High Volume Fly Ash constitutes about 50% fly ash, a lower water content, low cement content and a low water-cement ratio (W:C) (about 0.4-0.45%). A concrete mix with fly ash can provide environmental and economical benefits. Fly Ash concrete enhances the workability, compressive strength, flexural strength and also increases its  durability and concrete finishing. It also reduces corrosion, alkali silica reaction, sulphate reaction shrinkage as it decreases its permeability and bleeding in concrete.

Fly-ash is a by-product of some other process and it is used to reduce the cost of concrete which reduces the cement consumption by a good percentage. We know that  cement mfg process involves lot of co2 emission. So obviously use of fly-ash will reduce the co2 emission.

High Volume Fly Ash constitutes about 50% fly ash, a lower water content, low cement content and a low water-cement ratio (W:C) (about 0.4-0.45%). A concrete mix with fly ash can provide environmental and economical benefits. Fly Ash concrete enhances the workability, compressive strength, flexural strength and also increases its  durability and concrete finishing. It also reduces corrosion, alkali silica reaction, sulphate reaction shrinkage as it decreases its permeability and bleeding in concrete.

Fly-ash is a by-product of some other process and it is used to reduce the cost of concrete which reduces the cement consumption by a good percentage. We know that  cement mfg process involves lot of co2 emission. So obviously use of fly-ash will reduce the co2 emission.

Thank you so much!

Dear Mr. Andres Toro,

Mr. Mondal has discussed it in detail. For further aspect, refer following papers:

All the best

http://www.cement.org/docs/default-source/fc_concrete_technology/is548-optimizing-the-use-of-fly-ash-concrete.pdf

http://www.sciencedirect.com/science/article/pii/S095006181300336X

http://nvlpubs.nist.gov/nistpubs/TechnicalNOtes/NIST.TN.1812.pdf

Conference Paper Enhancing High Volume Fly Ash Concretes Using Fine Limestone Powder

There are several publications which indicates that, inclusion of Fly Ash (FA) has very good and beneficial effects on the properties of concrete in terms of durability and performance. But definitely, there is a limit of the percentages of FA you may add.

I know, different research papers deals with different types of concrete and proposed different optimum percentages, but I think following TWO publications will give you straight forward idea about the effects of FA on concrete.

Thanks and I hope it will help you.  

Conference Paper Effects of Silica Fume and Fly Ash as Partial Replacement of...

Deleted research item The research item mentioned here has been deleted

Use of Fly ash in concrete depends upon its size, reactivity, effective curing period and Calcium content in Fly ash. 

There are two actions fly ash plays in concrete 

1. Pozzolanic action increases strength (depends on above factors)

2. As a Filler material enhance durability considerably  (nano size)

I have seen experimentally that properly graded Fly ash is very good for durability of concrete. 

I conducted abrasion tests on normal cement paste and 50% of Fly ash paste. w/c of all were 0.42. The volume loss of 50% of Fly ash replaced sample was about 4 time more than normal cement paste. Maybe 50% of replacement was too much, however, it is hard for me to believe that fly ash is good for durability.

Addition to given information above, strenght development of high volume fly ash concrete is significantly lower than conventional concrete because of lower reactivity of fly ash than cement. In comparing of the two concrete types with regard to durability and etc., these concretes should be counterpart of each other. The comparison will be better on these samples reaching ultimate hyrdration product after sufficient curing period. If fly ash is preferred with satisfactory chemical and physical properties at a reasonable amount, the high volume fly ash concretes can be more durable than their conventional counterparts.

FYI, curing age was more than one year, 1year and 4 months.

The conclusions might be controversial. There are too many factors inherent in fly ash influencing common concrete. Among them chemical oxide compositions and their corresponding reactivities as well as the water absorptivity of fly ash would play major roles. You may look closer to one of my technical papers details as attached.

Heard an interesting story about 'our fly ash', back 20 years ago. We had found a buyer, a new start-up company, of our fly ash. We apologized - that roughly half of our fly ash was floating during the quench process of recovering it.

Surprisingly, that floating fly ash was what the new company really wanted. Someone, on our side, got a bit interested - and was said to have put samples of the floating fly ash vs. the sinking fly ash under a microscope ... where the floating fly ash was supposedly determined to be made up of tiny, hollow spheres, while the fly ash sample that sank was composed of broken fly ash spheres.

Supposedly, the floating fly ash made a cement that would float on water.  Supposedly, because of the cement's lighter weight - a 6 story concrete building could now be built to 10 stories. (Big economic advantage.)

I hope this artical is useful for you

High volume flyash concrete may or may not be better than plain concrete. It depends upon the desired strength and durability properties. For example, in concrete pavements inclusions of 30% fly ash as part replacement of OPC is recommended. With further replacement it may reduce the mechanical properties of concrete, however may enhance the durability properties (depending upon the lime and silica content and specific surface area of particles). Moreover, high content of flyash has been reported to cause formation of ettringite in concrete structure which may be harmful for the same lying in the vicinity of sulphate environment. Therefore before taking any decision, please ensure the chemical properties of flyash, specific surface area, strength activity index and other durability related properties,