WATER AND FIRE RESISTENT BUILDING MATERIAL

Abstract: The application concerns a water and fire resistant building material consisting of a layered, shaped and hardened compo­ sition of one or more absorbant components, magnesia cement, chemically active fumed silica, alkali silicate, one or several inorganic fillers, one or several lignin sulphonates, eventually ethyl silicate, whereby the final product is built up of a two binder system, one consisting of fumed silica, alkali silicate and possibly magnesium oxide and the other consisting of magnesia cement and a lignin sulphonate salt. The application also concerns the method of producing the product. The procedure is characterized by forming a dual layered binder system and by having a very short press time.

Description: This invention concerns water and fire resistant building materials based on a combination of magnesia cement, one or more absorbant materials, lignin sulphonate, chemically active fumed silica, alkali silicate, water as well as one or more additives. The invention also concerns the method of producing these materials. Magnesia or Sorel cement has been known for about 100 years. It has the advantage over Portland cement in that it cures faster and gets harder. On the other hand magnesia cement is slightly water soluble, which results in a reduced water resistance for products made from magnesia cement. However, according to Norwegian patent No-PS 151035 its water resistance can be greatly improved by the addition of 0.5-2.0% by weight of ethyl silicate. Building materials in sheet or strip form made by hot pressing and curing of a mixture consisting mainly of wood fibers, inorganic fillers, finely divided light calcined magnesia (MgO) and an aqueous magnesium chloride solution, and a method for producing them is described in Norwegian patent NO-PS 141889. Such a building product according to NO-PS 141889 is characterized by the cured mixture having: (a) a weight ratio of MgO to wood fiber of 1:3-1:4, (b) a weight ratio MgCl₂ to wood fiber material 1:9-1:12, (c) chemically inactive silica of 2-15% based on the wood fiber content (d) possibly up to 5%, preferably 2-4% waterglass, based on the wood fiber content. The procedure according to NO-PS 141889 is characterized by 30-40 parts by weight finely divided light calcined magnesia being mixed with 3-4 times its weight of a wood fiber filler which consists mainly of splinters with a length of at the most 20 mm, 2-8 parts by weight of inactive silica, at least one aqueous liquid containing 9-12 parts by weight MgCl₂ and 30-60 parts by weight of water, with possibly 1-5 parts waterglass, and where this mixture is formed and cured from 3-20 minutes at a pressure of 15-50 bar and a temperature of 120-220°C. Production of wood fiber boards according to NO-PS 141889 can be continuous by extrusion or piece by piece in a flat press. Wood fiber boards made according to NO-PS 141889 are claimed to be dimensionally stable and "showed, even after long submersion in water no noticeable swelling" (NO-PS 141889), page 7 lines 1-4. The present invention concerns a water and fire resistant building material which is characterized by being a shaped and cured structure consisting of a layered combination of one or more absorbant components, magnesia cement, one or more lignin sulphonates, chemically active fumed silica, alkali silicate, possibly one or more inorganic additives (fillers) and possibly ethyl silicate. The final product thereby consists of two binder systems, one consisting of water resistant magnesia cement, lignin sulphonate, preferably magnesium lignin sulphonate, and the other consisting of the reaction product of the chemically active fumed silica, alkali silicate and possibly magnesium oxide. The invention further concerns the method of producing the above mentioned building material, and is characterized by the thorough mixing of one or more absorbant materials with a dispersion of fumed silica in alkali silicate, possibly with ethyl silicate, and then with magnesium oxide and inorganic fillers, followed by a solution of magnesium salt containing lignin sulphonate in which also may be dispersed inorganic fillers, after which the finished composition is formed and cured under suitable pressure and temperature conditions until the free water in the mixture is bound as hydrate, and the material is shaped and hardened to form the desired building material. The new and essential feature of this invention is that the final product is built up by a combination of a two binder systems. One of them, system A consists of water resistant magnesia cement with a lignin sulphonate salt, while the other, system B, consists of the reaction product of chemically active fumed silica, alkali silicate and possibly magnesium oxide. By the layered structuring of the final product the two binder systems are separated from one another during the initial stages of curing, at which time they are incompatible with one another, and the curing reactions are assumed to take place independently of one another. System A gives good early strength and short press time and contributes to high water- and fire resistance. System B develops and increases strength over a longer period of time as well as also having a beneficial effect on both water and fire resistance. In addition the use of the lignin sulphonate in combination with system A increases both strength and water resistance, especially when the absorbant base material consists of wood fibers. The short press time is of vital importance in a commercial operation. According to this invention the cure time is in the order of 2 minutes at a temperature of between 150-175°C. In contrast to this the Sorel cement described in US Patent 2,466,145 apparently requires much longer cure times. Usual practice with Sorel bonded wood fiber systems requires cure times up to 20 minutes. An essential feature of the present invention is the layered addition of the reactive components. In contrast to this the cited US patent 1,175,427 states that it is immaterial how the different ingredients are mixed. The layered concept of the present invention is required because of the nature of the dual binder system. A preferred embodiment of the procedure according to this invention requires the absorbant component to be covered as much as possible by a continuous layer of a dispersion of fumed silica in alkali silicate (water glass). The layer is rendered insoluble by the following addition of a layer or coating of magnesium oxide. After this the magnesium chloride or sulphate solution is added along with the lignin sulphonate, which may also contain dispersed inorganic filler materials. Under high pressure the absorbant components and binders are consolidated and at elevated temperature the magnesium cement hydrate is formed removing free water from the mix and storing it in the form of crystalline water. When exposed to high temperature, as in a fire, the alkali silicate in the product expands and helps to shut off the supply of air (oxygen). The magnesia cement also under these conditions, gives off water over a wide temperature range, and in this way acts to limit the temperature and to smother the fire. The lignin sulphonate acts as a bridge between the magnesia cement structure and the cellulose in the wood fiber base material, and has the further advantage that it surprisingly improves the water resistance. Of the inorganic filler additives dolomite is especially attractive because under fire conditions it gives off carbon dioxide gas. The following examples show that a building material made according to this invention has high bending strength and tensile strength little swelling and low water absorbsion under submersion in water, and good fire resistance. The components in the following examples were mixed in the indicated order and propotions. The completely cured building panels were then tested for the following properties: Bending strength Tensile strength Per cent swelling and water absorption in water after 2 and 24 hours submersion in water. The panels were further tested for fire resistance according to Norwegian procedure NS 3903 and NT Fire 004. Referance is made to the curves for combustion gas temperature and smoke density which were carried out at the Laboratory for Investigation of Fire Technology (Brannteknisk Lab.) SINTEF in Trondheim.

Claims: Water and fire resistant building material, characterized by composition built up in layers and then shaped and hardened, consisting of one or more absorbant components, magnesia cement, one or more lignin sulphonates, chemically active fumed silica, alkali silicate, possibly one or more inorganic filler additives, and possibly ethyl silicate, whereby the final product includes two binder systems, one consisting of water resistant magnesia cement and lignin sulphonate, the other consisting of the reaction product between chemically reactive fumed silica, alkali silicate and possibly magnesium oxide. Building material as in claim 1, characterized by containing 10-70 weight per cent absorbant material. Building material as in claims 1 - 2, characterized by containing 10-70 per cent magnesia cement. Building material according to claims 1 - 3, characterized by containing 0.1-15 weight per cent lignin sulphonate. Building material according to claims 1 - 4, characterized by containing 1-15 per cent chemically active fumed silica. Building material as in claims 1 - 5, characterized by containing 1-25 per cent alkali silicate. Building material according to claims 1 - 6, characterized by containing 0-5 per cent ethyl silicate. Building material according to claims 1 - 7, characterized by containing 0-30 per cent inorganic filler additives. Building material according to claims 1 - 8, characterized by having the absorbant component consisting of cellulose fiber, wood fiber, perlite, fly ash, mineral wool, glass wool, diatomaceous earth, or a mixture of 2 or more of these single components. Building material according to claims 1 - 9, characterized by the magnesium cement consisting of magnesiumoxychloride hydrate, magnesiumoxysulphate hydrate, or a mixture of these oxysalt hydrates. Building material according to claims 1 - 10, characterized by the lignin sulphonate component consisting of calcium or magnesium salts, or a combination of them, or some other lignin sulphonate salt which can be converted to the magnesium salt. Building material according to claims 1 - 11, characterized by the fine silica component being chemically active fumed silica. Building material according to claims 1 - 12, characterized by the alkali silicate consisting of sodiumsilicate water glass or potasium silicate water glass or a mixture of these water glasses. Building material according to claims 1 - 13, characterized by the inorganic filler additives being dolomite or feldspar or a combination of them. A process for making a building material according to claim 1, characterized by forming a composition comprising one or more absorbent materials, magnesium oxide, lignin sulphonate, a magnesium salt, water, alkali silicate, reactive fumed silica and, optionally, ethyl silicate and inorganic filler additives in layers such that it contains two binder systems, one comprising water resistant magnesia cement and lignin sulphonate and the other comprising the reaction product between reactive fumed silica and alkali silicate, wherein each binder system forms a layer in the product, and then shaping and curing the completed composition under elevated pressure and temperature until the free water in the mixture is converted to a hydrate and the material is shaped and hardened into the desired building material. A process according to claim 15, characterized by thoroughly mixing a premix comprising absorbent materials, an aqueous solution of magnesium chloride, possibly, magnesium sulphate, and a lignin sulphonate, and adding to this premix magnesium oxide and, eventually, inorganic filler additives, reactive fumed silica and alkali silicate, after which the resultant mixture is pressed in a formed shape at elevated temperature and pressure, until the free water is combined as hydrate water and the material has been converted to the desired building article.

Inventors: BERG, JOHANNES G., SMITH-JOHANNSEN, ROBERT
Applicants: NORSK PROCO A/S
Application year: 1987
Main classification: C04B28
IPC codes: C04B28