Calcium silicate building board

Abstract

A calcium silicate building board with improved thermal stability and industrial applicability contains a hydraulic binder, xonotlite spherical particles, organic and inorganic fibers, clay minerals and ettringite that is decomposed by heat with consumption of energy. Improved thermal stability is obtained by modifying pore structure of the material to avoid board cracks and sagging at high temperatures.

Description

FIELD OF THE INVENTION The present invention relates to a building material composition, a building material, in particular a xonotlite-ettringite based building board having improved thermal stability at high temperatures and improved (safer) industrial applicability; to methods for the manufacture thereof; and to fire-resistant building elements comprising this material. BACKGROUND OF THE INVENTION In most building codes, requirements for building materials are incorporated that relate to both reaction to fire and resistance to fire. The reaction to fire is the contribution of a material, applied in a construction (e.g. a building, a vessel, ...) to the spread of the fire. Sometimes the emission of smoke and toxic gases in case of fire, is seen as part of the reaction to fire. The resistance to fire of a building element is a measurement of the time that this element fulfils its function in case of a standardized fire, such as the EN 1366 nowadays. For a good fire resistance, thermal stability and thermal insulation of the materials in the building element play an important role. Fire resistance of construction elements is measured in specialized test laboratories. In these laboratories, the construction elements are tested and evaluated to the criteria defined in corresponding technical standards (e.g. ISO 834, EN 1366 and dependent standards, ASTM 119, ...). According to these standards the function of a fire resistant structural element, when exposed to a theoretical fire curve, is evaluated as the time in minutes, during which the element fulfils the requirements imposed to its dimensional stability, integrity (tightness to flames or smoke), and thermal insulation, to the extend these requirements are applicable to the construction element. Very often this time period is classified in comparison to the standard requirement in the building codes. Among the materials used in the field of fire protection, xonotlite-ettringite based building board is of particular interest regarding its use in constructions. This interest is due not only to the fact that it is incombustible, but also to its good thermal insulation and thermal stability thanks to the considerable endothermic effect that takes place when this material is subjected to fire. The amount of energy consumed during fire from dehydration of both the calcium silicate hydrates and ettringite gives it excellent properties to act as fire protection for underlying materials. WO9635649 A1 describes a building board comprising a binder, synthetic xonotlite spherical particles and at least 5 percent by weight of ettringite and / or metavariscite. It has very good thermal insulation and thermal stability when tested according to national norms such as that of Germany (DIN), France (NF) or UK (BS) used at that time. Nevertheless, when subjecting the board to fire in accordance with the current European EN norm such as EN 1366 (all versions since 2000) , which is more severe than these national norms , primarily due to the utilization of plate thermal couples, there is noticeable sagging in the board. In certain instances, this sagging is so pronounced that the board collapses before reaching the specified duration of the fire test. Another problem of the board of WO9635649 A1 is that the xonotlite in the material composition contains TiO2 and / or ZrO2, as specified by the EP0231460. These raw ingredients are considered carcinogenic today, it poses a safety concern for the production and public health. In 2020, the EU classified TiO2 in its powder form as a suspected carcinogen by inhalation under the EU’s Classification and Labelling (CLP) Regulation. This classification of TiO2 by the EU poses a serious issue to ensure health safety of workers active in the industrial use of TiO2. For the similar reason, the use of ZrO2 should better be eliminated. There is a need to improve high temperature stability of the material of WO9635649, to pass fire test according to European norms such as the EN 1366 (all versions since 2000), and to remove TiO2 and ZrO2 from the material which lead to an improved (safer) industrial applicability. Summary of the invention Therefore, it is an objective of the present invention to provide a composition for manufacturing a building material which has improved thermal stability under European norms such as EN 13501, EN 1366 and EN 13381 (valid versions since 2000). Another objective of the invention is to eliminate of TiO2 or ZrO2 from the material, to avoid possible carcinogenic effect and thus improve industrial applicability. Accordingly, the present invention provides a building material composition comprising less than 30wt.% of hydraulic cement, preferably less than 20 wt.% relative to the total dry weight of the composition, more than 5wt.% of ettringite, preferably more than 10wt.%, less than 5 wt.% of organic fibers selected from the group of polypropylene (PP), polyethylene (PE) and polyvinyl alcohol (PVA) fibres , less than 5 wt.% of reinforcing fibers, less than8 wt.% of clays, a balanced amount of calcium silicate hydrate production waste , more than 30 wt.% of porous, spherical calcium silicate hydrate aggregates free of TiO2 or ZrO2 and which are composed mainly of xonotlite crystals and a balanced of amount water. In accordance with the current invention, the hydraulic cement is defined as cementitious material which will set by adding water, including the group selected from all types of Ordinary Portland Cement (OPC), Calcium Aluminate Cement (CAC) and Calcium Sulphoaluminate Cement (CSA), the CAC and CSA being preferred, used alone or in combination thereof. The advantage of CSA is that it will produce ettringite by hydration, while the hydration of CAC forms aluminum hydroxide as byproduct, both being endothermic fillers. The ettringite is added as powder of a diameter <1mm measured using a laser method such ISO13320:2020 or it is formed in situ by the hydration of CSC cement. The porous spherical calcium silicate hydrate aggregates without Ti02 or Zr02 are obtained beforehand by hydrothermal synthesis in a stirred medium using an aqueous lime and silica suspension wherein said lime and silica suspension is obtained in the presence of 0.1 to 2% by weight of sulfate with respect to total weight of lime and silica used in the production of said calcium silicate aggregates and in the presence of 0.1 to 2 % by weight of alkali hydroxides with respect to total weight of lime and silica used in the production of said calcium silicate hydrate. The porous spherical calcium silicate aggregates are mainly composed by xonotlite crystals. These particles having mean diameter of between 20 and 200 micrometers measured according to ISO 13320-2020. The reinforced fibers are selected among cellulose fibers or a mixture of cellulose fibers and glass fibers, including alkaline resistant glass fibers. The clay minerals are selected among kaolinite, dickite, montmorillonite, illite and preferably bentonite. The building material composition is a fire resistance building material composition. According to a second aspect, the invention provides a process for manufacturing a building material, in particular a xonotlite-ettringite based material by using a slurry comprising <30 wt.% of hydraulic cement preferably < than 20 wt.% relative to the total dry weight of the composition, >30 wt.% of porous, spherical calcium silicate hydrate aggregates free of TiO2 or ZrO2, said calcium silicate hydrate aggregates are composed mainly of xonotlite crystals, >5 wt.% of Ettringite , preferably > 10 wt.%, <5 wt.% of organic fibers selected among PP, PE, PVA fibers used alone or in combination thereof <5 wt.% of Reinforcing fibers <8 wt.%, of Clay minerals < 30 wt.% of calcium silicate hydrate production waste balanced amount of water. The wt.% are relative to the total dry weight of the composition. The porous spherical calcium silicate hydrate aggregates free of TiO2 and ZrO2 and composed mainly of xonotlite crystals is obtained by hydrothermal synthesis in a stirred medium using an aqueous lime and silica suspension wherein said lime and silica suspension is obtained in the presence of 0.1 to 2% by weight of sulfate with respect to total weight of lime and silica used in the production of said calcium silicate aggregates and in the presence of 0.1 to 2 % by weight of alkali hydroxides with respect to total weight of lime and silica used in the production of said calcium silicate hydrate aggregates. The alkali hydroxide is chosen from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, or a mixture thereof. The slurry is shaped in in a molded body. The molded body is dried in an oven until the free water content is below about 5%. The material (molded body) is not autoclaved. The building material is a fire resistance building material. Another advantage of the composition according to the invention is that it can be processed by known industrial process, such as Hatcheck process, Gypsum board process, Flow-on process, Filter press process, Magnani process, Casting process and Spray process. According to a third aspect, the invention relates a fire protection building element manufactured according to the process of the invention and having a dry density of 300 kg / m3 to 1000 kg / m3. A preferred embodiment of the fire protection building element of the invention is a xonotlite-ettringite based building board of 15 to 100 mm of thickness. Detailed description of the invention The fire test standard according to EN norm is more severe than according to national norm, primarily because it incorporates plate thermal couples. With the implementation of EN 1366, the previously satisfactory high-temperature stability of the fire-resistant board composed of the material described by WO9635649-A1 is found inadequate. In contrast to its good performance under, such as , DIN norm, the board now exhibits sagging (bending toward the ground) during the fire test, in particular when tested the boards horizontally. In some instances, this sagging is so pronounced that the board collapses during the test. Evidently, there is a need to enhance the thermal stability of the material. It is surprised to find that by adding organic fibers, such as PP (polypropylene), PE (polyethylene) and PVA (polyvinyl alcohol), used alone or in combination thereof, has reliable effect to solve the sagging problem. Although exact mechanism is not yet known, it is believed the inferior sagging behavior is caused by thermal shock related to rapid temperature increase in the norm EN 1366. As result, the water vapor from the dehydration of calcium silicate hydrates and ettringite is not able to escape from the material structure within a short period of time, leading to small cracks on fire side and gradually resulting in sagging. With help of these organic fibers having melting temperature between 100-250°C, they create extra pore structures inside of the material, make it easier to evacuate water vapor associate with dehydration, stop crack propagation and help improved thermal stability. On the other hand, to avoid the TiO2 and ZrO2, it is found that the spherical calcium silicate aggregates mainly composed of xonotlite of WO2020152335 has unexpected good effect in the current invention. The spherical calcium silicate aggregates mainly composed of xonotlite such made is more homogeneous and lighter in weight, it can provide with improved thermal insulation under the EN 1366, and, on the other hand, improves safety and industrial applicability. Cement In accordance of the current invention, the hydraulic cement is used as binder. The hydraulic cement is any inorganic cementitious material which sets by adding water, including the group comprising all types of Ordinary Portland Cement (OPC), Calcium Aluminate Cement (CAC) and Calcium Sulphoaluminate Cement (CSA), used alone or in combination. The hydraulic cement that produces endothermic phases is preferred, such as the CAC and / or CSA. Amount of cement is below 30 wt.%, preferably below 20 wt.% with respect to the total dry weight of the composition. A typical amount of cement is between 8 and 29%. Calcium silicate hydrate aggregates The porous spherical calcium silicate hydrate aggregates , mainly xonotlite crystals, are capable of being obtained by hydrothermal synthesis in a stirred medium, using an aqueous lime suspension and silica suspension, said aqueous lime suspension and silica suspension being obtained in the presence of 0.1 to 2 % by weight, preferably 0.1 to 1 % by weight of sulfate with respect to total weight of lime and silica used in the production of the porous calcium silicate aggregates, and in the presence of 0.1 to 2 % by weight, preferably 0.1 to 1 % by weight of alkali hydroxides with respect to total weight of lime and silica used in the production of the porous calcium silica aggregates. Here, mainly xonotlite crystals means more than 50 wt.% of the calcium silicate aggregates. In the present invention the lime can be either hydrated lime Ca(OH)2 or quick lime CaO. Specifically, the silica suspension does not comprise TiO2 nor ZrO2. The aggregates have an internal part in which the crystals are loosely entangled and distributed rather uniformly and an external layer in which the crystals are entangled more tightly than in the internal part. The spherical calcium silicate hydrate aggregates are composed mainly of xonotlite crystals. The spherical calcium silicate hydrate are then present in the form of xonotlite particles. The spherical calcium silicate hydrates aggregates may also contain tobermorite. The percentage of tobermorite is less than 50 wt.% , preferably less than 20 wt.% of the total weight of the xonotlite particles. A preferred embodiment is a composition wherein the amount of xonotlite spherical particles is > 30 wt.%, preferably >40wt.% based on the total weight of the dry weight composition. A typical amount of xonotlite spherical particles is between 31 and 65 wt% based on the total weight of the dry weigh composition. Ettringite Ettringite is an endothermic filler. It is used either as a powder with a diameter <1mm measured according to ISO13320:2020, or formed in situ by the hydration of Calcium Sulphoaluminate Cement (CSA). The ettringite formation via hydration of CSA is preferred. An amount of the ettringite is >5 wt.% related to total dry weight of the composition and preferably >10 wt.%. Clay Minerals In accordance of the current invention, clay mineral plays a role of rheological agent during processing, it helps homogeneity and prevents mixture from sedimentation during mixing. The clay mineral is selected from the group comprising kaolinite, dickite, montmorillonite, illite. Bentonite is preferred. Organic fibers In accordance of current invention, organic fibers are chosen from the group comprising polypropylene (PP) ; polyvinyl alcohol (PVA) and polyethylene (PE) , used alone or in combination thereof. They are characterized in capable to melt in range of 100-250°C , and create extra porosity to help evacuation of water vapor, thus avoids material from cracks and board sagging . Amount of the organic fiber of current invention is below 5 wt.% , preferably at least 0.5 wt%, more preferably at least 1 wt.%. Suitable fiber diameter will be 10-50 pm. Reinforced fibers In accordance of the current invention, the reinforcing fibers are presented in the form of individual fibers homogeneously dispersed in the hydraulic setting composition. Such individual fibers may, for example, have an average length of below 20 mm, preferably below 12 mm. These fibers have dosage in the composition below 5 wt% preferably between 0.1 and 5.0% by weight relative to the total dry wt. of material. According to another advantageous embodiment, the reinforcing fibers consisting, at least in part, of cellulose fibers or of a mixture of cellulose fibers and glass fibers, including alkaline resistant glass fibers. The cellulose fibers have the advantage of further improving the mechanical properties of the building element without deteriorating its fireproof properties. Further, the final product has less crack-propagation during fire exposure when cellulose fibers have been incorporated therein. Recycled calcium silicate hydrates production waste For obvious ecological reasons, the building material composition further comprises balanced amount of recycled production waste, namely sanding dust and cutting waste of claim silicate hydrate boards. The amount of the calcium silicate waste in below 30 wt.% relative to the total dry wt. of material, preferably in the form of dust. Other functional fillers can be used in current invention, such as wollastonite , bauxite , dolomite , calcite, gypsum, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and their carbonates, or combination thereof. Water In accordance of the present invention, balanced amount of water is used during production, in an amount of 5-25 times as much as that of the total dry weight of the composition, to form a water slurry before shaping the board. Examples Calcium silicate building board of current invention is produced according to the following procedure: all dry components shown in the Tab. 1 and a balanced amount of water are homogeneously mixed. Forming is done by filter press. The molded body is oven dried until free water content is below about 5% of total mass. The test results are in the Tab.1 . The invention shows only slight sagging when tested according to EN 1366-2021 and passes the fire test of 90 min., while the reference has remarkable sagging and it collapses and test fails at ca 80 min. It evidently demonstrates that the current invention has improved sagging resistance at high temperatures according to EN 1366 , and improved industrial applicability, thanks to free of TiO2 and ZrO2 in the material, compared to the reference (Tab.2). CSA cement Xo without TiO2 / ZrO2 WO20152335 Dust Bentonite Ettringite Glass fiber PP fiber Cellulose fiber Total Invention 10.0 47.0 15.0 2.0 20.0 2.0 1.0 3.0 100.0 CSA cement Xo with TiO2 / ZrO2 WO09635649 Dust Bentonite Ettringite Glass fiber PP fiber Cellulose fiber Total Reference 10.0 54.7 12.3 2.0 15.0 3.0 0.0 3.0 100.0 Tab.1 composition of comparative test Thickness Density Bending strength Thermal shrinkage at 1000°C Sagging during fire test Fire test for 90° EN 1366-1 Containing TiO2 / ZrO2 mm kg / m3 Mpa % Invention 35.0 510 2.4 1.5 a little 95’ no Reference 35.0 508 2.8 1.3 severe 80’ yes Tab.2 results of comparative test

Claims

1. A building material composition comprisinga. <30 wt.% of hydraulic cement preferably < than 20 wt.%,b. >30 wt.% of porous, spherical calcium silicate hydrate aggregates free of TiO2 orZrO2, said calcium silicate hydrate aggregates are composed mainly of xonotlite crystals,c. >5 wt.% of Ettringite , preferably > 10 wt.%,d. <5 wt.% of organic fibers selected among PP, PE, PVA fibers used alone or in combination thereof,e. <5 wt.% of Reinforcing fibers,f. <8 wt.%, of Clay minerals,g. < 30 wt.% of calcium silicate hydrate production waste,h. balanced amount of water, and wherein the wt.% is relative to the total dry weight of the composition.

2. A building material composition according to claim 1 wherein the hydraulic cement is any cementitious material that will set by adding water, including the group selected from all types selected from Ordinary Portland Cement (OPC), Calcium Aluminate Cement (CAC) and Calcium Sulphoaluminate Cement (CSA), preferably the hydraulic cement that will produce endothermic phases,including CAC and CSA used alone or in combination thereof.

3. A building material composition according to claim 1 wherein the ettringite is a powder of a diameter <1mm measured according to ISO13320:2020.

4. A building material composition according to claim 2 wherein the ettringite is formed in situ, by the hydration of CSA cement.

5. A building material composition according to claim 2 wherein the CSA and CAC cement are used in combination.

6. A building material composition according to any one of claims 1 to 5 wherein the calcium silicate hydrate aggregates being obtained by hydrothermal synthesis in a stirred medium using an aqueous lime and silica suspension wherein said lime and silica suspension is obtained in the presence of 0.1 to 2% by weight of sulfate with respect to total weight of lime and silica used in the production of said calcium silicate aggregates and in the presence of 0.1 to 2 % by weight of alkali hydroxides with respect to total weight of lime and silica used in the production of said calcium silicate hydrate.

7. A building material composition according to any one of claims 1 to 6 wherein said calcium silicate hydrate aggregates have a mean diameter of between 20 and 200 micrometers measured according to ISO13320:2020.

8. A building material composition according to any one of the claims 1 to 7 wherein said clay minerals are selected among kaolinite, dickite, montmorillonite, illite and preferably bentonite.

9. A building material composition according to any one of the claims 1 to 8 wherein the organic fibers have a diameter between 10- 50 micrometers.

10. A process for manufacturing a building material, in particular a xonotlite-ettringite based material comprising the following steps ,a. Prepare a homogenous slurry comprising the building composition according to claim 1 to 6 wherein the porous spherical calcium silicate hydrate aggregates are free of TiO2 and ZrO2 and are composed mainly of xonotlite crystals obtained by hydrothermal synthesis in a stirred medium using an aqueous lime and silica suspension wherein said lime and silica suspension is obtained in the presence of 0.1 to 2% by weight of sulfate with respect to total weight of lime and silica used in the production of said calcium silicate hydrate aggregates and in the presence of 0.1 to 2 % by weight of alkali hydroxides with respect to total weight of lime and silica used in the production of said calcium silicate hydrate,b. Shape the slurry in a molded body and,c. Oven dry said molded body until the free water content is below about 5%.

11. A process according to claim 10 wherein the oven temperature is below 150°C,12. A process for manufacturing a building material according to claim 10 or 11 being selected from the Hatcheck process, Flow-on process, Filter press process, Magnani process, Casting process, Gypsum board process or Spray process.

13. A fire protection building element according to the process of claims 10-12, having a dry density of 300 kg / m3 to 1000 kg / m3.

14. A fire protection building element manufactured according to the process of claims 10-12 in a shape of a xonotlite-ettringite based building board of 15 to 100 mm of thickness.