Method of preparing the construction material with the addition of a mixture of mineral dusts and post-industrial dusts

Technical Field

[0001 ] The present invention relates to the method of preparing the construction material with the addition of mineral dusts and post-industrial dusts.

Background Art

[0002] In prior art, are known methods for the preparation of building materials, which as raw material, comprise waste materials. European Patent Application EP2660288 discloses a process for producing panels of printed circuit boards of electronic systems ground into dust with the addition of, among the others, montmorillonite, as an anti-flammable supplement.

[0003] British Patent Application GB2067174 discloses, among others, inorganic rigid foam with a cellular structure, comprising montmorillonite, and its use as construction material and refractory material.

[0004] Chinese Patent Application CN104386953A discloses the fire resistant, thermal-insulating mortar, comprising 46-56 weight parts of

montmorillonite, 40-45 weight parts of rice husks dust.

[0005] Russian Patent RU No. 2173674 discloses a process for the preparation of swollen silicates, which consists of mixing water glass, crushed foam silicate, mineral filler, oleic acid and a saturated aqueous solution of sugar and water. The mixture undergoes granulation and, after initial drying-up of the granules, is sintered in moulds.

[0006] The main disadvantages of the above-described processes comprise the use of scarce and expensive substrates or alimentary raw materials, which adversely affects the cost of manufacturing the final product. Furthermore, due to the used raw materials, the obtained materials will have low mechanical resistance, and in contact with high temperature (e.g. during thermal treatment at the stage of production or as a result of fire in a building in which such materials were used), harmful gases will be released into the environment.

Disclosure of Invention [0007] The object of the invention is to provide a process for preparing a construction material with improved compressive resistance at a low cost of manufacture. The object of the invention is also to eliminate the problem of emitting the harmful gases while contacting the construction material with high temperature both at the stage of producing the material, and in case of fire in object, in which such construction materials were used.

[0008] The present invention relates to a method for preparing the construction material wherein an aqueous solution of vitreous sodium silicates, amorphous silica, post-industrial wastes and mineral wastes are mixed to produce a dense sol, which is dried, crushed and annealed, characterised in that 27-16 parts of amorphous silica and 31 -8 parts of a mixture of post- industrial dusts and mineral dusts are added to 68-47 parts of sodium water glass with a modulus M of 2.5-3.5 and a density of 1 .35-1 .45 g/cm ³ , wherein the mass ratio of post-industrial dusts to mineral dusts is from 1 :3 to 3:4 and, optionally, is added to 6 parts of water, then the ingredients are mixed to produce a homogenous dense sol, then the sol is subjected to drying at temperature of 75-90°C for a period of approximately 2 hours until gelation of the sol, and then the dried gel is subjected to mechanical crushing into pieces having the size of beans, then a steel mould is filled with crushed gel and thermal treatment is conducted in an oven to obtain a construction material of the shape determined by the mould after complete cooling, wherein the thermal treatment is conducted in a single step, wherein the rise of the temperature occurs at a rate of 10 min until the temperature is obtained, and then the mould is annealed at a temperature of 320-425°C for a period of 90 minutes. The finished construction material adopts the shape of the mould in which it was annealed, for example of a panel, disc, cylinder, tube, cube and the like.

[0009] During annealing, the water bound to the gel is released in the form of superheated steam, which causes foaming of the material. The role of Na ^t¬ ions, originating from the water glass, consists of binding hydroxyl groups (OH-) and free water molecules. In the process of thermal gelation, hydrated molecules of NaOhPnh O, developed in the form of stable clusters, are formed. These clusters are closed in the pores of the forming SiO2 matrix and retain water until the initial step of formation of a rigid silica structure. Upon further temperature increase, (NaOH)x*nH2O

clusters undergo decomposition to form sodium oxide and remaining molecules of water, which also transforms into steam. The superheated steam causes further foaming and distension of the gel block to form foam glass in the form of a volumetric porous block.

[0010] Optionally, in the process of the invention, the addition of boric acid H3BO3 in an amount from 1 to 5 g of the acid per 100 g of dust mixture is applied. The addition of boric acid ensures homogeneity of foaming, and thus a uniform distribution and pore size throughout the entire volume of the produced material block.

[001 1 ] Preferably, in the process of the invention, amorphous silica of a maximum bulk density of 150 g/dm ³ and content of S1O2 at minimum of 80%, hereinafter: material A, is used.

[0012] Preferably, in the process of the invention, a mixture of: amorphous silica - material A, post-industrial dusts and mineral dusts containing 77.7-89.8% of SiO ₂ ; 1 .05-9.14% of AI2O3; 0.10-3.30% of Fe ₂ O ₃ ; 0.1 1 -1 .64% of MgO; 0.15-8.6% of CaO; 0.12-0.33% of K ₂ O; 0.10-0.33% of Na ₂ O, is used.

[0013] Preferably, mineral dusts used in the process of the invention are selected from a group consisting of:

material B, which is a dusty micro- and nanomaterial, containing montmorillonite, also known as bentonite, Al2[(OH)2Si ₄ Oio] ^» nH2O, or hydrated aluminum hydrosilicate, which contains metals in the form of oxides of the following oxide percentage composition: S1O2 67%, AI2O3 19.5%, Fe ₂ O ₃ 2.5%, MgO 3.5%, CaO 2.2% , Na ₂ O 0.4%, P2O5 0.1 % , TiO ₂ 0.2% , K ₂ O 0.5% and

material D, which is diatomaceous earth with average oxide levels of:

89.5% of SiO2; 4.1 % of AI2O3; 1.5% of Fe2O3; 0.6% of CaO; 0.3% of

MgO and 4% of the remaining oxides, respectively.

[0014] Preferably, in the process of the invention, a mixture of post-industrial dusts having a particle size from 25 μιτι to approximately 25 nm is used.

[0015] Preferably, post-industrial dusts used in the process of the invention are selected from a group consisting of material S, which is an post-industrial waste in a dusty form, preferably micro-granular silica dust comprising: min. 85-90% of S1O2, 0.5-2.5% of Fe ₂ O ₃ , 0.1 -1 % of CaO, 0.1-1.5% of AI2O3, such as dust containing 90% of S1O2 and having a specific surface area of 15-35 m ² /g and a bulk density of 350 kg/m ³ or another dust having a bulk density of 450-650 kg/m ³ , as well as sludge - a 50:50 suspension of dust in water, wherein 1 m ³ of the sludge contains 700 kg of dust;

material K, which is an post-industrial waste in the form of a by-product of combustion of an organic material, preferably coal, preferably lignite, wherein the content of oxides in the combustion by-product is: S1O2 76- 20%; CaO 45-0.2%; K ₂ O 8-0.01 %; SO ₃ 15-0.01 %; P2O5 10-0.01 %; MgO 15-0.01 %; Fe ₂ O ₃ 27-0.01 %; AI2O3 40-5%; Na ₂ O 8-0.01 %; TiO ₂ 8-0.01 %, respectively.

[0016] The process for preparing a construction material of the invention allows using of waste materials, which are environmentally burdensome, solving the problem of post-industrial dust disposal. The partial replacement of an expensive raw material, which is an amorphous silica - material A - with a mixture of post-industrial dust (K, S) and mineral dust (B, D), also allows for the reduction of the annealing temperature, which contributes to decreasing the manufacturing cost of the construction material produced using the process of the invention. Furthermore, as shown in the

embodiments, the construction material produced by the process of the invention has improved compressive strength properties, mainly thanks to the use of appropriate mass ratios of post-industrial dusts to mineral dusts, which equal from 1 :3 to 3:4.

[0017] The present invention also relates to the use of the construction material produced by the process of the invention in civil engineering, especially as a construction material in buildings, where a high compressive strength of a construction material is required, for example in tower blocks.

[0018] The construction material obtained by the process of the invention has a high fire resistance in the range of 835-900°C, and in case of the contact with a high temperature (e.g. as a result of a fire in a building in which the material of the invention was used for the construction), it melts without releasing harmful gases into the environment. Because of these specific properties, the construction material produced in process of the invention can be used in public utility buildings, such as sports facilities, hospitals, schools, kindergartens or other facilities, where many people gather at the same time.

[0019] The invention is illustrated in more detail in embodiments that do not limit the scope thereof.

[0020] Example 1

[0021] 950 g (18 parts) of amorphous silica - material A, 400 g (8 parts) of

mineral dust - material B, and 300 g (6 parts) of post-industrial dust - material S, and 200 ml (4 parts) of water were sequentially added to 2400 ml (64 parts) of sodium water glass with continuous mechanical stirring. The raw materials were mixed to obtain a homogenous, dense mixture, which was dried at 90°C for 2 hours. After this time, a hard gel was obtained, which was mechanically crushed into pieces having the size of beans. A mould was then filled with the crushed gel, and the mould was closed and placed in an oven, in which the temperature was increased at a rate of 10 min until a final temperature of 420°C was obtained. After the temperature of 420°C was reached in the oven, it was maintained for 1.5 h, and then the oven was turned off. Gradual cooling of the mould occurred in the oven. After complete cooling, the construction material was removed from the mould in the form of a block having dimensions of (60 x 320 x 320) mm.

[0022] Example 2

[0023] 900 g (16 parts) of amorphous silica - material A, 600 g (10 parts) of

mineral dust - material B, and 600 g (10 parts) of post-industrial dust - material S, and 200 ml (4 parts) of water were sequentially added to 2500 ml (60 parts) of sodium water glass with continuous mechanical stirring. The raw materials were mixed to obtain a homogenous, dense mixture, which was dried at 90°C for 2 hours. After this time, a hard gel was obtained, which was mechanically crushed into pieces having the size of beans. A mould was then filled with the crushed gel, and the mould was closed and placed in an oven, in which the temperature was increased at a rate of 10 min until a final temperature of 400°C was obtained. After the temperature of 400°C was reached in the oven, it was maintained for 1.5 h, and then the oven was turned off. Gradual cooling of the mould occurred in the oven. After complete cooling, the construction material was removed from the mould in the form of a block having dimensions of (60 x 320 x 320) mm.

[0024] Example 3

[0025] 850 g (17 parts) of amorphous silica - material A, 550 g (11 parts) of

mineral dust - material B, and 200 g (4 parts) of post-industrial dust - material S, were sequentially added to 2500 ml (68 parts) of sodium water glass with continuous mechanical stirring. The raw materials were mixed to obtain a homogenous, dense mixture, which was dried at 75°C for 2 hours. After this time, a hard gel was obtained, which was mechanically crushed into pieces having the size of beans. A mould was then filled with the crushed gel, and the mould was closed and placed in an oven, in which the temperature was increased at a rate of 10 min until a final temperature of 425°C was obtained. After the temperature of 425°C was reached in the oven, it was maintained for 1.5 h, and then the oven was turned off. Gradual cooling of the mould occurred in the oven. After complete cooling, the construction material was removed from the mould in the form of a block having dimensions of (60 x 320 x 320) mm.

[0026] Example 4 Reference sample

[0027] 1250 g (26 parts) of amorphous silica - material A, and 125 g (3 parts) of water and 15 g (0.3 parts) of boric acid were sequentially added to 2500 ml (71 parts) of sodium water glass with continuous mechanical stirring. The raw materials were mixed to obtain a homogenous, dense mixture, which was dried at 90°C for 2 hours. After this time, a hard gel was obtained, which was mechanically crushed into pieces having the size of beans. A mould was then filled with the crushed gel, and the mould was closed and placed in an oven, in which the temperature was increased at a rate of 10 min until a final temperature of 450°C was obtained. After the temperature of 450°C was reached in the oven, it was maintained for 1.5 h, and then the oven was turned off. Gradual cooling of the mould occurred in the oven. After complete cooling, the material was removed from the mould in the form of a block having dimensions of (60 x 320 x 320) mm.

[0028] Example 5

[0029] 850 g (18 parts) of amorphous silica - material A, 750 g (16 parts) of

mineral dust - material B, and 300 ml (6 parts) of water and 15 g (0.3 parts) of boric acid were sequentially added to 2100 ml (60 parts) of sodium water glass with continuous mechanical stirring. The raw materials were mixed to obtain a homogenous, dense mixture, which was dried at 85°C for 2 hours. After this time, a hard gel was obtained, which was mechanically crushed into pieces having the size of beans. A mould was then filled with the crushed gel, and the mould was closed and placed in an oven, in which the temperature was increased at a rate of 10 min until a final temperature of 320°C was obtained. After the temperature of 320°C was reached in the oven, it was maintained for 1.5 h, and then the oven was turned off. Gradual cooling of the mould occurred in the oven. After complete cooling, the construction material was removed from the mould in the form of a block having dimensions of (60 x 320 x 320) mm.

[0030] Example 6

[0031] 1050 g (16 parts) of amorphous silica - material A, and 2100 g (31 parts) of combustion by-products - material K, and 400 ml (6 parts) of water were sequentially added to 2300 ml (47 parts) of sodium water glass with continuous mechanical stirring. The raw materials were mixed to obtain a homogenous mixture, which was placed in a mould. The filled mould was maintained at 250°C for 1 hour, which was followed by cooling to room temperature for a subsequent 2 hours. The mould was then heated for 4 hours until a temperature of 395°C was reached and was maintained at this temperature for 1 hour. The mould was then cooled to room

temperature for a subsequent 4 hours. After complete cooling, the construction material was removed from the mould in the form of a block having dimensions of (60 x 320 x 320) mm.

[0032] Example 7 [0033] 850 g (17 parts) of amorphous silica - material A, and 900 g (18 parts) of diatomaceous earth - material D, were sequentially added to 2400 ml (65 parts) of sodium water glass with continuous mechanical stirring. The raw materials were mixed to obtain a homogenous, dense mixture, which was dried at 90°C for 2 hours. After this time, a hard gel was obtained, which was mechanically crushed into pieces having the size of beans. A mould was then filled with the crushed gel, and the mould was closed and placed in an oven, in which the temperature was increased at a rate of 10 min until a final temperature of 400°C was obtained. After the temperature of 400°C was reached in the oven, it was maintained for 1.5 h, and then the oven was turned off. Gradual cooling of the mould occurred in the oven. After complete cooling, the construction material was removed from the mould in the form of a block having dimensions of (60 x 320 x 320) mm.

[0034] Example 8

[0035] 900 g (21 parts) of amorphous silica - material A, and 350 g (8 parts) of post-industrial dust - material S, and 200 ml (4 parts) of water were sequentially added to 2100 ml (67 parts) of sodium water glass with continuous mechanical stirring. The raw materials were mixed to obtain a homogenous, dense mixture, which was dried at 90°C for 2 hours. After this time, a hard gel was obtained, which was mechanically crushed into pieces having the size of beans. A mould was then filled with the crushed gel, and the mould was closed and placed in an oven, in which the temperature was increased at a rate of 10 min until a final temperature of 350°C was obtained. After the temperature of 350°C was reached in the oven, it was maintained for 1.5 h, and then the oven was turned off.

Gradual cooling of the mould occurred in the oven. After complete cooling, the construction material was removed from the mould in the form of a block having dimensions of (60 x 320 x 320) mm.

[0036] Example 9

[0037] 900 g (18 parts) of amorphous silica - material A, and 900 g (18 parts) of diatomaceous earth - material D, were sequentially added to 2250 ml (64 parts) of sodium water glass with continuous mechanical stirring. The raw materials were mixed to obtain a homogenous, dense mixture, which was dried at 85°C for 2 hours. After this time, a hard gel was obtained, which was mechanically crushed into pieces having the size of beans. A mould was then filled with the crushed gel, and the mould was closed and placed in an oven, in which the temperature was increased at a rate of 10 min until a final temperature of 425°C was obtained. After the temperature of 425°C was reached in the oven, it was maintained for 1.5 h, and then the oven was turned off. Gradual cooling of the mould occurred in the oven. After complete cooling, the construction material was removed from the mould in the form of a block having dimensions of (60 x 320 x 320) mm.

[0038] Example 10

[0039] 1300 g (26 parts) of amorphous silica - material A, and 450 g (9 parts) of diatomaceous earth - material D, and 200 ml (4 parts) of water were sequentially added to 2200 ml (61 parts) of sodium water glass with continuous mechanical stirring. The raw materials were mixed to obtain a homogenous, dense mixture, which was dried at 90°C for 2 hours. After this time, a hard gel was obtained, which was mechanically crushed into pieces having the size of beans. A mould was then filled with the crushed gel, and the mould was closed and placed in an oven, in which the temperature was increased at a rate of 10 min until a final temperature of 400°C was obtained. After the temperature of 400°C was reached in the oven, it was maintained for 1.5 h, and then the oven was turned off.

Gradual cooling of the mould occurred in the oven. After complete cooling, the construction material was removed from the mould in the form of a block having dimensions of (60 x 320 x 320) mm.

[0040] Example 11

[0041] 1000 g (21 parts) of amorphous silica - material A, and 600 g (13 parts) of diatomaceous soil - material D, and 200 ml (4 parts) of water were sequentially added to 2100 ml (62 parts) of sodium water glass, at continuous mechanical stirring. The raw materials were mixed to obtain a homogenous, dense mixture, which was dried at 90°C for 2 hours. After this time, a hard gel was obtained, which was mechanically crushed into pieces having the size of beans. A mould was then filled with the crushed gel, and the mould was closed and placed in an oven, in which the temperature was increased at a rate of 10 min until a final temperature of 400°C was obtained. After the temperature of 400°C was reached in the oven, it was maintained for 1.5 h, and then the oven was turned off.

Gradual cooling of the mould occurred in the oven. After complete cooling, the construction material was removed from the mould in the form of a block having dimensions of (60 x 320 x 320) mm.

[0042] Example 12

[0043] 1300 g (27 parts) of amorphous silica - material A, 450 g (9 parts) of post- industrial dust - material S, and 200 ml (4 parts) of water were sequentially added to 2100 ml (60 parts) of sodium water glass with continuous mechanical stirring. The raw materials were mixed to obtain a

homogenous, dense mixture, which was dried at 87°C for 2 hours. After this time, a hard gel was obtained, which was mechanically crushed into pieces having the size of beans. A mould was then filled with the crushed gel, and the mould was closed and placed in an oven, in which the temperature was increased at a rate of 107min until a final temperature of 400°C was obtained. After the temperature of 400°C was reached in the oven, it was maintained for 1.5 h, and then the oven was turned off.

Gradual cooling of the mould occurred in the oven. After complete cooling, the construction material was removed from the mould in the form of a block having dimensions of (60 x 320 x 320) mm.

[0044] Example 13 Reference sample

[0045] 350 g (6 parts) of ground sand and 2000 ml (35 parts) of water were

sequentially added to 2100 ml (59 parts) of sodium water glass with continuous mechanical stirring. The raw materials were mixed to obtain a homogenous, dense mixture, which was dried at 90°C for 2 hours. After this time, a hard gel was obtained, which was mechanically crushed into pieces having the size of beans. A mould was then filled with the crushed gel, and the mould was closed and placed in an oven, in which the temperature was increased at a rate of 107min until a final temperature of 400°C was obtained. After the temperature of 400°C was reached in the oven, it was maintained for 1.5 h, and then the oven was turned off.

Gradual cooling of the mould occurred in the oven. After complete cooling, the material was removed from the mould in the form of a block having dimensions of (60 x 320 x 320) mm.

[0046] Assessment of parameters of the samples of examples 1 -13.

For all the samples of examples 1 -13, a measurement of compressive resistance, according to PN-EN 826: 2013-07, was performed. For samples 1 , 2, 3 and 4, the additional investigation of normal fire resistance according to PN-EN 993-12:2000 was conducted. The results were obtained for the following samples: 1 - 845°C, 2 - 835°C, 3 - 900°C and 4 - 1050°C, respectively. The results of compressive resistance are presented in Table 1 , which also contains the annealing temperature as an important differentiating parameter.

[0047] Table 1

CONCLUSIONS:

Based on the results of endurance tests, it can be observed that a partial replacement of amorphous silica with a mixture of post-industrial dusts and mineral dusts at the specific mass ratio from 1 :3 to 3:4, results in a significant increase of the compressive resistance of the obtained materials. It can also be noticed that a partial replacement of amorphous silica with only post-industrial dusts or mineral dusts does not give the same results. As appears from examples 5 and 8, the use of too low annealing temperature leads to deterioration in the compressive resistance of the obtained materials.

[0049] The best results were obtained from the samples of examples 1 and 3, consisting of mixtures of amorphous silica - material A, mineral dust - material B, and post-industrial dusts - material S, mixed at determined mass ratio from 9:4:3 to 17:1 1 :4.

[0050] The survey of fire resistance and compressive resistance of the samples, demonstrates that the process of the invention, wherein amorphous silica is partially replaced by post-industrial wastes and mineral wastes, leads to a construction material of good fire resistance and good compressive resistance, at significantly reduced production costs. Moreover, during the examination of normal fire resistance of samples prepared by the process of the invention, no release of harmful gases during contact with high temperature was observed.