CA2093652C

CA2093652C - Molding of calcium silicate having high strength and its manufacturing method

Info

Publication number: CA2093652C
Application number: CA 2093652
Authority: CA
Inventors: Masayuki Nakano; Ryozo Kuramoto; Shigeo Otozaki; Katsuaki Kaneko; Hideo Shibasaki; Noritoshi Tamura
Original assignee: Chichibu Onoda Cement Corp
Current assignee: Nihon Cement Co Ltd
Priority date: 1990-02-09
Filing date: 1991-08-09
Publication date: 1997-12-09
Anticipated expiration: 2011-08-09
Also published as: EP0562112B1; WO1993002986A1; JPH03237051A; CA2093652A1; EP0562112A1; JP2514734B2; EP0562112A4; US5330573A

Abstract

A calcium silicate molding having high strength, and properties similar to a natural timber, is obtained by mixing tobermorite, calcium silate hydrate and quartz with the addition of 2 to 10% by weight glass of each of glass fiber and pulp, the resulting material having a Ti/Qi peak ratio obtained by powder X-ray diffraction between 0.1 and 1.0, and an absolute bulk density in the range 0.3 to 0.7 g/cc.

Description

- 1 - 2~936 5 2 MOLDING OF CALCIUM SILICATE HAVING
HIGH STRENGTH AND ITS MANUFACTURING METHOD
The present invention relates to a molding of calcium silicate having high strength, useful as a building material.
Background Art A calcium silicate molding, obtained by hydrothermally synthesizing calcareous material and silicic material, has been widely used as a building material having light weight, high strength, high heat resistance, and incombustibility. In recent years, such calcium silicate moldings have been further improved, and there have been various proposals for calcium silicate moldings having specific working properties such as bulk specific gravity, strength, abating, cutting, polishing, screw or nail holding properties, and adhesive properties.

However, in the actual fact, however, it is not easy to obtain such a molding having the above-mentioned properties to a desirable degree, and the manufacture of a building material having properties similar to natural timber has not yet been realized. Conventionally, a matrix of xonotlite, which is reinforced with glass fiber, is typically used as a material of the above-mentioned type.

The strength of adhesion in such a material between the glass fiber and the xonotlite is however low, and 5 to 10~ by weight of synthetic resin is normally added so as to enhance the adhesive strength. Indeed, high adhesive A

~ ~ 9 3 6 5 2 strength to the glass fiber can thus be obtained as well as satisfactory bending strength. Such a material is however easily burned because of the synthetic resin content. Heat resistance and incombustibility of such a material are low, and its workability is much lower than that of timber.

An object of the present invention is to provide a high strength molding of calcium silicate in which glass fiber and pulp are dispersed and strongly adhered without the inclusion of synthetic resin, thereby obtaining an incombustible building material which is similar to natural timber.

More specifically, the present invention provides a molding of calcium silicate having high strength comprising calcium silicate hydrate, quartz, tobermorite and a reinforcing material made of glass fiber and pulp, wherein said molding contains 2 to 10 wt~ of said glass fiber and 2 to 10~ wt~ of said pulp, a Ti/Qi ratio obtained by powder-X-ray diffraction is 0.1 to 1.0, wherein Ti represents the intensity of the X-ray diffraction of a (002) face of tobermorite crystal, andQi represents the intensity of the X-ray diffraction of a (101) face of quartz crystal, and said molding has an absolute bulk density of 0.3 to 0.7 g/cc.

The invention extends to a method of manufacturing a molding of calcium silicate containing tobermorite and 3 2~93652 quartz and having high strength, from a calcareous material, a silicic material, and a fiber material, as raw materials, wherein the silicic material is formed of crystalline silica and amorphous silica mixed at a weight ratio of the amorphous silica to the total of the crystalline silica and the amorphous silica, of 0.2 to 0.8, the fiber material consists of alkali-proof glass fiber and pulp, the calcareous material and the silicic material are added such that the CaO/SiO2 molar ratio is 0.6 to 0.9, and the fiber material is added such that the amount of each of the alkali-proof glass fiber and the pulp is 2 to 10 wt~, comprising the steps of:
(a) mixing all of the calcareous material, and part or all of the non-crystalline silica, of the raw materials, with water to form a slurry having a temperature of 50~C;
(b) making said slurry into a gel by heating said slurry at a temperature of 80~C or higher atmospheric pressure;
(c) Uniformly mixing said gel obtained in the above step (b) with the rest of said raw material;
(d) molding a mixture obtained in the above step (c) by dehydration at a pressure of 3 to 30 kg/cm2 to form a molding; and (e) pressurizing and heating the molding obtained in the above step (d) in an autoclave under a saturation vapor pressure, at a temperature of 140 to 200OC, for 2 to 18 hours until the Ti/Qi ratio measured by powder-X-ray-diffraction is 0.1 to 1.0, wherein Ti represents an intensity of the X-ray diffraction of a (002) face of ~ ~ ~ 3 ~ 5 2 tobermorite crystal, and Qi represents an intensity of the X-ray diffraction of a (101) face of quartz crystal, respectively.
Brief Description of the Drawings Fig. 1 is an SEM (scanning electronic microscope) photograph showing a crystal structure of a molding of calcium silicate of Example 1 of the present invention;
Fig. 2 is a view explaining a method for testing an abating property of the molding of calcium silicate according to the present invention;
Fig. 3 is an SEM (Scanning Electron Microscope) photograph showing a crystal structure of a molding of calcium silicate of Example 5 of the present invention;
Fig. 4 is a powder X-ray diffraction chart of the molding of calcium silicate of Example 5;
Fig. 5(A), 5(B) and Figs. 6(A) and 6(B) are SEM
photographs showing a broken surface of glass fiber and that of pulp when the molding of calcium silicate of Example 5 is bent and broken.
Description of the Preferred Embodiments In a first embodiment of the aspect of the invention, there is provided a calcium silicate molding in which glass fiber and pulp are dispersed and adhered to calcium silicate in which tobermorite calcium silicate hydrate, (C
- S - H) and quartz are mixed. The content of glass fiber and pulp ranges in each case from 2 to 10~. If the content of either is below 2~, sufficient strength cannot be obtained. If the content of either exceeds 10~, the strength of the material is not advantageously improved.

A

~ ~ ~ 3 fi 5 2 Powder X-ray diffraction of calcium silicate consisting the molding shows a Ti/Qi ratio is 0.1 to 1.0, and the molding has an absolute bulk density of 0.3 to 0.7 g/cc. Ti and Qi are respectively the intensity of the X-ray diffraction of a tobermorite crystal (002) face and of a silica crystal (101) face. The strength of calcium silicate matrix itself should be high.

For obtaining material, which is similar to a natural timber, by adding reinforcing material to calcium silicate, glass fiber is advantageously used as a reinforcing material. However, in order to enhance strength of the calcium silicate base material by use of glass fiber, the following requirements must be met. Thus the strength of the calcium silicate matrix itself must be high; adhesion strength of the calcium silicate matrix to glass fiber must be high; and the strength of calcium silicate should not be reduced by erosion of glass fiber serving as reinforcing material.

The inventors carried out various experiments and determined the following facts.

Where the calcium silicate matrix was formed only of C
- S - H and quartz, the strength of the matrix to glass fiber was insufficient. As a result, glass fiber was drawn from the matrix in the event of bending breakage, and a desirable level of strength could not be obtained. Where most of the matrix was formed of tobermorite crystals, the ,_ ~, - 6 - ~ 2 strength of the glass fiber was lowered, and the matrix and glass fiber were lowered, and the matrix and glass fiber were simultaneously broken in the event of bending breakage, or the glass fiber was broken before breakage of the matrix, thus showing an absence of reinforcing effect of the glass fiber. In contrast, where tobermorite, C - S
- H, and quartz were mixed in the matrix, and glass fiber was adhered to such the matrix, the strength of the matrix was high, and both adhesion strength of the matrix of calcium silicate to glass fiber and the strength of glass fiber itself were high. Particularly, regarding the strength of the matrix, where the Ti/Qi ratio (Ti and Qi being defined as above) was 0.1 to 1.0, high strength was demonstrated, but when the Ti/Qi ratio was outside the range of 0.1 to 1.0, the strength of the glass fiber was lowered.

In order to improve working properties of the material of the molding, such as its cutting, abating, polishing, and screw or nail holding properties, 2 to 10~ by weight of pulp must be incorporated in the matrix. If the amount is below 2~, no improvement is achieved, and if the value is over 10~, resistance to combustion is considerably lowered.

In addition, if the absolute bulk density is below 0.3, sufficient screw and nail holding properties cannot be expected. Moreover, if the absolute bulk density is over 0.7, it is difficult to perform nailing or cutting, abating, and the like. Therefore, the absolute bulk A

density is set to 0.3 to 0.7 g/cc.

A second aspect of the invention relates to a method for manufacturing the calcium silicate molding of the first invention.

As a raw calcareous material, hydrated lime, quicklime or milk of lime may be used. As a silicic material, crystalline silica and amorphous silica may be used in a weight ratio of amorphous silica/(crystalline silica +
amorphous silica) which ranges from 0.2 to 0.8. If the value is out of this range, the high strength calcium silicate molding of the present invention is not obtained.
As crystalline silica, normal silica powder can be used.
As amorphous silica, diatomaceous earth, zeolite or silica flour can be used, but diatomaceous earth is preferred, with a particle size of 50~m or less. The mixing ratio of calcareous material to silicic material is from 0.6 to 0.9 in terms of CaO/SiO2 molar ratio. If the ratio is out of this range the product of the invention is not obtained.
Moreover, if the value is below 0.6, generation of tobermorite becomes difficult. If the value is over 0.9, the glass fiber is eroded, so that a molding having a desired bending strength cannot be obtained. The compounding ratio of calcareous material to silicic material is set to preferably 0.7 to 0.85 at the CaO/SiO2 molar ratio.
Regarding glass fiber, a chopped strand, which is obtained by cutting alkali proof glass fiber to have a suitable length, may be used, and its compounding ratio is 2 to 10% by weight. If the value is below 2% by weight, a desired reinforcing effect cannot be obtained.
If the value is over 10% by weight, it is difficult to perform the molding process, and the reinforcing effect is not desirably increased. Pulp is also used together with glass fiber. The use of pulp improves dispersi-bility of glass fiber, and largely distributes improve-ment of processing and working of the molding in addition to reinforcing effect. A normal timber pulp is used after being disaggregated in a wet manner or a dry manner. Regarding the compounding ratio of the pulp, if the ratio is below 2% by weight, the reinforcing effect cannot be obtained. And, if the ratio is over 10% by weight, incombustibility of the molding is considerably reduced, and the reinforcing effect is little improved.
Regarding the compound of these materials, calcareous material and at least a part of amorphous silica are mixed with water, and used as slurry. The residual amorphous silica is added later similar to crystalline silica. Then, the adding ratio of the final amorphous silica preferably ranges from 0.2 to 0.8 at the amorphous silica/(crystalline silica + amorphous silica) ratio. If the value is low, the strength of the gel after being galled is weak, and the shape maintaining property is insufficient at the time of drawing the molding from a metal molding after the mixed materials are dehydrated and molded, and the handling of the molding becomes difficult. Moreover, if the value is high, pressure rises too much at the time of drawing the molding from the metal molding, and this is unfavorable in view of the manufacturing of the molding.
Regarding the addition of calcareous material to amorphous material, the CaO/SiO2 molar ratio is preferably 0.8 or more. If the ratio is below 0.8, gelation does not largely advance. In this case, it is of course that all calcareous material may be added thereto. However, addition of alkali proof glass fiber is unfavorable since glass fiber is eroded by free lime.
Regarding a water/solid weight ratio, there is no special limitation, but the value preferably ranges from 3 to 10. At such a water ratio, gelation sufficiently advances, and swelling of gel does not enlarged too much. The important point when the materials are mixed is that the mixture is performed at temperature of 50~C
or less. If the mixture is performed at temperature of over 50~C, tobermorite, which is generated by the reaction in the autoclave, is considerably delayed, there is a possibility that the initial product cannot be obtained. The following reason can be considered.

That is, a large amount of C - S - H, which is difficult to transfer to tobermorite, is generated if calcareous material and amorphous silica are mixed with each other at temperature of over 50~C. It is desirable that gelation be performed at 80~C under normal pressure.
Though gel time is influenced by reactivity of amorphous silica, gel time is normally 1 to 5 hours. It is preferable that mixing for gel time be intermittently performed.
Then, residual materials are added to the above-obtained gel, and uniformly mixed. In this case, the above residual materials are materials in which the materials excepting materials, which are added before gelation, from the materials to be used, and alkali proof glass fiber is always included in the above residual materials. Though water is further added thereto, the water/solid weight ratio is not particularly limited. For uniformly mixing fiber material, the above water ratio preferably ranges from 2.0 to 4Ø As a mixer to be used in this case, a diffusion type mixer such as an omni type mixer is preferably used. Then, mixing time within 5 minutes is sufficient for this case. Thereafter, the mixture is introduced into the metal molding, pressurized and dehydrated to be molded. Pressure to be applied in this case is suitably 3 to 30 kgf/cm2. If pressure is below 3 kgf/cm2, the shape maintaining property, which is after drawing the molding from the metal molding, is not good, and deformation is generated at the time of transferring. If pressure is over 30 kgf/cm2, layer-shape cracks are easily generated in the molding after the molding is pressurized and cured. A molding box can be arbitrarily used. However, the molding box having a thickness of 100 mm or less is preferably used since the uniformity of the reaction may be lost if the thickness is too large. The water/solid weight ratio of the obtained molding normally ranges from 1.0 to 3Ø
In this case, the bulk density of the dried product is about 0.3 to 0.7 g/cc.
Then, the above molding is thermally reacted in the autoclave. The reaction is normally performed at temperature of 140 to 200~C under saturated aqueous vapor. If the temperature is below 140~C, generation of tobermorite is considerably delayed, and if the temperature is over 200~C, xonotlite is partially generated. Therefore, either condition is unfavorable since the strength of the product is lowered.
In view of economy and stability of the quality of the product, the reaction is preferably performed at temperature of 160 to 195~C, and more preferably 170 to 190~C. The reaction time is set to the condition that Ti/Qi ratio is 0.1 to 1.0 in the case that powder X-ray-diffraction of the reacted molding is performed.
For example, in Examples 1 to 4 of the present invention, the reaction time is 3 to 8 hours in the case that the temperature is 180~C, 5 to 18 hours in the case that the temperature is 160~C, and 2 to 6 hours in the case that the temperature is 195~C. The present invention is, of course, not limited to the above temperature and time. After the cured molding is synthesized, the cured molding is dried, and a final product is obtained.
The following will explain Examples 1 to 4 and comparisons 1 to 3.
2.47 kg of quicklime powder was introduced into 8.
65 kg of hot water having temperature of 90~C, and slacked, so that milk of lime was obtained. The obtained milk of lime was cooled at temperature of 32~C.
Thereafter, 0.67 kg of diatomaceous earth fine powder (325 mesh whole-under) was added to the cooled milk of lime, and cold water was added thereto such that the water/solid weight ratio was set to 3.5, and was uniformly mixed. Thereafter, the mixture was heated in a warm bath, and gelled at temperature of 80 to 92OC for two hours. After gelation, the gelled substance was cooled to 60~C. Then, 2.02 kg of silica powder (Toyane silica powder 250 mesh under), 0.67 kg of diatomaceous earth powder, and 0.37 kg of alkali proof glass fiber, and 0.37 kg of pulp were added thereto, and uniformly mixed for two minutes by the omni type mixer. The compositions of this mixture were as follows:

CaO/SiO2 molar ratio ... 0.83 amorphous silica/(crystalline silica + amorphous silica) ... 0.4 alkali proof glass fiber compounding ratio ... 5%
pulp compounding ratio ...... 5%.
The mixture was introduced into the metal mold having an inner size of 610 x 1220 mm, and dehydrated at 12.0 kgf/cm2 to obtain a molding. The thickness of the molding drawn from the metal mold was 18 mm. The molding was put in the autoclave and reacted for a predetermined time at temperature of 180~C under saturated aqueous vapor, taken out of the autoclave, and dried in an absolute dry manner at 105~C by a dryer.
The bulk density of the dried product was 0.54 to 0.56 g/cc. However, the size and the thickness of the product were unchanged, that is, 610 x 1220 mm of the size and 18 mm of the thickness.
Fig. 1 shows an SEM photograph of Example 1. In the photograph, the entire surface of quartz is covered with C - S - H presenting white agglomeration, and it is shown that tobermorite is partially generated.
Table 1 shows the measuring result of the physical properties of the products obtained according to Examples 1 to 4 and comparisons 1 to 3.
In Table 1, the products shown in the comparisons are formed such that the Ti/Qi ratio is set to be out of the range of 0.1 to 1Ø The bending strength shown in Table 1 were measured in accordance with JIS-A-1408.
The size of the object to be measured was set to 80 mm of the width x 180 mm of the length x 15 mm of the thickness, and the span length is set to 100 mm.
Combustibility was measured in accordance with JIS-A- 1 3 2 1 .
Regarding the abating property, the object having the size of 50 mm of length (X), 10 mm of width (z) and 50 mm of thickness (y) is cut from the portion close to substantially the center of the product. By use of a blade whose angle is 28~, the object whose depth of cut is 1 mm is abated at a cutting speed of 20 mm/min. In Table 1, a symbol o denotes a good abating property in which abatement is continuous, x denotes a bad abating property in which abatement is discontinuous, and shows an intermediate abating property.

- 15 - ~ ~Q~365-2 ~' -C ,, o o o o X C X
~, P~
a a a a a a a a) a) c ~ a) c a) a~ c U
H ~) ~1 0 ~ ~1 0 ~ H O ~ ~1 0 ~ ~ O 1~ ~1 0 ~ ~1 0 O C
C ~1 ~ _ ~; H U~ C) -,C(~
E
U
C ~
a~ x ~1 _ ~1U ~ Ln X U~U ~ U~
,~ C~ ~ . . . . . . .
~5 a) ~ o o o o o o o a) m a CL--g I ~y C 0 ~ I
o P~ ~ 0 -~1 C O
U ~ 0 ~ o o o o o I h ~~1 X ~ E~ H
C a~ ~ ~ ~ ~ ~ ~
~1h U h ~1 ~ h ~ h ~ h ~ ~1 0 h ~1 0 h ) O a) O O O a) o a) ~1 o ~ o ~ ~ E ~i vl E a) ~ E a) ~ F a3 :~ E a) :> O X ~ E O x ~c3 ~
a) ~h ~ g ~ h g S-l ~ h g S~ X h g h ~C -I g h ~1 a) h ~-1 a) h ~: V~ V' I a) h o I a) a3 1 a) a) I a) a~ I a) a) ~ h E a) ~ 'I ~ C) ~Ll g a u~ g t~ U~ g C V ~n g C Vl cn g C V U~ ,~ C V~ V~ g V~--I h g u? o ~ I o ~5 a) I o al ~- I O (~ I o ~ g O ~ O O O ~ O O
C) E~ O~ g U E-~ U O V E~ ~ O U E~ U O U '~ U O ~
a ~ Y a ~ C ' C
r~
~ ~ v~ ~ ~ m ~ ~ o u~
o v, v a a E
::5 0 h -~1 U ~ E~

.,~ I U
Vl ~ C
0~ ~C
C E v E a) o., U h 20936~2 Example 5 will be explained as follows:
The product was obtained by the same method as Example 1 excepting that the reaction time in the autoclave was set to 5 hours 30 minutes. Fig. 3 shows an SEM photograph of the matrix of the molding of calcium silicate obtained in Example 5.
It can be understood from Fig. 3 that tobermorite and C - S - H are mixed with each other. Fig. 4 is a chart of powder X-ray diffraction of the matrix of the molding of calcium silicate obtained in Example 5. As shown in Fig. 4, the peak of tobermorite and that of quartz are shown, and the intensity ratio of Ti/Qi was 0.64 wherein Ti = (002) surface of tobermorite (2~ =
7.82~) and Qi = (101) surface of quartz (20 = 26.65~).
Figs. 5(A), 5(B) and Figs. 6(A) and 6(B) are SEM
photographs showing the broken surfaces of glass fiber and pulp when the molding of Example 5 is bent and broken.
More specifically, Fig. 5(A) shows the state that the surface of glass fiber is covered with a base material of calcium silicate. Fig. 5(s) shows one enlarged glass fiber, which is shown in Fig. 5(A). It can be understood from Fig. 5(s) that C - S - H and tobermorite are strongly adhered to the surface of the glass fiber, thereby the base material and glass fiber are strongly adhered to each other. Fig. 6(A) shows the same type of broken surface as Fig. 5(A). Specifically, Fig. 6(A) shows the state that the surface of pulp is covered with a base material of calcium silicate.
Fig. 6(B) shows an enlarged pulp, which is shown in Fig. 6(A). It can be understood from Fig. 6(B) that C - S - H and part of tobermorite are strongly adhered to the surface of the pulp, thereby the base material and pulp are strongly adhered to each other.
The following will explain Examples 6 to 8 and comparisons 4 to 6.
In Examples 6 to 8 and comparisons 4 to 6, the product was obtained by the same method as Example 4 excepting that the ratio of amorphous silica and the adding method were changed. The results are shown in Table 2.

C' X '~ ~o U
~ o 0 P~
C ~ C C ~~ L~
a) -, 3 ,/ :~ ~ a) V C
~ ~ C ~1 ~ P~
C ~ O O~ r ,~
>1 ~ S ~
S~ C -- ~~ I O
1 ~ C ~ ~
~ Q~ 3 ~ ~
~ o s ~ s~
sc O ~: Q~

P~ U2 SC
c -- C ~ ~ . . I .
a~ x L U2 0 ~
~r~
U In Ln Ln Ln In -~ U . . . I
a) x u~ ~ o o o o o ~1 C ~
m ~
E~ C
o U ~1 a) ~o ~ ~ o r,l ~ o o o O
U
~ O
s a) -~1 o _ s~ ~~ ~ ~ ~ Ln s' ., o ~
~ o ~ o o o o o o ~:~ m~

~ V
V ~ +
~ ~ ~s ~
S ~ ~ U ~ U c~ r~
; U vl ~1 ~ ,1 . . . . .
0 ~1 0 0 0 0 0 0 0 ~1 ~1 -~1 ~ --I
-~ U U~
U~ ~

.,1 I Vl C
0~ ~0 C ~ v~
O
U

Industrial Applicability According to the present invention, the molding of calcium silicate having bulk density of 0.3 to 0.7 g/cc is light, and the strength ratio = (bending strength)/
(bulk density)2 is 260 or more. Also, working processes such as cutting, abating, polishing can be easily performed, no dust is generated, and holding force of bisscrew is large. Furthermore, since a crack, swelling, a pore are not generated on the surface and the inside of the product, and the molding of the present invention has good incombustibility, heat resistance, and stability of size, the molding of the present invention can be widely used in a wall material, a partition material, a floor material, and a heat insulating material.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A molding of calcium silicate having high strength comprising calcium silicate hydrate, quartz, tobermorite and a reinforcing material made of glass fiber and pulp, wherein said molding contains 2 to 10 wt% of said glass fiber and 2 to 10 wt% of said pulp, a Ti/Qi ratio obtained by powder-X-ray diffraction is 0.1 to 1.0, wherein Ti represents the intensity of the X-ray diffraction of a (002) face of tobermorite crystal, and Qi represents the intensity of the X-ray diffraction of a (101) face of quartz crystal, and said molding has an absolute bulk density of 0.3 to 0.7 g/cc.

2. A method of manufacturing a molding of calcium silicate containing tobermorite and quartz and having high strength, from a calcareous material, a silicic material, and a fiber material, as raw materials, wherein the silicic material is formed of crystalline silica and amorphous silica mixed at a weight ratio of the amorphous silica to the total of the crystalline silica and the amorphous silica, of 0.2 to 0.8, the fiber material consists of alkali-proof glass fiber and pulp, the calcareous material and the silicic material are added such that the CaO/SiO2 molar ratio is 0.6 to 0.9, and the fiber material is added such that the amount of each of the alkali-proof glass fiber and the pulp is 2 to 10 wt%, comprising the steps of:
(a) mixing all of the calcareous material, and part or all of the non-crystalline silica, of the raw materials, with water to form a slurry having a temperature of 50°C ;
(b) making said slurry into a gel by heating said slurry at a temperature of 80°C or higher at atmospheric pressure;
(c) uniformly mixing said gel obtained in the above step (b) with the rest of said raw material;
(d) molding a mixture obtained in the above step (c) by dehydration at a pressure of 3 to 30 kg/cm2 to form a molding;
and (f) pressurizing and heating the molding obtained in the above step (d) in an autoclave under a saturation vapor pressure, at a temperature of 140 to 200°C , for 2 to 18 hours until the Ti/Qi ratio measured by powder-X-ray-diffraction is 0.1 to 1.0, wherein Ti represents an intensity of the X-ray diffraction of a (002) face of tobermorite crystal, and Qi represents an intensity of the X-ray diffraction of a (101) face of quartz crystal, respectively.