A range of Bayferrox pigments, produced by Lanxess Inorganic Pigments, was extensively used in the design and construction of Plaza de la Libertad, a new landmark and iconic structure in Medelin, in central Colombia.

Lanxess Inorganic Pigments based in Germany is one of the largest pigment suppliers to the global construction industry. Chryso Southern Africa is the sole distributor of Lanxess inorganic iron oxide pigments for the South African construction industry and 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 at competitive rates

Medelin’s 12 000sq m Plaza de la Libertad features two towers (24- and 17-storeys high) resembling tall tree trunks, designed to blend in with the surrounding forest’s trees and their trunks and barks. The design concept of Architect and Interior Designer, Alejandro Toro Posada – which liberally features concrete coloured with Bayferrox pigments to add natural inspiration also employs the building’s wings as branching structures emanating from the giant ‘trees’.

The structural elements of Plaza de la Libertad are based on a temperature-regulating and extremely weather resistant concrete coloured with 60 metric tons of Bayferrox 918 LOM yellow pigments in the main building, and seven metric tons Bayferrox 130 M (red) and 318 M (black) pigments in the auditorium. A major benefit of using integrally coloured concrete is that the façade will require no follow-up maintenance.

Designer Posada adds: “Furthermore, the facades have been designed to conserve resources, reducing conventional air conditioning and lighting costs by around 40%.”

The avant-garde building accommodates government institutions, a business hotel, TV studios, businesses, cultural centre, open-air theatre and exhibition halls.  Described as a ‘place of expressive power’, it has won top prize in a major international competition organised by the National Association of Architects.

Hannes Engelbrecht, Chryso S.A. Business Manager: Concrete Aesthetics, says there are some vital factors to consider when producing pigmented concrete:  

• 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. 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 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.
• Formwork: The type, colour and condition of formwork can influence surface colour. Formwork with different rates of absorption will create surfaces with different colour shades.
• Dispersion: 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.
• Efflorescence:  Admixtures with high levels of calcium chloride can cause primary efflorescence.

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 CE quality mark on their packaging. Lanxess operates from sites in Germany, Brazil and China, as well as additional mixing and milling plants in Australia, China, Spain, the UK and USA.