Thursday, 1 March 2012

LIGHT WEIGHT CONCRETE


Foaming

Foaming agentEvery liter of foaming agent is diluted 30 times with water, which expands another 22 times in the foaming generator.

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Light weight concrete

What is it ?

Light weight concrete - or foamed concrete - is a versatile material which consists primarily of a cement based mortar mixed with at least 20% of volume air. The material is now being used in an ever increasing number of applications, ranging from onestep house casting to low density void fills.
Foamed concrete has a surprisingly long history and was first patented in 1923, mainly for use as an insulation material. Although there is evidence that the Romans used air entrainers to decrease density, this was not really a true foamed concrete. Significant improvements over the past 20 years in production equipment and better quality surfactants (foaming agents) has enabled the use of foamed concrete on a larger scale.
Lightweight and free flowing, it is a material suitable for a wide range of purposes such as, but not limited to, panels and block production, floor and roof screeds, wall casting, complete house casting, sound barrier walls, floating homes, void infills, slope protection, outdoor furniture and many more applications.
Not everyone knows that density and compressive strength can be controlled. In the light weight concrete this is done by introducing air through the proprietary foam process which enables one to control density and strength precisely.
Normal concrete has a density of 2,400 kg/m3 while densities range from 1,800, 1,700, 1,600 down to 300 kg/m3. Compressive strengths range from up to 40 mpa down to almost zero for the really low densities. Generally it has more than excellent thermal and sound insulating properties, a good fire rating, is non combustible and features cost savings through construction speed and ease of handling.
The technology is the result of over 20 years of R&D, fine tuning the product and researching the possible applications. It is used in over 40 countries world wide today and has not reached the end of its possible uses.

Frequently asked questions

  • How strong is it ?

    Strength is a relative term. Concrete mixes should be designed based on end use. High compressive strength is useful where deadload or abrasion are factors, but are unnecessary for roofs and non-structural partitions. All concrete is deficient in tensile and shear strengths, however these are supplemented through structural reinforcement. Compressive strength can be made up to 40 Mpa, exceeding most structural requirements.


  • What are the advantages of pre-formed foam ?

    The pre-formed foam process offers excellent quality control and assurance of specified density. Preformed foam, unlike gas-forming chemicals, assures a consistent three-dimensional distribution of the engineered air cell system. Pre-formed foam produces a consistent matrix of relatively small air cells which are more desirable than a disorganized matrix of different size bubbles often created with the gas method of reactive admixtures.


  • What are the disadvantages of lightweight concrete, compared to typical concrete ?

    In the lower density ranges lightweight concrete does not develop the compressive strength of plain concrete. While this may be a disadvantage in plain concrete applications, it is an advantage in a lightweight concrete application. It should be considered that lightweight concrete and plain concrete are typically used for different types of applications. Each form of concrete exhibits a unique family of performance characteristics. Each should be utilized in the appropriate type of project. But a high strength of 33 Mpa has been achieved with a high cement content mix.


  • Is segregation a problem ?

    Unlike plain concrete there is little to segregate in lightweight concrete which makes segregation a moot point. The lightweight concrete equivalent to segregation would be a collapse of the air cell system and a volume reduction in material. To prevent this one should use the most stable liquid foam concentrates and treat the mixed lightweight concrete with some care in placing. Fresh lightweight concrete is not fragile and can be pumped for long distances.


  • Is lightweight concrete chemically compatible with common additives ?

    Lightweight concrete is compatible with common concrete construction additives; however, most common admixtures are added to plain concrete to effect a change in the characteristics of the concrete that are not applicable to lightweight concrete application performance. As an example, lightweight concrete needs no air entrainment or finishing aids; however, colour admixtures and strength enhancing admixtures work well if they are applicable to the project.


  • What additives are common to cellular concrete ?

    Fiber reinforcement, Heat-of-hydration reducers (iced water or chemicals), Compressive strength enhancers, Colouring pigments or colour enhancing admixtures


  • What is the correct water to cement ratio for the cement water slurry ?

    Typically, a .5 water to cement ratio slurry consisting of two parts cement to one part water is typically used as a base mixture for lightweight concrete. The water cement ratio varies according to specific project requirements. Note that lightweight concrete obtains it's natural fluidity from the air bubble structure, not from excess water content.


  • Does lightweight concrete mix contain either fine or course aggregate ?

    Lightweight concrete may also contain normal or lightweight, fine and/or coarse aggregates. The rigid foam air cell system differs from conventional aggregate concrete in the methods of production and in the more extensive range of end uses. Lightweight concrete may be either cast-in-place or pre-cast. Lightweight concrete mix designs in general are designed to create a product with a low density and resultant relatively lower compressive strength (when compared to plain concrete). When higher compressive strengths are required, the addition of fine and/or course aggregate will result in a stronger lightweight concrete with resultant higher densities. We should note that most lightweight concrete applications call for a lightweight material. When considering the addition of course aggregate, one must consider how appropriate this heavy aggregate will be to a project, which typically calls for lightweight material. The inclusion of aggregate, particularly course aggregate may be counter productive to the materials intended performance.


  • What type of cement is appropriate for lightweight concrete ?

    Lightweight concrete may be produce with any type of portland cement or portland cement & fly ash mixture. The performance characteristics of type II, type III and specialty cements carries forward into the performance of the lightweight concrete.


  • Is it appropriate to add fly ash to the cement and water slurry for lightweight concrete ?

    Fly ash added to the cement does not adversely affect the basic hardened state of lightweight concrete. Infusing and supporting the lightweight concrete with the air cell system is a mechanical action and is not problematic with fly ash or other additives. Note that some fly ash mixes may take longer to set than pure portland cement applications. Mixes with large percentages of fly ash may take an very extended time to set up. High carbon content fly ash such as typical "bottom ash" should be generally avoided in most cellular or plain concrete mixes.


  • Is it appropriate to reinforce cellular concrete with synthetic fibers ?

    Synthetic fiber reinforcement is a mechanical process and does not have any effect on the chemistry of concrete. It is therefore perfectly acceptable to design fiber reinforced lightweight concrete. Fiber reinforced cellular concrete is becoming a standard material for roof decks and Insulated Concrete Form (ICF) construction. Oil palm fibers are also successfully being added and it produces a very good design mix of 900 kg density per meter cube most suitable for high rise buildings wall panels.


  • Is it appropriate to reinforce cellular concrete with steel fibers ?

    There is no chemical or mechanical reason not to reinforce lightweight concrete with steel fibers. However, most lightweight concrete applications require a lightweight material. Most steel fiber concrete applications require heavy, high compressive strength steel fiber reinforced concrete. It would seem somewhat unlikely that an application would require steel fiber reinforce lightweight concrete, but there is no technical reason not to design a steel fiber reinforced lightweight concrete.


  • Do the bubbles in lightweight concrete collapse, reducing its volume ?

    Not with well engineered liquid foam concentrates. The pre-formed foam lightweight concrete products made from top quality liquid foam concentrates do not collapse. Air cell stability is the mark of a superior foam concentrate and foam generator combination. Which is not to say that all lightweight concrete products are stable. Particular care should be taken to test foams from water pressure type foam generators, and gas-off chemical products. The proposed pre-formed foam for an application should be tested for stability or certified for stability before actual project placement.


  • Densities and Strengths

    One of the most useful features of a lightweight concrete system is the system's ability to be manufactured in a wide range of low densities and strengths. Application requirements for lightweight concrete range from very light density low strength fill dirt replacement to higher strength structural lightweight concrete. To accommodate this wide range of performance properties lightweight concrete has developed a mix design chart, which will illustrate the basics of making this wide range of materials from just one lightweight concrete concentrate. With a lightweight concrete foam generator and a single liquid foam concentrate the contractor now has available to them a wide variety of cost effective, high performance, lighter lightweight concrete products.


  • What are the different densities and strengths available ?

    Lightweight concrete exhibits a much lighter density than typical aggregate concrete. Typical plain concrete has a density of 2400 kg/m3, lightweight concrete densities range from 300 kg/m3 to 1800 kg / m3. Lightweight concrete is an insulator and can be used in a variety of applications which require an insulating material that can also exhibit some integrity and strength. Lightweight concrete at its lightest density is still more stable and strong than well compacted soil. When replacing soils, lightweight concrete can be designed to provide whatever strengths and characteristics needed for the soil stabilization project. Some soil engineers lightheartedly refer to lightweight concrete used in Geotechnical stabilization projects as "designer dirt." They know that lightweight concrete can be specified to easily exceed whatever compacted soil requirements are needed.


  • How much does lightweight concrete cost ?

    Cost effective lightweight concrete varies in price by geographical area and by application requirements such as density and strength requirement. A typical concrete structure project will be much less expensive cubic meter to cubic meter when compared to plain concrete due to labour savings, less cost of forming works, less steelworks, eliminate brickworks, cement renderings work and the price savings is very substantial when compare to conventional methods.


  • Is lightweight concrete suitable for long-term use as a marine float device ?

    At the lower densities, lightweight concrete will float, and in many cases float indefinitely. Because of its limited impact and abrasion resistance, lightweight concrete used for marine flotation should be encased and used for the fill of a float. For example, a marine float could be made with sealed drums filled with low-density lightweight concrete.


  • Where do I purchase lightweight concrete ?

    Lightweight concrete is purchased through a licensing system. For Australia the master licensee is LYNKFS Pty Ltd and can be contacted through its representatives.


  • How to produce lightweight concrete ?

    The pre-formed foam is added to the cement slurry and mixed in the concrete mixer or in a continuous process. From that point, lightweight concrete is placed in any way that a fluid mix can be transported. Pumping is the most common method of placement. Tailgate ready mix truck delivery, bucket cranes, wheelbarrows, hand carried buckets and any other acceptable method of delivering a fluid mix works well.


  • Can lightweight concrete be under mixed ?

    The cement and water slurry should be mixed until there are no dry clumps or balls of cement. The pre-formed foam mixture is then added into the mixture. The foam mixes quite rapidly into the slurry and only requires modest mixing times depending upon the mixing equipment.


  • Can cellular concrete be over mixed ?

    Mixing until there is a reduction of volume of product is not recommended. Air cell stability is the mark of our liquid foam concentrates and our Foam Generators. With typical mixing procedures, lightweight concrete formulated with pre-formed foam is very stable even with modestly extended mixing times.


  • How far can lightweight concrete be pumped ?

    Lightweight concrete is a very easily pumped, highly fluid mixture. The bulk of lightweight concrete is placed by pumping. Lightweight concrete typically will move through the pump lines using less pressure than typical heavier grout mixes


  • How do you finish lightweight concrete ?

    Most lightweight concrete is left to self-seek a level and not surface "finished" in the traditional sense. Much lightweight concrete is covered by another material. A floor overlayment type smoother tool can be used simply to break the surface air cells and create a more uniform and polished look to the surface in the rare case when a more uniform surface appearance is desired.


  • How do I test lightweight concrete to determine it is performing to specs ?

    Test procedures for lightweight concrete are beyond the scope of this FAQ document; however, lightweight concrete representatives will be happy to assist you in the actual testing or furnishing descriptions of common tests. Properties commonly tested are for its compressive strength The majority of regular concrete produced is in the density range of 2400 kg permeter cube. The last decade has seen great strides in the realm of dense concrete and fantastic compressive strengths which mix designers have been achieved. Yet regular concrete has some drawbacks. It is heavy, hard to work with, and after it sets, one cannot be cut or nailed into it without some difficulty or use of special tools. Some complaints about it include the perception that it is cold and damp. Still, it is a remarkable building material - fluid, strong, relatively cheap, and environmentally innocuous and available in almost every part of the world. Lightweight concrete begins in the density range of less than 300 kg/m3 to 1800 kg per/m3. It has traditionally been made using such aggregates as expanded shale, clay, vermiculite, pumice, and scoria among others. Each has their peculiarities in handling, especially the volcanic aggregates which need careful moisture monitoring and are difficult to pump. Decreasing the weight and density produces significant changes which improves many properties of concrete, both in placement and application. Although this has been accomplished primarily through the use of lightweight aggregates, since 1960 various preformed foams have been added to mixes, further reducing weight. The very lightest mixes (from 300 kg /m3 to 800 kg / m3) are often made using only foam as the sand and aggregate are eliminated, and are referred to as floating lightweight concrete. The entrapped air takes the form of small, macroscopic, spherically shaped bubbles uniformly dispersed in the concrete mix. Today foams are available which have a high degree of compatibility with many of the admixtures currently used in modern concrete mix designs. Foam used with either lightweight aggregates and/or admixtures such as fly ash, silica fume, synthetic fiber reinforcement, and high range water reducers (aka superplasticizers), has produced a new hybrid of concrete called lightweight concrete materials. For the most part, implementation of Lightweight Composite design and construction utilizes existing technology. Its uniqueness, however, is the novel combination drawing from several fields at once: architecture, mix design chemistry, structural engineering, and concrete placement.

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