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Introduction<br />
Portland cement is most often a gray or slightly brownish color due to the presence of<br />
coloring oxides in the clinker. For certain applications, usually aesthetic ones, it may be<br />
desirable to use a lighter or white Portland cement. While white cement is seen as a luxury<br />
product, there are a number of practical applications. Superficially, white cement can be used on<br />
its own for surface treatments, such as in a dry shake on flatwork, with or without a pigment.<br />
Decoratively, white cement concrete can be used to make terrazzo, architectural fixtures, and<br />
sculptures or exterior cladding. In this way, decorative concrete can be cast with the flexibility<br />
of concrete, letting the imagination dictate the size and shape, while at the same time mimicking<br />
more convincingly the appearance of natural stone. Practically, white cement concrete can be<br />
used to increase safety or energy efficiency. Because it is highly reflective, it can either<br />
highlight median barriers or increase the light in large industrial building. Alternatively, the<br />
reflectance can be used to maintain the same level of light in a room with fewer light fixtures or<br />
can be used to reduce the costs of heating/cooling. Examples of these uses can be seen below in<br />
Figure 1 1 .<br />
Figure 1: Practical and decorative uses of white cement and white cement concrete (a)<br />
a median barrier, (b) a highly reflective floor 1 .<br />
(a) (b)<br />
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Figure 1: (c) a balustrade 1 .<br />
Finally, white cement concrete can be used structurally, in the same manner as gray cement<br />
concrete, with the added drama of color. Unlike the dry shake or exterior cladding, the color is<br />
integral with the structure and less maintenance is required of the surface if there is chipping or<br />
cracking exposing the interior concrete. A case study of structural white cement concrete, the<br />
new Jubilee Cathedral (Dio Padre Misericordioso) in Rome, is discussed at the end of this report.<br />
Particularly interesting is the attention given by Italcementi Gruppo, the precast concrete supplier<br />
on this project, to aesthetic durability.<br />
This report will address the following questions common in the discussion of white cement<br />
concrete:<br />
Where is white cement being produced? Where and how is it being used?<br />
In what ways do gray Portland cement and white Portland cement differ with respect to<br />
chemical composition and manufacture?<br />
How does this cement type influence mix designs, aggregate choice, and admixture<br />
usage?<br />
How is the construction process influenced by the use of white cement concrete?<br />
Are there differences in mechanical properties?<br />
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What are the long-term concerns that must be addressed with white cement concrete?<br />
Geography<br />
Though produced and available in all around the globe (North America, Europe, Africa,<br />
Middle East, Asia), the world-wide market is dominated by the Aalborg <strong>White</strong>, part of Aalborg<br />
Portland A/S which is the only cement producer in Denmark, whose world-wide production is<br />
estimated at 1.5 million metric tons 2 .<br />
As a luxury product, white cement concrete is most often seen in high profile buildings,<br />
such as cathedrals and major hotels. Here, the white cement concrete is one of the architect’s<br />
most novel tools and has been increasing in popularity. For such projects, it is necessary to use a<br />
major producer of white cement to ensure that the large amounts of concrete have uniform color.<br />
However, for the low-profile, decorative or practical applications mentioned earlier, local white<br />
cement manufacturers, selling by the 20-50kg bag, are adequate and convenient.<br />
<strong>White</strong> Portland <strong>Cement</strong><br />
“Remove all the coloring components in Portland cement to make white Portland cement” is<br />
much easer said than done. The raw materials that are used must be chosen carefully and<br />
screened to minimize the presence of coloring oxides, and the production process must be<br />
monitored to maintain the lightness and whiteness.<br />
Raw Materials<br />
Because the gray color of concrete can be attributed to its iron content, it is expected that<br />
the first step taken to make a lighter and whiter cement would be to keep the iron content in the<br />
raw materials as low as possible. Lightness can be measured by reflectance, and compared to a<br />
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very light reference standard (MgO powder is considered to have a reflectance of 100%).<br />
Furthermore, other coloring oxides include manganese, chromium and magnesium, and though<br />
the lightness of the resulting cement may be the same, there may be some hint of color that is<br />
undesirable in the white cement 3, 4 . Therefore, it is recommended to keep these coloring oxides<br />
below the following values in the raw mix:<br />
Table 1: Recommended maximum values of coloring oxides in raw materials in the production<br />
of white cement clinker 3 .<br />
Compound Recommended<br />
limit<br />
Color influence on clinker<br />
Fe2O3 < 0.4 % gray<br />
Mn2O3 < 0.02% grayish-violet,<br />
reddish-violet<br />
Cr2O3 < 0.01 % greenish<br />
MgO < 3% greenish-brown<br />
To keep these values below these recommended values, the raw materials used to make<br />
the clinker should have low amounts of these oxides. Examples of these are china clay<br />
(kaolinite) and white chalk or limestone. However, if they do not contain enough free silica,<br />
ground white sand is added to the mix 5 . To further lower the content of these coloring oxides in<br />
the raw materials, it can be beneficial “to remove the fine particles, in which the undesirable<br />
(coloring) oxides are more particularly concentrated, by preliminary screening before the<br />
material is fed to the crusher” 3 .<br />
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Production / Manufacture<br />
As a result of keeping the iron levels as well as the levels of other coloring oxides low,<br />
“white cement manufacture requires higher clinkering temperatures than (gray) cement<br />
manufacture does in order to achieve more or less complete combining of lime in the burning<br />
process” 4 . This is one reason why white cement manufacture is more expensive than gray<br />
cement manufacture.<br />
Keeping the raw materials constant, the resulting cement clinker can still have varying<br />
lightness and color. Therefore, though much effort may be taken to ensure that the raw materials<br />
have the appropriate composition, further care must be taken during the production process,<br />
when other sources of coloring oxides are present and may adversely affect the lightness or<br />
whiteness of the cement. These sources include the grinding media and mill lining materials and<br />
the fuel used for burning the clinker. It is recommended that ceramic grinding media and mill<br />
liners be used instead of metallic ones, because iron and chromium may be mixed in as it is<br />
abraded from those surfaces. This is particularly crucial if there is a high amount of free quartz<br />
in the raw meal. In addition, “oil fuel is often used in place of pulverized coal in the burning<br />
process to avoid contamination by coal ash” 3 .<br />
Titanium dioxide is sometimes added to cement for a brightening effect, but tests have<br />
shown that it may not have any actual affect on the brightness of the cement. However, as will<br />
discussed in the case study, titanium dioxide can be added to maintain the whiteness of the<br />
cement over time.<br />
Regulations and Standards of Practice<br />
ASTM has no specification explicitly for white cement, though producers of white<br />
cement will conform to the requirements in ASTM C 150 for cement Types I, II, III and V or the<br />
corresponding European or country standards. Because there are such low amounts of C4AF,<br />
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there are usually higher amounts of C3S and C3A, which makes Types I and III more common.<br />
However, ASTM C 150 does not address the issue of the cement’s lightness or color 6 .<br />
As mentioned before, it is useful to quantify the cement’s lightness using its reflectance<br />
compared to a reference standard, which is the industry norm for rating the whiteness of a<br />
producer’s cement. “Ordinary commercial grades of white cement (have) a whiteness of 80 – 84<br />
per cent; superior grades of ‘world market’ quality have a whiteness of 84 – 88 per cent.<br />
<strong>White</strong>ness values above 88 per cent are attainable only by using very special raw materials” 3 .<br />
Chemical Composition of Clinker<br />
The following tables list the ASTM requirements for various types of cement and typical<br />
chemical compositions of white cement available. Figure 2 is the product information given<br />
from Aalborg <strong>White</strong>, which can certainly be classified as “world market” quality. It should be<br />
noted that the “lightness (brightness of colour) of the clinker is enhanced by grinding to a high<br />
degree of fineness,” so white Portland cements are generally finer than gray ones 4 .<br />
Table 2: Comparison of gray and white cement compositions 5<br />
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Table 3: ASTM cement composition requirements 7<br />
Figure 2: Commercially available white cements, from Aalborg <strong>White</strong> 8 .<br />
C3A levels are often very high for white cements, making it easier for cement<br />
manufacturers to conform to Types I and III, though Types II and V are also available. This<br />
cement available from Aalborg <strong>White</strong> conforms to all of those types. Because the raw materials<br />
are so carefully chosen, white cement usually has a low alkali content, making alkali-silica<br />
reaction less of a concern 1 .<br />
<strong>Concrete</strong> Mix Design<br />
As mentioned before, white cement can be used alone for surface treatments of gray<br />
cement concrete. In white cement concrete, the aggregates added are usually colored.<br />
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Therefore, to maintain uniform color in white cement concrete, the mix design will be changed.<br />
It is generally richer in cement and has higher fine sand content 6 . Generally, it is favorable to<br />
have a continuously graded aggregate, but surface effects can be made when gap grading<br />
aggregates.<br />
Because aggregates impart a pigmenting effect on the final concrete, aggregate choice is<br />
often dictated by color. This is particularly true of the fine aggregates, and it is usually<br />
recommended that light colored sand be used. If a very white concrete is desired, white coarse<br />
aggregates, marble or limestone, are used. However, the white cement can allow dramatic color<br />
play to be made with distinctly colored aggregates. This is done particularly for terrazzo. The<br />
following figure shows what surface textures can be achieved with white cement and various<br />
aggregates.<br />
Figure 3. Various effects achieved with white cement concrete and white or colored aggregate 8 .<br />
Mineral admixtures may still be added to (or used as replacement for) white cement in<br />
concrete, but these should be as close to white as possible. For very white concrete, common<br />
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pozzolans (fly ash) are not used. Instead, there are choices between white silica fume,<br />
metakaolin, and slag 1 .<br />
Chemical admixtures should also be colorless, and their use be evaluated on a test<br />
specimen before actual usage. Interestingly, the testing of compatibility of white cement with<br />
various superplasticizers has shown that white cement concrete will exhibit higher fluidity with<br />
the same dosage of superplasticizer than gray cement concrete. This has been attributed to the<br />
uneven adsorption of superplasticizer on different cement particles. “It adsorbs more readily on<br />
C3A and C4AF than on C3S and C2S” and the “more even the adsorption of (superplasticizer) on<br />
cement mineral, the higher the fluidity of the paste will be.” <strong>White</strong> cement will have a more<br />
even adsorption because of its low C3A + C4AF and low alkali content. Thus, it exhibits higher<br />
fluidity even though it is most often finer than gray cement. The results vary in degree for<br />
various types of superplasticizer, but all those tested showed this same trend 9 .<br />
Figure 4: Effect of cement type<br />
on fluidity, with varying<br />
dosages of superplasticizer (a)<br />
ordinary, (b) low alkali, (c)<br />
white cements 9 .<br />
(a)<br />
(b) (c)<br />
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Construction<br />
Even with the best white cement and mix design, however, one can still obtain variable<br />
qualities of final product because of the construction methods used. With white cement concrete,<br />
especially when using pigments, one must be more vigilant about keeping equipment clean,<br />
maintaining quality of forms and finishing equipment, and using experienced finishers with the<br />
right technique. Maintaining uniformity throughout the project cannot be stressed enough.<br />
Batching of ingredients should be measured accurately and consistently 1 . Otherwise,<br />
there will be local variations that will adversely affect the overall appearance of the structure. A<br />
“low water-cement ratio paste is almost always darker than a high water-cement ratio paste made<br />
with the same cement,” which can be seen in the figure below. Therefore, if there are variations<br />
in water content from batch to batch, there will most likely be blocking of colors or shades.<br />
Figure 5: Color variations with different water-cement ratios 6 .<br />
The mixing procedure of white cement concrete is done in a similar manner to gray<br />
cement concrete, though the mixing time is usually extended to ensure proper dispersion of<br />
cement and pigment (if any) throughout the mixture. This is also necessary not only for color,<br />
but also because concretes having higher cement content and more finely ground cement, which<br />
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white cement concrete has, take longer to blend 6 . As with the measurements in batching, the<br />
mixing times should be kept constant from batch to batch.<br />
The usual placing techniques are still used with white cement concrete, but there are a<br />
few points that can affect the appearance of white cement concrete in particular. Firstly, if there<br />
is splattering of concrete onto the forms, there will be defects on the surface of the concrete.<br />
This can be prevented by having a moderate slump and using an elephant trunk to guide the<br />
concrete into place.<br />
Formwork can also influence the color and surface condition of the completed concrete.<br />
As with the metallic grinding media in the production of the clinker, the material of the<br />
formwork can stain the concrete. For this reason, steel forms that impart coloring oxides are<br />
either avoided or treated with rust-inhibiting compounds. Plastic forms, coated or uncoated,<br />
have been used, but they may not be as durable unless a release agent is used. “Untreated wood<br />
can (also) discolor white or colored concrete” 1 . Furthermore, the untreated wooden formwork<br />
can absorb water from the surface of the concrete, resulting in local variations of water-cement<br />
ratios that will, as mentioned before, different regions of lighter and darker concrete. Lacquering<br />
can alleviate this as well as extend the life of the form. With all types of formwork, there is the<br />
possibility of leakage that will also compromise local color and overall appearance. Tight forms<br />
that do not leak will take care of this.<br />
For white cement concrete flatwork, the finishing crew should be experienced so that<br />
“burning” or “blackening” of the surface does not occur. This can happen when a metal trowel is<br />
abraded by stiff concrete, but the primary reason is that the concrete is overfinished “to the point<br />
where the water-cement ratio is drastically reduced”. Curing of white cement concrete should be<br />
given as much or more attention as gray cement concrete. Plastic sheets should be avoided<br />
because they can produce a “mottled” effect with incomplete contact to the surface of the<br />
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concrete. Non-staining waterproof paper with a layer of dry sand have worked well. Curing<br />
compounds are also safe to use without much risk of discoloration 1 .<br />
Mechanical properties<br />
The mechanical properties of white cement concrete are generally assumed to be the<br />
same as those of gray cement concrete. However, because of the cement composition, there are<br />
things to note about the strength evolution. Looking again at the chemistry of white cement,<br />
there is generally more C3A and C3S than with gray cement. It is also ground finer. Because of<br />
these reasons, the set time for white cement is usually shorter and the early strength usually<br />
higher. The following figure compares gray and white cement concretes of different nominal<br />
strengths at different ages. The early strength is much more pronounced in the concretes of<br />
higher nominal strength. Note that in this experiment, the white cement used was coarser than<br />
the gray cement. Therefore, it would be expected that for most white cements, the difference<br />
would be even more marked 10 .<br />
Figure 6: Variations of cylinder compressive strength of concrete with age 10 .<br />
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Case Study<br />
The Jubilee Cathedral, as seen in Figures 7 and 8, is a prime example of why and how<br />
white cement concrete is used. It is located in the suburbs of Rome, where there are dozens of<br />
cathedrals from hundreds of years of Roman Catholic Church history. This one, made to mark<br />
the third millennium, still, as the architect Richard Meier puts it,<br />
“‘upholds … the city’s rich architectural tradition . . . (but) was always intended to be a<br />
work of contemporary architecture, meaningful for our time and one that is marked by<br />
openness. Transparency and light cascade down from the skylit roof, literally invading<br />
the interior of the church….People in the atrium are enveloped with mystical light. ’” 11<br />
Figure 7: exterior of the Jubilee Cathedral, Tor Tre Teste, near Rome 11 .<br />
The precast, post-tensioned white cement concrete panels are indeed contemporary while<br />
still giving the air of marble that so characterizes the Roman Catholic Cathedrals of the past.<br />
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The motivation to use white cement is obvious when Mr. Meier describes the affect of light in<br />
the atrium not only on the image of the exterior and interior, but also the state of mind of the<br />
viewer. Such brightness cannot be accomplished with gray cement, and a masonry structure<br />
would lack the elegance. Here, the ultra-modern is beautifully combined with the times of yore.<br />
Figure 8: Interior of the Jubilee Cathedral 11 .<br />
The cement was provided locally by Italcementi Gruppo. The most remarkable feature of<br />
the cement used was not that it is white, but rather that Italcementi designed it to have “aesthetic<br />
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durability.” In what they have patented as “Bianco TX Millenium,” Italcementi have added<br />
titanium dioxide to the cement to maintain its whiteness over time. The “photocatalytic particles<br />
contained in the white cement allow it, once it has hardened in the form of paste, mortar, or<br />
concrete, to oxidize the organic and inorganic air pollutants in the presence of air and light”.<br />
This attention to aesthetic durability is warranted, especially when one considers the effect of the<br />
urban pollution on such famous structures in nearby Greece (i.e. the Acropolis) 12 .<br />
Conclusion<br />
<strong>White</strong> cement technology has been used for primarily the luxury cement market and was<br />
developed not out of need, but out of creativity. The structures and various other applications<br />
have exploited the flexibility in form despite its increased cost, both of money and of attention.<br />
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