Pore Structure as a Response to the Freeze/Thaw Resistance of Mortars

Abstract

In this paper, the resistance to the freeze/thaw cycles for four groups of mortars (lime—LM, lime based—LBM, cement—CM, and aerated cement—ACM mortars) with different amount of mortar components within each group is quantified via a ratio of flexural/compressive strength after and before exposure to freeze/thaw cycles. Using a pore system obtained by three different methods (mercury intrusion porosimetry, X-ray micro-computed tomography analysis, and SEM (Scanning Electron Microscopy) analysis), an attempt was made to explain why some mortars achieved better resistance to freeze/thaw cycles than others. The mortars with lime as a binder in the composition (LM and LBM groups) did not survive the freezing and thawing regime, while no visible damage was recorded in samples of the CM and ACM group. It is concluded that the low initial value of the mechanical properties of the LM and LBM mortars, as well as the higher proportion of harmful pores (pores greater than 0.064 μm) compared to CM and ACM mortars are responsible for their poor durability. According the results of nanotomography, it is concluded that the most important factor influencing freeze/thaw resistance is pore connectivity—the higher the connectivity of the macropores, the higher the freeze/thaw resistance of the mortar. SEM analysis proved to be a very useful method for aerated cement mortars as it revealed the pore sizes that were not covered by mercury porosimetry and nanotomography.

Additional Porosity as a Side Effect of Polycarboxylate Addition and Its Influence on Concrete’s Scaling Resistance

“…In order to determine the air void system in hardened concrete that will protect against freeze-thaw cycles [7,16], Figures 5-8 show the quantitative, described by mathematical equations and quantitative relationships of AVP and SP in both the NEAC and AEC mixes together with an assessment of scaling [6]. The use of constant AE content in AEC mixtures CA1-CA4 (Table 8) resulted in a 1.0-1.9% increase in total air content in the hardened concretes as compared to NAEC mixtures C1-C4 ( Figure 5).…”

“…The AE meter is the proper air-entrained structure for hardened concrete, and protects against freeze-thaw cycles if ice forms in an air pore and is compressed by the surrounding matrix [7,16]. The basic parameter that characterizes the AE meter is the spacing factor (L) [8,17,18], which is the average distance at which each point in the paste will be protected against the formation of destructive scratches that can result from harmful expansion during internal crystallization [7,19].…”

“…The impact of the side effect of SP use in the form of additional pores, as a consequence of shaping the air void structure (AVS) and the relationship with the concrete's resistance to freeze-thaw cycles, has been the subject of many studies. These studies have particularly been concerned with SCC concretes with a very complex system of compatible admixtures and rheological problems [13,14,16,25,29,[31][32][33][34][35][36][37][38][39][40][41]. Despite the numerous studies in this area, it is not yet possible to clearly determine the effect of an SP on the AVS due to the complexity of the parameters, particularly the rheological ones, that shape the AE of SCC concretes.…”

Experimental Examination of Electrical Characteristics for Portland Cement Mortar Frost Damage Evaluation

“…Since the activation energy is mainly correlated to the microstructure properties [27,35], it has potential to be used for evaluation of salt-frost damage. When the microstructure properties changed, the mechanical properties change as well [40]. For partially-saturated samples, the activation energy can be calculated based on the activation energy of fully-saturated samples and the saturation degree [36].…”

“…However, under the lowest temperature, the electrical resistivity changes not only with pore size but also with the saturation degree whose contributions are difficult to distinguish. On the one hand, frost damage increases the porosity [40] and connectivity, thereby decreasing the electrical resistivity. Frost damage causes water to move from the smaller pores to the larger pores and freeze in these large pores at the lowest temperature, thereby reducing the movable water content; the decrease in the saturation degree (amount of liquid water) increases the electrical resistivity.…”