Stone

Figure 8.8 Pre-cast modular concrete units, Telefónica office park, Madrid, Spain.

Figure 8.9 Construction detail of a concrete wall faced with quarried stone, Manzanares River Park, Madrid, Spain, by West 8.

walls were then faced with pre-cast concrete units or quarried rock. See Figure 8.9 for details of attaching granite rock facing on a wall. The pavement surface is made from two sizes of modular concrete units: a smaller square unit at the base of the seat bench and a larger square unit for the walking surface.

Stone is a common material found in nature. Stone is quarried from many geologic origins including igneous, metamorphic, or sedimentary. The choice of geologic formation is based on use as well as achieving some aesthetic intention. Stone comes in many different forms as shown in Figure 8.10. It can be a processed product such as crushed rock or rock quarried with specific dimensions cut into a modular form (such as for paving) or cut in a variety of predetermined shapes for walls, outdoor furniture, or a variety of designed

Figure 8.10 Stone comes in many forms, colors, and dimensions: A: Dreamworks campus in San Francisco, by Lawrence Halprin; B: Whole Foods in Austin, Texas; C: San Antonio Arts & Crafts College; D: Calle Portugal in Madrid, Spain, by West 8; E: Chinese Academy of Art in Hangzhou, China, by Wang Shu.

structures such as signs, fountains, or architectural elements. And of course stone and boulders can be selected, as they are found in situ in nature, then transported to the construction site, as was the case for the Levi Strauss Plaza shown in Figure 5.11. Stones excavated from rivers or quarried from geologic strata are further processed and separated by size, perhaps washed clean for use in exposed aggregate concrete mixes, or placed directly loose on the ground as a mulch or decorative surface.

Examples of the various applications of stone are shown in Figure 8.10 (A–E). The stone shown in Figure 8.10A consists of two different materials, including natural boulders used for informal seating and for definition of a small employee seating area. A processed product in the form of crushed rock is used as a walking surface in the seating area. Poured-in-place concrete paving provides access to the area. The outdoor eating area of the Whole Foods store in Austin, Texas, shown in Figure 8.10B consists of both quarried flagstone and natural stone of varying sizes to create the flowing stream feature. Quarried limestone was used to face the low seating wall and flagstone pieces set in mortar1 over a concrete sub-base provide the walking and seating surfaces. Figure 8.10C demonstrates the use of quarried limestone as facing materials for the low garden walls, pavement, and the classroom building. Quarried rock processed into modular sizes was installed on a sand base to create the black and white pattern of the paved plaza shown in Figure 8.10D. The seating walls were made with poured-in-place concrete. Figure 8.10E is an entrance walk and garden to a conference facility at the Chinese Academy of Art, by Wang Shu.2 A variety of stone materials were used to add interest, including a boulder found in nature, crushed rock, and broken clay tile for the central walking surface. A small vessel formed from rock was placed opposite the boulder.

The two examples in Figure 8.11 were paired together to show the contrasting range of visual effects one is able to achieve by selecting stone as a surface material. The walk and stairs shown in Figure 8.11A were constructed with river-washed stones arranged with a flower motif and set in mortar to secure the stones. Larger quarried rock pieces form a border for the washed stone pattern. The width of the walk was extended with a similar quarried rock as well as in constructing the stairway. Quarried igneous rock was used in the construction of the plaza shown in Figure 8.11B. The modular rock units were secured with mortar with an added mortar joint between the units. The

Figure 8.11 A: Stone walk and stairs at the Summer Palace, Beijing, China; B: Broken fragments of flagstone and modular stone pavers, plaza in front of the Church of Santo Domingo, Zacatecas, Mexico.

broken rock portion of the paved surface was given a wider spacing with smaller broken rock pieces used to infill the joint spaces. Since occasional traffic from motorized vehicles was anticipated, the plaza surfaces were constructed over a concrete sub-base at least 4 to 6 inches (10–15 cm) thick with compacted fill underneath for structural support.

Stone and rock materials support a wide variety of applications and potential patterns from the exuberant (see Figure 8.12A) to modular and symmetrical patterns (see Figure 8.12B). Both examples used quarried stone and in the case of the stone used in Figure 8.12A, it was set in a sand base. A great many of the public sidewalks and public spaces in Portugal—and to some degree in Brazil—use a similar stone and construction method. One of the benefits of stone set in sand is that it allows portions of the pavement to be removed in order to repair underground utilities and other maintenance operations. After the underground work is completed, the stone is replaced on a new sand base with sand swept in to fill the cracks, thus locking the stone in place. The stone in the Madrid, Spain, example was set on a concrete base and filled in with mortar. A solid base was necessary as trucks and other heavy equipment are driven into the space to set up many public events.

Two more examples to demonstrate stone’s versatility are shown in Figure 8.13. The two examples have been paired to show the contrast in size of stone that can be specified. The limestone stone in Figure 8.13A was quarried from a local source and used in the construction of a contemporary visitor center. The same stone was used to match the much older Spanish Colonial mission complex, a decision made by the US National Park Service to provide visual cohesion between the architecture of two time periods. Though the architectural styles of the mission and visitor center are very different, a successful visual cohesion was created. A crushed limestone-like material was used in the construction of the linear pathway and several gathering areas in the Madrid park shown in Figure 8.13B. The rock is manufactured mechanically with rock crushing equipment.

Figure 8.12 A: Dom Pedro IV Plaza, Lisbon, Portugal; B: Plaza Mayor, Madrid, Spain.

Figure 8.13 A: Quarried local limestone used for paving and facing of National Park Service visitors center, Mission San Jose, San Antonio, Texas; B: Crushed rock walkway, Parque Lineal del Manzanares, Madrid, Spain, by West 8.

Figure 8.14 A: Stone and concrete wall, Taliesin West, Scottsdale, Arizona, by Frank Lloyd Wright, architect; B: Gabion wall, Phoenix Waterworks Park, by Christine Ten Eyck.

The material produced has sharp edges, facilitating compaction to 95 percent density that can support occasional vehicle maintenance traffic but, more importantly, allows surface water to percolate to the soil below. The crushed rock also enhances the experience of pedestrians as their footsteps produce a soft crunching noise. The crushed rock produces a more resilient surface than concrete, affording greater comfort for pedestrians.