THE COLOURING OF CONCRETEPROCESSING INSTRUCTIONS

The raw materials in the manufacture of coloured concrete products

1 The Pigment

The choice of pigment is of major importancefor the quality of the end-product. Years oftests on coloured concrete products exposedto different climate conditions all over theworld have shown that inorganic oxide pig-ments have particularly good fastness proper-ties.

LANXESS's Bayferrox and Chrome OxideGreen pigments satisfy these conditions andthus offer

"Quality for life".

Modern production facilities and a provenquality system have been setting standardsfor the processing of inorganic pigments inconcrete.

Which shades can be produced?

The oxide pigments commonly used in build-ing materials cover all the most popular col-ours. The shades are oriented to the opaquecolours as they occur in nature, and thus fitharmoniously in with the environment:

Red : yellowish bluish redYellow: greenish to reddish yellowBrown: light to dark brown / red brownBlack: dark grey to charcoal

In addition, white, green and blue can be pro-duced. Pure colours like yellow can be madeby using white cement.

Brilliant, glossy shades, like those obtained inplastics and surface coatings, are very difficultto produce in building materials because ofthe composition and structure of the concrete.

Planners, architects and builders nowadays have a variety of modern building materialsat their disposal which not only satisfy the primary technical requirements, but also haveaesthetic appeal. The use of coloured building materials like concrete roofing blocks,pavers etc. is an important element in designing the world we live in. Coloured concreteproducts have, in fact, been on the market for several decades, and their method of pro-duction differs only slightly from that of uncoloured products.

This brochure summarises the results of laboratory trials we carried out on the colouringof concrete, and also takes into account the experiences of the building industry. The aimis to provide the user of colour pigments with a guide for the manufacture of high-qualityproducts.

The most important oxide pigments

Colour Name LANXESS pigment_______________________________________________________________

Black Iron oxide black Bayferrox BlackRed Iron oxide red Bayferrox RedYellow Iron oxide yellow Bayferrox YellowBrown Iron oxide brown Bayferrox BrownGreen Chrome oxide green Chrome Oxide

Green

Demands made on pigments for colouringconcrete

Pigments must withstand the aggressive in-fluence of the strongly alkaline cement paste.They must also be lightfast and weather-stable, as well as insoluble in the mixing waterduring processing they must become firmlyintegrated in the concrete matrix. Inorganicpigments, and especially oxide pigments, areparticularly suitable for this.

The tinting strength of pigments

The tinting strength of pigments is an impor-tant quality characteristic which is essential inevaluating their cost-effectiveness. The tintingstrength is defined as the ability of a pigmentto impart its natural colour to the medium be-ing coloured. Let me give an example to ex-plain this.

The picture on the right shows two red pow-ders: brick dust on the left and a Bayferrox redpigment on the right. Only when they are usedto colour concrete or are tested in the labdoes the difference in tinting strength of thetwo samples become evident.

The laboratory test is carried out by mixing adefined amount of pigment with a definedamount of barium sulphate according toEN 12 878. This is the basis for the tintingstrength tolerances given in the productspecification for Bayferrox pigments.

Let us come back to a practical situation in theconcrete factory. An iron oxide red pigment"A" is currently being used. To attain a givencolour shade, a pigment concentration of10 % of this pigment is required.

However, as the concrete pavers show, it isequally possible to obtain the desired shadeby adding 3 % of red pigment "B".

The conclusion is that even if pigment "A" ischeaper, it is certainly not always the mosteconomical.

How are pigments supplied?

The demands made on the processability ofpigments have changed over the years.Whereas it was nearly always powder pig-ments that were used in the building industryin the initial years, aqueous pigment slurrieshave now also been making their mark.

Apart from the fact that the processor doesnot have any dust problems, there is also theadvantage of simple handling and metering.On the other hand, they contain a relativelyhigh proportion of water, which means highertransport costs than for powder pigments. Inaddition, the pigment may settle at the bottomif the pigment suspensions have not beenstirred for a long time. For these reasons, it isreally only worthwhile purchasing ready-to-usepigment suspensions if the supplier is in thelocal vicinity.

The latest development as regards the supplyform of pigments is as free-flowing dry pig-ment preparations. These have been devel-oped specifically for use in the building indus-try and allow easy emptying of silos, sacksand bulk bags, and make both silo storageand metering a perfectly clean affair becauseof their low-dust formation.

More information on supply forms and pack-aging is available on request.

Pigments and the environment

The production of Bayferrox and Chrome Ox-ide Green pigments at LANXESS DeutschlandGmbH involves the use of modern processeswhich ensure that the impact on the environ-ment and resources is kept to a minimum.

These pigments have neither a toxic nor anirritant effect on the skin or mucous mem-branes. Nevertheless, the development ofdust should be avoided for basic occupationalhealth reasons.

Although Bayferrox and Chrome Oxide Greenpigments do not harm aquatic organisms be-cause of their insolubility, they do lead toheavy discoloration of the water. Spilled pig-ments should therefore be mopped up wet ordry.

2 The influence of the cement colour onthe colour of the concrete

Grey not only makes the washing look grubby,it takes the brilliance out of absolutely anycolour, wherever it is used. This is why con-crete manufactured with normal Portland ce-ment is never going to produce such brightcolours as one made with white cement.

However, the gain in colour clarity obtained byusing white cement depends on which pig-ment is used. If the pigment is black, there isvirtually no difference between concrete madeof white and grey cement. With dark brownand red, the difference is slight, and with yel-low and blue, it is very pronounced. Thebrighter and cleaner the desired shade, thegreater the dependency on white cement.

This difference in the colouring of white andgrey cement is easily understandable even forthe layman. People in the trade will, however,also be aware of the fact that grey cement canvary appreciably in colour from light to darkgrey. When changing over the grade of ce-ment or cement supplier, it often happens thatthere are differences in the natural colour ofthe cement which can have an appreciableinfluence on the final colour.

3 The aggregates

In the production of coloured concrete, theaggregate particles are covered by the pig-mented cement paste. It is possible that thegrains of an intensively coloured aggregate donot become completely covered, resulting inthe colour of the final concrete being affectedby the natural colour of the aggregate. Whilethis effect can be apparent even during theproduction of the coloured concrete, it be-comes particularly evident when the end-product is exposed to the weather, as the ag-gregate particles become visible throughweathering of the surface. What we then seeis a mixed shade made up of the colour of thecement paste and the exposed aggregate.

Like cement, the natural colour of the sandalso has a more marked effect on light-coloured concrete (e.g. yellow, green) than ondark concrete (e.g. brown, black).

Influence of the cement colouron the final colour shade

Influence of the aggregate colouron the final colour shade

Influence of the formulation on the colour of the concrete

1 Influence of the pigment concentrationon colour

Knowing the optimum pigment concentrationhelps to save money because we then knowwe are not adding more pigment than is ab-solutely needed.

If increasing amounts of pigment are added toa concrete mix, the colour intensity initiallyrises linearly with the pigment concentration.

However, as more and more pigment isadded, we move into a range in which theaddition of further pigment does not signifi-cantly deepen the shade and is therefore un-economical. Establishing the saturation rangeis dependent among other things on the sys-tem parameters of the concrete but, in gen-eral, additions above 5 % (calculated on thebinder) are not necessary for the high-strengthBayferrox pigments.

With the weaker pigments, the saturationrange is not reached until much largeramounts of pigment are added. The amount ofpigment required to produce a given shadecan sometimes be so large that this increasein the quantity of fines has a negative effecton the technical properties of the concrete.

2 Water-cement ratio and the colour ofconcrete

Have you ever wondered when looking at aglass of beer why the froth is white eventhough the beer itself is yellow?

The foam consists of many tiny air bubbles,which scatter the light in the same way that

white pigments do. This digression is impor-tant because it explains the relationship be-tween the colour of the concrete and its water-cement ratio. The excess mixing water evapo-rates from the concrete and leaves behindcavities in the form of fine pores. These actlike the bubbles in the beer froth. They scatterthe incident light and thus make the concretelighter. Thus the higher the water-cement ra-tio, the lighter the concrete appears. As thephoto on the right shows, grey concrete with-out any pigment is just as much subject to thislaw as pigmented concrete.

What does this mean in practical applica-tion?

If we compare the colour of different concretewith varying water content (e.g. concretepavers and in-situ concrete), we find that,even if the pigment concentration is the same,the colour differs.

If we make comparisons within a single prod-uct line, we get a different picture. To ensureunproblematical processing of the concretemixture through a concrete manufacturingunit, its consistency normally has to be keptwithin narrow limits, which means that themanufacturer must meter the mixing watervery carefully. For this reason, colour fluctua

Influence of the pigmentationlevel on the final colour shade

Influence of the water-cement (w/c) ratioon the colour of the concrete

tions within a production line due to the water-cement ratio tend to be the exception ratherthan the rule. On the other hand, the differ-ences in shade can be appreciable if the ex-cessive moisture in the concrete results in theformation of a surface sludge on the concrete.This sludge – also called 'orange-peel' inpaving block manufacture – contains the veryfine components of the concrete such as ce-ment, fines and an above-average accumula-tion of pigment, so that the concrete takes ona different appearance than if there were littleor no sludge on the surface.

3 The colour of the concrete in relation tot

Igpu

Fmosac"accwmcal

he cement content

n the colouring of concrete, it is not the ag-regate that is pigmented, but the cementaste, which then forms a layer on the individ-al aggregate particles.

or our considerations as to whether the ce-ent content exerts an influence on the colour

f the pigmented concrete, we will, for theake of simplicity, assume that we are talkingbout a mixture of two substances: colouredement paste and aggregate. The more wedilute" the coloured cement paste with theggregate, the less intensive the colour of theoncrete. This theoretical consideration isonfirmed by practical experience. A concreteith a high cement content will, at equal pig-

ent concentration (which is usually a per-

entage based on the weight of cement) have much stronger colour than a concrete with a

ower cement content.

Influence of the cement contenton the colour of the concrete

Influence of the cement content on the colour of the concrete

1 Metering and dispersion of the pigmentsin the concrete

Today, quality plays an increasingly importantrole.

Because accurate metering and homogene-ous dispersion of the pigments are essentialfactors in the manufacture of high-quality col-oured concrete products, the building industryhas devoted considerable effort to establish-ing the optimum parameters.

As regards the dispersion of the pigments, ithas been found that it is very critical to knowwhen the pigment should be added to themixer. Experience has shown that the idealsequence is to mix the pigment with the ag-gregate for about 15 seconds before the ce-ment is added.

From then on, the mixing proc-ess is the same as with unpig-mented concrete. Somethingwhich must be avoided at allcosts is the adding of all thecomponents simultaneously, orthat cement is mixed in immedi-ately after the sand. The mixingtime naturally also plays an im-portant role in whether or not ahomogeneous dispersion of thepigment is achieved.

Every mixer needs a minimummixing time. With forced circula-tion mixers, this is 1.5 – 2 min. Ifthe time is reduced, it will not be

possible to produce a homogenous mix evenby altering the individual mixing time or theadding sequence for the individual compo-nents.

Once the amount of pigment used in a con-crete factory reaches a certain level, thequestion automatically poses itself as towhether the addition of the pigment can beautomated. As is often the case with technicalsolutions, there are advantages and disad-vantages. There is no all-embracing answer to

the question of whether wet ordry metering is the most fa-vourable. All we can do is pro-vide suggestions to help plantengineers decide one way orthe other, while taking commer-cial aspects into account. Thetable on the right endeavours toshow, in simplified form, theadvantages (+), disadvantages(–) and comparability (=) of thevarious metering methods.

Alongside the obvious advan-tages of automatic pigmentmetering, the concrete pro-ducer also has the possibility ofproducing additional shadeshimself. Bayferrox pigments are

manufactured in the basic colours red, blackand yellow. Various shades are also availablewithin each of these colour ranges.

By combining two or three Bayferrox pig-ments, it is possible to produce an almost un

Dispersion of the pigments

Recommended sequence for adding to the concrete mixer:Aggregates + premixed pigment + cement + water

Mixing time with forced circulation mixer: 1.5 - 2 min

Mixing time:Sand + pigment approx. 15 - 20 sSand + pigment + cement approx. 15 - 20 sSand + pigment + cement + water approx. 1 - 1.5 min

Every type of mixer has a minimum mixing time. With shorter mixingtimes, homogeneity is not longer possible, even if the mixing times ofthe individual ingredients or the order in which these are added arechanged.

The required mixing times are highly dependent on the performance ofthe concrete mixer. The data given here on mixing time are only a roughguide.

Pros and cons for the various metering methods

1 = powder; 2 = micro granules;3 = on site slurry: 4 = pre-manufactured slurry

Dry metering Liquid metering

1 2 3 4

Accuracy = ++ = =

Space requirements - ++ + +

Cleanliness + ++ + ++

Aggregates (wet sand) ++ ++ -- (+)

CostInvestment -- + -- (+)Operating cost (+) (+) + --

Colour change = = = =

limited number of shades. Here, for example,a Bayferrox red pigment has been combinedwith a Bayferrox black to produce a brownshade.

Present-day concrete mixing technology al-lows several individual pigments to be addedsimultaneously to the concrete mixer. There isno need to premix the pigments.

2 Influence of the hardening conditions onthe shade of the concrete

The hardened cement paste, which is formedfrom the reaction between the mixing waterand the cement, produces crystals of varyingsize, depending on the temperature at whichthe concrete is hardened. The size of thesecrystals is, in turn, responsible for how thelight which falls onto the concrete is scattered.The following principle basically applies:higher hardening temperatures result in finercrystal needles, and the more pronouncedlight scattering of fine crystal needles makesthe colour of the concrete lighter than that ofthe same concrete hardened at lower tem-peratures. However, this phenomenon gener-ally only becomes recognisable when the dif-ference in temperature reaches a certain or-der of magnitude, for example, when steam-hardened concrete is compared with concretehardened at normal room temperature.

Combination of Bayferrox pigments Influence of the hardening temperature

The weathering behaviour of pigmented concrete

The Roman aqueduct, which supplied Co-logne with water from the Eifel hills two thou-sand years ago, was built with trass orposzolanic cement. Had this antique "con-crete" been pigmented with natural iron ox-ides – which at that time were already known– the structure (parts of which can still beviewed) would still have been coloured today.The difference from the original shade wouldhave been quite small. These colourchanges, which manifest themselves just asmuch on uncoloured as on coloured concrete,have various causes and may be both of atemporary (e.g. efflorescence) or a perma-nent (e.g. surface exposure of the aggregate)nature.

1 Efflorescence

Efflorescence is the curse of all concretemanufacturers, especially when colour is in-volved and when particularly high demandsare made on the appearance of the concrete.To begin with, it is important to note that nei-ther Bayferrox nor Chrome Oxide Green pig-ments exert any influence on the occurrenceof efflorescence. Nevertheless, it is obviousthat deposits of white lime are more notice-able on a coloured concrete than on naturalgrey or even white concrete.

Efflorescence is the result of free lime, whichis dissolved in the mixing water (primary efflo-rescence) or in rain or dew (secondary efflo-rescence), depositing on the surface of theconcrete, where it reacts with carbon dioxide

in the air to form insoluble calcium carbonate.The porosity of the concrete plays an impor-tant role here. The more compact it is, thelower the tendency to efflorescence. In a slowreaction, the calcium carbonate on the sur-face of the concrete is able to react with car-bon dioxide dissolved in water to form cal-cium bicarbonate, which, in turn, is soluble inwater. In this way, the efflorescence iswashed off again by the weather. Acid con-stituents in the atmosphere naturally alsohave a dissolving effect on lime deposits onthe concrete surface.

A special report on the subject of "Efflores-cence on concrete" has been published byLANXESS Deutschland GmbH and is avail-able to customers on request.

2 Weathering of the hardened cementpaste

On the surface of the concrete there is asludge layer consisting of the aggregate fines

and the cement. Its thick-ness depends on the for-mulation, method of com-paction etc. This layer isgradually weathered awayand, after a few years, theaggregate particles in thesurface become exposedresulting in their contrib-uting more to the overallcolour of the system.

The next photo shows thatthe colour changes inpigmented building mate-rials are relatively small.Compared with the un-weathered specimen inthe foreground, concrete

Weathering of efflorescence

bricks exposed for 25 years to the weather onthe weathering stand show very little changeapart from a slight soiling of the surface.

3 Weather stability of the pigments

Provided weather-stable pigments such asBayferrox and Chrome Oxide Green pig-ments – in other words, oxide pigments – areused for colouring building materials, the col-our is permanent. This statement is based onthe experience gathered during a quarter of acentury of systematic trials on the stability ofpigmented building materials. In these stud-ies, which deal with a variety of stabilityproblems, it was also found that only our out-door weathering tests are really able to pro-vide reliable information on the weather sta-bility of pigments in building materials.

Technical properties of the coloured concrete

1 Strength of the concrete and solidifica-tion behaviour of the cement

In EN 12 878 the demands made on pig-ments for the colouring of cement and lime-based building materials are defined. Besidesdealing with questions regarding the testingof pigments etc., the standard also lays downthresholds for the extent to which pigmentsmay exert an influence on the solidificationbehaviour of the cement and the strength ofthe concrete. In corresponding tests at an in-dependent testing institute which have beencarried out at regular intervals for some timenow, it was found that the Bayferrox pigmentscomply with the limits laid down in the stan-dard.

2 Consistency of the concrete

Pigments have very fine particles. Exact de-tails on the mean particle size, which canvary considerably depending on the type, canbe found in the Bayferrox colour card. As arough guide, it can be said that pigments areapproximately 10 - 20 times finer than ce-ment. With this in mind, a pigment processormay well ask whether the addition of such afine product does not have an influence onthe water requirement of the concrete.

As far as the Bayferrox pigments are con-cerned, the amounts of Bayferrox red andblack that are normally added in practicehave virtually no effect in this regard.

However, iron oxide yellow pigments differfrom black and red iron oxides in that theyhave a needle-shaped structure and cantherefore adsorb more water on the surface.Nevertheless, this effect only becomes no-ticeable at pigment concentrations aboveapprox. 4 - 5 %. Where pigments with hightinting strength are concerned, such as theBayferrox yellows, this value is generally notexceeded, which means that the higher wateradsorption of the yellow pigments is only oflimited interest to concrete manufacturer.

Slump (water/cement ratio 0.56)

FORSCHUNGSINSTITUT DER ZEMENTINDUSTRIE, DÜSSELDORF

Grundprüfung für Pigmentenach DIN EN 12878

Tagebuch-Nr.081t11

Pigment:

Bezeichnung durchHersteller - Einlieferer:

Eingeliefert von:

Rotpigment

Bayferrox 110

LANXESS Deutschland GmbH, Werk Uerdingen Einsans ami 08.1 1 .2004

Leim/Mörtel (CEM | 42,5 R) Ohne Pigment mit Pigment*) Differenz

Erstarren

Beginn 140 min 125 min - 1 5 m i n

Ende 165 min 165 min 0 mtn

Wasseranspruch 28.5 M.-% 30.0 M.-o/o

Raumbeständigkeit (Le Chatelier) 1 . 0 mm 1 . 0 mm

Druckfestigkeit Einzetwerte28 Tage(in MPa)

Mittelwert

55.455.855.256.155.656.4

55.456.257.156.855.656.5

55.8 56.3 + 0.9 '2"

Mikroskopischer und chemischer Befund

Wasserlösliche Anteile 0.08 M.-%

Chloridgehalt <0.01 M.-o/o

Nitratgehalt <0.01 M.-%

Sulfatgehalt als SOa2- <0.01 M.-o/o

Hauptbestandteile

Hämatit (FezOs)

Die Überprüfung erfolgte durch Röntgenbeugungsanalyse

Anmerkungen

Die Anforderungen an Einzelpigmente bei der Grundprüfung nach DIN EN 12878wurden erfüllt.

Die Hauptbestandteile des Pigments entsprachen nach Art den Angabendes Pigmentherstellers.

*)Die Pigmentzugabe bei Erstanungs- und Druckfestigkeitsprüfung betrug 5 % bezogen auf die Zementmenge.

wiB z.B. Messoeräto. Messverfahren Kalibrierdaten und

Düsseldorf, den

Sachbearbeiter

01.02.2005

,K*tngsinstitut der ZementindustrieO

Abteilung Qualitätssicherung

LSybertz)

t(Dipl.-lng. Loewe)