Cafe del Bosque / Castro Arquitectos

Curated by ArchDaily

Architects: Castro Arquitectos
Area: 2116 m²
Year: 2006
Manufacturers: Corona

Text description provided by the architects. The building consists of two independent curved walls that supports cantilevered roofs. In their perimeter this concrete elements cover both interior and exterior spaces and define the botanical garden entrance (49). The main feature of this concrete elements is their geometrical complexity: the walls at the ground level have 4 different curvature centers and each of them tilts around 15 degrees. At the roof level, the overhanging slabs have distances between 2 m and 10 m (32).

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Structural analysis and model development in SAP 2000 v.11 helped to develop a structure where safety and economy found a balance. The building geometrical complexity and the small bearing capacity of foundation soil required a foundation system composed by 13 m long driven piles with a square cross section of 0.40 m (04). The piles were joined at the ground level by a beam with a square cross section of 0.60 m and spaced every 2 m (05,12). The two reinforced concrete walls (0.40 m of thickness) are recessed in the foundation system (07, 08, 09). At the roof level, the walls are joined to each other: their unstable condition required a contact point between them just under the overlap of the roof slabs (27). The roof structure consist of a reinforced concrete slab that decreases in thickness along the cantilever (33). At the intersection with the walls, the slab reaches 0.40 m; at the end of the cantilever, the slab reaches 0.25 m (31). The roof, in its transverse direction, was built as a post-tensioned element. In this way, tensions were offset and filtrations were avoided.

The soil has a high water table due to proximity to the Quebrada el Molino. This situation required the construction of an earth fill (3 m high) that could make more appropriate the implantation site. The foundation system has 56 driven piles (13 m long) that follow the axis of the main walls. The heads of the piles are joined by the foundation beam. This concrete element (thickness 0.4 m, high 5.5 m) will be the sloping walls base (10).

Due to the absence of any coating, many samples of concrete were made. Those helped to evaluate the concrete finish given by the different formworks (wood type, wooden strip modulation, joints and cuttings of the wooden boards) and features of the different concretes (colors, aggregates, pigmentation, plasticity, expansion joints). At the end of the process, the formwork is made with Soho wood (36). To get a Ochre finish, the chosen concrete had oxifer pigment and aggregates found in the region (37). The steel rods that assemble the concrete reinforcement have a diameter ranging between 1½” and ¾”(17, 20).

The pouring of concrete walls starts with the construction of the pavilion which will serve as a technical room. This building allows to verify the features of the concrete (01, 02, 03). The pouring of the main walls is divided in three steps: in the first two steps, the walls reached 2m of high (21, 23, 24, 25). During the last step, the walls are completed and the pouring of the roof slab starts. At the same time, secondary walls are builded.

Once the walls are completed, the construction of the roof reinforcement starts. The pouring of the roof slab is divided in steps. To ensure the stability of the ensemble, the process begin in the points where walls overlap (30, 33). The pouring process ends with the hardened concrete floor. For interior spaces grey concrete is used (40), while the ochre concrete is choosen for exterior spaces and the main courtyard (39).

In both cases, concrete is treated with hardeners and then polished with power trowel. After this process, the joints are made by cutting and then sealed with semi-rigid materials with epoxy base.