PREPARATION METHODS Field of the Invention

The technical field of the invention relates to hydraulic mineral binders including Ground Granulated Blast Slag (GGBS), which are used in settable and hardenable compositions, such as mortar or concrete compositions.

More particularly, the invention relates to binders and to settable and hardenable compositions for the building industry, that include at least GGBS as hydraulic binder as well as an additive that reduces or eliminates undesirable colouring on the surface of these compositions as they are set and hardened.

The invention concerns also the methods of preparation of these GGBS-based binders, of these dry or wet settable and hardenable compositions.

The building applications of the so-obtained set and hardened products are also in the field of the invention.

Background Art

Slag rich mortars and concretes, including slag portland blended and geopolymer-based cements, turn a blue/green colour after setting & hardening. When the concrete or the mortar is exposed to air, the specific blue green colour of exterior surface turns to "grey" (cement concrete) or "white" (slag concrete). However, if the concrete rests long time in the framework or cured under the water (cases for precast), it maintains the blue/green colour for up to the entire service life of the concrete. This specific colour is of particular concern in concrete applications where visual aesthetics are important.

The cause of this blue/green colour is not well understood. However, most of the researchers attribute the colouration to the complex reaction of sulfur from GGBS raw material (containing approximately 1% S) with other compounds during the hydration process.

Moreover, WO2012/083384A1 discloses a settable composition comprising a cementitious component including slag, a sulfur scavenging component including a zinc compound (zinc oxide, zinc sulfate and zinc carbonate), and an alkaline activator. Zinc oxide, zinc sulfate or zinc carbonate is supposed to eliminate colouration of the settable material.

WO2014/013199A1 also describes a binder comprising a ground granulated blast furnace slag and at least one mono-, di- or trivalent metal salt selected from the group consisting of bismuth, copper, silver and tin salts, (ranked in a decreased order of effectiveness in preventing discolouration : Bi ₂ (S0 ₄ ) ₃ > CuS0 ₄ > CuN0 ₃ > Cu(OH) ₂ > SnS0 ₄ ). These salts are presented as capable of forming, during mixing with said slag, a metal sulfide for which the solubility product K _sp , measured at 25°C, is less than 10 ^~10 .

Both inventions according to WO2012/083384A1 and WO2014/013199A1 are based on the hypothesis that the undesirable colour comes from sulfides (S ^2~ ), and that the addition of the claimed salts in the binder can precipitate the sulfides as ZnS, and then solve the colour issues. But this hypothesis is disputable. This could explain the proposals according to WO2012/083384A1 and WO2014/013199 A 1 are improvable. Obj ectives of the invention

In this context, the invention aims at addressing at least one of the above problems and/or needs, through fulfilling at least one of the following objectives:

»**Providmg a GGBS-based binder or a mortar or concrete composition including said GGBS-based binder, which are not prone to develop an undesirable colour as the setting and the hardening occur.

Ί>* Providing a GGBS-based binder or a mortar or concrete composition including said GGBS-based binder, comprising an active discolourating additive which is more efficient than the known zinc oxide, zinc sulfate, zinc carbonate, Bi ₂ (S0 ₄ ) ₃ , CuS0 ₄ , CuN0 ₃ , Cu(OH) ₂ , and SnS0 ₄ .

^•Providing a GGBS-based binder or a mortar or concrete composition including said GGBS-based binder, comprising an active discolourating additive which is efficient and cheap.

Providing a GGBS-based binder or a mortar or concrete composition including said GGBS-based binder, comprising an active discolourating additive which is efficient and Environmentally- friendly.

Providing a simple and cheap method of preparation of the GGBS-based binder or the mortar or concrete composition including said GGBS-based binder, which complies with at least one of the objectives -a- to -d-.

»f* Providing a simple and cheap method of preparation of a wet form of the

GGBS-based binder or a mortar or concrete composition including said GGBS- based binder.

Providing hardened products for the building industry including GGBS as at least partial binder, which are not undesirably coloured, all their life long. Ίΐ* Providing a new ingredient for binder or settable and hardenable compositions, which prevents undesirable colouration in the final set and hardened products (e.g. buildings or civil engineering works or elements thereof, coatings, fillers, screeds, tiles adhesives and/or internal or external insulation systems).

Summary of the invention

It follows that the invention pertains to a GGBS-based binder comprising:

• at least one GGBS;

• at least one oxidation agent OA of the GGBS sulphur compounds, particularly of the species S3 ^" of said GGBS sulphur compounds.

It is to the credit of the inventors to have discovered that one of the possible causes of the undesirable colouration could be the S ₃ ^" species and to have judiciously selected adapted oxidation agents OA, notably of these S ₃ ^" species.

In another aspect, the invention concerns a method for the preparation of the GGBS-based binder as above mentioned, said method comprising mixing of at least one GGBS with at least one oxidation agent OA of the GGBS sulphur compounds, particularly of the species S ₃ ^" of said GGBS sulphur compounds, said mixing preferably occurring at dry state.

In another aspect, the invention concerns a mortar or concrete composition comprising:

• at least one GGBS-based binder; particularly the GGBS-based binder as above mentioned,

· at least one oxidation agent OA of the GGBS sulphur compounds, particularly of the species S ₃ ^" of said GGBS sulphur compounds,

and aggregates,

and, optionally at least one additive.

In another aspect, the invention concerns a method for the preparation of the composition as above mentioned, said method comprising mixing of all the components of the composition, the introduction of the oxidation agent OA occurring in one or several times at any time of the mixing.

In another aspect, the invention concerns a wet formulation comprising a mixture of water the GGBS-based binder as above mentioned and/or the mortar or concrete composition as above mentioned. In another aspect, the invention concerns a method for the preparation of a wet formulation as above mentioned, said method comprising mixing water with the whole or a part of the GGBS-based binder as above mentioned and/or with the whole or a part of the mortar or concrete composition as above mentioned, the introduction the whole or a part of the oxidation agent OA possibly occurring before and/or during and/or after the introduction of water.

In another aspect, the invention concerns a method of making buildings or civil engineering works or elements thereof, coatings, fillers, screeds, tiles adhesives and/or internal or external insulation systems, from the wet formulation as above mentioned, which hardens when exposed to the air.

In another aspect, the invention concerns the use of at least one oxidation agent OA of the GGBS sulphur compounds, particularly of the species S ₃ ^" of said GGBS sulphur compounds, for discolouring hardened GGBS containing mortars or concrete.

In another aspect, the invention concerns a method for discolouring hardened GGBS containing mortars or concrete consisting in combining GGBS with at least one oxidation agent OA of the GGBS sulphur compounds, particularly of the species S ₃ ^" of said GGBS sulphur compounds.

Definitions

According to the terminology of this text, the following non limitative definitions have to be taken into consideration:

- Every singular designates a plural and reciprocally.

"binder" refers to any material or substance that holds or draws other materials together to form a cohesive whole mechanically, chemically, or as an adhesive.

"mortar" refers to a material composed of binder(s), sand, water and admixtures.

- "concrete" refers to a material composed of binder(s), gravel, sand, water and admixtures etc..

"cement" is a mineral binder, free from any organic compound. It includes slag Portland blended and geopolymer-based cements Detailed description of the invention

Binder

The binder contains GGBS also named Grounded granulated blast furnace slag (GGBFS). GGBS is a glassy granular material obtained by quenching molten GGBFS in water, and then by grinding the quenched product to improve GGBS reactivity. GGBS is essentially composed of Si0 ₂ , CaO, MgO, and A1 ₂ 0 ₃ , which are also common components in commercial silicate glasses. GGBS is used as partial substitute of Portland cement in OPC binder (OPC: Ordinary Portland Cement). Replacement levels for GGBS vary from 30% to up to 85%. Typically 40 to 50%> is used in most instances. GGBS makes it possible to decrease the hydration heat of cement and improve the binder resistance to freezing, thawing, chemicals and seawater. GGBS is also beneficial to concrete structures that require high durability. As substitute of OPC clinkers, GGBS shrinks the environmental impact of OPC manufacture which is energy-guzzling which generates huge amounts of C0 ₂ issued from the thermal decomposition of limestone, a material used to produce OPC clinkers.

GGBS reacts like Portland cement when in contact with water. But as the rate of reaction is slower, an activator is necessary. The calcium hydroxide released when Portland cement reacts with water serves to activate GGBS, hence GGBS is normally combined with Portland cement. It can be also, sulfate salts, alkaline solution etc. Among these activators, high alkaline solution can boost the rate of hydration much efficiently

In a preferred embodiment, the binder is characterized by an OA concentration [OA] expressed in % w/w with respect to GGBS, and given hereafter in an increased order of preference is :

0.01 < [OA] < 15 ; 0.05 < [OA] < 14; 0.08 < [OA] < 12 ; 0.1 < [OA] < 10.

According to a first embodiment of the invention, OA is chosen among the oxidants, preferably in the group comprising - or even better consisting in- :

peroxides, preferably H ₂ 0 ₂ ;

peroxide salts, preferably perborates, peroxydisulfuric salts;

halogens, preferably halogens which oxidation state is greater than or equal to

1, more preferably halogen-oxo-acid salts; chlorates (I), (III), (V) and/or(VII), iodates, periodates, bromates, borates, perborates;

peroxhydrates;

sulfite salts, preferably sodium sulfites;

transition metals and their oxides, preferably transition metals which oxidation state is greater than or equal to 1, more preferably chromate salts, dichromate salts, Mn0 ₂ , permanganate salts, Co (III), Pb(IV); Pb0 ₂ , Ni0 ₂ ;

and mixtures thereof. In this first embodiment, the OA concentration [OA] expressed in % w/w with respect to GGBS, and given hereafter in an increased order of preference is:

0.1 < [OA] < 10 ; 0.5 < [OA] < 8 ; 1 < [OA] < 7 ; 2 < [OA] < 6. According to a second embodiment of the invention, OA is chosen among the oxidation catalysts, preferably the oxidation catalysts which the active component(s), is (are) in the group comprising - or even better consisting in - : Mn0 ₂ ; MnO ; V ₂ 0 ₅ ; activated carbon ; Cr ₂ 0 ₃ ; Fe ₂ 0 ₃ ; Ti0 ₂ ; CuO ; Co ₂ 0 ₃ ; NiO ; Ni0 ₂ ; and mixtures thereof. The oxidation catalysts OA according to the invention includes non-supported (or bulk catalysts) and supported catalysts with supports as Si0 ₂ , A1 ₂ 0 ₃ , zeolites, nanotubes etc. According to a noteworthy feature of the invention, the supported catalysts are prepared as indicated hereafter: the active components are synthesized on the support like Si0 ₂ , A1 ₂ 0, zeolites, nanotubes etc. by impregnation technique using metal precursors to deposit onto the support surface, and then by post-treatments (like drying, calcinations, forming, activation) to transform the precursors into the required active compound, e.g. : Mn0 ₂ /Si0 ₂ .

The supported catalyst has the advantage to have a great specific surface. In this second embodiment, the OA concentration [OA] expressed in % w/w with respect to GGBS, and given hereafter in an increased order of preference is:

0.01 < [OA] < 10 ; 0.1 < [OA] < 8 ; 0.5 < [OA] < 7 ; 0.1 < [OA] < 5.

It important to emphasize the fact OA behaves as a catalyst in this second embodiment. Its concentration is low and OA is still present at the end of the reaction.

This low concentration of activity is interesting because it limits the risk of damaging the settable and hardenable composition including the GGBS-based binder. This low concentration is also not insignificant on an economic point of view. It is quite surprising to note that the catalytic way of action of OA in this second embodiment, is possible a so complex medium, namely a cementitious composition including GGBS. One could have feared a catalyst poisoning.

Mortar r concrete compositions

The mortar or concrete compositions according to the invention comprise:

• at least one GGBS-based binder; particularly the GGBS-based binder as above defined, • at least one oxidation agent OA of the GGBS sulphur compounds, particularly of the species S3 ^" of said GGBS sulphur compounds,

• and aggregates/fillers,

• and, optionally at least one additive.

GGBS-based binder

Advantageously, the weight ratio GGBS-based binder I whole hydraulic binder of the mortar/concrete composition is between 20/80 and 100/0. Non GGBS-based binder

These mortar or concrete composition preferably comprises at least one binder different from the GGBS-based binder, preferably selected in the group comprising - or even better consisting in- : Portland cements, Portland-fly ash cements, Portland pozzolan cement, Portland silica fume cements, masonry cements, expansive cements, White blended cements, coloured cements, very finely ground cements, pozzolan- lime cements, supersulfated cements, belite cements, calcium sulfoaluminate cements, "natural" cements, geopolymer cements, cements formed of pozzolanic mixtures optionally comprising fly ash, fumed silicas, limestone, calcined schiste and/or natural or calcined pozzolans; and mixtures thereof.

Aggregates/Fillers

Aggregates comprise a large category of particulate material used in construction, including sands, gravels, crushed stones, slag (non-ground), recycled concrete and geosynthetic aggregates. They serve as reinforcement to add strength to the overall composite material.

The mortar/concrete composition can also include:

^fillers such as flours, for example based on quartz, limestone, barite or clays and mixtures thereof;

*as well as light fillers, such as perlites, kieselguhr (diatomaceous earth), expanded mica (vermiculite) and foamed sand, and mixtures thereof.

The quantity of the aggregates/fillers in the mortar or concrete composition can suitably be (in % by weight) between 0 and 90, preferably between 20 and 80, and more preferably between 50 and 70, based on the total weight of the mortar or concrete composition and depending on the application. Additives

Activators)

In order to promote the setting and/or the curing and/or the hardening of the binder, the mortar/concrete composition, advantageously, comprises at least one activator chosen in the group comprising - or even better consisting in- : the activators, preferably the alkaline activators and/or the sulfate activators and/or the slag microparticles based activators and/or the cement-based activators.

As examples of alkaline activators, one can quoted slaked lime, sodium hydroxide, potassium hydroxide, sodium silicate or potassium silicate.

Sulfate activators can be for instance calcium sulfates.

The activator is preferably incorporated under pulverulent form in the dry composition, before its mixing with water, so that a so-called ready-mix mortar/concrete composition is produced.

The dry activator can be mixed with the binders and/or aggregates/fillers.

Alternatively, an aqueous, preferably alkaline activating solution can be added to the other pulverulent components. In this case, the term two-component binder is used.

A concentration from 1 % to 10% by weight, with respect to the total weight of the composition, is an illustration of a preferred embodiment of the mortar/concrete according to the invention.

Other Additives than the activator(s)

Water retentive agent

A water retentive agent has the property to keep the water of mixing before the setting. The water is so trapped in the wet formulation paste which improves its bond. To some extent, the water is less absorbed by the support. Salting out on the surface is limited and evaporation is reduced.

The water retentive agent is preferably chosen in the group comprising: modified cellulose ethers and/or starches ethers and/or guar ether and their mixes, more preferably consisting of: methylcelluloses, methylhydroxypropylcelluloses, methylhydroxyethyl-celluloses and their mixes.

Rheological agent

The possible rheological agent (also named a "thickener") is preferably chosen in the group comprising, more preferably consisting of : clays, starch ethers, cellulose ethers and/or gums (e.g. Welan guar xanthane, succinoglycans), modified polysaccharides -preferably among modified starch ethers-, polyvinylic alcohols, polyacrylamides, clays, sepiolites, bentonites, and their mixes, and more preferably chosen in the group of clays, bentonite, montmorillonite. Defoamer/ Antifoams

The possible defoamer is preferably chosen in the group comprising, more preferably consisting of: polyether polyols and mixes thereof.

Biocide

The possible biocide is preferably chosen in the group comprising, more preferably consisting of: mineral oxides like zinc oxide and mixes thereof.

Pigment

The possible pigment is preferably chosen in the group comprising, more preferably consisting of: Ti0 ₂ , iron oxide and mixes thereof.

Flame retardant

The possible flame retardant (or flame proof agent), which makes it possible to increase the fire resistance and/or to shrink the speed of flame spreading of the composition is preferably chosen in the group comprising, more preferably consisting of:

^■ minerals preferably aluminium hydroxide [Al(OH) ₃ , ATH], magnesium hydroxide MDH, hydromagnesite, hydrates, red phosphorus, and boron compounds, preferably borates,

^■ organohalogen compounds, preferably organo chlorines and more preferably such as chlorendic acid derivatives and chlorinated paraffins; organobromines such as decabromodiphenyl ether (decaBDE), decabromodiphenyl ethane,

^■ polymeric brominated compounds preferably brominated polystyrenes, brominated carbonate oligomers (BCO's), brominated epoxy oligomers (BEO's), tetrabromophthalic anyhydride, Tetrabromobisphenol A(TBBPA) and hexabromocyclododecane (HBCD).

^■ antimony preferably pentoxide and sodium antimonite

^■ organophosphorus compounds preferably organophosphate, TPP, RDP, BPADP, tri-o-cresyl phosphate,

^■ phosphonates preferably DMMP and phosphinates.

^■ chlorophosphates like TMCP and TDCP.

■

The composition according to the invention can also comprise some optional functional ingredients like

air-entraining agents (surfactants e.g. natural resins, sulfated or sulfonated compounds, synthetic detergents, organic fatty acids and their mixes, preferably among the lignosulfonates, the basic soaps of fatty acids and their mixes, and, more preferably in the group comprising the sulfonate olefins, the sodium lauryl sulfate de sodium and their mixes; accelerators (calcium salts, carbonates, preferably lithium or sodium and their mixes);

retarders (tartric acid and its salts: sodium or potassium salts, citric acid and its salts: sodium (trisodic citrate) and their mixes;

- plasticizers;

fibres;

dispersion powders;

wetting agents;

polymeric resins;

- complexing agents and;

aqueous dispersions.

Additives' concentration can be from 0,1% to 10% by weight of the total weight of the composition. EXAMPLES

-A- Materials and methods

GGBS: delivered from ECOCEM France (Fos/Mer) 2013.

Non GGBS-based binder: Portland cement (in short CEMI): CEMI 52.5R, Lafarge.

Activator: Sodium metasilicate: provided by SILMACO NV, powder, disodium metasilicate anhydrous (module 1.0) 2013.

OA1 : Calcium peroxide: Ixper from Solvay, 79% purity.

OA2: Sodium carbonate peroxyhydrate-coated: Oxyper-S CS from Solvay, 89% purity. OA3: MnQ ₇ : CDMA 52, 81% purity.

OA4: KMnQ ₄ : RHONE - POULENC, for quantitative analysis in laboratory.

The chemical agents were added to the dry mixtures before casting. The paste was casted into a plastic tube covered with lid to avoid the contact with air. Several days after casting, the samples were demoulded, and split into half to observe the interior colour. The tested oxidation agents OA include two families: peroxide family (like Ca0 ₂ , 2Na ₂ C0 ₃ -3H ₂ 0 ₂ ) and manganese family (like Mn0 ₂ , KMn0 ₄ ).

-B- Experiments (1) OA1: Calcium peroxide

Calcium peroxide is a strong oxidant, used usually in agriculture as an oxygen fertilizer or in the aquaculture industry to disinfect water. When the product is in contact with water, it can decompose and release oxygen as the equations (1) and (2). Calcium peroxide is easily dissolved in acid, but almost insoluble in water (solubility: 1.65 g/1 at 20°C) or basic solution. Ca0 ₂ +2H ₂ 0→ Ca(OH) ₂ +H ₂ 0 ₂ Eq.(l)

H ₂ 0 ₂ → H ₂ 0 + ½ 0 ₂ Eq.(2)

Binders with different addition of Ca0 ₂ were prepared. The pastes were casted with 100% GGBS activated by 4% sodium metasilicate with water/binder ratio of 0.47. Several days after casting, the samples were demoulded, and split into half to observe the interior colour. The exterior and interior colour of the samples varies from blue to colourless with the increasing of Ca0 ₂ percentage. 4% seems appropriate to eliminate the blue/green colour.

See Figure 1

(2) OA 2: Sodium carbonate peroxydrate

Sodiumcarbonate peroxydrate is in the same family as calcium peroxide, also used as an oxidation agent. It is produced industrially through absorbing hydrogen peroxide by sodium carbonate. When the product gets into contact with water, it can dissociate into hydrogen peroxide and sodium carbonate, and the hydrogen peroxide releases oxygen, as in equations (3) and (4). Comparing to calcium peroxide, sodiumcarbonate peroxydrate is soluble in water (solubility: 140 g/1 at 20°C). It can release oxygen much faster.

2Na ₂ C(V3H ₂ 0 ₂ → 2Na ₂ C0 ₃ + 3H ₂ 0 ₂ Eq.(3)

H ₂ 0 ₂ → H ₂ 0 + ½ 0 ₂ Eq.(4)

Binders with different addition of 2Na ₂ C0 ₃ '3H ₂ 0 ₂ were prepared. The pastes were casted with 100% GGBS activated by 4% sodium metasilicate with water/binder ratio of 0.47. Several days after casting, the samples were demoulded, and split into half to observe the interior colour. From Figure 2, it can be seen that from 0.5% of addition, the porosity of the sample becomes important, until 2% a foam was created. At the same time, along with the increasing of 2Na ₂ C0 ₃ '3H ₂ 0 ₂ content, the "blue" colour gets lighter and lighter.

See Figure 2 (3) OA3: Manganese dioxide

Manganese dioxide, having a black or brown colour, occurs naturally as the mineral pyrolusite. Mn0 ₂ can oxidize and catalyze sulphide solution with the following equations (5) and (6). Mn ₂ 0 ₃ can be oxidized by oxygen in atmosphere to Mn0 ₂ for reuse. 2R ₂ S + 8Mn0 ₂ + H ₂ 0→ R ₂ S ₂ 0 ₃ + 2ROH + 4Mn ₂ 0 ₃ Eq. (5)

2Mn ₂ 0 ₃ + 0 ₂ → 4Mn0 ₂ Eq. (6) Binders with different addition of Mn0 ₂ were prepared. The pastes were casted with 100% GGBS activated by 4% sodium metasilicate with water/binder ratio of 0.47. Several days after casting, the samples were demoulded, and split into half to observe the interior colour. The exterior and interior colour of the samples varies from blue to colourless with the increasing of Mn0 ₂ percentage. An addition of 0.5% is effective to eliminate completely the blue colour.

See Figure 3

(4) OA4: Potassium permanganate

Binders with different addition of KMn0 ₄ were prepared. The pastes were casted with 100% GGBS activated by 4% sodium metasilicate with water/binder ratio of 0.47. Figure 4 shows the photos taken with different reaction times after the mixture of raw materials. Colour evolution was remarked along with mixture time: from violet to green, and then yellow, probably another green which depends on the added quantity. The "violet" is the typical colour of KMn0 ₄ dissolving in water. The following "green" is likely due to the K ₂ Mn0 ₄ green colour. The "brown-yellow" colour can be attributed to the Mn0 ₂ or MnOOH brown colour. For 0.3% KMn0 ₄ addition, another "green" colour appeared at 5 days, however, this colour is different with the first appearance of "clear green" colour observed at 5h, it looks like the green colour issued in our study. In summary, 0.5%> KMn0 ₄ seems effective to eliminate the blue/green colour, although the final product is not totally white, it has more or less brown colour in sample.

(5) Mortar test with Mn0 ₂

In example 5, normalised mortar tests were effectuated. 0.5% Mn0 ₂ was added into the binder in the purpose of verifying its discolouration capacity. Two modes of storage were tested: in water and in mould maintained for two weeks respectively, which are typically found in the precast industry. At the same time, the influence of Mn0 ₂ addition on compressive strength was researched.

5.1 Material and method

Two types of binders were tested: GGBS activated by 4% sodium metasilicate and mix of 70% GGBS and 30% CEMI. The mortars were casted with normalised sable (< 2mm) and w/b 0.47. Mn0 ₂ (0.5%> in mass of GGBS) was added in the dry mix. The casting was effectuated according to the Norm EN 196-1 : slow mix for 30 second, fast mix for 30 second, followed by a rest for 90 second, and finally fast mix for 60 second. Then the samples were casted in polystyrene mould, covered with plastic film and conserved at ambient. One part of the samples was demoulded after 2 days, and conserved into water for two weeks. The rest of samples were kept in moulds for 2 weeks. The compressive 5 strength was measured after 2 weeks of conservation in water or in mould on a 3R 260K press with a load speed of 2.4K /sec.

5.2 Results

Figure 5 shows the surfaces of samples after 2 weeks of storage. For GGBS activated by0 4% sodium metasilicate, the reference manifested the traditional blue colour as observed before. With the addition of 0.5% Mn0 ₂ , this blue colour disappeared. The phenomenon was observed for both two cases of conservation: in mould and in water. For the mix of 70% GGBS and 30%> CEMI, the reference displayed only a zone of blue colour at the bottom of the sample in the case of conservation in mould. The blue colour was more5 concentrated and remarkable when the sample was kept in water (see the non-free surface in water). With the addition of 0.5% Mn0 ₂ , this blue colour was not observed at all. Table 1 gives the comparison of compressive strength with and without added Mn0 ₂ . Considering the diversity of samples, the difference of compressive strength is considered as negligible. So, the addition of Mn0 ₂ has no side effect on compressive strength of0 mortars.

Table 1. Compressive strength with and without the addition of MnC>2 in the mortar tests

Conservation Reference +0.5% Mn0 ₂

GGBS In mould 30.2(±0.9) 28.8 (±1.1)

+4% Si a In water 30.9(±0.1) 28.3(±0.8)

70% GGBS In mould 48.2(±0.1) 49.1 (±2.0)

+30% CEMI In water 55(±1.8) 53.8(±1.3)

5.3 Minimization of Mn0 ₂ quantity for mortar tests

5 Under the consideration of economic benefits, the manganese addition was minimized for colour issues. A series of Mn0 ₂ from 0.1% to 0.4% was investigated with the formulation of GGBS activated by 4% sodium metasilicate. Two curing conditions were used: in mould or in water for two weeks. After curing, the samples were taken for photos immediately (marked as t=0 day) as well as exposing to air for one day (marked as t=l day). Figure 60 gives the images of samples. For curing in mould and t=0 day, the blue colour maintained for all of these four samples (from 0.1% to 0.4% of addition); but the colour intensity reduced for high Mn0 ₂ addition. When the samples were exposed to air for one day (t = 1 day), the colour faded, and it completely disappeared with 0.4%> addition of Mn0 ₂ . For curing in water, only some blue spots were found on the surfaces of samples (notably 0.1 % and 0.2%>) at t=0 day. When they were exposed to air for one day (t = 1 day), the blue colour totally disappeared for all the percentages of addition, the samples displayed a white colour.

In summary, the minimal quantity of Mn0 ₂ depends on the curing condition. When the samples are cured in mould, the addition of 0.4%> meets some given aesthetic requirements, if the samples are allowed to expose to air for at least one day. When the samples are cured in water, 0.1% Mn0 ₂ makes it possible to comply with said aesthetic requirements, if the samples are allowed to expose to air for at least one day.