GB2377930A

GB2377930A - A self-levelling concrete composition

Info

Publication number: GB2377930A
Application number: GB0213230A
Authority: GB
Inventors: Anthony M Hartley
Original assignee: RMC READYMIX Ltd
Current assignee: RMC READYMIX Ltd
Priority date: 2001-06-08
Filing date: 2002-06-10
Publication date: 2003-01-29
Anticipated expiration: 2022-06-10
Also published as: GB0213230D0; GB0114012D0; GB2376462A; GB2377930B

Abstract

A low cement content composition for mixing with water to form a concrete for foundation applications, comprising: <SL> <LI>(i) cement in an amount of at most 300 kg/m<SP>3</SP> when the composition is mixed with water; <LI>(ii) aggregate; <LI>(iii) a plasticiser effective to achieve a flow of at least 500mm when the composition is mixed with water, (where the flow is measured by method defined in BS 1881: part 102: 1983); and <LI>(iv) an air-entrainer. </SL> The aggregate:cement ratio by weight is preferably from 5:1 to 12:1. The water: cement ratio by weight is from 0.6:1 to 1:1. The concrete may further comprise a thickener such as a polysaccharide. The plasticiser is may be a lignosulfonate. The air-entrainer may be a surfactant such as a fatty acid soap. A further invention claims a method of delivering a concrete composition to a site comprising providing a first mixture of aggregate and water, providing a second mixture comprising one or more admixtures, adding the first mixture to the second and conveying to a site, wherein there is substantially no mixing of the first and second mixtures, and then mixing the first and second mixtures together at site prior to application.

Description

A Cementitious ComooSition The present invention relates to concrete

materials and, in particular, to a free-flowing concrete for 5 foundation applications such as for houses and other buildings. The present invention also provides a method for adding one or more admixtures to a cementitious composition.

10 Concrete is comprised principally of cement, coarse aggregate, fine aggregate and water. The coarse and fine aggregates provide strength and are classified according to their type, shape and particle size.

They are embedded in a matrix of cement paste.

Examples of naturally occurring aggregates are, processed land based and marine gravels and crushed rocks such as limestones and granites. Aggregates can be sub-divided into coarse and fine fractions 20 and are combined proportionally to a desired overall particle distribution for a concrete mixture.

In the production of concrete using "hydraulic" cement, the addition of water initiates the chemical 25 process associated with the setting and hardening of the cement paste. This crystallization reaction is known as hydration. Ideally the aggregates are evenly coated with the cement paste thus binding the whole mass together.

The most commonly used cement, especially in the UK, is Portland cement; this is often blended or mixed

-2 with other hydraulic cement materials such as ground granulated blast furnace slag (gghs) and pulverized fuel ash (pfa) to obtain specific concrete characteristics. Portland cement is made from a mixture of approximately 75% of a calcareous material such as limestone or chalk and 25% of a siliceous material such as clay or shale. Both materials are 10 intimately mixed and together with some minor components are heated (burned) to a high temperature at which they fuse together. The resultant clinker is finely ground to form Portland Cement, which is a complex mixture of multi-component, mineral solid 15 solutions. Among these, are compounds of calcium silicate and calcium aluminate that hydrate in the presence of water. The essential binding component has been identified as calcium silicate hydrate (CSH).

Whilst the basic formulation of a concrete mix approximates to 80% aggregate, 15% cement and 5% water, many commercially produced concretes are specially designed mixes. These mixes are produced 25 for specific applications, e.g. for placing underwater and for placing by concrete pumping and for other purposes. These concrete types may incorporate small amounts of chemicals known as admixtures. Admixtures modify a specific property 30 of the fresh or hardened concrete.

For example, a retarding admixture will defer the setting of the concrete. This is useful when slow rates of placement are envisaged or for placing under high summer temperatures.

Other admixtures are used to control properties such as water permeability, water demand and resistance to freeze/thaw damage and concrete consistence and workability. The workability of concrete is related to the wafer: cement ratio and the mix constituents, including the particle size distribution of aggregate and cement particles. For a given 15 aggregate: cement ratio, the higher the wafer: cement ratio, generally the more workable the concrete is.

Despite the advantages of high workability, a high wafer: cement ratio can, however, adversely affect 20 the strength of the concrete. For example, if excess free water is present, which has not been absorbed into the aggregate and cement or is not adsorbed and used in the hydration reaction, this leaves voids in the hardened concrete as it dries out. The result 25 of this is lower strength and increased porosity leading to a potential reduction in the durability of the concrete in the structure. Additionally, excess water can result in segregation of the mix during placement. Accordingly, it is desirable to 30 produce highly workable concrete without significantly increasing the wafer: cement ratio.

-4 This has led to the use of admixtures such as plasticizers and superplasticisers, which impart increased workability when added to concrete, without the necessity of adding water to help 5 achieve the effect. WO 99/55632 and EP-A-O 208 535 describe the use of superplasticisers in high cement content compositions.

In addition to modifying the workability of 10 concrete, admixtures may be used, together with mix proportioning, to enhance the durability of concrete. The durability of concrete is dependent upon a 15 number of factors, such as permeability. Since aggregates such as sand and gravel are themselves durable materials, the packing density of the aggregate is significant. Careful grading of aggregate material ensuring good packing to a 20 maximum density helps to reduce inter-particle porosity. Ideally, the paste of cement and water then fills the spaces among the graded aggregate particles. However, in practice, some voids still remain. The voids may be classified as either closed pores (which are impermeable) or open pores, which are permeable voids, and these are in addition to the entrapped air voids present in the concrete paste.

The use of an air-entrainer as a class of admixture has been demonstrated to improve the durability of

concrete, particularly with regard to increasing resistance to damage due to cycles of freezing and thawing in exposed conditions.

5 The process of air-entrainment results in the presence of millions of evenly spaced air bubbles (typically of diameters between 0.025 and l mm) throughout the cement paste. This has the effect of relieving the expansion pressures that build up in 10 the capillary pores as freezing occurs by blocking the capillary structure to prevent water ingress.

The air bubbles introduced through air-entrainment should be differentiated from the randomly sized air 15 voids already entrapped in the concrete.

In addition to their role in increasing the durability of hardened concrete, air-entrainers also improve workability and reduce bleeding and 20 segregation of concrete in its newly mixed state.

For example, the multitude of microscopic air bubbles may be regarded as increasing workability by having a lubricating effect on the relative motion of aggregate particles.

In the case of the bleeding of fresh concrete, the air bubbles are understood to block the spaces between cement particles, thereby minimising the flow of water and the sedimentation of solids 30 throughout the cement-aggregate mix.

-6 As with the use of admixtures aimed primarily at increasing the workability of concrete, the use of air-entrainers has been directed to high cement content concrete compositions.

The present invention aims to address at least some of the problems associated with the prior art.

Accordingly, in a first aspect, the present 10 invention provides a low cement content composition for mixing with water to form a concrete for foundation applications, the composition comprising: (i) cement in an amount of at most 300 kg/m3 when 15 the composition is mixed with water; (it) aggregate; (iii)a plasticizer effective to achieve a flow of at 20 least 500 mm when the composition is mixed with water; and (iv) an airentrainer.

25 The term plasticizer as used herein is meant to encompass both conventional plasticizers and superplasticisers. However, preferably, a superplasticiser is used in the low cement composition of the present invention.

The low cement composition, as herein described, refers to a composition that when mixed with water

-7- has a cement content of at most 300 kg/m3.

Preferably, the cement content is in the range of from 100 to 300 kg/m3, more preferably from 150 to 300 kg/m3, still more preferably from 175 to 300 5 kg/m3, still more preferably from 175 to 250 kg/m3.

In the low cement content composition according to the present invention, the aggregate: cement ratio by weight is typically from 5:1 to 12:1, preferably 10 from 6:1 to 10:1, more preferably from 7:1 to 9:1.

The weight of coarse aggregate as a percentage of the weight of the total aggregate is typically from 40 to 70% and more preferably from 49 to 60%.

The weight of fine aggregate as a percentage of the weight of the total aggregate is typically from 30 to 60% and more preferably from 40 to 51%.

20 The mix proportioning in the composition according to the present invention is aimed at maintaining inter-particle voidage at an optimum level.

Aggregates will typically comply with the grading requirements of BS 882. The optimum amount of fine 25 material passing the 300 micron sieve test, including the cement (or cement and gabs or pfa combinations) is dependent upon the type of aggregate used and may preferably be in the ranges as follows: Smooth rounded gravels with medium to coarse sand, 25- 30;

-8- Smooth rounded gravels with medium to fine sand, 24-28; Angular and irregular gravels with medium to coarse sand, 28-31%; 5 Angular and irregular gravels with medium to fine sand, 25-30%; Crushed rock with medium to fine natural sand, 27-319; and Crushed rock with crushed rock fines and fine 10 natural sand, 28-34%.

The plasticizer is selected and provided in an amount sufficient to achieve a flow" of at least 500 mm, when the low cement composition is mixed 15 with water. The workability or the consistence of concrete is related to its ease-of-placing and is commonly quantified by the "slump" test, outlined in BS 1881, Part 102: 1983. However, the measurement of "slump" tends to be less appropriate for higher 20 workability concrete, particularly the workability of highly fluid concrete. At very high levels of workability a different test is applied. Known as the "flow table test", as outlined in BS 1881, Part 105: 1984, this method is more sensitive to the 25 behaviour of Theological highly mobile or thixotropic concrete mixtures. An accepted, industry-wide standard is that when the diameter of spread of concrete, measured by the flow table test, exceeds a value of approximately 510 mm, concrete is 30 classified as having a flowing consistency. The flow, as herein defined, is preferably in the range of from 550 mm to 650 mm.

Examples of commercially available high performance plasticizers are: Plastiment FN, manufactured by Sika 5 Pozzalith LD34, manufactured by Feb MET Conplast P165, manufactured by Foeroc Concrete Plasticiser DA4/36/00, manufactured by RMC Admixtures 10 Plasticisers tend to be formulated from modified lignosulfonates and polycarboxylic acids. The lignosulfonates may be derived from fermented wood, for example, spruce.

15 Examples of commercially available superplasticisers are: Sikament N. manufactured by Sika Rheobuild SP3, manufactured by Feb MAT 20 Conplast SP430, manufactured by Foeroc Superplasticisers fall generally into the categories of sulphonated melamine-formaldehyde condensates; sulphonated napthalene-formaldehyde condensates; 25 modified lignosulfonates; acid amide/polysaccharide mixtures and other high molecular weight hydroxylated polymers and copolymers.

The plasticizer is typically added in a dosage of 30 from 0.01 to 5\ by weight of cement, preferably from 0.05 to 2% by weight of cement, more preferably from 0.2 to 1.5% by weight of cement, still more

-10 preferably from 0.3 to 1% by weight of cement.

The air-entrainer is provided in an amount sufficient to cause a substantially controlled and 5 stable quantity of air to be incorporated during the mixing of the concrete without significantly affecting the strength of the hardened concrete.

The resulting air content of the fresh (plastic) concrete is measured by the procedure outlined in BS 10 1881:1983: Part 106 (BSEN 12350 Part 7) and is preferably in the range of from 3 to 10%, typically from 4 to 9%, more typically from 6 to 9%.

The most commonly used classes of material for the 15 purpose of airentrainment are alkali salts of wood resins; fatty acid soaps; alkyl aryl sulphonates; alkyl sulphates and salts of fatty acids derived from animal and vegetable fats and oils. A feature which tends to be common to many air-entrainers is 20 that they are surface active agents, or surfactants.

Examples of commercially available air-entrainers are: 25 FRO-BE, manufactured by Sika Conplast AE383, manufactured by Foeroc Micro-air 100, manufactured by Feb MBT Concrete air-entrainer DA9/16/00, manufactured by RMC Admixtures Air-entrainer is typically added in a dosage of from O. ol to 5% by weight of cement, preferably from 0.02

- 1 1 to lo by weight of cement, more preferably from 0.04 to 0.5% by weight of cement, still more preferably from 0.08 to 0.2% by weight of cement.

5 The plasticizer and air-entrainer may be added as a single admixture or separately as two distinct admixtures. A preferred admixture for use in the low cement 10 content composition according to the present invention is a single product admixture comprising both a plasticiser and airentrainer, and which comprises blended metal salt lignosulfonates, naturally occurring fructofuranose, with minor 15 levels of hydroxyethyl amines, phosphate esters, alkyl benzene and ether sulfonates. An example of an admixture of this type is FF400, available from RMC Admixtures. 20 In addition to the benefit of ease of placement, the free-flowing concrete produced from the present invention is typically highly cohesive and exhibits minimal surface bleeding.

25 The composition may further include a viscosity modifying agent or thickening agent, for example in the form of a high molecular weight biopolymer, such as a polyeaccharide. An example of this is DA3 from RMC Admixtures.

The thickening admixture is typically added in a dosage of from O.Ol to 0. 5% by weight of cement,

-12 preferably from 0.05 to 0.3i, more preferably from 0.08 to 0.2%, still more preferably from 0.1 to 0.15%.

5 Where used, the thickening admixture will normally be added separately. Any or all admixtures may be used in a liquid, powdered or granular form.

In a preferred embodiment, the free-flowing concrete 10 according to the present invention is substantially self-compacting and/or substantially self-levelling and shows sufficient strength in as little as typically 24 hours after installation in order to allow bricklaying to proceed.

The low cement content composition according to the present invention may be mixed with water such that, preferably, a wafer: cement ratio of from 0.6:1 to 1:1, more preferably from 0.70:1 to 0.95:1 and more 20 preferably still from 0.75:1 to 0.85:1 is obtained.

The self-levelling property of the concrete compositions is typically most effective where the depth of concrete in the foundation exceeds 25 approximately 400 mm.

The typical workability of the free-flowiny concrete prior to the addition of one or more admixtures formulated in the present invention is in the range 30 of 80 mm to 110 mm when measured by the slump test outlined in BS 1881: part 102: 1983.

-13 The increase in the workability to the preferred range of flow of from 550 mm to 650 mm following addition of one or more admixtures enables an entire house foundation to be poured from a single 5 discharge point, or at least a restricted number of discharge points in the case of a large or complex foundation. As well as significantly increasing the speed of 10 construction, site labour and plant requirements are reduced. Further, the fluidity of the concrete reduces the temptation for site operatives to modify the mix by introducing further water, which would reduce the foundation integrity by reducing concrete IS strength.

The benefits of ready mixed concrete are well known in the industry. Of particular advantages are the consistency in quality and content of concrete mix 20 provided, the reduced labour and supervisory costs, and the prevention of wastage of cement, aggregate and mixture on site.

The free-flowing nature of the concrete described in 25 the present invention provides a challenge regarding how fully mixed concrete can be transported to site in full loads, without spillage.

In a second aspect of the present invention, there 30 is provided a process for delivering a concrete composition to a site, the process comprising:

-14 i) providing a first mixture comprising cement, aggregate and water; providing a second mixture comprising one or 5 more admixtures; iii) adding the second mixture to the first mixture; iv) conveying the first and second mixtures to a 10 site, whereby there is no mixing or substantially no mixing of the first and second mixtures during transit; and v) mixing the first and second mixtures together 15 at site prior to application.

The second mixture may comprise a plasticizer and an air-entrainer, preferably in an amount sufficient to achieve a flow of at least 500 mm.

Preferably, the first mixture is substantially fully mixed to the required base-mix workability, preferably in the range of from 80 mm to llO mm slump. In the process according to the present invention, the cementitious composition will preferably be conveyed from a plant to site in a truck-mixer drum.

In this case, the mixer drum may be held stationary 30 while the second mixture defined in step (ii) of the above process is added to the rear of the load, but the second mixture is not mixed into the concrete.

-15 In other words, the second mixture is in contact with the first mixture but is not homogeneously mixed therewith. The load is then dispatched to site without rotation of the truck-mixer drum during 5 transit.

The second mixture may comprise one or more powdered or granulated admixtures. These may be added intact, for example in a container which slowly 10 dissolves during transit or is broken by the action of mixing prior to discharge. The container may take any suitable form such as a sachet, pouch, packet, bottle, or wrapping. The container may preferably be formed of a water-soluble material.

A substantially homogeneous mixture is only formed when the delivery vehicle arrives at its destination. This is achieved by mixing the first and second mixtures within the drum of the truck 20 mixer, typically by rotation of the drum.

As well as enabling full loads of ready mixed concrete to be transported to site, the method described above has been shown to have substantially 25 no adverse effects on workability retention or any set-retardation. Preferably, prior to discharge, the concrete is remixed at normal mixing speed for a minimum of 30 approximately three minutes. No additional water is added to the concrete mix, as this may be detrimental to the flow characteristics of the mix.

-16 During transportation, some initial bleeding may occur during transit due to vehicle vibration. This is advantageous to the process as it provides free water to dilute the second mixture defined in step 5 (ii) of the above process in order that it can be rapidly dispersed into the concrete mixture during the remix cycle prior to discharge into a foundation. 10 The concrete compositions described in the present invention will now be exemplified, with reference to the following mix designs.

Example 1

Concrete was batched in a pan mixer to a nominal slump of 80 mm with the mix proportions as shown in Table 1.

20 Table 1

Material Proportion 2Omm Thames Valley 44% by weight total gravel aggregate lOmm Thames Valley 15% by weight total 25 gravel aggregate Thames Valley sand 41% by weight total aggregate Nominal cement content 220 kg/m3 Presoaked Thames Valley flint gravel aggregates and 30 Seament Portland cement were used. Admixtures were added in the proportions given in Table 2.

-17 Table 2

Material Proportion Plasticiser 0.40% by weight of cement 5 Air-entrainer 0.12% by weight of cement The plasticizer used was Concrete plasticizer DA4/36/00, manufactured by RMC Admixtures and based on lignosulfonates derived from fermented spruce 10 wood. The air-entrainer was Concrete airentrainer DA9/16/00, manufactured by RMC Admixtures and based on a blend of synthetic surfactants and fatty acid soaps. 15 After a period of further mixing the flow (mm) was determined together with the plastic density (kg/m3) and air content (a). Table 3 summarizes the results of tests for fresh concrete.

20 Table 3

Result |Fresh Concrete Flow (mm) 650 Air Content (%) 8.7 Plastic Density (kg/m3) 2105 Example 2

Concrete was batched in a pan mixer to a nominal

-18 slump of 80 mm with the mix proportions as shown in Table 4.

Table 4

5 Material Proportion 20mm Thames Valley 44% by weight total gravel aggregate lOmm Thames Valley 15% by weight total gravel aggregate 10 Thames Valley sand 41% by weight total aggregate Nominal cement content 220 kg/m3 Presoaked Thames Valley flint gravel aggregates and Seament Portland cement were used. Admixtures were 15 added in the proportions given in Table 5.

Table 5

Material Proportion Plasticiser 0.40% by weight of cement 20 Airentrainer 0.08% by weight of cement The plasticizer was Concrete plasticiser DA4/36/00, manufactured by RMC Admixtures and based on lignosulfonates derived from fermented spruce wood.

25 The air-entrainer was Concrete air-entrainer DA9/16/00, manufactured by RMC Admixtures and based on a blend of synthetic surfactants and fatty acid soaps.

-19 After a period of further mixing the flow (mm) was determined together with the plastic density (kg/m3) and air content (%). In addition, lOO mm cubes were cast for testing compressive strength (N/mm2). Table 5 6 summarises the results of tests for fresh and hardened concrete.

Table 6

Result Fresh Hardened Concrete Concrete 10 Flow (mm) 650 Air Content (%) 6.5 | Plastic Density 2155 _ (kg/m3) Compressive Strength 3.9 15 (N/mm2) after l day

Claims

-20 CLAIMS:

1. A low cement content composition for mixing with water to form a concrete for foundation 5 applications, the composition comprising: (i) cement in an amount of at most 300 kg/m3 when the composition is mixed with water; lO (ii) aggregate; (iii)a plasticizer effective to achieve a flow of at least 500 mm when the composition is mixed with water; and (iv) an air-entrainer.

2. A low cement content composition as claimed in claim 1, wherein the cement content is in the range 20 of from 100 to 300 kg/m3, more preferably from 150 to 300 kg/m3, still more preferably from 175 to 300 kg/m3, still more preferably 175 to 250 kg/m3.

3. A low cement content composition as claimed in 25 claim 1 or claim 2, wherein the aggregate: cement ratio by weight is from 5:1 to 12:1, preferably from 6:1 to 10:1, more preferably from 7:1 to 9:1.

4. A low cement content composition as claimed in 30 any one of claims 1 to 3, wherein the aggregate comprises coarse and fine aggregate.

-21 5. A low cement content composition as claimed in any one of the preceding claims, wherein the weight of coarse aggregate as a percentage of the weight of the total aggregate is from 40 to 70%, more S preferably from 49 to 60%.

6. A low cement content composition as claimed in any one of the preceding claims, wherein the weight of fine aggregate as a percentage of the weight of 10 the total aggregate is from 30 to 60%, preferably from 40 to 51%.

7. A low cement content composition as claimed in any one of the preceding claims, wherein the coarse 15 aggregate is or comprises crushed rock, preferably limestone. >3. A low cement content composition as claimed in any one of the preceding claims, wherein the coarse 20 aggregate is or comprises land based and/or marine gravels. 9. A low cement content composition as claimed in any one of the preceding claims, wherein the fine 25 aggregate is or comprises sand.

10. A low cement content composition as claimed in any one of the preceding claims, wherein the plasticizer and air entrainer are added as a single 30 admixture.

11. A low cement content composition as claimed in

-22 claim 10, wherein the single admixture comprises blended metal salt lignosulfonates, naturally occurring fructofuranose, with minor levels of hydroxyethyl amines, phosphate esters, alkyl benzene 5 and ether sulfonates.

12. A low cement content composition as claimed in any one of the preceding claims, wherein the composition comprises the plasticizer in a dosage of 10 from 0.01 to 5% by weight of cement, preferably from 0.05 to 2% by weight of cement, more preferably from 0.2 to 1.5% by weight of cement, still more preferably from 0.3 to 1% by weight of cement.

15 13. A low cement content composition as claimed in any one of the preceding claims, wherein the plasticizer comprises one or more lignosulfonates, preferably being derived from fermented wood.

20 14. A low cement content composition as claimed in any one of the preceding claims, wherein the composition comprises the air-entrainer in a dosage of from o.O1 to 5% by weight of cement, preferably from 0.02 to 1% by weight of cement, more preferably 25 from 0.04 to 0.5% by weight of cement, still more preferably from 0.08 to 0.2% by weight of cement.

15. A low cement content composition as claimed in any one of the preceding claims, wherein the air 30 entrainer comprises one or more surfactants.

16. A low cement content composition as claimed in

-23 any one of the preceding claims, wherein the air-

entrainer comprises one or more fatty acid soaps.

17. A low cement content composition as claimed in 5 any one of the preceding claims, further comprising a viscosity modifying agent or a thickener.

18. A low cement content composition as claimed in claim 17, wherein the viscosity modifying agent or 10 thickener is or comprises a polyeaccharide.

19. A low cement content composition as claimed in claim 17 or claim 18, wherein the viscosity modifying agent or thickener is added in a dosage of 15 from 0.01 to 0.5% by weight of cement, preferably from 0.05 to 0.3%, more preferably from 0.08 to 0.2%, still more preferably from 0.1 to 0. 15%.

20. A low cement content composition as claimed in 20 any one of the preceding claims, wherein the cement is or comprises Portland cement.

21. A free-flowing concrete for foundation applications having a cement content of at most 300 25 kg/m3 and formed by adding water to the composition as defined in any one of claims 1 to 20.

22. A free-flowing concrete as claimed in claim 21, wherein the wafer: cement ratio by weight is from 30 0.6:1 to 1:1, preferably from 0.70:1 to 0.95:1, more preferably from 0.75:1 to 0.85:1.

-24 23. A free-flowing concrete as claimed in claim 21 or 22 having a flow of at least 500 mm, more preferably from 550 to 650 mm.

5 24. A free-flowing concrete as claimed in any one of claims 21 to 23, having an air content in the range of from 3 to 10.

25. A hardened concrete composition formed from a JO free-flowing concrete as defined in any one of claims 21 to 24.

26. Use of the free-flowing concrete as defined in any one of claims 21 to 24 in a foundation.

27. Use as claimed in claim 26, wherein the foundation is for a house or building.

23. A process for delivering a concrete composition 20 to a site, the process comprising: (i) providing a first mixture comprising cement, aggregate and water; 25 (ii) providing a second mixture comprising one or more admixtures; (iii)adding the second mixture to the first mixture; 30 (iv) conveying the first and second mixtures to a site, wherein there is no mixing or substantially no mixing of the first and second mixtures during

-25 transit; and (v) mixing the first and second mixtures together at site prior to application.

29. A process as claimed in claim 28, wherein the second mixture comprises a plasticiser and/or an air-entrainer. 10 30. A process as claimed in claim 28 or claim 29, wherein the second mixture comprises one or more powdered or granulated admixtures.

31. A process as claimed in any one of claims 28 to IS 30, wherein the second mixture is provided in a container which slowly dissolves during transit or is broken by the action of mixing prior to discharge. 20 32. A process as claimed in claim 31, wherein the container is water soluble.

33. A process as claimed in any one of claims 28 to 32, wherein the concrete composition is or comprises 25 a free-flowing concrete as defined in any one of claims 21 to 24.

34. A process as claimed in any one of claims 28 to 33, wherein the mixed concrete composition is 30 deposited in a foundation.

35. A process as claimed in claim 34, wherein the

-26 mixed concrete composition s deposited in a foundation for a house or building.

36. A process as claimed in any one of claims 28 to 5 35, wherein in step (iii) the second mixture is added to the first mixture in a truck-mixer drum.

37. A process as claimed in any one of claims 28 to 36, wherein in step (iv) the first and second 10 mixtures are conveyed to a site in a truckmixer drum. 38. A process as claimed in any one of claims 28 to 37, wherein in step (v) the first and second 15 mixtures are mixed together at site, prior to application, in a truck-mixer drum.

39. A free-flowing concrete whenever delivered to a site by the process as defined in any one of claims 20 28 to 38.

40. A process for making a free-flowing concrete for foundation applications as defined in any one of claims 21 to 24, the process comprising: (a) providing a low cement content composition as defined in any one of claims 1 to 20; (b) mixing the low cement content composition with 30 water, wherein the cement content is at most 300 kg/m3 and the flow is at least 500 mm.

-27 41. A free-flowing concrete composition substantially as herein described with reference to any one of the Examples.