Recent design recommendations for concrete structures take into account the environmental cost of the production of building materials and the impact of construction on nature [
1]. Hence, the aim is to achieve the highest possible lifespan of buildings. Infrastructure such as bridges is designed for a service life of 100 years [
2]. Therefore, durability is a leading consideration in concrete project stages and construction. However, one of the most significant causes of decreased service life for concrete structures in countries with sub-zero temperatures is deterioration caused by freeze–thaw cycles (FTC), with and without the use of de-icing salts. Two types of damage can occur in concrete structures subjected to FTC: scaling from the surface of the concrete and internal damage in the form of microcracks [
3]. Requirements for such forms of damage are moisture and ion absorption as well as moisture and ion redistribution in the material. These transport processes depend on the distribution, amount, type, size, and shape of the capillary pores in the concrete [
4]. The pores are caused by surplus water, which is not required for the hydration of the fresh concrete and is therefore bound neither chemically nor physically. The resulting capillary pore structure allows ingress of gases and liquids into the concrete [
5]. Durability assessment of concrete is based on selecting a test that replicates the environmental conditions in which the structure is located. Various standards and recommendations for measuring freeze–thaw resistance exist, including DIN CEN/TS 12390-9:2017-05 [
6] or regional guidelines like the recommendation from the Federal Institute of Water Infrastructure in Germany [
7]. The strain in concrete during FTC is mainly influenced by thermal gradients within the material and the pore pressure resulting from the freezing and thawing of the water within the pores [
8]. Monitoring the strain of concrete is considered a possible method of detecting internal cracking [
9,
10]. As the deterioration progresses, residual strain starts to accumulate, indicating more significant internal damage. Analyzing the incremental strain can be a reliable approach to assessing concrete damage, making it potentially valuable for monitoring specific areas of real concrete structures exposed to freeze–thaw environments [
11]. Monitoring the freeze–thaw induced strain of concrete over an extended period of time can be challenging due to surface deterioration. This causes the detachment of sensors such as strain gauges, which are usually attached to the surface of the concrete [
11]. A novel approach to determining the dilatation of concrete using a high resolution 3D scanner (Creaform HandySCAN Black Elite) with an accuracy of 25
m is used in the proposed work. The presented methodology is based on the surface deterioration evaluation algorithm by Haynack et al. [
12]. For this study, specimens are exposed to a freeze–thaw cycle between 20 °C and −20 °C over the course of twelve hours and scanned periodically. The resulting change in length of the specimens is used to determine the temperature-induced strain.
To better understand the involved phenomena and confirm the reliability of the proposed measuring technique, a 3D FE numerical analysis is carried out and the results are compared with the experimental data. A number of models are developed to numerically predict the thermo-mechanical behaviour of porous materials, specifically cement paste, subjected to freeze–thaw action. Powers’ hydraulic and osmotic pressure theories formed the basis of freeze–thaw damage theory [
13,
14]. Bažant et al. established a mathematical model based on pore size distribution and desorption and adsorption isotherms for concrete [
15]. Zuber et al. presented a numerical model based on poromechanics and local thermodynamic equilibrium to predict the behaviour of completely saturated cement-based materials subjected to freezing temperatures [
16,
17]. Yang et al. proposed a micromechanical model to simulate the expansion of cement paste, taking into account thermal dilatation of the matrix and pressure in the pore space [
18]. Timothy et al. proposed a multiscale framework for estimating the critical pore pressure required to initiate microcracks during a freeze–thaw exposition of cementitious materials [
19]. Despite the models proposed by various researchers, the freezing process in porous materials like concrete still remains a complex topic due to the interaction between heat transfer, moisture, temperature dependent phase change, pore saturation, and deformation. There are only a few studies available in the literature on the coupled thermo-hygro-mechanical behaviour of concrete under freezing conditions. The goal of the numerical part of this study is to use a 3D coupled hygro-thermo-mechanical model implemented in the in-house FE code MASA [
20] to investigate the freeze–thaw behaviour of the cement mortars under fully and partially saturated conditions with two different salt concentrations. The mechanical part of the model is based on the microplane theory [
21]. The mechanical and non-mechanical processes are coupled using a staggered solution procedure. The model is validated based on the experimental part of this study and is shown to accurately capture the freezing deformation of the cement mortar during a single freeze–thaw cycle.