18-02-2015, 07:36 PM
ADVANTAGES & DISADVANTAGES OF BUBBLE POWER
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effect of cement replacement by silica fume and fly ash ppt
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ADVANTAGES & DISADVANTAGES OF BUBBLE POWER
17-03-2017, 03:34 PM
The earlier idea of using large amounts of cement for concrete has now changed in favor of the increasing use of high amounts of mineral additives and super plasticizers with reduced amounts of cement and water in concrete mixtures. Energy plays a crucial role in the growth of developing countries, such as India. In the context of the low availability of non-recoverable energy sources together with the requirements of large amounts of energy to materials such as cement, steel, etc., the importance of industrial waste as building materials can not be underestimated. In India, about 110 million tonnes of fly ash have been produced by 68 large thermal power plants and are likely to double in the next 10 years. It has been a published fact of research that waste materials such as fly ash; Smoke from silica, etc., through its use as building materials can be converted into significant wealth. In addition, a partial replacement of fly ash is desirable, and in fact is essential due to a variety of technical, economic and ecological reasons. Researchers have reported that the smallest silica fume in round shape and size fills gaps between the thicker cement particles that may otherwise be filled with water. Proportionally proportioned fumed ash and silica smoke improves concrete properties that can not be achieved by using Portland cement alone. The resulting concrete mixture becomes strong, durable and economical and also ecological, as it uses a hazardous ecological material.
MATERIALS USED - SPECIFICATIONS
1.Ordinary Portland Cement (OPC), grade 53.
2. Silica (silicon, sodium 63.1%) as mineral addition (MA) in densified dry form obtained from ELKEM INDIA Pvt.Ltd., Mumbai.
3. Superplasticizer (chemical mixture) based on naphthalene-formaldehyde sulphonate-CONPLAST SP 430.
4. Locally available graduated additive of nominal size 12.5 mm with specific gravity 2.68 and modulus of fineness, 5.08 for coarse aggregate (CA).
5. River sand available locally confirming classification Zone II with specific gravity 2.58 and fineness modulus 2.54 for fine aggregate (FA).
6. Water: Drinking water was used to mix concrete.
7. The fly ash from the Vijayawada thermal power station, Vijayawada, AP, is used.
FLY ASH CHEMISTRY AND SILICA FUME
The fly ash in concrete makes an efficient use of the cement hydration product such as calcium hydroxide (C-H) which otherwise is a source of cement weakness. Normal cement makes it C-S-H denser and stronger by pozzolanic reaction. The heat generated during the hydration initiates the pozzolanic reaction of the fly ash. Silica smoke is a by-product of silicon or the Ferro-silica industry and is 100 times thinner than cement. It consists of amorphous silica and has high reactivity towards lime. The level of substitution of silica smoke is generally low by about 10%.
When SF is used in the concrete mix, its introduction affects the physical layout of the system, particularly near the surface of the aggregate where porosity exists. Silica smoke begins to react in the early phase of the hydration process. The pozzolanic action of the silica fume substantially reduces the amount and size of the crystals "CH" in paste of hydrated cement. This phenomenon coupled with a low W / C ratio reduces the thickness of the transition zones and therefore, the preferential orientation of the CH crystals is greatly reduced. All these results in more uniform, stronger micro-cracking potential transition zone.
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