A PHOTO-LUMINESCENT CALCIUM SILICATE MATERIAL, CONCRETE AND GRAVEL MATERIAL CONTAINING IT AND A METHOD OF PRODUCING A PHOTO-LUMINESCENT CALCIUM SILICATE MATERIAL

Abstract: A photo-luminescent calcium silicate material, comprising photo-luminescent fibro-crystalline wollastonite crystals activated with an activator comprising at least one element selected from the group consisting of Mn, Pb, Er, Tm, W, Nb, Ti, Cr, Sn, and Bi, and disseminated in a calcium silicate glass matrix having a low content of alkali metal oxides. This material is produced by: introducing a raw material comprising a mixture of calcareous and siliceous materials and activators selected from the group consisting of oxides, hydroxides and salts of the above-mentioned elements into a rotary kiln; melting said mixture at least partially; withdrawing this mixture from the rotary kiln; cooling the withdrawn material to a partially crystallized product; and if desired subjecting this product to further crystallisation in a recrystallization step. A photo-luminescent concrete containing the above-mentioned photo-luminescent material as aggregate as well as a photo-luminescent gravel material consisting of the above-mentioned photo-luminescent concrete.

Description: A photo-luminescent calcium silicate material, concrete and gravel material containing it and a method of pro- ducing a photo-luminescent calcium silicate material The present invention concerns a photo-luminescent calcium silicate material and a method of producing this material. The invention moreover concerns photo-luminescent con- crete, in particular high strength concrete, as well as a gravel material produced by crushing said concrete. US Patent No. 3 266 879 discloses a method of making a crystallizable glass material which in a subsequent devitrifying or recrystallization step may be devitrified or recrystallized to an end product consisting of syn¬ thetic fibro-crystalline wollastonite crystals disseminat¬ ed in a calcium silicate glass matrix, wherein a selected composition of raw materials suitable for forming a crystallizable glass material comprising calcareous and siliceous materials, such as chalk and sand, as well as preferably dolomite are partly introduced from the upper end of the rotary kiln, partly injected from the lower end of the rotary kiln in a manner such that part of the injected raw materials is distributed over the burning zone. The part of the raw materials injected in the lower end is preferably quartz sand. When introduced in the rotary kiln the raw material is gradually heated, calcined and melted. The resulting molten material flows out of the kiln and is solidified and granulated by cooling, preferably by quenching, in a water bath. Due to the quenching the resulting product is a glass containing fine crystalline material. Further crystallization may be obtained by re-heating this material. In this manner it is possible to produce a white or whitish, partially crystallized, granular material having a rough surface. The obtained product is extensive¬ ly used, i.a. in the manufacture of sand-lime bricks and as aggregate in white concrete or in bituminous road surfaces and can be produced from relatively readily accessible starting materials. US Patent No. 3 458 301 describes a development of the method disclosed in US Patent No. 3 266 879, which comprises mixing a thermally crystallizable vitreous material and quartz sand wherein the ratio of quartz to vitreous materials is no greater than 5:1 parts, heating the mixture of said vitreous material in a rotary kiln to form a kneadable mass in which the sand grains are embedded and subsequently thermally crystallizing the crystallizable vitreous material to produce a devitrified glass aggregate. US Patent No. 4 119 434 describes another development of the method disclosed in US Patent No. 3 266 879, which comprises injecting calcium sulfate, preferably in the form of powdered gypsum, optionally with simultaneous injection of sand into the lower end of the rotary kiln to produce a synthetic wollastonite having a particularly low content of cristobalite. The obtained materials, like the materials produced according to US Patent No. 3 266 879, are useful for numerous purposes, such as production of additives for ceramics, so-called low- emperature ceramics, as described in US Patent No. 4 157 907, and plate-shaped products, in particular corrugated plates, construction materials and road surfaces, as described in US Patent No. 4 202 851. For a number of purposes, in particular with a view to improving traffic security or for decorative purposes, it is desirable to provide materials which, in addition to the properties, in particular with respect to strength, achievable by the prior art, exhibit photo-luminescent properties such that they emit light with a wavelength within the visible range above 420 nm, when irradiated with light having a shorter wavelength, e.g. soft ultra¬ violet light with a wavelength greater than 315 nm, whereby it seems as if the material were luminescent in the dark. Such a material can be used e.g. where a photo- luminescent effect is needed in road surfaces, in edge markings, as part of the fillers in concrete and mortar, and in general where it may be an advantage to use materials having a photo-luminescent effect. The concept photo-luminescence is exhaustively described in An Introduction to Luminescence of Solids by Humboldt W. Leverenz, Dover. N.Y., 1968, which also contains an exhaustive discussion of photo-luminescent materials and the production of these with extensive references. In this context, photo-luminescent materials are defined as materials absorbing energy quanta from photons, and emitting at least part of the absorbed energy by emission of photons. Characteristically, the emitted photons will have a longer wavelength than the wavelength of the absorbed photons. The material will be present in an excited state between the absorption of an incoming photon and the emission of an outgoing photon. The duration of this state determines whether fluorescence (brief duration, i.e. less than about 10 —8 s) or phosphorescence (longer duration, i.e. greater than about 10 —8 s) is involved. Photo-luminescent materials typically consist of a so- called base material which is not photo-luminescent per se, or only to a limited degree, but contains a relatively small amount of an activating material, typically an ele¬ ment, called an "activator" which gives rise to the photo- luminescent effect. The term "M:A" is used below for designating a photo- luminescent material with base material M and activator A. US Patent No. 2 297 108 describes a plurality of europium- activated silicates of alkaline earth metals, i.a. CaSiO tEu, which fluoresces when irradiated with 365 nm photons. These materials are prepared by a sintering process comprising heating e.g. a mixture of calcium oxide and silica gel containing about 0.1% by weight Eu in air at 800 °C for 15 minutes; regrinding the product thus obtained; reheating the reground material at 800 °C in another 15 minutes in hydrogen; and cooling in a hydrogen atmosphere. The basic principle of using photo-luminescent materials absorbing ultraviolet light, i.e. photons with a wave¬ length of typically 100-420 nm, and emitting visible light, i.e. photons with a wavelength of typically 420- 640 nm, for marking and illuminating roadways, illuminat- ing edges markings and the like is known. Thus, US Patent No. 4 208 300 concerns a type of paint comprising a synthetic binder, crystalline material, e.g. ground quartz, and one or more phosphorescent sulfides, which are applied to the objects to be marked. US Patent No. 3 253 146 concerns a similar material of the paint type, where, however, fluorescent organic pigments are used. GB Patent Application No. 2 043 673 describes a photo- luminescent composition which may be used for road markings. This composition comprises from 60 to 90% by weight of a hard porous or rough translucent support and from 40 to 10% by weight of a luminescent pigment retained in the pores or roughness of the support. The support is preferably particulate alumina, quartz or an alumino- silicate whose surface has been rendered porous or rough by etching and has a hardness not less than 7 on the Moh scale. The luminescent pigment may be Ce, Cs, Na or Pr uranates, or organic material. This composition is mixed with a styrene or di-isocyanate resin system which cures during moulding. However, these materials leave much to be desired with respect to weather and in particular wear resistance. GB Patent No. 1 034 037 describes small transparent glass spheres having diameters less than 50 mils, preferably between 0.5 and 10 mils, and containing 0.1-0.4% by weight of U0-., which flouresce in the presence of ultraviolet light. These materials may be used in e.g. painted highway markings and signs. JP Patent Application No. 60-176933 describes glass fibers and spherules containing a flourescent powder, e.g. ZnS. Finally, the international patent application, publ. No. WO 90/02226 concerns a road surfacing material comprising a binder, e.g. tar, a crushed mineral material, e.g. quartzite, as well as 2-25, preferably 10-15% by weight of an UV excitable fluorescent material which has been produced by melting a mineral in a furnace of the kind used in the manufacture of mineral wool and doping said mineral with an activator by introducing said activator into the molten mineral-bath, granulating or casting the resulting melt, and crushing the solidified material to size corresponding to the size of the mineral material. The object of the invention is to provide a photo-lumine cent material which is well suited for marking and illum nating roadways, which has improved weather and wear resistance compared with the known materials, and which can be produced in a simple way using environmentally acceptable, inexpensive and easy available raw materials. The invention is based on the finding that when incorpora ting one or more activators in a raw material mixture of the type described above in connection with production of materials consisting of synthetic wollastonite crystals disseminated in a calcium silicate glass matrix, it is possible to produce a partially crystallized material having photo-luminescent properties and excellent weather and wear resistance. Accordingly, the present invention relates to a photo- luminescent calcium silicate material, which is character ized by comprising photo-luminescent fibro-crystalline wollastonite crystals activated with an activator in a quantity effective for ensuring photo-luminescence, said activator comprising at least one element selected from the group consisting of Mn, Pb, Er, Tm, W, Nb, Ti, Cr, Sn, and Bi, and disseminated in a calcium silicate glass matrix having a low content of alkali metal oxides. This material has excellent strength properties because the fibro-crystalline wollastonite provides a strong fibro-crystalline reinforcement of the glass matrix. Due to the high surface/volume-ratio of the photo-luminescent component, i.e. the fibro-crystalline photo-luminescent wollastonite crystals typically having average particle sizes in the μm range, this material exhibits an intense photo-luminescence. The quantity of the added element/elements used as activa¬ tor necessary for ensuring a photo-luminescent end product is easily determined by laboratory tests comprising melt¬ ing mixtures prepared from a stock mixture of calcarious and siliceous materials having varying contents of activa¬ tors in a crucible, cooling the melted material, recrys- tallizing the cooled material, and subsequently subjecting the recrystallized material to a photo-luminescence test, e.g. as described below. According to preferred embodiments: - said material contains 30-70% by weight photo- luminescent fibro-crystalline wollastonite crystals; said material has the following analysis: a CaO content of about 20-30% by weight, a SiO-, content of about 65-80% by weight, an A1 2 0-. content less than about 5% by weight, an alkali metal oxide content less than about 5% by weight, and a mole ratio activator/CaO within the range 0.0005-0.35, preferably within the range 0.0010-0.25; - said activator provides a photo-luminescent fibro- crystalline wollastonite which emits visible light when excitated by photons having a wavelength greater than 315 nm, in particular within the interval 315-400 nm; - said photo-luminescent fibro-crystalline wollastonite crystals are activated with Mn as an activator in an amount of 0.044-0.20 mole Mn/mole CaO; said photo-luminescent fibro-crystalline wollastonite crystals are activated with Mn and Ti as activators, Mn in an amount of 0.044-0.20 mole Mn/mole CaO and Ti in an amount of 0.025-0.15 mole Ti/mole CaO; said photo-luminescent fibro-crystalline wollastonite crystals are activated with Nb as an activator in an amount of 0.005-0.20 mole Nb/mole CaO. According to another aspect the present invention relates to a method of producing said photo-luminescent calcium silicate material which is characterized by introducing a raw material comprising a mixture of calcareous and sili¬ ceous materials and activators in a quantity suitable for ensuring photo-luminescence, selected from the group con¬ sisting of oxides, hydroxides and salts of Mn, Pb, Er, Tm, W, Nb, Ti, Cr, Sn, and Bi, into a rotary kiln; melting said mixture at least partially; withdrawing the at least partially melted mixture from the rotary kiln; and cool¬ ing, preferably quenching the withdrawn material- to a par¬ tially crystallized product comprising photo-luminescent fibro-crystalline wollastonite crystals disseminated in a calcium silicate glass matrix. According to preferred embodiments of this method: the cooled, partially crystallized material withdrawn from the rotary kiln is subjected to recrystallization in a recrystallization and annealing step at a temperature within the range from about 900 °C to about 1100 °C for a period of time from about 0.5 to about 4 h. - the raw material contains amorphous carbon in an amount corresponding to 2-3 times the stoichiometric amount needed for reducing an activator to a desired valency. the raw mixture has the following analysis: a CaO content of about 20-30% by weight, a SiO-, content of about 65-80% by weight, an Al^O-, content less than about 5% by weight, an alkali metal oxide content less than about 5% by weight, and a mole ratio activator/CaO within the range 0.0005-0.35, preferably within the range 0.0010-0.25. - the activator is chosen to provide a photo-luminescent wollastonite which emits visible light when excitated by photons having a wavelength greater than 315 nm, in par¬ ticular within the interval 315-400 nm. - the raw material contains Mn as an activator in an amount of 0.044-0.20 mole Mn/mole CaO. the raw material contains Mn and Ti as activators, Mn in an amount of 0.044-0.20 mole Mn/mole CaO and Ti in an amount of 0.025-0.15 mole Ti/mole CaO. the raw material contains Nb as an activator in an amount of 0.005-0.20 mole Nb/mole CaO. - a part of the raw material is injected from the lower end of the kiln. at least part of the raw material, preferably of that injected from the lower end of the kiln, consists of filter dust collected in a filter arranged in connection with the rotary kiln. The method according to the invention can conveniently be performed in a rotary kiln of the type usually employed in the manufacture of materials comprising synthetic wollas¬ tonite disseminated in a calcium silicate glass matrix, e.g. as described in US Patent No. 3 266 879. The method is extremely flexible since the kiln can be adjusted to provide differently photo-luminescent, materials by varying the amount and type of the raw materials, the points where they are introduced, the kiln temperature and the rotary speed of the kiln. As mentioned above, the activators used in the method according to the present invention are introduced into the rotary kiln as a mixture with calcareous and siliceous materials. This raw mixture may be introduced into the rotary kiln as an aqueous suspension or as a dry powder. If desired, the raw material is completely melted in the rotary kiln. However, it may be advantageous to operate with only partially melting of the raw material, because unmelted material may act as nucleating agents in the subsequent crystallization process. The process according to the invention may be performed using well-known technique from the state of the art, cf. the above-mentioned US patent specification, e.g. by pump¬ ing an aqueous suspension of the raw materials, such as sand, chalk, dolomite, and activators for calcium silicate in the rotary kiln, followed by continuous melting in the rotary kiln. The molten mass may advantageously be crystallized during slow cooling, optionally followed by re-heating. Particu- larly advantageously, the molten mass is transferred to a cold conveyor belt and allowed to stabilize in a layer having a suitable thickness of some centimeters by cooling of the surface with water and/or air to provide slow crystallization. Variation of the photo-luminescent properties of the end product may be obtained by varying the activator used. As mentioned above the activators are selected from the group consisting of oxides, hydroxides and salts of Mn, Pb, Er, Tm, W, Nb, Ti, Cr, Sn and Bi, which elements may be used alone or in a suitable combination. Suitable combinations of these agents can be found by simple tests. The selection will depend upon the desired excitation wavelength and the temperature at which the manufacturing process takes place. As mentioned, combination of various substances is possible and preferred in many cases. In the performance of the method of the invention the activator may be mixed in a slurry of chalk, dolomite and sand. A suitable dosage shall at least amount to 0.2% of the total dry matter. However, in many cases 0.5% will be suitable, and a mixing percent of 5 will be acceptable as the upper limit. Melting, cooling and crystallization are performed according to the above-mentioned methods known per se in connection with the conventional production of partially crystallized glass material. The product produced by the above-mentioned embodiments of the method according to the invention can be obtained in alkali resistant form by suitable composition of the starting materials. This material is particularly suitable as aggregate in a photo-luminescent high strength concrete. According to another aspect of the present invention a photo-luminescent concrete, in particular high strength concrete, is provided. This photo-luminescent concrete is characterized in that it contains the photo-luminescent calcium silicate material according to the present inven¬ tion as an aggregate, preferably together with an aggre¬ gate consisting of non photo-luminescent synthetic wollas- tonite disseminated in a glass matrix. The binder used in this concrete is preferentially Port¬ land cement and optionally a mixture of Portland cement and pozzolans in a ratio providing high strength and work¬ ability. The compressive strength shall preferably be at least 40 MPa. If desired, various additives may be used to improve the workability of the concrete and its strength, e.g. super plastifying agents. According to another aspect of the present invention a photo-luminescent gravel material is provided. This gravel material is characterized in that it consists of the above-mentioned photo-luminescent concrete, preferentially of the above-mentioned photo-luminescent high strength concrete. This gravel material can be produced by crushing e.g. slabs of the above-mentioned photo-luminescent concrete. The gravel material is preferably crushed to fractions of e.g. 2-5 mm, in particular 5-8 mm, but also 8-12 mm and 12-16 mm. However, the gravel material can also be pro¬ duced by breaking uncured photo-luminescent concrete into fragments of desired size and subsequently curing these fragments. This gravel material may also be produced by preparing single nodules or lumps of uncured photo- luminescent concrete of desired size, preferentially below 5 and 15 mm, and subsequently curing these nodules or lumps. For the preparation of the above-mentioned gravel material addition of a photo-luminescent calcium silicate material having a particle size within the interval from about 0 to about 5 mm is preferred. This gravel material is particularly useful as a wear and weather resistant photo-luminescent aggregate for road surfaces or the like based on as well bitumen as concrete. In the following the invention will be illustrated by examples with reference to the drawing, wherein fig. 1-3 show flourescence spectra of selected materials according to the invention. EXAMPLE 1 A raw mixture was prepared as an aqueous well-mixed uni- form suspension of finely comminuted chalk and siliceous sand containing 2.80% by weight Mn0 2 equivalent to 0.126 mole Mn/mol CaO. The analysis of the raw mixture was: Si0 2 : 71%; CaO: 25%; Al 2 0 3 : 2.4%; MgO: 1.7%; Na-,0: 0.6%; K 2 0: 0.8% and Fe 2 0-.: 0.4%, calculated without loss of ignition. This mixture was continuously introduced into a rotary kiln at the upper end of the kiln. The raw materials were thereby heated to the calcination temperature at which the C0 2 was expelled from the carbonate, and subsequently further heated to complete melting at a temperature about 1550 °C. The melt was withdrawn at the lower end of the rotary kiln and quenched in water providing an intermediate product, in the following referred to as the glass fritte. This glass fritte contains a limited number of a small wollas¬ tonite crystals disseminated in a calcium silicate glass matrix, the amount and size of crystalline material depending on the rate of cooling. The glass fritte is a brittle material exhibiting numerous cracks and therefore this intermediate product has only a low compressive strength and weak abrasion resistance. In a second recrystallisation and annealing step this glass fritte was reheated in a rotary kiln to a tempera- ture of 950 °C for 3 hours and to 1050 °C for 1 hour. After this heat treatment the material was withdrawn from the rotary kiln as an end product which was subjected to subsequent cooling. This end product was consisting of photo-luminescent fibro-crystalline wollastonite crystals disseminated in a calcium silicate glass matrix having a low content of alkali metal oxides. It had a whitish colour and exhibited high compressive strength and good abrasion resistance. The product exhibited a distinct red fluorescence when excitated with white light, using a 415 nm primary filter. The emission spectrum for this product measured on a spec- trofotometer when irradiated with a mercury lamp using a 415 nm primary filter is shown in fig. 1. EXAMPLES 2 and 3 Similar products were produced using the same composition as described in Example 1 the only difference being that Mn0 2 was added in an amount of 3.75 and 1.90% by weight in example 2 and 3, respectively, corresponding to Mn/CaO mole ratios of 0.169 and 0.085, respectively. The end products were also consisting of a photo-lumines¬ cent fibro-crystalline wollastonite crystals disseminated in a calcium silicate glass matrix having a low content of alkali metal oxides. They also had a whitish colour and exhibited high compressive strength and good abrasion resistance. Also these products exhibited a distinct red fluorescence when excitated with white light, using a 415 nm primary filter. The emission spectra for these products are shown in fig. 1. EXAMPLES 4-6 Similar products were produced using the same composition as described in Example 1 the only difference being that a mixture of Mn and Ti was used as activator. The amounts of added Mn0 2 and Ti0 2 are indicated in Table 1. TABLE 1 Example No. MnO-,, % τi0 2 ' % Mn/CaO, MR Ti/CaO, MR MR = molar ratio The end products were also consisting of photo-luminescent fibro-crystalline wollastonite crystals disseminated in a calcium silicate glass matrix having a low content of al¬ kali metal oxides. They had a whitish colour and exhibited high compressive strength and good abrasion resistance. These products exhibited an orange fluorescence when excitated with white light, using a 415 nm primary filter. The emission spectra for these products are shown in fig. 2. EXAMPLE 7 A similar product was produced using the same composition as described in Example 1 the only difference being that Nb was used as activator, added as Nb-,0-. in an amount of 1.65% by weight, corresponding to a Nb/CaO mole ratio of 0.082. The end product had the same texture as the products described in example 1-6. It had a whitish colour and exhibited high compressive strength and good abrasion resistance. This product exhibited when observed in a fluorescence mircoscope a weak greenish fluorescence when excitated with light from a mercury lamp, using a 415 nm primary filter. The emission spectrum for this product is shown in fig. 3. EXAMPLE 8 A photo-luminescent high strength concrete having the following composition was produced: White portland cement 630 kg Miσrosilica 70 kg (Filter dust from electrothermal production of Si; Si0 2 content: about 95%; specific surface: about 25 m 2 /g) Water 190 kg Sikamentβ FF 28 kg (Super plastifying agent, marketed by SIKA Beton A/S) Photo-luminescent calcium silicate material according to Example 1 115 kg Concrete sand (0-3 mm) 285 kg Synthetic wollastonite (0-5 mm) 950 kg The material was mixed in a paddle mixer, with premixing of cement, microsilica and aggregate for two minutes. Then the water was added, with mixing for one minute. After addition of the super plastifying agent mixing was per¬ formed for another four minutes. The concrete mixture was cast as small slabs having the dimensions 200 x 200 x 150 mm, which was hardened at a relative air moisture of about 100% at about 20°C for 28 days. Further, a photo-luminescent gravel material was produced from these slabs: The slabs described above were crushed in a jaw crusher, followed by additional crushing in a cone crusher. The crushed material was then sorted according to size in an ordinary gravel sorting system in fractions of 2-5 mm, 5-8 mm, 8-12 mm and >12 mm.

Claims: P a t e n t C l a i m s : 1. A photo-luminescent calcium silicate material, c h a r a c t e r i z e d by comprising photo-luminescent fibro-crystalline wollastonite crystals activated with an activator in a quantity effective for ensuring photo- luminescence, said activator comprising at least one element selected from the group consisting of Mn, Pb, Er, Tm, W, Nb, Ti, Cr, Sn, and Bi, and disseminated in a calcium silicate glass matrix having a low content of alkali metal oxides. 2. A photo-luminescent calcium silicate material accord- ing to claim 1, c h a r a c t e r i z e d in that the material contains 30-70% by weight photo-luminescent fibro-crystalline wollastonite crystals. 3. A photo-luminescent calcium silicate material accord- ing to claims 1-2, c h a r a c t e r i z e d in that material has the following analysis: a CaO content of about 20-30% by weight, a Si0 2 content of about 65-80% by weight, an A1 2 0 3 content less than about 5% by weight, an alkali metal oxide content less than about 5% by weight, and a mole ratio activator/CaO within the range 0.0005- 0.35, preferably within the range 0.0010-0.25. 4. A photo-luminescent calcium silicate material accord¬ ing to claims 1-3, c h a r a c t e r i z e d in that the activator provides a photo-luminescent wollastonite which emits visible light when excitated by photons having a wavelength greater than 315 nm, in particular within the interval 315-400 nm. 5. A photo-luminescent calcium silicate material accord¬ ing to claims 1-4, c h a r a c t e r i z e d in that the photo-luminescent fibro-crystalline wollastonite crystals are activated with Mn as an activator in an amount of 0.044-0.20 mole Mn/mole CaO. 6. A photo-luminescent calcium silicate material accord- ing to claims 1-5, c h a r a c t e r i z e d in that the photo-luminescent fibro-crystalline wollastonite crystals are activated with Mn and Ti as activators, Mn in an amount of 0.044-0.20 mole Mn/mole CaO and Ti in an amount of 0.025-0.15 mole Ti/mole CaO. 7. A photo-luminescent calcium silicate material accord¬ ing to claims 1-4, c h a r a c t e r i z e d in that the photo-luminescent fibro-crystalline wollastonite crystals are activated with Nb as an activator in an amount of 0.005-0.20 mole Nb/mole CaO. 8. A method of producing a photo-luminescent calcium silicate material according to claims 1-7, c h a r a c ¬ t e r i z e d by introducing a raw material comprising a mixture of calcareous and siliceous materials and activa¬ tors in a quantity suitable for ensuring photo-lumines¬ cence, selected from the group consisting of oxides, hydroxides and salts of Mn, Pb, Er, Tm, W, Nb, Ti, Cr, Sn, and Bi, into a rotary kiln; melting said mixture at least partially; withdrawing the at least partially melted mixture from the rotary kiln; and cooling, preferably quenching the withdrawn material to a partially crystal¬ lized product comprising photo-luminescent fibro- crystalline wollastonite crystals disseminated in a calcium silicate glass matrix. 9. A method according to claim 8, c h a r a c t e r ¬ i z e d in that the cooled, partially crystallized material withdrawn from the rotary kiln is subjected to recrystallization in a recrystallization and annealing step at a temperature within the range from about 900 °C to about 1100 °C for a period of time from about 0.5 to about 4 h. 10. A method according to claims 8-9, c h a r a c - t e r i z e d in that the raw material contains amorphous carbon in an amount corresponding to 2-3 times the stoichiometric amount needed for reducing an activator to a desired valency. 11. A method according to claims 8-10, c h a r a c ¬ t e r i z e d in that the raw mixture has the following analysis: a CaO content of about 20-30% by weight, a SiO-, content of about 65-80% by weight, an Al 2 0 3 content less than about 5% by weight, an alkali metal oxide content less than about 5% by weight, and a mole ratio activator/CaO within the range 0.0005-0.35, preferably within the range 0.0010-0.25. 12. A method according to claims 8-11, c h a r a c - t e r i z e d in that the activator is chosen to provide a photo-luminescent wollastonite which emits visible light when excitated by photons having a wavelength greater than 315 nm, in particular within the interval 315-400 nm. 13. A method according to claims 8-12, c h a r a c ¬ t e r i z e d in that the raw material contains Mn as an activator in an amount of 0.044-0.20 mole Mn/mole CaO. 14. A method according to claims 8-13, c h a r a c - t e r i z e d in that the raw material contains Mn and Ti as activators, Mn in an amount of 0.044-0.20 mole Mn/mole CaO and Ti in an amount of 0.025-0.15 mole Ti/mole CaO. 15. A method according to claims 8-12, c h a r a c ¬ t e r i z e d in that the raw material contains Nb as an activator in an amount of 0.005-0.20 mole Nb/mole CaO. 16. A method according to claims 8-15, c h a r a c ¬ t e r i z e d in that a part of the raw material is injected from the lower end of the kiln. 17. A method according to claim 16, c h a r a c t e r ¬ i z e d in that at least part of the raw material, preferably of that injected from the lower end of the kiln, consists of filter dust collected in a filter arranged in connection with the rotary kiln. 18. A photo-luminescent concrete, in particular high strength concrete, c h a r a c t e r i z e d in that it contains a photo-luminescent calcium silicate material according to claims 1-7 as an aggregate. 19. A photo-luminescent gravel material, c h a r a c ¬ t e r i z e d in that it consists of photo-luminescent concrete material according to claim 18. A photo-luminescent calcium silicate material, concrete and gravel material containing it and a method of producing a photo-luminescent calcium silicate material ABSTRACT A photo-luminescent calcium silicate material, comprising photo-luminescent fibro-crystalline wollastonite crystals activated with an activator comprising at least one element selected from the group consisting of Mn, Pb, Er, Tm, W, Nb, Ti, Cr, Sn, and Bi, and disseminated in a calcium silicate glass matrix having a low content of alkali metal oxides. This material is produced by: Introducing a raw material comprising a mixture of cal¬ careous and siliceous materials and activators selected from the group consisting of oxides, hydroxides and salts of the above-mentioned elements into a rotary kiln; melting said mixture at least partially; withdrawing this mixture from the rotary kiln; cooling the withdrawn material to a partially crystallized product; and if desired subjecting this product to further crystallization in a recrystallization step. A photo-luminescent concrete containing the above- mentioned photo-luminescent material as aggregate as well as a photo-luminescent gravel material consisting of the above-mentioned photo-luminescent concrete.

Inventors: FUNDAL ERLING, KROGH STEEN M, FUNDAL, ERLING, KROGH, STEEN, M.
Applicants: KROGH STEEN M, KROGH, STEEN, M.
Application year: 1991
Main classification: C04B14
IPC codes: C04B14, C09K11