FIELD OF THE INVENTION

The present invention is in the field of self-compacting alkali-activated concrete for prefabricated production, a method of forming said concrete, and a prefabricate, such as pre stressed elements, pre-cast elements, structural building elements, such as floors, walls, ceil ings, supports, and frames. The prefabricate has improved characteristics and for production less carbon dioxide is required.

BACKGROUND OF THE INVENTION

Concrete is a composite construction material composed primarily of aggregate, ce ment and water, with mortar being similar thereto, however using finer aggregates. There are many formulations that have varied properties. The aggregate is generally a coarse gravel or crushed rocks such as limestone, or granite, along with a fine aggregate such as sand. The cement, commonly Portland cement, and other cementing materials such as fly ash, blast furnace slag, ground calcium carbonate, etc. serve as apart of binder for the concrete. Typi cally further additives are present.

Various chemical admixtures can be added to achieve varied properties. Water is typi cally thereafter mixed with this dry or moist composite which enables it to be shaped (typi cally poured) and then solidified and hardened into rock-hard strength through a mineralogi- cal transformation known as hydration and/or pozzolanic reaction. Also particle size and polarity of materials play a role in the performance of concrete. Concrete may be reinforced with materials that are strong in tension (often steel, such as steel bars).

Admixtures are ingredients other than water, fine aggregates, (hydraulic) cement, and fibres that are added to the concrete batch immediately before or during mixing, in order to change certain characteristics of the concrete, when set. The present invention is specifically related to adding further ingredients.

For concrete production the various ingredients mentioned above are mixed. It is noted that concrete production is time-sensitive. Once the ingredients are mixed, the concrete must be put in place before it hardens, such as by casting. Then, quite critical as well, care must be taken to properly cure concrete, e.g. to achieve a required strength and hardness. It is noted that cement requires a moist, controlled environment to gain strength and harden fully. Such a controlled environment is often difficult to provide and to maintain. The cement paste hardens over a relatively long period of time, initially setting and becoming rigid though very weak and gaining in strength in the weeks following. It is noted that hydration and hardening of concrete initially, i.e. during the first three days, is considered critical. Abnor mally fast drying and/or shrinkage are unwanted. It is considered of importance that concrete is kept sealed during the initial process. Such may be achieved by spraying or ponding the concrete surface with water, thereby protecting the concrete mass from harmful effects of ambient conditions. Additional common curing methods include wet burlap and/or plastic or paper sheeting covering the fresh concrete, or by spraying on a water-impermeable tempo rary curing membrane. In a prior art example a minimum thickness of e.g. 0.01 mm is re quired to ensure adequate strength in the (membrane) sheet (see e.g. ASTM C 171). Con crete should therein be covered with a membrane, either of plastic or of a chemical com pound that will likely seal off the pores and retard the evaporation of water from concrete. After use such a sheet is typically removed.

The mixed cement-based composition comprising further ingredients, or the composi tion itself, may have unfavourable characteristics, such as sub-optimal rheology, ductility, mixing properties, etc., whereas a cured cement-based composition may suffer from sub- optimal elasticity, compressive strength, autogenous shrinkage, internal water availability, ductility, and morphology.

Some additives are added to cement-based materials. A prior art alternative to affect the autogenous shrinkage are Super Absorbent Polymers (SAPs), and water-saturated clay particles (Litag). Despite high expectations these materials have important drawbacks, and are therefore typically not put into practice.

Some prior art may be noted. For instance Patel et al. (doi: 10.1016/j.seq.2018.08.004) investigate the effect of temperature curing and ambient curing on mechanical properties of Self Compacting Geopolymer Concrete (SCGC) blended using Ground Granulated Blast Furnace Slag (GGBFS) and Rice Husk Ash (RHA). The research also studied the effect of percentage (0, 5, 15 and 25%) replacement of RHA on the properties of SCGC. The com pressive strength, split tensile strength and flexure strength were tested at 3, 7 and 28 days. Scanning Electron Microscopy (SEM) imaging was performed to understand the microstruc ture of SCGC specimens. The optimum percentage replacement of RHA with GGBFS is 5% at ambient curing and 15% at 70 °C temperature curing. The higher strength is obtained at 70 °C temperature curing than at ambient curing. The SEM imaging reveals that 5% RHA at ambient temperature and 15% RHA at 70 °C temperature have a dense microstructure and hence higher strength. Gul§an et al. (doi:10.1016/J.CONBU!LDMAT.2019.03.228) inves tigate the simultaneous effect of nano-silica and steel fiber on the fresh and hardened state performance of self-compacting geopolymer concretes (SCGC). For this purpose, self compacting geopolymer concretes without and with nano-silica (0, 1% and 2%), and without and with steel fiber (0, 0.5% and 1%) were produced. Hooked-end steel fibers were used with a length of 30 mm and an aspect ratio of 40. Self-compacting geopolymer mixes were produced using 50% fly ash (FA) and 50% ground granulated blast furnace slag (GGBFS) with a constant alkaline activator to binder ratio of 0.5. For the alkaline activator, sodium silicate solution (Na2Si03) and sodium hydroxide solution (NaOH) were utilized with a ra tio (Na2Si03/Na0H) of 2.5. Fresh state experiments were carried out via slump flow, L- Box, and V-funnel tests, while hardened state experiments were conducted using compres sive strength, flexural strength, and bonding strength tests to estimate the effects of nano silica and steel fiber together on the resulting performances of SCGC specimens. Test results were also evaluated statistically in order to clarify the contributions of the important parame ters on the resulting performance. Moreover, correlations between the experimental data were studied to investigate the relationships between the fresh and hardened state perfor mances. The results demonstrated that incorporation of nano-silica and steel fiber affected the fresh state properties adversely; however, a combined utilization of them improved bond strength and flexural performance of the SCGC specimens significantly. In addition, the ef fect of nano-silica was found to be dominant on fresh state properties and compressive strength, while the effect of steel fiber was found to be superior on flexural performance and bonding strength.

Prefabrication relates typically to assembling components of a structure in a factory or the like, and thereafter transporting complete assemblies or sub-assemblies to a construction site where the structure is to be assembled. The term is used to distinguish this process from the more conventional construction practice of transporting the basic materials to the con struction site where all assembly is carried out. An example thereof is house-building. In a conventional method of building a house components thereof, such as bricks, timber, ce ment, sand, steel, and construction aggregate, etc. are transported to the site of construction, and thereafter constructed into the house on site. In prefabricated construction, typically only the foundations are constructed in this way, while sections of walls, floors and roof are pre fabricated (assembled) in a factory (possibly with window and door frames included), trans ported to the site, lifted into place by a crane and bolted together.

Despite a long history there still is a need for improved concrete composition, or at least improvement from one or more characteristics thereof. In particular at least one of the 1-day strength, elastic modulus, strength class, slump flow class, viscosity class, passing ability class, segregation resistance class, and slump retention, may be of interest.

The present invention relates in particular to an improved concrete for a prefabricate and various aspects thereof which overcomes one or more of the above disadvantages, with out jeopardizing functionality and advantages.

SUMMARY OF THE INVENTION

The present invention relates in a first aspect to a self-compacting alkali- activated concrete for prefabricated production, with limited environmental impact, increased durability, and increased service life. Typically the 1-day strength is >30 MPa, the elastic modulus is > 30 GPa at 28 days, the strength class is C45/55, the slump flow class is SF2 according to EN206-1, the viscosity class is VS1 according to the European Guide lines for self-compacting concrete (EFNARC), the passing ability class is J-ring blocking step < 10 mm„ the segregation resistance class is SR2<15% according to EFNARC, and the slump retention after 45 min is >580 mm (SF1). The self-compacting alkali-activated con crete for prefabricated production comprises as main components 400-600 kg blast furnace slag, in particular 500-560 kg slag, 250-350 kg of at least one alkaline activator (AA), the AA comprising an alkali alkaline component, such as OH , and CO3 ² , or a combination thereof, combined with an alkali metal cation, such as Na ⁺ , K ⁺ , and combinations thereof, a silicate, and as a remainder water, in particular 280-320 kg AA, 1200-1800 kg of a concrete aggregate, in particular 1300-1600 kg aggregate, and 1.30-1.50 kg of a retarder, in particular 1.35-1.40 kg retarder, more in particular 1.37-1.38 kg retarder, wherein the retarder compris es a divalent cation, wherein amounts are based on 1 m ³ concrete. The present alkaline acti vator typically comprises 5-15 wt.% solids, in particular 7-12 wt.% solids, more in particular 8-10 wt.% solids, such as 8.5-9.5 wt.% solids, in particular wherein the solids are Na ₂ 0 and SiC , or a suitable form thereof, based on the total weight, of the binder mass of the slag.

The alkaline activator to binder (slag) ratio of the present invention is typically 0.35-0.6, in particular 0.4-0.5, more in particular 0.43-0.48, such as 0.46. These main components are typically intimately mixed and thereafter cured. Typically thereto the present method is ap plied. The present self-compacting alkali-activated concrete is particularly suited for prefabricated production, such as pre-stressed elements, pre-cast elements, and structural building elements, in particular for bridge girders, sections of walls, sections of floors, and sections of roof, possibly with window and door frames included. Depending on a size the term “section” may relate to a “full” wall or the like. Typically the size of the prefabricated product is limited by transport limitations, such as a height of bridges, a width of the road, etc. Structures of up to 10 meters in length, and 3-5 meters in height are feasible, a thickness being as required, such as from 10-40 cm. The prefabricated product is typically lifted on a transportation vehicle, and likewise lifted to its intended place on the construction site.

In a second aspect the present invention relates to a method of producing a self compacting alkali-activated concrete for prefabricated production according to the invention, comprising providing 400-600 kg slag, such as blast furnace slag, in particular ground granu lated blast-furnace slag (GGBFS), 500-560 kg slag, in particular 250-350 kg of at least one alkaline activator (AA), the AA comprising an alkali alkaline component, a silicate, and as a remainder water, in particular 280-320 kg AA, 1200-1800 kg of a concrete aggregate, in particular 1300-1600 kg aggregate, and 1.30-1.50 kg of a retarder, in particular 1.35-1.40 kg retarder, more in particular 1.37-1.38 kg retarder, wherein amounts are based on 1 m ³ con crete, thoroughly dry-mixing slag, sand, and pebbles forming a dry-mix, adding an aqueous alkaline activator solution to the dry-mix and mixing said aqueous alkaline activator solution through the aggregate forming a fresh-mix, and adding an aqueous retarder solution to the fresh-mix forming flowable concrete. The aqueous alkaline activator solution is preferably prepared by mixing the alkali compound, such as a hydroxide, such as sodium hydroxide, the silicate, such as sodium silicate, in water. Typically the hydroxide is added first, and then the silicate. Mixing typically takes at least five minutes. After mixing the solution is preferably homogenized, such as for 30-120 minutes, such as for 60 minutes. Preferably relatively fresh aqueous alkaline activator solution is used, such as less than one day old solution. Likewise the retarder is prepared by dissolving into water, typically wherein the retarder comprises a divalent cation, in particular selected from Mg, Ca, and Ba, and an anion, such as Cl , more in particular BaCh. Mixing thereof typically takes more than 20 minutes, such as more than 35 minutes. The obtained concrete reaches an optimum flowability, whereafter it is typically cast into a mould or the like, typically after 10-15 minutes.

In a further aspect the present invention relates to a method of curing the self- com pacting alkali-activated concrete for prefabricated production according to the invention, comprising obtaining the flowable concrete, applying the flowable concrete in a mould, in creasing the temperature to at least 5 K above an ambient temperature during a period of at least 60 minutes, thereby curing the mixed components. The self-compacting alkali- activated concrete mixture is preferably sealed from the environment, such as with a plastic film. It is preferably heat-cured under an increased temperature, such as of 25 °C, in particu lar for at least 24 hours, such as 36 hours. Thereafter it is preferably moisture-cured, such as in a climate chamber, at an ambient temperature, such as at 20 °C, under a relative humidity (RH) >95%, for a period of typically at least 3 days. For curing it is preferred to use wet bur laps to cover the surface of the prefabricated product, and thereafter seal it, such as with a plastic film. Early age water loss is best prevented from happening thereby.

In a further aspect the present invention relates to a prefabricated product obtained by the present method, or obtainable by a similar method, in particular wherein the prefabricat ed product is selected from pre-stressed elements, pre-cast elements, structural building ele ments, such as bridge girders, floors, walls, ceilings, supports, and frames.

Thereby the present invention provides a solution to one or more of the above- mentioned problems.

Advantages of the present description are detailed throughout the description. Refer ences to the figures are not limiting, and are only intended to guide the person skilled in the art through details of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In an exemplary embodiment the present self -compacting alkali -activated concrete for prefabricated production may comprise as further component water.

In an exemplary embodiment of the present self -compacting alkali-activated con crete for prefabricated production the slag may be selected from blast furnace slag, prefera bly granulated blast furnace slag, and combinations thereof.

In an exemplary embodiment of the present self -compacting alkali-activated con crete for prefabricated production the retarder may comprise a divalent cation, in particular selected from Mg, Ca, and Ba, and an anion, such as Cl , more in particular BaCh.

In an exemplary embodiment of the present self -compacting alkali-activated con crete for prefabricated production the AA may be in solid or in fluid form.

In an exemplary embodiment of the present self -compacting alkali-activated con crete for prefabricated production the silicate may have a modulus of <1.2, preferably < 1.0, in particular from 0.8-0.98, more in particular from 0.86-0.97, such as 0.90-0.92, wherein the modulus is defined as the ratio S1O2/X2O, wherein X is selected from monovalent cations, such as from Li, Na, K, and combinations thereof.

In an exemplary embodiment of the present self -compacting alkali-activated con crete for prefabricated production in the silicate X _y Si _z O _q the ratio z:y may be <1.2, prefera bly < 1.0, in particular from 0.8-0.98, more in particular from 0.86-0.97, such as 0.90-0.92.

In an exemplary embodiment of the present self -compacting alkali-activated con crete for prefabricated production the silicate may be selected from crystalline and amor phous cyclic and single chain silicate (SiCh+n ²ⁿ ), a pyrosilicate (S12O7 ⁶ ), a branched silicate, and a component that forms a silicate, and combinations thereof, such as from nesosilicates I Si O41 ⁴ . such as olivine, from sorosilicates | Si 2O7 | . such as epidote, from cyclosilicates [Sin03n] ²ⁿ , such as tourmaline, from inosilicates with single chains |Si _n Ckn| ² " . such as py roxene, from inosilicates with double chains | SianO 1 1 _n | ^> " . such as amphibole, from phyllosil- icates | Si _2n Os _n | ² " . such as mica and clay minerals; and from tectosilicates, preferably where in the silicate comprises a monovalent cation, such as Na ⁺ and K ⁺ .

In an exemplary embodiment of the present self -compacting alkali-activated con crete for prefabricated production the concrete aggregate may comprise as major compo nents 40-60 wt.% sand, in particular <4mm sand, more in particular dry sand, 40-60 wt.% pebbles, such as pebble aggregate, in particular mixed pebbles selected from 20-30 wt.% 4-8 mm pebbles and 20-30 wt.% 8-16 mm pebbles, wherein all wt.% are based on the total weight of the concrete aggregate.

In an exemplary embodiment of the present self -compacting alkali-activated con crete for prefabricated production an average particle size of the slag is 16± 2pm, and where in three times the standard deviation ranges from 1-60 pm.

In an exemplary embodiment of the present self -compacting alkali-activated con crete for prefabricated production an average particle size of the sand is 580± 20pm, and wherein three times the standard deviation ranges from 100 pm -7 mm.

In an exemplary embodiment of the present self -compacting alkali-activated con crete for prefabricated production an average particle size of the 4-8 mm pebbles is 6.8± lmm, and wherein three times the standard deviation ranges from 1-12 mm.

In an exemplary embodiment of the present self -compacting alkali-activated con crete for prefabricated production an average particle size of the 8-18 mm pebbles is 10.2± lmm, and wherein three times the standard deviation ranges from 1-20 mm.

In an exemplary embodiment of the present self -compacting alkali-activated con crete for prefabricated production an average particle size of dry-mix is 1.5± 0.2mm, and wherein three times the standard deviation ranges from 2 pm -15 mm.

In an exemplary embodiment of the present self -compacting alkali-activated con crete for prefabricated production the average particle size of 8-16 mm pebbles is 15-30 times the average particle size of the sand, in particular 18-22 times the average particle size of the sand.

In an exemplary embodiment of the present self -compacting alkali-activated con- crete for prefabricated production the average particle size of 4-8 mm pebbles is 8-12 times the average particle size of the sand, in particular 9-11 times the average particle size of the sand.

In an exemplary embodiment of the present self -compacting alkali-activated con crete for prefabricated production the average particle size of sand is 20-30 times the average particle size of the slag, in particular 24-26 times the average particle size of the sand,

The average particle size and standard deviation are based on a cumulative volume, and wherein particle sizes are measured using laser diffraction, such as by using a Malvern Mastersizer 3000.

In an exemplary embodiment of the present self -compacting alkali-activated con crete for prefabricated production the retarder/slag ratio may be from 0.0015-0.0030: 1, in particular from 0.002-0.0025: 1, wherein the water/solids ratio is from 0.40-0.45: 1, in par ticular from 0.42-0.43: 1.

In an exemplary embodiment of the present self -compacting alkali-activated con crete for prefabricated production the 1-day strength may be >10 MPa, in particular >30 MPa (1 day curing @ 25°C, measured according to EN12390-3).

In an exemplary embodiment of the present self -compacting alkali-activated con crete for prefabricated production the strength class may be C45/55 (@ ambient temperature curing after 1 day curing in mould at 25°C, measured according to EN12390-3).

In an exemplary embodiment of the present self -compacting alkali-activated con crete for prefabricated production the elastic modulus may be >20 GPa, in particular >30 GPa (after 28 days, measured according to EN12390-3).

In an exemplary embodiment of the present self -compacting alkali-activated con crete for prefabricated production the slump flow class may be SF2 (initial slump-flow 660- 750 mm, measured according to EN 12350-2).

In an exemplary embodiment of the present self -compacting alkali-activated con crete for prefabricated production the slump after 45 min may be >580 mm, in particular >600 mm (SF1, measured according to EN12350-2).

In an exemplary embodiment of the present self -compacting alkali-activated con crete for prefabricated production the viscosity flow class may be VS1 (T500<2s, measured according to EN 12350-2).

In an exemplary embodiment of the present self -compacting alkali-activated con crete for prefabricated production the passing ability class J-ring may be blocking step <10mm, measured according to EN12350-12 at 10-15 min after mixing).

In an exemplary embodiment of the present self -compacting alkali-activated con crete for prefabricated production a mass of a sample passing a sieve according to segrega tion resistance class SR2 may be < 15% (sieve segregation, measured according to EN 12350-11).

In an exemplary embodiment of the present self -compacting alkali-activated con- Crete for prefabricated production the slag comprises 30-35 wt.% S1O2, in particular 31.5-33 wt.% S1O2, 10-13 wt.% AI2O3, in particular 11-12 wt.% AI2O3, 0-2 wt.% Fe ₂ C> ₃ , in particular 0.3-1.2 wt.% Fe ₂ C> ₃ , 35-45 wt.% CaO, in particular 38-42 wt.% CaO, 8-12 wt.% MgO, in particular 9-10 wt.% MgO, 0.1-2.5 wt.% SO3, in particular 1-2 wt.% SO3, 0-1.2 wt.% Na ₂ 0, in particular 0.1-0.4 wt.% Na ₂ 0,and 0.1-1.2 wt.% K2O, in particular 0.2-0.9 wt.% K2O, wherein all weight percentages are based on the total weight of the slag.

The invention is further detailed by the accompanying figures and examples, which are exemplary and explanatory of nature and are not limiting the scope of the invention. To the person skilled in the art it may be clear that many variants, being obvious or not, may be conceivable falling within the scope of protection, defined by the present claims.

SUMMARY OF FIGURES Figures 1, 2a-b, 3, 4a-b, 5-9 show experimental results.

DETAIUED DESCRIPTION OF FIGURES

Figure 1 shows the cumulative volume versus particle diameter of individual com pounds and mixture. The particle size packing of all materials is to fit the best packing ac cording to modified Andreassen and Anderson model.

Figs. 2a shows J-ring slump performance overtime. Figs. 2b shows the J-ring passing ability (blocking step) over time

Fig. 3 shows compressive strength as a function of curing temperature at early age. Figs. 4a-b show compressive strength and splitting tensile strength as a function of time.

Fig. 5 shows the development of the elastic modulus and Poisson ratio overtime, re spectively.

Fig. 6 shows drying shrinkage and weight change overtime.

Fig. 7 shows the compressive strength development over time for different silicate modulus of alkaline activator (Ms).

Figures 8 and 9 show the difference between a composition with and without (left lines) retarder, in terms of J-ring passing ability (mm) (Fig. 8) and J-ring slump (mm)(Fig.

9).

The figures are further detailed in the description.

The invention although described in detailed explanatory context may be best understood in conjunction with the accompanying figures.

Experimental results

1. Requirements for self-compacting geopolymer concrete (SCGC)

Self-compacting geopolymer concrete (SCGC)

1-day compressive strength (N/mm ² ):

• 7-meter span: demoulding strength C25/30 28-day compressive strength:

I. · 7-meter span: C45/55 tested according to EN12390-3 II. Strength Class C45/55 tested according to EN12390-3

III. 1-day strength: >30 MPa tested according to EN 12350-2

IV. Slump flow class: SF2 (initial slump-flow 660-750 mm) tested according to

EN12350-2

V. Viscosity class: VS1 (T500 < 2 s) tested according to EN12350-12 VI. Passing ability classes J-ring (Blocking step <10 mm) EN 12350-12 VII. Segregation resistance class (sieve segregation): SR2 <15% tested according to EN12350-11

VIII. Slump retention: 45 min > 580 (580-640) mm SF1 tested according to EN12350-2 2. Development of SCGC (C45/55)

• Raw materials characterization (Chemical and physical properties)

• Mixture packing optimization

• Fresh properties: (J-ring) slump flow, J-ring passing-ability, setting time, segregation resistance

• Curing regime definition Self-compacting Geopolymer Concrete C45/55 Composition Supplier Amount kg/m ³

Binder GGBFS Ecocem 550.0

Alkaline activator NaOH Sol. (50.0 wt.%) Brentag 36.85

Sodium silicate Sol.

(48 wt.%, MS=2.0) PQ 80.44

Water 184

Admixture BaC12 retarder Sigma-Aldrich 1.375

Water 7.5

Aggregate Sand 0-4 mm Dekker 762.2

Coarse pebble aggregate 4-8 mm Sibelco 315.9

Coarse pebble aggregate 8-16 mm Sibelco 359.1

• Mechanical properties: compressive strength, elastic modulus/poison ratio, and ten sile splitting strength

• Volume stability: drying shrinkage 3. Performance evaluation of SCGC

• Strength Class C45/55 - 59.3 MPa at 28d/

• 1-day strength: <30 Mpa -> 33 MPa /

• Slump flow class: SF2 -> SF2 until 30 min /

• Viscosity class: VS1 (T500 <= 2 s) / • Passing ability classes J-ring (Blocking step <10 mm) /

• 6. Segregation resistance class (sieve segregation): SR2 <15% /

• 7. Slump retention: 45 min > 580 (580-640) mm /

Exemplary mixing procedure

Prepare alkaline activator solution

The alkaline activator solution is prepared using sodium hydroxide solution, so dium silicate solution and water. The mixing procedure is first adding water, then add ing NaOH solution (50%), and in the end the water-glass solution(48%). The solution is further mixed for at least 5 min and is left for homogenization at least for 1 hour. Afterwards, the alkaline activator solution could be used for geopolymer concrete casting. The prepared alkaline activator solution is best used for casting on the same day.

Preparation of Ba-retarder

The Ba retarder is prepared by dissolving BaCh salt in water. The mixing pro cess takes 3 to 5 min.

Sequence of adding materials and mixing time

A free fall concrete mixer with capacity of 40 L is used. The binder material (GGBFS) is dry mixed with the fine sand 0-4 mm and coarse aggregates (both 4-8 mm and 8-16 mm) for 3 to 5 min. The alkaline activator solution is then gradually added in the mixer within 30s. The mixture is mixed further for 1-2 min before the Ba retarder solution is added. The mixing then continues until the concrete reached optimum flowability, which is normally achieved around 10-15 min.

Curing condition

The obtained concrete mixture is sealed with plastic film and is heat-cured under 25 °C for 1 day and afterward moisture-cured in the climate chamber at 20 °C with relative humidity (RH) >95% until testing ages. It is recommended for curing to use wet burlaps to cover the surface of the specimen and then seal it with a plastic film. This is very important to prevent early age water loss.

Exemplary slag composition (calculated on oxide basis)

Oxide (wt .%) Si0 ₂ A1 ₂ 0 ₃ Fe ₂ 0 ₃ CaO MgO S0 ₃ Na ₂ 0 K ₂ 0 LOI Slag 32.91 11.84 0.46 40.96 9.23 1.60 - 0.33 1.15

Comparative example

The mixture of Patel et al. (see above) of Self Compacting Geopolymer Concrete (SCGC) blended using Ground Granulated Blast Furnace Slag (GGBFS) and Rice Husk Ash (RHA) was reworked. Thereto inventors closely followed the method and materials disclosed in Section 2.1 thereof to prepare the raw materials. The sand and gravel are similar as specified in the article. The slag used has a similar chemical compositions on oxide basis as the one disclosed in table 1, GGBFS. The average par ticle size of slag is 17 pm in the reworked case, compared to 14 pm used in the article. The slag used is locally produced in the Netherlands. The activator is made by the NaOH solutions and Na-silicate solution as suggested in the article. The 12M NaOH is prepared by dissolving NaOH solution (50%) with water. The Na-Silicate solution used has similar Na20, S1O2, and water composition as of the article. The final AA composition in the form of Na ₂ 0, S1O2, and water is in the end exactly the same as indicated in the article. It is noted that in the article the alkaline activator (AA) con centration with respect to binder (slag) content is Na20 =8.30%, Si02=9.71%, and water to binder ratio 0.325. The total solid content in AA is 18.09%. In the article su perplasticizer master Glenium sky8784 is used. Inventors used superplasticizer master Glenium 51, which is considered to provide the same characteristics to the flowability of concrete. The solid content in these two superplasticizers is similar (30%) and they are both PCE-based superplasticizers. In the end, the reworked mixture does not show self-compacting behavior, as provided by the present invention. In fact, it is not able to be cast into molds. A major improvement over the disclosure of the article is there- fore provided, as exemplified throughout the description.

It should be appreciated that for commercial application it may be preferable to use one or more variations of the present system, which would be similar to the ones disclosed in the present application and are within the spirit of the invention.