WO2015051210A1

WO2015051210A1 - Cementitious product

Info

Publication number: WO2015051210A1
Application number: PCT/US2014/058960
Authority: WO
Inventors: John Alfred Fifield; Leonard Browning
Original assignee: Oldcastle Architectural, Inc.
Priority date: 2013-10-03
Filing date: 2014-10-03
Publication date: 2015-04-09
Also published as: EP3052712A1; EP3052712A4

Abstract

A building product is described which is molded from a cementitious material mix, the building product including a bulk portion of cementitious material mix and a top stratum that includes a surface of the building product, the top stratum including cementitious material mix into which a cementitious material enhancing agent has been migrated. Also described are methods and apparatus for making such a building product.

Description

CEMENTITIOUS PRODUCT

Cross reference to related applications

The present application claims priority to and the benefit of US Provisional Patent

Application No. 61/ 886,323, filed October 3, 2013, the disclosure of which is incorporated herein by this reference.

Field of the invention

The invention relates to building products made from a cementitious material. More specifically, the invention relates to the manufacture of a cementitious product incorporating an enhancing agent such as a pigment. Background to the invention

Cementitious products, such as paving, blocks, bricks and tiles, sills and floors have been made for many years by pressing or molding processes. Cementitious products are typically made of a mixture including water, sand and cement (known as 'fines'), aggregates (such as gravel or stone chippings), filler, and other components. The cementitious product may be coloured by the aggregate it contains, or alternatively the cementitious product may contain a pigment, to provide colour.

A typical pressing process for making a cementitious block involves charging a cementitious mix such as concrete is into a mold cavity, and then pressing the cementitious mix for compaction. Typically, a static block making machine is used. A pallet is fed into the block-making machine by a conveying means and is located in position under a mold. The mold is lowered onto the pallet and held in frictional contact with the pallet. Once lowered into position, the mold defines the side walls of the block to be produced, while the pallet defines the base wall (i.e. the underside) underside of the block, such that together the mold and pallet define the mold cavity.

The mold cavity is then filled with a cementitious mix using a feeder tray for loose filling. The mix may be levelled, for example, by vibration, to achieve a desired profile of concrete, before a compacting head is lowered and pressed on the cementitious mix to exert a compacting force either as direct pressure, vibration or both.

During the compaction process the different components of the cementitious mix move in a different manner: in particular, the large aggregate particles move differently to the finer particles of sand and cement (known as "fines"). At the top surface of the mixture, nearest the compacting head, aggregate protrude beyond the fines, such that the aggregate particles are partially exposed. As the compacting head presses on the cementitious mix, and gradually moves downwards to compact the mix, the head first comes into contact with these exposed aggregate particles. Consequently, the aggregate becomes positioned up against the compacting head as it advances. In response, the fines move around the aggregate particles to accommodate the new position of the aggregates.

In this way, the fines that initially covered the larger aggregate particles are forced

downwards relative to the aggregates during the compaction process to occupy spaces between the aggregate particles below the level of the compacting head. Meanwhile, the aggregate particles near the top surface that were initially partially exposed are pushed downwards into the fines by the compacting head. This downward motion of the aggregate particles into the fines creates a relative upward and sideways motion of the nearby fines with respect to the aggregate particles, such that the fines move to fill the gaps around the aggregate particle under the level of compacting head. The end result is a compacted cementitious mix in which aggregates are densely distributed, including a top layer that is positioned up against the compacting head, with fines between the aggregates to fill the gaps.

Once the cementitious mix has been sufficiently compacted, the compacting forces are stopped. The pallet and the compacting head are held in stationary alignment while the mold is raised from the pallet to raise the mold clear of the block. Next, the compacting head is also raised, and the pallet and block are conveyed together out of the block making machine.

The block on the pallet may then be conveyed to a secondary processing area, such as a washing station, and then on to a curing area where it is allowed to cure to a hardened state. Having been cured to a sufficiently hardened strength the block is then conveyed on the pallet to a depalleting station where the pallet is removed. The cured block may then be conveyed to a further processing area where it may be subjected to the action of secondary processing apparatus such as a shot blasting machine, a bush hammer, a chain flailer or the like. Once the secondary processing is complete after it is taken for packaging and delivery.

It is often necessary to include an enhancing agent in the block, such as a pigment or an active ingredient for enhancing the natural properties of the cementitious material itself. Such active ingredients include admixtures, agents for case hardening the concrete, a

waterproofing agent, and a biologically active material such as titanium dioxide (Ti0₂).

The enhancing agent may be incorporated by various techniques and at various stages of the block manufacturing process. One traditional way of incorporating a cementitious material enhancing agent is simply to mix the enhancing agent into the cementitious mix at the start of the block manufacturing process before the cementitious mix is poured from the feeder tray and charged into the mold cavity. This approach works well for example for incorporating pigment into a cementitious product such as a paver, and results in a product having the pigment mixed evenly throughout. However, a disadvantage of this approach is that the inside of the product is pigmented but never seen, so the approach is unduly wasteful of the pigment which may be expensive.

If the enhancing agent is required only at the surface of the product, the quantity of enhancing agent needed for a particular mass or volume of cementitious product, can be reduced by preparing a separate batch of cementitious mix which is used to provide a top stratum of enhanced cementitious material at the top of the block. The majority of the block is made using standard, unenhanced cementitious mix, which is compacted in a mold cavity as described above. However, in this case, after partial compaction of the unenhanced cementitious mix, a layer of enhanced cementitious mix is poured on top of the partially- compacted cement and this additional, enhanced layer is then compacted down to form a top layer of the cementitious product that displays the enhanced properties.

This is an effective means of reducing the amount of unnecessary pigment; however, the extent to which the amount of enhancing agent can be reduced depends on the depth of the enhanced top stratum compared to the unenhanced main section of the block, and in practice the top stratum in such blocks is still substantial. Furthermore, the method necessarily requires the additional manufacturing steps associated with preparing separate batches of unenhanced and enhanced cementitious material and the two-stage mold-filling and compacting process, which can lead to increased manufacturing costs.

To reduce the amount of enhancing material still further, a layer of enhancing agent such as pigment can be coated onto to the cementitious block after it has been cured. This approach is commonly adopted for applying a layer of titanium oxide to a surface of a block. A titanium oxide suspension is sprayed onto the block and dried, to form a thin layer, typically a few microns in depth. Applying a thin layer towards the end of the cementitious block

manufacturing process in this way avoids undue wastage of expensive enhancing agents However, the thin layer is vulnerable to wear and chipping, and typically such layers of enhancing agent have a short lifespan before they become worn, unsightly and ineffective in serving their proper function.

Accordingly, it is an object of the invention to address one or more of the disadvantages associated with the prior art. In particular, the invention aims to provide a cementitious product which, in use, has at least one exposed surface in a way that makes economical use of a cementitious material enhancing agent, whilst also ensuring that the enhancement of the exposed surface is more resistant to wear.

Summary of the invention

Against this background, the invention resides in a building product molded from a cementitious material mix, the building product including a bulk portion of cementitious material mix and a top stratum that includes a surface of the building product, the top stratum including cementitious material mix into which a cementitious material enhancing agent has been migrated.

The cementitious material enhancing agent may be of decreasing concentration moving from the surface of the building product towards the bulk portion.

The top stratum may have a top surface portion that is predominantly of unmigrated cementitious material enhancing agent. For example, the top surface portion of the top stratum may be substantially free of cementitious material mix.

The cementitious material mix may include agglomerates, and within the top stratum the material enhancing agent may be distributed both between and within the agglomerates.

The agglomerates may have an average diameter, and the top stratum has a depth less than or equal to half the average diameter of the agglomerates. For example, the top stratum may have a depth of approximately 3 mm.

The cementitious material enhancing agent may include a pigment or a photo-catalytically active material such as titanium dioxide.

The invention also extends to a method of making a building product from a cementitious material mix, the method including: delivering a cementitious material mix into a mold; applying a layer of cementitious material enhancing agent onto a top surface of the cementitious material mix; and allowing the cementitious material enhancing agent to migrate into the top stratum of the cementitious material mix. The method may include compacting the cementitious material mix and the cementitious material enhancing agent to migrate the cementitious material enhancing agent into the top stratum of the cementitious material mix. The cementitious material enhancing agent may be applied by spraying.

The cementitious material mix may be delivered into the mold and the layer of cementitious material enhancing agent may be applied to the top layer of the cementitious material mix by passing a combined deliverer and applicator over the mold.

The cementitious material mix may be delivered to the mold on a first pass of the combined deliverer and applicator, and the layer of cementitious material enhancing agent may be applied on a second pass of the combined deliverer and applicator. The combined deliverer and applicator may be moved in a first direction during the first pass and a second direction opposite to the first direction during the second pass.

The invention extends further to apparatus for making a building product, the apparatus including: a mold for receiving a cementitious material mix; a deliverer for delivering cementitious material mix to the mold; an applicator for applying a layer of cementitious material enhancing agent to a top surface of the cementitious material mix; and a compacting head for compacting the cementitious material mix and the layer of cementitious material enhancing agent to migrate the cementitious material enhancing agent into the cementitious material mix.

The applicator may be attached to and movable with the deliverer. The applicator and deliverer may be movable back and forth across the mold. The deliverer may be configured to deliver cementitious material mix to the mold on a first pass across the mold, and the applicator may be configured to apply a layer of cementitious material enhancing agent to the top surface of the cementitious material mix on a second pass across the mold. The first pass may be in an opposite direction to the second pass.

The invention may also be expressed as a method of manufacturing a block or other article made from a cementitious material mix and having a top stratum, the method including selectively migrating a cementitious material enhancing agent into a top stratum of the cementitious material of the mix. By selectively migrating the cementitious material enhancing agent into the cementitious material of the mix, the cementitious material enhancing agent migrates into the cementitious material to a sufficient depth to provide increased resistance to wear. By means of this aspect of the invention the sufficient depth is achieved whilst using an economical quantity of the cementitious material enhancing agent. Conveniently, the cementitious material enhancing agent may be provided as or within a flowable material. In that case, the method may suitably comprise spraying the flowable material onto the cementitious material before pressing.

Expressed in another way, the invention resides in a cementitious product molded from a cementitious material mix. The cementitious material mix has a top stratum into which a cementitious material enhancing agent has been migrated during molding. The cementitious product may also include a top layer that consists substantially of a cementitious product enhancing agent. An interface between the cementitious material and the cementitious material enhancing agent may be in the form of an undulating boundary. The undulating boundary may be suitably formed by the cementitious material enhancing agent having been migrated into the cementitious material mix.

Preferably, the cementitious material enhancing agent extends into the compacted cementitious material of the final product from a surface of the product by a maximum of 3 mm. Put another way, the top stratum has a depth of about 3mm. This provides a particularly suitable depth of cementitious product enhancing agent to provide increased resistance to wear whilst minimising the amount of cementitious product enhancing agent in the final product.

The invention also extends to a pressing apparatus for manufacturing a block or other article made from a cementitious material. From a further aspect, therefore, the invention resides in an applicator for applying a cementitious material enhancing agent to non-compacted cementitious material, and a pressing means for migrating the cementitious material enhancing agent into the non-compacted cementitious material.

Suitably, the applicator may be arranged for applying the cementitious material enhancing agent to the cementitious material by spraying.

In any aspect of the invention, the building product may be a paver, a block, a brick or a tile. The cementitious material mix may include sand, and/or cement and/or aggregates.

It will be appreciated that preferred and/or optional features of each aspect of the invention may be incorporated alone, or in appropriate combination, within the other aspects of the invention also.

Brief description of the drawings

In order that the invention may be more readily understood, specific embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, of which:

Fig. 1 is a schematic view of a pressing apparatus for making a block of a

cementitious material in accordance with an embodiment of the invention;

Fig. 2 is a sectional schematic view of part of the pressing apparatus of Figure 1 holding a charge of a mix of a cementitious material including sand, cement and aggregate particles in a mold cavity of the pressing apparatus, with the compacting head of the pressing apparatus brought into proximity with the charge of the cementitious mix;

Fig. 3 is a sectional view of an agglomeration of cementitious material showing that the agglomeration comprises coarse aggregates, sand and fines;

Fig. 4 is a sectional view showing detail of the charge of cementitious mix of Figure 2 before compaction;

Fig. 5 is a sectional view showing the effects of a pressing action of the pressing apparatus on the charge of cementitious mix of Figure 2, including arrows representing migration of a layer of enhancing agent into the cementitious mix;

Fig. 6A is a sectional view of a layer of enhancing agent covering part of an agglomeration, the agglomeration including a coarse aggregate particle that stands partially proud of the fines;

Fig. 6B is a sectional view of the part of the agglomeration of Figure 6 A showing some of the enhancing agent having been migrated into the agglomeration along with the coarse aggregate particle;

Fig. 7 is a sectional view showing the effects of a pressing action of the pressing apparatus on the charge of cementitious mix of Figure 2, including arrows representing the folding of an overhang of cementitious mix and the subsequent migration into the cementitous mix of a resulting double layer of enhancing agent; and

Fig. 8 is a schematic view of a block of cementitious material molded in accordance with an embodiment of the invention that has been cut to reveal cross-sections of the block.

Throughout the figures, like reference numerals are used to denote like features. Detailed description of preferred embodiments

A pressing apparatus 10 for making blocks of a cementitious material in accordance with the invention is shown in Fig. 1. The pressing apparatus 10 includes a pallet 12 on which the cementitious blocks are made and a mold 14 that can be held in frictional contact with the pallet 12 to form four mold cavities 15. A deliverer in the form of a feeder tray 16 is also included for feeding a cementitious material mix 22 (hereinafter 'cementitious mix') into the mold cavities 15. The feeder tray 16 is located above the level of the mold cavities, and is reciprocable horizontally over the mold cavities 15 as shown by the arrows 20 and 24. The pressing apparatus also includes an applicator 18 that is coupled to the feeder tray 16 to form a combined deliverer and applicator. The applicator 18 is capable of spraying a cementitious material enhancing agent 26 such as a pigment (hereinafter 'enhancing agent') downwards towards and into the mold cavities 15 so as to applying the enhancing agent 26 to the upper surfaces of the cementitious mix 22. Four compacting heads 28 which are of piston-like construction are located in vertical alignment with each of the respective mold cavities 15. The compacting heads 28 are moveable in a substantially vertical direction towards and away from the mold cavities 15, so as to exert a pressing action on the charges of cementitious mix 22 in the mold cavities 15, as will be appreciated more fully from Figs. 2 to 5. To make a cementitious block in accordance with the invention, the pressing apparatus 10 is initially configured with the mold 14 arranged on the pallet 12 such that the mold 14 and pallet 12 define the mold cavities 15. Next, loosely-bound cementitious mix 22 is supplied to the feeder tray 16 to prepare for loose filling of the mold cavities 15. The feeder tray 16 and applicator 18 are then caused to move generally horizontally across the mold cavities. Referring to Figure 1, in this example, the feeder tray 16 and applicator 18 initially move in a generally rightwards direction over the mold cavities 15 as indicated by arrow 20. As the feeder tray 16 is moved, it feeds the loosely-bound cementitious mix 22 into each of the mold cavities 15 as it passes above the mold 14, such that a resulting charge of loosely bound cementitious mix 22 is delivered into each of the mold cavities 15. Each charge will later form a cementitious product. Once this stage is complete, the feeder 16 and applicator 18 finish at the right hand side of the pressing apparatus 10.

With the charges of loosely bound cementitious mix 22 in the respective mold cavities 15, the coupled feeder tray 16 and applicator 18 are then caused to move steadily back to their original position passing over the mold cavities 15 in a leftwards direction as indicated by the arrow 24. As the feeder tray 16 and applicator 18 pass leftwards, the applicator 18 sprays a flowable material incorporating the enhancing agent 26 over each of the charges of cementitious mix 22 to form a covering of enhancing agent 26 over the tops of the loosely bound cementitious mix 22 in the mold cavities 15. At the end of this second pass over the mold 14, the feeder tray 16 and applicator 18 are returned to their original location on the left side of the pressing apparatus 10, as shown in Figure 1.

Next, the loosely bound cementitious mix 22 and layer of enhancing agent 26 are compacted. To this end, each of the compacting heads 28 is caused to move downwardly towards its respective mold cavity 15 until it contacts the enhancing agent 26 and cementitious mix 22. The compacting head 28 exerts a compacting force on the layer of enhancing agent 26. This compacting force firstly causes the enhancing agent 26 to migrate into the cementitious mix 22 and secondly compacts and densifies the loosely bound cementitious mix 22 to form a compacted block. The densification and migration processes will now be described in further detail with reference to Figs 2 to 8.

A more detailed view of a mold cavity 15 containing a charge of cementitious mix 22 with a sprayed-on layer of enhancing agent 26 is shown in Fig. 2. The compacting head 28 is shown in close proximity to the mold cavity 15, representing a moment shortly before the start of the compaction process. As shown in Fig. 2, the cementitious mix 22 is loosely-bound in the sense that it comprises discrete agglomerations 30 of material, in loosely-bound contact with its neighbours with spaces 32 between the agglomerations 30. These spaces 32 enable the cementitious mix 22 to be compacted: as the compacting head 28 is moved downwards towards the mold cavity 15, the cementitious mix 22 is compacted and the spaces 32 are substantially eliminated.

Referring to Fig. 3, an agglomeration 30 comprises coarse aggregate particles 34 such as gravel or stone chippings, grains of sand 36 in different, graded sizes, so-called fines 38, which comprise cement and water optionally mixed with fillers such as limestone powder and fly ash, and a proportion of entrapped air (not shown). The amount of water is moderate, being low enough that the agglomeration 30 is not wet, and consequently is not pourable and does not run, but high enough that the aggregate 30 is able to stay together and hold its shape. The natural formation of the cementitious mix 22 into discrete agglomerations 30 may also be expressed by describing the cementitious mix 22 as a granulate, or more specifically a loosely bound granulate.

As shown in Fig. 4, in the mold cavity 15, the tops of the uppermost agglomerations 30 present an undulating top surface 40 upon which the layer of enhancing agent 26 is distributed as it is sprayed by the applicator 18. As a result, the sprayed-on layer of enhancing agent 26 defines an undulating layer. It is this undulating layer of enhancing agent 26 and the undulating top surface 40 of the uppermost agglomerations 30 that are subsequently subjected to a downward pressing action of the compacting head 28.

The enhancing agent 26 is migrated into the top stratum of the cementitious mix 22 by at least three different mechanisms, as will now be described.

Firstly, the downward pressure of the compacting head causes the enhancing agent 26 to migrate between the agglomerates 30 in the top strata of the cementitious mix 22. A very early stage of the pressing process is shown in Fig. 5, in which the compacting head 28 has begun moving in a downward direction as indicated at arrow 42, and has just begun to exert a downward pressing action on the uppermost portions of the charge of cementitious mix 22 as shown at the middle and right of the mold cavity 15. As indicated by arrows 44, as the compacting head 28 moves downwards it forces the layer of enhancing agent 26 and the underlying agglomerations 30 downwards and sideways to reduce the volume of the spaces 32 between the agglomerations 30. In this way, the layer of enhancing agent 26 tends to migrate between the agglomerations 30. This downward migration between the

agglomerations 30 causes the enhancing agent 26 to penetrate into the top stratum of the cementitious mix 22.

Secondly, the downward pressure of the compacting head 28 also causes the enhancing agent 26 to migrate into the agglomerations 30, as will now be described with reference to Figs. 6A and 6B. Fig. 6A illustrates an agglomeration 30 having an uppermost portion that includes a coarse aggregate particle 34 standing proud of the surrounding grains of sand 36 and fines 38. A layer of enhancing agent 26 covers the top surface of the coarse aggregate particle 34, and this layer is consequently the first material to engage with the advancing compacting head 28.

As the compacting head 28 progresses downwards, it exerts a downward pressing action on the coarse aggregate particle 34 and on the uppermost portion of the layer of enhancing agent 26. As the aggregate 34 and the layer of enhancing agent 26 are pressed downwards by the compacting head, the enhancing agent 26 is adhered to the sides of the coarse aggregate particle 34 by the action of Van de Waals forces, indicated by arrows 46 in Fig. 6B. As a result, a proportion of the enhancing agent 26 migrates downwards into the agglomerate. Thirdly, the enhancing agent 26 is incorporated into the cementitious mix 22 by a folding motion that may take place as the cementitious mix 22 is pressed.

Referring Fig. 7, areas of higher relief in the undulating top surface 40 of the uppermost agglomerations 30 present the possibility of a folding motion during the compaction process. An overhanging portion 47 of an agglomeration 30, coated with a layer of enhancing agent 26, can be folded onto an adjacent agglomeration 30 so that the layers of enhancing agent 26 are dispersed deeper into the agglomerations 30. This folding mechanism serves to fold enhancing agent 26 into the cementitious mix 22, further effecting downward migration of the enhancing agent 26 into the top stratum of the cementitious mix as the block of cementitious material mix is being molded. As the pressing process progresses and the compacting head 28 moves further downwards, continuing to exert a downward pressing action on the cementitious mix 22, the layer of enhancing agent 26 is migrated further into the cementitious mix 22 by continuation of the three mechanisms described above and indicated by arrows 44, 46 and 48 in Figs. 5, 6B, and 7 respectively. As the compacting head 28 progresses downwardly in the mold cavity 15, the larger aggregate particles 34 become more closely compacted and move further down the mold cavity 15.

When the pressing process is complete, the compacting head 28 has pressed the cementitious mix 22 to an extent that the spaces 32 have been substantially eliminated and the aggregate particles 34 cannot be further compacted. At this point the block is in a compacted state.

In the final configuration, the compacting head 28 is fully engaged with the upper surface of the cementitious mix 22. In this state, the enhancing agent 26 is distributed into and around the coarse aggregate particles 34 and has migrated alongside and folded into the fines 38.

To complete the molding process, with the block in a compacted state, the mold 14 is raised from the pallet with both the pallet and the compacting head being held in stationary alignment. When the mold has been raised clear of the compacted block, the compacting heads 28 are also raised. The compacted block can be removed with the pallet 12 for various additional processes such as curing, depalleting and secondary processing.

The resulting block of cementitious material, is illustrated in cut-away in Fig. 8. The block 60 includes a top stratum 64 that is made up of two layers 62, 66.

The uppermost layer 62 of the top stratum 64 is a top surface portion 62 that is formed predominately of unmigrated enhancing agent in its sprayed-on state. This top surface portion 62 is a few microns thick.

Beneath the top surface portion 62 is a migrated layer 66. The migrated layer consists of a layer of cementitious mix 22 into which the enhancing agent 26 has been migrated. In this way, the migrated layer includes of cured agglomerate particles with regions of enhancing agent incorporated between and inside the agglomerate particles. Because the enhancing agent 26 is migrated into the cementitious mix 22 from its upper surface, the concentration of the enhancing agent 26 is greater towards the uppermost part of the migrated layer, and gradually tapers off moving towards the bulk part of the cementitious block.

In preferred embodiments, the top stratum 64 has a depth that is less than or equal to half the diameter of the largest aggregate in the cementitious mixture, and is preferably no more than 3 mm as this presents the lowest cost of adding the enhancing agent whilst preserving its efficacy following erosion due to natural weathering.

Applying a thin layer of enhancing agent 26 and migrating it into the cementitious material 22 in this way means that only a small amount of the enhancing agent 26 is required to form a layer over the top surface of the product 10. The migration of the enhancing agent 26 into the top stratum 64 means that the enhancing agent 26 is integrated with the cementitious material 22, such that it cannot be easily chipped or worn off. Thus, the migration of the enhancing agent 26 into the top stratum 64 increases the durability of the enhanced region of the block, whilst keeping the amount of enhancing agent required to a minimum, thereby reducing the cost of the final product. Furthermore, the enhancing agent 26 can be applied to the cementitious mix 22 using modified apparatus, requiring only a single additional pass of the feeder tray 16 over the mold 14. The enhancing agent 26 can be migrated into the cementitious mix 22 using the existing compacting process, such that no additional processing steps are required to integrate the enhancing agent 26 into the product 10. Thus, the enhancing agent 26 can be applied and migrated quickly and easily without increasing the manufacturing costs of the product.

Although the invention involves migrating an enhancing agent into the block of cementitious mix during the molding process, this does not exclude the possibility of further, secondary processing after the initial compacting stages, in which further enhancing agents may be added to the block. For example, the compacted block may be sprayed with further enhancing agents such as a waterproofing agent to obtain effects to those of the pressed-in enhancing agent.

It will be appreciated by a person skilled in the art that the invention could be modified to take various alternative forms to those described herein, without departing from the scope of the invention as defined in the appended claims. For example, the cementitious mix may be made of other materials such as fine particles of clay and coarse aggregate particles. As a further example the mix may comprise aggregates and a resin, or the binder may be a material other than cement such as gypsum. Accordingly, the use of the term 'cementitious mix' in this specification also covers such alternative mixes. Furthermore, the embodiment described herein involves a unitary cementitious mix, but a variation within the meaning of the invention could include producing a block as a composite of two or more cementitious mixes if desired or required, for example provided as horizontal layers within the mold cavities.

A further variation of the invention is envisaged in which the underside of the compacting head may be provided with any suitable kind of pattern to provide a decorative and/or skid resisting surface finish to the exposed surface of the formed cementitious block, or to incorporate features such as signage, lettering, logos and the like.

Finally, other cementitious articles and products and their manufacture according to the invention are envisaged, including paving, flagstones, bricks, posts, lintels, slabs and the like. Throughout this specification the term building product extends to the building, construction and civil and structural engineering industries.

A person skilled in the art will appreciate other variations not explicitly described but falling within the scope of the invention, as defined by the appended claims.

The invention may also be expressed as defined in the following numbered clauses: 1. A building product moulded from a cementitious material mix and having a top stratum into which a cementitious material enhancing agent has been migrated during moulding.

2. A building product according to clause 1, wherein the top stratum has a depth of 3 mm. 3. A building product according to clause 1, wherein the top stratum has a top surface portion which is predominantly of unmigrated cementitious material enhancing agent. 4. A building product according to clause 1, wherein the cementitious material enhancing agent is a pigment.

5. A building product according to clause 1 wherein the cementitious material enhancing agent is a photo catalytically active material such as titanium dioxide.

6. A method of moulding a building product from a cementitious material mix, in which a cementitious material enhancing agent is migrated into a top stratum of the cementitious material mix.

7. A method of moulding a building product from a cementitious material mix, in which a cementitious material enhancing agent is sprayed onto, and migrated into, a top stratum of the cementitious material mix.

Claims

1. A building product molded from a cementitious material mix, the building product including a bulk portion of cementitious material mix and a top stratum that includes a surface of the building product, the top stratum including cementitious material mix into which a cementitious material enhancing agent has been migrated.

2. A building product according to claim 1, wherein the cementitious material enhancing agent is of decreasing concentration moving from the surface of the building product towards the bulk portion.

3. A building product according to claim 2, wherein the top stratum has a top surface portion that is predominantly of unmigrated cementitious material enhancing agent.

4. A building product according to claim 3, wherein the top surface portion of the top stratum is substantially free of cementitious material mix.

5. A building product according to claim 1, wherein the cementitious material mix

includes agglomerates, and within the top stratum the material enhancing agent is distributed between and within the agglomerates.

6. A building product according to claim 1, wherein the cementitious material mix

includes agglomerates having an average diameter, and the top stratum has a depth less than or equal to half the average diameter of the agglomerates.

7. A building product according to claim 6, wherein the top stratum has a depth of

approximately 3 mm.

8. A building product according to claim 1, wherein the cementitious material enhancing agent includes a pigment.

9. A building product according to claim 1 wherein the cementitious material enhancing agent includes a photo-catalytically active material such as titanium dioxide.

10. The building product of claim 1, wherein the building product is a paver, a block, a brick or a tile.

11. The building product of claim 1 wherein the cementitious material mix includes sand, and/or cement and/or aggregates.

12. A method of making a building product from a cementitious material mix, the method including:

delivering a cementitious material mix into a mold;

applying a layer of cementitious material enhancing agent onto a top surface of the cementitious material mix; and

allowing the cementitious material enhancing agent to migrate into the top stratum of the cementitious material mix.

13. The method of claim 12, including compacting the cementitious material mix and the cementitious material enhancing agent to migrate the cementitious material enhancing agent into the top stratum of the cementitious material mix.

14. The method of claim 12, including applying the cementitious material enhancing agent by spraying.

15. The method of claim 12, including delivering the cementitious material mix into the mold and applying the layer of cementitious material enhancing agent by passing a combined deliverer and applicator over the mold.

16. The method of claim 15, wherein the cementitious material mix is delivered to the mold on a first pass of the combined deliverer and applicator, and the layer of cementitious material enhancing agent is applied on a second pass of the combined deliverer and applicator.

17. The method of claim 16 wherein the combined deliverer and applicator is moved in a first direction during the first pass and a second direction opposite to the first direction during the second pass.

18. Apparatus for making a building product, the apparatus including:

a mold for receiving a cementitious material mix;

a deliverer for delivering cementitious material mix to the mold;

an applicator for applying a layer of cementitious material enhancing agent to a top surface of the cementitious material mix; and

a compacting head for compacting the cementitious material mix and the layer of cementitious material enhancing agent to migrate the cementitious material enhancing agent into the cementitious material mix.

19. The apparatus of claim 18, wherein the applicator is attached to and movable with the deliverer.

20. The apparatus of claim 19, wherein the applicator and deliverer are movable back and forth across the mold.

21. The apparatus of claim 20, wherein the deliverer is configured to deliver cementitious material mix to the mold on a first pass across the mold, and the applicator is configured to apply a layer of cementitious material enhancing agent to the top surface of the cementitious material mix on a second pass across the mold.

22. The apparatus of claim 21, wherein the first pass is in an opposite direction to the second pass.