A typical light-weight block weighs 22-28 lb (10.0-12.7 kg) and is used to build non-load-bearing walls and partitions. At this temperature the material bloats, or puffs up, because of the rapid generation of gases caused by theĬombustion of small quantities of organic material trapped inside. Expanded clay, shale, and slate are produced by crushing the raw materials and heating them to about 2000☏ (1093☌). Lightweight concrete blocks are made by replacing the sand and gravel with expanded clay, shale, or slate. A typical cinder block weighs 26-33 lb (11.8-15.0 kg). This produces a dark gray block with a medium-to-coarse surface texture, good strength, good sound-deadening properties, and a higher thermal insulating value than a concrete block. If granulated coal or volcanic cinders are used instead of sand and gravel, the resulting block is commonly called a cinder block. This produces a very dry, stiff mixture that holds its shape when it is removed from the block mold. In general, the concrete mixture used for blocks has a higher percentage of sand and a lower percentage of gravel and water than the concrete mixtures used for general construction purposes. A typical concrete block weighs 38-43 lb (17.2-19.5 kg). This produces a light gray block with a fine surface texture and a high compressive strength. The concrete commonly used to make concrete blocks is a mixture of powdered portland cement, water, sand, and gravel. Today, concrete block manufacturing is a highly automated process that can produce up to 2,000 blocks per hour. These early blocks were usually cast by hand, and the average output was about 10 blocks per person per hour. By 1905, an estimated 1,500 companies were manufacturing concrete blocks in the United States. Palmer's blocks were 8 in (20.3 cm) by 10 in (25.4 cm) by 30 in (76.2 cm), and they were so heavy they had to be lifted into place with a small crane. After 10 years of experimenting, Palmer patented the design in 1900. The first hollow concrete block was designed in 1890 by Harmon S. It was not until 1824 that the English stonemason Joseph Aspdin developed portland cement, which became one of the key components of modern concrete. Much of the concrete technology developed by the Romans was lost after the fall of the Roman Empire in the fifth century. During the reign of the Roman emperor Caligula, in 37-41 a.d., small blocks of precast concrete were used as a construction material in the region around present-day Naples, Italy. to bind shaped stones together in the construction of buildings. In use, concrete blocks are stacked one at a time and held together with fresh concrete mortar to form the desired length and height of the wall.Ĭoncrete mortar was used by the Romans as early as 200 b.c. Most concrete blocks have one or more hollow cavities, and their sides may be cast smooth or with a design. The term precast refers to the fact that the blocks are formed and hardened before they are brought to the job site. A concrete block is one of several precast concrete products used in construction. It is sometimes called a concrete masonry unit (CMU). A concrete block is primarily used as a building material in the construction of walls.
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