AU607039B2 - Magnesium cements comprising a partially dehydrated magnesium salt and a very reactive magnesia, magnesium binders with accelerated setting and improved water resistance, obtained from such cements, and non-expanded or expanded material obtained with such a magnesium binder - Google Patents

Description

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4' AUSTRALIA 07 39 PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE Application Number: Lodged: Complete Specification Lodged: Accepted: Published: aImendii,:fl{s rnt e i l Sct:U).l 49 a ,L is uo 11 ccL tur printing Priority: Related Art: TO BE COMPLETED BY APPLICANT Name of Applicant: SAddress of Applicant: Actual Inventor: CENTRE SCIENTIFIQUE TECHNIQUE DU BATIMENT 4, avenue du Recteur Poincarre 75782 PARIS CEDEX 16, FRANCE4 1. GABRIEL ROUX 2. ANDRE BALME 3. ERIC BURIOT 4. MARCEL RUBAUD ANDRE FUMEZ 6. PATRICE HAMELIN ARTHUR S. CAVE CO.

Patent Trade Mark Attorneys Level Barrack Street SYDNEY N.S.W. 2000

AUSTRALIA

CO

Address for Service: .,Complete Specification for the invention entitled MAGNESIUM oEMENTS COMPRISING A PARTIALLY DEHYDRATED MAGNESIUM SALT AND A VERY REACTIVE MAGNESIA, MAGNESIUM BINDERS WITH ACCELERATED SETTING AND IMPROVED WATER RESISTANCE, OBTAINED FROM SUCH CEMENTS, AND NON-EXPANDED OF EXPANDED MATERIAL OBTAINED WITH SUCH A MAGNESIUM BINDER.

The following statement is a full description of this invention including the best method of performing it known to me:- 1 ASC 49 1: i; i -i 1A- Magnesium cements comprising a partially dehydrated magnesium salt and a very reactive magnesia, magnesium binders with accelerated setting and improved water resistance, obtained from such cements, and non-expanded or expanded material obtained with such a magnesium binder The present invention relates essentially to magnesium cements comprising a partially dehydrated magnesium salt and a very reactive magnesia, to magnesium binders with accelerated setting and improved water

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r resistance, obtained from such cements, and to a nonexpanded or expanded material obtained with such a magnesium binder.

Magnesium binders comprising a magnesium salt, magnesia and water are already known for forming products which can be used especially in the b *lding industry. The characteristics of the products obtained differ according to the proportions of the various base components. A hydrated magnesium sulfate (MgSO 4 .7H20) normally used as the magnesium salt.

Thus French patent document A-2 479 182 has described a process for the manufacture of facings for 'a 'building units and the building units obtained hy o 25 application of this process. According to the process described, the hydraulic resin is made up of a mixture comprising from 20 to 30% of magnesium chloride and from 70 to 80% of magnesium oxide, to which the smallest possible variable amount of water is added to give a mixture which can be poured and molded (page 2, lines 26 to 31, and claim Setting due to the formation of oxychloride is obtained by applying external heat, especially at a temperature of between 40 and 500°C (page 2, lines 24-25, and claim 1).

15 as their various combinations. Thus the amount of water can be varied within certain limits in order to ensure the correct handling properties. It is essential in all -2- It is indicated that this application of I external heat accelerates the setting time from about 48 h in the open air to between 4 and 6 h (page 4, lines to 11).

It is indicated that the product obtained is characterized by a high degree of hardness, a finegrained appearance, a remarkable dimensional stability, an extremely low crosslinking shrinkage and fireproofing properties (page 4, lines 12 to It is further indicated that it is advantageous to introduce fillers such as sand, laterite, calcium carbonate or powdered marble, the percentage incorporated generally being from 25 to 30 (page 4, lines 26 to 29).

STus the teaching of the said document consists in shortening the setting time by external heating of the magnesium binder comprising a conventional magnesium chloride, i.e. a hydrated magnesium chloride (MgCl 2 .6H 2 0).

An improvement to this process has been described in French patent document A-2 487 816. According to this improved process, a substantial exothermic reaction is caused which enables a temperature of the order of 150°C to be reached in a period of time of between 1 and 3 h in particular (page 2, lines 4 to 11, and claim 1).

The means by which this exothermic reaction can 25 be produced is either an ultrasonic emission at 20 kHz C CC and at an amplitude of between 5 and 40 Pm (Example 1), *I c or ultraviolet radiation, on the one hand at long wavelengths and on the other hand at short wavelengths (Example or chemical activation by the addition of a mixture of hydrochloric acid and an oxidizing product, for example Javelle water, in a proportion of the order of 15 to 30% (Example 3).

Furthermore, French patent document A-2 499 550 has proposed a foaming mineral composition, in particular a mineral resin based on magnesium oxychloride or oxy- -3sulfate, which is in the form of a mineral paste ready i for expansion and is characterized by a mixture of magnesium chloride or sulfate, water, magnesium oxide, a foaming agent and carbon black.

In the prior art, the magnesium salt is always in the conventional form, i.e. hydrated (6H 20 for 'C 2 or 7H20 for the sulfate).

Moreover, in the magnesium binder formulations of the prior art, the setting time is relatively long, which is why attempts have been made to shorten this setting time by the external application of heat (French S. patent document A-2 487 816) without thereby minimizing this setting time.

C r r Furthermore, the moisture resistance of the S 15 material obtained still leaves something to be desired

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in certain cases.

The object of the present invention is therefore to solve the novel technical problem which consists in providing a novel magnesium cement making it possible to prepare a magnesium binder with accelerated setting, i.e. with a reduced setting time, even at ambient temperature, of a few minutes to about 1 h.

i1 A further object of the present invention is to solve the novel technical problem which consists in S 25 providing a novel magnesium cement making it possible to r (rprepare a magnesium binder having improved moisture .i resistance.

Finally, a further object of the present invention is to solve the novel technical problem which consists in providing a magnesium cement making it possible to prepare a novel magnesium binder with accelerated setting ard high moisture resistance, which simultaneously has excellent mechanical properties.

The present invention solves all these technical problems simultaneously by providing a magnesium cement, 4 with accelerated setting, which consists essentially of a mixture of the ternary type comprising, as the active components, at least one magnesium salt and magnesia, to which setting water is added, wherein the magnesium salt is a partially dehydrated magnesium salt, preferably a magnesium salt having an average degree of hydration of between 0 and about 5, more preferably of between about 2 and about 4, expressed in molecules of water per molecule of magnesium salt.

A magnesium chloride or a magnesium sulfate is preferably used as the magnesium salt.

This partially dehydrated magnesium salt can be obtained by any known salt dehydration process,. These anhydrous or partially dehydrated salts can be prepared in a static oven or in rotary kilns which mix the product in a stream of hot air at about 100"C for a sufficient time to give the desired average degree of hydration, or by blending with products of different degrees of hydration.

Preferably, the second component of the magnesium cement according to the invention consists of caustic magnesia, which is preferably a very reactive magnesia having an iodine number greater than or equal to 30 mg of 1 2 /g of magnesia and a AT 25 0 C, determined by a hydrogen peroxide test according to the following method: Add 2 g of magnesia to 10 ml of 30% H202 in a 50 ml <4 'beaker, shake by hand for 5 seconds and record thei increase in temperature of the solution test carvied out Pt a laboratory temperature of 23-25 0

C.

In another particularly preferred embodiment, the magnesia has the following characteristics: a reactivity of more than 30 mg of 1 2 /g of magnesia, measured by the iodine absorption number according to Standard NFT 45006; a specific surface area of 20 to 40 m 2 determined by the BET method; an untamped apparent density of more than 0.8.

The invention further relates to the magnesium binders obtained with the above-mentioned cement to which setting water is added, the said binders being obtained by mixing the dry cement formulation with the setting water.

The water used for mixing in order to prepare a magnesium binder is advantageously approximately neutral and can optionally be heated to accelerate the reaction, especially when the outside temperature is too cold, as in winter.

In a particularly preferred embodiment, the relative proportions of partially dehydrated magnesium salt according to the invention, magnesia and setting water are within the areas ABC and A'B'C' of the ternary diagrams, corresponding to area no. 1 in the attached Figure no. 1 or Figure no. 2.

Preferably, the relative proportions are within the more restricted area CDEF of the ternary diagram, this more restricted area corresponding to area no. 2 in Figure no, 1 and making it possible to obtain not only accelerated setting but also improved moisture resistance through a reduction of the solubility. This reduction of the solubility results from a shift of the final composition towards brucite (Mg(OH) 2 which is a virtually insoluble mineral.

The invention further relates to a process for the preparation of a magnesium cement, with accelerated setting, which consists essentially of a mixture of the ternary type comprising, as the active components, at least one magnesium salt and magnesia, to which setting water is added, whereJn the magnesium salt used is a partially dehydrated magncfsium salt, preferably a magnesium salt having an averege degree of hydration of between 0 and 6 about 5, more preferably of between about 2 and about 4, expressed in molecules of water per molecule of magnesium salt.

Preferably, very reactive caustic magnesia is used which has an iodine number of more than 30 mg of 1 2 /g of magnesia and a AT 4 25°C, determined by a hydrogen peroxide test.

Further objects, characteristics and advantages of the invention will be clearly apparent to those skilled in the art on reading the following explanatory description, which is given with reference to several Examples and to the attached drawings, in which: Figure 1 represents the ternary diagram I0C MgO-MgC12- 20 showing the preferred area of relative proportions defined by the letters A-B-C (area no. 1), for which particularly accelerated setting of the Smagnesium binder is obtained, as well as the even more preferred restricted area no. 2 defined by the letters c C-D-E-F, for which the setting is particularly 20 accelerated and the moisture resistance is particularly

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improved through a reduction of the solubility in water.

Figure 2 represents the analogous ternary diagram obtained with MgO-MgSO 4

-H

2 0, in which the abovementioned area no. 1 is defined by the letters tCt 25 Figure 3 represents the ternary composition LM85.14 obtained in Example 1.

*o Figure 4 represents the ternary compositions obtained with a slab of the FA type (no. 1) and a slab of the FNA type (no. 2) based on the initial compositions of Example 3. The points 1' and 2' represent the final ternary compositions recalculated from the mineralogical compositions.

Figure 5 represents the diffraction pattern of the mortar of Example 4 according to the invention, which has a brucite composition.

7 SIn the following Examples, the percentages are given by weight and the temperatures in degrees Celsius, 6 unless stated otherwise.

Example 1 according to the invention Composition of magnesium binder of reference LM85.14.

In this Example, a magnesium binder of low I magnesium salt content, with accelerated setting, is prepared by using the cement according to the invention, which here consists of a partially dehydrated magnesium chloride containing 4 molecules of water and a very reactive natural magnesia.

c r The characteristics of the magnesium chloride are as follows: j c t CHARACTERISTICS OF THE PARTIALLY DEHYDRATED MAGNESIUM i 15 CHLORIDE ACCORDING TO THE INVENTION This is a partially dehydrated magnesium chloride containing an average of 4 molecules of water, expressed as the number of molecules of water per molecule of magnesium chloride. This salt is obtained by dehydrating wafers of bischofite, of the formula MgCl 2 .6H 2 0, .n an oven at a temperature below 100 0 C for 7 h, which makes it possible to obtain a degree of hydration of 4H 2 0 (43% of bound water).

This salt is reduced to very fine powder in order to facilitate dispersion.

A very reactive natural magnesia having the following characteristics is used as the second component of the magnesium cement according to the invention: CHARACTERISTICS OF THE MAGNESIA Commercial reference: MG2.150 from GUYON S.A.

Origin: Greece Caustic magnesia Iodine absorption number: 48 mg of 1 2 /g of magnesia Blaine specific surface area (0.65 of porosity) a 172 BET 30 m'/g i.

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i 8 Particle density: 3.1 (pycnometry with CC1 4 Mineralogical composition: quartz 7% olivine (ferromagnesium silicate) 10.5% periclase 82.5% Particle size distribution: 75% passage at 40 p.

Density: 0.84 g/cm 3 As this magnesia can be of variable quality, it is important to check that it corresponds to the preferred characteristics steted above.

A magnesium binder formulation is prepared according to the following proportions: Formulation Dry products: magnesia (described above) 56.94% MgCl 2 .4H 2 0 (described above) 20.68% Neutral water: 22.34% The various components of the formulation are then mixed by gradually adding the water to the dry products, with concomitant mixing, to give a magnesium binder forhuilation which can be poured or molded and which makes it possible to obtain the following ternary composition of reference LM85.14, mentioned in the ternary diagram MgO-MgC 2 -H20 in Figure 3, allowing for a periclase content of 82.5% in the magnesia and a dry salt content of 57% in the MgCl 2 .4H 2 0: MgO 52.18; salt 13.08;

H

2 0 34.73.

The setting time is 6 min and the maximum tem- 30 perature reached is 180°C in 9 min.

The mineralogical composition, given by an X-ray diffraction pattern, is as follows: 28.6% of MgO (expressed as periclase), 41.36U of Mg(OH) 2 (expressed as brucite), 30% of oxychloride 5.1.8.

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-9- K After setting, a compressive strength of 91 MPa is obtained with this magnesium binder according to the invention.

The solubility reaches an upper limit of after 5 cycles in which 24 h of immersion in water is alternated with 24 h in a dry atmosphere (at Example 2 according to the invention Expanded magnesium binder of reference LME1.2456 This expanded magnesium binder is prepared witth the same salt, MgCl 2 .4H 0, as that used in Example 1 and the same magnesia as that ujsed in Example 1, according to the following proportions of the initial mixture: Composition of the initial mixture in percentages of the reactants: S 15 60.6 of magnesia of Example 1, 19.8 of MgCl 2 .4H 0 of Example 1, 19.5 of H 2 0, which, expressed in percentages of the ternary diagram, gives the following proportions: 55.2 of MgO (magnesia), 12.9 of MgCl 2

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31.9 of H 2 0.

The water is added to the mixture of powdered magnesia and salt, with mixing, after which the following 425 mixture is added to cause expansion: 1,17% of a solution of a high-molecular surfactant of the polyamine ty pe 0.3% of powdered MnO 2 1.17% o.~f 110 volume H 202 (these proportions being given by weight relative to the initial total mixture), which causes oxygen to be released into the mixed composition, expanding the magnesium binder.

Setting is obtained in about 1 Ii, the temperature reaching a maximum of 12000.

J- 10 The mineralogical composition of the solidified expanded magnesium binder is as follows: Mineralogical composition: periclase (expressed as MgO) 3.2% brucite (Mg(OH) 2 25.2% ternary composition 5.1.8. 42.6% ternary composition 3.1.8. 29.0% The compressive strength obtained with bars of dimensions 3 cm x 3 cm x 3 cm is 5 MPa.

The density is 0.54.

ct r r e The solubility reaches the upper limit at a Sweight loss of 10% after immersion in water alternated r c with drying according to the stress cycle of Example 1.

Example 3 of the invention Preparation of mortar with a magnesium chloride for making slabs of reference FNA-FA The magnesia used is the same as that used in Example 1, of reference MG2.150.

Also, the partially hydrated magnesium salt used is a mixture of anhydrous magnesium chloride and Smagnesium chloride hexahydrate in relative proportions by weight of 48% and 52% respectively, giving an average degree of hydration of 2H 2 0 (27.4% by weight).

I This salt is powdered to give a good dispersion.

a 25 The filler used to prepare the mortar is siliceous sand with a mean particle size of 0.4 mm and a fineness index of AFA42, of reference SIKA HOSTUN RF.

A mortar formulation of reference FA is prepared which has the following composition: Formulation of PA Binder 55% Sand Composition of the binder: magnesia according to Example 1 57% SMgC1 2 with average of "2H20" 14.2% 120 e 28.8% 11 Allowing for a periclase content of 82.5% in the magnesia, the following ternary composition is obtained: MgO 52.2 MgC12 11.5 H20 36.3.

A formulation of reference FNA is also prepared which has the following composition: Formulation of FNA Binder 64.5% Sand 35.5% Composition of the binder: magnesia 54.2% MgCl 2 with average of ou t °o 2H 2 0 13.5% Th n* H 2 0 32.3% I The ternary composition thus obtained, allowing j cc for the purity of the magnesia, is therefore: e 15 MgO 49.4 MgCl2 10.8 H 2 0 39.8.

Slabs of small thickness (about 5 and 7 mm) consisting of the magnesium mortar with activated setting are prepared in the conventional manner with each formulation, by pouring or molding, after the components have been mixed. Slabs of large dimensions are not deformed after setting, the composition of the binder being the same. The slab containing the greater proportion of silica filler, FA, was placed outside for weathering.

Its mechanical properties did not vary in two years, despite the fact that the mineralogical composition of the binder was a priori rather unfavorable (very rich in oxychlorides).

The initial ternary compositions are shown on the ternary diagram (Figure 4) under no, 1 for the FA sabs and under no. 2 for the FNA slabs, and the references 1' and 2' represent the final ternary compositions as calculated below.

It should be noted that the content of crystalline silica was systematically overestimated by X-ray _1 i i *1 -12diffraction analysis. In fact, FA gives 60% (instead i of 45%) and FNA gives 42% (instead of 35.5%).

As regards the composition of the binder, on i the other hand, when the percentages by weight of MgO, MgC12 and H20 have been recalculated from the minera- S logical compositions given by analysis, they are found to correspond to the formulations less about 10% of water. In fact, a loss of about 10% of water is measured at the time of exothermic setting. This gives the following analysis for the binder part of the mortar: i Formulation- 10% of FA periclase: 28% MgO 58.54 58 brucite 10.3% MgC120 11.06 12.7 5.1.8. 61.7% H 2 0 30.4 29.2 FNA periclase: 22% MgO 55.28 54.95 brucite 12% MgC12 11.86 12.01 5.1.8. 66.2% H 2 0 32.83 33.03 The dominant mineralogical species is seen to be the oxychloride which represents 60 to 66% of the binder composition.

Setting is obtained in 30 min and the temperature reached is above 100C.

The mechanical characteristics obtained by 3point bending tests between two supports 100 mm apart give a breaking stress, calculated according to the following formula: 3 Fma x x distance between supports C width x (thickness) 2 of: 18.2 MPa for the FA slab 14 MPa for the FNA slab.

13 113 It can also be seen that the FA slab, which remained outside for 2 years and suffered no apparent damage, shows a greater bending strength than the FNA slab, confirming the good weather resistance.

Example 4 of the invention Magnesium mortar containing sulfate According to this Example, an activated formulation is prepared using a blend of natural and chemical magnesia, together with partially hydrated sulfates (an average of about 2H 2 Siliceous fillers are added to these two essential products of the magnesium binder according to the invention. The product can be expanded by the addition of hydrogen peroxide (the volume increase is about The formulation of the magnesium binder is as follows: Formulation by weight 1) magnesia: Salins du Midi "active 120" (chemical) 6% Eraclit or MG2.150 (natural) 2) magnesium sulfate, average degree of hydration: 2H20 23% of H20 42% 3) siliceous sands 82.3% The magnesia 120 from Salins du Midi has a l specific surface area of 120 measured by the BET method; this magnesia is very reactive and has an iodine number IN of about 70 mg/g of magnesia; it is a very pure magnesia of chemical origin ("marine").

The Eraclit and the MG2.150 have a specific surface area of between 40 and 60 m'/g and an iodine number IN of between 20 and They are natural magnesias originating from the

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"r 1111~--II- _-I-L._IILII^ II -14 calcination of cryptocrystalline giobertite.

It is preferable to use a blend because very reactive natural magnesias are currently unavailable on the market (unless produced by accident).

Mixing is carried out in the following manner.

Mixing dry product 78.5% water expanding agent (110 V H 2 0 2 diluted 1-fold) abovementioned surfactant Mixing is carried out by injection in a modified plaster machine, which mixes the dry product with the water.

The setting rate depends on the outside temperature and this rate can be adjusted using hot water.

Two tests were carried out: in the summer (June 1986): outside temperature 28°C water temperature 22 0

C.

Exothermic setting is obtained in 15 min.

in the winter (November 1986): outside temperature water temperature 45 0

C.

SAgain exothermic setting is obtained in 15 min.

The magnesium mortar obtained without expdnding (re agent has a low solubility, mainly because there is only 25 20% of dry salt.

SThe mechanical strength is not very high: R C is approximately equal to a few MPa which is not a problem for the use envisaged (injection into hollow building units to improve the acoustic insulation).

The mineralogical composition is that of a brucite composition, the X-ray diffraction pattern of which is given in Figure 5. It should be noted that the peaks of this mineral are very broad.

Of course, the invention includes all means which are technically equivalent to the means described, as well j as their various combinations. Thus the amount of water can be varied within certain limits in order to ensure the correct handling properties. It is essential in all cases to avoid an excess of water and hence not to use a magnesia of too fine a particle size (like some "marine" magnesias). In fact, the excess water used to wet the particles, and hence to ensure the handling properties of the mixture, has to drain off gradually as it cannot be integrated with the constituent minerals of the cement. This gradual drying can damage the material by shrinkage and cracking, this phenomenon being enhanced in the case of the preparation of an expanded material.

Moreover, all the ternary diagrams in the oi, Figures form an integral part of the invention.

S, 15 At least one filler and/or at least one aggregate 'can be added to the hydraulic binder at the mixing stage, there being no limitations as to their type mineral, vegetable, organic or their particle size.

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Claims (10)

1. A magnesium cement, with accelerated setting, which comprises a mixture of a ternary type comprising, as the active components, at least one magnesium salt and magnesia, to which setting water is added, wherein the magnesium salt is a partially dehydrated magnesium salt having an average degree of hydration of between 0 and about 5 expressed in molecules of water per molecule of magnesium salt.

2. A magnesium cement according to claim 1 having an average degree of hydration preferably of between about 2 and about 4.

3. A magnesium cement according to claim 1 or claim 2, wherein the magnesia used is caustic magnesia and is very reactive, having an iodine number of more than 30 mg of I 2 /g of magnesia and a AT<25 0 C, determined by a hydrogen peroxide test. oo, 4. A magnesium cement according to any one of claims 1 to 3, 0 o o wherein the magnesium salt is a partially dehydrated ^r 0°o0 anhydrous magnesium chloride or magnesium sulfate, or a mixture 0o0 of anhydrous salt and partially dehydrated salt giving the desired average degree of hydration. A magnesium binder obtained using the cement according to any one of claims 1 to 4, wherein the relative proportions of magnesium salt, magnesia, expressed as periclase, and water are j t defined by area no. 1 in Figure 1 or Figure 2, bounded by the letters A-B-C or respectively.

6. A magnesium binder according to claim 5, wherein the relative proportions of magnesium salt, magnesia and water are Swithin the restricted area no. 2 in Figure 1, defined by the letters C-D-E-F.

7. A magnesium binder according to claim 5 or claim 6, which also comprises an expanding agent.

8. A magnesium binder according to any one of claims 5 to 7, wherein the water used is approximately neutral and is optionally heated.

9. A material obtained with a magnesium binder as defined in any one of claims 5 to 8, in a non-expanded or expanded state. 0063y/AMR 16 r 1 A material according to claim 9, which contains a filler and/or an aggregate.

11. A process for the preparation of a magnesium cement, with accelerated setting, which comprises a mixture of a ternary type comprising, as the active components, at least one magnesium salt and magnesia, to which setting water is added, wherein the magnesium salt used is a partially dehydrated magnesium salt, having an average degree of hydration of between 0 and about 5 expressed in molecules of water per molecule of magnesium salt.

12. A process according to claim 11, having an average degree of hydration of between about 2 and about 4.

13. The process according to claim 11 or claim 12, wherein very reactive caustic magnesia is used which has an iodine a o o number of more than 30 mg of I2/g of magnesia and a AT<25 0 C, 08 determined by a hydrogen peroxide test. 0 000 o 1 14. A magnesium cement substantially as herein described 0" with reference to any one of the drawings. S 15. A magnesium cement substantially as herein described with 00 0 reference to any one of the Examples. DATED this 4th day of June, 1990. oite CENTRE SCIENTIFIOUE ET *TECHNIQUE DU BATIMENT S* By Its Patent Attorneys ARTHUR S. CAVE CO. 0063y/ 17