5. Mix Design NomographThe experimental utilisation of a timber industrial ash (TIA) and rice husk ash (RHA) to address the escalating ash proliferation and disposal problems have been investigated and reported by Lee, et. al [17-23]. TIA is derived mainly from the controlled incineration of rubberwood bark. A concrete mix design nomograph to simplify the concrete mix design process has been proposed. It caters for the need to specify durability performance in the concrete mix design stage.
Water permeability of concrete cover is proposed to be the indicator for durability performance. The plot of water permeability against water/binder ratio was placed in the first quadrant of the nomograph. The plot of compressive strength against water binder ratio was placed in the second quadrant. The relationship between the optimum dosage of TIA, minimum duration of moist-curing and cement content was placed in the third quadrant. The relationship between workability, water permeability and the cement content was placed in the fourth quadrant.
The interpretation of the concrete mix design nomograph is based on the inter-relationship between workability, water permeability, compressive strength against the water/binder ratio. For enhanced durability performance, the water/binder ratio in the mix proportions is recommended to be lower than 0.45. If early strength is an important requirement, it is suggested that the TIA dosage should be around 5 % for high strength concrete and not greater than 10% for concrete of grades ranging from 25 to 45 MPa. The minimum duration of moist curing for different grades of concrete has also been proposed.
