Aggregate
Discuss the advantages, disadvantages of types of aggregate being used in construction projects.
Introduction:
Aggregates are inert granular materials such as sand, gravel, or crushed stone that, along with water and Portland cement. Aggregates are essential ingredient in concrete. For a good concrete mix, aggregates need to be clean, hard, strong particles free of absorbed chemicals or coatings of clay and other fine materials that could cause the deterioration of concrete. Aggregates, which account for 60 to 75 percent of the total volume of concrete, are divided into two distinct categories - fine and coarse. Fine aggregates generally consist of natural sand or crushed stone with most particles passing through a 3/8-inch (9.5-mm) sieve. Coarse aggregates are any particles greater than 0.19 inch (4.75 mm), but generally range between 3/8 and 1.5 inches (9.5 mm to 37.5 mm) in diameter. Gravels constitute the majority of coarse aggregate used in concrete with crushed stone making up most of the remainder.
Natural gravel and sand are usually dug or dredged from a pit, river, lake, or seabed. Crushed aggregate is produced by crushing quarry rock, boulders, cobbles, or large-size gravel. Once aggregates have been processed, the aggregates are handled and stored in a way that minimizes segregation and degradation and prevents contamination. Aggregates strongly influence concrete 's freshly mixed and hardened properties, mixture proportions, and economy. Consequently, selection of aggregates is an important process.
Although some variation in aggregate properties is expected, characteristics that are considered when selecting aggregate include grading, durability, particle shape and surface texture, abrasion and skid resistance, unit weights and voids and absorption and surface moisture. Grading refers to the determination of the particle-size distribution for aggregate. Grading limits and maximum aggregate size are specified because grading and
Introduction:
Aggregates are inert granular materials such as sand, gravel, or crushed stone that, along with water and Portland cement. Aggregates are essential ingredient in concrete. For a good concrete mix, aggregates need to be clean, hard, strong particles free of absorbed chemicals or coatings of clay and other fine materials that could cause the deterioration of concrete. Aggregates, which account for 60 to 75 percent of the total volume of concrete, are divided into two distinct categories - fine and coarse. Fine aggregates generally consist of natural sand or crushed stone with most particles passing through a 3/8-inch (9.5-mm) sieve. Coarse aggregates are any particles greater than 0.19 inch (4.75 mm), but generally range between 3/8 and 1.5 inches (9.5 mm to 37.5 mm) in diameter. Gravels constitute the majority of coarse aggregate used in concrete with crushed stone making up most of the remainder.
Natural gravel and sand are usually dug or dredged from a pit, river, lake, or seabed. Crushed aggregate is produced by crushing quarry rock, boulders, cobbles, or large-size gravel. Once aggregates have been processed, the aggregates are handled and stored in a way that minimizes segregation and degradation and prevents contamination. Aggregates strongly influence concrete 's freshly mixed and hardened properties, mixture proportions, and economy. Consequently, selection of aggregates is an important process.
Although some variation in aggregate properties is expected, characteristics that are considered when selecting aggregate include grading, durability, particle shape and surface texture, abrasion and skid resistance, unit weights and voids and absorption and surface moisture. Grading refers to the determination of the particle-size distribution for aggregate. Grading limits and maximum aggregate size are specified because grading and
References: * http://www.aggregate-uk.com * Young, J. F., Mindess, S., Gray, R. J., & Bentur, A. (1998). The science and technology of civil engineering materials. Saddle River, NJ: Prentice-Hall * ACI Committee 221, “Guide for Use of Normal Weight Aggregates for Concrete (ACI 221R-96),” American Concrete Institute, Farmington Hills, Mich., 1996, 29 pp. * http://www.concretebasics.org/articlesinfo/scc8.php * M.L. Gambhir, Concrete Technology (Theory and Practice), fourth ed.