## 1 Introduction  
Magnesium oxychloride cement, also known as MOC or Sorel cement, was discovered in 1867 by [PERSON] [1] shortly after the discovery of the well-known Portland cement (PC). It can be obtained by mixing magnesium oxide with an aqueous solution of magnesium chloride in a certain ratio. Because MOC is a non-hydraulic binder, it does not need humid curing conditions. Magnesium oxychloride cements have various superior properties compared to Portland cement. Firstly, the specific density is significantly lower giving the material higher compressive and flexural strengths. Moreover, it has elevated fire resistance [2], good resistance to abrasions [3], and low thermal conductivity, and it does not get affected by oils, grease, and paints. These properties are developed in a relatively short curing time, making the material suitable for quick repairs. The lower alkalinity (pH-10) allows the usage of MOC together with glass fibers, preventing the aging process. Moreover, the MOCs are suitable for use with a variety of aggregates [4; 5] such as tire rubber [6; 7], fly ash [8], synthetic resin, and wood particles [9]. A wide variety of applications for magnesium oxychloride cements were found, primarily as a flooring material for its elastic and acoustic properties, resistance to a charge accumulation, and decorative ivory-like appearance [10]. Moreover, it was successfully used in fire protective systems [11], grinding wheels [12], decorative elements [13], wall insulation [14], ship decks, underground armament factories, and bunkers [15]. Nevertheless, some difficulties were discovered in the use of MOC, especially for outdoor applications or any other applications where water contact is possible. Magnesium oxychloride cements show low water resistance; in fact, with longer exposure to water, the magnesium chloride is leached out from the structure leaving only hydrated brucite (Mg(OH)\({}_{2}\)) as the binding phase. The magnesium chloride washed out from the binder is corrosive and can cause severe metal damage [16]. There are numerous ways of improving the stability of Sorel cement in humid conditions. The most natural one is letting the surface of MOC react with CO\({}_{2}\) from air, forming magnesium chlorocarbonates [17]. The water resistance can be also improved by a very small amount of additive, e.g., phosphoric acid and soluble phosphates, including ammonium, iron, aluminum, alkali metal, and alkali earth metal phosphates [18; 19]. By adding the additives listed above, insoluble phosphate complexes are formed, resulting in the cement becoming waterproof [19]. Another reported way to improve the water resistance property of MOC is the incorporation of fly ash or silica fume into the material [20; 21]. Four main phases can be identified within the MgO-MgCl\({}_{2}\)-H\({}_{2}\)O system according to the ratio of the input compounds. Two of the hydrate phases, 3 Mg(OH)\({}_{2}\)-MgCl\({}_{2}\)-8H\({}_{2}\)O (Phase 3, MOC 3-1-8) and 5 Mg(OH)\({}_{2}\)-MgCl\({}_{2}\)-8H\({}_{2}\)O (Phase 5, MOC 5-1-8), can be prepared in ambient conditions and remain stable until the reaction with CO\({}_{2}\) or H\({}_{2}\)O. These two phases are the fundamental products responsible for the hardness and strength of MOC [22]. The great mechanical properties are a result of the needle-like structure of both Phase 3 and Phase 5 [23]. Needles in the structure can be described as scroll-tubular whiskers which interlock in rapid growth, resulting in a very tough structure, which becomes denser due to the needle intergrowth when there is a lack of space for growth [24]. The remaining two phases, 2 Mg(OH)\({}_{2}\)-MgCl\({}_{2}\)-4H\({}_{2}\)O (Phase 2, MOC 2-1-4) and 9 Mg(OH)\({}_{2}\)-MgCl\({}_{2}\)-5H\({}_{2}\)O (Phase 9, MOC 9-1-5), can be prepared and are also stable at a temperature of -100 \({}^{\circ}\)C [23; 25; 26].