Concrete

• Definitions (concepts found in the text) **CONCRETE** **1:** a mass formed by concretion or coalescence of separate particles of matter in one body **2:** a hard strong building material made by mixing a cementing material (as portland cement) and a mineral aggregate (as sand and gravel) with sufficient water to cause the cement to set and bind the entire mass **3:** a waxy essence of flowers prepared by extraction and evaporation and used in perfumery

**REINFORCED CONCRETE** **1:** concrete in which metal (as steel) is embedded so that the two materials act together in resisting forces

CONCRETE SHELL CONSTRUCTION 1: Also commonly called //thin shell concrete structure//, is a structure composed of a relatively thin shell of concrete, usually with no interior columns or exterior buttresses. The shells are most commonly flat plates and domes, but may also take the form of ellipsoids or cylindrical sections, or some combination thereof. The first concrete shell dates back to the 2nd century.

PRECAST CONCRRETE CONSTRUCTION **Precast concrete** is a construction product produced by casting concrete in a reusable mold or "form" which is then cured in a controlled environment, transported to the construction site and lifted into place. In contrast, standart concrete is poured into site-specific forms and cured on site. **Precast stone** is distinguished from precast concrete by using a fine aggregate in the mixture, so the final product approaches the appearance of naturally occurring rock or stone.

PRESTRESSED CONCRETE CONSTRUCTION **Prestressed concrete** is a method for overcoming concrete's natural weakness in tension. It can be used to produce beams, floors or bridgets with a longerspan than is practical with ordinary reinforced concrete. Prestressing tendons are used to provide a clamping load which produces a compressive stress that balances the tensile stress that the concrete compression member would otherwise experience due to a bending load. Traditional reinforced concrete is based on the use of steel reinforcement bars, rebars, inside poured concrete.

IMAGES Reinforced Concrete (Hanoi Museum in Vietnam) Prestressed Concrete Roof <span style="font-family: Arial,Helvetica,sans-serif; font-size: 90%;">Precast Concrete <span style="font-family: Arial,Helvetica,sans-serif; font-size: 90%;"> Concrete Shell Structure

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 90%;">• What is the difference between tilt wall construction, tilt-up panel construction and pre-cast concrete construction?

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 90%;">Tilt-up and tilt wall are two terms used to describe a precast concrete building construction. For a tilt-up concrete building, the walls are created by assembling forms and pouring large slabs of concrete called panels directly at the job site. The panels are then tilted up into position around the building's slab. Because the concrete tiltwall forms are assembled and poured directly at the job site, no transportation of panels is required <span style="font-family: Arial,Helvetica,sans-serif; font-size: 90%;">For precast concrete buildings, work crews do not set up forms at the job site to create the panels. Instead, workers pre cast concrete panels at a large manufacturing facility. Because the precast concrete forms are poured indoors, this activity can take place regardless the weather conditions. After curing, the precast concrete panels are trucked to the job site. From this point, precast concrete buildings are assembled in much the same manner as tiltwall buildings. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 90%;">The fact that precast concrete walls are formed at a manufacturing facility resolves the weather issue, but presents a different limitation not found in tilt-up construction. Because the panels must be transported - sometimes over long distances - places a substantial limitation on how wide or tall each panel can be. It would be impossible to load precast panels that were 60 feet wide or 90 feet long onto trucks and transport them any distance. For a precast construction project, the panels must be smaller and more manageable to allow trucks to haul them over the road to their final destination. This places greater design restrictions on architects and limits the applications where precast construction can be used. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 90%;">Clearly, tilt-up or tiltwall construction and precast concrete are similar processes. Because tilt-up affords more flexibility, it is the method of choice in locations where the weather allows it. Precast concrete is a suitable choice in circumstances where environmental factors and the construction schedule preclude tiltwall as a viable option.