The Determination of the Optimal Material Proportion in Natural Fiber-Cement Composites Using Design of Mixture Experiments

This research aims to determine the optimal material proportion in a natural fiber-cement composite as an alternative to an asbestos fibercement composite while the materials cost is minimized and the properties still comply with Thai Industrial Standard (TIS) for applications of profile sheet roof tiles. Two experimental sets were studied in this research. First, a three-component mixture of (i) virgin natural fiber, (ii) synthetic fiber and (iii) cement was studied while the proportion of calcium carbonate was kept constant. Second, an additional material, recycled natural fiber from recycled paper, was used in the mixture. The four-component mixture was then studied. Constrained mixture design was applied to design the two experimental sets above. The experimental data were then analyzed to build the mixture model. In addition, the cost of each material was used to build the materials cost model. These two mathematical models were then employed to optimize the material proportion of the natural fiber-cement composites. In the three-component mixture, it was found that the optimal material proportion was as follows: 3.14% virgin natural fiber, 1.20% synthetic fiber and 75.67% cement while the materials cost was reduced by 12%. In the four-component mixture, it was found that the optimal material proportion was as follows: 3.00% virgin natural fiber, 0.50% recycled natural fiber, 1.08% synthetic fiber, and 75.42% cement. The materials cost was reduced by 14%. The confirmation runs of 30 experiments were also analyzed statistically to verify the results.