GB2564129A

GB2564129A - Self-compacting concrete composition

Info

Publication number: GB2564129A
Application number: GB1710724.4A
Authority: GB
Inventors: James William Jowett Nicholas
Original assignee: Marshalls Mono Ltd
Current assignee: Marshalls Mono Ltd
Priority date: 2017-07-04
Filing date: 2017-07-04
Publication date: 2019-01-09
Anticipated expiration: 2037-07-04
Also published as: GB201710724D0; GB2564129B

Abstract

The present invention provides a self-compacting concrete composition for forming a self compacting concrete, the composition comprising: 55.5 to 70.5 % by weight of one or more coarse and fine aggregates; 6 to 16 % by weight of one or more filler aggregates; 0.1 to 0.3 % by weight of one or more self-compacting admixture agents (e.g. water reducer, superplasticiser); 10 to 20 % by weight of cement; and 5 to 15 % by weight of water. The cement may be Ordinary Portland Cement. The filler aggregates may be limestone powder. The concrete may also comprise a binder, a self-cleaning agent such as titanium dioxide or a pigment.

Description

The present invention relates to a self-compacting concrete composition for forming a selfcompacting concrete. The present invention also relates to a hardened concrete article formed from the self-compacting concrete composition and to a method of forming a hardened concrete article from the self-compacting concrete composition.

BACKGROUND

Concrete is a composite material comprised of aggregates and cement. The aggregates are comprised of coarse, fine and filler aggregates, which are defined in BS EN 12620:2002 + A1:2008. Concrete is prepared by adding water to a mixture of the coarse, fine and filler aggregates and cement. The resulting concrete composition (i.e. comprising aggregates, cement and water) is mouldable such that it can be shaped into an article, typically by pouring it into a mould. The water reacts with the cement (the aggregates being inert) which causes the composition to solidify and harden so as to bond the coarse, fine and filler aggregates together to form a hardened (solid) concrete article. The cement also fills voids within the concrete structure.

There are many different types of concrete available, having different proportions of the aggregates, cement and water to provide the desired properties. It is also known to use chemical admixtures in the preparation of concrete compositions to achieve varied properties. For example, chemical admixtures may accelerate or slow down the rate at which the mouldable concrete composition solidifies and hardens and/or can impart other useful properties such as increased tensile strength, entrainment of air and water resistance.

Typically, once the mouldable concrete composition has been placed into a mould it is necessary to compact it, for example by vibration, so as to remove pockets of air and ensure a uniform suspension of solid particles. Alternatively, the mouldable concrete composition can be made so that it is “selfcompacting”, which means that the concrete composition is able to consolidate under its own weight. Self-compacting concrete compositions typically have a low yield stress, high deformability and moderate viscosity necessary to ensure uniform suspension of solid particles during placement into a mould and thereafter until the concrete hardens. Self-compacting concrete compositions usually comprise a self-compacting chemical admixture to enhance flowability and stability. Self-compacting concrete compositions (for forming self-compacting concrete) have known advantages when compared to more traditional concrete compositions that require compaction, for example by vibration. Removing the requirement for compacting by vibration reduces the energy requirements and improves health and safety for the operating staff, as well as enabling compaction of complex shapes. Self-compacting concrete compositions typically also help to prevent aggregate segregation and reduce surface imperfections (such as pin holes) on the cast surface.

Concrete is used in many areas of the construction industry, for example in the construction of buildings and bridges. Concrete is also used to form articles such as paving slabs, tiles and blocks, and for providing surfaces which may be decorative.

It is desirable to use concrete to form relatively thin slabs, tiles and blocks, for example to provide surfaces for patios, recreation areas, roads and driveways. Typically, relatively thin slabs, tiles and blocks are prepared using traditional vibration methods. It is difficult to prepare relatively thin slabs, tiles and blocks using self-compacting concrete instead of vibration methods. This is because selfcompacting concrete relies on the mass of the material to flow and achieve appropriate compaction, and the volume or mass of concrete required for relatively thin slabs, tiles and blocks is not sufficient to achieve this. Thus, there is a need to provide a concrete composition that can be used to form relatively thin slabs, tiles and blocks, which typically are strong and have a long lifetime in use. The concrete composition should also be self-compacting, so as to provide ease of use and desirable flow characteristics and workability for forming articles such as relatively thin slabs, tiles and blocks. It would be desirable for the concrete composition to substantially avoid segregation, have a low porosity and/or have a high durability (for example when undergoing freeze-thaw cycles and/or abrasion) and/or have an imperfection free surface (for example removing the occurrence of “pinholes”).

SUMMARY

It is one aim of the present invention, amongst others, to provide self-compacting concrete compositions that can readily be formed into hardened articles, such as relatively thin slabs, tiles and blocks, which articles are strong and have a long lifetime in use.

Another aim of the invention is to provide a self-compacting concrete composition for forming a selfcompacting concrete which composition has a desirable workability for forming desired articles such as relatively thin slabs, tiles and blocks. For example, it would be desirable to provide a selfcompacting concrete composition which hardens/sets in a desirable time period, for example that provides an initial set in a period of about 3 hours, and/or that has a desirable workability retention. The reference to an “initial set” means that the concrete composition cannot be further moulded.

References herein to articles such as slabs, tiles and blocks being “relatively thin” means articles having a height of about 10 to 125 mm, such as about 15 to 80 mm, for example about 15 to 50 mm. For example, a “relatively thin” slab, tile or block may have the dimensions of a width and length each independently in the range of about 300 to 1800 mm, such as about 450 to 1200 mm, for example a width and length each of about 500 mm and 500 mm, particularly of about 450 mm and 450 mm, and a height of about 10 to 125 mm, such as about 15 to 80 mm, for example about 15 mm to 50 mm.

The present invention provides a self-compacting concrete composition for forming a self-compacting concrete, a hardened concrete article formed from the self-compacting concrete composition and a method of forming a hardened concrete article from the self-compacting concrete composition as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description, which follows.

A first aspect of the present invention provides a self-compacting concrete composition for forming a self-compacting concrete, the composition comprising:

55.5 to 70.5 % by weight of one or more coarse and fine aggregates;

to 16 % by weight of one or more filler aggregates;

0.1 to 0.3 % by weight of one or more self-compacting admixture agents;

to 20 % by weight of cement; and to 15 % by weight of water.

A second aspect of the invention provides a hardened concrete article formed from a self-compacting concrete composition according to the first aspect of the invention.

A third aspect of the invention provides a method of forming a hardened concrete article comprising:

(i) providing a self-compacting concrete composition according to the first aspect of the invention; and (ii) forming an article from the self-compacting concrete composition.

A fourth aspect of the invention provides a hardened concrete article obtained by a method according to the third aspect of the invention.

A fifth aspect of the invention provides a hardened concrete article obtainable by a method according to the third aspect of the invention.

A sixth aspect of the invention provides a pre-mix composition for mixing with water to form a selfcompacting concrete composition, the pre-mix composition comprising:

50.1 to 63.6 % by weight of one or more coarse and fine aggregates;

5.4 to 14.4 % by weight of one or more filler aggregates;

0.2 to 0.3 % by weight of one or more self-compacting admixture agents; and

9.0 to 18.0 % by weight of cement.

Throughout this specification, the term “comprising” or “comprises” means including the component(s) specified but not to the exclusion of the presence of other components.

The optional features set out herein may be used either individually or in combination with each other where appropriate and particularly in the combinations as set out in the accompanying claims. The optional features for each exemplary embodiment of the invention, as set out herein are also applicable to any other aspects or exemplary embodiments of the invention, where appropriate. In other words, the skilled person reading this specification should consider the optional features for each aspect or embodiment of the invention as interchangeable and combinable between different aspects of the invention.

The first aspect of the invention provides a self-compacting concrete composition for forming a selfcompacting concrete.

The term “self-compacting concrete composition” is used herein to mean a flowing concrete composition that can consolidate under its own weight, i.e. without the need for mechanical compaction, such as by vibration. In other words, a self-compacting concrete composition is characterised by its ability to compact under its own weight whilst having the viscosity necessary to ensure uniform suspension of particles during placement and movement until full set occurs and the concrete hardens and solidifies.

The self-compacting concrete composition according to the first aspect of the invention comprises:

55.5 to 70.5 % by weight of one or more coarse and fine aggregates;

to 16 % by weight of one or more filler aggregates;

0.1 to 0.3 % by weight of one or more self-compacting admixture agents;

to 20 % by weight of cement; and to 15 % by weight of water.

The term “aggregates” is used herein to mean granular material used in construction and may be natural, manufactured or recycled. The aggregates comprise coarse, fine and filler aggregates. References herein to “total aggregate” mean the total of the coarse, fine and filler aggregates.

As discussed above, the coarse, fine and filler aggregates are defined according to their particle sizes which are defined in BS EN 12620:2002 + A1:2008. The terms “coarse aggregate”, “fine aggregate” and “filler aggregate” are well understood by persons skilled in the art.

The particle size distribution of coarse and fine aggregate may be determined according to BS EN 933-1:2012. This test consists of dividing and separating a material into several particle size classifications of decreasing sizes by means of a series of sieves. The aperture sizes and the number of sieves are selected in accordance with the nature of the sample and the accuracy required. The mass of the particles retained on the various sieves is related to the initial mass of the material.

The cumulative percentages passing each sieve are reported in numerical form and, when required, in graphical form. Typically, for coarse and fine aggregates, dry sieving is used.

The particle size distribution of a filler aggregate may be determined by wet sieving (for example according to ISO 787-7:2009) or by other techniques, such as laser particle size distribution analysis.

By the term “coarse aggregate” we mean aggregates which have a particle size of greater than or equal to 4 mm, i.e. a particle size wherein 100 % by weight of the aggregate is retained on a 4 mm sieve when dry sieved.

By the term “fine aggregate” we mean aggregates which have a particle size of less than 4 mm and greater than 0.063 mm, i.e. a particle size wherein 100 % by weight of the aggregate passes a 4 mm sieve when dry sieved and wherein 0 % by weight of the aggregate passes a 0.063 mm sieve when dry sieved.

By the term “filler aggregate” we mean aggregates wherein most (for example suitably 90 % or more by weight) of the particles have a particle size of less than 0.063 mm, i.e. a particle size wherein 10 % by weight or less of the aggregate is retained on a 0.063 mm sieve when wet sieved.

Any suitable coarse and fine aggregates may be used. For example, the coarse and fine aggregates may comprise limestone, granite, gravel, sandstone and/or silica sand. Examples of commercially available coarse and fine aggregates include Swinden limestone, Swinden limestone dust and Nosterfield sand.

Any suitable filler aggregate may be used. For example, filler aggregates may comprise a natural material which is processed, for example by grinding, to provide a powder. Typically, the filler aggregates comprise limestone powder. An example of a commercially available filler aggregate is limestone powder such as Betocarb 80BT.

The aggregates are inert, such that they do not substantially react with the other components of the composition, for example they do not substantially react with the water.

The self-compacting concrete composition of the first aspect of the present invention may have coarse, fine and filler aggregates having a particle size distribution as set out below. The particle size distribution is typically expressed as a percentage by weight of the materials that can pass through a specified set of sieves and in this case the percentage by weight relates to the percentage of the aggregate, i.e. of the total of the coarse, fine and filler aggregates. The classification of the materials into approximate size fractions is also known as the “grading”. In Europe, a series of sieve sizes is used as follows (according to BS EN 933-1:2012) to measure the particle size distribution or grading:

Sieve size, mm
0.063
0.125
0.250
0.500
1.00
2.00
2.8
4.0
6.3
8.0
10.0
14.0
20.0

As discussed above, for coarse and fine aggregate, the particle size distribution (or grading) is typically determined according to BS EN 933-1:2012. This test consists of dividing and separating a material into several particle size classifications of decreasing sizes by means of a series of sieves. The aperture sizes and the number of sieves are selected in accordance with the nature of the sample and the accuracy required, and in this instance are selected as set out above. The method adopted is dry sieving. The mass of the particles retained on the various sieves is related to the initial mass of the material. The cumulative percentages passing each sieve are reported in numerical form and, when required, in graphical form. For filler aggregate, the particle size distribution (or grading) may be determined by wet sieving methods or by other techniques, such as laser particle size distribution analysis. Typically, two or more of the aforementioned methods are conducted so as to provide a combined grading for a composition of different aggregates (for example a composition of coarse, fine and filler aggregates). For example, individual aggregates are graded (using a method appropriate to the particular material) and then the individual gradings are combined mathematically in the ratio of the aggregates in the overall composition, as would be understood by persons skilled in the art.

In the self-compacting concrete compositions of the first aspect of the invention, the total aggregate content (i.e. including coarse, fine and filler aggregates) preferably has a particle size distribution or grading wherein 100 % by weight of the total aggregate may pass through a 8 mm sieve.

In the self-compacting concrete compositions of the first aspect of the invention, the total aggregate content (i.e. including coarse, fine and filler aggregates) preferably has a particle size distribution or grading wherein 90 to 100 % by weight, suitably about 95 % by weight, of the total aggregate may pass through a 6.3 mm sieve.

In the self-compacting concrete compositions of the first aspect of the invention, the total aggregate content (i.e. including coarse, fine and filler aggregates) preferably has a particle size distribution or grading wherein 69 to 77 % by weight, suitably about 73 % by weight, of the total aggregate may pass through a 4 mm sieve.

In the self-compacting concrete compositions of the first aspect of the invention, the total aggregate content (i.e. including coarse, fine and filler aggregates) preferably has a particle size distribution or grading wherein 60 to 66 % by weight, suitably about 63 % by weight, of the total aggregate may pass through a 2.8 mm sieve.

In the self-compacting concrete compositions of the first aspect of the invention, the total aggregate content (i.e. including coarse, fine and filler aggregates) preferably has a particle size distribution or grading wherein 52 to 58 % by weight, suitably about 55 % by weight, of the total aggregate may pass through a 2 mm sieve.

In the self-compacting concrete compositions of the first aspect of the invention, the total aggregate content (i.e. including coarse, fine and filler aggregates) preferably has a particle size distribution or grading wherein 43 to 47 % by weight, suitably about 45 % by weight, of the total aggregate may pass through a 1 mm sieve.

In the self-compacting concrete compositions of the first aspect of the invention, the total aggregate content (i.e. including coarse, fine and filler aggregates) preferably has a particle size distribution or grading wherein 34 to 38 % by weight, suitably about 36 % by weight, of the total aggregate may pass through a 0.5 mm sieve.

In the self-compacting concrete compositions of the first aspect of the invention, the total aggregate content (i.e. including coarse, fine and filler aggregates) preferably has a particle size distribution or grading wherein 26 to 28 % by weight, suitably about 27 % by weight, of the total aggregate may pass through a 0.25 mm sieve.

In the self-compacting concrete compositions of the first aspect of the invention, the total aggregate content (i.e. including coarse, fine and filler aggregates) preferably has a particle size distribution or grading wherein 19 to 21 % by weight, suitably about 20 % by weight, of the total aggregate may pass through a 0.125 mm sieve.

In the self-compacting concrete compositions of the first aspect of the invention, the total aggregate content (i.e. including coarse, fine and filler aggregates) preferably has a particle size distribution or grading wherein 17 to 19 % by weight, suitably about 18 % by weight, of the total aggregate may pass through a 0.063 mm sieve.

In the self-compacting concrete compositions of the first aspect of the invention, the total aggregate content (i.e. including coarse, fine and filler aggregates) preferably has a particle size distribution or grading wherein 90 to 100 % by weight, suitably about 100 % by weight, of the total aggregate may pass through a 8 mm sieve, 69 to 77 % by weight, suitably about 73 % by weight, of the total aggregate may pass through a 4 mm sieve and 17 to 19 % by weight, suitably about 18 % by weight, of the total aggregate may pass through a 0.063 mm sieve.

Suitably, in the self-compacting concrete compositions of the first aspect of the invention, the total aggregate content (i.e. including coarse, fine and filler aggregates) preferably has a particle size distribution or grading wherein 69 to 77 % by weight, suitably about 73 % by weight, of the total aggregate may pass through a 4 mm sieve and 17 to 19 % by weight, suitably about 18 % by weight, of the total aggregate may pass through a 0.063 mm sieve. In other words, in the composition of the first aspect of the invention, the total aggregate (i.e. including coarse, fine and filler aggregates) preferably comprise about 31 to 23 % by weight, suitably about 27 % by weight, of coarse aggregate, about 50 to 60 % by weight, suitably about 55 % by weight, of fine aggregate and about 17 to 19 % by weight, suitably about 18 % by weight, of filler aggregate.

In the compositions of the first aspect of the invention, the total aggregate content may have a particle size distribution (or grading) as follows:

Sieve size, mm	% by weight of aggregate passing through the sieve
0.063	17-19
0.125	19-21
0.250	26-28
0.500	34-38
1.00	43-47
2.00	52-58
2.8	60-66
4.0	69-77
6.3	90-100
8.0	100
10.0	100
14.0	100
20.0	100

For example, in the compositions of the first aspect of the invention, the total aggregate content may have a particle size distribution (or grading) wherein preferably 90 to 100 % by weight of the total aggregate passes through a 6.3 mm sieve, preferably 60 to 66 % by weight of the total aggregate passes through a 2.8 mm sieve, preferably 52 to 58 % by weight of the total aggregate passes through a 2.0 mm sieve, preferably 43 to 47 % by weight of the total aggregate passes through a 1.0 mm sieve, preferably 34 to 38 % by weight of the total aggregate passes through a 0.5 mm sieve, preferably 26 to 28 % by weight of the total aggregate passes through a 0.25 mm sieve and/or preferably 19 to 21 % by weight of the total aggregate passes through a 0.125 mm sieve.

For example, in the compositions of the first aspect of the invention, the total aggregate content may have a particle size distribution (or grading) wherein preferably 90 to 100 % by weight of the total aggregate passes through a 6.3 mm sieve, preferably 60 to 66 % by weight of the total aggregate passes through a 2.8 mm sieve, preferably 52 to 58 % by weight of the total aggregate passes through a 2.0 mm sieve, preferably 43 to 47 % by weight of the total aggregate passes through a 1.0 mm sieve, preferably 34 to 38 % by weight of the total aggregate passes through a 0.5 mm sieve, preferably 26 to 28 % by weight of the total aggregate passes through a 0.25 mm sieve, preferably 19 to 21 % by weight of the total aggregate passes through a 0.125 mm sieve and/or preferably 17 to 19 % by weight of the total aggregate passes through a 0.063 mm sieve.

Sieve size, mm	% by weight of aggregate passing through the sieve
0.063	18
0.125	20
0.250	27
0.500	36
1.00	45
2.00	56
2.8	63
4.0	73
6.3	95
8.0	100
10.0	100
14.0	100
20.0	100

For example in the compositions of the first aspect of the invention, the total aggregate content may have a particle size distribution (or grading) wherein preferably about 95 % by weight of the total aggregate passes through a 6.3 mm sieve, preferably about 63 % by weight of the total aggregate passes through a 2.8 mm sieve, preferably about 55 % by weight of the total aggregate passes through a 2.0 mm sieve, preferably about 45 % by weight of the total aggregate passes through a 1.0 mm sieve, preferably about 36 % by weight of the total aggregate passes through a 0.5 mm sieve, preferably about 27 % by weight of the total aggregate passes through a 0.25 mm sieve and/or preferably about 20 % by weight of the total aggregate passes through a 0.125 mm sieve.

For example, in the compositions of the first aspect of the invention, the total aggregate content may have a particle size distribution (or grading) wherein preferably about 95 % by weight of the total aggregate passes through a 6.3 mm sieve, preferably about 63 % by weight of the total aggregate passes through a 2.8 mm sieve, preferably about 55 % by weight of the total aggregate passes through a 2.0 mm sieve, preferably about 45 % by weight of the total aggregate passes through a 1.0 mm sieve, preferably about 36 % by weight of the total aggregate passes through a 0.5 mm sieve, preferably about 27 % by weight of the total aggregate passes through a 0.25 mm sieve, preferably about 20 % by weight of the total aggregate passes through a 0.125 mm sieve and/or preferably about 18 % by weight of the total aggregate passes through a 0.063 mm sieve.

The preferred particle size distributions or gradings as discussed herein may be determined by any suitable method, such as a method as described herein

The particle size of the filler aggregates may alternatively be defined by d50 values. Suitably, the filler aggregates have a d50 value of from 6 to 10 gm, for example of from 7 to 9 gm, such as about 8 gm. d50 values can be determined using methods well known to persons skilled in the art, such as by using laser diffraction or dynamic light scattering techniques.

Suitably, the self-compacting concrete composition comprises 55.5 to 70.5 % by weight, particularly 60 to 65 % by weight, such as 63 to 64 % by weight, of one or more coarse and fine aggregates.

Suitably, the self-compacting concrete composition comprises 6 to 16 % by weight, for example 8 to 13 % by weight, particularly 9 to 12 % by weight, such as 11 to 12 % by weight, of one or more filler aggregates.

The term “self-compacting admixture agent” is used herein to mean a water reducing high range super plasticiser. Any suitable self-compacting admixture agent may be used. The exact nature of the self-compacting admixture agent used may depend on the particular cement included in the composition according to the first aspect of the invention.

The self-compacting admixture agent may comprise water. The water may be present in an amount of from 30 to 40 % by weight of the overall self-compacting admixture agent.

The self-compacting admixture agent may comprise a polymer, such as a synthetic copolymer, for viscosity modification. The polymer, such as a synthetic copolymer, for viscosity modification may be present in an amount of from 0 to 5 % by weight of the overall self-compacting admixture agent. An example of a suitable synthetic copolymer for viscosity modification may be a water-soluble, sulphogroup containing copolymer. A suitable water-soluble, sulpho-group containing copolymer may have a number average molecular weight of from 50,000 to 20,000,000 g/mol. Examples of suitable watersoluble, sulpho-group containing copolymers are, for example, provided in EP 1763546 A1.

The self-compacting admixture agent may comprise a polymer, such as a synthetic copolymer, for water reduction. The polymer, such as a synthetic copolymer, for water reduction may be present in an amount of from 50 to 60 % by weight of the overall self-compacting admixture agent. An example of a suitable polymer, such as a synthetic copolymer, for water reduction may be a copolymer based on radicals of unsaturated monocarboxylic or dicarboxylic acid derivatives and oxyalkylene glycol alkenyl ethers. Examples of suitable copolymers based on radicals of unsaturated monocarboxylic or dicarboxylic acid derivatives and oxyalkylene glycol alkenyl ethers are, for example, provided in EP 1189955 A1.

The self-compacting admixture agent may comprise a polymer, such as a synthetic copolymer, for workability retention. The polymer, such as a synthetic copolymer, for workability retention may be present in an amount of from 5 to 15 % by weight of the overall self-compacting admixture agent. An example of a suitable polymer, such as a synthetic copolymer, for workability retention may comprise a copolymer based on radicals of monocarboxylic or dicarboxylic acid derivatives and polyether macromonomers.

The self-compacting admixture agent may comprise one or more additional ingredients selected from a defoamer agent and/or a biocidal agent. Any such additional ingredient may each be present in an amount of from 0 to 5 % by weight of the overall self-compacting admixture agent.

The self-compacting admixture agent may comprise water, a water-soluble, sulpho-group containing copolymer (for example having a number average molecular weight of from 50,000 to 20,000,000 g/mol), a copolymer based on radicals of unsaturated monocarboxylic or dicarboxylic acid derivatives and oxyalkylene glycol alkenyl ethers, a copolymer based on radicals of monocarboxylic or dicarboxylic acid derivatives and polyether macromonomers and, optionally, one or more additional ingredients selected from a defoamer agent and/or a biocidal agent.

The self-compacting admixture agent may comprise from 30 to 40 % by weight of water, from 0 to 5 % by weight of a synthetic copolymer for viscosity modification, from 50 to 60 % by weight of a synthetic copolymer for water reduction, from 5 to 15 % by weight of a synthetic copolymer for workability retention and from 0 to 5 % by weight of one or more additional ingredients which additional ingredients may be selected from a defoamer agent and/or a biocidal agent.

The self-compacting admixture agent may comprise from 30 to 40 % by weight of water, from 0 to 5 % by weight of a water-soluble, sulpho-group containing copolymer (for example having a number average molecular weight of from 50,000 to 20,000,000 g/mol), from 50 to 60 % by weight of a copolymer based on radicals of unsaturated monocarboxylic or dicarboxylic acid derivatives and oxyalkylene glycol alkenyl ethers, from 5 to 15 % by weight of a copolymer based on radicals of monocarboxylic or dicarboxylic acid derivatives and polyether macromonomers and from 0 to 5 % by weight of one or more additional ingredients which additional ingredients may be selected from a defoamer agent and/or a biocidal agent.

It is believed that the self-compacting admixture agent enables the self-compacting concrete composition to be formed with low levels of water yet still retain a desirable flowability in terms of its being placed in a mould to form an article. Low levels of water are believed to be advantageous because this reduces the number of pores in the hardened articles, which improves the strength of the final concrete article.

An example of a suitable self-compacting admixture agent is Rheomatrix 233, which is commercially available from BASF.

The self-compacting concrete composition of the first aspect of the invention comprises 0.1 to 0.3 % by weight, such as about 0.2 % by weight, of one or more self-compacting admixture agents.

The self-compacting concrete composition of the first aspect of the invention comprises cement. Preferably, the cement comprises Portland cement, such as Ordinary Portland cement (OPC). An example of a suitable OPC is CEM1 OPC to BS EN197-1:2011.

The self-compacting concrete composition of the first aspect of the invention comprises 10 to 20 % by weight of cement. Suitably, the self-compacting concrete composition of the first aspect of the invention comprises 12 to 18 % by weight, particularly 14 to 17 % by weight, such as 14.5 to 15.5 % by weight, of cement.

Typically, in the self-compacting concrete composition of the first aspect of the invention the weight ratio of the coarse and fine aggregates to the filler aggregates is in the range of 5:1 to 6:1, for example in the range of 5.3:1 to 5.7:1.

Typically, in the self-compacting concrete composition of the first aspect of the invention the weight ratio of the coarse and fine aggregates to the total of filler aggregates and cement (i.e. wherein the combination of filler aggregates and cement represents the powder content) is in the range of 2.2:1 to 2.6:1, for example in the range of 2.3:1 to 2.5:1.

Typically, in the self-compacting concrete composition of the first aspect of the invention the weight ratio of the coarse and fine aggregates to the cement is in the range of 6:1 to 2:1, for example in the range of 5:1 to 3:1, particularly in the range of 5:1 to 3.3:1.

Typically, in the self-compacting concrete composition of the first aspect of the invention the weight ratio of the filler aggregates to the cement is in the range of 1:1 to 0.5:1, for example in the range of 0.85:1 to 0.65:1.

The weight ratio of water to cement in the self-compacting concrete composition of the first aspect of the invention may be in the range of from 0.37:1 to 0.7:1, preferably in the range of from 0.4:1 to 0.68:1, more preferably in the range of from 0.5:1 to 0.65:1. This ratio refers to the ratio in the selfcompacting concrete composition before it hardens and solidifies to provide an article formed of concrete. It would be understood by persons skilled in the art that the majority of the water is consumed in the reaction with the cement and/or evaporates (forming pores in the hardened concrete article) such that the hardened concrete article comprises a lower level of water than the amount initially present in the self-compacting concrete composition. Suitably, the hardened concrete article comprises substantially no water.

The above defined weight ratio of water to cement in the self-compacting concrete composition is believed to provide the desired workability and results in a hardened concrete article having the desired strength.

The self-compacting concrete composition of the first aspect of the invention may comprise one or more suitable additional ingredients, as would be appreciated by a person skilled in the art. Examples of suitable additional ingredients include a binder, a self-cleaning agent and/or a pigment (i.e. a construction pigment). Any suitable binder, self-cleaning agent and/or pigment may be used.

Suitably, the pigment is a substance which is substantially insoluble in the self-compacting concrete composition (i.e. prior to hardening) and which has the sole purpose of colouring the resultant hardened concrete article. The pigment is typically in the form of fine particles. When present, the pigment may be present in an amount of 1.5 to 6 % by weight based on the weight of the cement.

Examples of suitable self-cleaning agents include titanium dioxide. Examples of suitable pigments include iron or organic oxides and titanium dioxide. Titanium dioxide is preferred as this acts as a self-cleaning agent in addition to being a pigment.

The coarse, fine and filler aggregates, self-compacting admixture agent and cement of the selfcompacting concrete composition of the first aspect of the invention are all substantially dry, although they may comprise small amounts of water as discussed herein. When the coarse, fine and filler aggregates, self-compacting admixture agent and cement are combined with additional water, the water forms a mouldable paste with the cement, which paste solidifies and hardens by means of a reaction between the water and cement. When the paste solidifies and hardens it bonds the inert coarse, fine and filler aggregates together and fills the voids so as to form a hardened (solid) concrete article.

The water present in the self-compacting concrete composition may be added to the composition and/or may be present in other components of the composition. For example, it is typical for the aggregates to include some water, which will contribute to the overall amount of water in the selfcompacting concrete composition. The references herein to the amount (% by weight) and weight ratios of water in the self-compacting concrete composition of the first aspect of the invention relate to the water content of the composition including that inherently present in aggregates but not including the water present in the self-compacting admixture agent and can be considered as “free water”, i.e. the water which is in excess in the composition and so available to react with the cement and aid workability.

Typically, the self-compacting concrete composition of the first aspect of the invention has a value of 700 to 800 mm in a concrete slump-flow test. The test may be conducted according to BS EN 123508:2010. The slump-flow test is used to assess the flowability and the flow rate of self-compacting concrete compositions in the absence of obstructions. It is based on the slump test described in EN 12350-2:2009. The result is an indication of the filling ability of self-compacting concrete composition. In the test, a suitable amount of a concrete composition (i.e. freshly formed by addition of water as discussed herein) is poured into a cone as used for the EN 12350-2:2009 slump test. The cone is then withdrawn and the liquid concrete composition is allowed to flow until it comes to rest. The largest diameter of the flow spread of the concrete composition and the diameter of the spread at right angles to it are then measured and the mean is the slump-flow value quoted in millimetres.

Typically, the self-compacting concrete composition of the first aspect of the invention has a value of 5 seconds or less in a V-funnel test. The V-funnel test may be conducted according to BS EN 123509:2010. The V-funnel test measures the viscosity and filling ability of a self-compacting concrete composition. In the test, a V shaped funnel is filled with a concrete composition (i.e. freshly formed by addition of water as discussed herein) and the time taken for the concrete composition to flow out of the funnel is measured and recorded as the V-funnel flow time.

Typically, the self-compacting concrete composition of the second aspect of the invention has a value of 700 to 800 mm in a concrete slump-flow test and a value of 5 seconds or less in a V-funnel test.

Typically, the self-compacting concrete composition of the first aspect of the invention has a value of workability retention of a minimum of 42 minutes, typically of 45 to 55 minutes, for example about 50 minutes. The workability retention is the time at which the self-compacting concrete composition remains between the limits set in the slump-flow test and may be measured according to the method set out in BS EN 12350-8:2010.

Typically, the self-compacting concrete composition of the second aspect of the invention has a value of 700 to 800 mm in a concrete slump-flow test and a value of 45 to 55 minutes in the workability retention test.

Typically, the self-compacting concrete composition of the second aspect of the invention has a value of 700 to 800 mm in a concrete slump-flow test, a value of 5 seconds or less in a V-funnel test and a value of 45 to 55 minutes in the workability retention test.

The second aspect of the invention provides a hardened concrete article formed from a selfcompacting concrete composition according to the first aspect of the invention.

As discussed above, in order for the hardened concrete article to be formed from a self-compacting concrete composition according to the first aspect of the invention, there is a reaction between the water and the cement.

The hardened concrete article may be any article which it is desired to form from concrete, including but not limited to, paving slabs, tiles and blocks. For example, the articles may be “relatively thin” slabs, tiles and blocks, for example having a height of about 10 to 125 mm, such as about 15 to 80 mm, for example about 15 to 50 mm. The article may be a slab, tile or block having the dimensions of a width and length each independently in the range of about 300 to 1800 mm, such as about 450 to 1200 mm, for example a width and length each of about 500 mm and 500 mm, particularly of about 450 mm and 450 mm, and a height of about 10 to 125 mm, such as about 15 to 80 mm, for example about 15 mm to 50 mm.

The third aspect of the invention provides a method of forming a hardened concrete article comprising:

The self-compacting concrete composition provided in step (i) of the method of the third aspect of the invention is as defined above in relation to the first aspect of the invention.

Typically, the step (ii) of the method according to the third aspect of the invention comprises forming the article in a mould and curing the self-compacting concrete composition to provide the hardened concrete article. The self-compacting concrete composition may be cured by any suitable means, for example by heating. In particular, the curing may be conducted by heating at a specified humidity, for example by heating to a temperature of from 22 to 26°C at a humidity of at least 80 %. The initial curing step to achieve demoulding and/or handling strength may take a minimum of 6 hours, typically from 10 to 24 hours. Once the curing step is complete, the article is removed from the mould by any suitable method.

Typically, an article of the second aspect of the invention and/or formed by a method of the third aspect of the invention has a minimum demoulding strength of 15 MPa and an ultimate compressive strength of 50 to 80 MPa such as 60 to 70 MPa. Compressive strength may be determined according to BS EN 12390-3:2003.

The fourth aspect of the invention provides a hardened concrete article obtained by a method according to the third aspect of the invention.

The fifth aspect of the invention provides a hardened concrete article obtainable by a method according to the third aspect of the invention.

Typically, an article of the fourth or fifth aspect of the invention has a minimum demoulding strength of 15 MPa and an ultimate compressive strength of 50 to 80 MPa such as 60 to 70 MPa.

The invention will now be described with reference to the following non-limiting examples.

EXAMPLES

Cement, limestone powder, aggregates and self-compacting admixture agent was mixed in a reactor and then water added in the proportions set out in Table 1 below, in which all amounts are expressed in kilograms.

Table 1

Water: Cement Ratio	oo ό	0.64	0.64	0.44	0.44
Water 1	78	CD OO	CD OO	OO	OO
Admixture 3			CO
Admixture 2	CD
Admixture 1		CO		co	co
Aggregate 4	205	o	o	o	o
Aggregate 3	140	154	154	154	154
Aggregate 2	214	180	180	180	180
Aggregate 1	o	226	226	226	226
Limestone Powder	o	100	100	50	o
Cement	162	134	134	184	184
Example	-	CM	CO		ID

CM	Q	o
CD	CD	o	CD
C	c		C
o	o	Ό	o
ω	ω	C	ω
CD	CD	CO	CD
E	E	ω	E
_1	—1	Ό	—1
c	c	CD	c
CD	CD	Έ	CD
Ό	Ό	CD	Ό
C	C	H—< ω o	C
£	£	£
ω	ω	Z	ω

o	□_	CD	T-	CM	co
	II	CD	,N	CD	CD	CD	CD
	H—<	C	C/)	co	co	co	co
	c	UP	CD	σ>	σ>	σ>	σ>
	CD	ω	O	CD	CD	CD	CD
>	E	CD E	σ>	σ>	σ>	σ>
LU	CD	CO	σ>	σ>	σ>	σ>
	o	_l	Q_	<	<	<	<

Admixture 3 = Self-Compacting Concrete Admixture Agent - Development Product (according to the definition of the self-compacting admixture agent defined herein)

Water 1 = Water added to the concrete mixture

RESULTS:

The example formulations were tested for slump flow, V funnel reading and workability retention time immediately following mixing and whilst the concrete was in a fresh state. The concrete was then placed into steel cube moulds as described below to allow compressive strength testing to be carried out. These cubes were then tested at 28 days. The results are shown in Table 2 below.

Table 2

Example	Slump Flow (mm)	V Funnel (seconds)	Workability Retention (minutes)	Average Strength at 28 days (MPa)
1	760	11	25	72.5
2	780	4	50	68.0
3	730	7	35	65.5
4	690	10	40	63.5
5	650	12	25	64.0

Slump Flow Test - Tested in accordance with BS EN 12350-8:2010 and shown in mm.

V Funnel Test - Tested in accordance with BS EN 12350-9:2010 and shown in seconds.

Workability Retention Time - Tested in accordance with BS EN 12350-8:2010, i.e. time at which the mix remains between the limits set in the Slump Flow test and shown in minutes.

Compressive Strength - The strength in MPa of a 100 mm concrete cube and tested in accordance with BSEN 12390-3:2003.

Table 2 shows that the self-compacting concrete compositions of Examples 2 and 3 provide hardened concrete articles having desired strength characteristics and also have desirable flow properties for use in making the hardened concrete articles, i.e. by meeting the preferred requirements in the slump and/or V funnel tests.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each 5 feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiments). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, and drawings), or to any novel one, or any 10 novel combination, of the steps of any method or process so disclosed.

Claims

1. A self-compacting concrete composition for forming a self-compacting concrete, the composition comprising:

55.5 to 70.5 % by weight of one or more coarse and fine aggregates;

6 to 16 % by weight of one or more filler aggregates;

0.1 to 0.3 % by weight of one or more self-compacting admixture agents;

10 to 20 % by weight of cement; and

5 to 15 % by weight of water.

2. A self-compacting concrete composition according to claim 1, wherein the coarse and fine aggregates comprise limestone, granite, gravel, sandstone and/or silica sand.

3. A self-compacting concrete composition according to any preceding claim, wherein the filler aggregates comprise limestone powder.

4. A self-compacting concrete composition according to any preceding claim, wherein the coarse, fine and filler aggregates represent the total aggregate in the composition and the total aggregate has a particle size distribution wherein 90 to 100 % by weight of the total aggregate passes through a 6.3 mm sieve, 60 to 66 % by weight of the total aggregate passes through a 2.8 mm sieve, 52 to 58 % by weight of the total aggregate passes through a 2.0 mm sieve, 43 to 47 % by weight of the total aggregate passes through a 1.0 mm sieve, 34 to 38 % by weight of the total aggregate passes through a 0.5 mm sieve, 26 to 28 % by weight of the total aggregate passes through a 0.25 mm sieve, 19 to 21 % by weight of the total aggregate passes through a 0.125 mm sieve and/or 17 to 19 % by weight of the total aggregate passes through a 0.063 mm sieve.

5. A self-compacting concrete composition according to any preceding claim, wherein the cement comprises Ordinary Portland cement.

6. A self-compacting concrete composition according to any preceding claim, further comprising one or more additional ingredients selected from a binder, a self-cleaning agent and/or a pigment.

7. A self-compacting concrete composition according to any preceding claim, which has a value of 700 to 800 mm in a slump test.

8. A self-compacting concrete composition according to any preceding claim, which has a value of 5 seconds or less in a V-funnel test.

9. A self-compacting concrete composition according to any preceding claim, which has a value of workability retention of a minimum of 42 minutes, for example of 45 to 55 minutes.

5 10. A hardened concrete article formed from a self-compacting concrete composition according to any preceding claim.

11. A method of forming a hardened concrete article comprising:

(i) providing a self-compacting concrete composition according to any of claims 1 to 9; 10 and (ii) forming an article from the self-compacting concrete composition.

12. A method of forming a hardened concrete article according to claim 11, wherein step (ii) comprises forming the article in a mould and curing the self-compacting concrete composition

15 to provide the hardened concrete article.

13. A hardened concrete article obtained by a method according to claim 11 or 12.

Amendments to the claims have been made as follows:

55.5 to 70.5 % by weight of one or more coarse and fine aggregates;

6 to 16 % by weight of one or more filler aggregates;

0.1 to 0.3 % by weight of one or more self-compacting admixture agents;

10 to 20 % by weight of cement; and

5 to 15 % by weight of water.

10. A hardened concrete article formed from a self-compacting concrete composition 5 according to any preceding claim.

11. A method of forming a hardened concrete article comprising:

(i) providing a self-compacting concrete composition according to any of claims 1 to 9; and

10 (ii) forming an article from the self-compacting concrete composition wherein step (ii) comprises forming the article in a mould and curing the self-compacting concrete composition to provide the hardened concrete article.