were prepared by mixing wood (3 g) either with 150 ml of deionized water (Millipore, mQ, USA), either with lime solution (1 g.l -1 ) or with cement suspension (7.5 g in 150 ml of water, water to cement weight ratio W/C=20 (w/w)), at 25 °C under stirring. This two-phase solution was filtered at different lengths of time ranging from 1 to 24 h. Then the wood was dried at 103 °C for 48 h and weighed. The weight loss was then calculated. Electrical conductivity Electrical conductivity measurement was performed in dilute suspensions with a W/C ratio of 20 (w/w). Conductivity equipment consisted of a 25 °C thermostated reactor, two stainless steel annular electrodes and a conductimeter (Tacussel CD810, France). The constant cell was first calibrated with a 0.1 M KCl solution. Cement (5 g) was mixed with 100 ml of the previously described wood soaks. The reference used for lime soaks was a 0.2 g.l -1 lime solution. It corresponded to the chemical composition of the lime solution after 1 h of leaching with poplar. After 24 h of leaching, the lime soaks corresponded to a 0.06 g.l -1 lime solution. However, the conductivity curve was identical. For experiments requiring both cement and wood, wood was introduced 30 seconds before the cement with a wood to cement weight ratio (wood/C) equal to 0.4 (w/w). Determination of wood chemical composition The amount of poplar extractives were quantified according to the ASTM D1105-56 standard. The content of Klason lignin and each sugar were obtained by acid hydrolysis of poplar according to the ASTM D1106-56 standard. The hydrolyzates were neutralized by Ba(OH) 2 , then centrifuged and filtered. The sugar concentrations were determined by means of HPLC. The apparatus was equipped with a pump (WATERS 916, USA) and a refractometer (WATERS 410, USA). A specific column for sugar analysis (SUPELCO, Supelcogel Pb 7.8 mm x 30 cm, USA), conditioned in furnace at 80 °C, was used. Deionized water, in-line degassed, was used as eluent and the flow was maintained at 0.5 ml.min -1 . Calibration of the apparatus was performed by the injection of Alen, R., Niemelä, K., Sjöström, E. (1984) Gas-liquid chromatographic separation of hydroxy monocarboxylic acids and dicarboxylic acids on a fused-silica capillary column. J. Chromatography. 301:273-276 Alberto, M.M., Mougel, E., Zoulalian, A. (2001) Influence des extractibles d'essences du Mozambique sur l'hydratation du ciment. 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doi:10.1515/hf.2005.054 fatcat:dtpj6z5livdgxdhjpbqxvmfytq