WO1992006052A1

WO1992006052A1 - A method of preparing a premixed dry sulphur concrete and premixed dry sulphur concrete prepared by said method

Info

Publication number: WO1992006052A1
Application number: PCT/DK1991/000304
Authority: WO
Inventors: Leif Holbaum Aarsleff Larsen
Original assignee: Kkkk A/S
Priority date: 1990-10-08
Filing date: 1991-10-07
Publication date: 1992-04-16
Also published as: DK243490D0; AU8717091A; DK243490A; MX9101431A

Abstract

A method of preparing a premixed dry sulphur concrete comprising sulphur cement and the other components conventionally used in sulphur concrete, where 1) the other components are divided into two portions, component A and component B, 2) while stirring, a first mixture of the sulphur cement and component A is prepared and the first mixture is adjusted at a temperature above the melting point of the sulphur cement, and subsequently, while stirring continuously, component B is added, component B having a temperature resulting in the total mixture of sulphur cement and component A + B when mixed having a temperature below the melting point of the sulphur cement. The dry ready-mixed sulphur concrete poses no problems with dust and is ready for use after heating to normal casting temperature.

Description

Title: A method of preparing a premixed dr sulphur con¬ crete and premixed dr sulphur concrete prepared bv said method

Teςhnjc?!. F eld

The present invention relates to a method of preparing a premixed dry sulphur concrete comprising sulphur cement and the other components conventionally used in sulphur concrete.

Background Art

Sulphur concrete is a thermoplastic material which is liquid or workable in the same manner as conventional concrete when heated to a temperature of about 120 to 140'C. The sulphur concrete contains sulphur cement as a binder. When the concrete cools down, said sulphur cement causes it to solidify and provides it with its unique properties, including extensive compressive strength and flexural strength, as well as high wear resistance and high impact strength. The sulphur concrete is conventional¬ ly used because of its particularly good resistance to acid and salt attacks and it is further used where fast solidification and a fast development of the finished strength are required.

As to the preparation and use of conventional sulphur concrete, reference is made to for instance WO publication No. 90/10606, which describes a method for the manufacture of sulphur concrete pipes and contains a general reference to several relevant patents.

The sulphur cement which may be used in the prepared premixed dry sulphur concrete, may be any known sulphur cement of which the sulphur cement formulations known from the US patents Nos . 4,311,826, 4,348,313 and 4,391,969 should be mentioned, that is elementary sulphur modified with a plasticizer, for instance in the form of 5% of a mixture in the ratio 1:1 of dicyclopentadien and oligomers of cyclopentadien. Other types of modified sulphur cement are described in for instance US patents Nos. 4,293,463 and 4,058,500.

Traditionally, sulphur concrete is prepared by mixing sulphur- cement and the other components, conventionally comprising aggregate such as fine aggregate and coarse aggregate and in most cases also a filler, for instance mineral filler or fly ash. The mixing temperature and the casting temperature are at about 120 to 140^βC.

The preparation may be carried out by heating fine ag¬ gregate and coarse aggregate to about 150-170°C and filling said aggregates into a mixing apparatus while adding fly ash and sulphur cement having ambient temperature. The heat from the aggregate materials melts the sulphur cement while being mixed, thereby obtaining the desired tempera¬ ture and consistency, whereupon the concrete is ready for use. The sulphur cement used may either be in a ground form having a particle size of about 1 to 4 mm or it may be in the form of pellets or flakes. The mixing time depends on the type of the mixer used and of the particle size of the sulphur cement.

As an alternative, the preparation of sulphur concrete may be carried out by preheating fine aggregate, coarse aggregate and filler to the desired temperature, that is 130-140^βC , whereupon the sulphur cement is added in a liquid state at a temperature of about 120^βC. In this method the preparation of sulphur concrete highly resembles the method used when preparing asphalt.

Specially built concrete mixers, truck mixers, may also be used for the preparation of sulphur concrete. The required quantities of fine aggregate, coarse aggregate and filler are filled into the mixing drum and heated, heat being provided to the mixing drum from the outside, for instance by means of oil burners. When the desired temperature has been obtained, the sulphur cement is added.

When preparing ready-mixed sulphur concrete mixtures a relatively large plant is conventionally used, which, how- ever, is problematic if the sulphur concrete is to be used under difficult conditions, for instance for the protection of pipeline joints within the offshore industry. In this case it is not possible to use a large plant and problems may easily arise when measuring out and admixing filler, fcr instance fly ash, as it raises dust and is easily carried along by the wind. There is thus a need for a premixed ready-for-use sulphur concrete for use under such conditions, said sulphur concrete only having to be heated to the right temperature and not raising dust.

Several attempts have been made at preparing such premixed ready-for-use sulphur concrete, but in the course of time such materials have displayed a tendency to segregate forming non-homogenous compositions. In order to solve the above problems, a pelletized sulphur concrete has been made by firstly preparing a quantity of the hot sulphur concrete in the conventional manner whereupon the hot, flowable concrete is led into a pelletizing chamber while at the same time air and liquid, for instance water, are supplied to the chamber under pressure. Concrete, air and liquid are subsequently intimately mixed to form hardened, frozen pellets of sulphur concrete which may then be remelted immediately prior to use, thereby forming a coherent, pourable mass. However, the above method requires complicated equipment, as the sulphur cement must firstly be mixed and then introduced into the pelletizing chamber, said pelletizing chamber being a mixing chamber with a screw conveyor mixing device and having means for the supply of pressurized air and water. The above method are further encumbered with the drawbacks that the apparatus used has a poor capacity and that the preparation process is costly.

Thus, there is still a need for a simple and inexpensive method of preparing a finished sulphur concrete mix, which remains homogenous and which does not raise dust.

Disclosure of Invention

Accordingly, the present invention provides a method of preparing premixed, dry sulphur concrete on the basis of sulphur cement and the other components conventionally used in sulphur concrete, which method is characterised by:

1) dividing the other components in two portions, component A and component B,

2) while stirring, preparing a first mixture of the sulphur cement and component A and adjusting the first mixture at a temperature above the melting point of the sulphur cement, and subsequently

3) while stirring continuously, adding component B, component B having a temperature resulting in the total mixture of sulphur cement and component A + B when mixed having a temperature below the melting point of the sulphur cement.

By such method, when component B is added, the sulphur cement quickly solidifies on the surface of the particles of component B. It is thereby ensured that no large co- herent lumps are formed which would render the sulphur concrete mixture non-homogenous. Component A may advan¬ tageously comprise the portion of the components of the sulphur concrete which have a special tendency to raise dust, that is the more fine-grained components. When preparing the first mixture, said fine-grained components are distributed in the melted sulphur cement and together with the sulphur cement the most fine-grained components form a sulphur cement paste wherein they are bound by the sulphur cement when said sulphur cement solidifies either as a surface coating on large particles in component B or as granulates. In both cases, particles are formed which do not raise or release dust, as even the smallest of the granulate particles will be substantially larger than those of the components of the sulphur concrete which demonstrate a tendency to raise dust, that is the smallest of the fine aggregate particles and especially the filler, which for instance may be fly ash, having a particle size where about 75 per cent are smaller than 45 micrometres.

In order to prevent dust, it is thus preferred that com¬ ponent A comprises constituents with a relatively small particle size and that component B comprises constituents having a relatively large particle size. This may for instance be ensured by component A comprising filler and fine aggregates having a particle size of up to 4 mm and component B comprising coarse aggregate with a particle size of 4 mm and above.

According to a particularly practical embodiment of the inventive method, step (2) may be carried out by heating component A or a portion thereof to a temperature sub- stantially above the melting point of the sulphur cement and subsequently while stirring adding the sulphur cement and a possible remaining quantity of component A, thereby forming the first mixture with a temperature above the melting point of the sulphur cement. By proceding in said manner a fast sequence of operations may be ensured. Component A or a portion thereof may be heated to the desired temperature, for instance 140^βC, beforehand, said temperature being fixed in such a manner that when adding the sulphur cement and the possible remaining portion of component A, a mixture is formed having a suitable tempera¬ ture, for instance 120"C, where the sulphur cement Is still liquid. Subsequently, component B is added, said component B possibly being unheated, for instance having a temperature of about 10-20"C, resulting in a mixture which quickly stabilizes at a temperature at which the sulphur cement solidifies and a rapid solidification of the sulphur- cement on the surface of the particles of component B takes place. When, during the stirring, the sulphur cement solidifies, the process is completed. The finished homogenous dry sulphur concrete mix may be removed from the mixer used and will be ready for transport or storage. A new portion of heated component A and unheated sulphur cement may then be supplied to the mixer and this again results in a temperature at which the sulphur cement is melted and component B may be added etc.

The temperature of the first mixture, which comprises the sulphur cement and component A, as well as the temperature of component B may vary within wide limits and will of course depend on the weight ratio between the first mixture and component B. The only condition is that the first mixture has a temperature above the melting point of the sulphur cement used and that component B has such a tem¬ perature that when component B is added, this quickly results in a temperature below the melting point of the sulphur cement.

Examples of the temperature of the first mixture include temperatures in the range from 115-160^βC, preferably 120- 140°C, more preferred 120-130^βC. The temperature of com¬ ponent B will conventionally be the ambient temperature which in practice is often 10-20^βC, but temperatures outside this range, for instance temperatures between 0 and 40^βC, are not precluded. When temperatures and quan- tities are adapted in this manner, step (3) of the inven¬ tive method will usually take place quickly and tradi¬ tionally it will not be necessary to carry out supplemen¬ tary cooling. However, the process may be accelerated by means of cooling, for instance by sprinkling with water. Step (3) may of course also be accelerated by cooling component B to a temperature below the ambient temperature.

The weight ratio when dividing the other components into component A and component B is not critical. Examples of the weight ratio between component A and B are 0.3:1-2:1, preferably 0.5:1-1.3:1, more preferred 0.7:1-1.1:1, most preferred 0.75:1-1.05:1.

The other components of the sulphur concrete, that is component A + component B, not only include usual aggre¬ gates such as fine aggregate and coarse aggregate and filler but also possible other auxiliary and/or additives including fibre-reinforcing material.

The 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 indica- ting preferred embodiments of the invention, are given by way of illustration only, since various changes and modi¬ fications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

Best Mode for Carrying Out the Invention

In the method according to the invention, the usual proce¬ dure is to preheat component A or a portion thereof, for instance fine aggregate and possibly also filler, to a temperature of for instance 135-150^βC, whereupon the sulphur cement and the possible remaining portion of component A, both having ambient temperature, are mixed with the preheated material whereby a temperature of the mixture of about 115-120^βC is obtained. The sulphur cement is liquid at said temperature and will cover all the particles of the mixture. Subsequently, component B, having ambient temperature, that is about 10-20*C, is added. During the continued stirring, the cold constituents of component B cool the remaining portion of the mixture and the sulphur cement changes from liquid to solid state, when passing the solidifying point, which for traditional modified sulphur cement is around 110-115'C.

The continuous stirring prevents the sulphur concrete from hardening in the conventional manner and developing into a massive coherent lump. Instead, dry sulphur concrete in granulate or grain form is the result of the above process, the largest particles being a little larger than the largest coarse aggregate particles, as they are covered with a thin membrane of sulphur cement paste, that is sulphur cement containing filler. All the fine particles, that is filler and the finest aggregate, are bound or cemented together by the solidified sulphur cement to form large sand-like, grainy particles, thereby providing a dry sulphur concrete which is not dust-releasing. At the subsequent use it is an important property that the dry sulphur concrete does not release dust. When it is to be used, the dry sulphur concrete mixture is heated to the desired temperature of about 120-140^βC during continuous stirring. The sulphur cement melts as a consequence of its thermoplastic properties and a sulphur concrete with the desired composition and workability is obtained in exactly the same manner as when preparing sulphur concrete in the conventional way.

The ready-mixed dry sulphur concrete may be prepared industrially on a large mixing plant, in principle functioning as a conventional asphalt plant. Such plant may for instance have a capacity of 20 to 40 ton per hour. A Vianova plant, supplied by Pedershaab Maskinf brik, Broenderslev, Denmark may be mentioned as an example of a conventional asphalt plant which may also be used as a mixing plant by the method according to the invention. However, the mixing plant used by the inventive method does not have to meet any special requirements. Thus, the inventive method may also be carried out in a conventional truck-mixer .

Examples

Materials used

Sulphur cement: the sulphur cement used is a modified sulphur cement which, in addition to elementary sulphur, contains 5% plasticizer. Such sulphur cement is supplied by K K K K A/S , Islands Brygge 22, DK-2300 Copenhagen S, Denmark.

Aggregate:

Coarse aggregate 8/16, grain size 8-16 mm

Coarse aggregate 4/8, grain size 4-8 mm

Fine aggregate 0/4, grain size up tp 4 mm.

Filler: fly ash.

Example 1

In a laboratory mixer of the paddle mixer type having a capacity of 50 kg and equipped with heating means a finished sulphur concrete mixture having the following composition is prepared:

sulphur cement 400 kg/m³ coarse aggregate 8/16 450 kg/m³ coarse aggregate 4/8 500 kg/m³ fine aggregate 0/4 800 kg/m³ fly ash 200 kg/m³ Fine aggregate and fly ash are filled into the mixer and heated, while stirred, to about 140*C. Subsequently, the sulphur cement is added and the temperature stabilizes around 120^βC. The supply of heat is cut off, whereupon the amount of coarse aggregate, having ambient temperature, is added during continuous stirring. In a few minutes a dust-free mixture which is easy to handle is formed wherein the largest grain size is only slightly larger than the largest grain size of the coarse aggregate added, while the smallest particles are substantially larger than 0.5 mm. The resulting mixture is directly applicable for reheating to a temperature of about 120-140"C and subse¬ quent casting.

Example 2

In the same manner as described in Example 1, but in full scale using a traditional asphalt mixer, a ready-mixed dry sulphur concrete mixture having the following compo¬ sition is prepared:

Sulphur cement 400 kg/m³ coarse aggregae 8/16 250 kg/m³ coarse aggegate 4/8 800 kg/m³ fine aggregate 0/4 700 kg/m³ fly ash 200 kg/m³

The above mixture may be used to fill in the missing protective concrete layer of pipeline joints when laying offshore pipelines. Ashore, said pipes have been provided with a protective layer of concrete for the greater part of the length of the pipes, but the portion near the ends of the pipes is not covered with concrete. Prior to the filling in, the dry sulphur concrete mixture is heated in a traditional asphalt heating boiler, of the type normally used for heating briquettes of asphalt mastic when working offshore. A test casting carried out in the above manner yielded a good result.

Example 3

In the same manner as described in Example 2, but using the sulphur concrete composition given in Example 1 a successful test casting was carried out.

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 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. A method of preparing a premixed dry sulphur concrete comprising sulphur cement and other components conven- tionally used in sulphur concrete, c h a r a c t e r ¬ i s e d by

1) dividing the other components in two portions, component A and component B,

2. A method as claimed in claim 1, c h a r a c t e r- i s e d in that component A comprises constituents having a relatively small particle size and that component B com- prises constituents having a relatively large particle size .

3. A method as claimed in claim 2, c h a r a c t e r - i s e d in that component A comprises filler and fine aggregate having a particle size of up to 4 mm and that component B comprises coarse aggregate having a particle size exceeding 4 mm.

4. A method as claimed in claim 1, c h a r a c t e r- i s e d in that step (2) is carried out by heating com¬ ponent A or a portion thereof to a temperature substan¬ tially above the melting point of the sulphur cement and subsequently while stirring, adding the sulphur cement and a possible remaining quantity of component A, thereby forming the first mixture with a temperature above the melting point of the sulphur cement.

5. Premixed, dry sulphur concrete, c h a r a c t e r ¬ i s e d in that it is prepared by the method as claimed in any of the preceding claims 1-4.