Study on Water Absorption and Thermal Conductivity of Tunnel Insulation Materials in a Cold Region under Freeze-Thaw Conditions

Figure 12

Micropore structures of the thermal insulation materials. (a) Polyurethane insulation that is not freeze-thawed. (b) Polyurethane insulation freeze-thawed 50 times. (c) Polyphenolic insulation that is not freeze-thawed. (d) Polyphenolic insulation freeze-thawed 50 times.

(a)

(b)

(c)

(d)