IE84535B1 - Improvements in and relating to decorative load bearing blocks - Google Patents

Description

PATENTS ACT, 1992 IMPROVEMENTS IN AND RELATING TO DECORATIVE LOAD BEARING BLOCKS DORSET FLINT & STONE BLOCKS LIMITED HVIPROVEMENTS IN AND RELATING TO DECORATIVE LOAD BEARING BLOCKS This invention relates to facing blocks of the type used in the construction of buildings and structures to provide natural stone efiects generally on the external surfaces of the building or structure but which can also be used internally as decor finishes or feature claddings or coverings such as fireplace surrounds etc.

In older villages and towns it is not uncommon to find buildings and structures built with a decorative arrangement of natural stone, pebbles, flint and the like laid up with mortar. The random arrangement of differently shaped and/or coloured pieces results in an attractive ruralistic appearance and is often admired by onlookers.

Over the years, this natural stone and mortar method has been used less and less primarily because it is a labour intensive, time consuming building method, which is highly reliant on dry conditions for its successful completion. Consequently, it is an expensive building process.‘ In recent years, such methods have been replaced by cheaper, faster more versatile building methods and materials such as bricks, concrete building blocks and various prefabricated structures.

In recent years products have become available which combine the aesthetic properties of natural stone methods with the convenience of modern methods. An example of this type of product is the Dorset Flintblock, one of a range of products manufactured by Dorset Flint and Stone Blocks Limited. These products consist of moulded blocks of concrete into one surface of which a decorative arrangement of pieces of natural stone, pebbles, flint and the like are hand-set. The blocks can then be assembled into a building structure using methods similar to those conventionally used with plain concrete blocks, the decorative surface facing externally in the wall structure to provide an appearance of a natural stone built wall. Similar products incorporate pebble, cobble and sand stone facings. Blocks such as these can be used in load bearing applications thus minimising the need for internal structural support.

Conventionally, simple square or rectangular shaped metal moulds are used to shape the blocks, the moulds being disassembled from the set concrete to release the block. Different shapes or patterns of stone work can be achieved by inserting shaped polystyrene pieces in strategic places about the mould to define the desired shape of the end product or different mould shapes can be used if required.

The set pieces of stone may be treated to improve or change the natural appearance of the stone, for example by staining, polishing or varnishing or it can be worked with tools which is generally known as dressing the stone. Alternatively the stone may be presented as it appears naturally, or undressed. Alternatively other materials may be set as required.

The simple shape of these stone faced blocks render them far easier to assemble into building structures than randomly shaped stone pieces. The blocks can be assembled using all-weather techniques conventionally used for plain concrete block and brick building providing a simple and cost effective route to an attractive, traditional or modern decorative external wall surface.

One problem with these blocks arises in the additional weight added to a typical sized concrete block by the inclusion of stone pieces on the surface. Ofien the mo st commonly used sizes of blocks are too heavy for a single person to handle and position safely. Also, whilst the stone pieces on the surface of an individual block can be randomly spaced to provide a realistic stone built efiect, the rectangular outline of the individual blocks can sometimes be seen to disrupt the random appearance on a completed surface comprising a number of the blocks.

An object of the present invention is to improve upon the decorative building blocks described above.

In a first aspect the present invention is a decorative building block comprising; a supportive load bearing body having applied to at least one surface a decorative arrangement of mineral pieces wherein the load bearing body comprises a mixture of a cement and lightweight aggregates.

The block according to the invention is significantly lighter in weight than existing decorative blocks. By adding various proportions of lightweight aggregate to the mould mix for the load bearing body the resulting block can be reduced sufficiently in weight that it compensates for at least some of the excess weight due to the stone facing and becomes manageable by one person.

For the purposes of the invention a “lightweight aggregate” should be interpreted as meaning an aggregate having a density significantly lower than a standard build spec concrete. Any suitable lightweight aggregate may be used either alone or in combination with other known lightweight aggregates. Such aggregates are well known and in common use in other applications and include sintered PFA; pumice; expanded mica; recycled furnace materials, refractory materials, spent solid fuels and the like. Preferably the lightweight aggregate portionwill comprise a significant proportion of both coarse and fine aggregates, to provide maximum weight reduction.

In order to meet the requirements of British Standards and any other relevant regulations load-bearing blocks must be able to Withstand any specified loads. The term “load-bearing body” as used herein should be interpreted accordingly. Varying proportions of cement and aggregates (both fighter and normal Weight) may be used in the body, provided that set moulding meets the specified strength criteria. Typically, in order to be considered load bearing a block should be able to withstand a load of at least about 7N/mm’.

In preparing the backing concrete material for moulding, the cement and aggregate mix is mixed with water. The particles of lightweight aggregate are highly absorbent and take up much of the water in the mix. On curing, the excess absorbed water evaporates from the aggregate leaving air pockets and thus further reducing the overall density of the block.

Additives may optionally be added to the concrete backing mix to further reduce the weight. A preferred additive is an air entrainment agent. These agents create air bubbles in the moulded block and the density of the structure is further reduced. The concrete mix is designed to ensure that there is no detriment to the load bearing capability of the structure.

Water reducing agents can also be added to the concrete backing mix. Such an agent will reduce the water content for any workability and can facilitate mixing and pouring of the mix material into the mould and improve strengths.

‘ K‘ The decorative arrangement of mineral pieces may comprise pieces of flint, sandstone, limestone, pebbles, cobbles or any similar attractive naturally occurring or other artificial materials such as bottles etc, stone or mineral. The pieces may be whole, particularly in the case of cobbles and pebbles, or cut and may be dressed or undressed.

Preferably, the proportions by weight of cement to lightweight aggregate are between about 1:7 and about 1:2, most preferably about 1:3 to 1:4. However, these will vary dependent on the type/s of aggregate used.

In a second aspect, the invention is a decorative building block comprising; a supportive load bearing body having applied to at least one surface a decorative arrangement of mineral pieces wherein the block is providedwith a peripheral lip on the at least one surface providing a greater surface area in which to set the mineral pieces.

The lip on the mould allows a decorative surface which extends slightly beyond the perimeter of the load bearing body, this enables some of the set decorative mineral pieces to be positioned to overhang the edge of the load bearing block. When two or more blocks are adjoined, say in building a wall, the overhanging mineral pieces can be aligned to fit into gaps on adjacent blocks. This results in a less apparent demarcation between blocks and a more random overall pattern of pieces on the completed wall surface.

In order to achieve a block according to this second aspect, the mould for the load bearing body is provided with a peripheral lip sufiiciently deep to receive pieces of mineral to be used in the decorative facing. The lip will typically extend up to about 3mm beyond the edge of the load-bearing block but can extend up to 5mm. This has been found to be sufficiently large to provide the desired effect without interfering with the laying of the blocks.

A Whilst it is preferred that this aspect be used in conjunction with lightweight blocks according to the first aspect, it will occur to the skilled addressee that this aspect may be equally used in the improvement of prior art facing blocks.

A further improvement is provided in the form of a frog, which is incorporated around the periphery of the block between the outer facing decorative surface and the inner-facing surface of the block. The frog is provided in the form of a groove of any suitable cross section such as a V or rectangle or square, preferably the cross-section is arcuate, most preferable semi-circular. Whilst the frog may be incorporated at any position between the decorative surface and the inner surface, it is preferably positioned about midway between the two surfaces. The width and depth of the frog are not critical but they are preferably of the order of a few centimetres for the width and a few millimetres for the depth. The frog provides a keying surface for the mortar when the blocks are laid as the blocks have to be laid with reduced bed and perpendicularjoints of ideally Smm but between 2mm and 8mm (normally 10mm) to achieve the best results.

Again, whilst it is preferred that this aspect be used in conjunction with the novel blocks according to other aspects of the invention, it will occur to the skilled addressee that this feature may be equally used in the improvement of prior art facing blocks.

Conveniently, by using a suitably adapted mould, the lip and frog can be incorporated when the block is moulded. Most conveniently, the blocks can be moulded in a “rubber” or similar flexible mould, which can be peeled away from the set block without risk of damage.

For the purposes of clarification and exemplification, an embodiment of the invention will now be described with reference to the following Figures. Other embodiments will no doubt occur to the skilled addressee without departing from the true scope of the invention as defined by the appended claims.

Figure 1 shows a block according to the present invention.

Figure 2 shows pairs of blocks according the present invention before and after alignment to form a single wall surface.

As can be seen from Figure 1 a block according to the present invention comprises a load bearing concrete or mortar body 1 onto the surface of which is provided a decorative facing 2 comprising a number of flint or similar mineral pieces 3 set into concrete. The mould has a peripheral lip extending from the upper surface into which pieces of flint or similar mineral pieces 3 can extend. Around the periphery of the load- bearing block is a frog 5 of semi-circular or other cross—section.

Figure 2 shows the top face of two facing blocks according to the present invention. It can be seen that the hand set mineral pieces provide a slightly irregular shaped periphery to the top surface of the facing block. Blocks can be then matched such that protrusions from one block can be aligned with indentations on adjacent blocks. As can be seen from Figire 2b this results in a far more random surface pattern when the blocks are laid together.

An example will now be given of one suitable composition for the manufacture of a lightweight-facing block in accordance with the invention.

In one embodiment the composition used to mould the load—bearing body comprises :1 Rugby Class 42.5N Portland cement as sold by Rugby Cement. The aggregate used is an all-in block mix provided by Lytag, the mix has a high proportion of fine aggregate particles. A water-reducing admixture and an air entrainment agent are also added. The relative proportions in kg/m3 are illustrated in Table l. The composition is mixed and fed into a mould using conventional techniques.

Blocks made using the above-described composition were tested and the following results achieved.

The Composition.

Used a lightweight “block mix” with a high proportion of fines appropriate to the materials used and the backing concrete to be produced. The mix gave satisfactory fresh concrete properties.

The mix details (rounded to the nearest 5 kg/1113) are summarised below: - TABLE 1 Mix Constituents - 360 1 145 .6 0.36 TESTING Two 100mrn—cube specimens were produced from the mix to enable estimation of mix density; weight loss with time and compressive strength.

The balance of the mix was used to produce blocks for determination of weight and compressive strength. Some cobble-faced blocks were also produced as well as the flint faced blocks to provide information on the bond of the backing concretes to the smoother faced materials.

Concrete Density The density results and the density reductions for the mixes with age were as follows: - TABLE 2 Age Days Density/Reduction in Density with Age — kg/m’ -Asstripped 1710 /80 /145 The lightweight aggregate is absorbent and takes up a significant amount of the mix water.

As the concrete cures and then dries out, a significant reduction in density occurs, as this absorbed water evaporates. This process has the potential to provide some useful additional curing for these “dry cured” blocks.

The test cubes were stored in air in the laboratory to simulate the treatment of the blocks on site. After 28 days the mix density had reduced by 145kg/m3 to l565kg/m3. The fiill density advantage of the lightweight thus takes some time to develop.

Compressive Strength The specimens were stored in their moulds under ambient site conditions until stripped after a weekend at about 64 hours age. They were then stored in air in the laboratory (at °C) until test. This curing regime was expected to simulate the air curing that would be received at the works.

The compressive strengths of the cube specimens were tested at 7 and 28 days. The results are based on single cubes. The cube strength results are summarised below: - TABLE 3 Age - Days 100m Cube Strength - N/mm‘ 7 25.4 .1 The blocks were weighed after stripping and four blocks were selected for strength testing from each mix. These were chosen as the four nearest to the normative weight (the highest and lowest weight blocks being discarded for strength testing).

TABLE 4 Age - Days Block Strength - N/mm‘ 7 10.6 .4 Weight Saving The weights of the original blocks averaged about 21kg. A significant part of this is the weight of the flint. Initial calculations suggested that the weight of flint be about 6.5kg.

The blocks were weighed on stripping and the average for these lightweight flint blocks was as follows: TABLE 5 Ave rage Block Weights - kg (All Block Weights include about 6.5kg weight of flint facigg On Shipping (corrected value) 18.9 Days 18 l2s Days 17.5 The preliminary tests have shown that a lower density backing concrete can be produced which can reduce total block weight by about 3.5 kilograms. The preferred mix uses a lightweight all-in aggregate.

Air entrainment was introduced into the mortar by use of an admixture. This was expected to have several advantages: - It would provide some further weight reduction; it would reduce bleeding which would hopefully increase bond; it would provide some durability advantages.

In view of the high strengths of the original blocks, the cement contents were reduced to produce some saving in cost. It is possible that some further cement content reduction could be made.

Awater reducingcplasticiser was also used to offset some of the strength reduction effects of: - The lowered cement content; the lower strength lightweight aggregate; the air content provided by the air entrainment.

The test results for this embodiment of the invention may be summarised as follows: TABLE 6 Results at 28 Da Cube S Block S /m’ Block Wt W ’ Sa '

Claims (7)

1. A decorative building block comprising: a load-bearing body having applied to at least one surface a decorative arrangement of mineral pieces wherein the block has a frog around its periphery.

2. A decorative building block as claimed in claim 1 wherein the decorative arrangement is applied to two adjacent surfaces to form a corner block.

3. A decorative building block as claimed in claim 1 or claim 2 wherein the load- bearing body is able to withstand loads of at least 7 Nlmmz.

4. A decorative building block as claimed in any preceding claim wherein the mould is provided with a peripheral lip such that the decorated surface can have a variably greater surface area.

5. A decorative building block as claimed in any preceding claim wherein the frog is arcuate in cross-section.

6. A decorative building block as claimed in any preceding claim wherein the frog is positioned about midway between the upper and lower face of the block.

7. A decorative building block substantially as described herein and with reference to the