Optimization of production variables of natural fibers- cement composites by response surface methodology (RSM)

The objective of thisstudy was to investigate the production of natural-cement composite fiber usingpoplar, wheat straw and three types of additives. In this study, variables inmaking the boards were: usage percent of wheat straw (0, 15 and 30%) and fibersof poplar (70, 85 and 100%), and levels and types of additives (three levelsand three types of additives, i.e. calcium chloride, magnesium chloride andcalcium hydroxide, respectively). After producing test specimens, compressivestrength (1, 3, 7 and 28 days), thickness swelling (TS), the modulus of rupture(MOR), and internal bond (IB), were evaluated. The highest and the lowestcompressive strength (32.5 and 7.1 MPa) after 28 days were respectively forsamples containing 7% calcium hydroxide and 3% magnesium chloride. Also, theboards with 30 percent wheat straw and 70 percent poplar wood fiber with theamount of 3% calcium chloride had a higher MOR compared to other boards. Ingeneral, the results suggest that calcium chloride additives with amount of 5%and the average value of 15% straw to 85% poplar is the appropriate amount forachieving acceptable values of IB and MOR. Due to its significance in thestatistical analysis, the model presented by Response Surface Methodologyprovided a suitable and significant estimate to determine the application ofthe variables.