Field

The present invention relates to compositions for forming an alkali-activated concrete material and to a method of forming an alkali-activated concrete material. In particular, the present invention relates to compositions and methods that make use of a binder comprising ground granulated blast furnace slag (GGBS) and clay filter cake (CFC). The present invention also relates to the use of the alkali-activated concrete material in construction.

Background

The use of concrete in construction is ubiquitous due to its versatility, high compressive strength and durability. However there are many issues associated with the production of concrete, including for example the destruction of natural resources, the high amount of energy needed in processing and the production of greenhouse gases.

Concrete traditionally comprises a mixture of aggregates and paste. The paste coats the surface of the aggregates and binds them together into a solid mass, i.e. concrete. The paste typically comprises cement and water, which react via a chemical reaction known as hydration. This chemical reaction causes the paste to harden and gain strength.

The manufacturing of cement is believed to account for approximately 7% of CO2 emissions worldwide, as the production of one tonne of cement results in approximately one tonne of CO2. There is an increasing drive to reduce CO2 emissions globally and thus in order to achieve this there is a need to provide viable alternatives to cement.

Geopolymer binders have been proposed as alternatives to cement. Geopolymers are formed by mixing an alumina-silicate precursor with an alkaline solution and may be considered as alkali-activated materials. The development of geopolymer binders is attractive as they can typically provide adequate strength in a very short curing time, whilst maintaining mechanical properties such as durability in the final concrete product.

It is also desirable to make use of construction and demolition wastes, such as brick, ceramic tiles and concrete, when forming alternative concrete and cement products. This potentially reduces the disposal requirements of such waste materials, for example transportation and disposal at landfill sites. One such waste material is clay filter cake (CFC). Clay filter cake is produced by a process including screening, breaking and crushing construction and demolition wastes to extract recycled construction materials. This process includes washing the recycled materials to remove clay and other fine particles. This generates high amounts of clay waste which is typically filter pressed to remove residual water and produce clay filter cake. If the clay filter cake cannot be put to any use, it is disposed of at landfill sites. It is therefore desirable to make use of the clay waste/clay filter cake to remove or reduce the need for such disposal. It would be desirable if one such use was in providing a viable alternative to cement, i.e. in providing a cementitious product. It is an object of aspects of the present invention to provide an alternative to traditional cement and concrete products, for example by providing an alkali-activated concrete material which addresses at least one disadvantage of the prior art, whether identified here or elsewhere, or to provide an alternative to existing alkali-activated concrete materials and methods of preparing them. For example, it may be an aim of the present invention to provide an alkali- activated concrete material comprising waste materials such as clay filter cake (CFC) whilst maintaining acceptable properties for use in construction.

Summary of the Invention

According to an aspect of the present invention, there are provided compositions (including a cementitious composition) for forming an alkali-activated concrete material, a method of forming an alkali-activated concrete material, an alkali-activated concrete material and structures prepared from the alkali-activated concrete material as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and from the description which follows.

According to a first aspect of the present invention, there is provided a cementitious composition for forming an alkali-activated concrete material, the composition comprising a binder and an alkaline activator; wherein the binder comprises ground granulated blast furnace slag (GGBS) and clay filter cake (CFC).

According to a second aspect of the present invention, there is provided a composition for forming an alkali-activated concrete material, the composition comprising a binder, an alkaline activator, and an aggregate; wherein the binder comprises ground granulated blast furnace slag (GGBS) and clay filter cake (CFC).

According to a third aspect of the present invention, there is provided a method of forming an alkali-activated concrete material, the method comprising:

(1) mixing an aggregate, a binder and an alkaline activator to produce a concrete mix; and

(2) curing the concrete mix obtained in step (1); wherein the binder comprises ground granulated blast furnace slag (GGBS) and clay filter cake (CFC). According to a fourth aspect of the present invention, there is provided an alkali-activated concrete material obtained or obtainable by the method of the third aspect of the invention.

According to a fifth aspect of the present invention, there is provided an alkali-activated concrete material comprising an aggregate and a binder; wherein the binder comprises ground granulated blast furnace slag (GGBS) and clay filter cake (CFC) and wherein the alkali- activated concrete material has a compressive strength of at least 10 MPa as measured by compression testing.

According to a sixth aspect of the present invention, there is provided a concrete structure formed from an alkali-activated concrete material according to the fourth or fifth aspect of the invention.

According to a seventh aspect of the present invention, there is provided a use of an alkali- activated concrete material according to the fourth or fifth aspect of the invention in construction.

According to an eighth aspect of the present invention, there is provided a use of a concrete structure according to the sixth aspect of the invention in construction.

The compositions and methods of the present invention provide an alternative to traditional cement and concrete products, such as fired bricks, and result in reduced CO2 emissions, as well as making use of waste products. The alkali-activated concrete material formed by the compositions and methods of the present invention further maintains acceptable mechanical properties, such as high compressive strength, desirable flexural strength, low chloride ion penetrability and/or low water absorption. The use of CFC in the binder makes use of a waste material that would otherwise have to be transported to landfill sites, where space is becoming increasingly limited.

Detailed Description of the Invention Unless otherwise stated, the following terms used in the specification and claims have the meanings set out below.

The first aspect of the present invention relates to a cementitious composition for forming an alkali-activated concrete material.

The second aspect of the present invention relates to a composition for forming an alkali- activated concrete material.

By the term “cementitious composition” we mean a composition that acts as a paste to bind aggregate together into a solid mass, i.e. concrete (which concrete may be formed into a structure such as a brick). The cementitious composition is suitable for forming an alkali- activated concrete material. As will be known by the skilled person, alkali-activation is a chemical reaction between an aluminosilicate or aluminosilicate precursor and an alkaline activator to produce a paste (or cementitious composition) that is capable of setting and hardening within a reasonable curing time period for construction purposes.

Thus, by the term “alkali-activated concrete material” we mean a concrete material comprising aggregate and a paste (or cementitious composition) that has been formed by means of alkali- activation. The compositions of the first and second aspects of the present invention comprise a binder comprising ground granulated blast furnace slag (GGBS) and clay filter cake (CFC). Ground granulated blast furnace slag (GGBS) is a commercially available product that is obtained as a by-product of iron and steel-making. Thus the exact chemical composition of GGBS varies dependent on the composition of the raw materials in the iron or steel production process.

Clay filter cake (CFC) is produced at construction and demolition waste washing plants. Thus the exact chemical composition of CFC varies dependent on the waste washing plants from which it originates.

GGBS and CFC each comprise oxide compounds. GGBS and CFC typically each comprise calcium oxide (CaO), silicon dioxide (S1O2), aluminium oxide (AI2O3) and iron oxide (Fe203). GGBS and CFC may each comprise one or more additional oxide compounds, for example one or more oxide compounds selected from magnesium oxide (MgO), sodium oxide (Na ₂ 0), potassium oxide (K2O), titanium oxide (T1O2), manganese oxide (MnO), copper oxide (CuO), zinc oxide (ZnO), barium oxide (BaO), phosphorus oxide (P2O5), cobalt oxide (C02O3), strontium oxide (SrO) and yttrium oxide (Y2O3). The GGBS and CFC may comprise the same or different oxide compounds. Suitably, the GGBS may have a calcium oxide content of up to 50 wt%, suitably up to 55 wt% or 60 wt%, for example up to 70 wt%. Suitably, the GGBS may have a calcium oxide content of at least 10 wt%, suitably at least 15 wt% or 20 wt%, for example at least 30 wt% or at least

35 wt%. Suitably, the GGBS may have a calcium oxide content of from 10 to 70 wt%, for example from 15 wt% to 60 wt% or from 20 wt% to 55 wt% or from 35 wt% to 55 wt%. Suitably, the GGBS may have a silicon dioxide content of up to 50 wt%, suitably up to 55 wt% or 60 wt%, for example up to 70 wt%. Suitably, the GGBS may have a silicon dioxide content of at least 10 wt%, suitably at least 15 wt% or 20 wt%, for example at least 30 wt% or at least

35 wt%. Suitably, the GGBS may have a silicon dioxide content of from 10 to 70 wt%, for example from 15 wt% to 60 wt% or from 20 wt% to 55 wt% or from 35 wt% to 55 wt%. Suitably, the GGBS content comprises a majority of calcium oxide and silicon dioxide, for example the GBBS content may comprise more than 50 wt% calcium oxide and silicon dioxide (i.e. more than 50 wt% of the GGBS is comprised of calcium oxide and silicon dioxide),, such as over 60 wt% or over 70 wt% calcium oxide and silicon dioxide. Suitably, the GGBS may comprise over 80 wt% calcium oxide and silicon dioxide, for example over 90 wt% calcium oxide and silicon dioxide.

Suitably, the GGBS may have an aluminium oxide content of up to 10 wt%, suitably up to 15 wt%. Suitably, the GGBS may have an aluminium oxide content of at least 1 wt%, suitably at least 3 wt%, suitably at least 5 wt%. Suitably, the GGBS may have an aluminium oxide content of from 1 to 15 wt%, for example from 3 wt% to 10 wt%.

Suitably, the GGBS may have an iron oxide content of up to 3 wt%, suitably up to 5 wt%. Suitably, the GGBS may have an iron oxide content of at least 0.01 wt%, for example at least 0.1 wt% or at least 0.5 wt%. Suitably, the GGBS may have an iron oxide content of from 0.01 to 5 wt%, for example from 0.5 wt% to 3 wt%. Suitably, the GGBS may have a magnesium oxide content of up to 10 wt%. Suitably, the GGBS may have a magnesium oxide content of at least 0.5 wt%. Suitably, the GGBS may have a magnesium oxide content from 0.5 wt% to 10 wt%.

Suitably, the GGBS may have a potassium oxide content of up to 10 wt%. Suitably, the GGBS may have a potassium oxide content of at least 0.5 wt%. Suitably, the GGBS may have a potassium oxide content from 0.5 wt% to 10 wt%.

Suitably, the GGBS may have a sodium oxide content of up to 10 wt%. Suitably, the GGBS may have a sodium oxide content of at least 0.5 wt%. Suitably, the GGBS may have a sodium oxide content of from 0.5 wt% to 10 wt%.

GGBS is suitably prepared commercially by quenching molten iron slag from a blast furnace and grinding the quenched product into a fine powder. Suitably, the GGBS comprises fine particles. Suitably, the GGBS comprises fine particles with a mean diameter of from 1 to 20 mhi. Suitably, the GGBS comprises fine particles with a median particle size distribution (dso) of from 1 to 20 mhi.

Methods of determining the mean particle diameter and particle size distribution of particles are well-known to those skilled in the art. For example the mean particle diameter may be determined using a mesh sieve. The particle size distribution may be determined using a laser particle size analyser. Suitably, the GGBS has a specific surface area (SSA) determined by the Blaine air- permeability method of from 2000 to 8000 cm ² /g and/or a specific gravity of from 1 to 5. Methods of determining specific surface area and specific gravity are well-known to those skilled in the art. Suitably, the specific surface area may be determined according to a method of standard BS EN 196-6:2018. The specific gravity may be determined using a pyknometer method of BS EN ISO 11508:2014.

Suitably, the CFC may have a calcium oxide content of up to 40 wt%, suitably up to 50 wt% or 55 wt%, for example up to 60 wt%. Suitably, the CFC may have a calcium oxide content of at least 1 wt%, suitably at least 5 wt% or 10 wt%, for example at least 15 wt%. Suitably, the CFC may have a calcium oxide content of from 1 to 60 wt%, for example from 5 wt% to 60 wt% or from 10 wt% to 55 wt% or from 15 wt% to 55 wt%.

Suitably, the CFC may have a silicon dioxide content of up to 60 wt%, suitably up to 70 wt% or 75 wt%, for example up to 80 wt%. Suitably, the CFC may have a silicon dioxide content of from 10 wt%, suitably from 15 wt% or 20 wt%, for example from 30 wt% or from 35 wt%. Suitably, the CFC may have a silicon dioxide content of from 10 to 80 wt%, for example from 15 wt% to 60 wt% or from 20 wt% to 55 wt% or from 35 wt% to 55 wt%, for example from 40 wt% to 50 wt%.

Suitably, the CFC content comprises a majority of calcium oxide and silicon dioxide, for example the CFC content may comprise more than 50 wt% of calcium oxide and silicon dioxide (i.e. more than 50 wt% of the CFC is comprised of calcium oxide and silicon dioxide), such as over 60 wt% or over 70 wt%. Suitably, the CFC content may comprise more than 80 wt% calcium oxide and silicon dioxide.

Suitably, the CFC may have an aluminium oxide content of up to 10 wt%, suitably up to 15 wt%. Suitably, the CFC may have an aluminium oxide content of at least 1 wt%, such as of at least 3 wt%, suitably at least 5 wt%. Suitably, the CFC may have an aluminium oxide content of from 1 to 15 wt%, such as from 3 to 15 wt%, for example from 5 wt% to 10 wt%.

Suitably, the CFC may have an iron oxide content of up to 10 wt%, suitably up to 15 wt%. Suitably, the CFC may have an iron oxide content of at least 1 wt%, suitably at least 3 wt%. Suitably, the CFC may have an iron oxide content of from 1 to 15 wt%, for example from 3 wt% to 10 wt%.

Suitably, the CFC may have a magnesium oxide content of up to 10 wt%. Suitably, the CFC may have a magnesium oxide content of at least 0.5 wt%. Suitably, the CFC may have a magnesium oxide content of from 0.5 wt% to 10 wt%. Suitably, the CFC may have a potassium oxide content of up to 10 wt%. Suitably, the CFC may have a potassium oxide content of at least 0.5 wt%. Suitably, the CFC may have a potassium oxide content of from 0.5 wt% to 10 wt%.

Suitably, the CFC may have a sodium oxide content of up to 10 wt%. Suitably, the CFC may have a sodium oxide content of at least 0.5 wt%. Suitably, the CFC may have a sodium oxide content of from 0.5 wt% to 10 wt%.

Suitably the CFC comprises particles with a mean diameter of from 1 to 100 mhi. Suitably the CFC comprises particles with a particle size distribution (dso) of from 1 to 100 mhi.

Suitably, the CFC has a specific surface area (SSA) by the Blaine air-permeability method of from 500 to 8000 cm ² /g and/or a specific gravity of from 1 to 5.

Typically, the CFC is supplied comprising water, for example having a water content of from 1 wt% to 70 wt%. Suitably, the CFC is dried prior to use in the present invention to substantially remove any water present, for example to provide CFC having a water content of from 0 wt% to 5 wt%. For example the CFC may be dried in an oven. Suitably the CFC is dried prior to use so as to be completely free of water.

Suitably, the binder consists of, or consists essentially of, GGBS and CFC.

Suitably, the binder comprises at least 10 wt%, for example at least 20 wt% or 30 wt% GGBS. Suitably, the binder comprises up to 70 wt%, for example up to 60 wt% or 50 wt% GGBS. Suitably, the binder comprises from 30 wt% to 70 wt%, for example from 40 wt% to 60 wt%, GGBS. For example, the binder may comprise about 50 wt% GGBS.

Suitably, the binder comprises at least 10 wt%, for example at least 20 wt% or 30 wt% CFC. Suitably, the binder comprises up to 70 wt%, for example up to 60 wt% or 50 wt% CFC. Suitably, the binder comprises from 30 wt% to 70 wt%, for example from 40 wt% to 60 wt%, GGBS. For example, the binder may comprise about 50 wt% CFC. Suitably, the binder may comprise from 30 wt% to 70 wt% of GGBS and from 30 wt% to 70 wt% of CFC. Suitably, the binder may comprise from 40 wt% to 60 wt% of GGBS and from 40 wt% to 60 wt% of CFC. For example, the binder may comprise about 50 wt% GGBS and about 50 wt% CFC.

Without being bound by any theory, it is believed that a hydration reaction occurs between the oxides in the GGBS and CFC and water to form a gel or paste that hardens and gains strength. The compositions of the first and second aspects of the present invention comprise an alkaline activator.

By the term “alkaline activator” we mean an alkaline compound that can react with an aluminosilicate or aluminosilicate precursor to produce a paste (or cementitious composition) that is capable of setting and hardening within a reasonable curing time period for construction purposes.

Suitably, the alkaline activator comprises sodium silicate (Na ₂ SiC>3), sodium hydroxide (NaOH) or combinations thereof.

Suitably, the alkaline activator comprises sodium silicate and sodium hydroxide. Suitably the weight ratio of sodium silicate to sodium hydroxide in the alkaline activator is from 1 :2 to 3:1 , for example from 1 :1 to 2.5:1 , such as about 2:1 .

Suitably, the weight ratio of alkaline activator to binder in the compositions of the present invention is from 1 :10 to 2:1 , for example from 1 :5 to 1 :1 , for example from 1 :3 to 1 :1 , for example from 1 :2.5 to 1 :1 , such as about 1 :2. Suitably, the weight ratio of alkaline activator to binder is at least 0.4. Suitably, the weight ratio of alkaline activator to binder is less than 1 .

Suitably, the alkaline activator is present as a solution, such as an aqueous solution. The alkaline activator may therefore alternatively be referred to as an “alkaline activating solution”. Suitably, the alkaline activator comprises a solvent, such as water.

Suitably, the weight ratio of water to sodium silicate and/or sodium hydroxide in the alkaline activator is from 1 :100 to 1 :2, for example from 1 :20 to 1 :5, such as about 1 :10.

Suitably, the alkaline activator comprises an aqueous solution of sodium silicate. Such a solution may be prepared by dissolving silicon dioxide and sodium oxide in water (for example distilled water). Suitably the sodium silicate solution may comprise from 25 wt% to 40 wt% silicon dioxide, from 5 to 30 wt% sodium oxide and from 30 to 80 wt% water. Suitably, the alkaline activator comprises an aqueous solution of sodium hydroxide. Such a solution may be prepared by dissolving sodium hydroxide (for example in the form of pellets) in water (for example distilled water). The aqueous sodium hydroxide solution may be of any suitable concentration, such as a concentration in the range of 1 to 16 M, for example of 2 to 5 M, such as about 4 M. The composition of the second aspect of the invention comprises an aggregate. Suitably, the aggregate comprises sand, gravel, limestone, sandstone, chalk, soil or combinations thereof. Suitably, the aggregate is a fine aggregate. By the term “fine aggregate” we mean that the aggregate comprises particles with a diameter of less than 20 mm. The particle size may be determined using the Particle Size Distribution test according to BS EN 933-1 :1997). For example, the aggregate may comprise particles with a diameter of less than 4 mm. Suitably, the aggregate may comprise particles with a diameter of less than 0.01 mm.

Suitably, the weight ratio of aggregate to binder in the composition of the second aspect may be from 1 :2 to 4:1 , for example from 1 :1 to 3:1 , such as about 2:1.

Suitably, the aggregate comprises sand. Suitably, the weight ratio of sand to binder in the composition of the second aspect may be from 1 :2 to 4:1 , for example from 1 :1 to 3:1 , such as about 2:1.

Suitably, the composition of the second aspect may comprise a binder, an alkaline activator, and an aggregate; wherein the binder comprises from 30 to 70 wt% ground granulated blast furnace slag (GGBS) and 30 to 70 wt% clay filter cake (CFC); wherein the weight ratio of aggregate to binder is from 1 :2 to 4:1; wherein the weight ratio of alkaline activator to binder is from 1 :10 to 2:1 and wherein the alkaline activator comprises sodium silicate and/or sodium hydroxide.

The composition of the second aspect may comprise a binder, an alkaline activator, and sand; wherein the binder comprises about 50 wt% ground granulated blast furnace slag (GGBS) and about 50 wt% clay filter cake (CFC); wherein the weight ratio of sand to binder is about 2:1 ; wherein the weight ratio of alkaline activator to binder is about 1 :2; wherein the alkaline activator comprises sodium silicate and sodium hydroxide and wherein the weight ratio of sodium silicate to sodium hydroxide is about 2:1.

The first and second aspects of the present invention provide compositions that are useful for forming an alkali-activated concrete material. The alkali-activated concrete material may be made by any suitable method.

The third aspect of the invention provides a method of forming an alkali-activated concrete material, the method comprising:

(1) mixing an aggregate, a binder and an alkaline activator to produce a concrete mix; and (2) curing the concrete mix obtained in step (1); wherein the binder comprises ground granulated blast furnace slag (GGBS) and clay filter cake (CFC). References and preferences set out above in relation to the aggregate, binder, alkaline activator, water, GGBS and CFC in relation to the first and second aspects of the invention apply equally to the third aspect of the invention.

Suitably, the steps of the method of the third aspect are carried out in the order of step (1) followed by step (2).

In step (1) the aggregate, binder and an alkaline activator are mixed to produce a concrete mix. Suitably, in step (1), water is present, for example by means of the use of an aqueous solution of the alkali-activator, and/or by means of addition of additional water. Thus, step (1) may comprise mixing an aggregate, a binder, an alkaline activator and water to produce a concrete mix.

In some embodiments, in step (1), the aggregate and binder are first mixed together and the alkaline activator is then added to the resultant mixture. For example, the CFC and GGBS may be first mixed together to produce a substantially dry binder, which is then mixed with an aggregate. Alternatively, the CFC, GGBS and aggregate may all be mixed together in one step. The concrete mix is in a flowable state following the mixing of the aforementioned components.

Suitably, the binder is prepared by mixing or blending the CFC and GGBS. Suitably the binder is formed as a substantially dry binder.

By a “substantially dry binder” we mean that the water content of the binder is from 0 wt% to 3 wt%. Suitably, the substantially dry binder may be completely free of water.

Mixing may be accomplished by any suitable means. Suitably, once combined, the binder and aggregate are mixed using a mechanical mixer. Suitably the binder and aggregate may be mixed for up to 20 minutes, for example up to 15 minutes or up to 10 minutes. Suitably the binder and aggregate may be mixed for at least 30 seconds, suitably at least 1 minute. Suitably the binder and aggregate may be mixed for 2 to 5 minutes.

In step (1) the binder and aggregate are mixed with an alkaline activator, which alkaline activator may be present as an aqueous solution. Further, in step (1), additional water may be added, i.e. in addition to any water present in the aqueous solution of the alkaline activator.

In step (1), the alkaline activator and optionally additional water may be added to the aforementioned pre-prepared aggregate and binder mix.

In step (1), the binder, aggregate, alkaline activator and optional additional water may be added together and mixed in a single step. For example, the CFC and GGBS may be combined and mixed with the aggregate, alkaline activator and optionally additional water. For example, the CFC and GGBS may be combined and mixed with sand, the alkaline activator and optionally additional water.

The presence of water is believed to ensure the hydrolysis of any dissolved Al ³⁺ , Ca ²⁺ and Si ⁴⁺ ions and dissolve solid particles.

Suitably, the binder, aggregate, alkaline activator and optional additional water are combined and mixed in a mechanical mixer. Suitably the binder, aggregate, alkaline activator and optional additional water are mixed for up to 20 minutes, for example up to 15 minutes or up to 10 minutes. Suitably the binder, aggregate, alkaline activator and optional additional water are combined and mixed for at least 30 seconds, suitably at least 1 minute. Suitably the binder, aggregate, alkaline activator and optional additional water are combined and mixed for 2 to 5 minutes.

The concrete mix obtained in step (1) may be placed in a mould of a desired shape to form a structure. For example, the concrete mix obtained in step (1) may be placed in a prism shaped mould to form a desired prism structure. Suitably the mould may have dimensions of 40 ^c 40 ^c 160 mm according to BS EN 196-1. Suitably the mould may be sealed once the concrete mix has been placed therein. Suitably the mould is prepared from steel or wood and sealed using a plastic cover.

Suitably, the concrete mix obtained in step (1) is left in the mould in air at room temperature for up to 24 hours. During this time, a geopolymerisation reaction occurs and the concrete mix undergoes a transition from its flowable state to a solid state. In other words, the concrete mix sets in the desired shape of the mould by means of the geopolymerisation reaction. At this stage however the concrete mix is not cured. Suitably the concrete mix obtained in step (1) hardens or sets to conform to the shape of the mould such that it retains this shape when removed from the mould, such that this step may be referred to as a “setting step”. Thus, step

(1) of the method may include a setting step.

The concrete mix obtained in step (1) is cured, for example after the setting step referred to above. Thus, the method of the third aspect of the invention comprises the step (2) of curing the concrete mix obtained in step (1). Suitably, in step (2), the concrete mix obtained in step (1) is cured for up to 28 days. Suitably, in step (2), the concrete mix obtained in step (1) is cured for at least 3 days. Suitably, in step

(2), the concrete mix obtained in step (1) is cured for from 3 days to 28 days. In some embodiments, in step (2), the concrete mix obtained in step (1) is cured for 7 days. Step (2) of the method of the third aspect, may comprise curing the concrete mix obtained in step (1) in the presence of air and/or water. Step (2) may be conducted after a setting step as discussed above.

Step (2) of the method of the third aspect may comprise curing the concrete mix obtained in step (1) in the presence of air. This may alternatively be referred to as “air curing”. Suitably the concrete mix obtained in step (1) may be cured in air at a temperature of from 18 to 25°C, for example 20°C. This temperature may also be referred to as “room temperature” or “ambient temperature”.

When the setting step has been conducted, the concrete mix obtained in step (1) may remain in the mould (after the setting step) for curing in air. Alternatively, the concrete mix obtained in step (1) may be removed from the mould for curing in air.

Step (2) of the method of the third aspect, may comprise curing the concrete mix obtained in step (1) in the presence of water. This may alternatively be referred to as “water curing”. Suitably, when the setting step has been conducted, the concrete mix obtained in step (1) may be removed from the mould for curing in water. Suitably, the concrete mix obtained in step (1), for example after the setting step, may be placed in water (such as in a water tank) at a suitable temperature. Suitably, the concrete mix obtained in step (1), for example after the setting step, may be fully immersed in water (such as in a water tank).

In some embodiments the water used for curing has a temperature of from 18 to 25°C. Suitably, the water used for curing may have a temperature of 20°C. Thus, step (2) of the method of the third aspect, may comprise curing the concrete mix obtained in step (1) in the presence of water at a temperature of from 18 to 25°C, for example at 20°C.

In some embodiments the water used for curing may have an elevated temperature. This may alternatively be referred to as “hydrothermal curing”. In some embodiments the water may have a temperature of 30°C or above, for example of 40°C and above. In some embodiments the water has a temperature of about 50°C. In some embodiments the water has a temperature of up to 50°C, for example up to 60°C or up to 70°C. In some embodiments the water has a temperature of up to 90°C. For example, the water may have a temperature of from 30°C to 90°C. Thus, step (2) of the method of the third aspect may comprise curing the concrete mix obtained in step (1) in the presence of water at a temperature of from 30 to 90°C.

Suitably, the concrete mix obtained in step (1) may be cured using one method or a combination of methods. In some embodiments the concrete mix obtained in step (1) is air cured and then water cured at ambient temperature. In some embodiments the concrete mix obtained in step (1) is air cured and then water cured at an elevated temperature (for example hydrothermally cured). In some embodiments the concrete mix obtained in step (1) is water cured at ambient temperature and then air cured. In some embodiments the concrete mix obtained in step (1) is water cured at an elevated temperature (i.e. hydrothermally cured) and then air cured. In some embodiments the concrete mix obtained in step (1) is water cured at ambient temperature and then water cured at an elevated temperature (i.e. hydrothermally cured). In some embodiments the concrete mix obtained in step (1) is water cured at an elevated temperature (i.e. hydrothermally cured) and then water cured at ambient temperature.

In some embodiments the concrete mix obtained in step (1) is water cured at an elevated temperature (i.e. hydrothermally cured) for 2 days and then air cured for 5, 12 or 26 days. In some embodiments the concrete mix obtained in step (1) is water cured at an elevated temperature (i.e. hydrothermally cured) for 2 days and then water cured at ambient temperature for 5, 12 or 26 days.

The method of the third aspect of the present invention may further comprise the step of forming the concrete mix into a concrete structure. Suitably, this step comprises casting the concrete mix in to the shape of the desired structure. A fourth aspect of the present invention provides an alkali-activated concrete material obtained or obtainable by the method of the third aspect of the invention.

A fifth aspect of the present invention provides an alkali-activated concrete material comprising an aggregate and a binder, wherein the binder comprises ground granulated blast furnace slag (GGBS) and clay filter cake (CFC) and wherein the alkali-activated concrete material has a compressive strength of at least 10 MPa as measured by compression testing. The alkali- activated concrete material, aggregate and binder are as described in relation to the first and second aspects.

Suitable methods of determining the compressive strength will be known to those skilled in the art. For example the compression strength may be determined by a method according to BS EN 196-1.

The alkali-activated concrete material of the present invention suitably has a compressive strength of at least 10 MPa. In some embodiments the alkali-activated concrete material has a compressive strength of at least 20 MPa, suitably of at least 30 MPa. In some embodiments the alkali-activated concrete material has a compressive strength of at least 40 MPa, for example at least 50 MPa. Suitably, the alkali-activated concrete material has a compressive strength of up to 60 MPa, for example up to 70 MPa. Suitably, the alkali-activated concrete material has a compressive strength of from 10 MPa to 70 MPa. Compressive strength is the maximum compressive stress that, under a gradually applied load, a given solid material can sustain without fracture. Suitably, the alkali-activated concrete material of the present invention can be classified according to BS 3921 :1985:

1) class A when the compressive strength is greater than 70 MPa; and 2) class B when the compressive strength is from 50 MPa to 70 MPa.

In some embodiments the alkali-activated concrete material of the present invention is classified as Class A or Class B.

Alternatively the alkali-activated concrete material of the present invention may be classified as a common brick. Suitably, the alkali-activated material has a compressive strength of from 20 MPa to 50 MPa.

Suitably, the alkali-activated concrete material of the present invention has a flexural strength of at least 0.5 MPa, for example of at least 1 MPa or at least 2 MPa. In some embodiments the alkali-activated concrete material has a flexural strength of at least 3 MPa, suitably at least 4 MPa, for example at least 5 MPa or at least 10 MPa. Suitably, the alkali-activated concrete material has a flexural strength of from 0.5 MPa to 10 MPa.

Suitable methods of determining the flexural strength will be known to those skilled in the art. For example the flexural strength may be determined by a method according to BS EN 196-1.

Suitably, the alkali-activated concrete material has an acceptable chloride ion penetrability, for example a moderate or low chloride ion penetrability. The chloride ion penetrability is suitably considered as a method to evaluate the durability of the material. Suitably, chloride ion penetrability may be determined by surface electrical resistivity testing. For example the surface electrical resistivity results may be compared with a chloride penetration classification, for example as published by AASHTO T 358. For example the skilled person may consider that a surface resistivity of about 15 kQ cm represents a moderate chloride ion penetrability and that a surface resistivity of about 25 kQ cm represents a low chloride ion penetrability. Suitably, the higher the surface resistivity the lower the chloride ion penetrability.

Suitably, the alkali-activated concrete material has a surface resistivity of more than 10 kQ cm, suitably more than 20 kQ cm, for example more than 30 kQ cm. In some embodiments the alkali-activated concrete material has a surface resistivity of more than 40 kQ cm, for example more than 50 kQ cm.

Suitably, the alkali-activated material has an acceptable water absorption rate, for example a moderate or low water absorption rate. A low water absorption rate provides better resistance to damage by freezing. Suitably, the alkali-activated material has a water absorption rate of less than 10%, for example less than 5%. Suitably, the alkali-activated material has a water absorption rate of less than 4%, for example less than 3%.

Suitably, the water absorption rate may be determined according to a method of BS EN 771 - 1 :2003.

A sixth aspect of the present invention provides a concrete structure formed from an alkali- activated concrete material according to the fourth or fifth aspect of the present invention.

Any desirable structure may be formed, such as a brick, block, pillar or column. Suitably the structure is a brick. A seventh aspect of the present invention provides the use of an alkali-activated concrete material according to the fourth or fifth aspect of the present invention in construction.

An eighth aspect of the present invention provides the use of a concrete structure according to the sixth aspect of the present invention in construction.

For a better understanding of the invention, and to show how exemplary embodiments of the same may be carried into effect, reference will be made, by way of example only, to the accompanying diagrammatic Figures, in which:

Figure 1 shows the compressive strength of alkali-activated bricks comprising different binder ratios over a range of curing methods.

Figure 2 shows the compressive strength of alkali-activated bricks comprising different sand to binder ratios over a range of curing methods.

Figure 3 shows the compressive strength of alkali-activated bricks comprising different alkaline activator to binder ratios over a range of curing methods.

Figure 4 shows the compressive strength of alkali-activated bricks comprising different Na ₂ SiC>3 to NaOH ratios over a range of curing methods. Figure 5 shows the compressive strength of alkali-activated bricks comprising 50 wt% CFC and 50 wt% GGBS over a range of curing methods.

Figure 6 shows the flexural strength of alkali-activated bricks comprising 50 wt% CFC and 50 wt% GGBS over a range of curing methods.

Figure 7 shows the surface resistivity of alkali-activated bricks comprising 50 wt% CFC and 50 wt% GGBS over a range of curing times in water at a temperature of 20°C. Figure 8 shows the water absorption of alkali-activated bricks comprising 50 wt% CFC and 50 wt% GGBS over a range of curing times in water at a temperature of 20°C.

Figure 9 shows SEM micrographs of the alkali-activated paste comprising 50 wt% CFC and 50 wt% GGBS after 3, 7 and 28 days of air curing. Figure 10 shows SEM micrographs of the alkali-activated paste comprising 50 wt% CFC and 50 wt% GGBS after 3, 7 and 28 days of water curing.

Figure 11 shows the compressive strength of alkali-activated bricks comprising 50 wt% CFC and 50 wt% GGBS over a range of curing methods.

Figure 12 shows the compressive strength of alkali-activated bricks comprising GGBS, metakaolin and fly ash.

Examples

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

The following materials were used in the examples:

GGBS: commercially available product that can be obtained from different suppliers within the UK. The GGBS used in the present examples was obtained from Hanson Heidelberg Cement Group, Scunthorpe, UK.

CFC: commercially available product that can obtained from different suppliers within the UK. The CFC used in the present examples was obtained from CCC Waste Management, Kirkby, UK. Table 1 shows the composition of GGBS and CFC used in the following examples. Table 2 shows the physical properties of the GGBS and CFC used in the following examples.

Table 1. Composition of the binder materials

Table 2: Physical properties of the binder materials

Aggregate: Normal building sand (Tarmac) having a specific gravity of 2.62 with a particle size of from 0.01 to 10 mm.

Alkaline activator: sodium silicate solution (Na ₂ SiC>3) and sodium hydroxide (NaOH) solution. Sodium hydroxide was used at a concentration of 4M. The Na ₂ SiC>3 solution consisted of 32.75% Si0 ₂ , 15.50% Na ₂ 0, and 51.75% H ₂ 0, by weight.

Water: tap water supplied by United Utilities. Tests were conducted as follows:

Compressive strength

Compression testing was conducted in accordance with BS EN 196-1. Three specimens of dimensions 40 ^c 40 ^c 160 mm, were prepared for each mixing proportion, curing age and curing method. Each specimen was broken into two halves using three point loading of the prism samples and averages of six halves were taken to represent the final values for compressive strength.

Flexural Strength Three prisms specimen of dimensions 40 ^c 40 ^c 160 mm. The flexural strength of the alkali- activated brick was determined by three point loading of the prism specimens and averages of the three samples were taken to represent the final values for flexural strength according to BS EN 196-1. Surface Electrical Resistivity

This test was conducted to assess the chloride penetration probability of the developed NAAUB because it is directly linked to the likelihood of corrosion due to chloride diffusion. This test was performed using a Resipod Proceq surface resistivity meter that operates on the Wenner probe principle, whereby electrical resistivity is measured according to AASHTO T 358. During this test, three cylinders with a height of 200 mm and a diameter of 100 mm were prepared. For each sample, 8 readings were obtained and the averages of 24 readings were taken to represent the final values for surface electrical resistivity. To ensure consistent measurements for all the samples, they were in the condition of saturated surface dry at the time of testing.

Water Absorption Test

The water absorption test was conducted for the brick specimens according to BS EN 771 - 1 :2003. Ten bricks were subjected to water absorption test and the mean % water absorption determined.

Microstructural Analysis

Scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) testing was used for evaluating the morphology of each of the binder materials, along with the morphology and the atomic changes in elemental composition of the paste. This testing was conducted using an EDX Oxford Inca x-act detector, an FEI SEM model Inspect S and a Quanta 200 with an accelerating voltage of 5-20 kV. In order to increase the visibility of the samples, the samples were coated with a layer of gold using a sputter coater before starting the SEM/EDS testing.

Example 1

CFC was firstly dried in an oven for 24 hours at 105°C and manually crushed using a hammer. The crushed CFC was then ground using a pestle and mortar grinder for 3 minutes to form a fine powder.

Sand (1050 g), CFC (262.5 g) and GGBS (262.5 g) were mixed together for 3 minutes, and then a liquid mixture of NaOH (70 g), Na ₂ Si03 (140 g) and water (52.5 g) was added to the mix and mixed for another 3 minutes. The mixture was cast inside the steel prism moulds with dimensions of 160mm x 40mm x 40mm and compacted by tamping rod according to BS EN 196-1 , which requires the casting to be in two layers with compaction of 25 tamps for each layer.

The prisms were demoulded after 24 hours from the start of the casting process . The samples were cured by three possible different methods as follows:

• air curing: by keeping the samples on a shelf in the lab at a temperature of from 18 to 25°C.

• water curing: by fully immersing the samples in water in a water tank in the lab at a temperature of 20°C.

• water/hydrothermal curing: by fully immersing the samples in water in a water bath at a temperature of 50°C.

This method produced a prism/brick having binder proportions of 50 wt% CFC and 50 wt% GGBS (hereinafter CF50) and the compressive strength for the air and water (20°C) cured materials is shown in Figure 1.

This same method was repeated for the different wt% of GGBS and CFC in the binder as outlined in Table 3.

Table 3. Mixing proportion of the binder materials

For evaluating the performance of the alkali-activated prism/brick under different curing conditions, samples were cured either at air (A) or immersed in water (W) with an average temperature of 20±2°C.

As can be seen in Figure 1 , alkali-activated prisms/bricks comprising a binder comprising GGBS and CFC in different ratios show good compressive strength using either air or water curing. Example 2

Further experiments were performed to investigate different sand to binder (S/B) weight ratios, activator to binder (A/B) weight ratios and the Na ₂ SiC>3 to NaOH weight ratios, with the preparation method as described above. A compressive strength test was conducted for evaluating each parameter on the performance of the alkali-activated brick.

Sand to Binder Ratio

Three different sand to binder weight ratios were investigated for compressive strength after 7, 14 and 28 days of both air and water (20°C) curing. The sand to binder weight ratios used were 1 :1 , 2:1 and 3:1 denoted as S1 , S2 and S3, respectively. The alkaline activator to binder weight ratio, the water to binder weight ratio and the Na ₂ SiC>3 to NaOH weight ratio were fixed as 0.4:1 , 0.1 :1 and 2:1 , respectively. The binder composition CF50 was used. The results for this are shown in Figure 2.

As can be seen in Figure 2, all alkali-activated bricks with a sand to binder weight ratio according to the present invention showed good compressive strength.

Alkali Activators to Binder Ratio

Three different alkaline activator to binder weight ratios were investigated for compressive strength after 7, 14 and 28 days of both air and water curing. Alkaline activator to binder weight ratios of 0.4:1 , 0.5:1 and 0.6:1 denoted as 0.4, 0.5 and 0.6 respectively, were used. The sand to binder weight ratio, the water to binder weight ratio and the Na ₂ SiC>3 to NaOH weight ratio were fixed as 2:1 , 0.1 :1 and 2:1 , respectively. The binder composition CF50 was used. The results are shown in Figure 3.

As can be seen in Figure 3, all alkali-activated bricks with alkaline activator to binder weight ratios according to the present invention were found to have good compressive strength. Na ₂ Si0 ₃ to A/a OH Ratio

Four different Na ₂ Si03 to NaOH weight ratios were tested for compressive strength after 7, 14 and 28 days of both air and water curing. Na ₂ Si03 to NaOH weight ratios of 0.5:1 , 1 :1 , 2:1 and 3:1 , denoted as 0.5, 1 , 2 and 3, respectively, were used. The alkaline activator to binder weight ratio, the water to binder weight ratio and the sand to binder weight ratio were fixed as 0.4:1 , 0.1 :1 and 2:1 , respectively. The binder composition CF50 was used. The results for this are shown in Figure 4. As can be seen in Figure 4, all alkali-activated bricks with Na ₂ Si03 to NaOH weight ratios according to the present invention were found to have good compressive strength.

Example 3

Mechanical and Durability Performance Alkali-activated bricks were formed as follows:

Table 4. Parameters for performance testing

Alkali-activated bricks according to Table 4 were cured immersed in water (NAAUB-W) or in air (NAAUB-A) with an average temperature of 20±2°C for up to 28 days. Measurements according to the tests described above were taken at 3, 7, 14 and 28 days.

As can be seen in Figure 5, the alkali-activated bricks according to the present invention were found to have good compressive strength over a range of curing conditions and times.As can be seen in Figure 6, the alkali-activated bricks according to the present invention were found to have good flexural strength over a range of curing conditions and times. As can be seen in Figure 7, the alkali-activated bricks according to the present invention were found to have moderate to low chloride ion penetrability over a range of curing times in water at a temperature of 20°C.

As can be seen in Figure 8, the alkali-activated bricks according to the present invention have a low water absorption rate over a range of curing times in water at a temperature of 20°C. As can be seen in Figures 9 and 10, SEM micrographs show that no intact powder particles of binder materials were detected; the particles of the CFC and GGBS, were transformed into hydration products due to a successful geopolymerisation reaction. It can be seen from Figures 9 and 10 that there is no noticeable difference in the SEM images of the alkali- activated brick paste cured in air or in water, indicating the high durability of the developed binder under different curing conditions.

Example 4 Curing Conditions

Alkali-activated bricks/prisms were formed under a variety of curing conditions according to the method of the present invention, as follows:

H50 7, 14 or 28 days in water at 50°C (hydrothermally cured)

HA50 2 days in water at 50°C (hydrothermally cured) followed by 5, 12 or 26 days in air at room temperature (air cured) resulting in a total curing time of 7, 14 or 28 days, respectively.

HW 2 days in water at 50°C (hydrothermally cured) followed by 5, 12 or 26 days water at room temperature (water cured) resulting in a total curing time of 7, 14 or 28 days, respectively.

A 7, 14 or 28 days in air at room temperature (air cured)

W 7, 14 or 28 days in water at room temperature (water cured)

The alkali-activated bricks were prepared according to the method described for CF50 above.

As can be seen in Figure 11 , alkali-activated bricks according to the present invention showed good compressive strength over all curing conditions. Example 5

Clay filter cake (CFC) waste was blended with different materials to produce a binder for an alkali-activated brick. The different materials were: ground granulated blast furnace slag (GGBS), metakaolin (MK) and fly ash (PFA). In order to evaluate the effect of the alkali- activated bricks, the compressive strength test after 7 days of different curing methods was evaluated. The mixing proportions of the produced bricks are summarised in Table 5. The results of the compressive strength tests are displayed in Figure 12. Table 5. Comparison of bricks

As shown in Figure 12, the binder of the present invention comprising 50 wt% GGBS and 50 wt% CFC showed considerably higher performance than the comparative binders for all curing methods.

Although a few preferred embodiments have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims.

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 term “consisting essentially of or “consists essentially of” means including the components specified but excluding other components except for materials present as impurities, unavoidable materials present as a result of processes used to provide the components, and components added for a purpose other than achieving the technical effect of the invention. Typically, when referring to compositions, a composition consisting essentially of a set of components will comprise less than 5% by weight, typically less than 3% by weight, more typically less than 1% by weight of non-specified components.

The term “consisting of” or “consists of means including the components specified but excluding addition of other components.

Whenever appropriate, depending upon the context, the use of the term “comprises” or “comprising” may also be taken to encompass or include the meaning “consists essentially of or “consisting essentially of, and may also be taken to include the meaning “consists of or “consisting of.

For the avoidance of doubt, wherein amounts of components in a composition are described in wt%, this means the weight percentage of the specified component in relation to the whole composition referred to. For example, “wherein the ground granulated blast furnace slag (GGBS) comprises 15 to 70 wt% calcium oxide” means that 15 to 70 wt% of the ground granulated blast furnace slag (GGBS) is provided by calcium oxide.

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 aspect or exemplary embodiment of the invention as set out herein are also to be read as applicable to any other aspect or exemplary embodiments of the invention, where appropriate. In other words, the skilled person reading this specification should consider the optional features for each exemplary embodiment of the invention as interchangeable and combinable between different exemplary embodiments.

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, 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 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 embodiment(s). 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 novel combination, of the steps of any method or process so disclosed.