Magnesium oxychloride boards: understanding a novel building material Aiken, T., Russell, M., McPolin, D., & Bagnall, L. (2020). Magnesium oxychloride boards: understanding a novel building material. Materials and Structures, 53, [118]. https://doi.org/10.1617/s11527-020-01547-z Published in: Materials and Structures Document Version: Publisher's PDF, also known as Version of record Queen's University Belfast - Research Portal: Link to publication record in Queen's University Belfast Research Portal Publisher rights Copyright 2020 the authors. This is an open access article published under a Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited. 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Daniel McPolin . Leo Bagnall Received: 14 May 2020 / Accepted: 12 August 2020 Ó The Author(s) 2020 Abstract Magnesium oxide type building boards are and chemically, between magnesium oxychloride a relatively new alternative to traditional sheeting boards supplied from different manufacturers. Cru- materials such as plywood, gypsum plasterboard and cially, the performance of each board when exposed to fibre-cement board. They have many advantages; high levels of relative humidity was vastly different. strength, lightweight, ease of use and excellent fire Some of the boards investigated displayed behaviour resistance, which has become increasingly important similar to that observed in Denmark, whilst other as demanded by industry and required by more boards exhibited substantial resistance to humid stringent legislation. Recently cases of durability environments and had not deteriorated after 60 weeks issues associated with magnesium oxychloride boards of exposure. in Denmark have emerged, however the precise nature of the problem was not established. These issues have Keywords Magnesium board Á Magnesium been related to magnesium oxychloride boards which oxychloride cement Á Humidity Á Water absorption Á were exposed to high levels of moisture. In this paper Permeability the mechanism of the failures observed in Denmark has been investigated. The difference in quality between various magnesium oxychloride boards available in the market was also studied. It was found 1 Introduction that there are significant differences, both physically Magnesium oxychloride building boards, a relatively new sheeting material outside China, are used in the Electronic supplementary material The online version of construction industry as an alternative to plywood, this article (https://doi.org/10.1617/s11527-020-01547-z) con- tains supplementary material, which is available to authorized gypsum plasterboard, fibre-cement and other sheeting users. materials [1]. They are used in a variety of internal and external applications including sheathing, wall/ceiling & T. A. Aiken ( ) Á M. Russell Á D. McPolin linings, render carrier systems and prefabricated wall School of Natural and Built Environment, Queen’s University Belfast, Stranmillis Road, Belfast BT9 5AG, systems [1–3]. Magnesium oxychloride boards are Northern Ireland, UK typically produced from magnesium oxychloride e-mail: [email protected] cement combined with filler materials such as wood and perlite [4]. L. Bagnall Resistant Building Products, 7 Duncrue Place, Magnesium oxychloride cement has been around Belfast BT3 9BU, Northern Ireland, UK for many years having been first reported by French 118 Page 2 of 16 Materials and Structures (2020) 53:118 scientist Stanislas Sorel in 1866 [5]. It is based on a generated interest due to their lower environmental reaction between magnesium oxide (MgO) powder impact when compared with Portland cement. This is and magnesium chloride (MgCl2) solutions [6]. Mag- due to the adoption of a lower calcination temperature nesium oxide powder is obtained from the extraction for light-burned magnesite (600–1300 °C) compared of magnesium carbonate (MgCO3), sometimes with the calcination of cement clinker (approx. referred to as magnesite. Almost 65% of the world’s 1400 °C) [19, 30, 31]. Additionally, Power et al. magnesite resources are found in China, North Korea [32] has suggested that approximately 20–40% of the and Russia [7]. Magnesite is calcined at temperatures CO2 emissions associated with the production of greater than 600 °C to produce magnesium oxide [8]. magnesium oxychloride boards may be offset due to The calcination temperature and duration has a passive carbonation over a 15 year period. Magne- significant influence on the crystal size, particle sium oxychloride boards are also considered less toxic surface area and degree of reactivity of the resultant to humans than conventional resin-based particle magnesium oxide [9–12]. Magnesium chloride is boards [33]. usually extracted from brines such as the Dead Sea Whilst magnesium oxychloride boards offer many and the Great Salt Lake followed by processing to virtues, recent reports [34–36] have highlighted dura- obtain the necessary composition and concentration bility issues with magnesium oxychloride wallboards [13, 14]. used in Denmark. Specifically, during periods of high There are two main hydrate phases (magnesium relative humidity (RH) water droplets formed on the chloride hydroxide hydrates) responsible for the surface of the boards. These water drops have been hardening and strength of magnesium oxychloride described as ‘tears’ and the process has been termed cement, these are 5 Mg(OH)2ÁMgCl2Á8H2O (5-phase) ‘crying’ or ‘sweating’. It has been claimed that the and 3 Mg(OH)2ÁMgCl2Á8H2O (3-phase) [15]. Other moisture caused mould growth and staining on phases of magnesium chloride hydroxide hydrate building elements. Additionally, metal fixtures and known as 2-phase and 9-phase can also be formed fittings had corroded due to high soluble chloride during the reaction process, but are not stable at content within the water droplets. In some instances ambient temperature [16]. Additionally, magnesium the phenomenon also appeared to cause structural hydroxide (Mg(OH)2), sometimes referred to as damage to the boards themselves as they were brucite, is a phase which occasionally forms depend- significantly cracked and damaged. It is not clear ing on the proportioning of raw materials [12]. whether these failures are an inherent problem with Many advantages of magnesium oxychloride magnesium oxychloride boards or were caused by an cements over other cements have been reported isolated quality issue with certain boards or due to including rapid hardening, high strength, good fire poor construction details. This paper aims to assess the resistance, low thermal conductivity and good resis- variability within magnesium oxychloride boards tance to abrasion [17–26]. Consequently, magnesium from different sources, to determine the process oxychloride boards have many advantages when behind the observed issues, and to assess if a quality compared with traditional board types such as ply- issue in the manufacturing process could account for wood, gypsum plasterboard, fibre-cement and oriented the failures reported in Denmark. Recently a steering strand board (OSB). For example, they are less dense group led by The British Standards Institution (BSI) than fibre-cement boards making handling easier for has been set up along with the Magnesium Oxide construction workers and reducing loads on buildings Building Board Trade Association (MOBBTA) to [27]. Additionally, cutting magnesium oxychloride develop a Publicly Available Specification (PAS) boards does not require sophisticated or expensive document for magnesium-based construction boards. equipment, a simple ‘score and snap’ method can be applied which requires only a knife. They are also much less susceptible to mould growth than boards made solely from wood. One of the key advantages of magnesium oxychloride boards is their fire resistance which is considerably better than gypsum plasterboard [28, 29]. Magnesium oxychloride cements have also Materials and Structures (2020) 53:118 Page 3 of 16 118 2 Experimental methods Diffraction patterns were obtained between 5 and 65° 2h with a step size of 0.02° 2h. The mineralogy of the 2.1 Board samples various samples was ascertained by using PANalyti- cals X’Pert Highscore Plus software in conjunction Six magnesium oxychloride board samples were with the Powder Diffraction File database. Once the obtained for analysis and comparison. Each board various phases were identified the crystallographic sample was available in the UK market and was details of each phase was refined