Air void structure and frost resistance: a challenge to Powers’ spacing factor

Abstract

Document Version AbstractThis article compiles results from 4 independent laboratory studies. In each study, the same type of concrete is tested at least 10 times, the air void structure being the only variable. For each concrete mix both air void analysis of the hardened concrete and a salt frost scaling test are conducted. Results were not originally presented in a way, which made comparison possible. Here the amount of scaled material is depicted as function of air voids parameters: total air content, specific surface, spacing factor, and total surface area of air voids. The total surface area of air voids is proportional to the product of total air content and specific surface.In all 4 cases, the conclusion is concurrent that the parameter of total surface area of air voids performs equally well or better than the spacing factor when linking air void characteristics to frost resistance (salt frost scaling). This observation is interesting as the parameter of total surface area of air voids normally is not included in air void analysis.The following reason for the finding is suggested: In the air voids conditions are favourable for ice nucleation. When a capillary pore is connected to an air void, ice formation will take place in the air void, being feed from the capillary, but without pressure build-up in the capillary. If the capillary is not connected to an air void, ice formation will take place in the capillary pore, where it can generate substantial pressure. Like this, frost resistance depends on that capillary pores are connected to air voids. The chance that a capillary pore is connected to an air void depends on the total surface area of air voids in the system, not the spacing factor.

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

“…The results of the research by Łaźniewska-Piekarczyk [25] showed that the air content in a self-compacting concrete (SCC) mix is a side effect of the SP and is very unstable. As a consequence, it shapes the AVPs, whose normally adopted values in concretes for the assessment of resistance to freeze-thaw cycles (L ≤ 0.200 mm and A 300 ≥ 1.5% [1,21]) are not correlated with the tested resistance to freeze-thaw cycles of SCC concretes.…”

“…The test was conducted on eight series of four samples with dimensions of 140 × 72 × 50 mm, which were subjected to 56 freeze-thaw cycles in the presence of 3% NaCl. After 7,14,21,28,35,42,49, and 56 cycles, mass loss was measured.…”

“…Powers and Helmuth established that the critical L value lies in the range of 250-300 µm [6][7][8]. Modern guidelines limit this value to 200 µm [20,21].…”

Assessing the efficiency of entrained air voids for freeze-thaw durability through modeling

“…L is also sensitive to outliers; for example, see chapter 4 of [11]. The results of laboratory tests have challenged the efficacy of the ASTM C457 spacing factor [12]. Alternative spacing factors have been proposed by Philleo [13], Attiogbe [14], and Pleau and Pigeon [15].…”

The finite body triangulation: algorithms, subgraphs, homogeneity estimation and application

“…As regards the spatial distribution of secondary phase objects in a binary composite, there exist a range of statistical methods, such as Ripley's K function (Myles et al, 1995), the Powers spacing factor (Hasholt, 2014), and the nearest neighbour test (Clark & Evans, 1954). Often, these distributions represent the secondary phase objects as zero-volume points, perhaps located at the object centroid, and develop various ways to analyse the measurements between these points (Li et al, 1999).…”