Effect of calcium stearate based foam stabilizer on pore characteristics and thermal conductivity of geopolymer foam material

Foam stabilizer plays a crucial role in the synthesis of geopolymer foam materials (GFMs). To better clarify the effects of calcium stearate based foam stabilizer (CSFS) on pore characteristics and thermal conductivity of materials, GFMs prepared with 0-2% CSFS were investigated for foam characterization, compressive strength, bulk density, geopolymerization products, pore distribution, and thermal conductivity. Results shows that (1) the foam time and initial setting time match optimally with 1.0% CSFS content. And at this point, the foam time and foam volume of GFMs were increased obviously by 42.8% and 28.6% respectively. (2) 28 d compressive strength of GFMs with a bulk density of 0.31 g/cm3 at 1.0% CSFS content were the lowest, 1.45 MPa, but still better than the standard of 1.0 MPa for 0.325 g/cm3 according to the Chinese National Standards GB11968-2006. (3) CSFS displayed limited effect on the quantity or type of geopolymerized products. (4) With CSFS/FA increasing from 0.5% to 2.0%, The quantity of macroscopic scale pores sized 10-100 µm rose considerably and then drop obviously, but still more than that of sample with free CSFS. The quantity of microscopic scale pores sized 10-100 nm grew stably. (5) Overall, 1.0% CSFS optimized pore characterization well with a largest porosity, 82%, where the thermal conductivity of GFMs reached a bottom point at 0.095 W/(m K). (6) The relationship between thermal conductivity and total porosity conforms to a Maxwell-Euchen or modified Cheng-Vachon model and the value of parameter t is determined as 1.1.