Abstract

This article discusses traditional building and construction products, ie, not made from synthetic polymers including wood, asphalt, gypsum, glass products, Portland cement, and bricks. Wood is arguably the oldest building material used by humans to construct their dwellings. It is a natural product obtained from trees, used in both structural and decorative applications. The chemical composition of wood is largely cellulose and lignin. Today there are a variety of composite or reconstituted wood products, such as plywood, particle board, wood fiber boards, and laminated structural beams, where small pieces of wood or wood fiber are combined with adhesives to make larger sheets or boards. Woods are classified as either hardwoods or softwoods, based on the seed- and leaf-type of the trees from which the wood comes. The common softwoods, such as pine, spruce, fir, cedar, and hemlock, have specific gravities between 0.03 and 0.55, which make them ideal for construction purposes. Because of these properties, softwoods are the common construction wood rather than the generally stronger hardwoods. The manufacture of lumber or sawn wood starts with cutting the tree and removing the limbs (limbing), followed by sawing the log into slabs parallel to the long direction of the log. The green wood of a fresh cut tree can have a moisture content of 60 to over 150%. These moisture levels are too high for most construction applications. Most construction wood is dried to below 19% moisture content, often to about 8%. Construction lumber is milled, ie, smoothed, after it has a dried to its finished dimensions. Finished lumber is visually sorted or graded based on industry organization standards. The United States is the largest single producer of lumber, with about 25% of all the logs cut in the world. The wood products or composite wood materials consist of products where the wood is cut into small or thin pieces and then the cut pieces are glued together to form a larger piece of wood product. The most common example is plywood. This category also includes reconstituted wood products subclassified into wood flake boards, particle boards, or wood fiberboards depending on the size of the wood particle glued together. Products in these categories include low density fiberboard (wood fiberboard), medium-density fiberboard (MDF), high density fiberboard (hardboard), flake board, oriented strand board (OSB), and particle boards. Bitumen describes a black or dark brown masticlike material that is thermoplastic in nature and softens upon heating. The sources of bitumen are petroleum or coal deposits. The natural product is commonly called gilsonite or pitch. Bitumen from petroleum or crude oil is called asphalt. It is the material left behind after all the valuable compounds, eg, gasolines, have been distilled out of the crude oil. Bitumen from coal is coal-tar pitch. It remains after the valuable coal oils and tars have been distilled out of the coal tars produced by distractive distillation. Most industrial applications for bitumen products use asphalt or coal-tar pitch. As a construction material, about 75% of all bitumens are used in paving, and about 20% are used in waterproofing. Of the waterproofing usage, 75% is in roofing applications. The use of coal tar is declining because of its listing as a human carcinogen by the U.S. Government. Asphalt is not an exact chemical composition but rather a mixture of organic compounds whose nature is dependent on many items. Gypsum, , is a naturally occurring mineral found mainly in the western United States and eastern Canada. The principal use of gypsum in construction is as a wall finishing material. The manufacturing process requires that the gypsum be partially dehydrated to the hemihydrate, commonly known as plaster of paris. When mixed with water the hemihydrate dissolves and the gypsum precipitates out as the interlocking crystals that make gypsum a hard monolithic material. In the United States, over 90% of the gypsum products sold are as gypsum board. Gypsum board is used as an interior wall surfacing in both residential and nonresidential construction and is referred to as drywall to differentiate it from the older wet plaster walls. The board is composed of a core of gypsum attached to a facing of heavy paper and is attached to the framing members using either nails or screws made especially for installing drywall. The joints between the board are cosmeticly treated with a reinforcing tape and joint compound. The standard sized sheets are four ft (1.22 m) wide and from 8 to 16 ft long. Sheets are available in thicknesses from ¼ up to 1 in. (0.63 to 2.5 cm), but the most common thicknesses are ½ and in. (1.3 and 1.6 cm). Portland cement is the most widely used construction material in the world, especially in Third World nations, because of its availability, ease of use, and versatility. Portland cement is classified as a hydraulic cement, ie, it sets or cures in the presence of water. Portland cement is not an exact composition but rather a range of compositions, which obtain the desired final properties. The compounds that make up Portland cements are calcium silicates, calcium aluminates, and calcium aluminoferrites. Portland cement is not useful by itself to the construction industry. Its value is in the resultant concrete in which it is used as a binder. Concrete is a mixture of smaller particles that coalesce into a solid mass, and the typical particles in a Portland cement concrete are aggregates of rock and sand. In general, the larger the aggregate size the stronger the Portland cement concrete. The primary market for Portland cement is in building construction, which historically takes approximately 65% of all Portland cement sold. Bricks are the oldest manufactured building material in use. Sun-dried bricks were manufactured as early as 6000 BC, and fired bricks were used during the Middle Ages. Today's bricks differ very little except in the efficiency of manufacture; they are still made from clay or shale, a clay-based sedimentary rock that is kiln-fired. There are three processes used to make bricks. All three start with clay that has been milled and screened to remove coarse materials and impurities. Water is added to the prepared clay in an amount appropriate for the brickmaking process that will be used. The clay and water mixture is kneaded to form a plastic mass, which is molded into a brick shape by one of the three processes. The stiff-mud process is the most common method in use. The soft-mud process is used to make handmade brick. The dry-press process is used to make good quality face brick. The products called glass are in the glassy state and are made mainly from silica (silicon oxide, SiO₂). Sodium oxide, Na₂O, and calcium oxide, CaO, are commonly added, up to 30% or more in combination. Glasses can contain a wide range of oxides, depending on the application and properties needed of the glass. Examples of other oxides include the oxides of boron, aluminum, potassium, magnesium, etc. Sand is the common silica source, but the sand must have only minor impurities. Uses of glass in construction products fit into three categories: flat glass (window glass); fibrous glass; and specialty glass products. Each is made by different processes and has different applications. Approximately 57% of flat glass is used in construction applications, mainly as windows. Fibrous glass is manufactured in two different forms, very fine intermingled fibers called insulation fibrous glass and fine but coarser fibers called continuous or textile fibers for reinforcement applications. Foam glass insulation and glass building blocks are two specialty glass products.