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Lightweight ConcreteResearch Paper

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Structural Performance of Lightweight Concrete

The Pantheon, built 18 centuries ago, demonstrates the structural performance of lightweight concrete to be superior to many contemporary building materials. In time, the use of lightweight concrete has spread across the U.S., the UK, Sweden and a number of other countries. The performance of the muti-faceted building material, nevertheless, depends on a myriad of components which range from and including the materials used to create the lightweight concrete to the manufacturing process also contribute to the characteristics and durability the finished product/s.

Based on the literature the author reviewed for the report, contemporary builders and developers could benefit from an intensive review of the way the Romans used lightweight concrete to construct the Parthenon eighteen centuries ago. Perhaps then, when future builders and develops examine contemporary projects; they will be compelled to study and replicate these projects.

STRUCTURAL PERFORMANCE of LIGHTWEIGHT CONCRETE

"As with all site installed materials, the quality of the finished product is based on the skill level of the applicator"

John a. D'Annunzio (2007, p. 2).

Introduction

Reports Regarding Lightweight Concrete

The Romans reportedly used lightweight concrete 18 centuries ago. "The application on the 'The Pantheon' where it uses pumice aggregate in the construction of cast in-situ concrete," according to Hjh Kamsiah Mohd Ismail, Mohamad Shazli Fathi and Norpadzlihatun bte Manaf (2003), all with the Universiti Teknologi Malaysia Institutional Repository, confirms the Romans use of lightweight concrete. In the journal article, "Study of lightweight concrete behavior," Ismail, Fathi and Manaf recount that during the late nineteenth century, American and English builders used clinker, a form of lightweight concrete in their construction projects like the British Museum as well as in low cost housing. During the research paper which investigates the structural performance of lightweight concrete, the author asserts the hypothesis: When the builder or developer uses lightweight concrete to construct contemporary projects, then the structural performance of the muti-faceted building material will simultaneously fortify the completed project.

In the article, "The Pantheon," David Moore, P.E. (1995) explains that although much of the Pantheon was constructed18 centuries ago, it still stands tall in Rome's business district. The Pantheon, with parts constructed with lightweight concrete, has remarkably withstood the negative effects of the elements and war "permitting a firsthand view of a unique product constructed by Roman hands. Now, it is exposed to acid rain and fumes from passing automobiles and overshadowed by buildings of inferior taste…" (Moore, ¶ 6). The Jutland Archaeological Society investigations report that builders constructed the lower section of thePantheon's dome with concrete, as they alternated layers of bricks and tufa.

[B]oth [bricks and tufa] have good affinity with the lime-pozzolan mortar which filled the voids. The upper dome above the step-rings (the top 30 feet/9.1 m) is concrete comprising about 9-inch lumps of light tufa and porous volcanic slag in alternating layers bonded with mortar.18 it was customary for the Romans to use larger stones in the dome concrete than in the walls. Selecting light stones for the aggregate is another case of gradation to get light-weight concrete, a process that seems to have been evolved about the middle of the first century B.C. (Moore, 1995, Dome Section, ¶ 6).

The Pantheon's design reveals numerous features unparalleled in contemporary design standards. Even though several major cracks have appeared in the dome, it continues to function unimpaired. Most consider it incredible that the expansive concrete dome of the ancient structure, which was built entirely without steel reinforcing rods, today deemed necessary in concrete members to resist tensile cracking, could last for centuries. In contemporary construction, an engineer would reinforce such a structure with steel rods.

The Emperor Hadrian rebuilt the Panthenon during 118 to 128 a.D., according to a Ward-Perkins. Lugli, however, disputes time estimation by Ward-Perkins and contends the building began after 123 a.D. And that Emperor Pius comploeted it about 140 a.D. Most of the bricks, nevertheless, were made and positioned in the Pantheon during 123 a.D., confirmed by a date the maker stamped on his bricks. George Chedanne, the French archaeologist discovered this in 1892. "It appears the construction of the rotunda walls took a period of 4 to 5 years, and the dome required a like period because of its height and the meager tools the Romans used" (Moore, 1995, ¶ 6). The extended construction period permitted th pozzolan concrete used in construcing the Panthenon ample time to cure and increase strength. The following figure portrays a photo of the Panthenon.

The Panthenon (Moore, 1995).

During the First World War in the United States (U.S.), builders and developers used lightweight concrete in numerous construction projects, primarily for making concrete blocks and for shipbuilding. "The foamed blast furnace-slag and pumice aggregate for block making were introduced in England and Sweden around 1930s" (Ismail, Fathi and Manaf, 2003, ¶ 10). Contemporary technology, albeit, has advanced lightweight concrete and expanded its uses; including applications for use in roof decks, vessels, and numerous other applications. Builders and developers have extensively used lightweight concrete in the form of perlite. They use perlite, for example, with its outstanding insulating characteristics as loose-fill insulation in masonry construction. Used in this area, it improves fire ratings and decreases noise transmission. Perlite proves to be termite resistant as it does not rot.

Since the late 1990s, builders, developers, and roofers have increasingly used lightweight concrete as a roof decking and as a component of the insulation system. In the article, "New Lightweight Concrete Technology," D'Annunzio (2003) asserts: "Lightweight concrete can achieve similar strengths as standard concrete, and it produces a more efficient strength-to-weight ratio in structural elements" (p. 2). Although the growing use of lightweight concrete in roof decking, insulation systems and a myriad of other building venues may be attributed to the recent industry-wide delamination deficiencies and insulation shortages, this increase may also be ascribed to the numerous economic and environmental advantages lightweight insulating concrete (LWIC) offers in roof assemblies.

Although lightweight concrete may initially appear to be more expensive than traditional concrete, the reduced volume of lightweight concrete offsets this expense as it allows designers to use less, consequently adding less cost. In addition to construction costs totaling lower when builders and developers choose to use structural lightweight concrete, the project proves ultimately more durable. In determining the validity of the hypothesis for the report, the writer presents the following subsections:

Components of Lightweight Concrete

Advantages and disadvantages of lightweight concrete;

High Performance Fiber Reinforced Lightweight Concrete;

Proper Mixing Methods;

Volcanic Pumice;

Conclusion.

Lightweight Concrete

Components of Lightweight Concrete

Lightweight concrete may be produced by injecting air into the composition, by leaving out the finer sizes of the aggregate, or by replacing the aggregate with hollow or porous aggregate. Ismail, Fathi, and Manaf (2003). Lightweight concrete comprises as a particular kind of concrete which includes an "expanding agent in that it increases the volume of the mixture while giving additional qualities such as nailbility and lessened the dead weight. It is lighter than the conventional concrete" (Preface Section, ¶ 1). In time, the use of lightweight concrete has spread across the U.S., the UK, Sweden and a number of other countries. Ismail, Fathi, and Manaf explain that lightweight concrete may be grouped into one of the following three catagories:

1. No-fines concrete

2. Lightweight aggregate concrete

3. Aerated/Foamed concrete (Ismail, Fathi, and Manaf, 2003, ¶ 5-7).

Builders and developers have used structural lightweight concrete, made with accumulation of lightweitght concrete aggregate, in the U.S. For more than 50 years. The article, "Concrete in practice, what, why and how?," (2003) explains "structural lightweight concrete has an in-place density (unit weight) on the order of 90 to 115lb/ft3 (1440 to 1840 kg/m3) compared to normal weight concrete with a density in the range of 140 lb to 150lb/ft3 (2240 to 2400kg/m3)" (p. 1). Manufactures typically use lightweight aggregates, like clay, shale or slate materials to make structural lightweight concrete. The firing of these lightweight aggregates in a rotary kiln causes this type concrete to have a porous structure.

Manufactures may also use air-cooled blast furnace slag may to create lightweight concrete aggregates. "There are other classes of non-structural lightweight concretes with lower density made with other aggregate materials and higher air voids in the cement paste matrix, such as in cellular concrete" (Concrete in practice…, 2003, p. 1). Builders and developers generally use this type of concrete only for its insulation properties.

Builders and Developers primarily use strucural lightweight concrete to minimize the dead load of a structure constructed with concrete. This construction practice permits the designer to decrease the size of columns and footings or other load bearing essential features. "Structural lightweight concrete mixtures can be designed to achieve similar strengths as normal weight concrete. The same is true for other mechanical and durability performance requirements" (Concrete in practice…, 2003, p. 1). Strucutral lightweight concrete also produces a better strength to weight ratio for structural materials.

Advantages of Lightweight Concrete

Two distincitive features of lightweight concrete include its low density and thermal conductivity.… [END OF PREVIEW]

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