Pigmented concrete constitutes a key feature of the two towers of the Plaza de la Libertad to help the 12 000m² building resemble tall tree trunks.
With the purpose of adding natural inspiration, the Bayferrox range of pigments was extensively used to fashion the coloured concrete that constitutes a fundamental feature of Plaza de la Libertad, a new landmark and iconic structure in Medellín, central Colombia.
The 12 000m² Plaza de la Libertad features two towers resembling tall tree trunks, designed to blend in with the surrounding forest’s trees. The design concept of the architect and interior designer, Alejandro Toro Posada, similarly employs the building’s wings as branching structures emanating from the giant “tree” towers, also liberally featuring concrete coloured with Bayferrox pigments.
The Bayferrox range of pigments, manufactured by German-based Lanxess Inorganic Pigments, one of the largest pigment suppliers to the construction industry, is locally only available through Chryso Southern Africa.
The structural elements of Plaza de la Libertad are based on a temperature-regulating and extremely weather-resistant concrete, coloured with 60t Bayferrox 918 LOM yellow pigments in the main building, and 7t Bayferrox 130 M red and 318 M black pigments in the auditorium.
According to Posada, the façades have been specifically designed to conserve resources, reducing conventional air-conditioning and lighting costs by about 40%. Another major benefit of using integrally coloured concrete is that the façades will require no follow-up maintenance.
As the sole local distributor of Lanxess inorganic iron-oxide pigments for the South African construction industry, Chryso SA has a colour laboratory in Jet Park that can measure the colour strengths of pigmentation and provide customers with specifications to colour-match available concrete masonry production lines.
Factors influencing pigmented concrete
Hannes Engelbrecht, Chryso SA’s business manager for concrete aesthetics, points out that there are some vital factors to consider when opting for pigmented concrete:
Portland cement can vary significantly in colour – from light to dark grey. This change in colour can influence the final colour of pigmented concrete. “This is why it is important to use the same cement throughout. The higher the cement content, the more intense the colour,” Engelbrecht explains.
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 for colour uniformity.
• 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.
The type, colour and condition of formwork can influence surface colour. Formwork with different rates of absorption will create surfaces with different colour shades.
The pigment must be mixed with the aggregate before the cement is added.
• Temperature during drying
In higher temperatures, fine crystals develop in the cement matrix and determine how the light that falls on the concrete is scattered. Smaller crystals produce lighter pigment.
Admixtures with high levels of calcium chloride can cause primary efflorescence.
All Bayferrox pigments are UV-stable and comply with quality standards EN 878 for the use of pigments for colouring building materials, as well as ASTM C979 in lieu of pigments for integrally coloured concrete, and carry the CE quality mark on their packaging.
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