Pigments transform concrete sculpture into a colorful star
A new star has risen above a former barracks site to the northwest of the Bavarian city of Augsburg in Germany. The so-called Urban Star is a sprawling star-shaped sculpture made of colored and illuminated concrete cubes for sitting and resting. A major part of the cubes consists of concrete dyed with inorganic pigments from the specialty chemicals group Lanxess. 24 cubes are made of translucent concrete, fitted on the inside with colored LEDs. During the day, colored cubes characterize the visual impression made by the site. As darkness sets in, the translucent concrete comes into full effect.
“The structure, as well as the desired color effect, were designed for a long-term lifetime. It was therefore decided to use iron-oxide pigments that are known to remain color-stable for decades and to stand up to wind and weather,” says Oliver Fleschentraeger, Market Segment Construction Manager in the Inorganic Pigments (IPG) business unit at Lanxess.
The Augsburg Urban Development Society has made use of the former barracks site that, until 1994, was occupied by the US Armed Forces, and has acquired it as trustee for the City of Augsburg for developing the areas step by step for subsequent civilian use.
Planning the Kobelcenter South Quarter
The objective of the development is a mix of trade, housing and green areas, blending well with the bordering areas being built-up. The Kobelcenter-South municipal development area on the former barracks site is one such quarter, being developed with residential and commercial buildings. In addition, green areas are planned with plant communities from North American prairies to help create the new-built quarter with an identity of its own.
The “stars” and the plants are reminiscent of the long utilization by the American military and the cultural character connected with it. They contain elements of American landscapes and legends, which contrast with the utilization of the site as functional residential and commercial estate. The utilization varies: The Urban Star is a meeting place and serves as connecting link between the barracks site and the urban space. The Desert Star, for example, is an intergenerational playground and the Dark Star serves as habitat for jackdaws. In planned subsequent construction phases, additional stars with individual characteristics will be realized.
Colorful day and night
The Urban Star, which is open to the public – planned by the Berlin architectural firm Annabau – is located at the center of an urban quarter’s square measuring approx. 800 sqm. The block-like structure of its cubes and the colorfulness of the concrete surfaces are meant to refer to the downtowns in the West of the USA.
The colorful concrete cubes are dyed with intensive colors and weather-resistant inorganic pigments of the time-tested Bayferrox brand from Lanxess. Here, the color shades black, red and yellow were primarily used. A cobalt-blue pigment from Harold Scholz & Co. GmbH, Recklinghausen, Germany, was additionally used. Die black translucent cubes from Aachener Lucern GmbH, are assembled from light-transmitting concrete slabs of approx. 2-cm thickness.
The blocks measure 84 x 84 cm and – adjusted to the downward-sloping topography of the square – have a height of 14 cm, up to maximum of 60 cm above upper edge of the ground. The surfaces of the concrete cubes are provided with a slightly sloping flat roof. Water does not collect on the surfaces, and the danger of freezing over in winter is low. The pavement of light-grey cast-stone blocks, together with the concrete cubes, results in a uniform joint pattern.
The City Star is founded on a reinforced-concrete ground slab of 25 cm thickness, with a projection of approx. 10 cm, which follows the contours of the Urban Star. The ground slab is supported on layered subsoil that has been compacted layer by layer. On the reinforced-concrete slab, a solid, stepped substructure of normal-weight concrete was erected to support the colored concrete cubes. The concrete surface has been sealed. Both the concrete and the translucent concrete cubes are mounted directly on the substructure and around the edges directly on the ground slab. Drainage mortar in combination with stepped drainage ensure the required drainage below the concrete cubes.
Inorganic pigments for structures with a long lifetime
Lanxess is the leading manufacturer of synthetic iron-oxide pigments worldwide and one of the leading manufacturers of inorganic pigments based on chromium oxides. The Inorganic Pigments Business Unit can draw on extensive knowhow in production and handling of pigments as well as for processing in concrete production. “Our technical service offer comprises extensive analyses of the color-metric and the physical properties of pigments and their effect on technological concrete and rheological properties for customer-specific applications, which can be reproduced on a laboratory scale,” explains Fleschentraeger, and adds: “For this, we work closely together with the producers of raw materials, plant engineers, architects and universities.
