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Introduction

Portland cement is most often a gray or slightly brownish color due to the presence of

coloring oxides in the clinker. For certain applications, usually aesthetic ones, it may be

desirable to use a lighter or white Portland cement. While white cement is seen as a luxury

product, there are a number of practical applications. Superficially, white cement can be used on

its own for surface treatments, such as in a dry shake on flatwork, with or without a pigment.

Decoratively, white cement concrete can be used to make terrazzo, architectural fixtures, and

sculptures or exterior cladding. In this way, decorative concrete can be cast with the flexibility

of concrete, letting the imagination dictate the size and shape, while at the same time mimicking

more convincingly the appearance of natural stone. Practically, white cement concrete can be

used to increase safety or energy efficiency. Because it is highly reflective, it can either

highlight median barriers or increase the light in large industrial building. Alternatively, the

reflectance can be used to maintain the same level of light in a room with fewer light fixtures or

can be used to reduce the costs of heating/cooling. Examples of these uses can be seen below in

Figure 11.

(a) (b)

Figure 1: Practical and decorative uses of white cement and white cement concrete (a)

a median barrier, (b) a highly reflective floor1.

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Finally, white cement concrete can be used structurally, in the same manner as gray cement

concrete, with the added drama of color. Unlike the dry shake or exterior cladding, the color is

integral with the structure and less maintenance is required of the surface if there is chipping or

cracking exposing the interior concrete. A case study of structural white cement concrete, the

new Jubilee Cathedral (Dio Padre Misericordioso) in Rome, is discussed at the end of this report.

Particularly interesting is the attention given by Italcementi Gruppo, the precast concrete supplier

on this project, to aesthetic durability.

This report will address the following questions common in the discussion of white cement

concrete:

Where is white cement being produced? Where and how is it being used? In what ways do gray Portland cement and white Portland cement differ with respect to

chemical composition and manufacture?

How does this cement type influence mix designs, aggregate choice, and admixtureusage?

How is the construction process influenced by the use of white cement concrete? Are there differences in mechanical properties?

Figure 1: (c) a balustrade1.

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What are the long-term concerns that must be addressed with white cement concrete?

Geography

Though produced and available in all around the globe (North America, Europe, Africa,

Middle East, Asia), the world-wide market is dominated by the Aalborg White, part of Aalborg

Portland A/S which is the only cement producer in Denmark, whose world-wide production is

estimated at 1.5 million metric tons2.

As a luxury product, white cement concrete is most often seen in high profile buildings,

such as cathedrals and major hotels. Here, the white cement concrete is one of the architects

most novel tools and has been increasing in popularity. For such projects, it is necessary to use a

major producer of white cement to ensure that the large amounts of concrete have uniform color.

However, for the low-profile, decorative or practical applications mentioned earlier, local white

cement manufacturers, selling by the 20-50kg bag, are adequate and convenient.

White Portland Cement

Remove all the coloring components in Portland cement to make white Portland cement is

much easer said than done. The raw materials that are used must be chosen carefully and

screened to minimize the presence of coloring oxides, and the production process must be

monitored to maintain the lightness and whiteness.

Raw Materials

Because the gray color of concrete can be attributed to its iron content, it is expected that

the first step taken to make a lighter and whiter cement would be to keep the iron content in the

raw materials as low as possible. Lightness can be measured by reflectance, and compared to a

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very light reference standard (MgO powder is considered to have a reflectance of 100%).

Furthermore, other coloring oxides include manganese, chromium and magnesium, and though

the lightness of the resulting cement may be the same, there may be some hint of color that is

undesirable in the white cement3, 4

. Therefore, it is recommended to keep these coloring oxides

below the following values in the raw mix:

Table 1: Recommended maximum values of coloring oxides in raw materials in the production

of white cement clinker3.

Compound Recommendedlimit

Color influence on clinker

Fe2O3 < 0.4 % gray

Mn2O3 < 0.02% grayish-violet,

reddish-violet

Cr2O3 < 0.01 % greenish

MgO < 3% greenish-brown

To keep these values below these recommended values, the raw materials used to make

the clinker should have low amounts of these oxides. Examples of these are china clay

(kaolinite) and white chalk or limestone. However, if they do not contain enough free silica,

ground white sand is added to the mix5. To further lower the content of these coloring oxides in

the raw materials, it can be beneficial to remove the fine particles, in which the undesirable

(coloring) oxides are more particularly concentrated, by preliminary screening before the

material is fed to the crusher3.

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Production / Manufacture

As a result of keeping the iron levels as well as the levels of other coloring oxides low,

white cement manufacture requires higher clinkering temperatures than (gray) cement

manufacture does in order to achieve more or less complete combining of lime in the burning

process4. This is one reason why white cement manufacture is more expensive than gray

cement manufacture.

Keeping the raw materials constant, the resulting cement clinker can still have varying

lightness and color. Therefore, though much effort may be taken to ensure that the raw materials

have the appropriate composition, further care must be taken during the production process,

when other sources of coloring oxides are present and may adversely affect the lightness or

whiteness of the cement. These sources include the grinding media and mill lining materials and

the fuel used for burning the clinker. It is recommended that ceramic grinding media and mill

liners be used instead of metallic ones, because iron and chromium may be mixed in as it is

abraded from those surfaces. This is particularly crucial if there is a high amount of free quartz

in the raw meal. In addition, oil fuel is often used in place of pulverized coal in the burning

process to avoid contamination by coal ash3.

Titanium dioxide is sometimes added to cement for a brightening effect, but tests have

shown that it may not have any actual affect on the brightness of the cement. However, as will

discussed in the case study, titanium dioxide can be added to maintain the whiteness of the

cement over time.

Regulations and Standards of Practice

ASTM has no specification explicitly for white cement, though producers of white

cement will conform to the requirements in ASTM C 150 for cement Types I, II, III and V or the

corresponding European or country standards. Because there are such low amounts of C4AF,

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there are usually higher amounts of C3S and C3A, which makes Types I and III more common.

However, ASTM C 150 does not address the issue of the cements lightness or color6.

As mentioned before, it is useful to quantify the cements lightness using its reflectance

compared to a reference standard, which is the industry norm for rating the whiteness of a

producers cement. Ordinary commercial grades of white cement (have) a whiteness of 80 84

per cent; superior grades of world market quality have a whiteness of 84 88 per cent.

Whiteness values above 88 per cent are attainable only by using very special raw materials3.

Chemical Composition of Clinker

The following tables list the ASTM requirements for various types of cement and typical

chemical compositions of white cement available. Figure 2 is the product information given

from Aalborg White, which can certainly be classified as world market quality. It should be

noted that the lightness (brightness of colour) of the clinker is enhanced by grinding to a high

degree of fineness, so white Portland cements are generally finer than gray ones4.

Table 2: Comparison of gray and white cement compositions5

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Table 3: ASTM cement composition requirements7

Figure 2: Commercially available white cements, from Aalborg White8.

C3A levels are often very high for white cements, making it easier for cement

manufacturers to conform to Types I and III, though Types II and V are also available. This

cement available from Aalborg White conforms to all of those types. Because the raw materials

are so carefully chosen, white cement usually has a low alkali content, making alkali-silica

reaction less of a concern1.

Concrete Mix Design

As mentioned before, white cement can be used alone for surface treatments of gray

cement concrete. In white cement concrete, the aggregates added are usually colored.

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Therefore, to maintain uniform color in white cement concrete, the mix design will be changed.

It is generally richer in cement and has higher fine sand content6. Generally, it is favorable to

have a continuously graded aggregate, but surface effects can be made when gap grading

aggregates.

Because aggregates impart a pigmenting effect on the final concrete, aggregate choice is

often dictated by color. This is particularly true of the fine aggregates, and it is usually

recommended that light colored sand be used. If a very white concrete is desired, white coarse

aggregates, marble or limestone, are used. However, the white cement can allow dramatic color

play to be made with distinctly colored aggregates. This is done particularly for terrazzo. The

following figure shows what surface textures can be achieved with white cement and various

aggregates.

Figure 3. Various effects achieved with white cement concrete and white or colored aggregate8.

Mineral admixtures may still be added to (or used as replacement for) white cement in

concrete, but these should be as close to white as possible. For very white concrete, common

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pozzolans (fly ash) are not used. Instead, there are choices between white silica fume,

metakaolin, and slag1.

Chemical admixtures should also be colorless, and their use be evaluated on a test

specimen before actual usage. Interestingly, the testing of compatibility of white cement with

various superplasticizers has shown that white cement concrete will exhibit higher fluidity with

the same dosage of superplasticizer than gray cement concrete. This has been attributed to the

uneven adsorption of superplasticizer on different cement particles. It adsorbs more readily on

C3A and C4AF than on C3S and C2S and the more even the adsorption of (superplasticizer) on

cement mineral, the higher the fluidity of the paste will be. White cement will have a more

even adsorption because of its low C3A + C4AF and low alkali content. Thus, it exhibits higher

fluidity even though it is most often finer than gray cement. The results vary in degree for

various types of superplasticizer, but all those tested showed this same trend9.

(a)

(b) (c)

Figure 4: Effect of cement type

on fluidity, with varying

dosages of superplasticizer (a)

ordinary, (b) low alkali, (c)white cements

9.

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Construction

Even with the best white cement and mix design, however, one can still obtain variable

qualities of final product because of the construction methods used. With white cement concrete,

especially when using pigments, one must be more vigilant about keeping equipment clean,

maintaining quality of forms and finishing equipment, and using experienced finishers with the

right technique. Maintaining uniformity throughout the project cannot be stressed enough.

Batching of ingredients should be measured accurately and consistently1. Otherwise,

there will be local variations that will adversely affect the overall appearance of the structure. A

low water-cement ratio paste is almost always darker than a high water-cement ratio paste made

with the same cement, which can be seen in the figure below. Therefore, if there are variations

in water content from batch to batch, there will most likely be blocking of colors or shades.

Figure 5: Color variations with different water-cement ratios6.

The mixing procedure of white cement concrete is done in a similar manner to gray

cement concrete, though the mixing time is usually extended to ensure proper dispersion of

cement and pigment (if any) throughout the mixture. This is also necessary not only for color,

but also because concretes having higher cement content and more finely ground cement, which

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white cement concrete has, take longer to blend6. As with the measurements in batching, the

mixing times should be kept constant from batch to batch.

The usual placing techniques are still used with white cement concrete, but there are a

few points that can affect the appearance of white cement concrete in particular. Firstly, if there

is splattering of concrete onto the forms, there will be defects on the surface of the concrete.

This can be prevented by having a moderate slump and using an elephant trunk to guide the

concrete into place.

Formwork can also influence the color and surface condition of the completed concrete.

As with the metallic grinding media in the production of the clinker, the material of the

formwork can stain the concrete. For this reason, steel forms that impart coloring oxides are

either avoided or treated with rust-inhibiting compounds. Plastic forms, coated or uncoated,

have been used, but they may not be as durable unless a release agent is used. Untreated wood

can (also) discolor white or colored concrete1. Furthermore, the untreated wooden formwork

can absorb water from the surface of the concrete, resulting in local variations of water-cement

ratios that will, as mentioned before, different regions of lighter and darker concrete. Lacquering

can alleviate this as well as extend the life of the form. With all types of formwork, there is the

possibility of leakage that will also compromise local color and overall appearance. Tight forms

that do not leak will take care of this.

For white cement concrete flatwork, the finishing crew should be experienced so that

burning or blackening of the surface does not occur. This can happen when a metal trowel is

abraded by stiff concrete, but the primary reason is that the concrete is overfinished to the point

where the water-cement ratio is drastically reduced. Curing of white cement concrete should be

given as much or more attention as gray cement concrete. Plastic sheets should be avoided

because they can produce a mottled effect with incomplete contact to the surface of the

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concrete. Non-staining waterproof paper with a layer of dry sand have worked well. Curing

compounds are also safe to use without much risk of discoloration1.

Mechanical properties

The mechanical properties of white cement concrete are generally assumed to be the

same as those of gray cement concrete. However, because of the cement composition, there are

things to note about the strength evolution. Looking again at the chemistry of white cement,

there is generally more C3A and C3S than with gray cement. It is also ground finer. Because of

these reasons, the set time for white cement is usually shorter and the early strength usually

higher. The following figure compares gray and white cement concretes of different nominal

strengths at different ages. The early strength is much more pronounced in the concretes of

higher nominal strength. Note that in this experiment, the white cement used was coarser than

the gray cement. Therefore, it would be expected that for most white cements, the difference

would be even more marked10

.

Figure 6: Variations of cylinder compressive strength of concrete with age10

.

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Case Study

The Jubilee Cathedral, as seen in Figures 7 and 8, is a prime example of why and how

white cement concrete is used. It is located in the suburbs of Rome, where there are dozens of

cathedrals from hundreds of years of Roman Catholic Church history. This one, made to mark

the third millennium, still, as the architect Richard Meier puts it,

upholds the citys rich architectural tradition . . . (but) was always intended to be a

work of contemporary architecture, meaningful for our time and one that is marked by

openness. Transparency and light cascade down from the skylit roof, literally invading

the interior of the church.People in the atrium are enveloped with mystical light.

11

Figure 7: exterior of the Jubilee Cathedral, Tor Tre Teste, near Rome11

.

The precast, post-tensioned white cement concrete panels are indeed contemporary while

still giving the air of marble that so characterizes the Roman Catholic Cathedrals of the past.

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durability. In what they have patented as Bianco TX Millenium, Italcementi have added

titanium dioxide to the cement to maintain its whiteness over time. The photocatalytic particles

contained in the white cement allow it, once it has hardened in the form of paste, mortar, or

concrete, to oxidize the organic and inorganic air pollutants in the presence of air and light.

This attention to aesthetic durability is warranted, especially when one considers the effect of the

urban pollution on such famous structures in nearby Greece (i.e. the Acropolis)12

.

Conclusion

White cement technology has been used for primarily the luxury cement market and was

developed not out of need, but out of creativity. The structures and various other applications

have exploited the flexibility in form despite its increased cost, both of money and of attention.