August 2013
CONSTRUCTION WORLD
59
precast concrete products
CHRYSO SOUTHERN AFRICA
is the sole
distributor of Lanxess inorganic iron oxide
Bayferrox pigments for the SouthernAfrican
construction industry. Based in Germany
with a global distribution network, Lanxess
is one of theworld’smost respectedproduc-
ers of pigments for coloured concrete.
Engelbrecht says the vital factors to
consider when producing pigmented
concrete are:
Cement
Portland cement can vary
significantly in colour – from light to dark
grey.This change in colour can influence the
final colour of pigmented concrete.“That is
why it is important to use the same cement
throughout theproductionof coloured con-
crete. White cement should be used when
producing pigmented concrete with great
colour clarity, particularly for bright colours.
The higher the cement content, the more
intense the colour,”Engelbrecht explains.
Aggregates
The colour of aggregates
also influences the ultimate colour so it is
important to ensure that the entire surface
area of the aggregate is coated with the
pigmented cement paste so that the final
product is not amixture of the colour of the
pigment and the colour of the aggregate.
Mixing water
Water dilutes the colour
of the pigments in the mix and excess
water evaporates from concrete, leaving
behind pores that scatter incidental light
and lighten the colour of the pigment.“Excess
water also causes excessive bleeding and a
non-uniform colour,”Engelbrecht states.
Formwork
The type, colour and condi-
tion of formwork can influence surface
colour. Formwork with different rates of
absorption will create surfaces with different
colour shades. Absorptiondiscolouration also
occurs when release agents are not applied
uniformly. Formwork that pulls away from
the concrete surface, or has leaky joints, can
cause uneven water loss from the concrete
and cause a streaky surface.
Dispersion
It is important tomix the pig-
ment with the aggregate before the cement
is added. From then on, the mixing process
is the same as for un-pigmented concrete.
Temperature during drying
In higher
temperatures, fine crystals develop in the
cement matrix.These crystals determine how
the light that falls on the concrete is scattered.
The smaller the crystals, the lighter the pig-
ment in the concrete.
Efflorescence
“This is the result of free
lime formed when the cement sets that,
dissolved in the mixing water or in external
water such as rain or dew, migrates through
capillaries in the concrete matrix to the sur-
face.There it reacts with carbon dioxide in the
Guidelines
for coloured
concrete
There are seven important
factors that influence the
quality of coloured concrete,
says Hannes Engelbrecht,
ChrysoS.A. businessmanager:
concrete aesthetics.
air to form insoluble and unsightly calcium
carbonate deposits particularly noticeable
on the surface of pigmented concrete,”
Engelbrecht says. “Care should be taken
when using admixtures with high levels of
calcium chloride as this can cause primary
efflorescence. The more impermeable the
concrete, the less likely that efflorescence
will appear.”
All Bayferrox pigments are UV-stable
and comply with quality standards EN 878
(the use of pigments for colouring building
materials), and ASTM C979 (pigments for
integrally coloured concrete), and carry the
CEmark on their packaging.The CEmark is a
mandatory conformitymarking for products
sold in the European Economic Area (EEA).
Chryso S.A. has a colour laboratory in Jet
Park that houses sophisticated equipment
such as a Colourimeter that canmeasure the
colour strength of pigmentation.
The laboratory can provide customers
with specifications to colour-match avail-
able concrete masonry production lines at
competitive rates.
●
Hannes Engelbrecht of Chryso says there are
seven important factors to consider when
producing coloured concrete.
Mike McDonald, AfriSam product manager,
comments that with carbon tax looming on
the horizon, the company is also focusing
substantial time and investment on develop-
ing carbon efficient products.
“We are proud to have achieved an ‘R’
rating with the two products offered to the
CPMs, while retaining an extremely low
carbon footprint,”he says.“In effect, we have
introduced technological advances that
have boosted performance in terms of the
strength, performance, durability and work-
ability associated with advanced composite
cements, without sacrificing sustainability.
●
All products are tested at the
company’s SANAS-accredited
laboratory in Roodepoort.
