On a roofed-over production area of more than 17,000 m², some 50 workers manufacture quality cast-stone products for interior and outdoor use, which are quality-controlled at regular intervals by the in-house and third-party quality control association Güteschutz Beton- und Fertigteilwerke Nord e. V. in accordance with DIN V 18500 and EN 13748-1/2. The sample portfolio comprises 18 standard samples, in addition to offerings of customer-specific special solutions for color and particle composition. All cast-stone products are mass-hydrophobized.
The already impressive list of reference projects and product developments was just recently further extended: for one, by large-dimensioned panels for the prestigious Rhein-Palais Bonner Bogen project and, secondly, by a new precast staircase – with the full cross-section manufactured of cast stone – with finished surface that was brought to market maturity.
Large-dimensioned panels for the Rhein-Palais
The client had requested concrete elements, large-dimensioned, if possible, for the exterior face, instead of the customary small- to middle-sized panels, which are, in the client’s opinion, more maintenance-intensive due to the relatively large amount of joints, are optically busy and are inclined to deformation.
For the joints to optically match the unit spacing of the building, a grid of 1.35 m was laid over the site. This grid size corresponds to the center line of the building on which various elements such as windows, projections of the building, etc. are aligned. The water-bearing level is the floor of the underground garage. During normal rain events, the water is drained via the joints and runs over the roof water inlets into a rainwater cistern. For heavy rain events, channels are arranged directly on the building that guide the water to drain freely to the floor of the underground garage. The structural design of the panels is such that they can sustain the weight of heavy fire-fighting vehicles. The upper side of the panels consists of a wear layer of approx. 5 cm thickness made of a classic cast-stone mix, the surface of which was subsequently fine-blasted.
Very narrow 6-mm joints and small chamfers on the edges of the panels were chosen in order to make them convenient to walk on and to achieve an optically harmonious surface. As a result, the requirements placed on the dimensional accuracy of the panels and on the laying work greatly exceed the allowable tolerance measure specified by DIN 18202. At unit spacing of 1 to 3 m, a deviation of ± 12 mm from the specified size would have been permitted. The other design elements, such as flower boxes, steps and parapets for the elevated terraces, were made of the same material and matching surface. The unit spacing of these elements is duplicated by the ground slabs and/or are doubled to 2.70 m.
New cast-stone staircase with finished surface
In the past, RBM had manufactured so-called precast staircases with full cross-section manufactured of cast stone and with finished surface. These were ready-to install stairs that were suspended in the unfinished building. The loadbearing elements of these stairs were stringers made of cast stone into which the treads with their substructure were integrated. With increasingly strict requirements placed on the structural design, fire protection aspects and the prevailing taste of architects, the time had come to develop a follow-up product.
The new staircase is a precast staircase in which the full cross-section consists of cast stone. The surfaces of the steps as well as the exposed surfaces of the stringers are ground in the plant and are delivered with a finished surface. The staircase derives its visual appeal from its clarity of design without projections on the stringers. The stringers and the soffits match the surface of the treads and steps.
With respect to structural design, the support situation and the dimensions, the same freedom of design exists as known from the unfinished precast stairflights. One result is a considerably improved flow of construction work. The stairs are suspended in the unfinished building and protected from the environment of the construction site by a protective cover. At the end of the construction phase, there is no need to block the stairways for installing the treads. Finally, only the protective covers need to be removed and final cleaning performed.