Effects of Water on Pore Structure and Thermal Conductivity of Fly Ash-Based Foam Geopolymers

Abstract

e influence of the water-to-solid ratio (W/S) on the viscosity, pore characteristics, bulk density, compressive strength, and thermal conductivity of foamed fly ash-based geopolymers with thermal conductivity less than 0.065 W/(m·K) was investigated, and their properties and cost analysis were also compared with that of foamed ordinary Portland cement (OPC). When the W/S varied from 0.38 to 0.5, the apparent viscosity of geopolymer paste 15 min after the preparation decreased significantly from 168 Pa·s to 6 Pa·s. e increasing W/S ratio contributed to the rise of the number of microcapillaries (φ < 50 nm) and macrocapillaries (50 nm < φ < 50 μm) but contributed to the decline of artificial air pores (φ > 50 μm). e refinement of pore characteristics lowered the 28 d thermal conductivity of foamed geopolymers from 0.06 W/(m·K) to 0.048 W/(m·K). Although the slight increase of total porosity of foamed geopolymers from 89% to 92% with the increase of the W/S ratio weakened their 28 d compressive strength from 0.75 MPa to 0.45 MPa, this strength still meets the Ordinary Portland Cement (OPC) based Foam Insulation Board standard of JC/T2200-2013 (>0.4 MPa for 0.25 g/cm 3 ). e production cost of foamed geopolymers was slightly higher by 1.1-1.5 times than that of foamed OPC. However, considering the more beneficial effect of environmental load reductions and better mechanical and thermal properties of foamed geopolymers than those of foamed OPC, slightly higher cost would be acceptable for practical application.

A review on the porous geopolymer preparation for structural and functional materials applications

“…According to the Knudsen effect, 180 the smaller the pore sizes are, the lower the thermal conductivity is. Generally, the air thermal conductivity is 0.002 W/(m•K) within the pore sized <50 nm, 0.015 W/(m•K) within the pore size between 50 nm and 50 μm, and 0.026 W/(m•K) within the pore sized >50 μm 85 .…”

“…Thermal conductivity‐density for building insulation 56,62,63,66,68,70,85,91,97,112–114,125,129,137,139,143,144,156–158,169,178,181–187 …”

Natural Fiber-Stabilized Geopolymer Foams—A Review

“…Cui and Wang studied the effect of the water-to-solid ratio on thermal conductivity. They could demonstrate that an increase in the water-to-solid ratio ( Figure 12 ) leads to a reduction in the thermal conductivity from 0.06 W/(m K) to 0.048 W/(m K) [ 86 ].…”

“…Figure 12.Porosity and thermal conductivity of geopolymers with different water-to-solid ratios according to Reference[86].…”

Strength Parameters of Foamed Geopolymer Reinforced with GFRP Mesh

“…The entrapment of air in the structure of a foamed geopolymer improves its thermal and sound insulating properties [ 21 , 22 , 23 ]. According to Cui et al [ 24 ], foamed geopolymers may have better thermal and mechanical properties than foamed OPC. The lower density means that the weight of the structure is reduced, which allows for an additional reserve of load capacity.…”