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Lightweight Concrete

Lightweight concrete, weighing from 35 to 115 pound per cubic foot, has been used in the United States for more than 50 years. The compressive strength is not as great as ordinary concrete, but it weathers just as well. Among its advantages are less need for structural steel reinforcement, smaller foundation requirements, better fire resistance and most importantly, the fact that it can serve as an insulation material! It can cost more that sand and gravel concrete, and it may shrink more upon drying.

 

 

 

 

Lightweight concrete may be made by using lightweight aggregates, or by the use of foaming agents, such as aluminum powder, which generates gas while the concrete is still plastic. Natural lightweight aggregates include pumice, scoria, volcanic cinders, tuff, and diatomite. Lightweight aggregate can also be produced by heating clay, shale, slate, diatomaceous shale, perlite, obsidian, and vermiculite. Industrial cinders and blast-furnace slag that has been specially cooled can also be used.

 

 

 

Pumice and scoria are the most widely used of the natural lightweight aggregates. They are porous, froth-like volcanic glass which come in various colors and are found in the Western United States. Concrete made with pumice and scoria aggregate weighs from 90 to 100 pounds per cubic foot.

 

 

 

 



The rock from which perlite is manufactured has a structure resembling tiny pearls and when it is heated it expands and breaks into small expanded particles the size of sand. Concrete made with expanded perlite weighs between 50 to 80 pounds per cubic foot and is a very good insulating material.

Vermiculite comes from biotite and other micas. It is found in California, Colorado, Montana, and North and South Carolina. When heated, vermiculite expands and becomes a fluffy mass, which may be 30 times the size of the material before heating! It is a very good insulating material and is used extensively for that purpose. Concrete made with expanded vermiculite aggregate weighs from 35 to 75 pounds per cubic foot.

 

 

 

 

 

Concrete made with expanded shale and clay is about as strong as ordinary concrete, but its insulation value is about four times better. Pumice, scoria, and some expanded slags produce a concrete of intermediate strength, but with even more impressive value as insulation. Perlite, vermiculite, and diatomite produce a concrete of very low strength, but with superior insulation properties; however these are subject to greater shrinkage. All of these kinds of lightweight concretes can be sawn to some extent, and they will hold fasteners, especially screws.

 


Lightweight aggregate should be wetted 24 hours before use. It is generally necessary to mix lightweight concrete for longer periods than conventional concrete to assure proper mixing and it should be cured by covering it with damp sand or by using a soaker hose.

The master sculptor/builder who created all of the images in this section is Steve Kornher, who is now living in Mexico. His website, Flying Concrete , describes more about these pictures, and has many more of these amazingly beautiful designs to be seen. Steve can be reached through his website for consultation. He used an unvitrified aggregate, kind of like perlite, but not manufactured; perhaps called tuff. It comes well graded, fine to 1 1/2", with a few rocks which are tossed out. He screens it a bit when doing shells and adds the coarser stuff when doing walls. Walls are mixed 8 espumilla/ one cement / 1/2 lime. Structural roofs are 5/1/ 1/2 -- 2-3" of this, then 3" or more of 8/1. Then 1/8" sand and cement on top, scratched, the same day so he can easily bond the next coat--polish coat or add more lt. wt. roof fill between vaults 10 / 1 / 1/2. Local blocks made out of the stuff are 10/1 vibrated. A dry, fluffy mix weighs about 75 pounds per cu. ft. He figures that 4" = 2" styrofoam, but he isn't sure.

 

 

   
 
Click on image for more information
 

Lightweight Aggregate Concrete by Satish Chandra , Leif Berntsson, 2002.

Structural Lightweight Aggregate Concrete by J.l. Clarke, 1993

Lightweight Concrete by Daniel P. Jenny, 1971.

Guide To the Structural use of Lightweight Aggregate Concrete by The Institution of Structural Engineers / The Concrete Society, 1987.

perlite.org various articles about the use of perlite in lightweight concrete.

geckostone.com informative article about lightweight concrete.

crescoconcrete.com manufactures a lightweight concrete block that is interlocking and doesn't require mortar.

elemix.com manufactures a concrete additive that produces a lighter, more insulating concrete.

papercrete.com shows how to make a shredder for EPS foam to use in lightweight concrete.

norishouse.com describes how to make and use EPS foam concrete.

Pumicecrete

Pumicecrete has been used in constructing buildings for many years. It is simply concrete that uses crushed volcanic rock as an aggregate rather than conventional sand and gravel. Both pumice and scoria, when used in this fashion, render a product that is much lighter than concrete. It also transforms what is usually considered a thermal mass material into something that is much more of an insulator (about R-1.5 per inch), because of all the trapped air. This is very useful, because it makes it possible to actually build a load-bearing structure with an insulating material, as with earthbags filledwith the same crushed volcanic rock.

When mixing pumicecrete, the idea is to use just enough wet cement to coat the aggregate so it will adhere to the surrounding particles. Too much cement will defeat the purpose of maintaining all of that trapped air; about three bags of portland cement per cubic yard of aggregate is recommended. Once the material has set up a bit, the surface can be washed to expose the natural color of the stone. The rough texture of pumicecrete is ideal for adhering to further plasters that might be used.

Pumicecrete is best placed on an ordinary concrete foundation, and most applications require a cement bond beam at the top of the wall, for structural strength and to tie the roof structure to. Entire domes of pumicecrete have been successfully constructed. A wall thickness of at least 14 inches is advised, with thicker walls providing more stability and insulation.



All of the photos shown in this section on pumicecrete are courtesy of Scott MacHardy of Pumice-crete Building Systems of New Mexico. His website, pumicecrete.com, has many more pictures and details about this useful material. Scott offers contracting services, training, consulting, etc.

Cellular Lightweight Concrete (CLC)

Extensive research has been undertaken in the use of industrial waste consisting of fly ash from power plants as a raw material for manufacturing building materials. The large volume of waste has became one of the most significant problems of environmental protection, as its disposal is expensive and non-productive. Experiments show that this waste material can be used for the production of high quality bricks, blocks and other building elements which are less energy intensive than their conventional counterparts. This research has yielded patented technology for the production of concrete-like blocks based on oil-shale and coal fly-ash, cured under normal atmospheric conditions.

A particularly interesting material that has been developed is ash-based cellular concrete, which in addition to being based on industrial waste, is also manufactured through a low-energy process. The manufacture of conventional cellular concrete of comparable properties requires very high energy input.

This material has been used in over 40 countries over the past 25 years to build residential and commercial buildings. It is an air-cured lightweight concrete that can be produced at the project site, using standard concrete equipment and molds. A typical mix for making blocks is:

Portland Cement..........190 kg
Sand............................430 kg
Fly Ash........................309 kg
Water..........................250 kg
plus a foaming agent

Here is a PDF file that explains more about this: CLC Brochure

For further information you might contact G. B. Singh at systembuildingATyahooDOTcom

cellularconcretetechnologies.com explains how structural lightweight concrete is made and used.

Perlite and Vermiculite Concrete

This type of lightweight concrete has a long history of industrial and construction uses; it can be highly insulating, and is especially useful where its light weight is an advantage, such as on roof structures. The following link, provided by the Shundler Company (a manufacturer of perlite and vermiculite) provides a wealth of information about this: schundler.com .

Hempcrete

Hempcrete is a mixture of chopped hemp, hydrated lime and a small amount of either Portland cement or quick-set gysum, and possibly includes sand or pozzolans. A reaction between the lime and the hemp results in a very lightweight material that still has reasonable compressive strength. The advantage of hempcrete over regular cement is that the hempcrete is both structural and insulative, so both ends are achieved in the same pour. It is also lower in embodied energy. The disadvantages are a longer set time (2-4 weeks) and lower strengths. It is easier to work than traditional lime mixes and acts as a moisture regulator. It lacks the strength and brittleness of cement and consequently does not need expansion joints . It is less dense than concrete and is marketed under names like Hemcrete, Canobiote, Canosmose, and Isochanvre. Where the high ultimate strength of concrete is not necessary, this option works well. 

 

www.gizmag.com is an excellent article about building a hempcrete home in Asheville, NC, describing the attributes of this very sustainable material.

Other Links

alliedfoamtech information about foamed concrete.

foamliteconcrete.com eps based light-weight concrete.

strongseal information about vermiculite concrete.

silbrico information about perlite concrete.

geckostone FAQs about lightweight concrete.

litebuilt information about this proprietary foaming technology.

ricehuskash details about the use of rice husk ash to make light-weight concrete.

sphereservices.com Cenospheres are hollow ceramic microspheres with unique properties which make them ideal for a wide variety of applications - especially those requiring high strength, light weight fillers.

greenearthstructures.com annotated links to a variety of lightweight concrete options.

prefabricadoslewels.jimdo.com features some lightweight concrete products.

enstyro.com manufactures a shredder to recycle styrofoam into a concrete addative.

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I specifically disclaim any warranty, either expressed or implied, concerning the information on these pages. Neither I nor any of the advisor/consultants associated with this site will have liability for loss, damage, or injury, resulting from the use of any information found on this, or any other page at this site. Kelly Hart, Hartworks, Inc.

 

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