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> Frequently Asked Questions
Lot 78, Jalan Beserah, ( Opposite TAN CHONG - NISSAN Showroom ), 25300 Kuantan, Pahang, Malaysia.
Tel : +6-09-5162911 or +6-09-5162912 Fax : +6-09-5162913
Email : alex@al-nct.com or lightweightconcrete@yahoo.com
- 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 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
in NCT can be made up to 24 Mpa, far exceeding most structural
requirements. NCT is in common use in many third world countries
lacking preconceived notions of how things ought to be. Unfortunately,
like most good things in life, you have to seek them out.
- How can concrete look anything but ugly?
Blame the architects who design ugly things. Designers resort to the box
look either because they lack imagination or they just want to get
something up as cheaply as possible. Keep in mind, there's no shortage
of residential wood boxes or plastic siding either. Concrete can be
virtually any shape, color and texture. People need to shed their
preconceived notions of what concrete buildings will look like.
- 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 off 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 is achieve with a high cement content mix.
- Is segregation a problem?
Unlike plain concrete there is little to segregate in lightweight concrete rendering 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 but conversely neither is it indestructible.
- Is lightweight concrete chemically compatible with common admixtures?
Lightweight concrete is compatible with common concrete construction
admixtures; 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, color 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
Coloring pigments or color 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 is varied according to
specific project requirements. We should note that lightweight
concrete obtains it's natural fluidity from the air bubble structure,
not from excess water content.
- Do lightweight concrete mix designs 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 carry 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 admixture concrete
chemistry. 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 to NCT and it produce 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 NCT 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 that well compacted soil. When
replacing soils, lightweight concrete can be designed to provide
whatever strengths and characteristics needed for the soil stabilization
project. Some soils 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. It generally boils down to between RM 85.00 ( USD 22.00 )to maximum RM 150.00 (USD 38.00 ) per meter cube.
- How does lightweight concrete compare in price to plain concrete?
A typical concrete structure project will be much less expensive cubic meter to cubic meter when compared to plain concrete due to labor 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. We should note that lightweight concrete is seldom ever used in an application where plain concrete would be applicable. Comparing prices of lightweight concrete and plain concrete is not a meaningful comparison. Lightweight concrete does compare favorably with prices for grout, mortar, and flowable fill.
- 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 superior marine float could be made with sealed 55-gallon drums full of low-density lightweight concrete.
- Is lightweight concrete a suitable material for a concrete canoe?
Once again, similar in scope to the above question regarding marine float applications, lightweight concrete could be used for the fill in a concrete canoe but should probably be encased in a waterproof membrane
- Where do I purchase lightweight concrete?
Lightweight concrete is purchased from NCT and all technology and know how will be transfer to any parties willing to be train in the field of lightweight concrete installation. Those interested will have access to a NCT Foam Generator and all methods of applications. These people purchase their liquid foam concentrates directly from NCT.
- How is lightweight concrete placed?
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 NCT liquid foam concentrates and our NCT Foam Generators. With typical mixing procedures, lightweight concrete formulated with NCT 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 short document; however, lightweight concrete NCT 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 achieved. Yet regular concrete has some drawbacks. It is
heavy, hard to work with, and after it sets, one cannot cut or nail 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, it is available in almost every part of
the world.
Regular concrete with microscopic air bubbles added up to 7% is called
air entrained concrete. It is generally used for increasing the
workability of wet concrete and reducing the freeze-thaw damage by
making it less permeable to water absorption. Conventional air
entrainment admixtures, while providing relatively stable air in small
quantities, have a limited range of application and aren't well suited
for specialty lightweight mix designs.
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 have 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, or NCT. 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.
Given the hoops that any new material or method must go through,
implementation of NCT construction can be much at the mercy of any
number of bureaucratic standards (licenses, approvals, etc.) including
fire ratings, material test data, environmental impacts, as well as
opposition from labor unions and existing suppliers supporting the
lumber industry and most of all it eliminates the claybricks and cement
bricks industries. Bureaucratic standards are sometimes easy enough to
achieve, but only if one has deep pockets. Another common problem is
engineers seems to not like it because using NCT is very much cheaper
overall and this effects thier percentage interms of charges. But these
costs are pretty much out of range for the average entrepreneurs in this
field. These individuals also have found reluctance within the ready mix
industry to take the initiative for R&D... their natural conservatism
and relative success in the last four decades only has reinforced their
will to keep things the same without added risk. They wait for the
entrepreneur's homework. Other technologies, such as synthetic fiber
manufacturers, also wait for the entrepreneur. It seems leadership,
unfortunately, is not likely to come from the industries with the most
available resources, but from those individuals who not only have a
vision for the future, but a persistent mission to make it a reality. We
daresay that NCT is in a future materials made available today.
NCT construction can be a partial solution for several environmental
problems.
Deforestation could be substantially reduced by relinquishing the demand
for timber used in residential construction and so is quarry operations
as aggregate is not required. Wood can be used for decorative trim
rather than structural elements. Steel can be used for what it does best
- strength. Structural lumber requires treatment with poisons; steel is
a dirty - albeit necessary - industry. The use of structural steel with
concrete may be curtailed in the future by the development of high
strength NCT design mix with the addition of material such as steel
fiber, basalt, carbon, and other fibers. Considering all the positive
characteristics of NCT, it is surprising so little attention has been
given to its possibilities. This may be due to an uninformed public, a
tradition to use wood and bricks for construction, and a bad rep for a
previously cold, stoney product. To put it in a fast point to point,
just imagine this, current conventional way of making a wall is like
this, skill carpenter is use to make wood formwork for the columns and
beams, steel workers are used to make reinforcement after all this,
comes the conventional concrete,dismantle the wood formwork, then comes
the brick layers and finally the cement plasterer. All this is not
require when NCT comes in, set up the formwork, mix the load-bearing NCT
design mix, pour and dismantle the very day, it is in fact a better
wall, cheaper and faster yet fire and sound-proof. Homes and other
buildings can achieve and maintain a higher degree of function and
permanence, resulting in greater intrinsic value. The only limitations
are the restraint of our imaginations, the reluctance of humanity to try
anything new, and the resistance of unions to efficient construction.
The latter may influence inordinate restrictions imposed by local,
state, and federal building codes. But recent increases of building
materials cost and labour shortage are now prompting people to take a
closer look at shelter permanency being of greater value than consumer
construction. The potential for the five hundred year house is here.
The greatest part of all is NCT has introduce the methods to make used of Fly-ash- a nuisance waste product from thermal power plants - as an over 25 % constituent material. This NCT can be produced in a density range of 400 kg/m3 to 1,800 kg/m3, with high insulation value and a 28-day cube crushing strength of up-to 275 kg/cm2. It is an excellent environment friendly substitute for burnt clay bricks, saving on Energy and avoiding ruining of precious agricultural land, badly needed to feed exploding population in all developing countries.
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