COMPOSITIONS FOR USE IN CONCRETE AND CONCRETE PRODUCTS OBTAINED THEREFROM

Abstract: Glass in a fine particulate state is used as an aggregate for concrete products. The glass has a significant number of particles less than 150 microns. The glass is preferably combined with slag more preferably after being fused together and then crushed to the required particle size. Products of the invention can have various desired properties such as imperviousness to water and acid and be resistant to alkali/silica degradation while retaining adequate strength. The preferred compositions are impervious to water and acid, are resistant to alkali/silica degradation and reach high strength rapidly on setting.

Description: COMPOSITIONS FOR USE IN CONCRETE AND CONCRETE PRODUCTS OBTAINED THEREFROM INTRODUCTION This invention relates to a cementitious mixture, articles produced from that mixture on setting and processes for producing such articles and the mixture itself. BACKGROUND OF THE INVENTION Concrete is generally formed from cement and an aggregate and additives for certain purposes mixed with water and allowed to set. There have been numerous suggestions of using different aggregates to obtain various alleged advantages some of which have lead to commercial products with various degrees of success. The desired properties of the concrete product will vary dependent on the use of that particular product. High strength and long life are two of the most desirable properties. High strength can also be a factor of time with some products needing to achieve high strength over a short period of time while with others a slow increase in strength is acceptable. The life of a concrete product is again dependent upon particular use and the environment. Factors which can reduce the life of the concrete are the reactivity of the concrete to acid, the permeability to moisture and the alkali/silica reactivity. The susceptibility of any particular concrete to degradation conditions can be improved by using particular additives or varying the type of cement but this usually increase costs and also to the loss of other desirable properties of that concrete. There is therefore a need for compositions for use in making concrete which can give an additional choice for selection of concretes having desired properties for a particular use. SUMMARY OF THE INVENTION In accordance with this invention there is provided a cementitious mixture suitable for mixing with water to form a cast or moulded article, comprising cement and glass particles such that a substantial part thereof are of a fine particle size. The cement for use in the invention can be any suitable cement used in the trade for forming concrete of various types. Portland cement will generally be suitable It is a feature of the present invention that additives usually added to cement mixtures to accelerate setting or retard setting etc are not necessary but they can be included if there is ever a particular need to do so. For example a defoaming agent for removing air (e.g. Bevaloid 5469DD - Rhone Poulenc) or a strength additive (e.g. Rockite from Hartline Products Co Inc Cleveland, Ohio) can be added. The important feature of the present invention is the particle size of the glass. A substantial proportion of the glass particles need to be of a fine size. Generally the glass will have a particle size ranging from what is generally known as sand down to silt/clay. The largest particles will not normally be greater than 5mm except for specific type of products. Particle size will vary from 5mm right down to submicron sizes. It is believed that the key characteristics of concrete produced by glass particles lies in having a substantial proportion of a fine particle size. By substantial is meant having sufficient particles present to influence the properties of the concrete in a favourable manner. By fine particles is meant particles generally having a size less than 1 50 microns, e.g. less than 1 00 microns. The particle size distribution can be produced by crushing larger glass particles to give a range of particle sizes of from less than 5mm down to 1 micron or less. The manner of crushing can be varied to increase the ratio of fine particle sizes which may be required in certain situations as trial and error may show The glass aggregate can be produced by any suitable crushing means. One particular method is to use recycled glass and reduce it first in an Australian made Hammer Mill down to particle size less than 1 9mm. The crushed glass can then be further crushed in a Los Angeles Abrasion Resistance Machine having 25 steel spheres each weighing approximately 350 grams The particle size will be reduced in this apparatus down to the required level dependent upon the time of operation. Crushing for an hour will give particles of a useful distribution for use in this invention. One particular glass aggregate of use in the invention is obtained by the above process after approximately one hour of crushing, and then screened over a 2mm BS sieve. A representative sample of the material passing the 2mm BS sieve was taken using the procedures set out in New Zealand standard 4402: 1 986. It was then tested to determine its particle size distribution. That distribution is as follows (Distribution 1 ): Sieve Size Cumulative Sieve Size Cumulative Percentage Percentage Passing Passing % % 2.00mm 1 00 21 2 microns 1 7.44 1 .1 8mm 86.32 1 50 microns 1 3.48 600 microns 41 .1 0 90 microns 9.28 425 microns 29.1 4 63 microns 6.84 300 microns 22.26 - - A portion of the 2mm sand was then sieved through a 600 micron BS sieve and the fraction was then again tested to determine its particle size distribution. That is as follows (Distribution 2): Sieve Size Cumulative Sieve Size Cumulative Percentage Percentage Passing Passing % % 600 microns 1 00 90 microns 25.3 425 microns 79.1 63 microns 1 5.2 300 microns 54.1 - - 21 2 microns 42.3 - - 1 50 microns 33.4 - - The procedure was then repeated through a 1 50 micron BS sieve giving the following particle size distribution (Distribution 3): Sieve Size Cumulative Sieve Size Cumulative Percentage Percentage Passing Passing % % 1 50 microns 100 8 microns 1 7.2 90 microns 71 .7 4 microns 1 1 .1 63 microns 54.2 2 microns 5.3 32 microns 38. 1 1 microns 2.4 1 6 microns 26.4 - - It is within the scope of the invention to use the crushed glass produced by the above abrasion mill directly or to screen it through a sieve to reduce the proportion of large particles, e.g having glass particles no greater than 2mm or no greater than 600 microns or no greater than 1 50 microns. It is also within the scope of the invention to add to any glass aggregate, specific sized particles, e.g. very fine particles passing a 1 50 micron sieve to increase the proportion of such fine particles. If larger aggregate particles are desired, then in accordance with the invention these can be chosen from glass aggregate of a size greater than 5mm. Where larger glass particles are added, then it is a preferred feature of the invention that these particles are scored by abrasion with finer glass particles entrapped in a Jetstream of air. This can happen in a suitable chamber which is rotated allowing the larger particles to tumble within the container and a compressed air blast is fed into the chamber from one end entrapping smaller particles within the Jetstream to impact on to the larger particles. Scoring the larger particles in this way adds to the keying effect of the other ingredients in the cementitious mixture. The glass particles of the invention can be chosen from a wide range of sources. Recycled glass, e.g. from bottles or other waste glass products is a primary source of material for use in this invention in view of its cheapness. Currently preferred glass is recycled glass because of its significant purity. This invention also envisages using glass specifically made for use in the invention. The glass can be in various colours but the invention also envisages forming concrete having various colours through use of pigments. Glass used in high radiation situations, e.g. light bulbs, fluorescent tubes, heating elements, cathode ray tubes and microwave ovens, which is generally known as toughened glass and which has high tensile strength can be used for products where high insulation (thermal or electrical) is desired. Mixtures of glass from various sources can also be used. One important difficulty with current concrete products is their instability under alkaline conditions. Diffusion of water into the concrete causes the alkaline cement to react with the silica in the aggregate resulting in expansion and hence a weakening of the concrete. This effect takes place slowly over a number of years but can lead to weakening and eventually failure of the concrete under stress. To overcome this difficulty a low alkaline cement can be used but this increases the cost. Some of the compositions of the invention are susceptible to the alkali/silica reaction and hence will need to be used in conditions where that reaction does not cause a problem or else can be used with a low alkaline cement. Alternatively, it has been found on tests conducted to date that compositions of the invention can be made using normal cement where the alkali/silica reactivity is acceptable. The alkali/silica reactivity test is an accelerated test designed to model the long term effect of the alkaline reaction and generally an expansion under this accelerated test of less than 0.1 % change in length after 1 4 days is acceptable. A preferred composition having virtually no expansion under the alkali/silica reactivity test after 1 4 days was a composition consisting of cement and the glass composition of the invention in which the particles have substantially 1 00% less than 1 50 microns. The strength of concrete produced using this composition with Portland cement at a ratio 1 :3 in a water cement ratio 0.5 is not as great as that of other compositions of the invention Its 28 day strength was 1 5.5 MPa. This, however, is still acceptable for a number of commercial purposes. Increasing the strength of the glass composition itself can be achieved by adding other materials but, again, generally within a similar particle size range to that of the glass, i e. less than 5 mm. One suitable additive is slag produced as a by-product from steel making. The slag has given a major increase in strength to the glass of up to 51 MPa after 28 days. The product does have a higher than acceptable expansion under the alkali silica reactivity test but its abnormal strength, particularly, within one day after moulding makes it suitable for a number of building purposes where the alkali silica reactivity issue is not a problem. Also additives may be included to counter that effect in any concrete composition. The ratio of slag to glass can vary widely, from 1 0:90 (glass/slag) down to 90: 1 0 (glass/slag) . Preferably the glass will be the major component of the composition, more preferably slag will be present up to 40 percent. The glass/slag mixture can be formed by simply crushing the glass and the black slag separately to a particle size in the desired range and then intimately mixing the dry ingredients. Alternatively a mixture of large particles of glass and slag can be ground to the desired particle size range. In accordance with this aspect of theinvention there is provided an aggregate for mixing with cement comprising particulate glass and slag. A preferred process for creating an aggregate consisting of a glass/slag mixture is to mix crushed glass and crushed slag together fusing the mixture to intimately combine the glass and slag, allowing the mixture to set and then crushing into the desired particle size. By this aspect of the invention a product can be obtained which has both low alkali/silica reactivity and has high strength after a short period of time. The fusion of the two ingredients will take place at a temperature sufficient for that to occur. The finer the particle the more rapid fusion will occur at a given temperature. A more preferred process for creating this aggregate is to mix crushed glass particles of less than 600 microns, more preferably 1 50 microns with crushed slag particles of less than 600 microns, more preferably 1 50 microns, liquifying the mixture under heat, mixing the liquified mixture, allowing to cool and then crushing. Desirably the cooled mixture is crushed to where the particles are between 1 mm and 5mm with the remainder of the mix then comprising the powdered glass of the invention with particles ranging from less than 1 mm down to less than 75 microns. When a mixture of glass/slag is first formed by mixing the two ingredients with a particle size less than 1 50 microns, liquefied by heating, cooled and then again ground to a particle size of less than 1 50 microns, the concrete formed with cement is found to be not only of a high strength but also has an acceptable result in the alkali silica reactivity test. Liquefaction of the mixture will usually occur at about 1 1 00 ° C but higher temperatures can be employed if required. The slag for use in this invention can be obtained as a by-product from steel making, which reduces the cost of the composition of the invention. However, the slag can also be produced directly from slag producing materials, for example iron sand. Other materials can be added to the composition if desired. One favourable additive is limestone as such or in the form of chalk or other natural source eg seashells such as pipi shells, which also appears to assist in the liquefaction of the slag/glass mixture. When added, limestone is present in a small proportion, e.g. less than 1 0%, more preferably less than 5 % , such as about 1 % . Similar effects are achieved with dolomite or Zinc oxide. The slag powder of the invention is first desirably screened to remove magnetic materials. That is most conveniently done by crushing the slag and then passing the crushed powder over a magnet and collecting the nonmagnetic material. Other materials can be added as long as they do not detract from the properties of the concrete product The concrete products of the invention are formed by mixing the cementitious product with water The dry ingredients can be first mixed together and then mixed with water. The ratio of cement to glass in total will generally be that chosen in normal concrete manufacture. This can vary from 1 % to 99 % (cement) to 99 % to 1 % (glass) . Varying the ratio will provide articles of different strength for use for different purposes. A suitable concrete product is formed using cement to dry ingredients ratio of from 1 : 2 to 1 :3. A feature of the invention is that the amount of water needed to form the strong concrete is substantially less than that required in normal concrete using river sand and river rock aggregate. This is believed to be because the glass particles do not absorb water and hence sufficient water is needed solely to rehydrate the cement to form the concrete bond. The amount of water can be selected to achieve the result required. Typically it will be in the range 0.4 up to 1 .3, preferably from 0.45 to 0.66. In accordance with a further feature of the invention there is provided a moulded article in which cement mixed with glass particles having a substantial proportion of a fine particle size, optionally together with other aggregate particles, and water is allowed to set on a smooth surface, to form a concrete article with a consequential glossy surface. The provision of a glossy surface is believed to be unique in a cementitous product. This is believed to be achievable because the fine particles of glass bind together at the surface to form a substantially continuous film which when set imparts the gloss to it. The glossiness can be improved by setting the concrete under pressure optionally with a system for removing air. The cementitious mixture together with the appropriate amount of water is poured into a mould in which the bottom surface is a smooth surface of a material to which the concrete does not adhere, e.g. of a suitable plastic such as Perspex or Teflon. The base of the mould rests on a suitable supporting surface. The open mould will be filled with the mix to an extent to allow the open surface to be subject to pressure. A number of methods are envisaged to put the mixture under pressure while it is setting. One method currently envisaged is to have a slab which fits neatly within the mould contours to rest on the open surface of the cement mixture which slab can transmit a force uniformly to that cement mixture. For example a suitable weight can be put on the slab. That slab for example could be of steel or other strong metal able to resist distortion forces. More economically, that slab can be of thick timber construction, e.g. a thick particle board, suitably strengthened on its upper face to avoid distortions and to allow a force to be transmitted evenly to the upper surface of the cementitious material. For example, a cradle can be formed, with a thick particle board as the base, of a size adapted to fit neatly within the mould, and having compartments constructed above its upper surface in a way to strengthen the particle board against distortion. These compartments are designed to carry heavy material. One of the most convenient heavy materials is iron sand because of its high weight to volume ratio. Moulded articles of the compositions of invention can be used to make building panels, e.g. for use in exterior surfaces of buildings. One advantage of the compositions of this invention for cladding panels is the low thermal conductivity leading to good insulation properties. The surface of the panel will generally be impervious to water and to acid conditions. The surface can be made glossy in the manner described above or have a matt finish if so desired. Pressure moulding can be also used to make decorative surfaced panels, e.g. for use in table tops such as coffee tables and such like. Many uses can be envisaged for such decorative surfaces. The degree of reflectiveness in the panels can be varied by varying the pressure applied during the settling procedure. The products of the invention can be coloured. Different colours can be achieved by adding a pigment to the cementitious mixture. The glass particles themselves are impervious to water and hence the water soluble pigment will be taken up solely in the cement, interstitial water or other aggregate when added. It is a further feature of the invention to be able to create multicoloured layers. When the cementitious composition of the invention is poured into a mould, the free surface is found to be significantly resistant to transfer of liquid. A "skin" appears to form on the surface. If another layer of cementitious product of a different colour is poured over a first layer while it is still wet, it is found that the migration of one colour into the other is not substantial. This is surprising since if a mixture of normal cement, river sand and aggregate is first poured into a mould and while still wet, a second layer of a different coloured cement/sand/aggregate is poured over the first, the ultimate intermingling of the two colours is haphazard with limited discernabi ty of individual layers. The invention therefore provides a multi-layered concrete product formed by pouring a first layer of a cementitious product containing glass particles a substantial proportion of which are of a fine particle size and a first colour into a mould, and then pouring over the first layer, before the first layer has substantially set, a second layer of a cementitious product containing cement and glass particles, a substantial proportion of which are of a fine particle size, and a second colour, and if desired pouring a third or more layers of a different colour. Another feature of the formed concrete product of the invention is in general the ease with which it can be cut Cutting with a normal concrete saw involves so much less effort than cutting a normal concrete panel This is despite the significant strength which the concrete products of the invention have. Exactly why the panels can be cut so much more easily is not known A further feature of the invention is that the surface along the cut will itself be smooth and even glossy depending upon the fineness of the saw blade used in the cutting process. The concrete also has low thermal conductivity. A sample of concrete subjected to accelerated drying of a week at 1 00° C with a density of 1 970 kg/rrι had a thermal conductivity as 0.75 W/m/°C. This is about 30% less than normal concrete ( 1 1 W/m/°C) . Even in a partially dried state (8 % moisture) the conductivity is 30% less than that of normal concrete. Products in accordance with the invention can be used for many purposes. For example, gravestones, insulators, roof tiles, floor tiles, external cladding, slate, concrete decking, e.g. swimming pools, surfaces and surrounds, ceramic style products, marble like products, pipes, precast panels, sink tops, bar tops, bathroom tops, table tops, file cabinets, fireplace tiles, fire proof walls, building blocks etc. The following examples illustrate the invention. The expansion test is ASTMC 1 260. This requires less than 0. 1 % expansion after 1 4 days. Example 1 Crushed glass having a maximum particle size of 1 50 microns was mixed with Portland cement and water at a glass:cement ratio of 3: 1 and a wateπcement ratio of 1 .25 and allowed to set. The 28 day strength was 1 5.5 MPa. The expansion after 1 4 days was 0.001 % . Example 2 85 parts glass particles less than 1 50 microns is first mixed with 1 5 parts of black slag particles (obtained from an induction furnace) of less than 1 50 microns, and then with Portland cement in a ratio glass/slag:cement of 2.25: 1 and a wateπcement ratio of 0.66 to produce a concrete. The 7 day strength was 27.0 MPa and the expansion after 1 4 days was - 0.009 % . Example 3 A mixture of 60 parts glass particles and 40 parts black slag particles (obtained from an induction furnace) both of less than 1 50 microns together with 1 % of limestone powder were heated in a furnace to about 1 1 00 ° C to melt the powders. The melt was stirred to intimately mix the components together and the whole mass was allowed to cool to room temperature. The solid rock like material can then be crushed to the desired particle size. Example 4 Particles of the glass/slag mix of Example 3 were mixed with cement and water in a ratio glass/slag:cement of 2.25: 1 and a wateπcement ratio of 0.66 and allowed to set. The strength after 7 days was 26.5 MPa and the expansion after 1 4 days was 0.002 % . Example 5 A glass/slag mix is prepared as in Example 3. The solid rock like product is crushed to the following particle size range. Sieve Size Cumulative Sieve Size Cumulative Percentage Percentage Passing Passing % % 4.75mm 1 00 600 microns 43 2.36mm 85 300 microns 26 1 .1 8mm 63 1 50 microns 1 9 - - 75 microns 1 6 This is then mixed with cement and water in a glass/slag:cement ratio of 2.25: 1 and a wateπcement ratio of 0.60, and then allowed to set. The strength after 1 day was 1 1 .0 MPa, after 2 days, 21 .0 MPa, and after 3 days was 25.5. MPa. Example 6 A glass/slag mix was prepared as in Example 3 except using 85 parts glass and 1 5 parts of black slag. The solid rock like product was then crushed to a particle size less than 4.75mm. This was then mixed with crushed glass of less than 1 .1 8mm size. The particle size distribution was as follows: glass/slag between 4.25mm and 2.36mm 1 5 % glass/slag between 2.36mm and 1 . 1 8mm 30% glass/slag between 1 .1 8mm and 600 microns 1 8 % glass/slag between 600 microns and 300 microns 1 2 % glass/slag between 300 microns and 1 50 microns 7% glass/slag between 1 50 microns and 75 microns 3 % glass/slag passing 75 microns 1 5 % This was then mixed with cement and water in a ratio glass/slag:cement of 2.25: 1 and a wateπcement ratio of 0.45. The compressive strength was as follows: Days since moulding Strength (MPa) 1 20.5 2 33.5 3 38.0 7 44 28 51 .5 The expansion test was 0.6% change after 1 4 days. While the expansion was too high for an acceptable product insofar as the alkaline/silica reactivity is concerned, the high strength makes it very suitable for concrete products that need to be shifted as soon as possible after forming or for building construction where time to reach suitable strength prior to continuing construction is important. Example 7 A mixture of 60 parts glass particles and 40 parts black slag particles obtained from Slag Reduction Company Waiuku New Zealand (code OBM GAP3) were mixed and fused together at 1 1 00 ° C together with 1 % of crushed pipi shells. The solid mixture obtained on cooling was then crushed to a particle size distribution of the following: Sieve Size Cumulative % MM Passing 6.70 1 00 4.75 81 2.36 48 1 .1 8 31 0.6 21 0.3 1 5 0.1 5 1 0 0.075 6 The concrete was formed with Portland cement in a ratio glass/slag: cement of 2.25 : 1 and wateπcement ratio of 0.66. The strength after 1 day was 30 MPa, after 2 days 50 MPa and after 3 days 55MPa. The expansion was - 0.002 after 1 4 days (i.e. a slight shrinkage) . While this invention has been described with reference to preferred embodiments it is not to be construed as being limited thereto. Furthermore, where specific features have been referred to and known equivalents exists therefor, such equivalents are incorporated herein as if specifically set forth. INDUSTRIAL APPLICABILITY The invention can be industrially applied in a number of ways. The aggregate consisting of the glass particles, glass/slag particles prior to or after fusion are potential commercial products as are the concrete products formed from the use of the aggregate together with cement for many purposes as setforth herein.

Claims: CLAIMS: 1 . A cementitious mixture suitable for mixing with water to form a cast or moulded article, comprising cement and glass particles such that a substantial part thereof are of a fine particle size. 2. A mixture as claimed in claim 1 wherein the fine particle size is 1 50 microns. 3. A mixture as claimed in claim 1 wherein all the particles are less than 1 50 microns. 4. A mixture as claimed in any one of claims 1 to 3 together with particulate slag. 5. A mixture as claimed in claim 2 wherein the slag particles are of substantially the same size and distribution as the glass. 6. A mixture as claimed in claim 4 or 5 wherein the slag and glass are first fused together and are then ground to the desired particle size range. 7. A mixture as claimed in claim 6 wherein limestone is added to the slag and glass before fusing. 8. A mixture as claimed in claim 7 when the limestone is obtained from crushed seashells. 9. An aggregate for mixing with cement comprising particulate glass and slag. 1 0. An aggregate as claimed in claim 9 wherein the glass and slag are first fused together before being ground to the desired particle size range. 1 1 . An aggregate as claimed in claim 1 0 wherein limestone is added to the slag and glass before fusing. 1 2. An aggregate as claimed in claim 1 1 wherein the limestone is obtained from crushed seashells. 1 3. A concrete product formed using the cementitious mixture of any one of claims 1 to 8 or using the aggregate of any one of claims 9 to 1 2. 1 4. A concrete product of claim 1 3 including a pigment to give a desired colour to the product. 1 5. A concrete product of claim 1 3 or 1 4 having a glossy surface. 1 6. A concrete product as claimed in claim 1 5 obtained by setting the concrete on a smooth surface. 7. A concrete product as claimed in claim 1 3 for use as a gravestone, insulator, roof tile, floor tile, external cladding, slate, concrete decking, ceramic style product, marble like product, pipe, precast panel, sink top, bar top, bathroom top, table top, file cabinet, fireplace tile, fire proof wall or building block. 8. A multilayer concrete product having different colours in each layer in which each layer is formed using the cementitious mixture of any one of claims 1 to 8 or the aggregate of any one of claims 9 to 1 2 in which a different coloured pigment is added to each layer.

Inventors: LEED CLIFF JAMES, LEED, CLIFF, JAMES
Applicants: LEED CLIFF JAMES, LEED NATALIE LYNETTE TIRA, LEED, CLIFF, JAMES, LEED, NATALIE, LYNETTE, TIRA
Application year: 1997
Main classification: C04B14
IPC codes: B28B1, B32B13, C04B5, C04B14, C04B18, C04B28