GB1593430A

GB1593430A - Method of producing light ballast concrete and a method of producing a cement mortar adapted thereto

Info

Publication number: GB1593430A
Application number: GB5384577A
Authority: GB
Original assignee: Bofors AB
Current assignee: Saab Bofors AB
Priority date: 1976-12-23
Filing date: 1977-12-23
Publication date: 1981-07-15
Also published as: JPS6119580B2; DE2756797A1; BR7708563A; SE7614519L; SE418852B; JPS5384024A

Description

(54) METHOD OF PRODUCING LIGHT BALLAST CONCRETE AND A METHOD OF PRODUCING A CEMENT MORTAR ADAPTED THERETO (71) We, AKTIEBOLAGET BOFORS, a joint stock company organized according to the laws of Sweden, of S-690 20, Bofors, Sweden, do hereby declare the invention for which we pray that a patent, may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a method of producing a cement mortar having a density of 1200 to 2000 kg./m.3. and good stability when freshly prepared.This invention also relates to a method of producing a light ballast concrete using said mortar as a bonding agent the concrete having a ballast content of 45 to 80 percent by volume and a density below 1400 kg./m.3, the ballast material having a particle density of less than 1200 kg./m.3 and the mortar entirely filling the space between the ballast particles.

The word "cement" is used in this Specification in a wide sense to include, in addition to Portland cement, other hydraulic bonding agents such as aluminate cement and slag cement.

According to the information sheet B8:1973 published by "Byggforskningen" ("Construction Research") and entitled "Betongtillsatsmedel" ' ("Concrete Additives") previously used concrete additives can be divided up into a plurality of different groups, of which the first two are "Luftporbildande tillsatsmedel" ("Air-pore-forming additives") and "Vattenreducerande (plasticerande) tillsatsmedel" ("Water-reducing (plasticizing) additives").

The present invention relates to these two groups of additives, although it can still not be referred entirely to one or the other or to both.

A fresh cement-based bonding agent mixture (cement mortar or concrete mass) consists of solid particles, water and air. The cement-bonded concrete, which from the point of view of volume is most widely used in the construction industry, substantially consists of approximately 100 litres of cement, 200 litres of water, 650 litres of ballast material, all of which having a diameter of less then 4 mm. is usually designated sand, and the remainder aggregate, and 50 litres of air, based on 1000 litres of fresh concrete mass. Of the 200 litres of water which is required in order to produce a workable mixture, approximately 60 litres is bonded chemically in the hardened cement, while the remainder is bonded physically as gel and capillary water.

The solid particles comprised in the cement mortar or the concrete consist of ballast, i.e.

aggregate and sand of various size fractions, the actual cement grains, and hydration products precipitated in water. The cement grains react with some of the water in the mixture to form a hydration product which consists of a colloidal binder, the cement gel.

The remaining water and the air are distributed in the basic mass formed by the cement gel and ballast. In the tresh mortar, the water will be found in the form of menisci in the cavities between solid cement and ballast particles, while the air, in turn, forms pores between these particles and the water menisci. The particle size of the previously mentioned precipitated hydration products is within the Angström range, while the mean grain size of the cement grains is approx. 5 clam. The sand and other ballast material can have a particle size of from approximately 0.1 mm. up to one or a few centimetres. If no special measures are taken, a fresh cement mortar will have an air content of from 1.5 to 3.5 percent by volume. In the hardened cement-bonded mass, there are both air and water-filled pores.In addition to these pores, the size of which in a well packed cement-bonded mass is from 10-1 to 1 mm., so-called capillary pores are also formed and have a pore size of 10-4 to 10-2 mm. and in the hardened cement gel so-called gel pores having a pore size of approximately 10-6 mm.

The water content of the original mixture influences the size and quantity of the gel pores only to a small extent, while the capillary pores are determined by the water/cement ratio.

A great many different ways of increasing the air pore content in fresh cement or concrete mass have been described in the literature.

In the aforesaid Construction Research information sheet it is stated that such air pore-forming agents increase the total air content in the fresh cement or concrete mixture, and also serve to provide a more uniform distribution of the air pores in the basic mass, at the same time as providing, to a certain extent, an increase in the content of small air bubbles, i.e. bubbles with a diameter of from 0.05 to 0.5 mm. The existence of these finely-distributed air bubbles gives the fresh mass an improved stability, which also contributes towards less water separation. If it is primarily desired to improve the stability of the fresh mass, without any requirements other than a certain air content, according to generally known technology, it is sufficient to provide for an air content of 3.0 to 4.0%.An increase in the amount of air added also has a certain improving effect on the flow of the fresh mass, as the air pores give rise to less friction between the solid particles in the mass, and thereby make this easier to work with. However, high contents of solid fine material with an increased air content are considered to give a tough, sticky concrete. As the consistency of a cement or concrete mass as a rule is used as a basis, the water content of the mixture can usually be lowered by the addition of an air-pore-forming agent. According to a rule of thumb given in literature, it should be possible to reduce the water content in fresh cement mortar, with unchanged consistency, by one-half of the air content increase achieved through the addition of an air-pore-forming agent.Together with the previously mentioned reduced water separation, an increase in the quantity of fine air pores in the basic mass also has the advantage that large ballast particles are not as easily separated out of the fresh mixture. However, the changes in consistency thereby achieved are comparatively limited, as they are directly dependent upon the quantity of stable air which in this way can be drawn into the mass. However, perhaps the most common reason for adding an air-pore-forming agent is that it is desired to make the hardened mass more resistant to frost, since the cavities achieved by the addition of the air-pore-forming agent will be available as expansion chambers for other water existing in the pore system when this increases its volume upon freezing.The walls of the pores are thereby prevented from being broken when the ambient temperature falls below the freezing point. An air pore volume of approximately 5 percent by volume is considered to give a maximum resistance to frost, and this can comparatively easily be achieved. As long as the strength of any ballast material is greater than that of the stiffened cement paste, the strength of this will determine the strength of the mass. The properties of the hardened mass will to a very large extent be dependent upon the water and air contents of the original mixture. A plurality of different materials has been used as air-pore-forming agents, such as saponified resins, alkyl aryl sulphonates, calcium ligno-sulphonates and hydroxy ethyl cellulose, in combination with surface-active agents.The purpose of these additives is to build up with the aid of the foaming agents comprised in them, a more or less stable foam with the aid of which increased quantities of air can be introduced into a fresh cement or concrete mass. The air pores thereby formed will substantially be of a magnitude of 0.1 to 1 mm. These additives make it possible to manufacture cement mortars and concretes with a reduced density.

However, foam bubbles of this size have little strength of their own, and the pore system build up can therefore collapse before the cement bonding agent has had time to harden.

This applies particularly when it is desired to introduce large quantities of air into the mass.

The mainly hydrophilic nature of the additives can also contribute towards an increased water absorption in the hardened mass. Through the addition of only a surface-active agent (either anionic or non-ionic) it is also possible, within certain limits, to change both the consistency and the quantity of the air comprised in a fresh cement composition. However, regardless of the type of agent which has been used, this procedure has proved to be very sensitive as regards the quantity of surface-active agent added, which at the most should comprise one or a few per mille of-the entire mixture. The surface-active agents used in this connection are highly effective, and can rapidly give a large quantity of air bubbles, the stability of which, however, varies considerably. As a rule, anionic surface-active agents lower the surface tension drastically when small quantities are added, while the non-ionic agents have a somewhat lesser effect for the same concentration. With these two types of agents, however, particularly if an over-dose is given, the air bubbles generated initially are rapidly recombined, i.e. they join together to form larger units. Particularly with the anionic agents, this recombination can take place to such an extent that air leaves the system, and a collapse occurs, i.e. the fresh mixture shrinks. Certain non-ionic agents show considerably better stability, and therefore a greater tolerance towards over-dosing, but it is very noticeable, however, that recombination increases with e.g. more intensive stirring.

Nor is it possible through regulating of such parameters as the choice of type of stirrer, the quantity of surface-active agent added, and the intensity of the stirring, to control the quantity of air mixed in or the size of the air pores, which will vary from 0.1 to several mm.

When additives of the kind described above and used, the intention can be to mix in air, or it maybe desired not to add more air to a concrete mixture. Through the choice of surface active agent and the quantity added, both of these effects can be achieved. In the Specification of Swedish published Patent Application No. 333 113, it is described how, through the addition of various surface-active agents plus a styrene acryl dispersion, the workability and flowability of a concrete mixture can be increased. As this addition permits a considerable reduction of the water/cement ratio of the fresh mixture, the hardened concrete mixture can be given a more compact structure and, consequently, increased strength. It is said that the dispersion in question, notwithstanding a high content of surface-active agents, does not have any foaming capability.It is also particularly pointed out that it does not give rise to the formation of any air pores. However, the quantity of surface-active agents added and the quantity of acrylonitrile comprised in the polymer will make the hardened concrete highly hydrophilic.

In the Specifications of Swiss Patents Nos. 493,438 and 515,862 cement and concrete additives are described consisting of plastics or natural latex dispersions containing water, to which, in addition to polymer components and emulsifiers, an anti-foaming agent has also been added.

Further, in the Specification of U.S. Patent No. 3,819,391, an air-pore forming cement additive has been described, consisting of a free-flowing, flaky solid product containing 12.5 to 37.5 percent by weight of a bituminous substance and the remainder, 87.5 to 62.5 percent by weight, of a surface-active substance. In this additive, the major portion thus consists of the surface-active substance.

In a proposed development of the additive described in the above-mentioned U.S.

Patent, the additive is in the form of a water-soluble powder of which 40 to 60 percent by weight is made up of the above-mentioned bituminous substance and a surface-active substance, while the remaining 60 to 40 percent by weight consists of polyethylene oxide resins, lignosulphonates and diatomaceous earth. The surface-active agent may be anionic cationic or non-ionic, but a mixture of agents is preferred, while the bituminous material may be asphalt, coal tar or derivatives thereof. In order that it may be used in this connection, however, it is a requirement that the substance in question shall be a liquid at room temperature. In addition to its air-pore-forming function, it is said that the additive also has a bonding-retarding effect on the cement.

It has also been proposed, with the aid of colloidal silica, surface-active substances and amphiphilic substances or hydrocarbons, to change the consistency, workability and uniform distribution of the fine portion of the cement the water/cement ratio being of importance for such a change. When, with the aid of the additive, more air is introduced into the concrete, the water content can be reduced at the same time. The most likely reason for any increase in strength must, presumably, be ascribed to the reduced water content. However, it should be possible to ascribe a complementary effect to the silica which is chemically active in connection with the hardening of the cement.

As indicated by the above-mentioned review of at least some of the concrete additives which have previously been proposed, there is nothing new in endeavouring to manipulate the structure of a fresh cement composition through miscellaneous additives, which primarily have an, albeit limited, effect of drawing in air. The fact that at least some of these air-pore-forming agents have also had a tendency to increase the content of fine air pores in the mixture is likewise previously known. In general, however, these older types of air-pore-forming agents have also given rise to the presence of large numbers of comparatively large pores, i.e. pores with a size of 0.1 to 1.0 mm. and more.

The present invention relates to a method of providing an extremely fine and uniformly pored structure in fresh cement mortar, this pore structure being achieved by incorporating a fine-particled material with a certain particle size and form and with certain defined surface properties into the fresh mortar. These specific properties give the material in question a marked capability of drawing in air, together with the capability of holding the air which has been drawn in together in extremely fine and stable bubbles, which during the working of the mortar are distributed therein, without being recombined with each other.

In this way, an extremely fine-pored mortar is obtained. The properties characteristic of the material include the fact that the individual particles show hydrophilic and hydrophobic properties concentrated to the respective particle surface, which in a certain way have been balanced in relation to each other. This combination of properties contradictory to each other obviously makes it possible for the particles in question to divide up large water menisci into smaller ones.

We have not been able to find any other explanation as to why a hardened cement mortar, produced in accordance with the invention, can show a pore structure in which the major portion of all pores are within the size range of 5 to 30 llm. Otherwise, large pores, achieved by large water menisci are very common. The pore structure of the hardened mortar has been measured in a sweep electron microscope. In the fresh mortar, this can be more difficult, but if no collapse of the pore system occurs before hardening, the pores of the fresh mortar correspond to the pores of the hardened mortar, but with the difference that some of the pores in the fresh mortar are filled with water.

The present method thus offers a method of producing a fresh cement mortar which, notwithstanding such an extreme air content as up to 40 percent by volume, nevertheless has a very good stability. This good stability makes its possible to mix in considerably greater quantities of ballast of another density into the mortar than would previously have been possible in practice. In a mortar with less good stability, the light ballast would have time to float up, and the really heavy ballast would sink to the bottom before the mortar had hardened.

The explanation of the good stability of the present mortar is that the surface-tension forces which prevent the air pores in fresh mortar from collapsing under the surrounding pressure of small pores or water menisci are considerably greater than the corresponding conditions for the larger ones.

Another effect which is achieved with such a fine-pored moertar is that its workability is improved. This is explained by the fact that the small air pores, as soon as the adhesive forces have been overcome, will facilitate the displacement of the solid particles in relation to each other. As a consequence of this, the mortar will have considerably improved pouring properties. As previously stated, the fine air pores are extremely well anchored in the fresh mortar at atmospheric pressure, but if the surrounding pressure is increased to such a high degree that the surface-tension forces acting upon the pores are exceeded, the entire structure will momentarily collapse when the fine pores, after the adhesive forces have been exceeded, make the solid particles so easily movable in relation to each other that it can practically be called a sheer quicksand effect.If the structure then collapses and the air leaves the system, a more complete particle contact will be achieved between the cement grains, ballast, if any, and the particle-formed material. The fine spherical particles will then particularly facilitate the movements of the extremely rough cement grains in relation to each other. Because of this effect, cement mortar produced according to the present method should be extremely well suited for extrusion under high pressure through a die to form products with an extremely high density and strength.

In a fresh cement mortar produced in accordance with the present invention, the structure collapsed at an increase in pressure corresponding to 4 atmospheres overpressure.

Generally, in this connection, air pores and capability of drawing in air are mentioned.

The reason for this is that the surrounding atmosphere in practically all cases will consist of air. If, for any reason, this should consist of another gas, a corresponding pore formation will be applicable. As the particle-shaped material which is incorporated into the mortar chiefly seems to function as nuclei for the fine pores, we consider it to be probable that the pore structure will be about the same with an in situ generated gas, i.e. a distribution of this into very fine gas bubbles.

The present invention thus relates to a method involving the incorporation in the fresh mortar of comparatively small quantities of a fine-particled polymeric material of a specific type, and of comparatively small quantities of finely distributed air. The polymeric particles that may be used in the present method also co-operate towards increasing the stability of the air pores in the mortar, and of reducing their tendency towards recombination. This property is presumably concerned with the accumulation of polymer particles which we have been able to notice in all phase boundaries in a hardened mortar through an electron microscope e.g. at the inner walls of the pores. This accumulation of particles at the phase boundaries involves that the inner walls of the pores, after the hardening of the cement, will to some extent consist of this material either in a particle form or, if the character of the particles is such that film formation can take place, of a more or less coherent film. The accumulation at the pore walls will also to a certain extent be applicable to the capillary pores. Primarily in moulded products we have also been able to notice an accumulation of the particles at the outer sides of the product. This gives a dense product with very little water absorption.

The polymeric particles which are used in the present method have also proved to serve as nuclei for dividing up large water menisci in the fresh mortar into smaller ones.

All of this together is an explanation of why the method according to the invention results in such a fine-ported mortar that, when hardened, it, substantially has pores only of the magnitude of 5 to 30 llm. In a fresh condition, this fine pore structure gives the mortar an extremely good stability, together with good pouring properties.According to the present invention there is thus provided a method of producing a cement mortar, wherein cement, ballast material and water are mixed to form the mortar into which there is incorporated from 0.2 to 5.0 percent by weight based on the weight of the cement of a fine-particled polymeric material in the form of spherical particles having a size of 0.1 to 1.0 yam., so as to provide in the mortar finely distributed air in an amount and distribution such as to give the mortar a density of 1200 to 2000, preferably 1600 to 2000 k./m.3 and a pore structure which in the hardened mortar gives pores of a size of 5 to 30 Clam, and wherein the polymeric material consists of from 95.0 to 99.9 percent by weight of a polymerized hydrophobic component and from 5.0 to 0.1 percent by weight of a polymerized hydrophobic component, the hydrophobic component comprising one or a plurality of esters of acrylic and/or methacrylic acid of the formula:

where R1 is a hydrogen atom or methyl group and R2 is a group derived from an alcohol R2OH and has 1 to 8 carbon atoms, or a styrene, butadiene or vinylidene chloride group, and the hydrophilic component comprising an ethylenically unsaturated polymerizable compound which contains at least one carboxyl, hydroxyl, amide, nitrile or sulphonate group, and which is soluble to an extent of at least 5% in an aqueous alkaline solution.

The particles must have a spherical form, and a particle size of 0.1 to 1.0 lem., preferably 0.2 to 0.6 Fm. Further, the surfaces of the particles have a balance adapted in a certain way between hydrophobic and hydrophilic properties.

As previously mentioned, in the present method comparatively large quantities of air are drawn into the mortar. We therefore primarily consider the present method to be suitable for the production of cement mortar with a density of 1200 to 2000, preferably 1600 to 2000 kg./m.3, which in mortar with an intrinsic density of 2300 kg./m.3 (without any air whatsoever contained in it) would correspond to air contents of from approximately 13 to 14 percent by volume up towards 40 percent by volume.

The formation of pores in accordance with the present method must not be disturbed by the simultaneous or previous admixture of a foaming agent, e.g. free surface-active agent as in such a case an uncontrolled foaming would be initiated, which has a disturbing effect on the desired structure.

The particles of polymeric material can be mixed with the cement as a dry powder before the water is added, or can be added dispersed in the water which is mixed in. However, it is necessary to ensure that the material is available in the form of free particles, and that the particles do not stick together and form large agglomerates.

Because of their size, corresponding to 1/50 to 1/5 of that of the cement particles, the spherical particles in question will have their place in the empty space in the particle distribution curve which there is in a conventional cement mortar between the previously mentioned hydration products released in the water and the actual cement particles. This explains why the particles do not disturb the cement structure, but rather contribute towards an improvement of it.

When mixed into the cement mortar, the particles primarily tend to be attracted to the nearest large particles, i.e. the cement grains, and there constitute the previously mentioned nuclei for dividing up the water menisci between these cement grains themselves and between the cement grains and the ballast particles.

The polymer particles used in the present method are made up of at least two different groups of ethylenically unsaturated monomers, one of which is of a hydrophobic character and the other of a hydrophilic character. As it is actually the properties which are localized at the surfaces of the particles which primarily determine their function in this connection, the internal composition of the particles is of minor importance. It should thus, for instance, be possible to polymerize a greater quantity of hydrophilic component in the particles than the 5.0 percent by weight indicated, without therefore, departing from the scope of the present invention, but in such a case, some of these hydrophilic components would be partly concealed in the insides of the particles. It would then, presumably, also be necessary to resort to special tricks of the trade in order to achieve this result.Theoretically, the hydrophobic and the hydrophilic components, respectively, can be of a plurality of kinds, just as well as components which in this connection can be considered as being neither hydrophilic nor hydrophobic can be included in the insides of the particles, and also in small quantities in parts of the particles which are at the surface or nearest below the surface.

The polymer particles used in conjunction with the present method are thus to be made up of at least two different groups of ethylenically unsaturated monomers, one group of which is to be included in a quantity corresponding to 95.0 to 99.9 percent by weight and which are of a hydrophobic character, while a second group which is to be included in a quantity corresponding to 5.0 to 0.1 percent by weight is to consist of a polymerizable compound of a hydrophilic character, which contains at least one of the hydrophilic groups carboxyl, sulphonate, hydroxyl, nitrile or amide.

Even if it is possible to produce particles which satisfy the above-mentioned boundary values, but totally seen contain e.g. more hydrophilic component, it should be easier, generally speaking, to allow the boundary values indicated to be applicable to the entire particle.

Spherical polymer particles which have a size of 0.1 to 1.0 Fm, and the surfaces of which has the desired balanced ratio between a hydrophobic and a hydrophilic character, are appropriately produced by emulsion polymerization. In this connection, no stabilizing and/or emulsifying agent is added, but the monomers used containing hydrophilic groups in their polymeric form constitute a non-desorbable electrostatic and/or steric stabilizing layer on the polymer particle produced through emulsion polymerization. This stabilizing layer can consist of polymer containing only hydrophilic monomer adsorbed on a hydrophobic polymer or can consist of a copolymer of a hydrophobic monomer and a hydrophilic monomer.With small quantities of hydrophilic monomer, the production method should be adapted so that a large portion of the hydrophilic monomer is localized on the surface of the particles produced, as is possible with one and the same total content of hydrophilic monomer, by varying the order in which the hydrophilic and the hydrophobic monomer are added, to vary the quantity of hydrophilic monomer which will be localized on the surface of the particles.

It is moreover known that the end groups of the polymer chains are to a large extent localized to the particle surfaces, and there contributed towards the stabilization of the particles in cases when water-soluble initiators are used.

In the monomer form, the hydrophobic component of the polymer particle can consist of one or a plurality of esters of acrylic acid or methacrylic acid with alcohols having 1 to 8 carbon atoms, while other appropriate materials include styrene, butadiene, and vinylidene chloride.

Examples of monomers containing hydrophilic groups include acrylic acid, methacrylic acid, itaconic acid, maleic acid and fumaric acid, all of which contain carboxyl groups; hydroxy ethyl methacrylate, hydroxy ethyl acrylate, hydroxy propyl methacrylate, hydroxy propyl acrylate, and hydroxy-terminated polyethylene oxide adducts bound to ethylenically unsaturated compounds, all of which contain hydroxyl groups; acryl amide which contains an amide group; and acrylonitrile which contains a nitrile group; and vinyl-sulphonic acid and 2-sulph-ethyl methacrylate which contain sulphonate groups.

Further, as regards the hydrophilic component of the polymer, in its monomer form this is to be soluble in an aqueous alkaline solution to at least 5%.

Polymer dispersions available in the market, primarily intended for paint, adhesive and other manufacture, when tested as cement additives have provided to involve an immediate change of the consistency of the fresh cement mortar, caused by a pronounced increased admixture of air. However, the effect has varied very much from case to case, at the same time as the air bubbles mixed in have been of different sizes (from 0.1 to several mm.). The tendency towards recombination between the bubbles also proved to be very great, at the same time as the reproducibility between different tests with the same product was poor.

An explanation for this is the comparatively high concentrations of surface-active substances which are generally present in polymer dispersions, and which are almost always present together with polymerizable hydrophilic substances and/or protective colloids. In such a dispersion there are thus sufficicntly high concentrations of surface-active substances which are not sufficiently strongly adsorbent on the polymer surface. The surface-active substances which are not adsorbed on the polymer surface give rise to air bubbles of an unstable character, which are quickly recombined or collapse. With the present method, it has now become possible to avoid or reduce problems of this kind.

In addition to the various methods of producing a fine-pored cement mortar as above, the present invention also comprises an application for utilizing a cement mortar produced in this way in connection with the production of a light ballast concrete with a total density of less than 1400 kg./m.3 in which the ballast material is a light ballast material having a density of 500 to 1300, preferably 650 to 750 kg./m.3 and of which the ballast percentage is 45 to 80 percent by volume. In this light ballast concrete, the cement mortar, with the exception of the pore system normally occurring in cement mortar, entirely fills out the space between particles of the ballast.

It has hitherto proved to be very difficult with the aid of cement additives available on the marker to achieve a coherent and pourable light ballast concrete with a ballast content exceeding 45 to 50 percent by volume. The reason for these difficulties can primarily be ascribed to the great difference in density between the cement mortar and the light ballast.

The adhesive forces of the mortar have been too weak to prevent the lighter ballast particles from separating and floating up in the mortar when the fresh concrete is being worked.

A concrete with cavities is then obtained, in which the cavities between the large ballast particles are not entirely filled out by the cement mortar. However, it is more simple to produce concrete with cavities of this type if, from the beginning, the quantity of cement added is limited to only the quantity required for adhesion between the ballast particles.

Such products, which are primarily used for cement blocks, are produced today by many manufacturers.

When a cement block of this type is immersed in water the spaces between the large ballast particles are almost instantaneously filled with water. Products of the type hollow cement blocks are not comprised in the invention. They can easily be produced with conventional cement mortar.

According to a modification of the invention it has thus become possible to manufacture a light ballast concrete with a density of less than 1400 kg./m.3 containing approximately 80 to 140 litres of cement/m.3 concrete, 450 to 800 litres of light ballast/m. concrete, 0 to 100 litres of sand (which can be replaced by other material which may possibly be included in the bonding agent part) per m. of concrete, 100 to 180 litres of water/m.3 concrete and 0.2 to 5.0 percent by weight based on the weight of the cement of the substantially spherical particles which are chemically inert in relation to the other components in the mortar, and which have a particle size of 0.1 to 1.0 llm. and the previously described composition.

Together with the quantity of finely distributed air which has been introduced into the mortar and which there forms pores of a magnitude of 5 to 30 Fm, a mortar is obtained with a density of 1200 to 2000 kg./m.3. Together with the above-mentioned quantities of light ballast this gives a well pourable light ballast concrete with a density of less than 1400 kg./m. . The particle density of the light ballast is calculated to be less than 1200 kg./m.3.

The present invention will now be further described in the following Examples.

Example 1 A three-necked flask provided with a stirrer, reflux cooler, thermometer and nitrogen gas supply and containing 1200 g. of deionized water and 1.6 g. of potassium persulphate was heated to 85"C. in a water bath while nitrogen gas was passed through it with stirring. Over a period of one hour, there was added continuously a monomer mixture which consisted of 692 g. methyl methacrylate (MMA), 80 g. butyl acrylate (BA), 24 g. 2-hydroxy ethyl methacrylate (HEMA) and 4 g acrylic acid (AS). When the monomer addition had been completed, the temperature was held at 850C. for another hour, after which the acrylate dispersion formed was cooled and filtered. The product was free from precipitations, had no monomer smell, and had a solids content (dry) of 40%.Through measuring in a sweep electron microscope, the particle size was measured as being 0.60 Rm. indicated as the mean value for the quantity.

Example 2 The same technique was used as in Example 1, but with a monomer mixture consisting of 696 g. MMA, 80 g. BA and 24 g. HEMA. The dispersion obtained was free from monomer smell, had a precipitation of approximately 1 g. of solids (dry) content of 40% and a particle diameter of 0.7 Fm.

Example 3 The same technique as for Example 1 was used, but with a monomer composition of 700 g. MMA, 80 g. BA and 20 g. 2-sulpho-ethyl methacrylate. The product had a particle diameter of 0.4 4m.

Example 4 The apparatus used in Example 1 was charged with 1200 g. deionized water and 1.6 g.

potassium persulphate. Heating to 85"C. took place in a water bath, while nitrogen gas was passed through. Over a period of 30 minutes, a monomer mixture with a composition of 27 g. MMA, 8 g. BA and 5 g. methacrylic acid (MAS) was dripped in continuously. A seed was then formed, which was allowed to react for a further 15 minutes. A second monomer mixture was thereafter added continuously over a period of 60 minutes, consisting of 608 g.

MMA and 152 g. BA. After a further 60 minutes on a hot bath, the product was cooled and filered. The particle size was measured and was 0.45 Fm.

Examples 5-6 The same technique as used in Example 4 was used, but with monomers added according to the following table.

Example 5 Example 6 MMA 124 g. 15 g.

monomer addition 1 BA 31 g. 5 g.

MAS 5 g. 5 g.

monomer addition 2 MMA 511 g. 620 g.

BA 129 g. 155 g.

particle size obtained 0.5 llm 0.45 iim Example 7 The same technique was used as in Example 4 to produce a styrene-based dispersion, the first monomer mixture consisting of 27.2 g. styrene, 11.6 g. 2-ethyl hexyl acrylate and 1.2 g.

itaconic acid. After the 30 minutes for adding the monomer and a further 15 minutes, the pH was adjusted to 8.5 with ammonia, after which a second addition of monomer consiting of 532 g. styrene and 228 g. 2-ethyl hexyl acrylate was made over a period of 90 minutes. After another hour, the dispersion was cooled. A precipitation of approximately 2 g. was filtered off. The particle size was measured and was 0.65 Clam.

Examples 8 to 11 Further dispersions were produced using the same technique as that used for Example 4.

The monomer compositions and particle sizes obtained are given in the following table: Ex. 8 Ex. 9 Ex. 10 monomer addition I methyl methacrylate 78g. 86g. 17g.

2-ethyl hexyl acrylate 18g. 22g. 3g.

methacrylic acid 24g. acrylonitrile 32g.

acrylic acid 4g. 4g.

monomer addition II methyl methacrylate 578g. 558g. 619g.

2-ethyl hexyl acrylate 102g. 98g. 157g.

particle size obtained 0.30 Fm 0.40 llm 0.50 llm Example 12 The same technique was used as in Example 4 but with the following monomer compositions: I methyl methacrylate 50 g.

ethyl acrylate 25 g.

methacrylic acid 25 g.

II methyl methacrylate 266.7 g.

ethyl acrylate 133.3 g.

A dispersion with 29% solids (dry) content and a particle size of 0.15 llm was obtained.

Example 13 The apparatus used in Example 1 was charged with 1200 g. deionized water, 1.6 g.

potassium persulphate and 12 g. acryl amide (AA) and 2 g. acrylic acid (AS). The aqueous solution was heated, while nitrogen gas was passed through It to 850C. on a heat bath. After 15 minutes at this temperature, 786 g. butyl methacrylate was added continuously over a period of 90 minutes. After another hour on the heat bath, the dispersion obtained was cooled and filtered and had a particle size of 0.4 llm.

Example 14 A cement mortar with the following composition was prepared according to the Swedish regulations for cement testing.

500 g. standard Portland cement 500 g. normal sand 0-0.5 mm.

500 g. normal sand 0.5-1 mm.

500 g. normal sand 1-2 mm.

250 g. water.

The pore structure in this standard mortar was modified in the way indicated.

Through the addition of the quantities indicated in the table, counted as dry polymer, of the particles produced as described in Examples 1, 2, 4, 7, 8, 10 and 12, the changes in the density of the mortar indicated in the table were obtained.

Percentage addition based on weight of cement.

0 1 2 4 Particles according to Ex 1 2140 1960 1840 1640 Ex 2 2140 1990 1850 1670 Ex 4 2140 2000 1880 1690 Ex 7 2140 1880 1790 1520 Ex 8 2140 1790 1590 1480 Ex 10 2140 1820 1650 1510 Ex 12 2140 1950 1840 1650 A characteristic feature of the particles according to Examples 1, 2, 4, 7, 8, 10, 12 was that the air mixed in was very stable. The air content was not changed when the mortar was vibrated on a vibratory table for 10 minutes. All examples enhibited air pores within the range of 5 to 30 Rm.

Example 15 In a concrete mixer, a light ballast concrete with the following composition was prepared.

Kg. Litre Cement (standard Portland) 350 112 Light ballast 0-5 mm. 180 200 Light ballast 5-12 mm.X/ 240 400 Sand , 0-2 mm. 265 100 Water 150 150 xl Light ballast in the form of ball-sintered clay.

The light ballast 5-12 mm. light ballast 0-5 mm., cement and sand were charged in the order mentioned, and mixed dry for 1 minute. Water together with particles, the quantity and type of which will be noted from the summary below, was added and mixed for 3 minutes. The concrete was poured into an open mould and vibrated. For a comparison, only surface-active agents Barra 55L and UCR were used. Barra 55L is a substance of the surface-active type but of composition unknown to us. UCR is a high-molecular weight polyethylene oxide, intended to thicken the water phase and thereby obtain a better cohesion in the concrete.

The following judging scale was used for the casting tests.

Casting properties and cohesion 1 = No cohesion whatsoever; upon vibration, the mixture segregates and light ballast leaves the system.

2 = Some cohesion, but separation; cement paste in bottom, and light clinker floats up to the surface.

3 = Very good cohesion; no tendency towards separation.

Consistency For measuring the consistency in light ballast concrete, a method is proposed which is described in the German DIN standard (1048-1972). The equipment consists of a spreading table 70 x 70 cm. which has a weight of 16 kg. and of which one edge should have a lifting height limited to 4 cm..

On the table, a frusto cone of concrete is formed using a mould with a height of 20 cm.

and upper and lower diameters of 13 and 20 cm., respectively. The mould is placed in the middle of the table and the concrete is compressed with a rod. The mould is filled in two layers of equal height, and each layer is packed with 10 blows with the rod. The mould is removed from the frusto cone after one-half minute. Thereafter, with the aid of a handle, the table is allowed to fall within the working range 15 times during 15 seconds. The spread is thereafter measured in two directions at right angles and is indicated in cm. The cohesion and separation tendencies of the concrete can also be determined ocularly.

Type of additive % additive based Consistency Cohesion on cement weight (spread in cm) Casting (solid substance) properties O x X 1 Particles according to Example 2 1.0 31 - 33 3 Example 2 3.7 36 - 38 3 Example 8 1.4 32 - 35 3 Example 12 0.8 29 - 32 3 Example 12 1.6 33 - 34 3 Example 13 2.3 36 - 37 3 Barra 55L 0.15 35 - 36 1 Barra 55L 0.6 36 - 37 1 UCR 0.03 33 - 34 1 Sodium Lauryl sulphate Adduct ethylene oxide nonyl phenol (20EO) 0.5 34 - 37 1 Adduct ethylene lauryl alcohol (i0EO) 1.0 33 - 36 1 X = segregation so heavy that no measurement can be made. Consistency changes immediately with use of Barra 55L, agents described and particles according to the invention. This appears in the form of an increased spread at the test of the consistency.No cohcsive effect whatsoever was obtained with the use of Barra 55L, UCR or other surface active agents.

Examples 16-18 describe different light ballast compositions with a constant volume of light ballast (65 percent by volume) and a varying quantity of cement in the mortar. The compositions used in the respective examples tested will be noted from the following tables.

Without extra additives, all of the mixtures were considered to be difficult to cast.

Example 16 Kg. Litres Cement, standard 250 80 Light clinker 0-3 mm. 175 163 Light clinker 3-10 mm. 195 325 Light clinker 10-20 mm. 85 162 Sand 0-2 mm. 239 90 Water > 180 ~ 180 Example 17 Kg. Litres Cement, standard 314 100 Light clinker 0-3 mm. 175 163 Light clinker 3-10 mm. 195 325 Light clinker 10-20 mm. 85 162 Sand 0-2 mm. 186 70.

Water > 180 t 180 Example 18 Kg. Litres Cement, standard 377 120 Light clinker 0-3 mm. 175 163 Light clinker 3-10 mm. 195 325 Light clinker 10-20 mm. 80 162 Sand 0-2 mm. 133 50 Water 180 180 The fresh mixtures were thereafter modified by the addition of the material described in Example 4.

Various quantities between 0 and 2% additive were tested. With an increased cement content and quantity of additive, better, casting properties were obtained. The compressive strength in kg./cm. of the compositions tested was checked after 28 days, at the same time as the bulk density in kg/m.3 was determined. The values then measured are shown in the upper and middle graphs of the accompanying drawings. All the values referring to well compacted mixtures. The water cement ratio of the various compositions is shown in lower graph.

In the upper graph, ranges I, II and III have been indicated. These show the approximate limits for Range I: concrete which cannot be cast Range II; concrete which can be cast but which, however, can segregate, i.e. a separation of the ballast can take place.

Range III: concrete which can be cast without any tendencies towards segregation.

From the upper and middle graphs it will be noted that, with small contents of additives within range I, particularly with quantities of cement, a remarkably low bulk density is obtained. This is explained by the great inner friction of these mixtures, which prevents compression of the cast mass. The low density thus refers to the comparatively large compression pores, and not the finely distributed mixed-in air.

WHAT WE CLAIM IS: 1. A method of producing a cement mortar, wherein cement, ballast material and water are mixed to form the mortar into which there is incorporated from 0.2 to 5.0 percent by weight based on the weight of the cement of a fine-particled polymeric material in the form of spherical particles having a size of 0.1 to 1.0 Rm, so as to provide in the mortar finely distributed air in an amount and distribution such as to give the mortar a density of 1200 to 2000 kg/m3 and a pore structure which in the hardened mortar gives pores of a size of 5 to 30 clam, and wherein the polymeric material consists of from 95.0 to 99.9 percent by weight of a

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Example 16 Kg. Litres Cement, standard 250 80 Light clinker 0-3 mm. 175 163 Light clinker 3-10 mm. 195 325 Light clinker 10-20 mm. 85 162 Sand 0-2 mm. 239 90 Water > 180 ~ 180 Example 17 Kg. Litres Cement, standard 314 100 Light clinker 0-3 mm. 175 163 Light clinker 3-10 mm. 195 325 Light clinker 10-20 mm. 85 162 Sand 0-2 mm. 186 70. Water > 180 t 180 Example 18 Kg. Litres Cement, standard 377 120 Light clinker 0-3 mm. 175 163 Light clinker 3-10 mm. 195 325 Light clinker 10-20 mm. 80 162 Sand 0-2 mm. 133 50 Water 180 180 The fresh mixtures were thereafter modified by the addition of the material described in Example 4. Various quantities between 0 and 2% additive were tested. With an increased cement content and quantity of additive, better, casting properties were obtained. The compressive strength in kg./cm. of the compositions tested was checked after 28 days, at the same time as the bulk density in kg/m.3 was determined. The values then measured are shown in the upper and middle graphs of the accompanying drawings. All the values referring to well compacted mixtures. The water cement ratio of the various compositions is shown in lower graph. In the upper graph, ranges I, II and III have been indicated. These show the approximate limits for Range I: concrete which cannot be cast Range II; concrete which can be cast but which, however, can segregate, i.e. a separation of the ballast can take place. Range III: concrete which can be cast without any tendencies towards segregation. From the upper and middle graphs it will be noted that, with small contents of additives within range I, particularly with quantities of cement, a remarkably low bulk density is obtained. This is explained by the great inner friction of these mixtures, which prevents compression of the cast mass. The low density thus refers to the comparatively large compression pores, and not the finely distributed mixed-in air. WHAT WE CLAIM IS:

1. A method of producing a cement mortar, wherein cement, ballast material and water are mixed to form the mortar into which there is incorporated from 0.2 to 5.0 percent by weight based on the weight of the cement of a fine-particled polymeric material in the form of spherical particles having a size of 0.1 to 1.0 Rm, so as to provide in the mortar finely distributed air in an amount and distribution such as to give the mortar a density of 1200 to 2000 kg/m3 and a pore structure which in the hardened mortar gives pores of a size of 5 to 30 clam, and wherein the polymeric material consists of from 95.0 to 99.9 percent by weight of a

polymerized hydrophobic component and from 5.0 to 0.1 percent by weight of a polymerized hydrophillic component, the hydrophobic component comprising one or a plurality of esters of acrylic and/or methacrylic acid of the formula:

2. A method as claimed in Claim 1, wherein the spherical polymer particles have a size of 0.2 to 0.6 Fm and are produced by emulsion polymerization.

3. A method as claimed in claim 1 or 2, wherein the ballast material is a light ballast material having a density of 500 to 1300 kg/m3 and there is produced a light ballast concrete with a ballast percentage of 45 to 80 percent by volume and a total density of less than 1400 kg/m3 in which the cement mortar with the exception of the pore system normally occurring in cement mortar entirely fills out the space between particles of the ballast.

4. A method as claimed in claim 3, wherein the light ballast material has a density of 650 to 750 kg/m3.

5. A method as claimed in any preceding claim, wherein the mortar is cast, vibrated and allowed to harden.

6. A method of producing a cement mortar in accordance with claim 1 substantially as hereinbefore described in any one of Examples 14 to 18 of the foregoing Examples.

7. Cement mortar produced by the method claimed in any preceding claim.