410 Landscape Design, Installation, and Management Copyright Goodheart-Willcox Co., Inc. • Fibers and porous aggregate, such as gravel, stone, or sand, can be added to modify strength and permeability. • Applying a thin layer of fi ne aggregate to the surface of the wet concrete (face mixing) to provide color and greater abrasion or texture. Locally Sourced Materials Many homeowners prefer a design that includes locally sourced or recycled materials. Locally sourced materials include those that are mined or harvested locally, such as a particular stone or native tree species. Using these materials is usually less expensive than importing materials and it helps support the local economy. Upcycled Materials Designers can incorporate pieces with historical signifi cance, such as portions of building facades or columns from buildings that have been demolished. These types of pieces may be incorporated into hardscape elements, such as fountains, gazebos, and built-in seating, or stand alone among the plant material. Upcycling mate- rials also keeps them from entering landfi lls. Asphalt Asphalt is a mixture of tar, sand, and gravel that creates a dark hardscape. It is softer and less expensive than many other hardscape materials and is often used for driveways and long pathways of public walking trails. Asphalt will fade to a dull gray color and become softer in extremely hot, sunny weather. Asphalt must be sealed periodically to prevent cracking and chipping. Apply- ing sealer will also restore the original dark color. Gravel Gravel consists of small pieces of loose rock. The rocks come in different colors, shapes, sizes, and durability. Gravel is used for walkways, driveways, paths, and often to cover areas in which it is diffi cult or impractical to grow plants. As with other hardscape materials, the type chosen depends primarily on the client’s wishes and its end use or how it is incorporated into a design. A solid edging will keep the gravel from traveling and properly preparing the ground below the gravel will minimize weed growth between the rocks. A commercial-grade landscaping fabric placed over the ground surface will help reduce weed growth. Gravel is considered a low-impact material because it creates a permeable groundcover that allows water to drain. It is a common component of xeriscape designs for its permeability and ability to add color to the landscape. Com- mon types of landscape gravel include pea gravel, churt, machine-crushed gravel, river rocks, decomposed granite, lava rocks, and crushed stone. See Figure 15-17. Pumbastyle/Shutterstock.com Figure 15-16. Concrete is commonly used for patios, walkways, and driveways. It is expensive but also versatile in that it can be stained, stamped, or texturized. p p Pro Tip The American Society for Testing and Materials (ASTM) provides standards for paving units. The standards define dimensions, tolerances, strength, and freeze/ thaw durability.