| Gypsum is a kind of green inorganic gelled building material popular all over the world. It is widely used in the areas of decoration, wall and sound absorption as well as heat preservation, fire protection and other fields. Building gypsum products usually just used in indoor because of its low tensile strength and impact resistance properties, brittle and lower waterproof ability that limited its application scope. In order to improve the performance and expand its application scope, researchers successfully prepare gypsum composite materials by fiber and other additives with the enhancement and padding method.Fiber has greater tensile strength and fracture toughness that can absorb most energy to inhibit microcrack growth to enhance the strength when fiber-reinforced gypsum matrix composites suffer stress, thereby improving the toughness and increasing the flexural strength and load-bearing capacity. Fibrous wollastonite with non-toxic, tasteless, non-radioactive, has excellent mechanical properties that can replace short asbestos fibers, glass fibers and talc fibers etc. as the reinforced materials.In this experiment, wollastonite fiber is mixed with gypsum to prepare gypsum composite. The contents of this study include:(1)Fiber dispersity and performance of composite materials by different mixing methods;(2)Effects of the fibers’ L/D ratio, quantity and dry modification on the properties of composite materials;(3) Discussing the mechanism of interface bonding and enhancement by compared the microstructure of composite materials;(4)Effects on the mechanical properties, adhesion and thermal insulation performance of the prepared composite gypsum boards.The experimental studies show that the craft that mixing fiber with water first and then adding gypsum powder are desirable. The sample test results of different fiber L/D ratio with 13:1,15:1and 20:1 indicated that flexural strength increased at first and decreased later, and the compressive strength gradually decreasing with the increase of fiber content. The optimum technological parameter is: the fiber L/D ratio is 15:1, the quantity is 1.5%, and the 2h flexural strength of composite materials increased from 2.66 MPa to 3.71 MPa which is increased by 38.58%, and the compressive strength decreased from 7.61 MPa to 7.61 MPa, which was decreased by 6.18% compared with the blank sample, which reach the first class requirements of standard GB/T9776—2008《Building Gypsum》that required the 2h flexural strength should be more than 3.0 MPa, and the compressive strength must be greater than or equal to 6.0 MPa.It is an important aspect of contact surface reliable union to analyze the properties of gypsum composite materials. The experimental results show that the modified wollastonite fiber has a good interface with the gypsum matrix that the mechanical properties of the composites are increased, and the dry modification optimum technological conditions is: the stearic acid dosage is 1.5%, stirring rate 1000r/min, modified temperature is 75℃, and the time is 15 min. The enhancement effect and water resistance of the sample were obviously improved after adding emulsion wax emulsion, 2h bending softening coefficient and compressive softening coefficient reached 0.85 and 0.82 respectively, which is satisfied the requirement of industry standard that water resistant products to resist softening coefficient greater than 0.8.With the increase of wollastonite fiber content to 1.5%, the thermal conductivity of prepared gypsum board decreased gradually from 0.2246 w/m·k to 0.1239 w/m·k even to 0.1069 w/m·k with a content of 10%, and the transverse and longitudinal loads were increased 35.4% and 29.4% and then lower than blank sample when continue to add fiber to 10%. The coefficient of thermal conductivity decreases faster when the content less than 3%, the reduction of board thermal conductivity, transverse and longitudinal loads and the adhesion of paper were gradually reduced while continue to add fiber. |
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