Effect of sodium methylsilicate on mechanical and water resistance of macro defect-free (MDF) gypsum

Abstract

Finding vicarious building materials for Portland cement and reducing the usage of cementitious materials is a key to reduce the carbon emission of cement production. Desulfurization (FGD) gypsum powder is a common solid waste which application is limited by its low mechanical strength and poor water resistance properties. This paper studies the effect of sodium methylsilicate on the mechanical performance and waterproofs of macro-defect free (MDF) gypsum involving pressurized processing. The compressive strength, flexural strength, water absorption rate, softening coefficient and water contact angle of the MDF gypsum are assessed. The results show that adding 1.6 wt% sodium methylsilicate achieves to the maximum strength of 7.5 MPa for flexural and 35.7 MPa for compressive, which increasing by 4.2% and 6.6% relative to the pure MDF gypsum, and increasing by 11.9 % and 138.0 % relative to traditional casting gypsum. With the increasing content of sodium methylsilicate, the waterproofs of MDF gypsum become better. When adding 1.6 wt% sodium methylsilicate, the water absorption rate, softening coefficient and water contact angle is 0.4 %, 0.78 and 93.5° for 2 h immersion, respectively. The pressurized production is recommended to prepare MDF gypsum.