| Tue Nov 17, 2009 | Post #1 | Girish
Administrator
Join date: Oct 2009 |  Post subject: FLY ASH
% Fly Ash = % Cement Reduction?
?? 30MPa Mix – 300 kg cement
?? 40% cement replacement = 120 kg
?? “40% Fly Ash Mix”
144 kg fly ash
216 kg cement
360 kg total CM
Actual cement reduction = 84 kg
( only a 28% reduction) | | |
|
| Tue Nov 17, 2009 | Post #2 | Girish
Administrator
Join date: Oct 2009 | Post subject: FLY ASH USE
?? 50% cement replacement
?? Footings
?? Columns
?? 45% cement replacement
?? Walls
?? 40% cement replacement
?? Suspended slabs
?? Slabs-on-grade | | |
|
| Tue Nov 17, 2009 | Post #3 | Girish
Administrator
Join date: Oct 2009 | Post subject: Why Fly Ash ?? replacing cement content ?
1 TONNE OF CEMENT:
- Releases 1 tonne of CO2
- Consumes 5 million BTU of energy
- Uses 2 tonnes of raw materials
FLY ASH:
- Is a waste product or the coal industry
- Benefits include:
- Improved concrete properties
- Environmental
- Economic
Challenges include:
- Lower early strength gain
- Curing | | |
|
| Sun Nov 22, 2009 | Post #4 | Girish
Administrator
Join date: Oct 2009 | Post subject: WATER CEMENT RATIO
What is this term Water Cement Ratio all about ??
Ratio of weight of Water to the weight of cement used in the concrete mix.
150 kg of water to a mix with 300 kg of cement is 50 %
Lesser the water – the concrete gets more strength and durability.
But workability reduces with reduction in water.
Solution.
Use admixtures.
Use of pozzolan maerials (Fly ash or blast furnace slag) or silica fume, rice hull ash or natural pozzolans.
The theory
Concrete hardens as a result of chemical reaction between cement and water which is known as hydration. For every 2 kg of cement 0,5 kg of water is needed to fully complete reaction. This result in water cement ratio – 25% ( 1:4)
But practically in such ratio, the mix is too dry and the reaction between water and cement doesn’t happen completely through out the mix as some of the water will be even taken by sand and stone. So more water is used to make sure their happens a complete hydration reaction.
So 30% to 40% is generally achieved and considered as a good water cement ratio.
Too much water will result in settling and segregation of sand and stone components in the mix. (sand on top layers and stone will be found then at the bottom)
More internal crack. Less strength will be problems to face in use of more water.
| | |
|
| Sun Nov 22, 2009 | Post #5 | Girish
Administrator
Join date: Oct 2009 | adding on to the above.
Water cement ration concept is more applicable to the Structural element of building.
columns, slabs etc Which actually take care of load factors.
The roof screed, floor screed etc doesnt considered as a structural element. rather as a protection element . | | |
|
| Sat Dec 05, 2009 | Post #6 | Girish
Administrator
Join date: Oct 2009 | Post subject: More about fly ash - Environmental Impacts
in the year 2008 india proudced about 140 Million tons of fly ash in its coal fired thermal power stations. Only about 25% of its being recyled in 2009. or put to beneficial use. with major portion being in the constuction industry.
Disposal of ununsed ash is mainly done by creating ash heaps or washign the ash with water in slurry form into large lagoons. Both disposal routes are costly and Environmentally damaging.
Nasik thermal power station is the second largest power station in Maharashtra consisting of 5 coal fired boilers with a total generation capacity of 910 MW.
the ashes been displosed into lagoons. and suprisingly these lagoons contain cumulative deposits of more than 37 million tons of ash
now reconsile the above figure with the fact that fly ash can replaces about 25% to 70% of Oridinary port land cement !!!!! | | |
|
|