A Hygro-Thermo-Mechanical Multiphase Model for Long-Term Water Absorption into Air-Entrained Concrete

Abstract

Many concrete structures located in cold climates and in contact with free water are cast with air-entrained concrete. The presence of air pores significantly affects the absorption of water into the concrete, and it may take decades before these are fully saturated. This generally improves the long-term performance of such structures and in particular their frost resistance. To study the long-term moisture conditions in air-entrained concrete, a hygrothermo-mechanical multiphase model is presented, where the rate of filling of air pores with water is described as a separate diffusion process. The driving potential is the concentration of dissolved air, obtained using an averaging procedure with the air pore size distribution as the weighting function. The model is derived using the thermodynamically constrained averaging theory as a starting point. Two examples are presented to demonstrate the capabilities and performance of the proposed model. These show that the model is capable of describing the complete absorption process of water in air-entrained concrete and yields results that comply with laboratory and in situ measurements. Keywords Air-entrained concrete • Multiphase model • Long-term absorption • Diffusion • Pore size distribution The research presented was carried out as a part of Swedish Hydropower Centre-SVC. SVC has been established by the Swedish Energy Agency, Energiforsk and Svenska Kraftnät together with

Dissolution kinetics of trapped air in a spherical void: Modeling the long-term saturation of cementitious materials

“…While the work in [10] [24] derived a multi-phase (i.e., solid, liquid, gas) transport and mechanics model to assess the entire saturation curve for air-entrained cementitious materials. Until the idealized specimen arrived at its value of matrix saturation, Sm, the model follows a similar imbibition study found in [23].…”

“…The approach has been adopted by AASHTO [9]. Additionally, based on the assumptions presented and found in [8,10,24], recent efforts have shown how a simple geometric model can be used to predict the evolution in Powers' spacing factor [27,28] between remaining air-filled voids, as more and more air voids become water-saturated [25]. The presented efforts have provided significant insight and advancement with respect to how airentrained cementitious materials may become increasingly saturated.…”

“…Nonetheless, numerous gaps remain with respect to governing mechanisms at the air void-scale. The central intention of the SVDK model is to then build on what has been presented in a complementary manner in effort to provide fundamental insight into the water-saturation mechanism for single air voids that occur below the REV scale for models similar to [24].…”

“…The SVDK model answers how air voids saturate over time by the dissolution-and transportdriven collapse of trapped gaseous air. An extension could make it possible to understand and model 3D systems in which the air void system is polydisperse -allowing for the prediction of the long-term saturation rate, S2, given a known air void size distribution and various material properties without assumptions on how air voids fill in relation to one another [10,24,25].…”

Mechanisms of Air Entraining of Proteins in Cementitious Materials

“…Other notable theories, including osmotic pressure, critical saturation, crystallization pressure, and microlens theories, have also been proposed to model the damage sustained during freeze–thaw cycles . Adjacent air-entrained voids can lessen the pressure of trapped water and ice in the capillary pores and reduce the damage to the microstructure, as well as reduce the overall degree of saturation of the concrete. ,− While the porosity of entrained air voids is important, parameters including void size distribution and spacing are also very influential on the freeze–thaw performance . Entrained air voids are usually between 0.01 to 1 mm in size and primarily near-spherical.…”