Concrete

4. Take notes on your **//Concrete//** wiki page.

Concrete: cement+watter with sand and stones Used by Egypt and Romans, Permitted de development and construction of bridges Middles aged and 20th centuries Reinforced concrete replaced it for pipes floors arches and bridges, foundations walls…

5.post-reading activity No. 2

• Definitions (concepts found in the text) __Concrete__ is a manufactured mixture of cement and water, with aggregates of sand and stones, which hardens rapidly by chemical combination to a stonelike, water-and-fire-resisting solid of great compressive but low tensile strength.

__Precast-concrete__ construction, employs bricks, slabs, and supports made under optimal factory conditions to increase waterproofing and solidity, to decrease time and cost in erection, and to reduce expansion and contractions.

__Prestressed concrete__ provides bearing members into which reinforcement is set under tension to produce a live force to resist a particular load. Since the member acts like a spring, it can carry a greater load than an unstressed member of the same size.

__Concrete-shell construction__ permits the erection of vast vaults and domes with a concrete and steel content so reduced that the thickness is comparatively less than that of an eggshell.

• Look for images of spaces created using: reinforced concrete, pre-cast concrete, prestressed concrete and concrete-shell

Reinforced concrete structure:

Pre-cast concrete structure

Prestressed concrete construction

Concrete-shell construction

• What is the difference between tiltwall construction, tilt-up panel construction and pre-cast concrete construction? (see the link for “precast concrete”) As previously stated in this article, tilt-up and tiltwall are two terms used to describe the same process. 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. One major benefit of this is that the size of the panels is limited only by the needs of the building and the strength of the concrete panels themselves.Tilt-up concrete buildings are built in northern areas, but the window of time for temperate weather is much smaller and less predictable, which can make construction schedules more difficult to meet. The precast concrete building process is similar to tilt-up construction, but it addresses the challenges presented by weather. 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. 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.

6. Write your conclusions on the use of concrete as a reply to the podcast.