Copyright Goodheart-Willcox Co., Inc. Unit 7 Construction Materials—Types and Uses 109 Characteristics of aggregates are: • Soundness • Chemical stability • Abrasion resistance • Grading and sieve analysis • Percentage of crushed particles • Particle shape • Surface texture • Specific gravity • Absorption • Moisture content • Volume stability Some gravel drawing symbols are shown in Figure 7-2. Division 03—Concrete Concrete is one of the oldest building materials, having been used by the Romans as early as 100 B.C. Concrete is a mixture of cement, sand, coarse and fine aggregates, admixtures, and water. When first mixed, it is plastic (able to flow and be shaped) and can be cast to take the shape of the formwork provided. Hardening of the concrete is caused by a chemical reaction between the cement and water called hydration. Most mixtures of concrete set within 4 hours but can take up to 12 hours, depending on the temperature, the volume of the pour, type of cement, and admixtures. When the temperature is below 70°F (20°C), the chemical reaction slows. Very little chemical reaction takes place below 40°F (4°C), and almost none occurs at 32°F (0°C). The rule of thumb is: if you are comfortable, the concrete is comfortable. Concrete continues to harden for months after the initial set, but most placements reach their compressive or design strength within 28 days. Forms can be removed after one to several days or when the concrete can support itself. This should be determined by an engineer and testing lab. Types of Cement Cement binds the concrete mixture together. There are t five basic types of cement. The most common, used for general construction, is called Type I Normal Portland cement. Another variation used in construction is white Portland cement. It is light-colored and used chiefly for architectural effects. White Portland cement is made from carefully selected raw materials and develops the same strength as the normal gray-colored Portland cement. Goodheart-Willcox Publisher Figure 7-2. Samples of drawing symbols for gravel. A—Plan view of a headwall with rip-rap used to prevent erosion from drainage water outflow. This type of structure would be found on a site plan. B—Plan view of a gravel driveway. C—Section view of pea gravel with a sand layer above the gravel. D—Section view of crushed gravel. D Crushed Gravel Section View B Gravel Gravel Driveway Plan View Headwall A Headwall and Rip-rap Plan View Rip-rap Pea Gravel and Sand Section View C Sand Pea gravel