**1. Introduction**

The alkali–silica reaction (ASR) is a chemical reaction between the alkali and hydroxyl ions present in the concrete pore solution and certain reactive forms of silica present in the aggregate [1]. This phenomenon is characterized by formation of an alkali–silica gel that absorbs water and expands, ultimately causing cracks in the aggregate and then in the cement matrix [2]. Although the predominant source of alkalis in concrete is Portland cement, other sources of alkalis, such as de-icing salts or agents, have been shown to contribute to ASR in concrete, [3–5].

Chloride based de-icers (NaCl, MgCl2 and CaCl2) are the most common de-icing salts used during winter months to clean the concrete road pavement and enable a normal flow of traffic [6]. However, they may have detrimental effects on concrete durability, which is often manifested by expansion, mass change, reduction in the dynamic modulus of elasticity [1] and, most of all, reduction in strength [5]. At the same time, due to the risk of aircraft corrosion, their use on airfield pavements is not allowed. Alternative agents used for de-icing airport pavements include sodium and potassium formates or acetates [7].

Studies on the effects of formate- and acetate-based de-icing agents have already been published, [3,4,8]. Wang et al. [3] analyzed the influence of de-icing agents on concrete degradation due to ASR. They used potassium acetate, which has a similar effect to potassium formate. The authors did not observe significant damage in the macro- or micro-scale and they did not find ASR products, despite using a high concentration of potassium acetate (54.4 wt. %). On the other hand, Rangaraju et al. [8] found that the two common airfield de-icing chemicals—potassium acetate and sodium acetate-based de-icer solutions—have significant potential to cause ASR in test specimens containing reactive aggregates. The research conducted by Giebson et al. [4] came to similar conclusions. They

revealed that deleterious ASR can be initiated and accelerated in concretes with reactive aggregates exposed to alkali-containing de-icers, especially ones based on acetates and formates. They showed that even low-alkali cement was not able to prevent the ASR.

Real-life experience shows that even in concrete made of nominally non-reactive aggregates, ASR can sometimes occur under adverse conditions of additional external alkali supply, humid environment, or heavy traffic and load [9]. The goal of the current research was to determine the impact of potassium formate on the potential for the occurrence of ASR in aggregates with different levels of reactivity.

#### **2. Materials**

Three aggregates characterized by different categories of reactivity were selected for testing. ASR reactivity was tested according to PB/1/18 [10], which is based on expansion measurements. Two granite aggregates (G1, G2) and one quartzite aggregate (Q) met the initial requirements of the research regarding the ASR reactivity category; they were R0—non-reactive (G2), R1—moderately reactive (G1), and R2—highly reactive (Q). The category of reactivity of aggregate according to PB/1/18 is presented in Table 1.



Ordinary Portland cement CEM I 42.5 R was used for mortar specimens. The alkali content in cement was 0.86%.
