WO2022129686A1

WO2022129686A1 - Compositions and concretes thereof and related methods and uses for capping mine waste rock piles

Info

Publication number: WO2022129686A1
Application number: PCT/FI2021/050857
Authority: WO
Inventors: Minna Sarkkinen; Juha Koskinen; Pauli Torvinen; Rinna KOKKO
Original assignee: Tapojärvi Oy
Priority date: 2020-12-18
Filing date: 2021-12-09
Publication date: 2022-06-23
Also published as: FI130206B; FI20206340A1; CA3205563A1; AU2021403883A1; EP4263082A1

Abstract

Described herein are compositions that can be used for geopolymer-based concrete manufacturing to be used for capping of mining waste rocks. Also described herein are methods of making geopolymer-based concrete from the compositions and forming a capping cover for mining waste rocks.

Description

COMPOSITIONS AND CONCRETES THEREOF AND RELATED METHODS

AND USES FOR CAPPING MINE WASTE ROCK PILES

Technical field

The present disclosure generally relates to concrete compositions and related methods. In particularly, however not exclusively, the present disclosure concerns geopolymer-based concrete compositions, their use and related methods for capping mine waste rock piles.

Background

The major fraction of mining waste such as waste rocks are disposed of in piles at the mine site. Depending on the mineral waste processing operations and parent rock involved this causes various types of environmental concerns. In a case of mineral separation of sulphide-based metallic ores said waste rock piles produce harmful acidic leachate as a result of oxidation of sulphide content when exposed to atmospheric oxidation.

There exists a variety of different applications and methods in the context of preventing undesirable acid generation in waste rock at mine sites. Capping waste rock piles by earthen, organic and geosynthetic materials covering, for instance, is used. However, most present applications when confronted with the requirements to tolerate harsh weather conditions and variations and constant exposure to multiple chemicals are insufficient for long-lasting prevention of acid generation. For example, soil layers such as compacted till have been insufficient to maintain adequate saturation throughout the year, till mixed with bentonite or clay have had performance problems when affected by desiccation or freeze-thaw cycling. Geosynthetic clay liners (i.e. bentonite clay and geotextiles) supported by needling, stitching, or chemical adhesion, have questionable effectiveness as an oxygen-diffusion barrier due to their short diffusion path length and susceptibility to desiccation. High-density polyethylene HDPE liner is sensitive to installation and in-situ performance can have problems with wrinkling, deformations and defects in the short term, and later with aging. As such, there exists a need for improved compositions which encompasses easy workability when produced into the geopolymer-based concrete thereof that is used to form a capping for mining waste rocks, in combination with high environmental durability and stability.

Summary

It is an aim of the present invention to provide a composition and geopolymerbased concrete thereof which will provide good workability properties such as pumpability, mouldability and compaction when formed to capping layer combined with following properties of cured, hardened concrete: environmental durability and stability, strength and chemical and mechanical stability.

It is also an aim to provide a method for producing geopolymer-based concrete which will provide chemically and mechanically and environmentally highly stabile capping for mine waste rock piles.

It is a further aim of the present invention to provide a composition suitable for capping mine waste rock piles so that at least some deficiencies related to prior art can be reduced.

It is a further aim of the present invention to provide a method for producing a capping covering of a mine waste rock pile so that at least some deficiencies related to prior art can be reduced.

It is still a further aim to provide a composition and geopolymer-based concrete thereof which in its fresh state reaches adequate flow to provide sufficient workability together with predetermined properties of compression and flexural strength, freeze-thaw resistance and deformation properties to provide mechanical durability and stability, low enough hydraulic conductivity to prevent adequately oxygen and water permeability and prevention of diffusion to provide environmental durability of the hardened concrete capping.

The aims of the invention are obtained with a composition and geopolymer-based concrete thereof, methods for producing said concrete and capping thereof, and use of the composition for forming a capping for mine waste rock pile, which are characterized in what is presented in the independent claims. Some advantageous embodiments of the invention are presented in the dependent claims.

Described herein are aspects of a composition for capping mine waste rock piles, wherein the composition comprising: binder comprising from 5 to 20 wt.% ground granulated blast furnace slag (GGBFS) and at least one alkaline activating agent; and from 67 to 90 wt.% aggregate.

Described herein are aspects of a composition for capping mine waste rock piles, wherein the composition comprising: binder comprising from 5 to 20 wt.% ground granulated blast furnace slag (GGBFS) and at least one dry alkaline activating agent; and from 67 to 90 wt.% aggregate. Also described herein are aspects of a geopolymer-based concrete for capping mine waste rock piles, the concrete comprising: a mixture of the present composition and water, provided that water-binder (w/b) ratio being between 0.35 to 0.75.

Also described herein are aspects of a method for producing geopolymer-based concrete, the method comprising: providing a composition according to the present composition; and mixing the composition with water, wherein water-binder (w/b) ratio being between 0.35 to 0.75.

Also described herein are aspects of a method for capping a mine waste rock pile comprising, the method comprising: producing concrete according to the present method for producing geopolymer-based concrete; forming the cover from the produced concrete onto said pile; and curing the formed cover.

Also described herein are aspects of use of the present composition as a dry composition of geopolymer-based concrete for forming a capping cover for a mine waste rock pile of mining.

Considerable advantages are obtained by the present invention.

Capping covers can be produced from the present compositions. Environmental durability and stability, strength and chemical and mechanical stability may be achieved and sustained due to chemically and physically homogeneous nature of the geopolymer-based concrete produced from the present compositions.

The present compositions can be used in capping cover to give reduced hydraulic conductivity properties of water and oxygen permeability. Still further improved properties may be given to capping cover by the novel compositions including weathering, environmental durability and stability, strength, deformation and chemical and mechanical stability.

The present compositions may allow to optimise workability of produced geopolymer-based concrete thereof so that its fresh-state properties such as pumpability, easy placement and rodability are suitable for the chosen placement method together with cost-effectiveness of layer thickness in the capping cover.

Thus, it can be mentioned by way of examples that hardened geopolymer-based concrete test specimens provided with the present compositions will have deformation below 1 .0 mm/m, providing considerably reduced risk for cracking and adequately low hydraulic conductivity. Another example provides freeze-thaw resistance of cured concrete specimens, defined as ratio of the compressive strength after 10 freeze-thaw cycles R_A divided by compressive strength after curing at normal temperature (20 °C) R_B, is at least 0.9, indicating sufficient freeze- thaw resistance of cured concrete. Still another example provides hydraulic conductivity k of cured concrete test cube being 5E-09, providing capability of cured concrete to prevent adequately oxygen and water permeability. Still further example provides compressive strength of geopolymer-based concrete test specimens being at least 7.0 MPa after 7d curing, which indicates sufficient early strength development of curing concrete having adequate durability against frost. Still another example provides compressive strength of geopolymer-based concrete test specimens being at least 10 MPa after 28d curing, which indicates sufficient mechanical strength of the hardened concrete.

Embodiments of the present technology provide geopolymer-based compositions that are suitable for producing capping cover by conventional placement or forming methods together with cost-efficient layer thicknesses.

The present compositions are capable to be used in forming and producing capping cover by using conventional and cost-efficient placement or forming methods including roller compacting, shotcrete method, and pumping.

Since the alkaline activating agent can be in dry state when mixed with other ingredients of the composition, improved safety compared to liquid-state activating agent(s) containing products is achieved during storage, transport, processing and/or production stages. Further improvements obtained with dry-state activating agent are easier dosage and premix possibility with other binder components and lower leaching of hazardous elements, for instance.

The embodiments in the following detailed description are given as examples only and someone skilled in the art can carry out the basic idea of the invention also in some other way than what is described in the description. Most embodiments can be actualised in a variety of combinations with other embodiments. Though the description may refer to a certain embodiment or embodiments in several places, this does not imply that the reference is directed towards only one described embodiment or that the described characteristic is usable only in one described embodiment. The individual characteristics of a plurality of embodiments may be combined and new embodiments of the invention may thus be provided.

Brief Explanation of the Drawings

Fig. 1 is a phase diagram of the binder composition of example 1. Fig. 2 is a hydraulic-conductivity graph of the chemical resistance test conducted for three different concretes TRF1 , TRF2, and TRF3. Fig. 3 illustrates images of specimens of TRF1 , TRF2 and TRF3 concretes before (i.e., an image on the left side) and after (i.e., an image on the right side) the conducted chemical resistance test.

Description of Preferred Embodiments

As briefly discussed above, the present invention generally achieves novel composition and concrete thereof for producing capping coverage with a combination of properties selected from hydraulic conductivity, weathering, environmental durability and stability, strength and chemical, deformation, mechanical stability, freeze-thaw resistance and dynamic monolithic cumulative diffusion.

In the present disclosure a “binder” is geopolymer-based binder comprising at least one geopolymer component to form geopolymer cement. When aluminosilicate and alkaline reagent contents of the geopolymer components are in contact with water pozzolanic reaction takes place forming geopolymer-based cement.

In the present disclosure “geopolymer-based concrete” is concrete which is produced of the present compositions and water. Geopolymer-based concrete means in this context geopolymer or concrete where Portland cement is replaced with geopolymer cement or hybrid cement wherein binder comprises max 30% Portland cement in addition to geopolymer cement.

In the present disclosure “ground granulated blast furnace slag” typically stands for slag, which is formed by water quenching. The glassy and granular material is generated when slag is rapidly chilled by immersion in water. Granulated slag is ground to an air-permeability (Blaine) fineness exceeding that of Portland cement to obtain increased hydraulic activity at early ages and sufficient initial strength development.

In the present disclosure “coarse aggregate” typically stands for particulates that are greater than 5 mm. The usual size range employed is between 5 mm and 32 mm in diameter.

In the present disclosure “fine aggregate” typically stands for particulates that are less than 1 mm.

In the present disclosure an “activating agent” is an alkaline activator, which in a chemical process is mixed with powdery aluminosilicate to produce a paste capable of setting and hardening the mixture within a reasonably short period of time. In the present document, unless otherwise stated, all percentages relate to wt.% calculated from total dry mass of the composition.

The novel compositions will be discussed below in greater detail. However, generally it can be noted that the composition comprises from 5 to 20 wt.% as suitable binder material of ground granulated blast furnace slag (GGBFS) and at least one alkaline activating agent. Typically, there are furthermore in the compositions from 67 to 90 wt.% aggregates. The aggregate may be consisted of coarse aggregate and fine aggregate.

Preferred embodiments 1-13 of the novel composition according to the present disclosure are presented in Table 1 .

The present compositions comprise GGBFS as precursor and binder material or geopolymer component for geopolymer-based concrete because it provides good encapsulation and stabilization characteristics allowing good usability with waste materials such as sulfidic waste rock. Further benefits of GGBFS in the present disclosure are listed in the following sentences of the paragraph. It provides dense microstructure for decreasing permeability of geopolymer-based concrete produced from the composition. It provides good durability in harsh weather conditions. It provides sufficient final compressive strength. It has good long-term performance. It is an efficient precursor to be used with the alkali-activators disclosed herein. It has very low-quality variety. It provides good durability under chemical stress, that is better than that of e.g. with Ordinary Portland Cement (OPC). It is ecological side-stream based secondary raw material, unlike OPC or commonly used geopolymer precursor metakaolin. It is much more adequately economically obtainable compared to other precursors, such as, OPC. It provides better stabilization efficiency (i.e. low leaching and diffusion) than plain OPC. It can be pre-mixed in dry state with other binder components or materials. It has official product status. It is safe to handle and use. It is safe to the environment.

In an embodiment, novel compositions are provided which have suitable properties to be used as concrete compositions for achieving the desired combinations of properties of concrete capping cover.

In particularly interesting embodiments, compositions are achieved which produce environmentally durable and stabile capping cover, whereas the capping has the mechanical properties to allow such durability and stability.

In an embodiment an amount of the GGBFS is between 7.5 to 15 wt.%.

In an embodiment an amount of the GGBFS is between 8.5 to 20 wt.%.

In an embodiment an amount of the GGBFS is between 10 to 15 wt.%.

In an embodiment an amount of the GGBFS is between 5 to 15 wt.%. In an embodiment an amount of the GGBFS is at least 10 wt.%.

In an embodiment an amount of the GGBFS is less than 20 wt.%.

In an embodiment an amount of aggregate is 70 to 90 wt.%.

In an embodiment an amount of aggregate is 70 to 85 wt.%.

In an embodiment an amount of aggregate is 72 to 90 wt.%.

In an embodiment an amount of aggregate is 72 to 85 wt.%.

In an embodiment an amount of binders is 15 to 25 wt.%.

In an embodiment an amount of binders is 15 to 28 wt.%.

In an embodiment an amount of binders is 10 to 30 wt.%.

In various embodiments, one activating agent comprises desulfurization dust.

In one embodiment, an amount of the desulfurization dust is between 0.1 and 6 wt.%, preferably between 0.2 and 5 wt.%, more preferably between 0.4 and 4 wt.% and most preferably between 0.5 and 3.5 wt.%.

In one embodiment an amount of the desulfurization dust is between 0.1 and 6 wt.%.

In one embodiment, an amount of the desulfurization dust is between 0.4 and 4 wt.%.

In one embodiment, an amount of the desulfurization dust is between 0.5 and 3.5 wt.%.

In one embodiment, an amount of the desulfurization dust is between 0.1 and 1 wt.%.

In one embodiment, wherein an amount of the desulfurization dust is between 2 and 3.5 wt.%.

Various embodiments of the present compositions comprise desulfurization dust as an alkaline activating agent and a geopolymer component because it provides sufficient or partial alkali-activation to GGBFS to ensure sufficient pozzolanic reaction. Further, it provides better initial strength development of fresh concrete for example compared to use of CaO due to higher Na2O content. Further benefits of desulfurization dust in the present disclosure are listed in the following sentences. It provides adequate final strength development. It provides adequate hydraulic conductivity. It provides adequate weather resistance. It provides adequate environmental safety, i.e. low leaching and diffusion. It provides good chemical resistance against acids. It provides sufficient rheological properties for pumping, transportation, and placement of geopolymer- based concrete produced from the composition. It is ecological based on industrial side stream. It is economical based on ready-to-use side stream. It is more economical and ecological in comparison with for example commercial CaO. It is in dry state when stored and has fine particle size which does not require additional processing. It is widely available in sufficient amounts and at moderate hauling distance. It can be mixed with other material components of the present compositions as a pre-mixed dry mixture (one component or one binder component). It is more user friendly than for example NaOH solution. It has lower CO2 emissions and environmental impacts compared to for example CaO or NaOH activators.

In various embodiments, the activating agent comprises Portland cement.

In one embodiment, an amount of Portland cement is between 1 ,5 and 8 wt. %, preferably between 2.5 and 6.5 wt.%, more preferably between 2.8 and 6 wt.% and most preferably between 3 and 5.5 wt.%.

In one embodiment, an amount of Portland cement is between 1 ,5 and 8 wt. %.

In one embodiment, an amount of Portland cement is between 2.5 and 6.5 wt. %.

In one embodiment, an amount of Portland cement is between 2.8 and 6 wt. %.

In one embodiment, an amount of Portland cement is between 3 and 5.5 wt. %.

In one embodiment, an amount of Portland cement is between 3 and 6 wt. %.

In one embodiment, an amount of Portland cement is less than 2 wt.%.

Various embodiments of the present material compositions comprise Portland cement as an alkaline activating agent and one of the binder material or components of the composition because it provides improved alkali-activation to GGBFS to ensure sufficient pozzolanic reaction compared to use of one alkali- activator only. Further, it provides sufficient open time (workability) as a solid activator and higher initial strength development compared to use of one alkali- activator only by ensuring sufficient resistance against early freezing. Further benefits of Portland cement in the present disclosure are listed in the following sentences. It provides enhanced final strength development to ensure sufficient mechanical strength and durability. It provides good rheological properties for long-distance transportation, pumping and placement of geopolymer-based concrete. It provides more compact microstructure compared to use of one alkali activator only providing lower hydraulic conductivity and enhanced chemical resistance and durability. It provides adequate environmental safety i.e. low leaching and diffusion.

In various embodiments, the activating agent comprises silica. In one embodiment, the activating agent comprises desulfurization dust and silica.

In one embodiment, an amount of the silica is between 0.2 and 2 wt.%, more preferably between 0.3 and 1 .6 wt.% and most preferably between 0.5 and 1 .2 wt.

Various embodiments of the present material compositions comprise desulfurization dust and silica as alkaline activating agents and geopolymer components. Additional silica source provides enhanced geopolymer reaction. The used silica source also contains Na2O providing additional alkali-activation property. Fine powder form of silica source enables pre-mixing with other dry components of the composition. Silica addition provides denser microstructure i.e. higher strength, lower hydraulic conductivity, and enhanced durability against weather and chemical stresses for produced geopolymer-based concrete. Fine silica powder improves rheology of the concrete, i.e. it provides higher cohesion and consistency, lower segregation tendency and improved pumpability and placement properties for produced fresh state concrete.

In one embodiment, the activating agent comprises desulfurization dust, Portland cement and silica.

Various embodiments of the present material compositions comprise desulfurization dust, Portland cement and silica as alkaline activating agents and geopolymer components. As different alkaline activating agents these three substances have complementary effects to pozzolanic reaction, and hence, use of these different alkali-activators provide more robust binder structure compared to use of only one activating agent. Further, use of different alkali-activators is more efficient than use of only one activating agent, wherein desulfurization dust provides principal Na2O source in addition to CaO, Silica powder provides principal SiO2 source, and Portland cement provides mainly CaO. Furthermore, silica powder has naturally small particle size providing more compact microstructure. Another role of desulfurization dust is to provide improvement to initial strength development for geopolymer-based concrete.

In various embodiments, the activating agent comprises limekiln dust (LKD).

In one embodiment, an amount of the limekiln dust is between 1 and 7 wt.%, preferably between 1.3 and 6.5 wt.%, more preferably between 1.6 and 6 wt.% and the most preferably between 1 .8 and 5.7 wt.%.

Various embodiments of the present compositions comprise LKD as an alkaline activating agent and binder material or geopolymer component. LKD provides sufficient alkali-activation properties compared to commercial CaO. Furthermore, as an industrial side stream use of LKD is more economical and ecological compared to commercial CaO. Furthermore, it provides adequate environmental safety i.e. low leaching and diffusion. It provides sufficient alkali-activation to GGBFS to ensure sufficient pozzolanic reaction. Further benefits of LKD in the present disclosure are listed in the following sentences. It provides adequate final strength development. It provides adequate hydraulic conductivity. It provides adequate weather resistance. It provides good chemical resistance against acids. It provides sufficient rheological properties for pumping, transportation, and placement of formed concrete by a paver or shotcreting. It does not contain hazardous substances to environment. It is in dry state when stored and has fine particle size, i.e. it does not require additional processing. It can be mixed with other binder components as a pre-mixed dry mixture (one component or binder component). It is more user friendly than for example NaOH solution. It has lower CO2 emissions and environmental impacts compared to for example CaO.

In one embodiment, an amount of the limekiln dust is between 2 and 3.5 wt.%.

In one embodiment, an amount of the limekiln dust is between 4 and 5.5 wt.%.

In various embodiments, the activating agent comprises wollastonite tailings.

In one embodiment, an amount of the wollastonite tailings is between 1.5 and 10 wt.%, preferably between 2 and 9 wt.%, more preferably between 2.5 and 8.5 wt.% and the most preferably between 3 and 8 wt.%.

In one embodiment, an amount of the wollastonite tailings is between 3 and 6 wt.%.

In one embodiment, an amount of the wollastonite tailings is between 7 and 8 wt.%.

In one embodiment, the activating agent comprises limekiln dust and wollastonite tailings.

Various embodiments of the present compositions comprise wollastonite-bearing tailings together with LKD as alkaline activating agents and binder material or geopolymer components. Wollastonite-bearing tailings provides together with LKD sufficient alkali-activation efficiency to pozzolanic reaction of GGBFS. Wollastonite-bearing tailings provide compact microstructure through its fine particle size, i.e. enhanced filler effect improving density, hydraulic conductivity, strength development, and durability. Furthermore, wollastonite improves economy of the geopolymer-based concrete produced while being industrial side stream. Further, wollastonite improves ecology of the product while being industrial side stream. Wollastonite together with LKD can be pre-mixed with GGBFS as a one-part of geopolymer cement, i.e. binder.

In various embodiments, the activating agent comprises calcium oxide (CaO).

As shown the examples below indicate that replacing commercial CaO with other CaO bearing by-products (i.e. desulfurization dust, LKD, wollastonite) provides besides economic and ecological advantages corresponding technical performance.

In one embodiment, an amount of the calcium oxide is between 0.25 and 2 wt.%, more preferably between 0.5 and 1 .5 wt.% and the most preferably between 0.75 and 1 .25 wt.%.

In one embodiment, the activating agent comprises limekiln dust, wollastonite tailings and sodium silicate.

In one embodiment, the activating agent comprises sodium silicate an amount of between 0.01 and 1 wt.%, more preferably between 0.05 and 0.5 wt.% and the most preferably between 0.075 and 0.25 wt.%.

In various embodiments, the activating agent comprises Portland cement and sodium carbonate.

In one embodiment, an amount of the sodium carbonate is between 0.05 and 1.5 wt.%, preferably between 0.1 and 1.25 wt.%, more preferably between 0.15 and 1 wt.% and the most preferably between 0.25 and 0.75 wt.%.

In one embodiment, the activating agent comprises sodium Portland cement and carbonate.

In various embodiments, the fine aggregate comprises sulphide-bearing gypsum.

Sulphide-bearing gypsum as a fine aggregate may be used to improve microstructure of the geopolymer-based concrete when it is hardened by improving its density, strength, and hydraulic conductivity properties. Furthermore, it has beneficial economic impact while being locally available mine waste, which can be used to replace natural fine filler or commercial fine fillers e.g. dolomite filler. It provides also an ecological benefit while reducing waste material storage within mining area. It may also improve rheological properties of the fresh geopolymer-based concrete by enhancing cohesiveness, compaction, pumpability, and segregation resistance during transportation.

In one embodiment, an amount of the gypsum is between 2.5 and 12.5 wt.%, preferably between 3.5 and 11.5 wt.%, more preferably between 4.5 and 11 wt.% and the most preferably between 5.5 and 10.5 wt.%.

In various embodiments, the fine aggregate comprises dolomite filler. Dolomite filler may improve microstructure of the formed geopolymer material by improving density, strength, and hydraulic conductivity. Furthermore, it may improve rheological properties of the fresh geopolymer-based concrete by enhancing cohesiveness, compaction, pumpability, and segregation resistance during transportation. In one embodiment, an amount of the dolomite filler is between 1 and 6 wt.%, preferably between 1 .3 and 5 wt.%, more preferably between 1 .6 and 5 wt.% and the most preferably between 2 and 4 wt.%.

The particle size distribution of employed fine aggregate can be between 0mm and 1 mm in diameter.

In various embodiments, the coarse aggregate comprises crushed mine waste rock.

The coarse aggregate can be a crushed rock and/or mine waste rock. The size range of employed coarse aggregate can be between 0 mm and 12 mm or between 0 mm and 16 mm or between 0 mm and 32 mm in diameter.

In various embodiments, the waste rock comprises sulphide-bearing mine waste rock. Use of waste rock provides economical benefit compared to virgin rock aggregate by local availability on the mine site and ecological benefit compared to use of virgin rock aggregate while being waste material from mining operations.

In various embodiments, the composition comprises from 0.05 to 0.25 wt.% plasticizer.

In various embodiments, the composition comprises stainless steel slag. Stainless Steel slag can be used as a filler material, constituting at least partially the aggregate of the composition. Stainless steel slag can be ferrochrome-based slag.

One advantage of stainless steel slag when introduced into the composition is that it can improve resistance against chemical attack.

Stainless steel slag can be introduced any embodiments of the composition of the present disclosure unless otherwise stated.

In one embodiment the composition comprises from 0.01 to 17 wt.% stainless steel slag.

In one embodiment the composition comprises from 0.0 to 17 wt.% or 1.0 to 15 wt.% or 5 to 10 wt.% stainless steel slag.

In one embodiment the composition has a stainless steel slag content is in between 1.0 wt.% and 17 wt.% or between 2.5 wt.% and 15 wt.% or between 5.0 wt.% and 10.

A stainless steel slag content can be 90 wt.% or less. It is possible that stainless steel slag is a major content of the aggregate of the composition. In one embodiment the aggregate consists of stainless steel slag. Stainless steel slag can be in various size. The size range of stainless steel slag can be between 0 mm and 12 mm or between 0 mm and 16 mm or between 0 mm and 32 mm in diameter, for instance, depending on embodiment.

Based on the afore-going, a geopolymer-based concrete for capping mine waste rock piles comprises a mixture of a composition according to the disclosure and water.

In the case of geopolymer-based concrete, percentages relate to wt.% calculated from total mass of the fresh concrete comprising the present composition and water.

In one embodiment, water-binder (w/b) ratio of the concrete is between 0.25 to 0.35.

In one embodiment, water-binder (w/b) ratio of the concrete is between 0.4 to 0.6.

In one embodiment, w/b ratio of the concrete is 0.5 at most.

The preferred w/b-ratio for pumpable concrete may be between 0.50 and 0.70, and the preferred w/b-ratio for roller compacting concrete may be between 0.40 and 0.50.

Based on the afore-going, a method of using the composition according to the disclosure for producing geopolymer-based concrete comprises: providing a composition according to the disclosure; and mixing the composition with water, water-binder (w/b) ratio being between 0.35 to 0.75.

Based on the afore-going, a method for capping a mine waste rock pile comprises: producing the concrete according to the disclosure; forming the cover from the concrete onto said pile; and curing the formed cover.

Typically, prior to forming the cover, in producing the concrete, w/b of the concrete is adjusted according to the used forming or placement method.

Typically, the composition according to the disclosure is mixed mechanically, for example in a planetary mixer, with water from 1 to 3 minutes until achieving a homogenous fresh-state concrete. The mixing is typically performed at normal temperature between 15 and 30 °C.

Typically, aggregate components are mixed first, followed by the step where the binder components of the composition are added into mixed aggregates. In the final step, an adequate amount of water is added into the mixture of aggregates and composition components. In one embodiment, the cover is formed by roller compacting.

When roller compacting is used for forming the cover, w/b of the concrete is adjusted preferably between 0.25 to 0.35.

In one embodiment, the cover is formed by shotcreting.

When the cover is formed by shotcreting w/b of the concrete is preferably between 0.5 to 0.7.

In one embodiment, the cover is formed by pumping (i.e. by casting with pumpable concrete).

In one embodiment, the cover is formed by a paver. Mixes or compositions of embodiments 1-3, and 10 are preferred for paver use due to high flow (165-190 mm).

Typically, when the cover is formed by paver, shotcreting or pumping w/b ratio of the concrete is between 0.5-0.7. In this case the geopolymer concrete is transported into the paver by a pump wherein the preferred w/b-ratio may be between 0.5 and 0.7.

In one embodiment, the cover is formed by pumping and w/b ratio of the concrete is between 0.4-0.59.

The thickness of the formed capping cover can be, for example, from 50 to 300 mm, in some cases preferably from 75 to 250 mm, in particular from 100 to 200 mm.

The present disclosure also relates to, based on the aforegoing, use of composition according to the disclosure for concrete forming suitable for a capping cover for mine waste rock pile of mining.

In one embodiment, said pile comprises sulphide-bearing waste rocks.

Embodiment 1 may further comprise plasticizer 0.05-0.75 wt. %.

Embodiment 2 may further comprise plasticizer 0.1 -0.8 wt. %.

Embodiment 3 may further comprise plasticizer 0.1 -0.7 wt. %.

Embodiment 4 may further comprise plasticizer 0.1 -0.7 wt. %.

Embodiment 5 may further comprise plasticizer 0.05-0.6 wt. %.

Embodiment 10 may further comprise plasticizer 0.05-0.55 wt. %. able 1. Embodiments 1-13 of the composition according to the Invention

The following non-limiting examples illustrate embodiments of the present disclosure.

EXAMPLES

Compositions

In Table 2 are presented 13 different test compositions according to the invention and one reference composition (Ref.1 ) representing general state of the art.

Experimental work

The experimental work was divided into two different parts: 1 ) the measuring of properties of geopolymer-based concrete samples made from the example compositions and a concrete sample made from the refence composition and 2) dynamic diffusion experiments with five geopolymer-based concrete samples made from the example compositions and a concrete sample made from the refence composition.

In part 3) of the experimental work the results of the field experiments are shown and discussed.

Measuring the example concretes’ properties (1)

In Table 3 are presented water content (i.e. water to binder ratio) of fresh concrete samples made from the example compositions. In their fresh state pH, temperature and density was measured.

Samples pH’s were measured with pH Phenomenal 11 OOH by VWR -pH- measurement device.

Compression and flexural strength

The compression strength tests of the cured, hardened concretes of example compositions were performed according to the standard EN 12390-1 .

The compression and flexural strengths were measured from hardened cubes of concretes of example compounds with dimensions of 50 x 50 x 50 mm and/or 100 x 100 x 100 mm. Flexural strength was measured using specimens of 160 x 40 x 40 mm.

The samples were tested at 7 and 28 days.

Hydraulic conductivity, k The hydraulic conductivity, k, tests of the cured, hardened concretes of example compositions were performed according to the ASTM D 5084 standard test methods for measurement of hydraulic conductivity of saturated porous materials using a flexible wall permeameter.

The hydraulic conductivities were measured from hardened cylinders of concretes of example compounds with dimensions of height and diameter of 100 mm. The measuring temperature was in the region of 20 °C. The hydraulic conductivity was determined after 28 days curing.

Freeze-thaw resistance RA/RB

Weathering of hardened concretes of example compositions were tested by freeze-thaw resistance measurement according to the FprCEN/TS 13286-54 standard (Unbound and hydraulically bound mixtures - Part 54: Test method for the determination of frost susceptibility - Resistance to freezing and thawing of hydraulically bound mixtures).

Ten freeze-thaw cycles were performed according to the FprCEN/TS 13286-54 standard, designed to covered soil structures. The freeze-thaw resistance tests were determined after 28 days curing of the specimens. The test was performed by using cubes with dimensions of 100 x 100 x 100 mm or 50 x 50 x 50 mm.

The results of the freeze-thaw resistance measurements are represented by the ratio of RA/RB, wherein RA is compression strength after ten freeze-thaw cycles of the hardened concrete cube of example compounds and RB compression strength of the corresponding reference hardened concrete cube kept in the water reservoir during the freeze-thaw cycles of corresponding test cube.

Flow

Flow of fresh (i.e. uncured, unhardened) concretes made from example compositions were performed according to the ASTM C124 standard by using the flow table.

Deformation

The deformation (i.e. shrinkage/expansion) tests of the cured, hardened concretes of example compositions were performed according to the EN 12617-4 (Products and systems for the protection and repair of concrete structures - Test methods - Part 4: Determination of shrinkage and expansion) standard. Results (1)

The results of the first part of the experimental work obtained are presented in Table 4.

Diffusion experiments (2)

Diffusion of hardened concretes of example compositions were determined by Dynamic monolithic leaching test according to the EN 12617-4 (Dynamic monolithic leaching test with periodic leachant renewal, under fixed conditions) standard.

The diffusion was determined by using cube specimens with dimensions of 100 x 100 x100 mm or 50 x 50 x 50 mm.

Results (2)

The results of the second part of the experimental work obtained are presented in Table 5.

Discussion

The results of the example compositions provide evidence of the properties required for the usability and technical performance of the capping material. The usability is justified for example by providing:

• sufficient open time for the geopolymer concrete in order to enable longdistance (e.g. 2 h) transport and time for application by a paver through activator and precursor optimisation as used in examples 1-13;

• pumpability, self-compacting, and cohesiveness to enable application by a paver on the steep slope (1 :3), or alternatively by compacting by a roller, through optimising binder content, water to binder ratio and flow as presented in the example compositions;

• usability in cold conditions by providing sufficient early strength development (min 5 MPa within 7d) in order to guarantee resistance against freezing as evidenced in examples 1-10;

• good weather resistance, as evidenced through freeze-thaw resistance min 0,9 in the examples 1-13;

• ability to reduce water and oxygen ingress through minimising hydraulic conductivity at level E-09 or less, as evidenced in all the examples; • good mechanical durability in order to resist erosion and enable machinery operation on the geopolymer material through sufficient compressive strength (min 10 MPa after 28d) as evidenced in all examples; • low thaw material-based tendency to cracking as shown in deformation values (below 1.0 mm/m) of the examples 1-3, 5, 6, 8, and 9, and in flexural/compressive strength values of the examples 1-9, in order reduce risk to water ingress;

• good environmental stability by low chemical leaching as shown by the dynamic monolithic diffusion test values of the example compositions

1 ,2,12, and 13; and

• good ecological and economic efficiency through using raw materials based on industrial by-products 95-100% as evidenced in all the example compositions.

3 O

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Table 2. Example compositions 1-14 and Ref.1 O is) bU

K) oe hd n H e o 'Ji O 00 'Ji

Table 3. Concretes of the example compositions 1 -13 and Ref.1

Table 4. Concretes of the example compositions 1 -13 and Ref.1

Table 5. Concretes of the example compositions 1-13 and Ref.1

(3) Field experiments In the field experiments capping covers were produced from the concretes of example compositions no 1 and no 2. In the first phase the concretes were pumpable and self-consolidating concrete (SCC) concretes when one capping cover was formed produced from example composition no 1 and another cover from example composition no 2, respectively. In the second phase of the field experiments one capping cover was formed from roller compacting concrete (RCC) manufactured form example composition no 1. Areas of the formed capping covers were in the first phase was about 800 m2 and in the second phase about 4500 m2 and thicknesses of the formed capping covers were about 200 mm and 150 mm, respectively. The amount of concrete per a formed cover was in the first phase about 300 m3 and about 700 m3 in the second phase, respectively.

Microscopical analysis

Binder composition of the concrete of the example composition 1 was analysed with Featuring method. It indicates that a main binder phase is calcium magnesium silicate (ca. 99 %). Positions of the phases Ca-AI-Si and Mg-AI-Si diagrams are illustrated in Fig. 1. The chemical compositions are average concentrations based on SEM-EDS analyses. The composition of the main phase, Ca-Mg-Si <40 pm is amorphous (Table 6). According to an XRD conducted, the quantity of amorphous phase is 76 %. The phases also include calcite, dolomite and portlandite, which are not included in the Featuring-analysis.

Table 6. SEM-EDS results

Hydraulic conductivity

Hydraulic conductivity k was measured from the core samples (height 100 mm and diameter 100 mm) drilled from the first phase capping cover produced from example composition no 1 after about 9 months after formation of the cover. Table 7 shows the results of the hydraulic conductivity analysis. The applied standard method was ASTM D 5084 Standard Test Methods for Measurement of Hydraulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter. The results indicate that the hydraulic conductivity reduces along with time due to continuing binder reactions.

Table 7. Hydraulic conductivity results

Air permeability

Air permeability analysis was conducted for oven dried specimens. Samples 1 and 2 were taken from ready mix concrete station during piloting and no 4 and 7 were prepared in laboratory. The used analysis method is based on Leeds permeameter (Ref. Magazine of Concrete Research, ISSN 0024-9831 , Volume 40 Issue 144, September 1988, pp. 177-182. A new gas permeameter for measuring the permeability of mortar and concrete. Authors: J. G. Cabrera, and C. J. Lynsdale). Table 8 includes the parameters/constants used in the analysis and Table 9 shows the results of the air permeability analysis.

Table 8. Parameters of the air permeability analysis

Table 9. Air permeability results

* KG E-16 m2 Water retention capacity

Water retention capacity was analysed by conducting a pF-test. Samples 1 and 2 were taken from ready mix concrete plant during the pilot construction and sample 3 was prepared in the laboratory. Table 8 shows the results of the analysis. Table 10. Water retention capacity results

Compressive strength, ultrasound pulse velocity (UPV) and E-modulus of the core samples drilled from the pilot structures

Compressive strength, ultrasound pulse velocity, density and E-modulus were determined from the core samples after 49 and 315 days. Table 11 shows the results.

Freeze-thaw resistance Four core samples were drilled after one winter season before freeze-thaw test, and hence, the samples had already faced a few freeze-thaw cycles. The impact of the additional freeze-thaw cycles was evaluated after 25 and 50 cycles with UPV-measurement. Table 11 shows the results.

Table 12. Results from freeze-thaw tests

Diffusion from monolithic sample

Sample (composition no1) used in the diffusion test was taken from the ready-mix concrete station during pilot construction. The applied standard was SFS-EN 15863:2015 (Characterization of waste. Leaching behaviour test for basic characterization. Dynamic monolithic leaching test with periodic leachant renewal, under fixed conditions). Table 13 shows the results.

Table 13. Results from diffusion test

Leaching behaviour, up-flow percolation test

Sample was drilled after one month from the pilot construction. The applied standard was SFS-EN 14405:2017. The results of the test are shown in Table 14.

Table 14. Results of the up-flow percolation test

Chemical resistance

Chemical resistance tests were performed according to CEN/TR 15697 (2008) for three different mixes of concretes named as TRF1 , TRF2, and TRF3. The characteristics of the used chemical liquid are described in Table 15. The compositions of the mixes are presented in Table 16.

Table 15. Results of the up-flow percolation test

Heikkinen, P., 2000. Haitta-aineiden sitoutuminen ja kulkeutuminen maaperassa.

Espoo: Geologian tutkimuskeskus. Tutkimusraportti 150, page 80. Table 16. Content of the test mixes used in the chemical resistance test

The purpose of admixture WT200P included in the mix TRF2 was to reduce water permeability. However, the hydraulic conductivity results indicated that the hydraulic conductivity of TRF2 was higher compared to TRF1 and TRF3, see Figure 2. Thus, it had no positive impact to better chemical resistance.

Fig. 3 shows the tested specimens (in the size of 40x40x160 mm) in the beginning of the test (on the left side of the figure) and after ten (10) months (on the right side of the figure). The figure shows that the specimen of the mix TRF2 containing milled stainless steel slag filler (FeCr) is clearly in better condition after the conducted test compared to specimens of the mixes TRF1 and TRF3.

Claims

1. A composition for capping mine waste rock piles, wherein the composition comprising: binder comprising from 5 to 20 wt.% ground granulated blast furnace slag (GGBFS) and at least one dry alkaline activating agent; and from 67 to 90 wt.% aggregate.

2. The composition of claim 1 , wherein the activating agent comprises desulfurization dust.

3. The composition of claim 2, wherein an amount of the desulfurization dust is between 0.1 and 6 wt.%, preferably between 0.2 and 5 wt.%, more preferably between 0.4 and 4 wt.% and most preferably between 0.5 and 3.5 wt.%.

4. The composition of claim 2, wherein an amount of the desulfurization dust is between 0.1 and 1 wt.%.

5. The composition of claim 2, wherein an amount of the desulfurization dust is between 2 and 3.5 wt.%.

6. The composition of any preceding claims, wherein the activating agent comprises Portland cement.

7. The composition of claim 6, wherein an amount of Portland cement is between 1 ,5 and 8 wt. %, preferably between 2.5 and 6.5 wt.%, more preferably between 2.8 and 6 wt.% and most preferably between 3 and 5.5 wt.%.

8. The composition of claim 6, wherein an amount of Portland cement is between 3 and 6 wt. %.

9. The composition of any preceding claim, wherein the activating agent comprises silica, wherein an amount of the silica is between 0.2 and 2 wt.%, more preferably between 0.3 and 1 .6 wt.% and most preferably between 0.5 and 1 .2 wt. %.

10. The composition of claim 1 , wherein the activating agent comprises limekiln dust.

11. The composition of claim 10, wherein an amount of the limekiln dust is between 1 and 7 wt.%, preferably between 1.3 and 6.5 wt.%, more preferably between 1 .6 and 6 wt.% and the most preferably between 1 .8 and 5.7 wt.%.

12. The composition of claim 10, wherein an amount of the limekiln dust is between 2 and 3.5 wt.%.

13. The composition of claim 10, wherein an amount of the limekiln dust is between 4 and 5.5 wt.%.

14. The composition of claim 1 or 10, wherein the activating agent comprises wollastonite tailings.

15. The composition of 14, wherein an amount of the wollastonite tailings is between 1.5 and 10 wt.%, preferably between 2 and 9 wt.%, more preferably between 2.5 and 8.5 wt.% and the most preferably between 3 and 8 wt.%.

16. The composition of 14, wherein an amount of the wollastonite tailings is between 3 and 6 wt.%.

17. The composition of 10, wherein an amount of the wollastonite tailings is between 7 and 8 wt.%.

18. The composition of claim 1 or claim 10 to 17, wherein the activating agent comprises sodium silicate, wherein an amount of the sodium silicate is between 0.01 and 1 wt.%, more preferably between 0.05 and 0.5 wt.% and the most preferably between 0.075 and 0.25 wt.%.

19. The composition of claim 1 or claim 10 to 18, wherein the activating agent comprises sodium carbonate, wherein an amount of the sodium carbonate is between 0.05 and 1.5 wt.%, preferably between 0.1 and 1.25 wt.%, more preferably between 0.15 and 1 wt.% and the most preferably between 0.25 and 0.75 wt.%.

20. The composition of any preceding claim, wherein the aggregate is consisted of coarse aggregate and fine aggregate.

21. The composition of any preceding claim, wherein the fine aggregate comprises sulphide-bearing gypsum, wherein an amount of the gypsum is between 2.5 and 12.5 wt.%, preferably between 3.5 and 11.5 wt.%, more preferably between 4.5 and 11 wt.% and the most preferably between 5.5 and 10.5 wt.%.

22. The composition of any preceding claim 1 to 19, wherein the fine aggregate comprises dolomite filler, wherein an amount of the waste sludge is between 1 and 6 wt.%, preferably between 1 .3 and 5 wt.%, more preferably between 1 .6 and 5 wt.% and the most preferably between 2 and 4 wt.%.

23. The composition of any preceding claim, wherein the coarse aggregate comprises crushed mine waste rock.

24. The composition of claim 23, wherein the waste rock comprises sulphide- bearing mine waste rock.

25. The composition of any preceding claim, wherein the composition comprises from 0.05 to 0.25 wt.% plasticizer.

26. The composition of any preceding claim, wherein the composition comprises from 0.00 to 17 wt.% stainless steel slag.

27. A geopolymer-based concrete for capping mine waste rock pile of mining, the concrete comprising: a mixture of the composition according to any of the preceding claim and water, provided that water-binder (w/b) ratio being between 0.35 to 0.75.

28. A method for producing geopolymer-based concrete, the method comprising: providing a composition of claim 1 ; and mixing the composition with water, wherein water-binder (w/b) ratio being between 0.35 to 0.75.

29. A method for forming a capping cover for a mine waste rock pile, the method comprising: producing concrete according to claim 28; forming the cover from the produced concrete onto said pile; and curing the formed cover.

30. The method of claim 29, wherein the cover is formed by roller compacting concreting.

31 . The method of claim 30, wherein w/b ratio is 0.5 at most.

32. The method of claim 29, wherein the cover is formed by shotcrete method.

33. The method of claim 29, wherein the cover is formed by casting with pumpable concrete.

34. The method of claim 32 or 33, wherein w/b ratio is between 0.5-0.7.

35. Use of the composition of claim 1 as a dry composition of geopolymer-based concrete for forming a capping cover for a mine waste rock pile of mining.

36. The use of claim 35, wherein said pile comprises sulphide-bearing waste rocks.