Foamed Concrete and its advantages & applications
Foamed concrete is also Known as cellular Lightweight Concrete (CLC) but it is not lightweight, building material, ideal for a wide range of applications. It can have dry densities typically from 400kg/m3 to 1600kg/m3 and compressive strengths varying from one MPa to 15Mpa. To make foamed concrete, special foam is blended into a mixture of sand, cement, fly ash and water. The quantities of these ingredients can be adjusted depending upon the application, balancing performance and cost.
Foamed concrete can be placed easily by pouring or pumping and does not require compaction, vibration or leveling. It is possible to make foamed concrete in different size batches depending upon the application. For large and medium construction projects 6m3 batches will be made in the mixer of a Ready Mix Truck. For smaller contracting jobs batches of 1.25m3 can be made in a large site mixer. It can even be made in 90 litre batches for very small projects.
Pre-Cast Lightweight Blocks
- There are many benefits for using foamed concrete.
- Does not settle, hence requires no compaction
- Lightweight, does not impose large loadings
- Free flowing, spreads to fill all voids
- Excellent load spreading characteristics
- Once placed requires no maintenance
- Excellent sound and thermal insulation.
- Excellent resistance to freeze-thaw cycle
- Does not impose lateral loads
- low water absorption over time
- Excellent fire resistant properties
- Highly cost effective
- Reliable quality control, so batches are easy to reproduce
The most widespread use of foamed concrete in India is for making Pre-cast lightweight blocks. These blocks are used to construct non-structural walls in apartments, hotels and offices. Foamed concrete is lightweight which means that the loading on the building is reduced. Therefore the amount of structural steelwork and structural concrete is also reduced resulting in significant cost savings. The thermal insulation properties of foamed concrete mean that there will be greater comfort and reduced air-conditioning and heating costs for tenants.
Making pre-cast foamed concrete is a straight forward process that involves minimal capital outlay. The most basic foamed concrete block factory can be set up on the building site where the blocks are to be used, minimizing transportation costs. The equipment needed consists of a cement mixer, foam generator, air compressor and battery moulds. Larger semi-automated block factories can include silos for cement, fly ash and sand that are connected directly to a high shear colloidal mixer which is used for making the sand cement slurry.
Cast In-Situ Lightweight Walls
In order to reduce the time and labor needed to makes pre-cast blocks, it is possible to cast in a lightweight foamed concrete walls in-situ. Heights of up to 1m can be cast in a single pour. Normal formwork suitable for concrete can be used. Casting in-situ foamed concrete walls is currently gaining popularity in India.
Roof and Floor Insulation Screeds
The cellular structure of foamed concrete restricts conduction of heat through the material, giving it good thermal insulation properties. The thermal conductivity of foamed concrete with a dry density of 600 kg/m3 is 0.1 W/mK. This makes it an ideal material for roof insulation. Since it is a low density material, it does not add significantly to the overall weight of roof. It is also used to make drainage slopes on flat roofs. This particular application has been very popular in the Middle East for over20 years and it is now starting to be used in India and China. Foamed concrete is an ideal material for floor screeds because it is easy to place and because it is lightweight. Also, floor levels can be raised and uneven floor surfaces can be leveled.
Foamed concrete does not shrink, is free flowing and fills every gap, even beneath overhangs. It can be placed quickly in large quantities through narrow openings, which means void filling can be tackled with minimal disruption. Both planned and emergency void filling are regularly carried out using foamed concrete.
In Lublin, Poland, foamed concrete was used to stabilize the ground in an emergency situation. A recently constructed roadway built over a previously inadequately compacted trench reinstatement was in danger of collapse when heavy rains washed away the ground beneath it. A large void was created under the roadway which remained suspended in mid air over a distance of 30 meters. Using traditional methods, the repair would have taken three weeks to be completed, including the dismantling and re-assembly of the road structure, which consisted of pavers bedded in mortar. Using foamed concrete, the whole job was completed and the road re-opened in 48 hours.
The lightweight nature and excellent load spreading characteristics of foamed concrete mean that it is ideal for ground stabilization. During construction of an expressway on a hillside in Japan, traditional granular fill materials were used to construct a large embankment. A landslide caused the embankment to fail. Instead of using traditional fill materials to reconstruct the embankment, a lightweight material needed to be used. Foamed concrete was specified to re-build the embankment. Lightweight foamed concrete with a density of 650 kg/m3 was poured into the void between the hillside and a specially constructed retaining wall. The revised design stopped the landslide movements enabling the Nagano expressway to be opened.
With traditional granular materials, there is a lot of sideways pressure against the bridge walls. With foamed concrete, this lateral load is practically eliminated, so the bridge walls can be thinner and the bridge foundations smaller. This results in huge cost savings and material savings.
Roads Over Soft Ground
When roads are built over soft ground, they often begin to sink in a non-uniform manner creating an uneven and broken road surface. By excavating the soft ground and replacing it with foamed concrete that is less dense, a floating road sub-base can be built. This stops the road from sinking and has been used for building roads in Holland.
Using foamed concrete for road sub-bases can reduce the cost of foundations. The re-development of Canary Wharf, in the docklands area of London, saw the use of 27,000 m3 of foamed concrete for a lightweight road sub-base. Here the cost of the pile foundation was reduced by a factor of three by using foamed concrete instead of sand.
Foamed concrete saves on the other materials. It directly saves on material usage since it can be made using fly ash, which is a bi-product of energy generation. Indirectly, since it is lightweight and does not impose large loadings, it reduces the amount steel work and structural concrete required in building construction and civil engineering projects. The most obvious environmental benefit of foamed concrete is its ability to provide thermal insulation.
NEW IN MARKET
We are now introducing Cool Roof Tiles. These tiles keep the Roof Temperature Lower in the summer months. These tiles are manufactured by in-organic Binders and do not contain conventional Sand, Stone Chips and Cement.
Tile dimensions - 300mm x 300mm (12mm + 1mm thickness)
Tile weight - 2.3 + 0.1kgs
Water absorption - < 5%
Fire resistance - 100 %
Colour - White
Thermal property - Up to 15* C Surface Temperature Reduction (depending on ambient temperature)
Compressive strength - 23 + 2 MPa
Flexural Strength - 5 + 1 MPa
For Cooler Roofs.
For Room temperature reduction.
For energy Conservation in Air Conditioning systems.
For Green Building Concepts.
Floor tile where bare foot walking is required, like Temples, swimming pool walkways, Gardens areas, etc.etc
Why should we use cool roofs
- Dark colored roofs soak up the SunÃ¢€™s energy, getting hotter and hotter as the day progresses.
- The roof space can become superheated up to 90*C on a 35*C day and the temperature of rooms below becomes unbearable, even with insulation.
- Air conditioning is overloaded and temperature extremes affect the durability life of the whole roof structure.
- Dark heat absorbing and bare metal roofs make up more than 75% of the colours used in our suburbs. Insulation helps, although once the heat is inside the roof space, ceiling insulation only delays the heat transfer process.
- The best method is to prevent the roof space heating up in the first place by reflecting heat away from the roof surface. Rooms below are kept cooler, reducing air conditioning energy consumption over the life time of the building.
- Air conditioning adds to greenhouse emissions and uses valuable natural resources damaging our environment. Cooling is becoming increasingly expensive due to rising energy costs, servicing and maintenance, so cost and resource saving in this area are very important.
- Hot buildings add to the Urban Heat Island effect.
Benefits of cool roof
Some Useful Terms
- Water savings from reduced evaporative air conditioning.
- Reduced electricity usage conserving energy and valuable resources and saving money.
- Reduced peak electricity demand due to summer air conditioning.
- Lower urban heat island build up resulting in reduced ozone and healthier leaving.
- Encourages recycling of older viable roof structures.
- Cooler buildings mean reduced chemical and pollution for healthier cities.
- Cooler buildings mean less dehydration and chemical emissions.
A cool roof should have both High TSR and high TE
- TSR-Total Solar Reflectance is the fraction of solar energy that is reflected by the roof surface. A roof surface with high TSR will reflect thermal energy and remain cooler than one with a low TSR.(where TSR 0=0% reflectance & TSR 100=100% reflectance)
- TE-Thermal Emittance is the relative ability of the roof surface to radiate absorbed thermal heat (far infrared) back into the atmosphere (where TE 0% = 0% emittance and TE 100% =100% emittance). A roof surface with a high TE can radiate heat it back into the atmosphere more readily than one with low TE.
: Substituting a cool roof for a warm roof reduces conduction of heat into the building, convection of heat into the outside air, and thermal radiation of heat into the atmosphere. This benefits our building, our cities and our planet
COMPARISON OF CONCRETE AND CLAY BRICKS
Clay bricks have been in use for more than a thousand years and so they are well known
Compared to concrete, that has been around for only 200 years in all over world prior to 1970, concrete products constituted less than 2% of the masonry market.
30 years later, thanks to a concerted marketing campaign by the CMA, concrete masonry claims 60% of building built. The industry has rapidly adjustment to its use. Notwithstanding, there still are those that prefer clay to concrete claiming that concrete exhibits poor resistance to damp, looks and is cold and cracks more than clay brick walls do.
The fact is, concrete bricks are different to clay and if used incorrectly will exhibit some of these nasty characteristics. Technically the products are quite different and concrete bricks are gaining market share.
Clay bricks are made in a process that starts with a suitable blend of clay that have to be mined, aged, then milled/mixed to even consistency. The clay is then extruded through a special press and sliced to size. These un-burnt bricks are dried out before being placed in a kiln that is heated to between 700c and 1100c. Thereafter, when the firing is complete, the bricks need to be cooled and classified as to a colour and strength. The process is very energy intensive, generates large amount of carbon dioxide, is quite difficult to control and takes up to 3 months to complete. If that was not all, the set-up cost of a reasonable factory is about 10 times that of concrete for the same output.
Concrete bricks are far simpler to manufacture: Suitable sands, stone and cement are proportionately mixed together with water, vibrated , allowed to cure for about 14-28 days and are then ready for use. The strength/quality of bricks can be controlled by manufacturer and total process time 15 to 30 days. Energy costs are quite low and there is minimal pollution.
PROPERTIES IN THE WALL-MOVEMENT.
Technically clay and concrete products have different properties that affect the way they should be built into a wall. Clay bricks tend to expand after manufacture in the first few years of their life-about 3mm to 5mm over 10 meters of wall length, So expansion joints need to be provided. Concrete bricks on the other hand tend to shrink about the same amount (partly curing and drying out) usually in the first 6 months after construction, so concrete masonry walls need construction joints. Both of these opposite movements require joints roughly every 5 to 6 metres otherwise cracks will appear.
Contrary to common belief concrete bricks have relatively low moisture absorption-about 5% to 7%, whereas clay bricks are very variable, depending on the burning and type of clay, can range from 5% to 20% moisture uptake. The significance of this is that clay bricks need to be wet before laying otherwise they suck the moisture out of the mortar, where as concrete bricks need to laid dry .If they are wet they Ã¢€˜floatÃ¢€™ and the mortar does not acquire sufficient early stiffness to keep the wall from sagging out of shape. In area where there is more rainfall the concrete bricks are more useful and better than half burnt clay bricks.
Individually, solid clay bricks have a lower heat transfer (better insulation) than concrete bricks. However once they are imbedded in mortar and plaster, the difference is minimal, especially if it is a cavity wall.
Another thermal issue is the retention and release of heat-a heat reservoir. In SA with relatively mild seasons the important comfort factor is the absorption of heat during the day and release at night. Concrete bricks are more effective than clay because they are generally denser and have a higher thermal capacity.
Generally concrete products are true to size and texture whereas clay bricks can vary considerably in size, shape and texture. Thus clay bricks will need a thicker coat of plaster than concrete to obtain an even finish. Once the plasterer has mastered the art working with lower suction concrete bricks he will be faster and more economical than on clay bricks.
Concrete bricks accept paint relatively well whereas clay does not. Clay bricks often exude metallic salts in their early years which cause paint to peel off.
Masonry walls by nature contain lots of free calcium salts from cement that convert to calcium carbonate in the air-a white efflorescence or weeping streak. This is exaggerated if the wall becomes soaked with water. Un plastered clay bricks (non facing) will sometimes exhibit a green stain which is caused by metallic salts washing out.
SRENGTH & DURABILTY
Building regulations stipulate the same strength of brick, clay, and concrete for a specific design of a wall. Durability is generally a function of strength. The clay brick by nature of its manufacturing process hardens from the outside inwards. If the outer face is damaged it is possible that the soft inner could deteriorate. Concrete on the other hand tends to have the same strength throughout. It has been seen that there is minimum breakage in concrete bricks than clay bricks. Concrete bricks are made by skilled persons in a factory with a machine and so the quality can be maintained but in case of clay bricks, the quality hardly maintained.