Effectiveness of wood waste sawdust to produce medium- to low-strength concrete materials

This paper investigates the use of sawdust as fine aggregate and its influence on the properties of hardened concrete, and examines the correlation between sawdust content and hydration days. In this study, untreated wood sawdust from a wood factory in Bangladesh is added to concrete mixtures. Concrete mixtures prepared by replacing fine aggregates with sawdust in the ratio of 10%-60% are evaluated for compressive, tensile, and flexural strength along with sulphate resistance for four different hydration periods. In addition, the microstructure of sawdust concrete is studied using scanning electron microscopic images. The micrographs show a wider formation of cracks, openings, and interface gaps in the cement matrix with the addition of sawdust. However, after sulphate immersion, the gaps and cracks are found to contract due to the ettringite filler effect. The addition of sawdust is found to reduce the workability and to have an adverse effect with increasing replacement levels. Similarly, reduced density of the hardened concrete is observed in the case of the sawdust concrete mixtures. Experimental results and cost comparison reveal that ten percent sawdust substitution is found to be optimal and low-cost replacement to natural fine aggregates with respect to the hardened properties, as it yields better performance in comparison with the other replacement ratios. Also, sulphate immersion for a period of 28 days is found to improve the compressive strength, even for mixtures with higher sawdust content. Moreover, a model is developed to predict the compressive and tensile strength of sawdust concrete using regression analysis.