Structural Performance Of Lightweight Concrete

The Romans reportedly first used lightweight concrete during the eighteenth centuries. “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. D’Annunzio (2003) reports: “Lightweight concrete can achieve similar strengths as standard concrete, and it produces a more efficient strength-to-weight ratio in structural elements” (p. 2). During the research paper which investigates the structural performance of lightweight concrete, the author asserts: When the builder or developer uses lightweight concrete, then … completing hypothesis…

the rest is just to show progress….

D’Annunzio (2003), reports “the use of lightweight concrete as a roof decking and insulation system has

expanded in the past five years. Increased usage can be attributed to the recent industry-wide insulation shortages and delamination deficiencies” (p. 1). The increase can also be attributed to the economic and environmental advantages that lightweight insulating concrete (LWIC) provides in roof assemblies.

Lightweight insulating concrete (LWIC) provides The reported recent industry-wide insulation shortages and delamination deficiencies.

The increase can also be attributed to the

economic and environmental advantages that in roof assemblies.

lightweight concrete as a roof decking and insulation system has

expanded in the past five years. Increased usage can be attributed to

The lightweight concrete was also used in

construction during the First World War. The United States used mainly for shipbuilding

and concrete blocks. The foamed blast furnace-slag and pumice aggregate for block

making were introduced in England and Sweden around 1930s.

Nowadays with the advancement of technology, lightweight concrete expands its

uses. For example, in the form of perlite with its outstanding insulating characteristics. It

is widely used as loose-fill insulation in masonry construction where it enhances fire

ratings, reduces noise transmission, does not rot and termite resistant. It is also used for

vessels, roof decks and other applications. Figure 5 shows some examples of lightweight

concrete used in different forms.

Lightweight insulating concrete (LWIC) provides The reported recent industry-wide insulation shortages and delamination deficiencies.

The increase can also be attributed to the

economic and environmental advantages that in roof assemblies.

lightweight concrete as a roof decking and insulation system has

expanded in the past five years. Increased usage can be attributed to

“Lightweight concrete can achieve similar strengths as standard concrete, and

it produces a more efficient strength-to-weight ratio in structural elements”

D’Annunzio (2007, p. 2).

John A. D’Annunzio (2003), president of IRT Inc., asserts in the article, “New Lightweight Concrete Technology,” “as with all site installed materials, the quality of the finished product is based on the skill level of the applicator.

Structural lightweight concrete, made with accumulation of lightweitght concrete aggregate, has been used in the United States for approximately 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). Lightweight aggregates, such as clay, shale or slate materials, are typically used to make structural lightweight concrete. These lightweight aggregates are fired in a rotary kiln to cause this type concrete to have a porous structure.

Air-cooled blast furnace slag may also be used 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). This type of concrete is typically used for insulation properties only.

Lightweight concrete may be produced by injecting air in to the composition, by leaving out the finer sizes of the aggregate or by replacing the aggregate with hollow or porous aggregate. Hjh Kamsiah Mohd Ismail, Mohamad Shazli Fathi and Norpadzlihatun bte Manaf (2003), all with the Universiti Teknologi Malaysia Institutional Repository, purport in the journal article, “Study of lightweight concrete behavior,” “particularly, lightweight concrete can be categorized into three groups:

No-fines concrete

Lightweight aggregate concrete

Aerated/Foamed concrete (p. 5).

No-fines concrete may be defined as lightweigh concrete that is created by combining cement and fine aggregate. This type of concrete has evenly spaced holes throughout it.

Strucural lightweight concrete is mainly used to minimize the dead load of a structure that is made out of concrete. This allows 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. Although lightweight concrete is more expensive than traditional concrete, the cost is offset because of the reduced volume of lightweight concrete, allowing designers to use less, which turns out to be less cost.

When builders and developers choose to use structural lightweight concrete, the construction costs are lower and the building is much more durable. The researcher will purport the:

Advantages and disadvantages of lightweight concrete;

High Performance Fiber Reinforced Lightweight Concrete

Proper Mixing Methods

Volcanic Pumice

Offer Conclusions

Advantages of Lightweight Concrete

Two of the distincitive features of lightweight concrete are its low density and thermal conductivity. Ismail, Fathi and Manaf (2003), explain “advantages are that there is a reduction of dead load, faster building rates in construction and lower haulage and handling costs. Lightweight concrete maintains its large voids and not forming laitance layers or cement films when placed on the wall” (p. 1). A great example of the durability of lightweight concrete is ‘The Pantheon’ in Rome, which was built over 18 centuries ago.

Sructural lightweight concrete is in high demand for use in construction because of its lower density which results in designers’ ability to have a smaller foundation due to the use of smaller load bearing elements or cross sections. Harun Tanyildizi and Ahmet Coskun (2008), both with the Department of construction education, Firat University Elazig, Turkey, explain in the journal article, “The effect of high temperature on compressive strength and splitting tensile strength of structural lightweight concrete containing fly ash,” “lightweight aggregates are broadly classified in to two types-natural (pumice, diatomite, volcanic cinders, etc.) and artificial (perlite, expanded shale, clay, slate, sintered PFA, etc.). Lightweight concrete can easily be produced by utilizing natural lightweight aggregate i.e., pumice or perlite aggregate” (¶ 2). The main advantages to using structural lightweight concrete are increased strength, more flexible and less coefficient of thermal expansion.

Disadvantages of Lightweight Concrete

Lightweight concrete applications do have certain disadvantages and liabilities, typically having to do with the cabability of the contractor istalling it. John A. D’Annunzio (2003), president of IRT Inc., asserts in the article, “New Lightweight Concrete Technology,” “as with all site installed materials, the quality of the finished product is based on the skill level of the applicator. Lightweight concrete has additional constraints because the success of the system is based on the proper mix ratio” (p. 2). One of the major problems with lightweight concrete is if the lightweight concrete is not mixed properly, it may have empty spaces that can lead to deficient strength.

The compressive strength of lightweight concrete come from a foam additive, when it is mixed correctly, this additive molds around the cement which serves as an aggregtae. “If the foam additive is not properly mixed, there is a probability of foam collapse, which weakens the product’s compressive strength” (D’Annunzio, 2003, p. 2). One of the factors that leads to lightweight concrete failing is the mixing process is typically done at a jobsite, which may lead to human errors. Concrecel USA has developed pumping equipment that percisley weighs the ingredients and accurately mixes the foam and cement, to elimante the problem of human error. Table 1 depicts the advantages and disadvantages of lightweight concrete.

Table 1: Lightweight Concrete Advantages/Disadvantages(Ismail, Fathi & Manaf, 2003, p. 8).

Advantages of Lightweight Concrete

Disadvantages of Lightweight Concrete

Quick and relatively simple construction

Very sensitive with water content in the mixtures

Economical in terms of transportation as well as reduction in manpower

Difficult to place and finish because of the porosity and angularity of the aggregate. In some mixes the cement mortar may separate the aggregate and float towards the surface.

Significant reduction of overall weight in saving structural frames, footing or piles

High Performance Fiber Reinforced Lightweight Concrete

Typical lightweight concrete is weaker than traditional weight concrete. It is critical to improve the strength of lightweight concrete in order to promote it for use for structural applications. Bengi Arisoy, Department of Civil Engineering, Faculty of Engineering, Ege University, Bornova, Turkey and Hwai-Chung Wu (2008), Advanced Infrastructure Materials Laboratory, Department of Civil and Environmental Engineering, Wayne State University, Milwakee, explain in the journal article, “Material characteristics of high performance lightweight concrete reinforced with PVA,” “with a much higher ductility high performance fiber reinforced lightweight concrete (HPFRLWC) becomes superior to regular concrete because of elimination of sudden catastrophic failure of otherwise brittle concrete. Ductility results from imposed crack resistance due to bridging fibers” (Theoretical background section, ¶ 1). The researchers found that fiber reinforced lightweight concrete, when made with lightweigh aggregates and air entraining agent, displays strain hardening by the addition of 1.5% fiber volume fraction.

By adding about 10-20% fine cement substitute such as fly ash and silica fume, it improves both ductility and flexural strength. Improvement of high performance FRLWC may be summarized as follows: 50-150 times (5000-15000%) increase in flexural displacement (ductility) at ultimate load than plain lightweight concrete, 50-250% increase in ultimate flexural strength than plain lightweight concrete, 30-65% decrease in weight than normal weight concrete (Arisoy & Wu, 2003, Conclusion section, ¶ 1).

Proper Mixing Methods

The concrete mixture design, especially for lightweight concrete, has stressed compressive strength, and also the durability of the concrete. Chao-Lung Hwang Department of Construction Engineering, National Taiwan University of Science and Technology, Taiwan and Meng-Feng Hung (2005), Department of Civil Engineering, National Taiwan University of Science and Technology, Taiwan assert in the journal article, “Durability design and performance of self-consolidating lightweight concrete,” “ACI 318 structure code stresses both the maximum w/cm ratio to highlight the usage of pozzolanic material, and the minimum 28-day compressive strength to guarantee construction safety while considering durability of normal weight concrete” (¶ 2). If a concrete structure cracks or become porous, it is more sustable to be subjective to harsh outside elements, such as acid rain and seawater, that may lead to its deterioration and the quality of a structure.

Lightweight aggregate has a porous feature, because of that its compressive strength is typically low and the capacity it has for absorpution is fairly high. “Hence, it needs large amount of cement paste to achieve suitable workability and designed compressive strength. This may violate the durability requirement of normal weight concrete as mentioned” (¶ 4). Because the porous aggregate reduces the density of the lightweight aggregate concrete (LWC) and because it fractures easily when mixed, it is critical to design the LWC with increased strength and durability.

In various field conditions, lightweigh concretes, in regards to carbonation performance, have typically performed adequately. T.Y. Lo, W.C. Tang and A. Nadeem (2008), all with the Department of Building and Construction, City University of Hong Kong, Kowloon, Hong Kong, explain in the journal article, “Comparison of carbonation of lightweight concrete with normal weight concrete at similar strength levels,” “some field investigations on the carbonation performance of LWC in ships and bridges at exposure age from 15 to 43 years, compressive strength from 23 to 35 MPa and density from 1650 to 1820 kg/m3 have been reported” (Carbonation of lightweight…section, ¶ 1). The depth of carbonation in these structures varied in regards to exposure conditions, density and strength, and was typically less than 10 mm.

What effect moisture content, porosity and cement to water ratio have on the limits of carbonation, have been studied by researchers. For example, Swenson and Sereda, prominent researchers found that the moisture content in lightweight concrete, whether high or low, was not favorable to rapid carbonation. “Swamy and Jiang found that carbonation was higher for concrete with higher total porosity at a given water to cement ratio. Bilodeau et al. attributed the low carbonation in high strength LWC to low water to cement ratio” (Lo, Tang & Nadeem, 2008, Carbonation of lightweight…section, ¶ 2). Finally, Gunduz and Ugur analysed the carbonation of pumice aggregate lightweight concrete and expressed the carbonation was lessened when the aggregate to cement ratio of lowered.

Volcanic Pumice

This one is way over my head need to add a little from 8-next page 80 in raw research

Pumice, a natural material, comes from volcanos when gases are released and the lava solidifies. Khandaker M. A. Hossain, Associate Professor in the Department of Civil Engineering at Ryerson University, Toronto, Canada and Mohamed Lachemi (2007), a Canada Research Chair in Sustainable Construction and a Professor in the Department of Civil Engineering at Ryerson University, both ACI members, assert in the journal publication, “Mixture Design, Strength, Durability, and Fire Resistance of Lightweight Pumice Concrete,” “world pumice production was 14.4 million metric tones Mt in 2004. Globally, Italy remains the dominant producer of pumice, with production estimated to be 4.6 Mt per year” (¶ 3). Pumice is mainly used an an aggregate in lightweight building block and other building products. Volcanic pumice (VP) has been utlizied as an aggregate in producing lightweight concrete.

Pumice has been used for builing over 2000 years, especially in Rome and Europe where many pumice structures are still standing to this day. “Lightweight concrete made with pumice and pozzolanic cement with volcanic ash/lime (developed in Mexico by the Totonacas) has survived more than 2000 years and provides an example of a low strength concrete and very long-term performance” (Hossain & Lachemi, 2007, ¶ 4). Using pumice and perlite as additives has been found to supply increased resistance to the freezing and thawing of concrete, cement pastes and mortar.