Mechanical and physical properties of mortar of partially replaced fine aggregates with sawdust

Abstract

Sawdust, a waste material produced from timber manufacturing process, is considered as an excellent bio based material. Sawdust is used in many applications; however, the use of sawdust with cementitious materials is minimum. The main reason for this is due to the fact that the sawdust is a bio based material where the durability of sawdust added cementitious materials is unknown. In addition to that, fresh, physical, and mechanical properties of concrete or mortar with sawdust are not well established. Therefore, the aim of this study is to explore the potential to use sawdust as a fine aggregate replacement material in typical Portland cement mortar. This study first aimed to investigate a proper pre-treatment method for sawdust which can be mixed in mortar. Results show that boiling sawdust with Sodium Hydroxide of 2% concentration for 2 hours and washing with boiling water for 30 minutes can produce better mechanical properties in comparison to original sawdust or sawdust boiled with water only. Adding sawdust decreases the density of mortar while increasing the water absorption capacity from 10% for normal mortar to 25% for mortar with 50% sawdust replacement level. Sawdust in mortar has a direct impact on its mechanical properties where compressive and flexural strength can be significantly reduced. However, even at 50% replacement level of sawdust, a reasonable compressive strength can be achieved which might be considered as sufficient for low grade applications. Sawdust addition can also significantly increase the drying shrinkage of mortar. Drying shrinkage of 1000 microns at 28 days’ age can be easily passed by mortar mixes with high sawdust content of above 30%. This study proves that the fine aggregates replacement with sawdust in mortar brings many disadvantages; however, still maintaining some reasonable mechanical properties. The effect on durability properties should be investigated further.