EP2574438A1

EP2574438A1 - Paving element and method for its manufacturing

Info

Publication number: EP2574438A1
Application number: EP12186278A
Authority: EP
Inventors: Robertus Petrus Maria Nijenhuis; Hendrik Van Steenbergen
Original assignee: Excluton BV
Current assignee: Excluton BV
Priority date: 2011-09-28
Filing date: 2012-09-27
Publication date: 2013-04-03
Also published as: NL2009483C2; NL2007489C2; NL2009483A

Abstract

The present invention relates to a paving element comprising an at least substantially block-shaped body of a composition comprising concrete and having a cover layer differing therefrom at least in respect of colour, structure and/or material. An additive applied in the cover layer is free of synthetic admixtures. The cover layer comprises one or more pigments and/or natural stone granulate of a wholly natural origin. The present invention also relates to a method for manufacturing a paving element, wherein concrete is composed of cement, water and at least one additive, a mould is partially filled with the concrete, a covering mortar is composed of cement, water and one or more additives, including at least one purely natural pigment and/or natural stone chippings, the mould is further filled with a cover layer of the covering mortar and the thus formed body is cured.

Description

The present invention relates to a paving element comprising an at least substantially block-shaped body of a composition comprising concrete and having a cover layer differing therefrom at least in respect of colour, structure and/or material. The present invention also relates to a method for manufacturing a paving element.
Paving elements are applied on a large scale as paving for roads, pavements, squares, patios and the like. The concrete paving stones or tiles applied here comprise a cement-bound body to which additives such as gravel and sand are added in order to impart strength and durability, as well as a pigment which serves as colouring agent in the stone to be finally formed. Within the context of the present invention the term block-shaped should otherwise be broadly interpreted such that it is understood to mean not only rectangular beam-shaped bodies, but also other geometric shapes and fantasy shapes.
A paving element of the type described in the preamble is for instance known from the American patent US 6,079,900 . The stone described herein comprises a basic body comprising concrete to which a synthetic cover layer of thermoset-bound granules of rubber and/or a plastic is adhered at a raised temperature and pressure.
Known in addition from German patent application DE 103 11124 is a paving element wherein a cover layer of thinly liquid fluid concrete, which can be made in a block pattern of differing colours, is cast in a mould before further filling the mould with a concrete mortar in order to form the basic body therefrom. The pattern of the cover layer is maintained here by means of narrow separating strips between successive block parts.
A drawback of these and other conventional concrete paving stones and tiles is that they are far from being CO₂-neutral. The production of the Portland cement often used here requires a large amount of heat which is generated by combustion of fossil fuels such as oil, gas, coal and brown coal. The synthetic pigments usually used in concrete stones are moreover of chemical nature and therefore have an environmental impact.
The present invention has for its object, among others, to provide a paving element which to at least considerably greater extent is environmentally-friendly.
In order to achieve the stated object a paving element of the type described in the preamble has the feature according to the invention that the cover layer is at least substantially free of artificial additives and that the cover layer comprises one or more pigments and/or natural stone granulate, which one or more pigments and/or natural stone granulate have been extracted from nature. By thus applying a pigment and/or natural stone granulate only in the cover layer, the use thereof can be limited to a minimum while, once applied in a paving, a desired aesthetic appearance is nevertheless wholly achieved. Furthermore, according to the invention use is made in the cover layer of at least substantially only a purely natural pigment, i.e. a pigment extracted directly from the natural environment and so having no (additional) impact at all on the environment when it is returned thereto.
A preferred embodiment of the paving element has the feature according to the invention that the cover layer comprises cement to which at least one natural pigment is added. The paving element thus comprises a cement-bound cover layer into which the pigment has been incorporated. Other additives, such as stone chippings and sand, can optionally also be added thereto. A further particular embodiment of the paving element according to the invention has in this respect the feature that the cover layer comprises cement-bound natural stone granulate. The natural stone material thus applied in the cover layer imparts a particularly attractive aesthetic quality thereto, while the use of at least mainly purely natural raw materials in this case also limits the environmental impact to a minimum.
Not only the origin but also the extraction of the pigment is advantageously as CO₂-neutral as possible. With a view thereto a further particular embodiment of the paving element according to the invention has the feature that the pigment comprises natural iron oxide, in particular iron oxide from Zaragoza extracted by opencast mining. Compared to mining, opencast mining requires considerably less effort, and so less use of fossil fuels.
In a further preferred embodiment the paving element according to the invention has the feature that the top layer comprises granular olivine. In the form of fine granules olivine has the capacity to convert carbon dioxide to magnesium(bi)carbonate in a humid atmosphere. Natural olivine also has the property that it binds with heavy metals without leaching. The cover layer applied in the paving element according to the invention thus even makes a positive contribution toward the environment. A considerable, active, environmentally-friendly surface can thus be created by covering entire road surfaces therewith.
Not only the origin but also the extraction of the olivine is advantageously as CO₂-neutral as possible. With a view thereto a further particular embodiment of the paving element according to the invention has the feature that the top layer is at least substantially wholly composed of bound granular olivine, in particular olivine from Norway extracted by opencast mining. Compared to mining, opencast mining requires considerably less effort, and so less use of fossil fuels.
Particularly advantageous results are achieved with a particular embodiment of the paving element according to the invention characterized in that the granular olivine mainly comprises granulate with a particle size greater than 0 millimetres and smaller than or equal to 3 millimetres. This particle size is on the one hand small enough to provide a relatively large reactive surface on which CO₂ can react, and is on the other large enough not to comminute completely, and so disappear, within a lifespan normally projected for the paving element.
Calculations show that a paving element according to the invention thus enriched with olivine is able, subject to the olivine content thereof, to convert a quantity of CO₂ per square metre. The top layer usually comprises between 11 and 14 kg of olivine and, based on a reactivity of about 1.25 kilogram of CO₂ per kilogram of olivine, can therefore convert 13.75 to 17.5 kg of CO₂. It is likewise possible to calculate that the production of a square metre of conventional paving elements of concrete requires a CO₂ impact in the order of 20 kg/m². This impact is thus compensated to a significant extent as a result of the invention.
The CO₂ impact of concrete is associated to a significant extent with the production of the Portland cement usually applied therein. For clinkering purposes this material has to be heated to a temperature in the order of 1500 degrees Celsius, this usually being achieved by the combustion of fossil fuels. A further preferred embodiment of the paving element according to the invention therefore has the feature that the composition comprising concrete comprises mainly blast furnace slag cement as binder. Blast furnace slag cement is produced from blast furnace slags, which are a by-product of the steel industry and as such do not have any additional environmental impact. The CO₂ impact therefore amounts to no more than about 10 kg/m² in respect of the concrete part in the paving elements (owing to the use of blast furnace slag cement, the use of concrete granulate and sand from a location within 10 kilometres of the production location, and the CO₂-reducing production process), which can be more than compensated by the CO₂ reduction with an olivine-enriched cover layer according to the invention.
In a further preferred embodiment the paving element according to the invention has the feature that the composition comprising concrete comprises granules of reused concrete. By thus making use of reused concrete as additive material for the production of new paving elements, the cement part can be reduced and a further CO₂ reduction thereby achieved.
The paving element according to the invention can be realized with diverse cover layers and various finishing treatments, in particular with a closed cover layer, a washed cover layer, a shot-blasted cover layer, a curled cover layer, a polished cover layer, a hammered cover layer or a combination thereof. Any appearance can thus be thereby realized.
The invention also relates to a method for manufacturing a paving element wherein concrete is composed of cement, water and at least one additive, a mould is partially filled with the concrete, a covering mortar is composed of cement, water and one or more additives, including at least one purely natural pigment and/or natural stone chippings, the mould is further filled with a cover layer of the covering mortar and the thus formed body is cured. Possible additives are for instance sand, gravel, concrete granulate and limestone meal. Blast furnace slag cement is preferably used here for the cement, concrete granules for reuse and locally extracted sand and recycled water are used as additive. The concrete is hereby largely made up of recycled substances or residual materials, and has a minimal environmental impact.
In a preferred embodiment the method according to the invention has the feature that the at least one additive for the concrete is preheated before it is mixed with the cement and the water, and a further embodiment of the method more particularly has the feature that the additive is preheated with steam. It has been found that with such a measure the method can be performed to relatively low ambient temperatures, while blast furnace slag cement is used as binder for the concrete instead of or in addition to the Portland cement which has considerably more of an environmental impact. The preheating of the additives, such as sand and gravel, in particular provides here for sufficient heat in the concrete mixture so that the temperature thereof lies above the activation temperature of blast furnace slag cement. It is therefore recommended that in a further preferred embodiment of the method blast furnace slag cement is at least mainly applied for the cement. Blast furnace slag cement is a by-product of the steel industry, so that a separate heating process is not required therefor, which would otherwise result in an additional CO₂ impact on the environment. Blast furnace slag cement with a high percentage of blast furnace slags (such as for instance CEM III A+B) is particularly suitable.
A further particular embodiment of the method has the feature according to the invention that olivine granulate is applied as additive for the cover layer and that the cover layer is subjected to a surface treatment, in particular a washing, before the body is wholly cured. Olivine has the useful property that it converts carbon dioxide into magnesium bicarbonate, which in turn serves as fertilizer and soil improvement. Owing to the surface washing, sufficient olivine is exposed to the air in the final end product to enable this property to be utilized to the full. The olivine does not however have to be washed, it can also be applied in a closed cover layer.
In a further preferred embodiment the method according to the invention has the feature that the body is air-cured in an atmosphere saturated with water vapour and at a raised temperature above 30 degrees Celsius, particularly at a temperature of around 40 degrees Celsius. It has been found in practice that such a drying of the stones results in a considerable reduction in the overall drying time and in a particularly durable stone quality.
The invention will now be further elucidated on the basis of several exemplary embodiments and an accompanying drawing. In the drawing:

figure 1: shows a first exemplary embodiment of a paving element according to the invention with a cement-bound cover layer into which a natural pigment has been incorporated;
figure 2: shows a second exemplary embodiment of a paving element according to the invention with cover layer which is composed substantially wholly of natural olivine grit; and
figure 3: shows a schematic view of a production environment for performing an embodiment of the method according to the invention.

The figures are otherwise purely schematic and not drawn to scale. Some dimensions in particular may be exaggerated to greater or lesser extent for the sake of clarity. Corresponding parts are designated as far as possible in the figures with the same reference numeral.
Figure 1 shows a first exemplary embodiment of a paving element according to the invention. In this embodiment paving element 1 has a block-shaped body 11 with a high percentage of recycled concrete. Situated on block-shaped body 11 is cover layer 12 which comprises cement-bound chippings, for instance a natural stone granulate or a mixture thereof, into which an purely natural pigment is incorporated. In this exemplary embodiment the pigment is natural iron oxide from Zaragoza extracted by opencast mining. This pigment is purely natural and free of chemicals. Because the pigment is incorporated in micronized form into cover layer 12, it has a consistent colour. The part of block-shaped body 11 located under cover layer 12 is substantially free of pigment. Paving element 1 has a light-fastness of 8 (on a scale of 1-8) and a weather-fastness of 5 (on a scale of 1-5).
Figure 2 shows a second exemplary embodiment of a paving element according to the invention. In this embodiment paving element 2 has an H-shaped block body 21 with a high percentage of recycled concrete. Situated on block-shaped body 21 is a cover layer 22 which in this case is composed at least substantially wholly of bound, granular, pure olivine from Norway extracted by opencast mining. In addition to cover layer 22 having a CO₂-reducing effect and binding heavy metals, cover layer 22 is moreover colour-fast, wear-resistant, durable and aesthetically particularly attractive.
The olivine is in cover layer 22 in the form of granulate with an average grain size of larger than 0 and smaller than or equal to 3 millimetres. 75-100% of the additive used for layer 22 consists of this material, which is able to break down up to 25% more than its own mass of carbon dioxide. A paving laid with the shown paving elements can thereby typically remove in the order of 13.75 to 17.5 kilograms of carbon dioxide per square metre during its projected lifespan. By making use in the production thereof of reused concrete, blast furnace slag cement with a high percentage of blast furnace slag and sand from a distance within 10 kilometres of the production location, the carbon dioxide impact associated with the production process can even be kept below these values, whereby the paving element according to the invention can make an active contribution toward a global CO₂ reduction. The main features of such a manufacturing process will be described below with reference to figure 3.
The installation shown in figure 3 comprises a number of storage silos having therein cement (11), sand (12), broken concrete (13) and gravel (14) as the most important components for concrete production. The cement comprises here a high content, up to 100%, of blast furnace slags, which are available on a large scale as a by-product of the heavy metal industry. More importantly, this material, in contrast to Portland cement, needs no so-called clinkering, so that the separate heating and combustion of fossil fuels otherwise necessary for this purpose are avoided. The use of broken concrete as additive material instead of pure gravel moreover allows a smaller cement portion here.
Situated at the bottom of the silos (12, 13, 14) for the additives for the purpose of enhancing the later concrete activation are steam lances (15), with which the material is heated to an increased temperature before it is removed from the silo. The production can hereby also take place at moderate ambient temperatures, such as outside in winter in northern regions.
A mixture of 60% sand, 20% broken concrete, 5% gravel, 13% blast furnace slag cement and 2% limestone meal is mixed with water in a first mixer (21). Used as water here is pumped-up groundwater, in addition to as much process water as possible recovered from previous production runs and filtered. The sand used is preferably extracted, if possible, in the immediate vicinity, for instance within 10 kilometres, of the installation so that transport costs and the associated CO₂ emission are limited to a minimum. Thus created is a concrete mixture with a minimal environmental impact which is pumped to a first dosing unit (31).
According to the invention paving elements are embodied with a top layer differing from the base. The installation comprises for this purpose a set of further storage silos (41, 42), respectively for natural olivine and natural pigment. The olivine comprises here pure olivine extracted in Norway in opencast mining and having a grain size greater than 0 millimetres and smaller than or equal to 3 millimetres. The pigment is likewise purely natural, and originates in Zaragoza. It comprises substantially iron oxide and is extracted in opencast mining. The pigment can be supplied in red or black. A number of pigment silos (42) can be applied if desired, each for a separate colour, from which it is possible to dose and mix in order to obtain different shades.
A mixture of pigment and/or olivine is fed together with a portion of cement to a second mixer (22) and bound therein to form a covering mortar with a set quantity of water. In this embodiment the covering mortar comprises pure cement-bound olivine without further addition of pigment. This mortar is pumped to a second dosing unit (32).
Plastic planks (50) are supplied on an endless conveyor belt (60) under the first and second dosing units (31, 32), usually referred to as filling carriages. In the first instance typically 90% of a mould is filled with concrete mortar from the first dosing unit (31) and then vibrated in order to compact the concrete therein. The vibrating device applied here is not further shown in the figure.
Not shown in this figure is that an up and downward moving upper mould (die) and a lower mould are present between the filling carriages (31, 32). This is placed on the plastic planks and repeatedly strikes a plastic plank with the stones thereon. The mould thus remains in the machine and only moves downward when it is about to be filled.
The mould is then carried under the second dosing device (32) or, conversely, the second dosing unit is carried above the mould in order to further fill the mould therefrom with a cover layer of cement-bound pure olivine granulate. The whole is then vibrated again in order to also compact the cover layer and impart a good adhesion to the concrete lying below.
The concrete body now has handling strength but is not yet cured. In this state the whole is carried under a spraying device (70) with which water is sprayed under increased pressure onto the cover layer in order to remove excess cement from the top layer. In the thus washed cover layer the olivine applied therein is thus exposed to air so as to enable optimal contact therewith. Furthermore, the attractive natural appearance of pure olivine is in this way shown to its best advantage.
Once the enclosing parts of the mould have been removed, the thus formed stones are dried in a drying chamber. The stones already have handling strength and retain their shape. The drying is performed in a conditioned environment at an increased temperature of 30-40 degrees Celsius. In this embodiment a temperature of about 40 degrees is maintained. After a curing time of no more than 8-10 hours the stones are ready. Drying in a normal drying chamber would require a considerably longer drying time of more than 24 hours, whereby the method also provides a significant improvement in this respect.
Although the invention has been further elucidated above with reference to only a single embodiment, it will be apparent that the invention is by no means limited thereto. On the contrary, many other variations and embodiments are possible within the scope of the invention for the person with ordinary skill in the art.
A skilled person will thus appreciate that the block-shaped body can be embodied in diverse dimensions and shapes, such as for instance small or large polygonal or round embodiments and numerous fantasy shapes. Other natural pigments can further be applied so that for instance red, black, yellow and other colours of cover layer can be obtained. Natural pigments or olivines extracted at other locations may also be particularly suitable and provide possible variations in appearance or properties. A skilled person will also appreciate that a non-sprayed closed top layer will also be very effective.

Claims

Paving element comprising an at least substantially block-shaped body of a composition comprising concrete and having a cover layer differing therefrom at least in respect of colour, structure and/or material, characterized in that the cover layer is at least substantially free of artificial additives and that the cover layer comprises one or more pigments and/or natural stone granulate, which one or more pigments and/or natural stone granulate have been extracted from nature.
Paving element as claimed in claim 1, characterized in that the cover layer comprises cement to which at least one natural pigment is added.
Paving element as claimed in claim 2, characterized in that the pigment comprises natural iron oxide, in particular iron oxide from Zaragoza extracted by opencast mining.
Paving element as claimed in one or more of the foregoing claims, characterized in that the cover layer comprises cement-bound natural stone granulate.
Paving element as claimed in claim 4, characterized in that the top layer comprises granular olivine.
Paving element as claimed in claim 5, characterized in that the top layer is at least substantially wholly composed of bound granular olivine, in particular olivine from Norway extracted by opencast mining.
Paving element as claimed in claim 5 or 6, characterized in that the granular olivine mainly comprises granulate with a particle size greater than 0 millimetres and smaller than or equal to 3 millimetres.
Paving element as claimed in one or more of the foregoing claims, characterized in that the composition comprising concrete mainly comprises blast furnace slag cement as binder.
Paving element as claimed in one or more of the foregoing claims, characterized in that the composition comprising concrete comprises granules of reused concrete.
Method for manufacturing a paving element, wherein concrete is composed of cement, water and at least one additive, a mould is partially filled with the concrete, a covering mortar is composed of cement, water and one or more additives, including at least one purely natural pigment and/or natural stone chippings, the mould is further filled with a cover layer of the covering mortar and the thus formed body is cured.
Method as claimed in claim 10, characterized in that the at least one additive for the concrete is preheated before it is mixed with the cement and the water.
Method as claimed in claim 11, characterized in that the additive is preheated with steam.
Method as claimed in claim 10 or 11, characterized in that blast furnace slag cement is at least mainly applied for the cement.
Method as claimed in claim 11, 12 or 13, characterized in that olivine granulate is applied as additive for the cover layer and that the cover layer is subjected to a surface treatment, in particular a washing, before the body is wholly cured.
Method as claimed in any of the claims 11 to 14, characterized in that the body is air-cured in an atmosphere saturated with water vapour and at a raised temperature above 30 degrees Celsius, particularly at a temperature of around 40 degrees Celsius.