NL2028226B1

NL2028226B1 - Self-compacting alkali-activated concrete for prefabricated production

Info

Publication number: NL2028226B1
Application number: NL2028226A
Authority: NL
Inventors: Dong Hua; Ye Guang; Zhang Shizhe
Original assignee: Univ Delft Tech
Priority date: 2021-05-17
Filing date: 2021-05-17
Publication date: 2022-12-02
Also published as: WO2022245201A1

Abstract

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 prestressed elements, pre-cast elements, structural building elements, such as floors, walls, ceilings, supports, and frames. The prefabricate has improved characteristics and for production less carbon dioxide is required.

Description

P100652NL00 Self-compacting alkali-activated concrete for prefabricated production

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 a part of binder for the concrete. Typi- cally further additives are present.

Various chemical admixtures can be added to achieve varied properties. Water 1s 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.

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 VSI 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 (SF 1). The self-compacting alkali-activated con- crete for prefabricated production comprises as main components 400-600 kg slag, such as blast furnace slag, in particular 500-560 kg slag, 250-350 kg of at least one alkaline activator (AA), the AA comprising an alkali component, a silicate, and as a remainder water, in par- ticular 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 particu- lar 1.37-1.38 kg retarder, wherein amounts are based on 1 m3 concrete. These main compo- nents are typically intimately mixed and thereafter cured. Typically thereto the present method is applied. 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 pre- fabricated 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 component, a silicate, and as a remain- der 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 m3 concrete, thor- oughly 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 homoge- nized, such as for 30-120 minutes, such as for 60 minutes. Preferably relatively fresh aque- ous 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 diva- lent cation, in particular selected from Mg, Ca, and Ba, and an anion, such as Cl, more in particular BaCl:. 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 BaCl:.

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 S102/X20, 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,Si,Oq 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.

5 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 (SiO2+?”), a pyrosilicate (Si207°), a branched silicate, and a component that forms a silicate, and combinations thereof, such as from nesosilicates [Si04]*", such as olivine, from sorosilicates [Si207]°", such as epidote, from cyclosilicates [SixOsn]*, such as tourmaline, from inosilicates with single chains [SiyO3a]*", such as py- roxene, from inosilicates with double chains [Sisn011]°”, such as amphibole, from phyllosil- icates [Si2nOsa]*™", 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+ 2um, and where- in three times the standard deviation ranges from 1-60 um.

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+ 20um, and wherein three times the standard deviation ranges from 100 um -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+ Imm, 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+ Imm, 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 EN12350-2).

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 (SF 1, 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 EN12350-2).

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).

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, 5-7 show experimental results.

DETAILED 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 over time. 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 over time, re- spectively. Fig. 6 shows drying shrinkage and weight change over time. Fig. 7 shows the compressive strength development over time for different silicate modulus of alkaline activator (Ms). 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/mm2): + 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 EN12350-2 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 VL Passing ability classes J-ring (Blocking step <10 mm) EN 12350-12 VII. Segregation resistance class (sieve segregation): SR2 <15% tested according to

Self-compacting Geopdlymer Concrete C45/55 C . Amount Unit omposition Supplier kg/m? NaOH Sol. (50.0 wi%) 36.85 Alkaline activa- Sodium silicate Sol. (48 wt%, PQ 80.44 tor Ms=2.0) we wm Admixture Aldrich ee Sand 0-4 mm 762.2 Coarse pebble aggregate 8-16 mm 359.1 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 « 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 Vv + 1-day strength: <30 Mpa — 33 MPa v « Slump flow class: SF2 — SF2 until 30 min v/ + Viscosity class: VSI (T500 <=25s) v + Passing ability classes J-ring (Blocking step <10 mm) v/ » 6. Segregation resistance class (sieve segregation): SR2 <15% / + 7. Slump retention: 45 min > 580 (580-640) mm v/

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 5S 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 BaCl:; 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 °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.

25 This is very important to prevent early age water loss.

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.

The following section is added to support the search, of which the next section is a translation into Dutch.

1. A self-compacting alkali-activated concrete for prefabricated production comprising as main components 400-600 kg slag, in particular grounded slag, such as blast furnace slag, in particular 500-560 kg slag, 250-350 kg of at least one alkaline activator (AA), the AA comprising an alkali com- ponent, 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

1.300-1.500 kg of a retarder, in particular 1.350-1.400 kg retarder, more in particular

1.370-1.380 kg retarder, wherein amounts are based on 1 m? concrete.

2. The self-compacting alkali-activated concrete for prefabricated production according to embodiment], comprising as further component water.

3. The self -compacting alkali-activated concrete for prefabricated production according to embodiment] or 2, wherein the slag is selected from blast furnace slag, preferably granulated blast furnace slag, and combinations thereof, and/or wherein the retarder comprises a divalent cation, in particular selected from Mg, Ca, and Ba, and an anion, such as Cl, more in particular BaCl:.

4 The self -compacting alkali-activated concrete for prefabricated production according to embodiment3, wherein the AA is in solid or in fluid form, and/or wherein the silicate has 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 S102/X20, wherein X is selected from monovalent cations, such as from Li, Na, K, and combinations thereof, and/or wherein in the silicate XyS1,04 the ratio z:y is <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, and/or wherein the silicate is selected from crystalline and amorphous cyclic and single chain sili- cate (SiO2:"™), a pyrosilicate (Si20:°), a branched silicate, and a component that forms a silicate, and combinations thereof, such as from nesosilicates [Si04]*", such as olivine, from sorosilicates [Si207]°, such as epidote, from cyclosilicates [SinO3:]?”", such as tourmaline, from inosilicates with single chains [Si103„]?*”, such as pyroxene, from inosilicates with double chains [SisnQ11a]**, such as amphibole, from phyllosilicates [Si2nOsa]*™, such as mica and clay minerals; and from tectosilicates.

5. Self-compacting alkali-activated concrete for prefabricated production according to any of embodiments3-4, wherein the concrete aggregate comprises as major components 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 con- crete aggregate, and/or wherein an average particle size of the slag is 16+ 24m, and wherein three times the standard deviation ranges from 1-60 um, and/or wherein an average particle size of the sand is 580+ 20pm, and wherein three times the standard deviation ranges from 100 um -7 mm, and/or wherein an average particle size of the 4-8 mm pebbles is 6.8+ Imm, and wherein three times the standard deviation ranges from 1-12 mm, and/or wherein an average particle size of the 8-16 mm pebbles is 10.2+ Imm, and wherein three times the standard deviation ranges from 1-20 mm, and/or wherein an average particle size of dry-mix is 1.5+ 0.2mm, and wherein three times the standard deviation ranges from 2 um -15 mm, and/or wherein 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, and/or wherein 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, and/or wherein 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, wherein 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.

6. The self -compacting alkali-activated concrete for prefabricated production according to any of embodiments 1-5, wherein the retarder/slag ratio is from 0.0015-0.0030:1, in particu- lar from 0.002-0.0025:1, and/or wherein the water/solids ratio is from 0.40-0.45:1, in particular from 0.42-0.43:1.

7. The self -compacting alkali-activated concrete for prefabricated production according to any of embodiments 1-6, wherein the 1-day strength is >10 MPa, in particular >30 MPa (1 day curing @ 25°C, measured according to EN12390-3).

8. The self -compacting alkali-activated concrete for prefabricated production according to any of embodiments1-7, wherein the strength class is C45/55 (@ ambient temperature curing after 1 day curing in mould at 25°C, measured according to EN12390-3).

9. The self -compacting alkali-activated concrete for prefabricated production according to any of embodiments1-9, wherein the elastic modulus is >20 GPa, in particular >30 GPa (af- ter 28 days, measured according to EN12390-3).

10. The self -compacting alkali-activated concrete for prefabricated production according to any of embodiments1-10, wherein the slump flow class is SF2 (initial slump-flow 660-750 mm, measured according to EN12350-2).

11. Self-compacting alkali-activated concrete for prefabricated production according to any of embodiments1-10, wherein the slump after 45 min is >580 mm, in particular >600 mm (SF1, measured according to EN12350-2).

12. Self-compacting alkali-activated concrete for prefabricated production according to any of embodiments1-12, wherein the viscosity flow class 1s VSI (T500<2s, measured according to EN12350-2).

13. The self -compacting alkali-activated concrete for prefabricated production according to any of embodiments1-12, wherein the passing ability class J-ring is blocking step <10mm, measured at 10-15 min after mixing according to EN12350-12).

14. The self -compacting alkali-activated concrete for prefabricated production according to any of embodiments1-14, wherein a segregation resistance class SR2 is < 15% (sieve segre- gation, measured according to EN 12350-11).

15. Method of producing a self- compacting alkali-activated concrete for prefabricated pro-

duction according to any of embodiments1-15, comprising providing 400-600 kg slag, such as blast furnace slag, in particular 500-560 kg slag, 250-350 kg of at least one alkaline activator (AA), the AA comprising an alkali component, a silicate, and as a remainder water, in particular 280-320 kg AA, 1200-1800 kg of a con- crete aggregate, in particular 1.300-1.600 kg aggregate, and 1.300-1.500 kg of a retarder, in particular 1.350-1.400 kg retarder, more in particular 1370-1380 kg retarder, wherein amounts are based on 1 m3 concrete, 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 dry-mix forming a fresh-mix, and adding an aqueous retarder solution to the fresh-mix forming flowable concrete.

16. Method of curing a self- compacting alkali-activated concrete for prefabricated produc- tion according to embodiment 16, comprising obtaining the flowable concrete, applying the flowable concrete in a mould, increasing the temperature to at least 5 K above an ambient temperature during a peri- od of at least 60 minutes, thereby curing the mixed components.

17. Prefabricate obtained by the method according to embodiment17, in particular wherein the prefabricated product is selected from pre-stressed elements, pre-cast elements, structural building elements, such as bridge girders, floors, walls, ceilings, supports, and frames.

Claims

Conclusions

1. A self-compacting alkali-activated concrete for the manufacture of prefabricated products, comprising as main components 400-600 kg of slag, in particular ground slag, such as blast furnace slag, in particular 500-560 kg of slag, 250-350 kg at least one alkaline activator (AA), wherein the AA comprises an alkali component, a silicate, and balance water, especially 280-320 kg AA, 1200-1800 kg concrete aggregate, especially 1300-1600 kg concrete aggregate, and 1,300-1,500 kg retarder , in particular 1,350-1,400 kg of retarder, more in particular 1,370-1,380 kg of retarder, the amounts being based on 1 m® of concrete.

The self-compacting alkali-activated concrete for prefabrication according to claim 1, comprising water as a further component.

The self-compacting alkali-activated concrete for prefabrication according to claim 1 or 2, wherein the slag is selected from blast furnace slag, preferably granulated blast furnace slag, and combinations thereof, and/or wherein the retarder comprises a divalent cation, in particular selected from Mg, Ca and Ba, and an anion, such as Cl-, more particularly BaCl-.

The self-compacting alkali-activated concrete for prefabrication according to claim 3, wherein the AA is in solid or liquid form, and/or wherein the silicate has a modulus of < 1.2, preferably < 1.0, in the particularly from 0.8-0.98, more particularly from 0.86-0.97, such as 0.90-0.92, in which the modulus is defined as the ratio S102/X20O, where X is chosen from monovalent cations, such as Li, Na, K, and combinations thereof, and/or where in the silicate XSi, 04 the ratio z:y is < 1.2, preferably < 1.0, in particular from 0.8 -0.98, more particularly from 0.86-0.97, such as 0.90-0.92, and/or wherein the silicate is selected from crystalline and amorphous cyclic and monochain silicate (SiO2+;?*), a pyrosilicate (Si20:°), a branched silicate, and a component that forms a silicate, and combinations thereof, such as from nesosilicates [SiO4]*, such as olivine, from sorosilicates [Si207]®, such as epidote, from cyclosilicates [SiOsq] *™, such as tourmaline, from inosilicates with single-chain [SiOsa]*™, such as pyroxene, from double-chain inosilicates [SisnO11a]®™, such as amphibole, from phyllosilicates [Si2nOsn]*™, such as mica, and clay minerals, and from tectosilicates.

5. Self-compacting alkali-activated concrete for prefabrication according to any one of claims 3-4, wherein the concrete granulate comprises as main components 40-60% by weight of sand, in particular sand <4mm, more in particular dry sand, 40-60% by weight of pebbles, such as granulated pebbles, in particular mixed pebbles selected from 20-30% by weight of 4-8mm pebbles, and 20-30% by weight of 8-16mm pebbles

nen, where all weight percentages are based on the total weight of the concrete granulate, and/or where the average particle size of the slag is 16+ 2um, and three times the standard deviation is between 1-60 um, and/or where an average grain size of the sand is 580+ 20um, and where three times the standard deviation is between 100 um -7mm, and/or where an average grain size of the 4-8mm pebbles is 6.8+ Imm, and where three times the standard deviation ranges from 1-12 mm, and/or where the average particle size of the 8-16 mm pebbles is 10.2+1 mm, and where three times the standard deviation ranges from 1-20 mm, and/or where the average particle size of dry mix is 1.5+ 0.2 mm, and in which three times the standard deviation ranges from 2 um -15 mm, and/or in which the average grain size of 8-16 mm pebbles is 15-30 times the average grain size of the sand, in particular 18-22 times as large as the average grain size of the sand, and/or in which the average grain size of 4-8 mm pebbles is 8-12 times the average grain size of the sand, in particular 9-11 times the average grain size of the sand, and/or in which 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 where the average particle size and standard deviation are based on cumulative volume, and where the particle size is measured by laser diffraction, for example using a Malvem Mastersizer 3000.

The self-compacting alkali-activated concrete for precast according to any one of claims 1-5, wherein the retarder/slag ratio is 0.0015-0.0030:1, especially 0.002-0.0025:1, and/or wherein the ratio of water to solids is 0.40-0.45:1, in particular 0.42-0.43:1.

The self-compacting alkali-activated concrete for prefabrication according to any one of claims 1-6, wherein the 1-day strength is >10 MPa, in particular >30 MPa (1 day curing @ 25°C, measured according to EN12390- 3).

The self-compacting alkali-activated concrete for prefabrication according to any one of claims 1-7, wherein the strength class is C45/55 ((@ cure at ambient temperature after 1 day curing in mold at 25°C, measured according to EN12390-3 ).

The self-compacting alkali-activated concrete for prefabrication according to any one of claims 1-9, wherein the modulus of elasticity is >20 GPa, in particular >30 GPa (after 28 days, measured according to EN12390-3).

10. The self-compacting alkali-activated concrete for prefabrication according to one of the con-

conclusion ss 1-10, where the slump flow is class SF2 (initial slump flow 660-750 mm, measured according to EN12350).

Self-compacting alkali-activated concrete for precast production according to any one of claims 1-10, wherein the slump size after 45 min is >580 mm, in particular >600 mm (SFI, measured according to EN12350-2).

Self-compacting alkali-activated concrete for prefabrication according to any one of claims 1-12, wherein the viscosity flow class is VSI (T500<2s, measured according to EN12350).

The self-compacting alkali-activated concrete for the production of precasts according to any one of claims 1-12, wherein the passability is class J-ring blocking step <10mm, measured according to EN12350-12 at 10-15 min after mixing).

The self-compacting alkali-activated concrete for prefabrication according to any one of claims 1-14, wherein a segregation resistance class SR2 is < 15% (sieve segregation, measured according to EN 12350).

A method for the production of a self-compacting alkali-activated concrete for prefabrication according to any one of claims 1-15, comprising providing 400-600 kg of slag, such as blast furnace slag, in particular 500-560 kg of slag, 250- 350 kg of at least one alkaline activator (AA), the AA comprising an alkali component, a silicate, and water as the balance, in particular 280-320 kg AA, 1200-1800 kg concrete granulate, in particular 1300-1600 kg aggregate, and 1,300-1,500 kg of retarder, in particular 1,350-1,400 kg of retarder, more in particular 1,370-1,380 kg of retarder, the amounts being based on 1 m3 of concrete, thorough dry mixing of slag, sand and pebbles to a dry mixture, adding an aqueous alkaline activating solution to the dry mixture and mixing said aqueous alkaline activating solution into the dry mixture into a fresh mixture, and adding an aqueous retarder solution to the fresh mixture, forming liquid concrete.

A method for curing a self-compacting alkali-activated concrete for precast according to claim 16, comprising obtaining the liquid concrete, placing the liquid concrete in a mold, raising the temperature to at least 5 K above an ambient temperature for a period of at least 60 minutes, which causes the mixed components to cure.

Prefabricated product obtained according to the method according to claim 17, in particular wherein the prefabricated product is selected from prestressed elements, precast elements, structural building elements, such as bridge girders, floors, walls, ceilings, supports, and frames.