Effect of Extraction and Chemical Additives on Compressive Strength and some Physical Properties of Wood Cement Mixtures

Abstract

This study was under taken to investigate the effect of extraction and chemical additives on compressive strength and some physical properties of wood-cement mixture. Three factorial experiments were conducted using completely randomized design. The woody materials were obtained from four species, namely, Acacia nilotica, Acacia senegal, Acacia .seyal and Eucalyptus microtheca. The first experiment was designed to determine the effect of twelve chemical treatments (2% based on cement-weight) on the compressive strength of pure Portland cement. In total, 36 specimens were prepared using mortar cubes (7.06 cm3). After 24 hours the molded samples were removed from the molds and then soaked in water and left to cure for 28 days. The specimens prepared were tested for compressive strength using a universal-testing machine. Some of the chemicals (CaCI2, FeCI3, MgCl2 and CaCO3) improved the strength of cement while others (MgSO4, CaSO4, MgCO3, Na2SO4, Fe2(SO4)3 and Na2CO3) reduced its strength compared to the untreated cement (control). NaCI was not significantly different from the control. The second experiment was conducted to study the effect of extraction and chemical additives on wood-cement compatibility. The wood was extracted for 14 days and 11 chemicals were added at 2% (based in cement weight) to the mixture of un extracted and extracted wood with cement at a ratio of 1:8. In total 288 specimens were prepared. Planner shavings, cement and water were mixed; mortar cubes were prepared and tested for compressive strength in a universal testing machine after soaking in water for 28 days. Each of the three main effects (species, extraction and chemical additives) had a significant influence on the compressive strength; however, none of these factors was acting independently. Differences among species were significant at all combinations of treatments and chemical additives. The performance of species varied with chemical additives and treatments, however, Eucalyptus microtheca was always ranking high regardless of the chemical additives treatment. Acacia nilotica (the most inhibitory species when unextracted) was among the best performing species when treated with cold water and treated by various additives. Extracted Acacia seyal was always ranking low, however, it revealed best performance when untreated with cold water and treated by various chemical additives. Significant improvements in cement setting were achieved by the removal of water soluble extractives and sugars from Acacia nilotica and Acacia senegal wood. Such improvement however did not take place in Eucalyptus microtheca and Acacia seyal. Compressive strength of the four species (unrestracted or extracted) was significantly affected by the type of chemical used. Most of the chemical additives improved the setting of cement and its mixture with unrestracted wood and extracted wood. CaC12, caused great improvement in the compressive strength of wood-cement mixture and it ranked high regardless of the species and water extraction treatment. The greatest improvement in the mixture of cement with extracted Acacia nilotica and unrestracted Acacia senegal wood was obtained by the addition of FeCl3 and Mg C12 respectively. Based on the results of the second experiment, the best combination of chemical additive and extraction treatment (extracted or unrestracted) was added for each of the four species. The selected chemical additives were applied at seven levels (0.5, 1.0, 1.5,2.0,2.5, 3.0 and 3.5) based on cement weight. Planner shavings and cement were mixed at a ratio of 2% mortar cubes were prepared; the specimens were tested for compressive strength, water absorption, dimensional stability and density. The results showed that, increasing the levels of chemical additives in the mixture of the four species with cement was associated with an increase in compressive strength. No significant differences in water absorption were found between the seven levels of chemical additives when using extracted Acacia nilotica, unextracted Acacia senegal and Eucalyptus microtheca. Increasing the level of chemical additive was associated with an increase in density of Acacia nilotica and Acacia senegal extracted wood. Dimension swelling for all four species was very low and was slightly affected by differences in the level of the chemical additive.