Sawdust
Sawdust is available abundantly in most places and has been used in some places for making low cost lightweight concrete for low-demand applications. Sawdust contains considerable quantities of water-soluble cement poisons which retard the hydration and hardening of cement paste. Physico-chemical treatments are necessary to neutralise the cement poisons which add to the cost of saw dust concrete appreciably. In the tests carried out at the National University of Singapore (3) sawdust was pretreated by soaking and washing with water before mixing was done to ensure that extractable materials in the saw dust do not interfere with the hardening of the concrete. Addition of lime, 1/6 to 1/3 volume per volume of cement, to the sawdust before mixing is a pretreatment method used by the Cement and Concrete Association of Australia (3).
The moisture movement in sawdust cement products is high and the high drying shrinkage of sawdust cement limits its use to designs where freedom of movement is possible.
Concrete made by using sawdust and magnesium oxychloride cement has been used in India for making reinforced concrete door and window frames (3). The process developed by the Central Building Research Institute in India consists of mixing magnesium oxide and dolomite powder with sawdust to which magnesium chloride solution is added and mixed into concrete which is poured into moulds with reinforcement in position. The door and window frames manufactured at the institute were found to possess adequate strength, machinability and, good screw holding and paint holding properties.
The moisture movement of sawdust concrete is 0.55% compared with 0.3% for rice husk aggregate concrete. (3).
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