CEMENTITIOUS ARTICLE

Abstract: A high flexural strength alternative to asbestos cement articles. The alternative being a cementitious article comprising 1) 50 to 200 parts by weight of cement; 2) 50 to 150 parts by weight of a filler; 3) 5 to 20 parts by weight of an acrylic modifier on a dry weight basis; 4) 27 to 30 percent by weight of the cement of water. The filler may be sand or another crystalline or non-crystalline silicate, glass, fly ash, rice hull ash or crushed quartz. The acrylic modifier is one of a range of powders or emulsions of acrylic acid polymers and copolymers. The articles are formed by mixing the ingredients, shaping to the desired shape, compressing the mixture at a pressure of at least 1200 p.s.i. and curing.

Description: CEMENTITIOUS ARTICLE TECHNICAL FIELD . The present invention relates to building articles form from cementitious materials and more particularly to buildin articles in the form of sheets formed from such materials. The invention further relates to a process for the formation of such building articles. BACKGROUND ART It has been conventional to form building articles such as cladding sheets and the like from asbestos cement which is a cementitious composition reinforced with asbestos fibres. In recent years it has been recognised that the extraction an processing of asbestos constitutes a serious health hazard an it is thought that the handling of asbestos containing products, including asbestos cement articles, could also be deleterious to human health. For this reason efforts have been made to find materials which exhibit the desirable properties of asbestos cement compositions without the health hazard of those asbestos cement compositions. These desirabl properties include cheapness, relative ease of working and high flexural strength. The present invention is designed to offer an alternative material for use in place of asbestos cement in at least some of its applications. DISCLOSURE OF INVENTION The present invention consists in a building article comprising from 50 to 200 parts by weight of cement, from 50 to 150 parts by weight of a filler, from 5 to 20 parts by weight of an acrylic modifier on a dry weight basis and from 27 to 30 percent by weight of the cement of water, including any water present in the modifier, which materials have been mixed, formed, into a desired shape, compressed at a pressure of at least 1200 p.s.i., and cured. The present invention further consists in a process for forming a building article comprising mixing together from 50 to 200 parts by weight of cement, from 50 to 150 parts by - weight of a filler, from 5 to 20 parts by weight of an acrylic modifier on a dry weight basis and from 27 to 30 percent by weight of the cement of water, including any water present in the modifier, forming the mixture into a desired shape, compressing the mixture at a pressure of at least 1200 p.s.i. and curing the compressed mixture. The building articles according to the present invention may comprise sheets or panels, blocks or formed shapes for use; as guttering, ducting or the like. It is however in the area of sheets and panels in which the present articles have particular applicability due to the high flexural strength exhibited by these articles when made by the process according to this invention. fleets having a thickness of from 1/4" to 1 1/2" for use as flooring materials are paticularly advantageously made from the present materials. The cement used in the present invention is preferably, conventional Portland cement. The cement should constitute from 50 to 200 parts by weight of the articles and preferably 80 to 120 parts by weight. For use in flooring sheets the cement content is most preferably 100 parts by weight. The filler preferably comprises a crystalline or non crystalline silicate such as sand or crushed glass however other fine fillers such as fly ash, rice hull ash, crushed quartz and the like could equally well be used. A preferred filler is a crushed naturally ocurring volcanic glass known as perlite. The filler may all be fine grade material, however, it is preferable to use a mixture of fine filler and coarser material. Advantageously 75 parts of fine material to 25 parts of 6/10 mesh material is used. The filler should be present in an amount of from 50 to 150 parts by weight, preferably from 75 to 125 parts by weight. It is most preferable that the filler comprises 100 parts by weight. The acrylic modifier is one of a range of commercially available cement additives which constitutes powders or emulsions of acrylic acid polymers and copolymers. These modifiers increase the impact and flexural strength of cement as well as improving its adhesion to a variety of substrates.Preferred examples of acrylic modifiers are the products MC76 and -BβOA sold by Rohm and Haas. The modifier i present in the article in an amount of 5 to 20 parts by weigh of modifier solids. If the modifier is an emulsion the water content is included in the total water content in the . articles. More preferably the modifier is present in an amount of 8 to 14 parts by weight and most preferably 11 part by weight. The amount of water in the mixture used to form the articles according to this invention should be from 27 to 30 percent by weight of the cement, including any water present in the acrylic modifier. The amount of water is sufficiently low that no water will be exuded when the mixture is compressed while being sufficient to bring about the appropriate hydration reaction involved in the setting of the cement content of the article. It is preferable that a surfactant should be added to th water to aid the wetting of the filler and the cement. The articles according to this invention may advantageously include a reinforcing material such as a metal or plastic mesh or fibrous material such as fibres of cellulose or glass. This reinforcing material is preferably applied as a layer between two layers of the ceraentitious mixture prior to the formed article being compressed. The process according to the invention is preferably carried out by mixing the filler with from 20 to 50% of the total water content and at least a proportion of the acrylic modifier and then adding the cement to form an esentially "dry" granular mixture which is flowab-le.. Half of this flowable mixture is then put into a suitable mould and levelled. A reinforcing mesh of steel wire is preferably laid on this layer of cementitious mixture and half of the remaining water sprayed in a fine spray evenly over the layer. The remaining mixture is then placed over the reinforcing mesh and levelled. The remaining water is then sprayed onto the top of the mixture and the whole mould passe into a press which compresses the formed mixture at a pressur of at least 1200 p.s.i. preferably between 1200 and 4000 p.s.i., most preferably at or about 3000 p.s.i. If necessary a panel may be placed over the formed mixture prior to its being compressed to ensure that the pressure is applied evenl over the whole article. In another embodiment of the invention the wire mesh may be supported in a suitable mould and all of the granular cementitious mixture added to the mould and vibrated down through the wire mesh into a uniform screeded condition. The remaining water is then added and the material pressed as described above. In tliis embodiment of the invention it is desirable to add a surfactant to the water to assist in- wetting the cementitious material. After the article has bee formed and compressed it must be cured. The article will generally have acquired sufficient 'green strength for the mould to be removed in a matter of hours, however, a period o from seven to twenty eight days is required for sheets formed by the present process to acquire sufficient strength to be freely handled. Panels formed by the process according to this invention have been found to be flame resistant and non-flamable, to have a very low moisture absorbtion after initial curing and to have a high flexural strength. BEST MODE OF CARRYING OUT THE INVENTION Hereinafter given by way of example only is a preferred embodiment of the present invention. A flooring sheet was formed from the following materials: Cement (Goliath "A") - 100 parts by weight. Fine sand - 75 parts by weight. Coarse sand - 100 parts by weight. Acrylic modifier (MC-76 Rohm and Haas) (dry weight basis) - 11 parts by weight. Water - 29.6 parts by weight. . Surfactant - 0.01 parts by weight in the water. The sheet was formed by the following process:- 1. The sand was measured and placed into a conventional concrete mixer. 2. The acrylic modifier was measured out and mixed with 20% of the total water requirement. 3. The water/acrylic modifier mixture was added to the sand in the mixer while the mixer was operating. 4. The cement was then measured and introduced into the operating mixer to produce a "dry" flowable granular moss. 5. Half of the mixture was then placed in a mould comprisin a base board on which was placed a rectangular frame defining a space 1200 mm. x 2400 mm. x 13 mm. The mixture was levelle in the frame on the base board. 6. A reinforcing mesh of steel 4 ram. wires having a grid spacing of 200 mm. and a size of 1100 x 2300 mm was placed on the levelled layer of mixture. 7. 50% of the remaining water was sprayed on the mixture in the mould in a fine spiray evenly applied over the whole layer. 8. The remaining cementitious mixture was placed in the mould and levelled to produce a void free screened surface. 9. The remaining water was sprayed onto the top surface of the mixture in the mould as in step 7. 10. A pressure levelling board 1200 mm. x 2400 ram. was place over the cementitious mixture in the mould. 11. The mould was introduced into an hydraulic press and the mixture in the mould compressed at a pressure of 2000 p.s.i. for one minute. 12. The mould was removed from the press and the pressure levelling board immediately removed. 13. After 2 hours the mould frame was removed from around the formed sheet leaving the sheet on the base board. 14. After 12 hours the formed cementitious sheet was removed - _ - from the base board and stacked horizontally with other similar sheets: a plastic sheet was placed between juxtapose cementitious sheets. 15. After seven days the cementitious sheets were found to b able to be freely handled, however, it was twenty eight days before the maximum strength was developed in the sheets. It was found that the sheets so formed showed a water absorption of only 5% by weight after 72 hours immersion in water. The cured sheets had a density of 2.32 grams/c.c. and a mass of 32.5 kg per square metre.

Claims: - T- - The claims defining the invention are as follows:- 1. A building article comprising from 50 to 200 parts by weight of cement, from 50 to 150 parts by weight of a filler, from 5 to 20 parts by weight of an acrylic modifier on a dry weight basis and from 27 to 30 percent by weight of the cement of water, including any water present in the modifier, which materials have been mixed, formed into a desired shape, compressed at a pressure of at least 1200 p.s.i., and cured. 2. A building article as claimed in claim 1 in which the cement comprises from 80 to 120 parts by weight of the article. 3. A building article as claimed in claim 1 or claim 2 in which the filler comprises sand, crushed glass or another crystalline or non-crystalline silicate. 4. A building article as claimed in any one of claims 1 to 3 in which the filler is present in an amount of from 75 to 125 parts by weight. 5. A building article as claimed in any one of claims 1 to 4 in which the acrylic modifier is an aqueous emulsion. 6. A building article as claimed in any one of claims 1 to 4 in which the acrylic modifier is present in an amount of 8 to 14 parts by weight on a dry weight basis. 7. A building article as claimed in any one of claims 1 to 6 in which the building article additionally contains a reinforcing material. 8. A building article as eia-imed in any one of claims 1 to 7 in which the building article is compressed at a pressure between 1200 and 4000 p.s.i. prior to being cured. 9. A building article substantially as hereinbefore described with reference to the example given herein. 10. A process for forming a building article comprising mixing together from 50 to 200 parts by weight of cement, from 50 to 150 parts by weight of a filler, from 5 to 20 parts by weight of an acrylic modifier on a dry weight basis and from 27 to 30 percent by weight of the cement of water - β . - including any water present in the modifier, forming the mixture into a desired shape, compressing the mixture at a pressure of at least 1200 p.s.i. and curing the compressed mixture. 11. A process for forming a building article as claimed in claim 10 in which the filler is mixed with from 20 to 50% of the total water content and at lest a proportion of the acrylic modifier and the cement then added to form a flowable "dry" grannular mixture, the mixture is placed in a mould and the remaining water sprayed onto the mixture, and the mixture' is compressed and cured. 12. A process for forming a building article substantially as hereinbefore described with reference to the example given herein.

Inventors: GRACE REGINALD FRANK
Applicants: GRACE REGINALD FRANK
Application year: 1981
Main classification: C04B13
IPC codes: C04B24