A 'Salt Crystal' Made with LUCEM Translucent Concrete

Ever since light-transmitting concrete appeared about ten years ago, we've eagerly awaited applications of the cutting-edge technology, where embedded optical fibers turn the normally opaque material into something that glows and in some cases appears translucent. Previously we highlighted two projects that integrate LUCEM Lichtbeton's light-transmitting concrete: a storefront in Berlin and a mosque in Abu Dhabi. In both cases integrated LEDs turned the facades into attention-getting and communicate devices, respectively. The small enclosure at Obermain Therme goes one step further by making the material part of an immersive experience.

Before Krieger's renovation of the bathing hall, it featured a cave made of natural stone and covered with artificial palm trees. Popular but in need of modernization, that cave went away in favor of the new salt-crystal cave, a 5x7-meter space covered in the colorful LUCEM shell and integrated with a sound system overhead and massage jets in the water. The changing colors of the RGB LEDs in the shell echo the colors in the adjacent pool, which can be activated and controlled easily by a computer or smartphone.

The biggest obstacle in detailing and building the enclosure was the salinity of the brine water taken from local wells, whose salt content is 3.5%, comparable to seawater. Most important was the steel structure framing the enclosure and supporting the LUCEM panels. Per a statement from the company, "Hot dip galvanizing has been applied in accordance with DIN EN ISO 1461 in combination with a coating system for corrosion category C5-H – the highest level of corrosion protection, similar to open sea oil drilling platforms - according to DIN EN ISO 12944-5 to be used. The steel frame was manufactured as a welded structure of steel frame, then completely galvanized and then a layer thickness of 320 microns primer was applied. Finally, the steel frame was coated again with at least 320 microns twice, after the installation on site."

The 200 square meters of LUCEM contain more than 2 million optical fibers that transmit the light of the LEDs to the surfaces. The 20-millimeter-thick panels were installed with KEIL undercut anchors and, according to LUCEM, "transparent polycarbonate elements in 2 cm thickness [were] inserted as spacers between the steel frame and the light transmitting concrete panels in order to minimize the shadow of the frame. In the center of the 240 mm thick steel frame2-sided RGB LED modules were installed." Lastly, "The modules [were] fully filled with epoxy resin to guarantee a long life despite the high humidity and salinity in the air."

The result, though small, is an impressive one and another small step forward for the architectural application of light-transmitting concrete.