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Floating concrete is a fluid mixture of density less than water, which is suitable to build floating structures, reducing the consumption of land for buildings. This project report addresses the procedure of preparation of mix proportion of floating concrete, materials used & various test results of compressive strength at the age of 7 days & flow, for acceptance of this concrete. Also, it presents an application of this concrete for canoe construction along with a light weight but, strong reinforcement. Despite the self weight of the canoe, it can bear a certain amount of external load.
What is concrete? (Conventional & Floating Concrete)
Concrete is the most widely-used composite material in the construction industry. It is durable, weather-resistant, environmentally neutral and economically affordable.
There are many types of concrete each designed for fulfilling specific technical, structural and aesthetic requirements. In the broadest definition, concrete is a mixture of Portland cement, aggregate (gravel and sand) and potable water.
Concrete compressive strength can easily surpass the compressive strength of many naturally occurring rocks; a compressive strength of 70 MPa can be easily achieved in a precast concrete factory and many cast-in-situ concrete elements achieve a compressive strength of 40 MPa and more.
What is floating concrete structure?
A floating concrete structure is usually a solid body made of reinforced concrete & an inner chain of chambers filled with a lightweight impermeable material, typically polystyrene but, here the concrete is made to float by addition of aluminium powder as an air entraining agent. In addition to this, the concrete includes polypropylene fibers for good binding, nano silica for increasing its strength, CaCl2 as an accelerator & Dr. Fixit for water proofing. Aluminium mesh instead of steel mesh is used for reinforcement, for making it light weight & corrosion resistant.
2. MATERIALS USED:
The cement used is somewhat similar to Ferrocement but, instead of steel wire mesh, aluminium wire mesh is used possessing a light weight than regular chicken mesh making an innovative type of “Aluminicement”(Carbon fiber mesh can also replace the aluminium mesh as it is the best among the light weight but strong meshes available). Pozzolanic Portland Cement (PPC) reinforced with polypropylene fibers, for increasing the binding among particles was used, pursuing following physical & chemical properties:
|Physical properties of Portland Pozzolanic Cement and OPC|
|Ordinary Portland Cement||Blended Pozzolanic Cement|
|Compressive Strength (MPa)|
|Setting time (min)|
Chemical properties of Portland Pozzolanic Cement and OPC
|Ordinary Portland Cement ( %)||Blended Pozzolanic Cement (%)|
|Loss on Ignition||2.05||1.05|
Ordinary Portland cement is replaced by PPC because of its pozzolanic property as well as making it economical by the use of cheaper pozzolanic material such as fly ash for sustainable development.
Locally available natural sand with 300 microns maximum size was used as fine aggregate.
Since we have made a light weight concrete with density less than that of water, it possesses a little less strength as compared to the conventional concrete. So, to overcome this drawback, nanotechnology is taken as a support.
Water proofing agent
One of the major requirements of floating concrete is it should not have any leakage through it. The porosity of the concrete mortar should almost be equal to zero.
For this reason a water proofing substance is required.
Light Weight: Density range from 650 Kg/m3 to 1850 Kg/m3 as compared to 1800 Kg/m3 to 2400 Kg/m3 for conventional brick and concrete respectively. Despite millions of tiny air filled cells, it is strong and durable. There is Lightweight advantage for the structure design, leading to savings in supporting structures and foundation.
Compressive Strength: 2.0 to 7.0N/mm2.
Excellent Acoustic Performance: It can be used as effective sound barrier and for acoustic solutions. Hence, highly suitable for partition walls, floor screens/roofing and panel material in auditoriums.
Earthquake Resistant: Since lighter than concrete & brick, the lightness of the material increases resistance against earthquake.
Insulation: Superior thermal insulation properties compared to that of conventional brick and concrete, so reduces the heating and cooling expenses. In buildings, light-weight concrete will produce a higher fire rated structure.
Workability: Products made from lightweight concrete are lightweight, making them easy to place using less skilled labor. The bricks can be sawed, drilled and shaped like wood using standard hand tools, regular screws and nails. It is simpler than brick or concrete.
Lifespan: Weather proof, termite resistant and fire proof.
Savings in Material: Reduces dead weight of filler walls in framed structures by more than 50% as compared to brickwork resulting in substantial savings. Due to the bigger and uniform shape of blocks, there is a saving in bed mortar and plaster thickness. In most cases the higher cost of the light-weight concrete is offset by a reduction of structural elements, less reinforcing steel and reduced volume of concrete.
Water Absorption: Closed cellular structures and hence have lower water absorption.
Skim Coating: Do not require plaster and water repellent paint suffices. Wallpapers and plasters can also be applied directly to the surface.
Modulus of Elasticity: The modulus of elasticity of the concrete with lightweight aggregates is lower, 0.5 – 0.75 to that of the normal concrete.
Therefore more deflection is there in lightweight concrete
4. EXPERIMENTAL VALUES
COMPRESSIVE STRENGTH TEST:
Concrete is primarily meant to withstand compressive stresses. Hence, behavior of concrete in compression is of foremost importance.
A cube of 10cm×10cm×10cm was prepared by taking cement:sand ratio as 1:3 & adding 0.08% of aluminium powder by volume of cement, polypropylene fibers in equal amount of cement, 2% CaCl2 by weight of cement, 10% nano silica by weight of cement & a small quantity of Dr. Fixit powder.
Recommended limit for compressive strength of the concrete is 2-7 N/mm2 & the calculated result came to be 3 N/mm2.
This test gives an indication to the quality of concrete with respect to consistency, cohesiveness & the proneness to segregation.
Concrete is filled in the mould in two layers, each layer is tamped 25 times & then after removal of the mould, the table on which mould is kept is raised & dropped for 15
The diameter of the spread concrete is measured in about 6 directions & average spread is
Flow is calculated as given below:
Flow, percent = (Spread diameter in cm-25) ×100) / 25
Conclusions on the basis of Compressive strength test:
Conclusions on the basis of Flow test:
6. REFERENCES & BIBLIOGRAPHY
1. Concrete Technology by M L Gambhir
2. Concrete Technology by M.S. Shetty
5. Brouwers H.J.H, Hüsken G. and Quercia G. “Research on use of nano silica”
8. Concretecanoe.engin.umich.edu, University of Michigan (Concrete Canoe)
We at engineeringcivil.com are thankful to Mr Vikramaditya Pandey for submitting this useful paper to us. We hope this would be helpful for engineers seeking information on Floating Concrete.
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