ABSTRACT
Lightweight concrete Method (LCM) was developed in Europe over 60 years ago and has since then been on the international market for more than 20 years. LCM has been used in the building industry for well over one hundred thousand apartments and houses in over 40 different countries. There fore In this paper we are looking at exploring use of foamed concrete with little modifications as it is beneficial in construction because of its easy application, sound insulation and other benefits over traditional concrete.
After the Second World War, this technology quickly spread to different parts of the world, mostly Europe and the Soviet Union. The applications were for economical large-size structural panel units. These were also used in site reconstruction and low-rise structures. Foam concrete, is an effective thermal insulation and constructional-thermal insulation material, is nowadays widely used in more than 50 countries. The world experience has shown that the special technological features of foamed concrete allow using it for multipurpose applications
1 .HISTORY OF AERATED FOAM CONCRETE
BRIEF HISTORY
cellular concrete was first developed in Stockholm, Sweden in the early 1900’s. The original material was known as “gas concrete” to be used in producing heat-insulated building materials. This led to the development of related lightweight concrete which are now known as cellular concrete, foamed concrete, aerated concrete and autoclaved cellular concrete.
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After the Second World War, this technology quickly spread to different parts of the world, mostly Europe and the Soviet Union. The applications were for economical large-size structural panel units. These were used in site reconstruction and low-rise structures.
It wasn’t till the late 1950’s when this was introduced to the US as foamed or cellular concrete. The applications were for floor, roof and wall units. Having low compression strengths, it limited this product to fills and insulation only.
CURRENTLY
The major use in recent years in the United States has been over plywood on wood floor systems or over hollow-core precast slabs. The material is also used in light density for roof fills 481 kilograms per cubic meter [30 pounds per cubic foot] providing good insulating properties.
Even today these materials still generate low compressive strengths limiting it to these two applications. Range options are 3.45 MPa [500 psi] to 6.89 MPa [1,000 psi] for midrange nonstructural densities and 10.3 MPa [1,500 psi] to 24.1 MPa [3,500 psi] for higher densities 1762 kg/m³ [110 lb/ft³].
2. INTRODUCTION OF AERATED FOAM CONCRETE
WHAT IS FOAM CONCRETE?
Aerated Concrete is created by inclusion of a multitude of micro air bubbles in a cement based mixture. This is achieved by mixing the concentrated Foaming Chemical with water and generating foam there from, generally by using compressed air. To achieve the optimum results, an Aerator is required. The foam is then mixed with the sand / cement / water slurry using conventional ready mix or permanent concrete mixing facilities. Aerated Concrete behaves like ordinary dense weight concrete in most aspects, such as curing.
PROCESS OF PRODUCING AERATED FOAM CONCRETE:
The Aerated Lightweight Concrete process is based on the principle of entrapping a multitude of air bubbles in the concrete mix, which retain their structure during the curing period. Firstly, the mix composition of cement / sand / water / foam according to specification has to be chosen. After batching the basic ingredients Foaming Agent is introduced to the mix which then can be poured into panel molds of virtually any shape or size. The Aerated Lightweight Concrete Mix normally cures in open air within about 24 hours (unless it is used in cold weather conditions) before handling is recommended. It is possible to add other products to Foam Mix to obtain lightweight composite concrete. Notably the use of various fibers increases the strength of the product and prevents cracking in adverse conditions.
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3. FOAM GENERATOR AND FOAMING AGENTS
FOAM GENERATOR
Foam generator, which runs from an air compressor, consists of components such as the MSD unit, foaming unit, and a lance unit. Unlike pressure tank systems, foam generator runs on a principle of providing continuous and constant foam with minimum refill. They are also more accurate and easier to run compared to fully air operated systems. These components allow great flexibility to the user in terms of the scale of production of foam concrete since it can accommodate to future production requirements. Foam generator units are lightweight, transportable and may be used on-site or adapted to existing concrete production plants. Its size, output, and mobility are also well suited for small to medium scale production and laboratory work on foam concrete. Several control devices on foam generator unit enable the adjustment of foam properties and allow it to work with different foaming agents (e.g. synthetic or protein).
The foaming generator can be attached to several other devices such as an auto-timer control, pressurized holding tanks and other proportioning systems which makes foam concrete production more efficient or gives greater flexibility to foam generation.
FOAMING AGENTS
There are two types of foaming agents;
a) Synthetic – suitable for densities of 1000 kg/m3 and above.
b) Protein – suitable for densities from 400 kg/m3 to 1600 kg/m3.
Foams from protein foaming agents comes from natural sources and have a weight of around 80 g /liter and expansion of about 12.5 x using foam generator. They generally are more stable than synthetic foams but have a shorter shelf life of about 6 months in open conditions. They also give a slightly higher strength of concrete compared to synthetic foams.
Synthetic foams have a density of about 40 g/liter with an expansion of about 25 x using Portafoam. They are very stable at concrete densities above 1000 kg/m3 and give good strength. Their shelf life is about 1 yr under sealed conditions. Synthetic foam has finer bubble sizes compared to protein but they generally give lower strength foamed concrete especially at densities below 1,000 kg/m3
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4. MIXING OF AERATED FOAMED CONCRETE
There are two principle mixtures which constitute the majority of Aerated Concrete construction.
CEMENT + FOAMING AGENT
While the cement mixer or premix concrete truck is in motion, the water and cement are introduced and allowed to mix until a thoroughly consistent mixture is achieved. When this has taken place, the required amount of foam can be injected into the mixer and the mixing continued until the foam is completely enveloped into the total mix. The mixture is then ready for discharging into the moulds or wherever it is to be placed. Note: Although it is possible to have neat cement mixes, the addition of some sand (about 25%) is recommended in order to prevent the formation of lumps.
CEMENT + SAND + FOAM
In this situation the water, sand, cement are added to the mixer in that order and thoroughly mixed into a homogenous mortar before adding the foam.
CEMENT + LIGHTWEIGHT AGGREGATE + FOAM
Because of the lightweight matrix formed by the mixture of cement, water and foam, lightweight aggregates can be used without the tendency to float when the mix is vibrated. Typical aggregates which are used are:- expanded shale or clay, scoria, pumice, vermiculite or fly ash. The inclusion of such material is only recommended if it is locally available as its procurement from afar often results in a higher cost of the final product. Moreover, it is often increasing the overall density for a given strength, since simply higher foam content can achieve better results.
5. MIX PROPORTIONS – SAND, CEMENT AND FOAM (TABLE- 1)
Quantity of Sand & Cement Kgs Per Cubic Meter |
DensityKg/m3 | 3:1 | 2:1 | 1:1 | |
| Sand onlyKg | CementKg | Sand onlyKg | CementKg | Sand onlyKg | CementKg | CementSand only |
1600 | 1148 | 383 | – | – | – | – | – |
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1400 | 1005 | 335 | – | – | – | – | – |
1200 | 861 | 287 | 756 | 378 | – | – | – |
1100 | 790 | 263 | 693 | 347 | – | – | – |
1000 | – | – | 630 | 315 | – | – | – |
900 | – | – | 567 | 284 | 412 | 412 | – |
800 | – | – | – | – | 360 | 366 | – |
700 | – | – | – | – | 320 | 320 | 581 |
600 | – | – | – | – | 275 | 275 | 498 |
500 | – | – | – | – | – | – | 415 |
400 | – | – | – | – | – | – | 332 |
300 | – | – | – | – | – | – | 249 |
Note: Water Content = 0.4 to 0.5 liter per Kg cement
6. PUMPING AERATED CONCRETE
Foam has an extremely strong bubble structure and can stand pumping to unusual heights without loss of entrained air. The most suitable pump for this purpose is a “squeeze” type pump. In some situations a screw feed pump is also satisfactory.
7. WATER: CEMENT RATIO
The amount of water to be added to the mix depends upon the moisture content of the sand, but as an average figure, 40-45 liters (40-45 pints) of water is used for every 100 kilograms (100 lbs) of cement. Additional water is added as a content of the foam, thereby bringing the total water: cement ratio up to the order to 0.6. In general, when the amount of foam is increased, as for lighter densities, the amount of water can therefore be decreased. The water: cement ratio should be kept as low as possible in order to avoid unnecessary shrinkage in the moulds, however, it should be remembered that, if the amount of water added to cement and sand in the first instance it too low, the necessary moisture to make a workable mix will be extracted from the foam when it is added, thereby destroying some of the foam which is naturally an expensive way of adding water to the mix.
Tests should be carried out on any particular mix which is required so that the resulting cellular concrete will have a flow able, creamy consistency.
8. CURING OF AERATED CONCRETE
Since many of the properties of Aerated Concrete depend upon the successful process of curing, outlined below are some of the methods whereby its strength can be increased.
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AIR CURING
This is probably the easiest and most popular method of curing. It is a slow, but acceptable system which enables a turn around of moulds every 24 hours on average, depending on the ambient temperature.
STEAM CURING
When precast Aerated Concrete panels and slabs are made under factory conditions in order to obtain a relatively fast turn-around of moulds, it may be economic to induce an early strength into the concrete by applying heat from steam to the underside of the moulds. This causes a rise in temperature in the concrete and a resulting increase in strength. The reason for steaming from the underside is to avoid the increase in temperature creating small cells of compressed air with sufficient pressure to fracture the cement shell around the cell. Due to the weight of concrete above the lower layers this does not take place and by the time the temperature increases on the upper face, the cement has already acquired sufficient strength to resist the cells exploding off and giving a rough surface to the slab or panel.
Depending upon the type of cement used in the mix, steam curing is not begun until at least five hours after casting, and even then the increase in temperature is well controlled and should not exceed 70°C (167°F).
The extent of steam curing depends upon the climate but as a general rule it can be subdivided into 2 hours required for raising the temperature, 4 hours maintaining the temperature and 2 hours lowering the temperature slowly to avoid thermal shock.
9. PROPERTIES OF AERATED FOAMED CONCRETE:
* COMPRESSIVE STRENGTH:-The compressive strength of a cellular concrete is affected by such factors as density, water cement ratio, properties of aggregates, method of manufacture, curing and moisture content. Foamed concrete with densities from 300 to 600 Kg/m3 can be produced at strength in the range 0.5 – 1.7 MPa. Cement content is generally 250 – 400 Kg/m3.
* TENSILE STRENGTH:-Depending on the method of curing, the tensile strength of foamed concrete can be as high as 0.25 of its compressive strength with a strain of around 0.1% at the time of rupture.
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* SHEAR STRENGTH:-Generally the shear strength varies between 6% and 10% of the compressive strength. Shear reinforcement is seldom required in flooring and roofing units.
* WATER ABSORPTION:- The water absorption of aerated lightweight concrete is low, due to its closed cellular structure.
* EXPANSION:-The coefficient of linear expansion for Aerated Concrete is of the same order as that of normal concrete, i.e. 0.000009 per degree centigrade (0.000005 per degree F).
This factor becomes important when using aerated lightweight concrete on large areas of roof slabs, which are exposed to heat and cold.
* ACOUSTIC INSULATION:- Aerated lightweight concrete has a high sound absorption capacity. In general, dense weight concrete tends to deflect sound whereas aerated lightweight concrete absorbs sound. Sound transmission, however, on conventional walls, over most of the audible frequency range may be higher by 2-3% when compared to dense weight concrete. This slight disadvantage is in most cases academic, since most walls are either rendered, painted or both. This in turn will make a wall deflect the sound as does dense weight concrete.
* THERMAL INSULATION: – Thermal insulation is one of the outstanding characteristics of aerated lightweight concrete Lightweight Concrete. Due to its cellular structure, aerated lightweight concrete offers a very low transmission of heat. This means that in most cases the use of supplementary insulation in floors and walls is unnecessary.
The high insulating value of the material becomes important as energy is saved by cutting both heating and air conditioning requirements, giving greater comfort in a wide range of climatic conditions.
FIRE RESISTANCE: – Aerated lightweight concrete is extremely fire resistant and thus well suited to fire rated applications. Furthermore, the application of intense heat, such as an oxy torch held close to the surface, does not cause the concrete to spall or explode as is the case with normal dense weight concrete. The result of this is that the reinforcing steel remains cool and protected for a much longer period. Tests and certificates from various authorities indicate that 150 mm (6″) of aerated lightweight concrete achieves in excess of a four hour fire rating. In tests undertaken in Australia, a aerated lightweight concrete wall panel, 150 mm (6″) in thickness was exposed to temperatures in the vicinity of 1200°C (2192°F), with the unexposed surface only increasing by 46°C (115°F) after 5 hours. The requirements for some specific authorities for 4 hour rating indicate: – Italy 133 mm (5¼”) – New Zealand 133 mm (5¼”) – Australia (EBRS-Ryde) 105 mm (4¼”).
All tests, both in Australia and internationally, indicate that aerated lightweight concrete is greatly superior to normal concrete. Even at reduced thicknesses aerated lightweight concrete will not burn, spall or give off toxic gases, fumes or smoke.
10. BENEFITS OF USING FOAM CONCRETE
* A low price for foam concrete to compare it with that of other materials;
* Good thermal insulation characteristics allow to save energy while exploitation (heating and air conditioning);
* Lightweight composite materials and foam concrete involve lower construction expenses and more effective construction design;
* Very low processing and transportation expenses;
* The weight of the concrete is from 10% to 80 % lower to compare it with the standard heavyweight concrete, depending on the composition of the mixture and the materials used;
* Considerable weight reduction results in the saving of framed constructions, bearers or piles. Such savings are often divisible by the actual value of the material.
* Saving of transportation expenses, reduction of the required carrying capacity of the lifting crane and reduction of human resources;
* Use of lightweight foam concrete in prefabricated and shell construction requires a crane of lower carrying capacity, minimum effort for erection;
* Lightweight foam concrete can be sawed with a handsaw, hewed and spiked.
SOME ADDITIONAL BENEFITS
* It does not sink and requires no consolidation;
* It is light-weigh and does not provide considerable loading;
* It is liquid and enables to infill any hollows;
* It possesses excellent load sharing characteristics;
* It does not require vibration compaction while laying;
* It does not require further servicing after the laying;
* High thermal and sound insulation;
The use of foam concrete in construction is becoming more and more common.
11. APPLICATIONS
* Cast in-place for a unit of low cost terrace houses and bungalows.
* In lightweight bricks or blocks for high-rise buildings.
* In panels and partition walls of various dimensions either pre-cast or poured in place.
* In all types of insulation works, including cavity walls.
* In roofing and ceiling panels.
* In sound proofing application.
* In pre-cast / in-place exterior wall facades for all sizes of buildings.
* In foundations for roads and sidewalks.
* In sub-surface for sport arenas, e.g. Tennis courts.
* In infill sections between beams of suspended floors.
* Aircraft arresting beds.
SOUND PROOFING APPLICATIONS:
Autoclaved Aerated Concrete is an excellent sound insulator. The millions of tiny air pockets and the uniform cellular structure of AAC inhibits the transfer of sound. An 8-inch AAC wall has a Sound Transmission Coefficient (STC) of 50. It has been found to provide up to 7dB higher sound absorption due to this cellular structure when compared to regular concrete or other materials of similar mass.
Hotels, multi-family housing, residence halls, and hospitals have benefited from this unique property. Few materials can offer the sound suppression qualities of AAC when it is used as a party wall system or a building envelop.
IN HIGHWAYS:
IN LARGE HOTELS:
APPLICATION IN SLAB:
12. THE FUTURE SCOPE OF FOAM CONCRETE IN INDIA:
* Monolithic building construction;
* Thermal insulation of roofs;
* Thermal and sound insulation of walls, floors, floor slabs ;
* Filling of hollow spaces;
* Making blocks slabs, etc.
* Thermal insulation of roofs – foam concrete of low density has excellent thermal properties of insulation;
* Filling of trench hollows – foam concrete does not sink, does not require vibration compaction, it possesses excellent load sharing characteristics, providing for high-quality filling;
* Filling of hollows – foam concrete is very fluid and it can be used for filling of any hollows, even in the most difficultly accessible places through small openings;
* Storage partitions – the walls bearing no loading can be cast of foam concrete immediately on the site;
* Lightening of bridges – the use of foam concrete enables to apply thinner concrete structures, to reduce the basement size and the number of the piers;
ADVANTAGES OF FOAM CONCRETE:
RELIABILITY
Foam Concrete is very long-lived material. After producing it in first 90 years it increases solidity. It does not decompose and is as durable as rock.
RESISTANCE TO COLD AND WARMTH
Foam Concrete is very effective isolating material. Buildings constructed from foam concrete are able to accumulate cold or heat, which allows to greatly minimizing conditioning or heating expenses. It is ideal material for countries with hot and cold climate and it is successfully used in Australia, India, Malaysia, Canada, Sweden, Russia and other countries.
MICROCLIMATE
Foam concrete control air humidity in a room by absorbing and output of moisture during the day and night. Also in foam concrete houses is favorable average temperature during the day. For example if in the night temperature is about 0 Celsius and in the day about +50 the average temperature in the house will be about + 19 Celsius.
ECO-COMPATIBILITY
Foam concrete does not produce any toxic substances and in its ecological compatibility is second only to wood.
HIGH WORKABLE
Foam concrete is a high workability material, so it is possible to build various shapes of corners, arches, pyramids, which will attach beauty and architectural expressiveness to your house.
BIG PROFIT
Foam concrete allow to save big money not only during living in the house, but during the construction the house too. It is cheaper to deliver, to build, to make foundation for this house, to plaster, to drive a wires and sewerage tubes, to build various shapes of corners and arches.
TRANSPORTATION SAVINGS
Favorable combination of weight, volume and packaging makes foam concrete blocks convenient for transportation and allow use motor or railway transport.
FOAM CONCRETE IN COMPARISON WITH OTHER MATERIALS:
When comparing foam concrete with other materials, one must keep in mind that:
1. it is ecologically clean, breathes, uninflammable.
2. easy to produce in steady-state conditions as well as on a construction site
3. It is produced from components available in any region
4. it’s prime cost is low
Below is a table in which thermal conductivity of foam concrete is compared with that of other materials. Again, one must keep in mind that foam concrete blocks can be laid on glue, which reduces frost bridges and, correspondingly, loss of heat.
Material | Density, kg/m3 | Thermal Conductivity
W/mk |
Marble | 2700 | 2.9 |
Concrete | 2400 | 1.3 |
Porous clay brick | 2000 | 0.8 |
Foam concrete | 1200 | 0.38 |
Foam concrete | 1000 | 0.23 |
Foam concrete | 800 | 0.18 |
Foam concrete | 600 | 0.14 |
Foam concrete | 400 | 0.10 |
Cork | 100 | 0.03 |
Silicate cotton | 100 | 0.032 |
Foamed polystyrene | 25 | 0.030 |
Foamed polystyrene | 35 | 0.022 |
13. CASESTUDY
HOUSE CASTING AT BATU PAHAT
Lightweight Concrete 1800 Density was used to cast the Raft footing foundation with 1 layer of BRC A-6 reinforcement, A total of 8 manpower (17 years old student of University Tun Hussein Onn (KHUITTHO) in Batu Pahat).
The Formwork was provided by formwork specialist EFCO ( M) Sdn Bhd.
Another licensee using LCM house casting methods with plywood formwork. Foundations were cast using higher density LCM and walls were cast using 1400 and 1500 density LCM lightweight Concrete.
Erecting of formwork process commence the very next day foundation was cast; only 2 units of normal concrete mixer was utilize for the mixing of LCM. A 1500 kg/m3 Density was used for all the walls.
Electrical conduits is inserted while erecting formwork, casting was done manually with small buckets, it is possible to cast the complete walls of a house in a single day and more units if mixing is done with ready-mix trucks and pouring / casting is by pumps
15. CONCLUSION
Lightweight Concrete Method (LCM) is found to be advantageous over all other types of concrete and it is developing a new era in the field of civil edifice
We are looking at exploring use of foamed concrete with little modifications as it is beneficial in construction because of its easy application, sound insulation and other benefits over traditional concrete.
I do hope this paper will help to change views towards foam concrete and it will be widely used in construction field.
References
* www.ownerbuilderbook.com
* www.mendeley.com
* www.sciencedirect.com
