GB2244996A - Extrusion-mouldable hydraulic cement-based composition - Google Patents

Abstract

An extrusion-mouldable hydraulic cement-based composition having excellent mouldability in extrusion moulding and capable of giving cured cement-based bodies having excellent mechanical strengths even when the amount of water- soluble organic binder is greatly reduced, is compounded using fibres of crude linter pulp before refinement, instead of the asbestos or wool pulp fibres conventionally used. Crude linter pulp is a fuzz of short fibres adhering to cotton seed after ginning, before a refining treatment such as degreasing.

Description

41 WRUSIM-MOMIA= HYMAULIC CEMENT-BASETD COMPOSITION The present invention

relates to an extrusion-muldable, hydraulic cement- based ccmposition, more particularly to an extrusion-mouldable hydraulic cement-based ccm-position having excellent extrusion-mouldability and capable of giving a cured cement-based article of high mechanical strengths, even with a relatively miall amount of an organic binder as an additive as compared with conventional extrusion-mouldable 10 hydraulic cement-based ccmpositions.- As is well known, pre-shaped cement-based boards and other articles reinforced with asbestos fibres are widely used in large quantities in building works as a material for outer walls, roofings, floorings and the like. Such pre-shaped cem.ent-based articles are prepared by curing a green body in the form of the article of a ccmposition consisting of a hydraulic cement, asbestos fibres in an amount of around 10% by ue-ight of the cement, aggregates, e.g. fine sand, and other additives with aanixture of water, as extruded out of a die of an extruder machine to give a desired cross-section.

Although various kinds of reinforcing n-aterials have been proposed and widely used besides the abover--menticned asbestos fibres, an overwhelmingly large proportion of the reinforcing materials heretofore used have been asbestos fibres, by virtue of their excellent properties. N&M-ely, asbestos fibres have very good dispersibility in cement based compositions and capable of giving an extruded green body with good shape-retentivity and waterretentivity.

Further, asbestos fibres have sufficiently high heat resistance to withstand the conditions of curing of the extruded body, which is usually performed in an autocla-ve under a superatmospheric pressure of steam at about 1709C or above so that the cared ceent-based board can be given the dimensional stability and niechanical strengths required for a building mterial. Thus asbestos f ibres are incmrparable in respect of the various requirements for the reinforcing material compounded in an extrusion-mouldable cement-based composition, such as dispersibility in the composition, shape-and water-retentivity, heat-resistance and so on.

In recent years, however, a serious problem which has become an issue of public interest is the suspected carcinogenicity of asbestos fibres, presmnably ascribable to the specific fibrous morphology thereof, with the result that asbestos fibres are likely to be entirely banned sooner or later as a reinforcing mterial in extrusion-mouldable " 3 - cement-based canpositions. Accordingly, it is eagerly desired, urgently for the nuTent, to greatly decrease the amount of asbestos fibres cunded in cement-based campositions or, finally, to formulate an extrusionmouldable cement-based amiposition without using asbestos fibres as a reinforcing material, by using a substitute for asbestos fibres.

Various kinds of synthetic organic fibres have been proposed and tested heretofore as a substitute for asbestos fibres as a reinforcing material in extrusion-muldable cement-based ccimpositions but none of them can satisfy all of the above-inentioned requirements. Even setting aside the relatively high costs of synthetic organic fibres as compared with asbestos fibres, none of the synthetic organic fibres is satisfactory in te= of dispersibility in the sition and shape- and water-retentivity of the extrusion-moulded body. Sm-e of the synthetic organic fibres, moreover, are poor in heat resistance and cannot therefore satisfactorily withstand the conditions of autoclaving in an atmosphere of high-pressure steam. In particular, synthetic organic fibres capable of iurparting high mechanical strengths to the cured body are generally very expensive.

Apart fram synthetic organic fibres, a proposal has been made to use pulp fibres as a ki nd of natural organic fibres as a substitute for asbestos fibres. In addition to the advantage of relatively low costs as compared with synthetic organic fibres, pulp fibres have good dispersibility in cament-based ccnipositions, although saTewhat inferior to that of asbestos fibres. moreover, pulp fibres can exhibit their own:merits hardly obtained with asbestos fibres, such as the adaptability of cured cament-based board reinforced therewith to sawing and nail driving. Thus, pulp fibres are high-lighted as a promising substitute for asbestos fibres in cement- based compositions.

As a consequence of the trend in recent years toward greater and greater efficiency in the extrusion mulding of cement-based compositions for the preparation of preshaped bodies, cement-based compositions reinforced with asbestos fibres or pulp fibres have been subjected to a high compressive force in the coarse of extrusion moulding, sometimes resulting in segregation of water in spite of the good water-retentivity imparted by these reinforcing fibres, so that the surface of the extruded bodies iray become covered with a layer of free water, which may cause adhesion of the bodies before the extruded bodies are fully coagulated and cured, leading to a greater or lesser extent to deforffation of the extruded bodies.

With the object of solving the above-iT.entioned problem of mouldability of cement-based compositions reinforced with asbestos or pulp fibres under high-pressure extrusion moulding, it has been proposed to admix an extrusion-mouldable cement-based ocniposition with a water-soluble organic polymer as a binder. Various kinds of water-soluble organic polymers have been proposed for this purpose including, besides te methyl cellulose, hydroxypropyl methyl cellulose and the like disclosed in Japanese Patent Publication 43-7134, hydroxyethyl cellulose, carboxymethyl hydroxyethyl cellulose, polyethylene oxide, poly(sodium acrylate), casein and the like, of which hydraxyalkyl alkyl celluloses are most widely used in view of the good dispersibility imparted to the particles of cement and aggregate and good xrater-retentivity and adhesive ness of the extruded bodies campounded therewith.

Various proposals have been made in the prior art for extrusion-mouldable cement-based compositions ccirrFounded with pulp fibres as a reinforcing material and admixed with such an organic binder. For example, Japanese Patent Publication 63-1276 discloses a cement-based ccmposition ccnipounded with pulp fibres, spherical particles of a synthetic resin having a cellular structure formed by primary foaming and a binder such as meth-yl cellulose, which can be extrusion-moulded and then cured to give a cured cement-based shaped body which is adaptable to sawing and nail-driving.

Pulp fibres -used as a reinforcing mterial as a substitute for asbestos fibres in an extrusion-muldable cement-based camposition also cannot be free frcm the problem i that, since the pulp usually used in the prior art is a mechanical wood pulp obtained by a grinding treatment of wood frcrn coniferous or broadleaf trees or a pulp reclaimed frcrn waste paper of such a mechanical wx)d pulp and contains a large amount of lignin originating in the starting wood which contains 30 to 50% by weight of lignin, the lignin constituent in the pulp has an adverse effect of retardation of curing of the hydraulic cement, so that the time taken for ccnplete curing of the extrusion-imulded body by autoclaving is unduly extended, resulting in an increase in the production cost.

The above-mentioned adverse influence of the lignin in the pulp is of course not a serious problem Vien a chE--Lical pulp containing little lignin after a chemical treatment is used as the reinforcing material, so that cho-acal pulps vnuld be satisfactory for the purpose if it were not for the expensiveness thereof as ccmpared with mechanical wood pulps. That is, chemical pulps cannot be used in practice in extrusion-muldable cement-based compositions in such an amount as to exhibit full reinforcing effect since, when used in such a large c-aTount, the ccr=,sition would be much more expensive than compositions compounded with asbestos fibres.

On the other hand, Japanese Patent Kokai 63-256558 discloses an extrusion-nouldable cement-based ccmposition comprising a hydraulic cement and a mechanical wood Fulp with admixture of a curing accelerator. Such a composition, however, provides no solution of the problem in the pulp,reinforced composition because of the expensiveness of the curing accelerator, which more than outweighs the cost decrease achieved by the use of an inexpensive mechanical vx)od pulp as ccnT pared with a chemical pulp.

Moreover, mechanical wood pulps also have a problem in respect of their rather poor reinforcing effect, in particular on the impact strength of the cured cEmentbased body reinforced therewith, because the fibre length in mechanical wood pulps is only about 6 mm at the longest or about 2 mm at the longest when the pulp is prepared from wood of coniferous trees or of broadleaf trees respectively, that is much shorter than the fibre length of about 25 rrm at the longest in chemical pulps. Reclaimed pulps from waste paper can be at least partly freed from the problem of retardation of curing by lignin by reducing the content of lignin therein, but the fibre length in reclaimed pulps is sometimes still shorter than in fresh mechanical wood pulps and may therefore fail to impart the desired reinforcing effect.

Another factor to cause an increase in the cost of a pulp reinforced cement-based composition, when the pulp is a mechanical wood pulp, is that, besides the increase in the cost of the pulp fibres campounded in such a large amount, the amount of the organic binder must be increased to remain in balance with the pulp fibres. In addition, the fireproofness of a cured cment-based body would be reduced by a significant amount when the extrusion-muldable cementbased csition is cunded with such a large amount of pulp fibres.

In -vriew of the above-described considerations, it is eagerly desired to develop an extrusion-nouldable cement- based composition satisfying various requirements including that: the amount of organic fibres added to the csition as a reinforcing material can be as small as possible; the pre-shaped ce-qemt-based body obtained frcrn the ccriposition by moulding and curing is adaptable to sa-wing and nail driving; the pre-shaped and cured cement-based body of the =position is highly resistant to mechanical shock so as to minimise the risk of damage while being transported; the pre-shaped and cured cement-based body of the composition has necessary and sufficient mechanical strengths in use, including impact strength, bending strength and cempressive strength; the amount of the organic binder required in the csition can be small enough without adversely affecting the extrusion-mouldability of the camposition; and the csition can be prepared with an overall production cost as low as possible.

The present invention accordingly has as an object to provide a novel and improved extrusion-nouldable cement-based composition reinforced with a fibrous reinforcing Tmterial without the above-described problems and disadvantages of the fibre-reinforced cenent-based compositions of the prior art.

Thus the enxtrusion-muldable cement-based composition of the present invention comprises, as a blend: (a) a hydraulic cement; (b) an inorganic aggregate mterial in the form of a powder; (c) an organic polyner as a binder; (d) fibres of crude linter pulp before refinement; and (e) water in an amount sufficient to inrpart to the composition a consistency suitable for extrusion mulding.

As is described above, the essential ingredients of the extrusionnouldable cement-based composition according to the invention include the components (a) to (e), of which the most characteristic is the component (d).

The base ingredient in the composition is a hydraulic cement as the component (a), which is not particularly lizaitative to a specific type of various hydraulic cements including Portland cement, blast furnace cement, flyash cement, alumina cement and the like, although Portland cement is preferred in most cases in view of the relatively low cost thereof. If compatible, two or nore kinds of hydraulic cements can be used in cm1bination.

The camponent (b) in the carposition according to the invention is an aggregate material, which can be any of the knc%m inorganic aggregate materials including fine sand, silica powders having a particle size equivalent to that of the hydraulic cement, perlite, vermiculite, flyash and the like. Fine silica sand can also be used in a limited amount. The particle size of the aggregate naterial depends on the particular type of the shaped and cured caTient- based bodies prepared frcm the inventive composition. The amount of the aggregate material relative to the hydraulic cement can be conventional as in ordinary cEnLent mortar ccmpositions.

The ccmPonent (c) is a wa-Iter-soluble organic polymer which serves as a binder. Exa7ples of suitable binder materials include water-soluble alkyl celluloses and hydroxyalkyl alkyl celluloses such as methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, hydroxyethyl ethyl cellulose and the like. Though not particularly limitative, the cellulose ether used as the ccmponent (c) should preferably have such an average degree of polymerization as to give a 2% by ueight aqueous solution having a viscosity of at least 15,000 centipoise or, preferably, at least 30,000 centipoise at 2CPC. The amount of the organic binder added to the ccnTposition should be as small as possible provided that good extrusion-muldability 1 can be imparted to the composition in view of the relatively high cost of an organic polymer. Typically and in most cases, the amount of the organic polymer as the binder is in the.

range from 0.2 to 1.0 part by weight or, preferably, from 0.3 to 0.5 part by weight per 10D parts by weight of the total amount of the hydraulic cement as the component (a) and the inorganic aggregate material as the component (b).

The component (d), which is the most characteristic of the ingredients in the composition according to the invention, is a crude linter pulp, which is a fuzz of short fibres adhering to cotton seed after ginning, before a refining treatment such as degreasing. It is usual that a crude linter before degreasing contains up to about 10% by weight of an oleaginous material. Quite unexpectedly, such an oleaginous or greasy material has no adverse influence on the curing behaviour of the cement-based composition according to the invention or, rather, has an advantageous effect to serve as a kind of lubricant to ensure more smooth extrusion mulding, giving a possibility of decreasing the amount of the water-soluble organic polymr as the binder. The amount of the crude linter as the ccnponent (d) in the composition can be as small as 2 to 5 parts by weight per 100 parts by weight of the total amount of the hydraulic cement as the component (a) and the inorganic aggregate material as the component (b), by which excellent impact strength can be :uTipartea to the shaped and cured body of the cerrent-basea composition.

It is optional that, if permissible, asbestos fibres are used in caTbination with the crude linter pulp as an auxiliary reinforcing material in a limited amount of 5 parts by weight or smller per 100 parts by weight of the hydraulic cement as the component (a) and the inorganic aggregate material as the component (b).

The component (e) is water, w1hich is of course essential to effect hydraulic curing of the cement-based composition.

The amount of water in the composition should be as miall as possible provided that the composition has a consistency suitable for extrusion moulding and uniformity of the composition can be ensured. Usually the amount of water in the caTposition according to the invention is in the range from 20 to 50 parts by weight per 100 parts by weight of the hydraulic cement as the component (a) and the inorganic aggregate material as the component (b).

In the following, the extrusion-mouldable hydraulic cement-based composition of the invention is described in mre detail by way of exar-ples and comparative exaTrples which, however, are not intended to limit the scope of the invention in any way. In the following description, the term "parts" always refers to "parts by weight".

Example

Six hydraulic cement-based ccmpositions, referred to as the ccupositions I, II, III, IV, V and VI hereinbelow, were prepared each by mixing, for 3 minutes in a Henschel n-Lixer rotating at 500 rpm, 70 parts of normal Portland cement, 30 parts of quartz sand having an average particle diameter of 12)n, an unrefined crude linter pulp in a fuzzy form of fibres having a length of 2 to 10 mm and a diameter of 10 to 40 jun in an amount of 1, 2, 3, 3, 4 and 5 parts respectively, 0. 5 parts (ccrapositions I, II, IV, V and VI) or 0. 4 part (composition III) of either one of the cellulose ethers, referred to as the binders I, II, III and 1%7 as specified below and indicated in Table 1, and water in an amount to give a water/cement ratio of 25 to 30% as indicated in Table 1, followed by re-kneading for 5 minutes in a double-arm kneader.

The above-mentioned cellulose ethers as the binders I to IV are characterized as follows.

I: Hydroxypropyl methyl cellulose giving a 2% by weight aqueous solution having a viscosity of 80,000 centipoise at 260C (90SH-100000, a product of Shin-Etsu Chemical Co.) II: Hydroxypropyl iriethyl cellulose giving a 2% by weight aqueous solution having a viscosity of 15,000 centipoise at 209C (90SH-15000, a product of the same ccmpany, supra) III: Hydrcxyethyl mthyl cellulose giving a 2% by weight aqueous solution having a viscosity of 15,000 centipoise at 209C (SEW-15T, a product of the same campany, supra).

IV: Vhthyl cellulose giving a 2% by weight aqueous solution having a viscosity of 8,000 centipoise at 209C (SM-8000, a product of the same ccmpany supra).

Each of the ccmpositions extruder and extrusion-Tnoulded width of 75 m-n and a thickness a green body in the form of a condition of the thus-extruded examined to record the results 1 to VI was transferred to an through a slit die, having a of 6 mm of the opening, into continuous-length board. The green body was visually as A or B when no cracks ware f ound or when cracks could be found respectively.

To test the length of time taken for curing the ccni)osition, a 30 9 portion was taken fram the green body as extruded and mde round into a ball, %,iich was put into a bag of a plastic fi.1m and kept in a thermostat at 45 0 c to record the length of time until no plastic deformation was caused in the ball when it was pressed with a weight of 20 kg.

The green body of the board as extruded fram the extruder was cured first for 24 hours in an atmosphere of 100% relative huntidity at 4EPC and then for 8 hours 1 - 15 in an autoclave at 17CPc under a pressure of 9 kg/cm 2 G. The thus- obtained cured board was subjected to the neasurements of the Charpy in- pact strength according to the procedure specified in JIS K 6971 and the bending strength and campressive strength according to the procedure specified in JIS R 5201.

Evaluation was also made of the adaptability to naildriving for cured boards prepared by extrusion moulding through a die of 15 nn thickness opening followed by curing under the same curing schedule as above. Iron nails of 2 mL diameter were driven into the board by hanTnering and the condition of the board was visually exancined to make a record of A or B when no cracks were found or when cracks were found respectively in the board. The results are shown in Table 1.

Ccnp,arative Example 1.

For camparison, four extrusion-mouldable cement-based csitions, referred to as the compositions R-I, R-II, R-III and R-IV hereinbelow, were prepared in substantially the sarne manner as in the above ExaTrple except that the unr efined crude linter pulp was replaced with 5 parts or 7 parts of a reclaimed pulp from waste paper, of which the fibre length was 0. 5 to 3 nTn and the fibre dimneter was 10 to 30 pm, the binder was the binder I in each formulation in an amount indicated in Table 2 below and the water/cement ratio was increased as indicated in Table 2.

The formulation and the results of the evaluation tests for each of the compositions R-I to R-W are suni=ized in Table 2 below.

Table 1

Camposition No.

Pulp addedr parts Binder added (parts) Water/cerrent ratio,% I II III IV V VI 1 2 3 3 4 5 TV III (0.5) (0.5) 26 1 11 1 1 (0.4) (0.5) (0.5) (0.5) 26 27 29 30 cure time, hours 3 3 3 3 3 3 Condition of A A A A A A green body Charpy impact 3.2 3.5 3.9 3.8 4.1 4.1 strength Nail driving A A A A A A adaptability Bending 2 200 200 200 210 200 200 strength, Canpressive 2 350 397 350 380 380 350 strength, kg/cn 1 " 17 - Table 2

Camposition No. R-1 R-11 R-II R-IV 0 Pulp added, 5 5 7 7 parts Binder added (parts).

1 1 1 1 (0. 8)- (Q. 9) (0.9) (1.0) water/cement 30 30 34 34 ratio,% Cure time, hours - 3 - 3 Condition of B B A green body Charpy impact - 2.1 2.1 strength Nail driving - A - A adaptability Bending 2 - 115 strength,kg/m Ccmpressive 2 - 300 - 250 strength,kg/cn - 18 Ccriparative EYle 2.

For further carrparison, four extrusion-mouldable carentbased compositions, referred to as the compositions B-It B-II, B-III and B-IV hereinbelow, were prepared in the same manner as in CaTiparative Example 1 above except that the reclaimed paper pulp vms replaced with a broadleaf wood pulp, of which the fibre length was 0. 5 to 4 nTn and the fibre diameter was 10 to 40 un, the binder was the binder I in each formulation in an amount indicated in Table 3 below and the water/cement ratio was as indicated in Table 3.

The formulation and the results of the evaluation tests for each of the compositions B-I to B-1V are sumnarized in Table 3 belcr.%,.

Table 3

Csition No. B-I B-II B-III B-1V Pulp added, 5 5 7 7 parts Binder added 1 1 1 (parts) (0.7) (0.9) (0.8) (0.9) Water/cement 30 30 34 34 ratio,% Cure t-ime, hours - 6 - 8 Condition of B A B A green body Charpy inpact 2.4 2.4 strength Nail driving A - A adaptability Bending 2 130 - 130 strength, Carrpressive 2 300 - 300 strength,kg/am t Comparative Example 3.

For still further comparison, four extrusion-Muldable cement-based carrpositionsp referred to as the compositions C-I, C-II, C-III and C-1V hereinbelow, were prepared in the same manner as in Comparative Example 1 above except that the reclaimed paper pulp was replaced with a coniferous wood pulp, of Which the fibre length was 0.9 to 6 nn and the fibre diameter was 10 to 70 n, the binder was the binder 1 in each formulation in an amount indicated in Table 4 below and the water/cement ratio was as indicated in Table 4.

The formulation and the results of the evaluation tests for each of the compositions C-I to C-IV are summarized in Table 4 below. Comparative Examples 4 and 5.

For additional comparison, four extrusion-mouldable ca'rKmt-based compositions, referred to as the compositions P-I, P-II, P-III and P-TV hereinbelow, were prepared in Ccuparative Example 4 in the same manner as in Comparative Example 1 above except that the reclaimed paper pulp was replaced with a refined linter pulp, of wtdch the fibre length was 1 to 7 = and the fibre diaueter was 10 to 40 pm, the binder was the binder I in each formulation in an amount indicated in Table 5 below and the water/cement ratio was as indicated in Table 5.

One:more comparative composition, referred to as A-1 Table 4

Csition No. C-I C-II C-Iii C-IV Pulp added, 5 5 7 7 parts Binder added 1 1 1 1 (parts) (0.7) (0.8) (0.8) (0.9) Water/cement 30 30 34 34 ratio,% Cure tIme, hours - 5 - 7 Condition of B A B A green body Charpy impact - 2.5 2.5 strength Nail driving - A - A adaptability Bending 2 - 130 strength, Ccmpressive 2 - 320 - 300 strength.

hereinbelow, was prepared in Ccrnparative Example 5 in the same n-amer as above except for the use of asbestos fibres, of which the fibre length was 1 to 10 nn and the fibre diameter was 1 to 10 Irn, in place oil the pulp, the binder was the binder I in an c-mx=t indicated in Table 5 below and the water/cement ratio was as indicated in Table 5.

The-fo = lation and the results of the evaluation tests for each of the campositions; P-I to P-1V and A-I are suwarized in Table 5 below.

Table 5 camposition No. P-I P-II P-III P-1V A-I pulp or asbestos 4 4 5 5 8 added, parts Binder added 1 1 1 1 1 (parts) (0.5) (o.5) (0.6) (o.7) (1.0) Water/cement 29 29 30 30 33 ratio,% Cur( tim,hours - 3 - 3 3 Condition of B A B A A green body Charpy ct 3.0 3.0 3.5 strength Nail driving A A B adaptability Bending 2 200 200 200 strength,kg/cm Ccrnpressive 2 350 320 340 strength,kg/cm CIADIS 1. An extrusion-mmldable cement-basea ccn-position which comprises, as a blend: (a) a hydraulic cement; (b) an inorganic aggregate material in the form of a powder; (c) an organic polymer as a binder; (d) fibres of crude linter pulp before refinement; and (e) water in an amount sufficient to impart to the ccuposition a consistency suitable for extrusion moulding.

2. An extrusion-mouldabie cement-based composition as claimed in claim 1, in which the amount of the fibres of crude linter pulp as the component (c) is in the range from 2 to 5 parts by weight per 100 parts by weight of the total amount of the components (a) and (b).

3. An extrusion-mouldable cement-based csition as claimed in either of the preceding claims, in which the organic polymer as a binder is a watersoluble cellulose ether.

4. An extrusion-mouldable cement-based c sition as claimed in clabn 3r in which the water-soluble cellulose ether has such a degree of polymerization that a 2% by weight aqueous solution thereof has a viscosity of at least 15,000 centipoise at 2CPC.

An extrusion-mauldable cement-based composition as i 1 claimed in any of the preceding claims, in wl-dch the amount of the organic polyner as a binder is in the range frcul 0. 2 to 1. 0 part by weight per 100 parts by weight of the total amount of the camponents (a) and (b). 10 6. An extrusion-mouldable ceTent-based ccniposition as claimed in any of the preceding claims, in which the amount of the water as the ccoponent (e) is in the range frcrn 20 to 50 parts by weight per 100 parts by weight of the total amount of the cnents (a) and (b).

7. An extrusion-inouldable carient-based cculposition as clabwd in any of the preceding claims, substantially as hereinbefore described in any of the foregoing Examples.

Published 1991 at The Patent Office. Concept House, Cardiff Road. Newport, Gwent NP9 I RI-i. Further copies rnay be obtained from F,Wes Branch, Unit 6. Nine Mile Point. Cwmfelinfach, Cross Keys, Newport, NP 1 7HZ. Printed by Multiplex techniques ltd, St Mary Cray. Kent.