Quality control of foam concrete is essential to obtain required properties of concrete mix. Applications of foamed concrete and its quality control is discussed in this article.
Foam concrete is a concrete mix that requires more quality check to ensure the complete delivery of its significance. The parameters that are checked quality foamed concrete production are given below.
Quality Control of Foam Concrete in Construction Works
Following are the quality control required for foamed concrete:
- Foam density and stability
- Plastic density
- Consistency and segregation
- Concrete cube strength
- Soundness of foam concrete
Quality Check for Foam Density and Stability of Foam Concrete
A good quality foam will provide a foam concrete with good properties. This shows that the quality of foam in terms of density and stability will affect the property of the manufactured foam concrete.
The wet density of the foam can be measured with the help of a glass measuring bucket or a cylinder. Here the known volume of foam must be measured.
The foam will undergo collapse of bubbles with time. This collapse with time varies with the different type and quality of the form.
Hence the stability of a given foam can be measured by measuring the collapse of the foam bubbles with time. For this, a measuring glass cylinder can be used. To avoid side restraints, it is recommended to use the wide plastic pipe.
Quality Measure of Foam Concrete by its Plastic Density
The plastic density of foam concrete is determined by measuring a known volume of foam concrete with a bucket. The method is outlined in BS EN 12350: Part 6: 2000– Testing fresh concrete.
Quality Measurement based on Consistency and Segregation of Foam Concrete
The foamed concrete possesses very high slump that is its property. Hence the slump test is not appropriate. But it can be used to find whether the workability of the foam concrete is very low or not.
The slump flow test as per BS EN 12350-5:2000 Testing Fresh Concrete Part 5, Flow table Test (BSI, 2000d), can be used to test the consistency of the foam concrete. The flow table test must be carried out without jolting the table.
The detection of foam rising to the top surface of the prepared mix or by the detection of a separate mix of paste that is formed at the bottom of the mixer will give the existence of segregation in the foam concrete mix. The two findings mentioned can only be visible when the mixing procedure is carried out in the mixer.
The difference of dry densities of 25mm thick slices that are taken from the top and bottom of a 100mm diameter core will give the quantification of segregation. The difference in oven dry densities of horizontal cores, that is taken from different heights can also be treated as a method to quantify the amount of segregation.
Cube Strength Quality of Foam Concrete
The preparation of concrete sample can be carried out based on BS EN 12350 – 1: 2000, Testing of fresh Concrete Sample (BSI, 2000b). The compressive strength of the foam concrete sample can be measured with respect to BS EN 12350 – 3:2000, Testing Hardened Concrete. The code BSI,2000 will provide the compressive strength of the test specimens.
The test specimens are manufactured in 150 mm rather than 100mm to ensure accuracy in measurement. To keep concrete left in the mold till the testing, special disposal polystyrene molds can be employed if necessary.
No kind of tamping or vibration is provided to the foam concrete. The specimen is kept undisturbed and in a covered state for 3 days. After which, the sample is de-molded and cured at 20 ± 20C by covering the sample with plastic bags.
The strength variation seen in foamed concrete is higher than that seen in normal concrete specimens.
Soundness as a Quality Check for Foam Concrete
The strength development in foam concrete can be assessed with the help of check for soundness. The BRE screed tester is used to determine the crushing resistance of the foam concrete in situ.
The test by screeds is mentioned in BS 8204-1:2003 Annex D (BSI-2003). The test involves successive blows on the specimen. The penetration into foam concrete, for each successive blow, must be measured and not the value of final blow alone.
Applications of Foam Concrete in Construction Works
The demand for foam concrete in its huge application is based on the following properties that it possesses:
- Good void filling capability
- Provides a rigid structure
- No deflection under lower load conditions
- Low density structure
- Enhanced thermal and fire resistance
Some of the widespread applications of foam concrete are mentioned below:
1. Foam Concrete for Void Filling
In the UK, foamed concrete has gained widespread application in the void filling, leveling and for self compacting properties. It is a rapid, effective and competitive solution.
The void filling application has become more prominent because of its connected series of advantages like thermal insulation, its rigidity, and controlled water absorption properties.
Ground instability issue is a problem mostly faced by old mines and tunnels. They have now employed foamed concrete to fill the voids as a solution to regain stability in sewers, service trenches and many highway structures like in subways and culverts.
Foam concrete in an amount of 13500m3 was employed to stabilize the collapsed tunnels at the Heathrow Express.
2. Foam Concrete for the Enlargement of Bearing Capacity
In weak soils, the foam concrete made as cast in situ piles are installed to serve the purpose of skin friction piles. The densities of foam concrete used for this purpose range in 1200kg/m3.
3. Replacement of Existing Soil by Using Foamed Concrete
The concept of balanced foundation can be employed with the help of foam concrete. Those areas having weak soils, the total weight i.e. the weight of the foam concrete plus the weight of the structure that must be constructed, is designed such a way that it is equal to the excavated soil. This will not let the increase of stress in the soil underneath thus reducing the chances for a settlement.
The foam concrete densities used for this purpose varies from 300-600kg/m3.
Wherever road construction must be conducted on poor soils, the foam concrete can be used as a foundation. Rather than being a light granular material construction, foam concrete behaves stable.
For the London Docklands Project, the foundation for the road was constructed by 27000m3 of foamed concrete (As per S Van Dikik, 1991).
4. Applications of Foam Concrete in Roof Slopes
As per the study conducted by L Cox and S Van,2003, the addition of sand to the mix, will provide sufficient slope and tolerances so that slope can be maintained in the roof construction.
Foam concrete of lower density can be employed for roof construction. But its higher application is gained in profiling the positive slope to drains in the construction of flat concrete roofs.
5. Applications of Foam Concrete for Raft Foundation Construction
This application is widespread in housing construction. To behave as a lightweight raft foundation along with thermal properties, the foam concrete is the best choice. This constructed layer is protected by means of a concrete blinding or a floor screed. The concrete blinding layer also behaves as a mode for load spreading.
Here the densities used is in the range of 500kg/m3 with an average thickness of 0.2m (As per R Jones and A Giannakou.2002)
Foam concrete with densities from 400 to 600kg/m3 is used in raft foundation manufacture. A thickness of 0.75m is employed for those dwelling that is built over water (In dykes, in the areas of Holland). In marinas, foamed concrete is used as floating Pontoons.
6. Applications of Foam Concrete for Trench Reinstatement
The excavations that are carried out by the utility companies are the main reason behind the deterioration of the road pavements. When there is a settlement of the backfill, there is damage to the surfacing of the pavement, with age. Constant Patching must be done to clear this problem.
The foamed concrete is a good solution, as it behaves as a better backfilling technique. It gains the following properties:
- The foamed concrete does not settle once placed
- It does not require any compaction
- No transmission of axle loads to the services in the trench
- The final resurfacing can be carried out next day
- The material is readily available
- Easy Excavation are permitted
- No need for skilled labor or complicated equipment
A compressive strength approximately 1N/mm2 is required (by the foamed concrete) to have satisfactory compaction of the bituminous surfacing with the foam concrete.
7. Soil Stabilization by Foam Concrete
The part of soil used in the backfill of embankments can be replaced by foam concrete to ensure slope stability. The weight reduction is the advantage of undergoing such method, as high degree of weight is the basic reason behind the collapse of backfill.
The foamed concrete of densities ranging from 400 – 600kg/m3 are employed for this purpose.
8. Floor Leveling Applications of Foamed Concrete
It is expensive to use the conventional concrete mix to meet the purpose of raising an old floor. Based on the height that is to be raised, the construction becomes expensive. It is recommended to lay a layer of foam concrete over the old floor initially.
Above this foam concrete floor, the conventional concrete can be laid. This is found to be more cost saving than the conventional method. Based on the thickness, the foam concrete of different densities is employed.
9. Blinding by Foam Concrete
The foamed concrete can be used over the conventional concrete to perform the purpose of blinding. The high workability and flexibility advantage of foamed concrete makes it best suitable for blinding purpose.
Now for areas where thermal insulation is a concern, densities of 500kg/m3 are used. If it is not concerned density of 1200kg/m3 can be employed.
10. Foam Concrete Help in Reduction of Lateral Load Reduction
Foamed concrete when used as a backfill, it helps in reduction of vertical loads and the connected lateral loads. This also reduces the chances of settlement. This great advantage help in the limited maintenance of the structure.
The application is widespread in harbor quays in the construction of sheet pile retaining wall or the diaphragm wall. The foamed concrete having densities from 400-600kg/m3 can be used for this purpose.
11. Application of Foam Concrete in Filling the Pipes
Foam concrete that has densities from 600 to 1100 kg/m3 can be used to fill the underground pipes, sewers or fuel tanks that are of no use anymore. Their negligence can create fire hazards or any kind of collapse. Once these are filled with foam concrete, they are supported and blocked.
12. Construction of Sports fields and the Athletic tracks
Foamed concrete construction with permeability property has gained greater application in those areas where water draining must be carried out quickly. The permeable foamed concrete has densities ranging from 600 to 650kg/m3. It was observed that they have high permeability, with Darcy permeability value of 300mm/hr.
These are also used as light weight foundation in sports fields for hockey, football, and tennis. This foundation is covered by gravel or any synthetic turfs.
13. Used to Support the Bottom of Tanks
The foamed concrete having densities ranging from 500 to 1000kg/m3 can be poured below the steel storage tanks. This will support the whole bottom of the tank.
14. Foam Concrete Application as Shock Absorbing Concrete
In the USA, a low density fiber reinforced foam concrete was developed, that was used in live fire military training facilities. The hazards caused due to ricochets during the urban training was reduced by this method. This is named as Shock Absorbing Concrete (SACON).
This concrete has the capability to capture small-arms bullets too. It was developed as in US Army Environmental Center,1999.