GB2109366A - A method for producing a fiber-reinforced gypsum-based hardened body - Google Patents

Abstract

A method for producing a gypsum based hardened body in which a main raw material composed of gypsum dihydrate, slag and a reaction- promoting agent is added with a reinforcing fiber other than asbestos, bentonite or bentonite and mica to water, and is cured. The obtained gypsum based hardened body is, in spite of using no asbestos, in its strength and length change similar to or superior to conventional gypsum based hardened bodies containing asbestos as a reinforcing fiber.

Description

SPECIFICATION A method for producing a fiber-reinforced gypsum-based hardened body The present invention relates to a method for producing a no-asbestos gypsum based hardened body which has a high strength and is small in length change.

Conventionally, in the production of such building materials as boards, asbestos has been mostly used as a reinforcing fiber. In these cases, the object of use of asbestos was to improve a bending strength, an impact strength, a weather resistance and a fire resistance of the produced board and further to secure a proper filterability of a slurry of these raw materials at sheet forming. However, recently owing to a strengthening of antipollution regulation, deasbestosization is now being demanded. In some cases, use of reinforcing fibers other than asbestos can substitute the function of asbestos to some degree. However, in the cases of building materials mainly composed of gypsum and slag, some defects are found, i. g. a strength is not sufficient and sheet forming becomes difficult by excessive filterability of a slurry of these materials.

In general, bentonite may be used as a regulating agent for such an excessive filterability as described above, but in that case, the use of bentonite is exclusively limited to regulate the filterability and has rather bad influences on other properties. Therefore, the use of bentonite has been thought to be unsuitable.

The present invention has been devised by overcoming the above mentioned defects of conventional methods which use asbestos as a reinforcing fiber.

The object of the present invention is to provide a method for producing a fiber-reinforced gypsum base hardened body which has a high strength and is small in length change in spite of use of no asbestos.

According to the present invention, there is provided: A method for producing a fiber-reinforced gypsum base hardened body comprising adding a reaction promoting agent to a mixture of gypsum dihydrate and slag in weight ratio of 3:7-7:3 to make a main raw material, and adding 0.1 - 1 5 weight % reinforcing fiber, 3 - 20 weight % bentonite and a proper quantity of water to said main raw material, and making said raw main material thus added with said reinforcing fiber, bentonite and water mixed, shaped and cured.

In the present invention, 2 - 10 weight % mica together with 3 - 20 weight % bentonite can be added to the main raw material.

The present invention will be better understood from the following detailed description.

In the conventional method for producing a gypsum base hardened body in which a main raw material compoded a gypsum digydrate and slag is added with a small quantity of a reaction promoting agent, the added reaction promoting agent accelerates a dissolution of such components as CaO, SiO2, A/203 from the slag and at the early stage of the reaction, ettringite is formed by a reaction of these dissolved components with the gypsum dihydrate, and as the reaction proceeds, C-S-H gel is formed, thereby there is obtained a hardened body having a high strength.

On the other hand, in the present invention, as bentonite is further added to these materials of the above conventional method, the slag is made to react with the bentonite and at the early stage of the reaction, there is formed C4AG,g (this material becomes subsequently ettringite by reaction with the gypsum dihydrate), and as the reaction proceeds, there is formed C-S-H gel.

Therefore, in the present invention, even when a reinforcing fiber other than asbestos is used, there can be obtained a hardened body having a required high strength by multiplied effects of these reactions of the present invention with those of the cónventional method.

Further, according to the measurement of heat liberation by hydration, the appearance of the second heat liberation peak of the present invention in which bentonite is added is remarkably different from that of the conventional method in which no bentonite is added, so in the system of the present invention, the addition of the bentonite seems to bring about not only a physical reinforcement effect, but also a chemical one.

The bentonite used in the present invention contains natural sodium-or calcium- bentonite, and the size thereof is in the range of 250 mesh - 350 mesh. When the size of the bentonite is over 250 mesh, hydration velocity becomes unsuitably slow. The added quantity of the bentonite is in the range of 3 weight % - 20 weight %, preferably in the range of 5 weight % - 10 weight %. When the added quantity of the bentonite is under 3 weight %, no addition effect appears, and when over 20 weight %, the filterability becomes low and the length change is increased.

The gypsum dihydrate slag hardened body of the present invention manufactored by adding bentonite in the range as described above is a hardened body having a remarkably high strength. On the other hand, the length change by immersion in water test tends to increase a little, as compared with that of the conventional method in which no bentonite is added.

Therefore, in the present invention, by adding mica together with bentonite, there can be controlled the increase of the length change of the obtained hardened body. The added quantity of the mica is in the range of 2 weight % - 10 weight %, preferably in the range of 3 weight % - 7 weight % of the main raw material. When the added quantity of the mica is under 2 weight %, the addition effect is low, and when over 10 weight %, the strength is subject to a bad influence. The reason why the length change can be controlled by addition of the mica is not yet clear. The mica used in the present invention contains natural mica, and the size thereof is preferably under 300 mesh.

In the present invention, as the reaction promoting agent which constitutes the main raw material with gypsum dihydrate and slag, there are preferable alkali and alkaline salt substances, aluminum sulfate containing substances, and phosphoric acids and phosphate substances. As the alkali and alkaline salt substances are used caustic soda, caustic potash, slaked lime, calcium oxide, sodium sulfate, potassium sulfate and cement, and as the aluminum sulfate containing substances are used hydrous aluminum sulfate, aluminum sulfate anhydride, sodium aluminum sulfate, and potassium aluminum sulfate. Further, as the phosphoric acids and the phosphate substances are used orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, ammonium phosphate, calcium dihydrogenphosphate.The added quantity of these reaction promoting agents is small and in the range of about 1 - 2 weight % of the sum of the gypsum dihydrate and the slag.

In the present invention, as described above, since at the early stage of the reaction, C4AH,g is formed by reaction of the slag with the bentonite and the C4AH,g reacts subsequently with the gypsum dihydrate to be ettringite, pH of the raw material mixture is lower than that of the case in which cement is used and is in the range of about 10.5 - 11.0. Thus, in the present invention, corrosion of glass fiber is smaller, so glass fiber can be also used as a reinforcing fiber. This is one of the advantages of the present invention. As a reinforcing fiber other than glass fiber, there are preferably styrol fiber, carbon fiber, nylon fiber, polypropylene fiber, and pulp. Added quantities of these reinforcing fibers are in the range of 0.1 weight % - 1 5 weight % of the main raw material.

In the present invention, compounded raw material is added with a proper quantity of water to be mixed, shaped and natural-cured or steam-cured below 90"C into a hardened body. For shaping, there can be used extruding machine, Hatschek-machine and wire net forming machine respectively.

Thus, the present invention provides a method for producing a fiber reinforced gypsum base hardened body by using gypsum dihydrate, slag, and a reinforcing fiber other than asbestos and adding bentonite or bentonite and mica, which is no asbestos and is in strength and length change similar to or superior to those of the conventional asbestos reinforced gypsum hardened body, therefore it is very effective for antipollution countermeasure.

The present invention will be understood more readily with reference to the following examples. The examples, however, are intended to illustrate the present invention and are not construed to limit the scope of the present invention. The gypsum dihydrate used in the examples is a by-product gypsum obtained by exhaust gas desulfurization and the slag is crushed water granulated slag of blast furnace having a specific surface area of 3,800 cm2/g.

Further, in the examples, the term % refers to weight %.

Reference Example 1 A mixture of 70% gypsum dihydrate and 30 % slag is added with slaked lime and aluminum sulfate each 1.5% (1.5 % to the mixture 100 %, hereinafter referred to A) to be a main raw material. The main raw material is added with 0-20% bentonite (0-20 % to the sum of the main raw material and bentonite, hereinafter referred to B) to be a compounded raw material.

The compounded raw material is added with about 32% water to be mixed. After mixing, coagulation test based on cement physical test of JIS-R 5201 (1964) is carried out on the compounded raw material, and the results are shown in Table 1 as examples No. 1- No. 5.

Table 1

sample NO, 1 2 3 5 elag (96) 30 29.1 28.5 27.0 24.0 ba diyarats(%) 70 67.9 66,5 63.0 56.0 q e;gpsxm slakea rims (6) 1 1,5 1.5 15 15 15 o a alumupi sulfate(%) 1 1.5 1.5 1.5 1.4 ?i s o o O thourwminute) 150 11-30 10-55 12-10 13-40 As table 1 shows, the coagulation velocity of the cases where bentonite is added is larger than that of the case where no bentonite is added. When the added quantity of bentonite is 5%, the coagulation belocity is maximum.

Reference Example 2 A mixture of 50% gypsum dihydrate and 50 % slag is added with slaked lime and aluminum sulfate each 1.5% (A) to be a main raw material. The main raw material is added with 0.20% (B) bentonite to be a compounded raw material.

The compounded raw material is added with about 32% water to be mixed. After mixing, strength test based on cement physical test of JIS-R (1964) is carried out on the compounded raw material, and the results are shown in Table 2 as samples NO. 6 - NO. 10.

Table 2

~ scimple Oi 6 7 8 9 io lag (96) 50 48.5 7.T 5.0 40,0 5ypsum dibydrate(b/P) 50 48.5 475 450 400 ss slaked lime (%) 1.5 1.5 1.5 1.5 a o 1inum sulfate(%) 1.5 1.5 1.5 0 03510 o ~~ bentonite o 0 5 5 10 20 e, ompression strength (k f/cm2) 233 268 291 275 250 (after one week) rt ompression strength (kg t/cm 2) 324 357 426 383 346 X (after three weeks) Example 1 A mixture of 70% gypsum dihydrate and 30% slag is added with slaked lime and aluminum sulfate each 1.5% (A) to be a main raw material. The main raw material is added with 0-20 R6 bentonite and 6% pulp (B) as a reinforcing fiber respectively and is further added with about tenfold water to be mixed.After mixing, the main raw material is shaped under 40 kg/cm2 of press pressure, and next is steam cured at 60"C for one day and further is cured at 20"C for seven days, folloeing by drying at 60"C with forced aeration, to be a hardened body. The bending strength, water, absorption by immersion in water test, bulk specific gravity and length change of the thus obtained hardened bodies are respectively measured. The results of the measurements are shown in Table 3 as examples NO. 1 - NO. 4 and comparative example NO.

'1.

Table 3

example comparative example NO.1 N0.2 NO.3 N0.4 NO.1 slag (%) 26.5 25.9 24.5 21.6 27.4 espsum dShydrate(O 61.8 60.5 57.1 50.3 63.9 slaked lime (%) 1.34 1.30 1.22 1.08 1.37 aluminum aluminum sulfate 1.34 1.30 1.22 1.08 1.37 (%) 0 c bentonite (%) 3 5 10 20 - pulp (0/3) 6 6 6 6 bendSng strength (ks f/cm) 130 143 174 14r 86 p Youn's modulus a, X10(kg f/cm2) 5.1 6.0 8.2 8.9 3.7 X waterabsorptionC%) 24.5 22.3 20.7 20.0 31.0 0 . bulk specific 1.51 ≈ gravity (-) 1.38 1.43 1.49 1.51 1.29 length change () 0.212 0.247 0.254 0.260 0.168.

Example 2 A mixture of 70% gypsum dihydrate and 30% slag is added with slaked lime and aluminum sulfate each 1.5% (A) to be a main raw material. The main raw material is added with 10% bentonite, 2-10% mica and 6% pulp (B) as a reinforcing fiber respectively, and is added with about tenfold water to be mixed. After mixing, the mixed main raw material is pressed under 40 kg/cm2 of press pressure and next is steam cured at 60"C for one day, and is subsequently cured at 20"C for seven days, and is dried at 60"C with forced aeration to be a hardened body.

The bending strength, water absorption by immersion in water test, bulk specific gravity and length change of the thus obtained hardened bodies are measured. The results of the measurements are shown in Table 4 as examples NO. 5 - NO. 7.

Table 4

example N9.5 1 N0.6 NO.

elag (%) 23.9 2.0 21.6 gypsum dihydrate (O 55.7 53.7 50.3 slaked lime (%) 1.19 1.15 1.08 aluminum sulfate (O 1.19 1.15 1.08 a bentonite (%) 10 10 10 0 ç mica (%) 2 5 10 pulp (%) 6 6 6 bending strength 164 140 132 (kg t/cm2) o Younç's modulus 7.7 7 2 6.9 a, XIO (kg f/cmZ) water absorption (%) 20.9 21.6 22.3 C) .rI m bulk specific gravity 1.48 1.46 1.44 A: (-) length change (%) 0.216 0.107 0,102 Example 3 A mixture of 30% gypsum dihydrate and 70% slag is added with slaked lime and aluminum sulfate each 1.5% (A) to be a main raw material. The main raw material is added with 10% bentonite, 5% mica, 6% pulp and 0.3% polypropylene fiber (B) and is further added with about tenfold water to be mixed. The mixed main raw material is formed by cylinder machine to be a board. Next, the board is cured at room temperature for three weeks and subsequently is dried at 60"C with forced aeration to be a hardened body. The physical properties of the thus obtained hardened body are measured and the results of the measurements are shown in Table 5 as example NO. 8.

As a comparative example, the physical properties of a board which contains no bentonite and mica, but contains asbestos are also shown in Table 5 as comparative example NO. 2.

Table 5

example comparative N0.8 example N0.2 slag (S/o) 53.4 44.0 gypsum dihydrate tso) 22.9 44.0 to slaked lime tO 1.15 1.5 a aluminum Bulrato (O 1.13 1. 5 g . ~ o bentonite (O 10.1 o mica (%) 5rO o pulp (O 6.0 4.0 polyproplene fiber (91.) 0.3 1.0 asbestos (%) 1 4.0 I bending strength(kg f/cm2) 204 160 Young s 8 modulus XlO'(kg f/cmZ) 5.3 S water absorption (%) 27.4 25.0 'n bulk specific gravity (-) 1.32 1.4 length change (O/o) 0.168 0.2 ri A fzod impact value(kg.f cm/cm2) 3.8 4.5 Brinell hardness HB(10/100) 4.0 break away strength /cm) 3.0 Example 4 A mixture of 70% gypsum dihydrate and 30% slag is added with slaked lime and aluminum sulfate each 1.5% (A) to be a main raw material. The main raw material is added with 8% bentonite, 3.5% mica, 3.8% pulp and 1.0% glass fiber (B) and is further added with about tenfold water to be mixed. The mixed main raw material is formed by Hatschek machine to be a board. The board is cured at room temperature for three weeks and subsequently is dried at 60eC with forced aeration to be a hardened body. The physical properties of the hardened body are measured and the results of the measurements are shown in Table 6 as example NO. 9.As comparative example, the same properties of a board which contains asbestos, but contains no bentonite are measured and the results of the measurements are also shown in Table 6 as comparative example No. 3.

Table 6

- l example comparative NO.9 example N0.3 slag ) 24. 3 26.5 gypsum dihydrate (%) 57.0 61.9 slaked lime (YO) 1.2 1.3 aluminum sulfate (bk) 1.2 1.3 Pd bentonite (%) o mica (%) o, o pulp (%) 3.8 5.O glass fiber (%) asbestos ( /0) - 4.0 bending strength (kg /cam2) 186 160 Young' a modulus X?OZ 7.? 9.5 (kg f/cm2) water absorption (ffi) 27.4 25.0 m bul e bulk specitic gravity t-) 1.4 1.4 X length change (9 0.16 0.18 o Izod impact valuo 3.3 4.5 to (kg cm/cm P) Brinell hardness HB (10/100) 5.0 5.Q break away strength 4.0 2.5 (kg f/cm2)

Claims (6)

1. A method for producing a fiber-reinforced gypsum based hardened body comprising adding a reaction-promoting agent to a mixture of gypsum dihydrate and slag in a weight ratio of from 3 : 7 to 7 : 3 to make a main raw material, adding from 0.1 to 1 5 weight % of a reinforcing fiber, from 3 to 20 weight % of bentonite, and water to the said main raw material, and curing the mixture thus formed.

2. A method as claimed in claim 1 wherein additionally from 2 to 10 weight % of mica is added to the said main raw material.

3. A method as claimed in claim 1 or claim 2, wherein the reinforcing fiber is at least one of glass fiber, styrol fiber, carbon fiber, nylon fiber, vinylon fiber, polypropylene fiber and or pulp.

4. A method as claimed in claim 1 substantially as hereinbefore described.

5. A method as claimed in claim 1 substantially as hereinbefore described in any one of the specific Examples.

6. A building material in board form when produced by a method as claimed in any one of the preceding claims.