Concrete History of Concrete the Term Paper
- Length: 10 pages
- Sources: 3
- Subject: Energy
- Type: Term Paper
- Paper: #9554215
Excerpt from Term Paper :
In homes and buildings, the thermal mass of concrete plays a big role in energy efficiency. The high thermal mass of concrete offers this benefit: it stores and releases the energy required for heating or cooling and hence, reduces "temperature swings in homes and buildings."
Interestingly, concrete also helps big rig trucks and "over-the-road trucks" use less fuel; that is because concrete's rigid pavement design is better than asphalt pavement in terms of fuel consumption. And concrete pavement is "light-reflective" and so it requires "less energy than other materials to illuminate." The Cement Americas narrative goes on to report that members of the Portland Cement Association have voted to adopt a goal of reducing carbon dioxide emissions "per ton of product by 10% (from 1990 levels) by the year 2020."
The Portland Cement Association (PCA), meantime, has its own informational Web site (www.cement.org) and the PCA claims that concrete is not only durable and easy to use in construction, but it "often is the most economical choice." That is because load-bearing concrete exterior walls in buildings "...serve not only to enclose the buildings" and of course keep the elements out; but also concrete walls "carry roof and wind loads, eliminating the need to erect separate cladding and structural systems."
Of course the manufacturers of concrete are in competition with steel manufacturers, so one would expect to read positive comparisons in favor of concrete; the PCA narrative does say that steel construction "can be advantageous" in certain areas of the U.S. "where local market conditions and traditions favor it." But in the south and western regions of the U.S. (that have traditionally strong "masonry" architecture), concrete is the most cost-effective choice.
Hurricanes are a reality in Florida, so concrete is frequently the material of choice PCA says because concrete can withstand high winds (tornadoes as well as hurricanes) in most instances. It is also resistant to insects (unlike wood), which are a huge pest issue in Florida. In California, where fires are a frequent yet tragic event, concrete is used because it doesn't burn.
The PCA explains that there are four methods of concrete construction used to build "load-bearing walls for low-rise construction;" Tilt-up, precast, concrete masonry and cast-in-place. Two of those will be described on the following page.
Tilt-up construction: this is suited to shopping center and warehouse construction because contractors "can form the windowless, unarticulated wall panels quickly and economically," PCA points out. Tilt-up can also be used for buildings that do have windows. The way tilt-up construction is done, the concrete is poured in a horizontal position, then lifted with a crane into place to actually construct the building.
Precast construction: this was discussed earlier, but suffice it to say this kind of concrete can be appropriate for buildings in which the concrete patter "can be repeated"; and the "...more times a concrete shape or panel can be repeated, the greater economy can be achieved." There is an advantage for contractors with precast concrete and that is "factory control"; the strength, appearance and quality is able to be very carefully monitored and regulated in a factory environment where supervision and oversight are part of the normal daily operations.
Earthquakes are commonplace in California, Japan, and elsewhere along the various tectonic plates, and as to concrete and its benefits during a big earthquake the PCA explains that depends on whether the structure was "properly designed, detailed, and constructed to resist the lateral side-to-side loading created by the shaking of the earth." And for a concrete association to admit that their product isn't necessarily the most effective is instructive to the reader. To wit, the likelihood of a given structure surviving a big earthquake depends "more on how the structure is engineered than on what type of material is used to build it." big earthquake struck Kobe, Japan in 1995, and the follow-up engineering data shows that only 4.9% of concrete buildings and 5.3% of steel constructed buildings collapsed. There were 5,000 deaths, and 34,000 injuries that resulted from the Kobe earthquake, and most of those, the PCA narrative points out, were caused by "the widespread collapse of traditional one-and-two-story, wood post-and-beam houses." The problem with these structures is they relied on interlocking pieces of wood, "rather than with nails or other positive connectors."
Earthquakes and concrete: An article in the publication of the American Society of Civil Engineers (Cardno, 2006) (Civil Engineering News) explains that "fiber-reinforced concrete can markedly increase the ability of slab-to-column connections" in terms of sustaining its integrity during an earthquake - without substantial damage resulting. Researcher from Michigan and Minnesota were searching for cost-effective ways to make slab-to-column framing systems more secure in seismically active locations. The amount of lateral movement that is possible in a slab-to-column connection before there is "punching shear damage" depends on the gravity load that is present, the article explains. It was a matter of trying reinforcing fibers of varying strength until the right combination would solve the problem, the writer explains.
In order to do the testing at various levels of earthquake-like shaking, wireless sensors are used as monitors to record the behavior of the fibers that are built into the concrete. And so, besides the advantage of stronger concrete, the sensors would, in the "immediate aftermath of a catastrophic event," record data that would then be instantaneously routed to emergency response centers "via satellite-based communications devices" which would very probably be able to sustain integrity during a big temblor. That way the damage done could be assessed electronically and digitally prior to a "catastrophic failure" would occur. Lives could be saved and damage minimized, all because small fibers (and sensors) would be planted inside concrete.
New West Virginia Concrete Bridge: The longest concrete box girder span in the United States is under construction across the Kanawha River in West Virginia, according to Civil Engineering News. The bridge will be 2,975 feet long and will link the cities of South Charleston and Dunbar. The main span will be 760 feet, a record in the U.S. according to the article, which explains that the bridge is being built using the "balanced-cantilever" method so no temporary structures will be needed during construction (Brown, 2007). Any temporary structures could have impacted commerce on the rive, because coal barges move up and down the river frequently. The bridge will be less expensive than a steel bridge would have been; the low bid for a steel constructed bridge was $113 million, while the low bid (winning bid) for a concrete bridge was $83 million.
The simple consistent form of the superstructure - a continuous box girder - "enhances its aesthetic appeal," the article explains, while at the same time simplifying construction. The bridge, which is to be completed in 2010, needed to have very dependable under footing, so crews drilled two test shafts into the sandstone rock layers, one near the location of each of the main piers. The tests showed that the rock was "more than adequate" to hold the enormous load the bridge will place on it.
Meanwhile, in the journal Rock Products, a new study shows there are benefits to "crushed concrete aggregate." The RMC Research & Education Foundation has completed a study called "Crushed Returned Concrete as Aggregates for New Concrete," conducted at the National Ready Mixed Concrete Association's (NRMCA) Research Laboratory. The report from that research evaluates the effects of using crushed concrete aggregate (CCA) on "fresh and hardened concrete properties" by making a comparison of those properties to concretes that only contain "virgin aggregates." The bottom line of this research is that the "ready-mixed concrete industry" could realizing savings of up to $300 million annually by using crushed "returned concrete as aggregates."
This savings, the journal article continues, has positive environmental implications as well. The use of CCA "...supports sustainable construction initiatives and adds to the benefits that concrete can provide in this arena." And so, companies that use concrete, produce concrete, are involved in construction and building can save money and increase recycling activities. This report shows that CCA is moving towards more widespread acceptance in terms of a sustainable solution, and of course savings are part of that advancement for CCA.
A possible solution for concrete bridges that are potentially in danger of collapsing. Meanwhile, an article in Popular Science magazine reports that "a tangy flavorant in junk food keeps concrete bricks and bridges from disintegrating." This article alludes to the terrible collapse of the interstate highway bridge in Minnesota earlier in 2007. That collapse, along with a bridge collapse in China earlier this year, took the lives of 58 people. The Minnesota bridge was apparently weakened by water intrusion into the concrete. Indeed, the article in Popular Science claims that when "water seeps through concrete's pores, cracking its exterior and damaging the steel beams within" (Aaronson 2007), a catastrophic collapse is possible. But by using sodium…