Abstract
Mesopores in porous solids can produce a pronounced sorption hysteresis at moderate and high reduced vapor pressures of the ambient gas that is condensed in the pores. Unlike to other conventional porous materials, cement pastes often behave exceptionally. The water sorption hysteresis frequently persists at very low humidity. This hysteresis is reflected in a corresponding hysteresis loop of the solid skeleton volume. We discuss a theoretical model based on the strong compression force exerted by a condensate on the walls of narrow slit pores embedded in an elastic solid. This compression force is shown to be capable of shifting walls of narrow slit pores. Humidity-dependent closing and reopening of slit pores can produce hysteresis loops even at low humidity.
Highlights
Hardening of cement pastes results from a hydration reaction that forms the C-S-H gel, where the notation C = CaO, S = SiO2, and H = H2O is used [1]
In a previous paper [11] we have shown that closing and reopening of slit pores in soft hydrophilic solids is possible by varying the capillary force, which depends on the air humidity in the environment
In this paper we consider the possibility of sorption hysteresis resulting from closing and reopening of narrow slit pores in solid materials with relatively high Young modulus such as hardened cement pastes
Summary
In a previous paper [11] we have shown that closing and reopening of slit pores in soft hydrophilic solids is possible by varying the capillary force, which depends on the air humidity in the environment This mechanism can produce hysteresis if the elastic energy required to close a pore by a capillary compression force is rather low. It can be shown that sorption hysteresis can appear even at low air humidity, if material parameters satisfy some conditions necessary for closing and reopening the slit pores If these conditions are satisfied, the resulting sorption hysteresis is reflected in a hysteresis of the volume change of the solid skeleton. In this paper we consider the possibility of sorption hysteresis resulting from closing and reopening of narrow slit pores in solid materials with relatively high Young modulus such as hardened cement pastes.
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