Investigation of the effect of waste paper fibers on the fracture behavior of fiber-gypsum board

Fibre-gypsum board is a composite, in which fiber used as the reinforcement in the matrix of gypsum. The purpose of this article is to investigate the effect of different amounts of waste paper fibers on the strength, resistance and the fracture behavior of fiber-gypsum board. For this purpose, amounts of zero, 5, 10, 15, 20, 25 and 35 percent of waste paper fibers have been used. The results of measuring bending strength, internal bonding and moisture absorption during one month exposure to 100% relative humidity show that increasing the percentage of fibers up to 20% has increased the mechanical properties. In general, By using twenty percent fibers the bending strength increased fifty percent and the internal bonding became double and half in comparison to the control samples. The load-displacement curve shows that an increase of 5 to 15 percent of fibers does not change the fracture behavior of the fiber-gypsum board and they had brittle fracture same as control samples. While in more substitution values, the flexibility increases and the failure becomes ductile. Therefore, the best conditions in terms of strength, resistance, and flexibility have been obtained in 20% replacement of gypsum with waste paper fibers.