ACID RESISTANT CONCRETE ARTICLES, ESPECIALLY SULPHUR CONCRETE PIPES AND A METHOD OF MANUFACTURING THEM

Abstract: Acid resistant concrete articles, especially sulphur concrete pipes manufactured from a material formulated on the basis of a composition of portland cement concrete suitable for the manufacture of pipes by means of the dry casting method, the volume of portland cement, filler and water being replaced by a substantially equivalent volume of sulphur cement and filler, while the amount of other components remains substantially unchanged. The sulphur concrete pipes are manufactured by mixing the components of the material and adjusting the mixture to a temperature, where sulphur cement is liquid. At this temperature the mixture is cast while subjected to vigorous vibration, using a casting mould preheated to a temperature of up to 160 DEG C. The cast pipes can be removed from the mould immediately after casting. After only 24 hours they have obtained sufficient strength to be delivered to a building site. Sulphur concrete pipes are most suitable in aggressive environments, since they are resistant to acid and salt attacks.

Description: Title: Acid resistant concrete articles, especially sulphur ' concrete pipes and a method of manufacturing: them Technical Field The present invention relates to acid resistant concrete articles, especially sulphur concrete pipes and a method of manufacturing them. Background Art US-PS Nos. 4.311.826, 4.348.313 and 4.391.969 disclose sulphur cement compositions comprising elemental sulphur and a plasticiser. The plasticiser is usually present in an amount of approx. 5% and comprises a mixture of dicyclo- pentadiene and oligomers of cyclopentadiene in a -ratio of 1:1. US-PS No. 4.293.463 discloses a sulphur cement com¬ position comprising sulphur, a viscosity- increasin , snilace -active , finely divided particulate stabiliser, such as fly ash, and an olefinic hydrocarbon polymer material derived from petroleum and having a non-volatile content larger than about 50% by weight and having a minimum ij s iodine number of about 100 cg/g, said polymer being capable of reacting with sulphur to form a sulphur- containing polymer, (cf. column 2, lines 29-37) . Corre¬ sponding sulphur cement compositions are described in US- PS No. 4.058.500. Sulphur cement is used to replace conventional cement for the preparation of concrete. In contrast to conventional portland cement concrete the obtained sulphur concrete is di-tii.guishec 1 , by bein_c resistant to salt and acid attacks. Sulphur cement is the only binder when preparing sulphur concrete. Sulphur cement becomes liquid when heated to a temperature of up to approx. 135°C thus rendering the sulphur concrete as workable as conventional concrete. During the cooling process usually lasting only a few hours the sulphur concrete develops unique properties, such as compressive strengths of approx. 40 to 60 MPa, flexural strengths of approx. 8 to 12 MPa, high impact strength, high wear resistance, absolute water impermeabi¬ lity, resistance to salt and acid attacks as well as resistance to freeze-thaw exposure. Examples of sulphur concrete and its preparation are disclosed in US-PS No . s 4.025.352, 4.496.659, 4.332.911 and 4.332.912. Due to thes-e excellent properties sulphur concrete has been applied in many fields of industry dealing with aggressive environment, where conventional portland cement concrete disintegrates. Typical fields of application where the particular properties of sulphur concrete are of special interest include the manufacture of floors, coatings, foundations, walls, acid reservoirs, tanks, sewer systems and the like. Although there are many good reasons for using sulphur concrete no acceptable method for the manufacture of sulphur concrete pipes from sulphur concrete has yet been found. Various methods for the manufacture of such pipes have indeed been suggested, but none of them can be con- sidered satisfactory from the technical and economical point of view. Examples of known methods for the manu¬ facture of sulphur concrete articles are mentioned in the following patent specifications. US-PS No. 3.954.480 discloses concrete compositions, con¬ crete articles and methods of producing the articles, where a portion of the cement is replaced by sulphur, preferably plasticised sulphur. The patent thus 'ti.sclose-. a combination of sulphur concrete and conventional concrete. During the production of the concrete articles the material is shaped into the desired shape and is compacted, whereupon the product is left to stand to permit partial or complete hydration of the cement therein. The hydratised product is then heated to a temperature above the melting point of sulphur to plastify the sulphur, whereupon the article is cooled and ready to be used. This method is very time-consuming since the partial or complete hydratisation of the cement requires a long time and the heat treatment is usually carried out during heating for between 1 and 5 h at a temperature of between 121 and 177 β C. Moreover, due to the content of conventional cement it is impossible to obtain all the above advan¬ tages of sulphur cement. US-PS No. 4.134.775 discloses articles to be used as structural members, such as bricks, building blocks, mouldings, cornices or the like substantially comprising a 3 -dimensional matrix of solidified elemental sulphur and a solid, particulate, inorganic material uniformly distributed throughout the matrix, said particulate, in¬ organic material amounting to 20 to 80% by weight of the article. At least one part of the particulate, inorganic material is unfragmented fly ash amounting to 20 to 60% by weight of the article. The particulate, inorganic material has a particle size in the range of from 0.0005 to 10. C mm, the maximum particle size being small in comparison to the smallest dimension of finished article. The article is manufactured by mixing sulphur concrete at room temperature and pouring the mixture into a mould. The mixture is then heated until the sulphur has melted. The necessary strength of the article is obtained during the subsequent cooling. Such an article has a hardness significantly greater than the one for solidified sulphur and a compressive strength higher than the one obtained with aged, cast concrete, "'he produced articles cn also be extruded in form of pellets to be remelted for in situ use. The method disclosed in US-PS No. 4.134.775 is time- consuming and only applicable in connection with small articles and can thus not be used for the manufacture of pipes on an industrial scale. US-PS No. 4.256.499 discloses shaped sulphur concrete articles and their production from a mouldable composition of mineral aggregate, mineral binder, a sulphur component, such as elemental sulphur, and a liquid vehicle, such as water. The mixture is compacted and formed into a shaped body at an elevated compacting pressure, dried to vola¬ tilise the liquid vehicle and heated to melt the sulphur. The article is subsequently cooled to solidify the sulphur, whereby the mineral materials are bonded into a matrix with the sulphur. The use of liquid vehicle renders the method inconvenient and time-consuming, as subsequent to compacting and casting the material has to be dried until substantially all liquid vehicle is volatilised. US-PS No. 4.426.458 discloses fibre-reinforced sulphur concrete compositions, which according to the specification are proposed for the preparation concrete articles, such as paving slabs, structural members, curbings, gutters and pipes, "he sulphur concrete compositions comprises sulphur cement, aggregate and fibre elements in form of bundles of filaments with a length of at least 3 cm. The aggregate may have the following distribution of particle sizes: 15 - 80% by weight of a particle size larger than 4.75 mm, preferably 1.5 to 4 cm, in diameter 5 - 85% by weight of a particle size of between 150 μn and 4.75 mm in diameter 5 - 15% by weight of a particle size less than approx. 150 μm in diameter. The preparation of rl-e sulphuϊ concrete articles according to this specification may be carried out by mixing the preheated aggregate with melted sulphur and fibre elements in a mixer at between approx. 120 and 140°C. Subsequently the hot mixture is cast. The patent specification deals exclusively with the problems connected with fibre-re¬ inforcing. The specification does not contain any refe¬ rence allowing the industrial-scale manufacture of pipes by a person skilled in the art. EP No. 0.048.106 Al discloses sulphur compositions in¬ cluding sulphur concrete , comprising particulate , inorganic aggregate bonded together in a matrix of the sulphur component having a plurality of small, entrained cells. According to the specification it is suggested that articles, such as paving slabs, structural members, curbing, gutters, pipes and the like, are to be manu¬ factured by casting such sulphur concretes. It is, however, not described how to manufacture pipes.. The entrained cells comprising a gas, such as air, oxygen, nitrogen, carbon dioxide or halocarbons , or a finely divided, porous, particulate material can be admixed the sulphur component in various ways during its preparation. In a preferred embodiment of the preparation of sulphur concrete the inorganic aggregate is first preheated to a temperature ranging from approx. 115 to approx. 160°C, whereupon it is mixed with the liquid sulphur cement in a suitable mixer until a substantially homogenous mixture is obtained, the temperature being maintained throughout the mixing. The hot mixture is subsequently cast using a conventional plant. The moment for introducing the small entrained cells depends on the cell-entraining method employed. This patent application discloses methods for the admixing of air but does not teach how to manufacture sulphur concrete pipes on an industrial-scale . The disadvantage of the preparation of the above and other sulphur concrete articles is in general that the .πolten sulphur concrete is of low viscosity. This may cause problems connected with for example the necessity for a large number of moulds, or cleaning the moulds between two casts due to the material sticking to the mould walls, or shrinkage resulting in incorrect final dimensions, or precipitation of aggregate or segregation of aggregate and molten sulphur during the cooling period. It has therefore been the general opinion of people skilled in the art that the manufacture of sulphur concrete pipes requires a special plant and particular handling. The above opinion among people skilled in the art that the •manufacture of pipes from sulphur concrete is a very difficult task, has been further supported by the general knowledge among those skilled in the art that 10 years ago a Canadian manufacturer went bankrupt in a futile attempt to manufacture sulphur concrete pipes. A US manu¬ facturer was also forced to abandon the manufacture of sulphur concrete pipes after an investment of 1 io US- dollars . Moreover, at the International Sulphur Concrete Symposium & Workshop, arranged by The Sulphur Institute, October 14-15, 1986, Washington, D.C. , Alfred Ecker (from OMV Aktiengesellschaft, Austria) communicated that "aggregate grading according to the specifications of portland cement concrete is unsatisfactory for sulphur concrete". With respect to the possibility of manufacturing pipes from sulphur concrete he communicated that the manufacture by means of the centrifugal method caused problems with segregation and internal tensions. Further A. Ecker communicated that "prefabrication of sulphur concrete parts seems to be very easy, but casting, vibrating and mould construction require extensive experience, in that sulphur concrete is a thermoplastic material for which specialised handling is necessary" . "The transmission of sulphur concrete technology f.oΩ laboratory to con*. ™ **-- cial production is difficult and expensive" . At this symposium the lecturers Thomas A. Sullivan (Consultant) and William C. McBee (U.S. Bureau of Mines) expressed corresponding opinions . Several methods for the manufacture of pipes from portland " cement concrete are known, for example the centrifugal method requiring complex equipment, the so-called wet method requiring long setting periods prior to demoulding and the dry casting method. The dry casting method involves vigorous vibration thus tightly compacting the solid particles in such a way that portland cement concrete pipes can be demoulded immediately after casting. Hardening of portland cement concrete pipes is due to a chemical reaction between portland cement and water as well as optional pozzolanas and additives. Usually 28 days are considered necessary for complete hardening. Thus the portland cement concrete pipes have a low strength during the first few days subsequent to casting. Portland cement concrete pipes are very sensitive to drying out, p specially during the first days after casting since the clieinical reaction requires water. As a result the quality of the finished portland cement concrete pipes varies greatly depending on the hardening conditions. Portland cement concrete pipes are not 100% waterimper- meable, since portland cement concrete has always a more or less closed capillary pore system. Aggressive substances, such as salts and acids, easily penetrate the concrete and disintegrate it. Portland cement concrete pipes do thus not resist acid attacks, for example by sulphuric acid. Due to various bacteria hydrogen sulphide is frequently formed in large sewer system. On the* top part of a sewer pipe hydrogen sulphide is oxidised to sulphuric acid, said acid rapidly corroding and disintegrating portland cement concrete pipes. This problem occurs particularly in warm climates. It is, for example, necessary to exchange the entire sewer system of Los Angeles. Portland cement concrete for the manufacture of pipes can be prepared from -■ mixture of fine aggregate (aggregate particles of less than 4 mm) and cement or a mixture of fine aggregate and coarse aggregate (aggregate particles of more than 4 mm) and cement. Typical compositions com¬ prise :. portland cement 200 - 400 kg/m 3 fly. ash 0 - 150 kg/m 3 fine aggregate 800 - 1800 kg/m 3 coarse * aggregate 0 - 1000 kg/m 3 water 120 - 140 kg/m 3 Moreover various chemical and mineral additives can be employed. Contrary to sulphur concrete portland cement concrete cannot be cast at temperature below 0°C due to the presence of water. Today methods are known to coat portland cement concrete pipes with, for example, epoxy. Such methods are, however, expensive and connected with various disadvantages. Owing to the health risk involved with handling of epoxy, such as its carcinogenous properties, safety requirements are extensive. Moreover it is not easy to ensure a sufficient impermeability of the coating. This also applies to another form of coating where the concrete pipe is lined with plastic material. In this case great problems concerning impermeability arise especially where the pipes are joint. In Denmark as well as in all other industrial countries there is an increasing demand for corrosion-resistant pipes in connection with the exchange of existing pipe systems as well as for hew systems. As mentioned above it has not yet been possible to manu¬ facture sulphur concrete pipes in a satisfactory manner in such a way that such pipes can be used in areas where conventional portland cement concrete pipes are not resis¬ tant enough. There is thus a great demand for sulphur concrete pipes manufactured in an economic and effective manner, such as by using existing conventional plants for the manufacture of portland cement concrete pipes. Surprisingly it has been shown that such sulphur concrete pipes are manufacturable from a material formulated in analogy with compositions of portland cement concrete suitable for the manufacture of pipes by means of the dry casting method, said analogy being based on a principle to be explained in greater detail below. According to this principle the paste components of port- land cement concrete*, i.e. cement, filler and water, are replaced by substantially an equivalent volume of sulphur paste, i.e. sulphur cement and filler. The other com¬ ponents, i.e. especially aggregate and air, remain sub¬ stantially unchanged with respect to volume and distribu¬ tion of aggregate particle size. To obtain the described analogy the mixing and casting are carried out at a tem¬ perature where sulphur paste has the same rheological properties as portland cement paste at normal casting temperatures. A suitable temperature of the sulphur paste is in the range of between 120 and 150 β C, especially between.130 and 140 β C. When employing the above analogy a material composition is obtained, which can be cast ^ -d while boi.ng subjecl_-?* to vigorous vibration. This ensures that the mould is filled completely and that the finished pipe is incollapsible immediately after the casting, i.e. immediately thereafter the pipe can be removed from the mould (demoulded) . Such a composition of the material and such casting conditions ensure a tight compaction of the particulate material. The individual particles are substantially in contact with each other since they are only surrounded by a thin layer of sulphur cement. Disclosure of Invention The object of the present invention is to provide a com- position of sulphur concrete rendering said concrete suitable for the manufacture of pipes substantially according to the known dry method for the manufacture of portland cement concrete pipes, as well as a method of manufacturing sulphur concrete pipes, said method being carried out with e.g. existing conventional plants for the manufacture of portland cement concrete pipes by means of the dry casting method. The object bf the invention i*-? accomplished by sulphur concrete pipes characterised in that they are manufactured by the dry casting method in a preheated mould using vigorous vibration at a temperature at which sulphur cement is liquid from a material formulated on the basis of the composition of a portland cement concrete suitable for pipe manufacture by means of the dry casting method, the volumes of portland cement, filler and water being replaced by substantially equivalent volumes of sulphur cement and filler. Sulphur concrete pipes according to the invention comprise such sulphur concrete articles cast while being subjected to vigorous vibration, whereafter they are immediately removed from the mouicl and are ible to stand without support. Such articles can, for example, comprise pipes for sewer systems. It is, of course, also possible to manufacture other, not easily castable or pourable articles having an intricate shape and/or such a size rendering the manufacture by means of simple casting or pouring difficult. It is not necessarily important whether the articles have a shape which can be defined as pipe-shaped. The sulphur cement for the inventive sulphur concrete pipes can be selected among any type of sulphur cement. Sulphur cement substantially comprises elemental sulphur, which can be unmodified or modified in different ways. Non-restrictive examples of sulphur cement include those described in the above US-PS Nos. 4.311.826, 4.348.313, 4.391.969, 4.293.463 and 4.058.500. Sulphur cement is typically used in amounts of between 5 and 30% by volume, preferably between 7 and 14% by volume. Apart from sulphur cement the sulphur paste also comprises a filler having a particle size of up to 0.25 mm. This corresponds substantially to the limits of the particle size in conventional portland cement. The average particle size is usually 0.016 mm, which also corresponds to the average particle size of portland cement and fly ash. Depending on the type of aggregate in the concrete mixture the filler may vary in size and amount and may optionally comprise two or more different types of material. To ensure a tight compaction of the solid particles it is necessary to use an amount of filler depending on the amount of sulphur cement. As a result of the tight compaction the sulphur concrete pipes can be removed from the moulds immediately subsequent to the casting without loosing their shape so that the pipes do not collapse. The filler content moreover ensures that a suitable paste of sulphur cement and filler is obtained so that the sulphur cement does not segregate from the sulphur concrete mixture. The filler also ensures that the manufactured sulphur coi.cr te pipes are sufficiently tight. Examples of suitable fillers include fly ash, pozzolanas, mineral filler, such as silica flour or rock flour or mixtures thereof. Any filler ful¬ filling the above requirements is suitable provided that the manufactured sulphur concrete pipes have the desired quality, such as with respect to acid resistance, for example to sulphuric acid. The filler is usually present in an amount ranging from 3 to 40% by volume, preferably from 10 to 20% by volume of the sulphur concrete. Usable aggregates include conventional aggregate. Aggregate having a particle size of less than 4 mm is termed "fine aggregate", whereas aggregate having a particle size of more than 4 mm is termed "coarse aggregate". The distribu¬ tion of aggregate particle sizes is essential for the casting as well as for the properties of the finished product. The distribution of aggregate particle sizes in the present invention may be exactly the same as the distribution of aggregate particle sizes in a corresponding portland cement concrete suitable for the manufacture of pipes. By using an equivalent distribution of aggregate particle sizes corresponding properties during casting are obtained. The distribution of aggregate particle sizes is variable depending on the thickness of the article. Advantageously large particles are used for a large thick¬ ness. A typical sulphur concrete mixture comprises between 0 and 70% by volume of coarse aggregate, preferably between 30 and 45% by volume, and between 10 and 80% by volume of fine aggregate, preferably between 28 and 40% by volume. The finished sulphur concrete pipes usually comprise between 1 and 10% by volume of air, preferably between 2 and 6% by volume, more preferred between 3 and 5% by volume, and most preferred about 4% by volume. The air is present in form of air bubbles entrapped during the mixing of the sulphur concrete. An air content of the above range, such as between 2 and 6% by vr.'ume, haε no negaf' v. influence on the quality of the concrete, for example with respect to impermeability, since the air bubbles are small and moreover not interconncted. On the contrary an air content in the above range has a positive effect on the finished pipes, as it reduces internal tensions in the concrete during the shrinkage caused by cooling. Finally, if desired, the sulphur concrete pipes may co - prise additives and/or adjuvants. Examples of such ad¬ juvants include substances for obtaining a microporous structure having an air content of for example between 4 and 8%. Usually the amount of additives and/or adjuvants does not exceed 10% by volume, for example not more than 5% by volume, 3% by volume or 1% by volume, calculated on the basis of volume of the sulphur concrete. It is furthermore possible to improve the strength of the sulphur concrete pipes by adding a reinforcing material, such as fibres or fibre elements in an amount ranging from 0 to 5% by volume. Adding such fibres or fibre elements considerably increases both the compressive and flexural strengths. Examples of fibres used in the in¬ ventive sulphur concrete include plastic fibres, glass fibres and steei fibres. The composition of sulphur concrete for the manufacture of pipes corresponds, as previously mentioned, to the composition of conventional portland cement concretes for the manufacture of pipes, ensuring that the above analogy is fulfilled. Following the analogy, substantially the same volume of fine aggregate, coarse aggregate , air and additives and/or adjuvants as well as substantially an equivalent volume of paste components is used. The paste components of portland cement concrete are portland cement, filler and water, whereas the paste components of sulphur concrete are sulphur cement and filler. To ensure the β τ___logy the sulphur concrete is preferably formulated in such a way that the volume of sulphur cement is substantially equivalent to the volume of water in portland cement concrete, while the volume of filler is substantially equivalent to the volume of portland cement and filler in portland cement concrete. A suitable composition of the material for the manufacture of sulphur concrete pipes according to the invention comprises in % by volume 5-30 % sulphur cement 0-70 . % coarse aggregate of a particle size of more than 4 mm 10-80 % fine aggregate of a particle size of up to 4 mm 3-40 % fil-ler 1-10 % air 0-5 % reinforcing fibres 0-10 % additives and/or adjuvants A more preferred material comprises in % by volume 7-14 % sulphur cement 30-45 % ccarce aggregate 28-40 % fine aggregate 10-20 % filler 2-6 % air 0-3 % reinforcing fibres 0-10 % additives and/or adjuvants The method according to the invention for the manufacture of sulphur concrete pipes is characterised by a) mixing the components of the material and adjusting the obtained mixture to a temperature where sulphur cement is liquid, b) casting the mixture at this temperature while sub¬ jecting it to vigorous vibration, using a mould pre¬ heated to a temperature of up to 160 β C, preferably between 120 and 140°C, c) removing the cast pipe from the mould. Best Mode for Carrying Out the Invention The inventive method can substantially be carried out as follows : The ma or components, such as fine aggregate, coarse aggregate and sulphur cement, are preheated to between 130 and 160 C C. Such a preheating considerably reduces the period for the adjustment of the mixture temperature for the casting. In practice, fine aggregate and coarse aggregate are each filled into its silo in an amount sufficient for one day's production of sulphur concrete. The aggregate is preheated inside the silo, for example electrically or by hot air. The manufacture starts by mixing the components in a mixer, such as a positive mixer, for example a pan mixer or a paddle mixer, and adjusting the mixture to a temperature, where the sulphur cement is liquid, i.e. to approx. 135°C. At this temperature the sulphur concrete is cast, using a plant used for the dry method manufacture of portland cement concrete pipes. Examples for plants used for carrying out the inventive method include pipe manufacturing plants with an vibrating inner core, for example available from Pedershaab Maskin- fabrik, Brønderslev, Denmark, and plants with vibration tables, for example available from Betodan, Vejle, Denmark. The plant used may, for example, comprise a vibration table with an immobile core, an outer, removable mould and a removable bottom ring. Prior to the manufacture the casting mould is preheated to up to 160°C, prefeably between 120 and 140°C, for example electrically or by means of hot air. The heating means used may advantageously be thermo¬ stat-controlled. It is necessary . «. preheat the casting mould to avoid too rapid cooling of the sulphur concrete mixture, which would result in the sulphur cement solidi¬ fying and sticking to the casting mould. During continuous manufacture, i.e. at a manufacture rate of 8 to 10 pipes per hour, the heat transfer is expected to be sufficient for maintaining a suitable temperature of the casting mould. It might thus only be necessary to supply heat prior to starting the process. The casting mould can, if practical, be heat- insulated. The sulphur concrete mixture is cast while subjected to vigorous vibration for approx. 4 min. The vibration causes a tight compaction of the aggregate particles , so that they together with the filler particles are almost in contact with each other, each particle only being surrounded by a thin layer of sulphur cement. Any known vibration means can be used in connection with the present invention. Such means include for example vibration tables or vibrating cores . Subsequent to casting the outer mould and the sulphur concrete pipe are together lifted off the internal core by a crane gripping the bottom ring. The pipe is then placed on the bottom ring in such a way that the outer mould can be removed. The pipe does not collapse after removal of the outer mould. If necessary form oil can be used in the casting mould to avoid a sticking of the sulphur concrete to the mould. This problem might also be solved by means of an anti- sticking coating, for example a polytetrafluorethylene coating. The bottom ring should furthermore be preheated to a temperature of between 145 and 160°C to ensure com- plete thermal expansion of the bottom ring prior, to the solidification of the sulphur concrete pipe. If this is not ensured the pipe tightens around the bottom ring during the cooling. Such a tightening may prevent the removal of the pipe from the bottom ring, and the pipe may crack. To solve the above problems the bottom ring may be made of a material having a higher coefficient of thermal expansion. It may also be possible to facilitate the removal of the pipe from the bottom ring by cooling the ring to for example 10 β C when the pipe has reached a temperature of for example 50° C. The strength of the sulphur concrete at this temperature permits this type of removal. Upon the demoulding the sulphur concrete article has obtained sufficient strength to be moved after 2 to 4 hours, all depending on the thickness of the article in question. The articles can be delivered to a building or piping site the day after their manufacture. Portland cement concrete articles, on the other hand, have to harden for a period of approx. 28 days before they can be de¬ livered. In contrast to conventional portland cement concrete production sulphur concrete articles can be manufactured 24 hours a day. This can be of importance since the costs involved in operating large, advanced pipe plants are considerable. The place required for storing sulphur concrete pipes is minimal and the short production time allows an adaptation of the production to current needs as well as fulfilling immediate demands of the customer. Sulphur concrete articles harden by cooling. They do not deteriorate due to drying out, as may be the case in portland cement concrete. Therefore sulphur concrete articles are of a much more uniform quality than portland cement concrete articles. A further advantage is that sulphur concrete is a corrosion-resistant material per se. Finally it does not contain water allowing the manu- facture of articles at temperatures below 0°C. The method according to the invention is advantageously carried out in . ■ casting mould preheated to a temperatu e of up to 160°C, preferably ranging between 80 to 150°C, more preferred between 100 to 145"C, even more preferred between 125 to 135°C prior to casting. The preheating ensures that sulphur does not stick to the wall material of the mould, since sulphur has a melting point of approx. 120°C. The above step a) of the method according to the invention is advantageously carried out by adjusting the mixture to a temperature of between 120 and 150" C, preferably between 130 and 140°C, thus ensuring that sulphur is liquid. For practical reasons one or more of the components of the material or mixtures of several components are individually preheated to a temperature of up to 170°C, preferably to between 130 and 160°C. Thus the time for adjusting the temperature is considerably reduced, as the obtained mixture already has a temperature close to the desired casting temperature. Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood, that the detailed description and specific examples, while in¬ dicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. The invention is described in greater detail below by means of the following, illustrative, non-restrictive examples . Example 1 The present example describe an iLlvoductory Lun based upon a portland cement concrete composition usually used for the manufacture of pipes with the plant in question. The composition was as follows: Component kg/m 3 1/m 3 portland cement 280 89 fly ash 100 45 fine aggregate 0-4 mm 900 346 coarse aggregate 4-8 mm 900 346 water 132 132 air --- 40 During the first run only water was replaced by an equi¬ valent volume of sulphur cement, i.e. in theory 251 kg/m 3 . In practice the desired consistency was obtained with a slightly lesser amount of sulphur cement. In the absence of water portland cement does no longer act as a binder but merely as a filler. The resulting sulphur concrete mixture had the following composition: Composition 1 Component kg/m 3 1/m 3 portland cement 288 92 fly ash 102 46 fine aggregate 0-4 mm 926 356 coarse aggregate 4-8 mm 926 356 sulphur cement* 209 * 110 air --- 40 * The sulphur cement used in all examples comprises 95% by weight of sulphur and 5% by weight of plasticiser in form of' a mixture of dicyclopentadiene .and oligomers of cyclopβ-itadiene in a ratio, of 1:1. This sulphur cement is available from KKKK A/S , Copenhagen, Denmark and from Chemical Enterprises, Houston, Texas, USA under the trade¬ mark CH__MENT R 2000. Composition 1 was used to manufacture full-scale articles on an existing plant for the preparation of conventional portland cement concrete articles . During the run the concrete was cast at a temperature of approx. 135°C, and the mould used was preheated to a temperature of between 80 and 120°C. The mixture was cast in a manner conventional for portland cement subjecting the mixture to vigorous vibration for about 4 min. The concrete articles were removed from the mould immediately after casting. Two different types of articles were cast: Euro pipe stoppers and GT cones. Euro pipe stoppers are used to close pipes ends. The manufactured Euro pipe stoppers are of a dimension suitable for pipes with an inner diameter of 60 cm. The shape of the Euro stoppers substantially corresponds to a cylindrical, flat-bottomed bowl its cylinder having an inner diameter of 60 cm and its largest outer diameter being 76 cm. The bowl has a height of 15 cm and its bottom has a thickness of 8 cm. The manufactured uT cones has a height of 40 cm and an inner diameter at each end of 80 and 60 cm respectively. Their thickness is 6 cm. Both articles are comparatively simple in shape, but experience from the portland cement concrete manu¬ facture had shown that they may tend to collapse when demoulded. With the exception ' of the two first attempts to manufacture pipe stoppers, where no form oil as used, 4 Euro stoppers were manufactured without problems, where¬ upon 5 GT cones were manufactured without problems . A laboratory test revealed that articles manufactured from Composition 1 are crack-free and have an air content of 3,4%. Their compressive strength is higher than 55 MPa. Example 2 On the basis of Composition 1 a new mixture was prepared, where the portland cement was replaced by an equivalent volume of fly ash. Composition 2 Component kg/m 3 1/m 3 fly ash 315 143 fine aggregate 0-4 mm 942 362 coarse aggregate 4-8 mm 942 362 sulphur cement 177 93 air 40 Using the same method as in Example 1, 7 GT cones were manufactured without problems. A laboratory test revealed that articles manufactured from Composition 2 are crack-free and have an air content of 3,1%. Their compressive strength is higher than 55 MPa. Example 3 Using the same method as in Examples 1 and 2, 8 GT cones were manufactured without problems from the following composition: Composition 3 Component kg/m 3 1/m 3 fly ash 313 142 fine aggregate 0-4 mm 838 322 coarse aggregate 4-8 mm 1047 403 sulphur cement 177 93 air --- 40 Example 4 Full-scale GT pipes were cast on a conventional plant for the manufacture of portland cement concrete articles , said pipes having the follwing dimensions: inner diameter: 60 cm 5 height: 200 cm wall thickness: 8 cm weight approx.: 1000 kg/article. The plant used comprised a vibration table with an immobile 0 core, an outer removable mould and a removable bottom ring. The outer mould was provided with a heat-insulating mantle. The mould was preheated to approx. 80 to 120°C by means of hot air. Subsequent to casting the material while subjecting it to vigorous vibration for 4 min the pipe was 5 lifted from the inner core by lifting the bottom ring with a crane. The bottom ring was placed on the ground, whereupon the outer mould was removed. 7 pipes were thus manufactured without problems from the 20 following composition: Composition 4 „ c Component kg/m 3 1/m 3 fly ash 320 145 fine aggregate 0-4 mm 850 327 coarse aggregate 4-8 mm 430 165 coarse aggregate 8-12 mm 600 240 30 sulphur cement 186 98 air 25 A destructive tes" ~ r determining the load capacity of the pipe was carried out by Dantest, Copenhagen, Denmark. 35 This test comprises subjecting the pipe to a vertical load perpendicular to the generatrix of the pipe cylinder until breaking. The breaking strength was measured to be 233 kN. The required minimum breaking strength of GT pipes of the manufactured type is 118 kN. The breaking strength of the manufactured pipes is thus 97% higher than required. A comparable portland cement concrete pipe of the above type has usually a breaking strength of 30 to 50% above the required minimum. Example 5 Using the method described in Example 4 5 GT pipes were manufactured without problems from a sulphur concrete reinforced with polypropylene fibres and having the following composition: Composition 5 Component kg/m 3 1/m 3 fly ash 300 136 fine aggregate 0-4 mm 820 315 coarse aggregate 4-8 mm 410 158 coarse aggregate 8-12 mm 600 240 sulphur cement 200 105 KRENIT R -fibres* 17 17 air 29 * Polypropylene fibres of a length of 12 mm, a thickness of between 20 and 40μm and a width of between 100 and 300 μm; available from Danaklon A/S , Varde , Denmark. The manufactured pipes have a breaking strength of 280 kN corresponding to 137% above the minimum requirement. Examples 1 to 5 show that a person skilled in the art can formulate the required material in a simple manner from known compositions of a portland cement concrete material suitable for the manufacture of pipes according to the dry casting method. The inventive method requires only small adjustments of theoretically calculated compositions to obtain a sulphur concrete composition suitable for the manufacture of pipes, such adjustments being well-known to a person skilled in the art. The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations .are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims: Claims 1. Acid resistant concrete articles in the form of sulphur concrete pipes, c h a r a c t e r i s e d in that they are manufactured by the dry casting method in a preheated mould using vigorous vibration at a temperature at which sulphur cement is liquid from a material formulated on the basis of the composition of a portland cement concrete suitable for pipe manufacture by means of the dry casting method, the volumes of portland cement, filler and water being replaced by substantially equivalent volumes of sulphur cement and filler. 2. Sulphur concrete pipes as claimed in claim 1, c h a r a c t e r i s e d in that the volume of sulphur cement is substantially equivalent to the volume of water in portland cement concrete, and that the volume of filler is substantially equivalent to the volume of portland cement and filler iτι portland cement concrete. 3. Sulphur concrete pipes as claimed in claim 1 or 2, c h a r a c t e r i s e d in that they are manufactured of a material comprising in % by volume 5-30 % sulphur cement 0-70 % coarse aggregate of a particle size of more than 4 mm 10-80 % fine aggregate of a particle size of up to 4 mm 3-40 % filler 1-10- % air 0-5 % reinforcing fibres 0-10 % • additives and/or adjuvants 4. Sulphur concrete pipes as claimed in any of the pre- ceding claims 1-3, c h a r a c t e r i s e d in that they are manufactured of a material comprising in % by volume 7-14 % sulphur cement 30-45 % coarse aggregate 28-40 % fine aggregate 10-20 % filler 2-6 % air 0-3 % reinforcing fibres 0-10 % additives and/or adjuvants 5. A method of manufacturing sulphur concrete pipes as claimed in any of the preceding claims 1-4, c h a r c¬ e r i s e d by a) mixing the components of the material and adjusting the obtained mixture to a temperature where sulphur - cement is liquid, b) casting the mixture at this temperature while sub¬ jecting it to vigorous vibration, using a mould pre¬ heated to a temperature of up to 160°C, preferably between 120 and 140°C, c) removing the cast pipe from the mould. 6. A method as claimed in claim 5, c h a r a c t e r - i s e d by a) mixing the components of the material and adjusting the obtained mixture to a temperature of between 120 and 150°C, preferably between 130 and 140°C, b) casting the mixture at this temperature while sub¬ jecting it to vigorous vibration, using a mould pre- heated to a temperature of up to 160°C, preferably between 120 and 140°C, c) removing the cast pipe from the mould. 7. A method as claimed in claim 5 or 6, c h a r a c - t e r i s e d by al) preheating one or more of the components of the material or mixtures of several components individually to a temperature of up to 170 C C, preferably between 130 and 160°C, a2) mixing the components and adjusting the obtained mixture to a temperature of between 120 and 150°C, preferably between 130 and 140°C, b) casting the mixture at this temperature while sub¬ jecting it to vigorous vibration, using a mould pre¬ heated to a temperature of up to 160°C, preferably between 120 and 140°C, c) removing the cast pipe from the mould. 8. A method as claimed in any of the preceding claims 5-7, c h a r a c t e r i s e d by the casting mould being preheated to a temperature ranging between 80 and 150°C, preferably between 100 and 145°C, more preferred between 125 and 135°C prior to casting.

Inventors: LARSEN LEIF HOLBAUM AARSLEFF, LARSEN, LEIF, HOLBAUM, AARSLEFF
Applicants: KKKK AS, KKKK A/S
Application year: 1990
Main classification: C04B28
IPC codes: B28B7, B28B17, B28B21, C04B14, C04B28, F16L9