This invention relates to soil-containing concrete.

The use of cement to stabilise soil in situ, for example in road bases is known. It is also known to produce building blocks containing cement and soil by heavy compression of the mixture in a mould. Such a procedure has been used in developing countries, where cement is an expensive commodity, in order to minimise its use and reduce costs. It is known that various types of soil can cause damage to set concretes. The presence of calcium, magnesium, sodium and potassium sulphates in soil can damage concrete structures in contact with them, causing expansion, cracking or spalling of the concrete or softening and disintegration. It is also known that certain water-soluble organic substances such as humic acid can retard or even prevent the normal setting and hardening of cement. The presence of clay minerals in concrete is also undesirable as they may expand and contract as they absorb or lose water.

It has now been discovered that soil-containing concrete possessing useful physical properties, for example useful compressive strength at 7 days, can be prepared if part of the cement is replaced by ground granulated blast furnace slag (ggbs) and/or pulverised fuel ash (pfa). The invention seeks to provide such a concrete.

The invention accordingly provides a composition which comprises cement; ground granulated blast furnace slag and/or pulverised fuel ash ; fine aggregate; coarse aggregate; soil; and water which composition, after setting, yields a soil-containing concrete.

The cement is preferably CEMI. When ggbs is used the mixture of cement and ggbs may correspond to CIIIA or CIIIB, preferably CIIIB. The CEMI and ggbs may be added separately to the compositions of the invention. It will be understood that a pre-prepared blend, for example a factory-produced CEMIII, may also be used.

The compositions of the invention generally comprise 300 to 500, preferably 350 - 450kg of concrete, ggbs and/or pfa per cubic metre of concrete.

The ggbs preferably complies with BS EN 15167-1. The pfa preferably complies with BS EN 450-1.

When ggbs is used the proportion of ggbs is generally in accordance with the limits defined in BS8500-2:2006. Generally 50 to 90%, preferably 65 to 70%, most preferably about 70% of cement is replaced by ggbs. When pfa is used generally up to 55% of the cement may be replaced (this limit is defined by BS8500). Preferably 20 to 50%, more preferably 25 to 35%, of the cement is replaced by pfa. Ggbs is preferred. A lower proportion of ggbs and/or pfa may be used in order to increase early strength gain.

The aggregate used in the compositions of the invention is a mixture of fine (generally 0/4) aggregate and coarse aggregate (maximum size 40mm, preferably 20mm). The proportion of fine aggregate in the aggregate mixture is preferably 45-50%: the proportion of coarse aggregate is preferably 55-50%. Part of the fine aggregate may be replaced by glass sand (crushed glass).

The compositions of the invention generally comprise 1100 to 500kg/m ³ of fine aggregate. The compositions of the invention generally comprise at least 10% of coarse aggregate and preferably comprise 600 to 1200kg/m ³ of coarse aggregate.

In the compositions of the invention generally 1 to 60%, preferably 10 to 40%, more preferably 20 to 30%, of the total aggregate (fine plus coarse) is replaced by soil.

Mineral particles in soil can be grouped into five broad classes as shown in the following Table. The size ranges given are in accordance with the UK system of classification.

In determining the classification, particles such as stones, boulders and gravel larger than 2mm are separated from soil material less than 2mm by sieving. The material which passes through a 2mm sieve, termed "fine earth", is then divided into three particle size fractions: sand, silt and clay.

The relative size of the different particle size fractions can be determined by the "mechanical analysis" method which is based on the different rates at which soil particles settle in water. The density of all the soil particles is generally similar. The rate at which they settle is determined principally by their size. A small sample of the fine earth to be classified is dispersed in a measured volume of water. Immediately after dispersion a first sample of measured volume is taken. Five minutes after dispersion a second sample of measured volume is taken. Eight hours after dispersion a third sample of measured volume is taken. The first, second and third samples contain, respectively, sand, silt and clay; silt and clay; and clay. The water in each sample is removed by evaporation and the weight of solid material remaining is determined. The separate weights of sand, silt and clay are then determined by calculation.

Clay content may also be measured using the known methylene blue test.

Soils in the UK can be classified into textural classes based on the Soil Survey of England and Wales size ranges. Figure 1 of the accompanying drawings depicts the resulting soil textural triangle. The soils comprise: sand; loamy sand; sandy loam; sandy silt loam; silt loam; silty clay loam; clay loam; clay loam; sandy clay loam; sandy clay; silty clay; and clay. A more general classification comprises: sands; light loams; medium loams; light silts; medium silts; and clays.

The soil used in the invention preferably has: a clay content of less than about 90%, more preferably less than about 80%; a silt content less than about 90%, more preferably less than about 85%; and/or a sand content of less than about 95%, more preferably less than about 90%, most preferably less than about 85%.

The water/cement ratio in the compositions of the invention is generally 0.4 to 0.8, preferably 0.5 - 0.7, more preferably 0.60 to 0.65. When calculating the w/c ratio the ggbs and/or fly ash are counted as cement, the combination being termed "binder".

The water/binder ratio may be adjusted using, for example, a water-reducing admixture or high water-reducing admixture (plasticizer/superplasticizer).

The term "superplasticizer" as used in this specification and the accompanying claims is to be understood as including both water reducers and superplasticizers as described in the Concrete Admixtures Handbook, Properties Science and Technology, V.S. amachandran, Noyes Publications, 1984.

A water reducer is defined as an additive which reduces the amount of mixing water of concrete for a given workability by typically 5 to 10%. Water reducers include, for example lignosulphonates, hydroxycarboxylic acids, carbohydrates, and other specialized organic compounds, for example glycerol, polyvinyl alcohol, sodium alumino-methyl-siliconate, sulfanilic acid and casein. Superplasticizers belong to a new class of water reducers chemically different from the previous water reducers and capable of reducing water contents by about 30%. The superplasticizers have been broadly classified into four groups: sulphonated naphthalene formaldehyde condensate (SNF) (generally a sodium salt); or sulphonated melamine formaldehyde condensate (SMF); modified lignosulfonates (MLS); and others. More recent superplasticizers include polycarboxylic compounds such as polyacrylates. The superplasticizer is preferably a new generation superplasticizer, for example a copolymer containing polyethylene glycol as graft chain and carboxylic functions in the main chain such as a polycarboxylic ether. Sodium polycarboxylate-polysulphonates and sodium polyacrylates may also be used. Phosphonic acid derivatives may also be used. The amount of superplasticizer required generally depends on the reactivity of the cement. The lower the reactivity the lower the amount of superplasticizer required. In order to reduce the total alkali content the superplasticizer may be used as a calcium rather than a sodium salt.

When the clay content of the soil used in the invention as measured by the methylene blue test is high the effectiveness of a water reducing agent or superplasticizer may be reduced, requiring increased amounts of such admixtures, thereby increasing cost. Soils having a lower clay content as measured by the methylene blue test are therefore preferred.

Other additives may be included in the composition according to the invention, for example, a defoaming agent (e.g. polydimethylsiloxane). These also include silicones in the form of a solution, a solid or preferably in the form of a resin, an oil or an emulsion, preferably in water. More particularly suitable are silicones comprising ( SiO0.5) and (R2SiO) moieties.

In these formulae, the R radicals, which may be the same or different, are preferably hydrogen or an alkyl group of 1 to 8 carbon atoms, the methyl group being preferred. The number of moieties is preferably from 30 to 120.

The amount of such an agent in the final cement is generally at most 5 parts in weight relative to the cement.

The soil-containing concrete preferably has a compressive strength greater than or equal to about lOMpa after 7 days. The compressive strength values refer to concrete which has been sampled, cured and tested in accordance with BS EN 12390-2:2000. The soil-containing concrete according to the invention is preferably not heat-cured, for example by steam curing. The in-situ concrete according to the invention will generally not be subjected to curing at a temperature greater than ambient temperature. The strength of the concrete of the invention depends, inter alia, on the proportion of soil in the concrete: the strength decreases as the proportion of soil increases.

The compositions and concretes according to the invention are intended to be suitable for use in groundworks, mass fill concretes or thick walls. They may also be useful in block making (in which case a lower water/cement ratio is preferably used).

Compositions and concretes according to the invention preferably comprising less than 15%, more preferably 10 to 15%, of soil may be used in the construction of structures having a plurality (preferably two or three) of storeys. The compositions of the invention, preferably those comprising less than 15%, more preferably 10 to 15%, of soil may also be used in the construction of composite structures in which ordinary concrete is used to provide early structural strength, for example as one leaf of a cavity wall, the other leaf comprising the soil-containing composition of the invention. Such structures and composite structures constitute features of the invention.

The compositions of the invention may be prepared using soil at or near the site where they are to be used, thereby reducing the cost of transporting aggregate to the site. The cost of removing excavated soil may also be reduced.

When the compositions are in shaped form, for example as building blocks, such blocks may be used after they have set and without a period of curing.

The invention provides a set concrete obtained from a composition according to the invention; and such a concrete in shaped form.

The invention also provides a substantially dry composition which comprises cement; ground granulated blast furnace slag and/or pulverised fuel ash ; fine aggregate; coarse aggregate; and soil.

The bulk density of the composition of the invention after mixing but before moulding is substantially the same as the density of the set concrete. When the concrete has been poured into place, for example into a mould such as concrete formwork, a concrete vibrator may be used to facilitate release of air from the composition. It is not generally necessary to compress the composition in a mould in order to obtain a set concrete having a 7-day compressive strength of at least lON/mm ² .

It is to be understood that in this specification, including the accompanying claims, unless otherwise specified: The ggbs is a by-product from the iron and steel industry; its compliance as a secondary cementitious material is based on EN 15167: 2006 "ground granulated blast furnace slag for use in concrete, mortar and grout";

Pulverised fuel ash (also known as pulverised fly ash) used in the compositions of the invention should conform to BS EN 450-1;

Percentages are by weight;

Compressive strength values are measured after water curing for 7 days in a tank thermostatically controlled at 20°C±1°C, on standard cube or cylindrical specimens (the preferred specimen is a 100 or 150mm cube). Fresh concrete is sampled in accordance with BS EN 12350-1:2009; specimens for strength tests are made and cured in accordance with BS EN 12390-2:2009; and the compressive strength of test specimens is measured in accordance with BS EN 12390-3:2009.

Slump values are measured in accordance with the test method and equipment described in BS EN 12350-2:2009.

Particle size distribution (between 0.02 μιτι and 2 mm) may be measured using a Malvern MS2000 laser granulometer. Measurement is effected in ethanol. The light source consists of a red He-Ne laser (632 nm) and a blue diode (466 nm). The optical model is that of Mie and the calculation matrix is of the polydisperse type.

The apparatus is checked before each working session by means of a standard sample (Sifraco CIO silica) for which the particle size distribution is known.

Measurements are performed with the following parameters: pump speed 2300rpm and stirrer speed 800rpm. The sample is introduced in order to establish an obscuration between 10 and 20%. Measurement is effected after stabilisation of the obscuration. Ultrasound at 80% is first applied for 1 minute to ensure the de-agglomeration of the sample. After about 30s (for possible air bubbles to clear), a measurement is carried out for 15 s (15000 analysed images). Without emptying the cell, measurement is repeated at least twice to verify the stability of the result and elimination of possible bubbles.

All values given in the description and the specified ranges correspond to average values obtained with ultrasound. The compositions and concretes according to the invention are preferably free, or substantially free of expansion material (anti-shrinkage material), CSA, metakaolin and/or thickening agent.

The compositions and concretes according to the invention are preferably free, or substantially free of the Korean mineral elvan.

In the compositions and concretes according to the invention when the composition comprises ggbs instead of or in association with pfa the coarse aggregate or the fine aggregate is preferably free, or substantially free of slag.

The following non-limiting Example illustrates the invention.

EXAMPLE 1 materials used in Example 1 are as follows.

The amount of soil in each of the two mixes, expressed as a percentage of the total aggregate, was as follows: MIX 1 :11% MIX 2 :20%

In both mixes 12% of the fine aggregate fraction is glass sand (crushed glass).

The soil used in this Example was from the Lafarge site at Long Sutton in the UK and had the following analysis:

Water-soluble sulphate (g/l S0 ₄ ) ¹ : 0.13

Total potential sulphate (%S0 ₄ ) ² : 0.12

Water soluble chloride (%) ³ : 0.01

Acid soluble alkali (% Na ₂ 0) ⁴ : 0.15

The methods used to determine the foregoing values were as follows: 1 T L447 Test 1

2 TRL447 Test 4

3 BS EN 1744-1:1998, clause 7

4 Method based on BS 1881: Part 124: 1998, clause 10.4.

Approximately 45% of the soil had a particle size less than 63μιτι (as determined by sieving). The mixes had the following properties after 7 days curing at 20°C: