Influence of Waste Plastic Aggregate and Water-Repellent Additive on the Properties of Lightweight Magnesium Oxychloride Cement Composite

Abstract

Featured Application: The results obtained in the paper can find use in the design and development of low-energy and low-carbon construction composites with the incorporation of waste expanded polypropylene. The developed "green materials" possess good thermal insulation function, minimum water absorption, sufficient permeability for water vapor, and resistance against the harmful water action. The mechanical strength of the lightened composites is acceptable for non-bearing purposes but if required, it can be further improved to meet the technical requirements of construction practice. Abstract:The aim of the present study is to improve the thermal and hygric performance of magnesium oxychloride (MOC) cement composites by the incorporation of waste plastic-based aggregate and the use of the inner and surface hydrophobic agents. The crushed waste expanded polypropylene particles were used as a full replacement of natural silica sand. The aggregate properties were evaluated in terms of their physical and thermal parameters. The caustic calcined magnesite was studied by SEM, XRF, and XRD spectroscopy. The MOC cement composites were characterized by SEM/EDS, XRD, and FT-IR spectroscopy and measurement of their structural properties, strength parameters, thermal conductivity, and volumetric heat capacity. Assessment of water-and water vapor transport properties was also conducted. The results show significantly improved thermal parameters of MOC cement composite containing expanded polypropylene (EPP) as aggregate and indicate high efficiency of surface hydrophobic agent (impregnation) as a barrier against the transport of liquid and gaseous moisture. The resulting lightweight EPP-MOC cement composite with improved thermal insulation function and suitable mechanical properties can be used to produce thermal insulation floors, ceilings, or wall panels reducing the operational energy demand of buildings. volume of CO 2 emissions can be attributed to building industry, whether related to construction materials production or energy needed for heating and cooling of insufficiently insulated buildings [1,2]. For example production of Portland cement (PC) contributes to circa 5-7% of the global CO 2 emissions [3,4].At present, there are efforts to find an alternative to PC that would have a low carbon footprint. One of the candidates may be cements based on the magnesium oxide (MgO). Magnesium oxychloride cement (also known as Sorel cement) is formed by the reaction of a light-burnt MgO powder with a solution of magnesium chloride (MgCl 2 ) [5], where the light-burnt (also called caustic c) MgO is produced by calcination of magnesite (MgCO 3 ) at a temperature of circa 750 • C [6]. This lower temperature, compared to~1450 • C used in the production of Portland clinker, allows the use of alternative fuels [3]. MOC cement-based composites are able to absorb high amount of CO 2 from the atmosphere during their service life to form carbonates and hydroxycarbonates, which leads to their denser microstructure and to higher streng...

Carbon Dioxide Uptake by MOC-Based Materials

“…At the same time, these materials have also some disadvantages, especially when they come into contact with water [18,19]. MOC has a low water resistance due to magnesium chloride leaching, a corrosive compound that causes severe damage when it comes in contact with metals [20][21][22].…”

Water-to-Cement Ratio of Magnesium Oxychloride Cement Foam Concrete with Caustic Dolomite Powder

“…Magnesium oxychloride cement (MOC) is formed by mixing magnesium chloride solution (MgCl 2 -H 2 O) with magnesium oxide powder (MgO) [1,2]. As an air-dried gel material, MOC is widely used in several fields, including construction, transportation and technology [3][4][5][6]. At room temperature and pressure, the chemical reactions in the MgO-MgCl 2 -H 2 O system are the following:…”

Foam Glass Lightened Sorel’s Cement Composites Doped with Coal Fly Ash

“…For instance, Zhou et al [ 21 ] and He et al [ 49 ] incorporated waste wood into MOC which reduced thermal conductivity and increased flexural strength, but also increased water absorption. Záleská et al [ 39 ] investigated MOC with waste expanded polypropylene aggregate which reduced heat transfer as well as mechanical strength of final material. Waste tire rubber used by Biel and Lee [ 50 ] or Pavlíková et al [ 51 ] resulted in a huge decrease of mechanical properties.…”

“…When immersed in water, the crystalline phases dissolve, which results in increasing porosity and loss of strength [37,38]. It is known that water resistance can be increased using additives such as organic and inorganic agents and acids [39][40][41], microfillers and nano-additives [42][43][44]. Also, some of these microfiller additives are produced as waste materials and their incorporation into MOC-composite increase its ecological value.…”