From 26th October 2009
Dr.V.V.Deshmukh
Managing Director
Surface Solutions Pvt.Ltd
Concrete technologies
Email vilasdes@gmail.com
Mobile 9869026667
To
Mr.Mahesh Zagade
The Commissioner
Pune Municipal Corporation
Sivaji Nagar
Pune 411005
Sub : UTWT at Bhosari colony in Pune city
Sir
The ULTRA THIN WHITE TOPPING (UTWT) which Pune Municipality is using for over lay to improve the damaged bituminous road is learnt by PMC Engineer along with contractor and consultant who visited our site in Thane which is developed by Dr.V.V.Deshmukh in consultation with Mr.P.Bongirwar. The same team have shown the successful demonstration to PMC engineer in Pune city.
Observing the performance of our work the Thane Municipality Corporation has sanctioned the budget of Rs 20 crores for UTWT to be used in city internal roads.
The present practice of that UTWT, which Pune Municipality Corporation is using, is not the correct technique and thereby not getting the expected benefits and this technique is optimised by us and proven from our experimental patch at Dahanukar Colony, Pune.
.
The following are the aspects that correct UTWT technology would help is
Cement use: one bag less per cubic meter which helps in reducing the carbon dioxide in the atmosphere and also the cost of surfacing. The idea of not using additive like fly ash, slag as substitute to cement is an old technique where as to achieve high strength we have to use this additive.
Use of fly ash: the fly ash, which is a by product of thermal power plant ,whose production of 100million tonnes per year and has problem of dumping., helps to be used as substitute to cement.
Process: the self compacted technique used by us in laying is faster and thus reducing times for unloading and completing the work faster. Use of machine
like vibrators for compaction is not required because of self compacting technique which is used by us. The mix which PMC is using is very harsh and takes two hours to unload where as our mix is semi self compacting and unloaded in half an hour.
The use of poly propylene strips helps to avoid cutting (1m X 1 m) , which results in less noise pollution and reduction of cost of Rs 100 per running meter.
The traffic can be opened in 72 hrs vs. 7 days, which reduces the inconvenience to pedestrians; less trouble to traffic diversion and traffic load to certain areas are avoided.
The above mentioned points are highlighted in light of correct UTWT technology which is today standardised by us
I also wish to highlight the following additional advantages of this UTWT technology.
Improved performance: The life of road is increased due use of UTWT than the bituminous road which saves maintenance cost and there is no rutting or wash boarding
In the recycle cost study it proves to be cheaper in the cycle of maintenance due to its longevity.
The light colour of the road increases illumino effect due to increased reflectivity and thereby reducing the heat content of the environment.
The less consumption of raw materials has direct bearing on the unit cost of the road surface laying.
Minimizes waste. Less material to landfill – most of the existing, worn asphalt pavement serves as a base for the UTWT, thus eliminating the need and expense to tear up and haul away the asphalt
Besides less cement consumption helps to earn Carbon credit and is lesser burden to environment.
Note: (1 ton of calcium carbonate the main raw product in manufacture of cement produces equivalent amount of carbon dioxide in atmosphere which is instrumental for global warming)
The world over to avoid the effect of global warming the use of flyash is giving the benefit if we can save carbon number.
In all the above mentioned contexts we should be given the chance to execute the above work in view of our experience in Thane and present work and the experimental patch at Pune.
Dr.Vilas.V.Deshmukh
Surface solutions Pvt. Ltd.
Cc
1 Vivek Kharwadkar, Addl.city engineer
2 Madhav Latkar, Development Engineer roads
Dr.Vilas Deshmukh
Wednesday, July 28, 2010
Tuesday, July 27, 2010
mahesh zagade
/home/ashima/vilas/dr deshmukh/pune commissionar.doc
From 26th October 2009
Dr.V.V.Deshmukh
Managing Director
Surface Solutions Pvt.Ltd
Concrete technologies
Email vilasdes@gmail.com
Mobile 9869026667
To
Mr.Mahesh Zagade
The Commissioner
Pune Municipal Corporation
Sivaji Nagar
Pune 411005
Sub : UTWT at Bhosari colony in Pune city
Sir
The ULTRA THIN WHITE TOPPING (UTWT) which Pune Municipality is using for over lay to improve the damaged bituminous road is learnt by PMC Engineer along with contractor and consultant who visited our site in Thane which is developed by Dr.V.V.Deshmukh in consultation with Mr.P.Bongirwar. The same team have shown the successful demonstration to PMC engineer in Pune city.
Observing the performance of our work the Thane Municipality Corporation has sanctioned the budget of Rs 20 crores for UTWT to be used in city internal roads.
The present practice of that UTWT, which Pune Municipality Corporation is using, is not the correct technique and thereby not getting the expected benefits and this technique is optimised by us and proven from our experimental patch at Dahanukar Colony, Pune.
.
The following are the aspects that correct UTWT technology would help is
Cement use: one bag less per cubic meter which helps in reducing the carbon dioxide in the atmosphere and also the cost of surfacing. The idea of not using additive like fly ash, slag as substitute to cement is an old technique where as to achieve high strength we have to use this additive.
Use of fly ash: the fly ash, which is a by product of thermal power plant ,whose production of 100million tonnes per year and has problem of dumping., helps to be used as substitute to cement.
Process: the self compacted technique used by us in laying is faster and thus reducing times for unloading and completing the work faster. Use of machine
like vibrators for compaction is not required because of self compacting technique which is used by us. The mix which PMC is using is very harsh and takes two hours to unload where as our mix is semi self compacting and unloaded in half an hour.
The use of poly propylene strips helps to avoid cutting (1m X 1 m) , which results in less noise pollution and reduction of cost of Rs 100 per running meter.
The traffic can be opened in 72 hrs vs. 7 days, which reduces the inconvenience to pedestrians; less trouble to traffic diversion and traffic load to certain areas are avoided.
The above mentioned points are highlighted in light of correct UTWT technology which is today standardised by us
I also wish to highlight the following additional advantages of this UTWT technology.
Improved performance: The life of road is increased due use of UTWT than the bituminous road which saves maintenance cost and there is no rutting or wash boarding
In the recycle cost study it proves to be cheaper in the cycle of maintenance due to its longevity.
The light colour of the road increases illumino effect due to increased reflectivity and thereby reducing the heat content of the environment.
The less consumption of raw materials has direct bearing on the unit cost of the road surface laying.
Minimizes waste. Less material to landfill – most of the existing, worn asphalt pavement serves as a base for the UTWT, thus eliminating the need and expense to tear up and haul away the asphalt
Besides less cement consumption helps to earn Carbon credit and is lesser burden to environment.
Note: (1 ton of calcium carbonate the main raw product in manufacture of cement produces equivalent amount of carbon dioxide in atmosphere which is instrumental for global warming)
The world over to avoid the effect of global warming the use of flyash is giving the benefit if we can save carbon number.
In all the above mentioned contexts we should be given the chance to execute the above work in view of our experience in Thane and present work and the experimental patch at Pune.
Dr.Vilas.V.Deshmukh
Surface solutions Pvt. Ltd.
Cc
1 Vivek Kharwadkar, Addl.city engineer
2 Madhav Latkar, Development Engineer roads
From 26th October 2009
Dr.V.V.Deshmukh
Managing Director
Surface Solutions Pvt.Ltd
Concrete technologies
Email vilasdes@gmail.com
Mobile 9869026667
To
Mr.Mahesh Zagade
The Commissioner
Pune Municipal Corporation
Sivaji Nagar
Pune 411005
Sub : UTWT at Bhosari colony in Pune city
Sir
The ULTRA THIN WHITE TOPPING (UTWT) which Pune Municipality is using for over lay to improve the damaged bituminous road is learnt by PMC Engineer along with contractor and consultant who visited our site in Thane which is developed by Dr.V.V.Deshmukh in consultation with Mr.P.Bongirwar. The same team have shown the successful demonstration to PMC engineer in Pune city.
Observing the performance of our work the Thane Municipality Corporation has sanctioned the budget of Rs 20 crores for UTWT to be used in city internal roads.
The present practice of that UTWT, which Pune Municipality Corporation is using, is not the correct technique and thereby not getting the expected benefits and this technique is optimised by us and proven from our experimental patch at Dahanukar Colony, Pune.
.
The following are the aspects that correct UTWT technology would help is
Cement use: one bag less per cubic meter which helps in reducing the carbon dioxide in the atmosphere and also the cost of surfacing. The idea of not using additive like fly ash, slag as substitute to cement is an old technique where as to achieve high strength we have to use this additive.
Use of fly ash: the fly ash, which is a by product of thermal power plant ,whose production of 100million tonnes per year and has problem of dumping., helps to be used as substitute to cement.
Process: the self compacted technique used by us in laying is faster and thus reducing times for unloading and completing the work faster. Use of machine
like vibrators for compaction is not required because of self compacting technique which is used by us. The mix which PMC is using is very harsh and takes two hours to unload where as our mix is semi self compacting and unloaded in half an hour.
The use of poly propylene strips helps to avoid cutting (1m X 1 m) , which results in less noise pollution and reduction of cost of Rs 100 per running meter.
The traffic can be opened in 72 hrs vs. 7 days, which reduces the inconvenience to pedestrians; less trouble to traffic diversion and traffic load to certain areas are avoided.
The above mentioned points are highlighted in light of correct UTWT technology which is today standardised by us
I also wish to highlight the following additional advantages of this UTWT technology.
Improved performance: The life of road is increased due use of UTWT than the bituminous road which saves maintenance cost and there is no rutting or wash boarding
In the recycle cost study it proves to be cheaper in the cycle of maintenance due to its longevity.
The light colour of the road increases illumino effect due to increased reflectivity and thereby reducing the heat content of the environment.
The less consumption of raw materials has direct bearing on the unit cost of the road surface laying.
Minimizes waste. Less material to landfill – most of the existing, worn asphalt pavement serves as a base for the UTWT, thus eliminating the need and expense to tear up and haul away the asphalt
Besides less cement consumption helps to earn Carbon credit and is lesser burden to environment.
Note: (1 ton of calcium carbonate the main raw product in manufacture of cement produces equivalent amount of carbon dioxide in atmosphere which is instrumental for global warming)
The world over to avoid the effect of global warming the use of flyash is giving the benefit if we can save carbon number.
In all the above mentioned contexts we should be given the chance to execute the above work in view of our experience in Thane and present work and the experimental patch at Pune.
Dr.Vilas.V.Deshmukh
Surface solutions Pvt. Ltd.
Cc
1 Vivek Kharwadkar, Addl.city engineer
2 Madhav Latkar, Development Engineer roads
Sunday, July 11, 2010
flyash grout
Grout using black colour Tata flyash
% Rate/kg cost
Cement 20 3.5 0.7
tata black flyash 80 0.75 0.6
suparex 0.75 73 0.5
1.8
% Rate/kg cost
Cement 20 3.5 0.7
tata black flyash 80 0.75 0.6
suparex 0.75 73 0.5
1.8
activation of flyash
Dear Mr Dekmush,
do you mean European standards then its EN 197?
I have not done alkali activation of fly ash myself and its not done in
Holcim yet but I have done a literature review, the summary I have
attached. To activate Class F fly ash as in India will be quite difficult
as its a relatively coarse and low reactiv fly ash. You need high
percentages of activators which might cause problems with regards to
standard limits on Cl and alkalies and in application e.g. corrosion and
ASR reaction. Therefore we will test this new combination of grinding aids
and quality improvers from South Africa as send to you as it seems to work
quite well. Fly ash content could be increased from 32 to 38% at same
perfomance.
Economically its difficult to say if grinding or activation is more
economic as it depends on the % and type of activator and the Blaine.
Grinding has a certain limit for activation of fly ash cement as beyond
around 4000 Blaine the activation effect through surface increase is
compensated by higher water demand in the concrete. So beyond a certain fly
ash content it should be probably a combination of both mechanical and
chemical activation. The cheapest activator is NaCl which mainhly acts on
the clinker, NaOH is more fly ash specific but also more costly.
Coarse fly ashes with a high reactive SiO2 content >30% react very well on
grinding, we have seen it in some of our Eastern European plants.
Another promising option are multiple blends like fly ash/slag or fly
ash/limestone blends. They combine very well and when ground separately
fineness of the components can be adjusted to maximise performance. But I
think the IS does not allow it right now, may be in the future.
Generally you can say its possible to activate each fly ash its just a
matter of concentration and thats also the problem. The majority of R&D was
on either activation via suspension or at elevated temperatures or US
specific Class C fly ashes were used which have cement like properties,
there are Class C fly ash based binders in US marketed as shown in the
file. Except HolcimAct admixture which should work also with your
clinker/FA, I do not see a magic powder which will push the fly ash
activity, I see more a combination of measures be it even another grinding
system like vibrating mills, one large scale operational in Texas and use
of certain activators partially activating the clinker and partially
activating fly ash. May be it should be also mentioned that Lafarge did
tests with injecting HCl in the finished mill to activate fly ash by
etching the surface of fly ash particles but problem in this case was
corrosion of mill parts. Another option of course would be air
classification of fly ash to increase fineness and thus reactivitiy but
this requires CAPEX and has about 5USD/t operation cost and you have to
take care of the residue as well.
So all together I do not have a final solution, sorry. I would certainly
start with HolcimAct first and see if it works.
What is your current project and program and what are the targets you want
to achieve?
Best regards
Stefan Dietz
(See attached file: Fly_ash_maximation Holcim.ppt)(See attached file: EN
197-1 en.pdf)(See attached file: Fly ash standards.ppt)
_____________________
Stefan Dietz
Holcim Group Support Ltd
Corporate Commercial Services
Product Innovation and Development
Im Schachen
5113 Holderbank
Phone +41 58 858 64 12
Fax +41 58 858 64 09
Mobile +41 79 373 7983
stefan.dietz@holcim.com
www.holcim.com
This e-mail is confidential and intended only for the use of the above
named addressee. If you have received this e-mail in error, please delete
it immediately and notify us by e-mail or telephone.
do you mean European standards then its EN 197?
I have not done alkali activation of fly ash myself and its not done in
Holcim yet but I have done a literature review, the summary I have
attached. To activate Class F fly ash as in India will be quite difficult
as its a relatively coarse and low reactiv fly ash. You need high
percentages of activators which might cause problems with regards to
standard limits on Cl and alkalies and in application e.g. corrosion and
ASR reaction. Therefore we will test this new combination of grinding aids
and quality improvers from South Africa as send to you as it seems to work
quite well. Fly ash content could be increased from 32 to 38% at same
perfomance.
Economically its difficult to say if grinding or activation is more
economic as it depends on the % and type of activator and the Blaine.
Grinding has a certain limit for activation of fly ash cement as beyond
around 4000 Blaine the activation effect through surface increase is
compensated by higher water demand in the concrete. So beyond a certain fly
ash content it should be probably a combination of both mechanical and
chemical activation. The cheapest activator is NaCl which mainhly acts on
the clinker, NaOH is more fly ash specific but also more costly.
Coarse fly ashes with a high reactive SiO2 content >30% react very well on
grinding, we have seen it in some of our Eastern European plants.
Another promising option are multiple blends like fly ash/slag or fly
ash/limestone blends. They combine very well and when ground separately
fineness of the components can be adjusted to maximise performance. But I
think the IS does not allow it right now, may be in the future.
Generally you can say its possible to activate each fly ash its just a
matter of concentration and thats also the problem. The majority of R&D was
on either activation via suspension or at elevated temperatures or US
specific Class C fly ashes were used which have cement like properties,
there are Class C fly ash based binders in US marketed as shown in the
file. Except HolcimAct admixture which should work also with your
clinker/FA, I do not see a magic powder which will push the fly ash
activity, I see more a combination of measures be it even another grinding
system like vibrating mills, one large scale operational in Texas and use
of certain activators partially activating the clinker and partially
activating fly ash. May be it should be also mentioned that Lafarge did
tests with injecting HCl in the finished mill to activate fly ash by
etching the surface of fly ash particles but problem in this case was
corrosion of mill parts. Another option of course would be air
classification of fly ash to increase fineness and thus reactivitiy but
this requires CAPEX and has about 5USD/t operation cost and you have to
take care of the residue as well.
So all together I do not have a final solution, sorry. I would certainly
start with HolcimAct first and see if it works.
What is your current project and program and what are the targets you want
to achieve?
Best regards
Stefan Dietz
(See attached file: Fly_ash_maximation Holcim.ppt)(See attached file: EN
197-1 en.pdf)(See attached file: Fly ash standards.ppt)
_____________________
Stefan Dietz
Holcim Group Support Ltd
Corporate Commercial Services
Product Innovation and Development
Im Schachen
5113 Holderbank
Phone +41 58 858 64 12
Fax +41 58 858 64 09
Mobile +41 79 373 7983
stefan.dietz@holcim.com
www.holcim.com
This e-mail is confidential and intended only for the use of the above
named addressee. If you have received this e-mail in error, please delete
it immediately and notify us by e-mail or telephone.
Friday, July 9, 2010
About Flyash
Fy ash is one of the residues generated in the combustion of coal. Fly ash is generally captured from the chimneys of coal-fired power plants, and is one of two types of ash that jointly are known as coal ash; the other, bottom ash, is removed from the bottom of coal furnaces. Depending upon the source and makeup of the coal being burned, the components of fly ash vary considerably, but all fly ash includes substantial amounts of silicon dioxide (SiO2) (both amorphous and crystalline) and calcium oxide (CaO), both being endemic ingredients in many coal bearing rock strata.
Toxic constituents depend upon the specific coal bed makeup, but may include one or more of the following elements or substances in quantities from trace amounts to several percent: arsenic, beryllium, boron, cadmium, chromium, chromium VI, cobalt, lead, manganese, mercury, molybdenum, selenium, strontium, thallium, and vanadium, along with dioxins and PAH compounds.
more on flyash -
http://en.wikipedia.org/wiki/Fly_ash
Role of Flyash in Sustainable Development
Concrete, Flyash, and the Environment - Proceedings
A forum held 8 December 1998 - Sponsored by EHDD Architecture and Pacific Energy Center
Role of Flyash in Sustainable Development
P.K. Mehta
Good evening, it's very nice to see so many of my friends here. You have heard a very eloquent presentation that we all have a responsibility to do something about global warming. All of us, architects, structural engineers, designers and others, we participate in decision making about concrete mix design, the quality of concrete, and it is here that we can do something about global warming. As was mentioned earlier, each ton of portland cement we consume throws out into the environmental loading about one ton of CO2. So if we are producing 1.3 billion tons of portland cement annually, this emits 1.3 billion tons of CO2 into the environment.
And in 25 years we expect that the demand for portland cement in the world will double up. This is because the developing countries with large populations and rapid population growth, mostly in Asia, South America and Africa, where about 5 billion of the globe's 6 billion people live, still have a long way to go in terms of socioeconomic development. And you cannot tell them "please do not do what the developed countries have done to achieve a high standard of living." They require just as we do, reasonably decent housing for their children, reasonably decent roadways for travel, etc. With globalization of technology and economy, their aspirations are very high; every country wants its citizens to participate in an affluent lifestyle.
So there is no way to stop the demand for more concrete. But any additional portland cement clinker capacity that we build is going to load the environment with an additional one ton of CO2 per ton of cement. There is no shortcut, there is no way around it, half of the CO2 comes from the decomposition of limestone, which is a major raw material for making portland cement, and half of it comes from the fuel. Since coal is the cheapest fuel, we are going to continue to use it for making portland cement. The question is can we continue to meet the increasing demand for cement and concrete in a sustainable manner.
Fortunately, within this scenario a new player has emerged that can save us. And that player is flyash. There are some problems because most of the literature on flyash, research on flyash, and the flyash codes are obsolete. They are not updated, and it will take time to do so.
Meanwhile, let's look at the current materials, and the current science and technology. Let's satisfy ourselves intellectually and with the help of some laboratory work, some field tests, and some real buildings; and it's our hope that we can solve the problem.
With this background, my job is to give you a brief introduction as to what flyash is and what flyash can do in concrete today, based on the current state of our knowledge. Although many of you know about flyash, my effort will be to take even those who don't know anything about flyash right from ground level to the latest that we know about it. I will first spend a few minutes talking about the source, because typically people don't know about it.
One of the important issues I will describe are the mechanisms by which flyash influences the properties of concrete. Because if you understand the mechanism, you don't have to worry about codes and standards. Once you have a good understanding of the way things work, you can be courageous enough to take some steps. So I'll dwell on mechanisms, and finally give you a brief introduction to the very latest developments, which 10 years from now will probably become a part of conventional concrete technology.
Characteristics of Flyash
Flyash is a powdery substance obtained from dust collectors, whether they are electrical precipitators or baghouses, in electrical power plants which use ground coal as fuel. The U.S. produces about 60 million tons per year, some say 55 million, some say 50, but I've been hearing 55 million for about the last 10 years so it must be 60 million tons. Because of many of the stigmas attached to flyash, the consumption of flyash in the cement and concrete industry is no more that 6 million tons which is only about 10%. And once I tell you what flyash can do, I think that it's a disgrace that most of it is ending up in the landfills, creating lots of problems with our groundwater, air, and land.
The physical and chemical characteristics of flyash which I'm going to discuss, and their effect on the properties of concrete are mainly from an EPRI Report based on a study funded by EPRI [The Electric Power Research Institute] in the early 1980is at UC Berkeley where I work. I was the principal investigator on the research project. My comments are based on not one flyash, but on about 20 U.S. flyashes from the East Coast, the Midwest, the State of Washington, and from Canada; so it's representative of most flyashes, and this report is available from EPRI as report CS3314, published in January 1984. Most of my comments about the characteristics of flyash are based on this source.
Flyash Chemistry
First, unfortunately, the codes, ASTM and so forth, have a very heavy emphasis on the chemistry of flyash. For example "Class F flyash must have more than 70% total of silica, alumina, and iron oxide, and Class C has more than 50% of these oxides" etc. And people get confused because there is really no direct relation between the chemistry of flyash and the properties in concrete. Most of the properties of flyash in concrete are determined by the flyash mineralogy and particle size, and not by chemistry. Don't worry about these various chemical percentages, there is a big range and this range doesn't mean anything. I'm just showing the range to show you that there is a lot of variability, and people get worried about variability. They worry that "what if today I'm getting flyash with 48% silica and tomorrow it goes to 44%". It's not important, nothing will happen.
Flyash Mineralogy
Most important is the flyash mineralogy, and with regard to the mineralogy of flyash, 60-90% is glass. It starts out as impurities in coal, mostly clays, shales, limestone, and dolomite. They cannot be burned so they end up as ash, and at high temperatures they fuse and become glass. Because of the high speed of the flue gases, the molten glass turns into glass beads, or tiny spheres of glass. I'm emphasizing this because it's the kind of material if we didn't have it, we would have to invent it in order to improve the workability and durability of concrete.
For flyash in the U.S., there are two ASTM Classes, Class F and Class C that are based on total amounts of silica, alumina, and iron oxide present. This doesn't have much significance. In Europe and the rest of the world there is a recognition that if you want to make some differentiation based on the chemistry, then divide flyash based on it's calcium content, because the calcium content of flyash has a great influence on the type of glass. And if a material is mostly glass, we should only be worrying about what kind of glass it is. There is too much emphasis on the remaining stuff that is not glass. Remember flyash is 60-90% glass, and modern flyashes are much closer to 70-80% glass.
Low calcium flyash also contains non-reactive crystalline minerals; say you have 80% glass, with the 20% remaining being a non-reactive mineral like quartz, mullite, which is an aluminum silicate, hematite and magnetite, which are iron oxides, and a less reactive alumino silicate glass. There are two glass types. If you have high calcium flyash then the alumino silicate glass has also a lot of calcium in it and that glass is more reactive. So that's why Class C flyash gives you higher early strength compared to Class F, because Class C tends to have much more calcium oxide. High calcium flyashes also contain reactive crystalline minerals such as free lime, tri-calcium aluminate, tetra-calcium alumino-sulfate, and calcium sulfate, depending on the sulfur content of the ash. And all of these are reactive crystalline minerals and the glass is also much more reactive.
Flyash Particle Size
There are two parameters that determine the reactivity of flyash, one is the mineralogy, and the second is the particle characteristics. Now you should pay very careful attention to the particle characteristics. Particles are mostly glassy, solid and spherical. There are some hollow cenospheres and so forth, but let's not spend time on that because most important is that most of the flyash consists of glassy particles that are solid and spherical. There is also some unburned carbon present, depending on the efficiency of burning. Today's furnaces are very efficient; you may have only 1% carbon, and this carbon is in the form of highly micro-porous large particles, they are just like Swiss cheese, they are large but are not round or spherical because they are not a molten material, it's like charcoal or coke.
The particles of flyash range in size from 1 to 100 microns (1,000 microns is 1 mm, so this largest size particle, 100 microns, equals 0.1 mm). The average size is about 20 microns which is similar to portland cement average particle size. Now what is more important for you to remember is that more that 40% of the particles are under 10 microns, and particles under 10 microns, regardless of the type of flyash, are the ones that contribute to the 7 and 28 day strengths. Under 10 microns is the magic number. And particles about 45 microns and larger, which is 325 sieve residue may be considered as inert. They do not participate in pozzolanic reactions, even after one year, so they behave like sand.
So with flyash, don't worry about the Blaine surface area. What is most important is the particle size distribution. Particles below 10 microns are the ones which are really beneficial for early strength. Particles about 45 microns and larger are not so useful. Between 10 and 45 microns are the ones that slowly react between 28 days and one year or so. Most flyashes have less than 15 or 20% particles which are above 45 microns, and more than 40% particles which are under 10 microns.
In the EPRI study we also worried about whether the furnace design would have any affect on the reactivity of flyash, but we found that the furnace design did not affect flyash reactivity. We found that modern furnaces generally produce a flyash that is low in carbon. ASTM has a 6% limit on carbon in flyash used in concrete, but flyash produced today typically contains 1.0% to 1.5% carbon. And today's flyashes are high in glass, they are 80-90% glass, and have good reactivity. A flyash of this composition will have a good reactivity when its composed of a large proportion of fine particles. So don't go by the residue of the 325 mesh; it only tells you the particles which are inert. To judge flyash reactivity, you will have to find out what percentage of the particles are below 10 microns.
What is the significance of any unburned carbon particles? Unburned carbon particles influence mostly the water demand and the air entraining agent required. In the East Coast and the Midwest where concrete is exposed to freezing & thawing cycles, there is always air entrainment in concrete. In this case, the carbon content is something to worry about because it would influence the dosage of the air entraining admixture.
Again, to continue the conclusions from the EPRI study, we found that except for calcium, flyash chemistry has little influence on reactivity. So except for calcium, don't worry about silica, alumina, iron oxide, etc., they have nothing to do with the properties. The superior reactivity of high calcium flyashes is related to the composition of glass and the presence of reactive crystalline phases.
How Flyash Works
Now that you have learned about what flyash is, let's look at how it works. The first equation in the illustration (see figure 2.2) shows you the chemistry of hydration of portland cement. About 50% of portland cement is composed of the primary mineral tri-calcium silicate, which on hydration forms calcium silicate hydrate and calcium hydroxide. If you have a portland-pozzolan cement, and flyash is the pozzolan, it can be represented by silica because non-crystalline silica glass is the principal constituent of flyash. The silica combines with the calcium hydroxide released on the hydration of portland cement. Calcium hydroxide in hydrated portland cement does not do anything for strength, so therefore you use it up with reactive silica. Slowly and gradually it forms additional calcium silicate hydrate which is a binder, and which fills up the space, and gives you impermeability and more and more strength. This is how the chemistry works.
Figure 2.1 Photograph of flyash enlarged many times
Figure 2.2 Flyash combines with excess and unwanted large crystals of calcium hydroxide (CH) to form additional useful binder (C-S-H)
Now in order to understand the benefits of flyash use we have to look at the physical manifestations of the chemical reaction. There is something called a transition zone in concrete. So far we have looked only at the cement paste, but in concrete you have sand and gravel, and many properties of concrete are controlled by the strength of the interfacial bond between the aggregate and the cement paste, and that interfacial bond is called the transition zone. The transition zone in portland cement concrete is very weak because of the presence of large crystals of calcium hydroxide which find space here due to the wall effect next to the coarse aggregate particles. You can see very clearly in the slide, these large calcium hydroxide crystals, they do not really bind with the aggregate, and they can be easily detached and cracked. And it is these cracks which are the ones that are responsible for the lack of impermeability, or lack of water tightness in concrete. So if you are able to build a stronger transition zone, then you can eliminate micro-cracking, and improve the impermeability, as well as improve the chemical durability, and thus end up with a highly durable concrete.
Also, the particles of coarse aggregate, due to the wall effect, tend to trap water next to the aggregate, and therefore what you see on the surface of the concrete as the visible bleed water is only part of the mixing water. A large amount of mixing water ends up as a locally high water-cement ratio type of cement paste next to the aggregate particles. When you vibrate concrete this is what happens: you have part of the extra mixing water on the surface as the visible bleed water, and a very large amount of bleed water due to internally trapped water next to the coarse aggregate.
The next slide shows you what happens (see figure 2.3). As a result of local high water cement ratio paste next to the coarse aggregate, you form the large crystals of calcium hydroxide, very large crystals, and you have large pores left over making this an area of weakness. If there is any stress, if there is any drying shrinkage, any thermal shrinkage, any loading and unloading effect, then these stress effects could very easily rupture the concrete. It would rupture next to the coarse aggregate particles because of the high porosity, and because this area is filled up with something which is not very strong, these are large plates of calcium hydroxide which can be cracked very easily.
The next slide shows you that this is what actually happens in the field. (see figure 2.4). From a thin section of concrete that deteriorated in a few years, you can trace the micro-cracks with a fluorescent dye. Sea water or de-icing chemicals can permeate very easily through these micro cracks, many of which are interconnected with the cracks which exist next to the aggregate particles. Most of the causes for lack of durability of reinforced concrete, whether it's alkali aggregate reaction, or the corrosion of steel, or sulfate attack, they can be very easily linked to the permeability of concrete, to its lack of water tightness. And this lack of water tightness is not there in freshly cured concrete; it comes later due to environmental effects: heating and cooling, wetting and drying, and because you have built in areas of weakness which micro-crack very easily. When these micro-cracks interconnect, you have channels of flow from outside, and that's how the aggressive chemicals get into the concrete.
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Figure 2.3 Large calcium hydroxide crystals create a plane of weakness next to the coarse aggregate
Figure 2.4 Cross section of concrete showing interconnected micro-cracks adjacent to coarse aggregate.
CANMET Research
Next slide. There are two recent developments regarding high volume flyash concrete, one is the CANMET study which I mentioned earlier, and I want to show you some of the results using these mixes, and how they work. What happens to the voids in the transition zone if you increase the portland cement content of the concrete mixtures? The fine particles of cement in the internal bleed water would dissolve and you will still have voids although smaller in size. Now imagine what would happen if, instead of using the more reactive material (that is portland cement), you add fine particles of a less reactive material such as flyash and also reduce the water content of the concrete mix. You will end up with a less porous transition zone because these tiny glass beads of flyash will obstruct the channels of flow and will make the water-cement ratio more homogeneous in concrete by preventing the formation of local bleed water. And this is exactly what CANMET has found, by limiting the water content, and by introducing a large amount of flyash in the concrete mix. In this mix (see figure 2.5) there is 60% or 215 kg per cubic meter of flyash (360#/CY), 120 kg of mixing water (200#/CY), and 150 kg of cement (260#/CY). The water to cementitious ratio is limited to 0.32 due to the use of a super plasticizer, as well as due to air entrainment which is always required in Canada. So this is a typical CANMET mix, and the next slide shows the properties.
The bleeding with this mix ranges from very low to negligible due to the very low water content of this type of concrete, and also due to the obstruction of channels of flow, you don't expect bleeding on the surface. One of the negative side effects of this is, that you have to take proper care to prevent plastic shrinkage cracking. There are a lot of benefits to this material, but you will also have to learn about the negatives, what is the flip side of the coin. The flip side of the coin is you don't have the luxury of too much bleed water. The construction workers cannot take a coffee break and go away until the sheen is gone, and then come back and finish it. Because there is no sheen to go away, there is no bleed water at all, so you have to be aware of that.
Next slide. With the CANMET mix, the setting time is somewhat longer because remember, the cement content is less that 300 pounds here, and it is the cement that hydrates very, very quickly. It is the hydration of cement that forms calcium silicate hydrate, and as these fibers of calcium silicate hydrate grow, they tend to weave into each other and give you the time of set and strength. So if the cement content is low, naturally the time of set will be slow. But in general, the experience both from the laboratory and the field mixture is that high volume flyash concrete does not show unacceptable retardation in setting time, and demonstrates enough strength development to produce adequate strength at one day. They have obtained 10 MPa (1,500 psi) strength at one day in many of these mixes.
Next slide. Another very important advantage of flyash in concrete is the reduction of thermal cracking. Well known structural engineers who have been in the business for a long time, Professor T.Y. Lin, Professor Ben Gerwick, from their field experience can tell you that many of the problems in concrete are due to thermal cracking. Heat of hydration impacts are usually only considered in mass concrete, such as massive dams. But even in structures which are much less massive, only two or three feet thick, it is massive enough to accumulate enough heat of hydration to cause thermal cracking. So CANMET did a study on 10 foot x 10 foot x 10 foot cubes with a high volume flyash mix. Using this mix the temperature rise was only 35 degrees C compared to 65 degrees C in the control mix using only portland cement. This is a very significant advantage for the durability of concrete because thermal cracking would reduce the watertightness.
The typical compressive strengths that we get with this mix (see figure 2.6) is 8-10 MPa at one day, 35 MPa at 28 days, about 43 MPa at 91 days, and about 55 MPa at one year.
Next slide. Very important from the standpoint of sustainable development is the durability of structures. A lot of structural damage, especially in reinforced concrete, occurs due to the corrosion of steel. There is an ASTM test, rapid chloride penetration test ASTM C1202, where at 28 days 500 to 2,000 coulomb rating was found for the CANMET mixes (see figure 2.7). There is a table showing that anything less than 2,000 coulombs is a very low permeability concrete, so the permeability to CO2, and to chlorides which are responsible for the corrosion of steel is very low in the high volume flyash concrete. And this coulomb rating continues to improve, because many flyash particles react very slowly, pushing the coulomb value lower and lower.
A field test was undertaken by the University of Toronto. Preliminary data is shown in the next slide (courtesy of Professor Michael Thomas). In ten years you can see that the chloride penetration is negligible at about 1 inch depth of cover if you have 50% flyash in the concrete mix. It is an ongoing study in a tidal zone exposed to sea water, with 25 MPA concrete.
The next slide shows another advantage, this is based on a study by Professor Schiessl at the University of Aachen. In Europe they are very much concerned about dumping of industrial by-products because of the potential for ground water contamination. Flyash contains very small amounts of toxic elements, so they wanted to find out about the potential for the leaching of elements such as zinc, chromium, etc. Schiessl and his coworkers found out in the study that flyash concrete is very effective at immobilizing even externally added heavy metals in mortars. Test B is not a very good test, test C is the correct test for mortars and concrete, it is called the tank test and is a leach test on uncrushed specimens. They introduced into the mix, 185 mg of zinc per kg of mix. Then in the leach test they could only leach out 0.09 mg in 56 days. So it's not only that flyash concrete would prevent outside ions from getting in, but it also keeps whatever is in the concrete all tied up, it will not permit it to get out. If you have a toxic metal that has been immobilized by using flyash in concrete, rest assured that it will stay there. In the case of chromium from 53 mg of added chromium, only 0.15 mg could be leached out from the flyash mortar specimens.
Next slide. So this is the mix for the future. In the future, because of so many of these advantages, and much concern about sustainable development, we'll have not only portland cement in the concrete mix, we'll have silica fume and other pozzolans. And in this witches brew a super plasticizer, an air entraining admixture, or other chemical admixtures may be incorporated. This is the future.
Let me go back to a few more transparencies and then I'll finish. I mentioned the ASTM C1202 which is based on AASHTOis T277 test. A 1,000 to 2,000 coulombs current flow in a 6 hour test is a rating of low chloride permeability (see figure 2.8). This is usually a portland cement concrete with less than a 0.4 water cement ratio. If you want very low permeability, less than 1,000 coulomb rating, this is typical of an internally sealed pore system such as with a latex modified concrete. Such low permeability ratings can be obtained with ternary cement blends which I will discuss next.
Chloride Permeability Ratings per AASHTO T-277
Charge Passed
coulombs
Chloride Permeability
Typical of:
> 4000
High
Portland Cement Concrete
W/C > 0.6
2000 - 4000
Moderate
Portland Cement Concrete
0.4 < W/C < 0.6
1000 - 2000
Low
Portland Cement Concrete
W/C < 0.4
A forum held 8 December 1998 - Sponsored by EHDD Architecture and Pacific Energy Center
Role of Flyash in Sustainable Development
P.K. Mehta
Good evening, it's very nice to see so many of my friends here. You have heard a very eloquent presentation that we all have a responsibility to do something about global warming. All of us, architects, structural engineers, designers and others, we participate in decision making about concrete mix design, the quality of concrete, and it is here that we can do something about global warming. As was mentioned earlier, each ton of portland cement we consume throws out into the environmental loading about one ton of CO2. So if we are producing 1.3 billion tons of portland cement annually, this emits 1.3 billion tons of CO2 into the environment.
And in 25 years we expect that the demand for portland cement in the world will double up. This is because the developing countries with large populations and rapid population growth, mostly in Asia, South America and Africa, where about 5 billion of the globe's 6 billion people live, still have a long way to go in terms of socioeconomic development. And you cannot tell them "please do not do what the developed countries have done to achieve a high standard of living." They require just as we do, reasonably decent housing for their children, reasonably decent roadways for travel, etc. With globalization of technology and economy, their aspirations are very high; every country wants its citizens to participate in an affluent lifestyle.
So there is no way to stop the demand for more concrete. But any additional portland cement clinker capacity that we build is going to load the environment with an additional one ton of CO2 per ton of cement. There is no shortcut, there is no way around it, half of the CO2 comes from the decomposition of limestone, which is a major raw material for making portland cement, and half of it comes from the fuel. Since coal is the cheapest fuel, we are going to continue to use it for making portland cement. The question is can we continue to meet the increasing demand for cement and concrete in a sustainable manner.
Fortunately, within this scenario a new player has emerged that can save us. And that player is flyash. There are some problems because most of the literature on flyash, research on flyash, and the flyash codes are obsolete. They are not updated, and it will take time to do so.
Meanwhile, let's look at the current materials, and the current science and technology. Let's satisfy ourselves intellectually and with the help of some laboratory work, some field tests, and some real buildings; and it's our hope that we can solve the problem.
With this background, my job is to give you a brief introduction as to what flyash is and what flyash can do in concrete today, based on the current state of our knowledge. Although many of you know about flyash, my effort will be to take even those who don't know anything about flyash right from ground level to the latest that we know about it. I will first spend a few minutes talking about the source, because typically people don't know about it.
One of the important issues I will describe are the mechanisms by which flyash influences the properties of concrete. Because if you understand the mechanism, you don't have to worry about codes and standards. Once you have a good understanding of the way things work, you can be courageous enough to take some steps. So I'll dwell on mechanisms, and finally give you a brief introduction to the very latest developments, which 10 years from now will probably become a part of conventional concrete technology.
Characteristics of Flyash
Flyash is a powdery substance obtained from dust collectors, whether they are electrical precipitators or baghouses, in electrical power plants which use ground coal as fuel. The U.S. produces about 60 million tons per year, some say 55 million, some say 50, but I've been hearing 55 million for about the last 10 years so it must be 60 million tons. Because of many of the stigmas attached to flyash, the consumption of flyash in the cement and concrete industry is no more that 6 million tons which is only about 10%. And once I tell you what flyash can do, I think that it's a disgrace that most of it is ending up in the landfills, creating lots of problems with our groundwater, air, and land.
The physical and chemical characteristics of flyash which I'm going to discuss, and their effect on the properties of concrete are mainly from an EPRI Report based on a study funded by EPRI [The Electric Power Research Institute] in the early 1980is at UC Berkeley where I work. I was the principal investigator on the research project. My comments are based on not one flyash, but on about 20 U.S. flyashes from the East Coast, the Midwest, the State of Washington, and from Canada; so it's representative of most flyashes, and this report is available from EPRI as report CS3314, published in January 1984. Most of my comments about the characteristics of flyash are based on this source.
Flyash Chemistry
First, unfortunately, the codes, ASTM and so forth, have a very heavy emphasis on the chemistry of flyash. For example "Class F flyash must have more than 70% total of silica, alumina, and iron oxide, and Class C has more than 50% of these oxides" etc. And people get confused because there is really no direct relation between the chemistry of flyash and the properties in concrete. Most of the properties of flyash in concrete are determined by the flyash mineralogy and particle size, and not by chemistry. Don't worry about these various chemical percentages, there is a big range and this range doesn't mean anything. I'm just showing the range to show you that there is a lot of variability, and people get worried about variability. They worry that "what if today I'm getting flyash with 48% silica and tomorrow it goes to 44%". It's not important, nothing will happen.
Flyash Mineralogy
Most important is the flyash mineralogy, and with regard to the mineralogy of flyash, 60-90% is glass. It starts out as impurities in coal, mostly clays, shales, limestone, and dolomite. They cannot be burned so they end up as ash, and at high temperatures they fuse and become glass. Because of the high speed of the flue gases, the molten glass turns into glass beads, or tiny spheres of glass. I'm emphasizing this because it's the kind of material if we didn't have it, we would have to invent it in order to improve the workability and durability of concrete.
For flyash in the U.S., there are two ASTM Classes, Class F and Class C that are based on total amounts of silica, alumina, and iron oxide present. This doesn't have much significance. In Europe and the rest of the world there is a recognition that if you want to make some differentiation based on the chemistry, then divide flyash based on it's calcium content, because the calcium content of flyash has a great influence on the type of glass. And if a material is mostly glass, we should only be worrying about what kind of glass it is. There is too much emphasis on the remaining stuff that is not glass. Remember flyash is 60-90% glass, and modern flyashes are much closer to 70-80% glass.
Low calcium flyash also contains non-reactive crystalline minerals; say you have 80% glass, with the 20% remaining being a non-reactive mineral like quartz, mullite, which is an aluminum silicate, hematite and magnetite, which are iron oxides, and a less reactive alumino silicate glass. There are two glass types. If you have high calcium flyash then the alumino silicate glass has also a lot of calcium in it and that glass is more reactive. So that's why Class C flyash gives you higher early strength compared to Class F, because Class C tends to have much more calcium oxide. High calcium flyashes also contain reactive crystalline minerals such as free lime, tri-calcium aluminate, tetra-calcium alumino-sulfate, and calcium sulfate, depending on the sulfur content of the ash. And all of these are reactive crystalline minerals and the glass is also much more reactive.
Flyash Particle Size
There are two parameters that determine the reactivity of flyash, one is the mineralogy, and the second is the particle characteristics. Now you should pay very careful attention to the particle characteristics. Particles are mostly glassy, solid and spherical. There are some hollow cenospheres and so forth, but let's not spend time on that because most important is that most of the flyash consists of glassy particles that are solid and spherical. There is also some unburned carbon present, depending on the efficiency of burning. Today's furnaces are very efficient; you may have only 1% carbon, and this carbon is in the form of highly micro-porous large particles, they are just like Swiss cheese, they are large but are not round or spherical because they are not a molten material, it's like charcoal or coke.
The particles of flyash range in size from 1 to 100 microns (1,000 microns is 1 mm, so this largest size particle, 100 microns, equals 0.1 mm). The average size is about 20 microns which is similar to portland cement average particle size. Now what is more important for you to remember is that more that 40% of the particles are under 10 microns, and particles under 10 microns, regardless of the type of flyash, are the ones that contribute to the 7 and 28 day strengths. Under 10 microns is the magic number. And particles about 45 microns and larger, which is 325 sieve residue may be considered as inert. They do not participate in pozzolanic reactions, even after one year, so they behave like sand.
So with flyash, don't worry about the Blaine surface area. What is most important is the particle size distribution. Particles below 10 microns are the ones which are really beneficial for early strength. Particles about 45 microns and larger are not so useful. Between 10 and 45 microns are the ones that slowly react between 28 days and one year or so. Most flyashes have less than 15 or 20% particles which are above 45 microns, and more than 40% particles which are under 10 microns.
In the EPRI study we also worried about whether the furnace design would have any affect on the reactivity of flyash, but we found that the furnace design did not affect flyash reactivity. We found that modern furnaces generally produce a flyash that is low in carbon. ASTM has a 6% limit on carbon in flyash used in concrete, but flyash produced today typically contains 1.0% to 1.5% carbon. And today's flyashes are high in glass, they are 80-90% glass, and have good reactivity. A flyash of this composition will have a good reactivity when its composed of a large proportion of fine particles. So don't go by the residue of the 325 mesh; it only tells you the particles which are inert. To judge flyash reactivity, you will have to find out what percentage of the particles are below 10 microns.
What is the significance of any unburned carbon particles? Unburned carbon particles influence mostly the water demand and the air entraining agent required. In the East Coast and the Midwest where concrete is exposed to freezing & thawing cycles, there is always air entrainment in concrete. In this case, the carbon content is something to worry about because it would influence the dosage of the air entraining admixture.
Again, to continue the conclusions from the EPRI study, we found that except for calcium, flyash chemistry has little influence on reactivity. So except for calcium, don't worry about silica, alumina, iron oxide, etc., they have nothing to do with the properties. The superior reactivity of high calcium flyashes is related to the composition of glass and the presence of reactive crystalline phases.
How Flyash Works
Now that you have learned about what flyash is, let's look at how it works. The first equation in the illustration (see figure 2.2) shows you the chemistry of hydration of portland cement. About 50% of portland cement is composed of the primary mineral tri-calcium silicate, which on hydration forms calcium silicate hydrate and calcium hydroxide. If you have a portland-pozzolan cement, and flyash is the pozzolan, it can be represented by silica because non-crystalline silica glass is the principal constituent of flyash. The silica combines with the calcium hydroxide released on the hydration of portland cement. Calcium hydroxide in hydrated portland cement does not do anything for strength, so therefore you use it up with reactive silica. Slowly and gradually it forms additional calcium silicate hydrate which is a binder, and which fills up the space, and gives you impermeability and more and more strength. This is how the chemistry works.
Figure 2.1 Photograph of flyash enlarged many times
Figure 2.2 Flyash combines with excess and unwanted large crystals of calcium hydroxide (CH) to form additional useful binder (C-S-H)
Now in order to understand the benefits of flyash use we have to look at the physical manifestations of the chemical reaction. There is something called a transition zone in concrete. So far we have looked only at the cement paste, but in concrete you have sand and gravel, and many properties of concrete are controlled by the strength of the interfacial bond between the aggregate and the cement paste, and that interfacial bond is called the transition zone. The transition zone in portland cement concrete is very weak because of the presence of large crystals of calcium hydroxide which find space here due to the wall effect next to the coarse aggregate particles. You can see very clearly in the slide, these large calcium hydroxide crystals, they do not really bind with the aggregate, and they can be easily detached and cracked. And it is these cracks which are the ones that are responsible for the lack of impermeability, or lack of water tightness in concrete. So if you are able to build a stronger transition zone, then you can eliminate micro-cracking, and improve the impermeability, as well as improve the chemical durability, and thus end up with a highly durable concrete.
Also, the particles of coarse aggregate, due to the wall effect, tend to trap water next to the aggregate, and therefore what you see on the surface of the concrete as the visible bleed water is only part of the mixing water. A large amount of mixing water ends up as a locally high water-cement ratio type of cement paste next to the aggregate particles. When you vibrate concrete this is what happens: you have part of the extra mixing water on the surface as the visible bleed water, and a very large amount of bleed water due to internally trapped water next to the coarse aggregate.
The next slide shows you what happens (see figure 2.3). As a result of local high water cement ratio paste next to the coarse aggregate, you form the large crystals of calcium hydroxide, very large crystals, and you have large pores left over making this an area of weakness. If there is any stress, if there is any drying shrinkage, any thermal shrinkage, any loading and unloading effect, then these stress effects could very easily rupture the concrete. It would rupture next to the coarse aggregate particles because of the high porosity, and because this area is filled up with something which is not very strong, these are large plates of calcium hydroxide which can be cracked very easily.
The next slide shows you that this is what actually happens in the field. (see figure 2.4). From a thin section of concrete that deteriorated in a few years, you can trace the micro-cracks with a fluorescent dye. Sea water or de-icing chemicals can permeate very easily through these micro cracks, many of which are interconnected with the cracks which exist next to the aggregate particles. Most of the causes for lack of durability of reinforced concrete, whether it's alkali aggregate reaction, or the corrosion of steel, or sulfate attack, they can be very easily linked to the permeability of concrete, to its lack of water tightness. And this lack of water tightness is not there in freshly cured concrete; it comes later due to environmental effects: heating and cooling, wetting and drying, and because you have built in areas of weakness which micro-crack very easily. When these micro-cracks interconnect, you have channels of flow from outside, and that's how the aggressive chemicals get into the concrete.
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Figure 2.3 Large calcium hydroxide crystals create a plane of weakness next to the coarse aggregate
Figure 2.4 Cross section of concrete showing interconnected micro-cracks adjacent to coarse aggregate.
CANMET Research
Next slide. There are two recent developments regarding high volume flyash concrete, one is the CANMET study which I mentioned earlier, and I want to show you some of the results using these mixes, and how they work. What happens to the voids in the transition zone if you increase the portland cement content of the concrete mixtures? The fine particles of cement in the internal bleed water would dissolve and you will still have voids although smaller in size. Now imagine what would happen if, instead of using the more reactive material (that is portland cement), you add fine particles of a less reactive material such as flyash and also reduce the water content of the concrete mix. You will end up with a less porous transition zone because these tiny glass beads of flyash will obstruct the channels of flow and will make the water-cement ratio more homogeneous in concrete by preventing the formation of local bleed water. And this is exactly what CANMET has found, by limiting the water content, and by introducing a large amount of flyash in the concrete mix. In this mix (see figure 2.5) there is 60% or 215 kg per cubic meter of flyash (360#/CY), 120 kg of mixing water (200#/CY), and 150 kg of cement (260#/CY). The water to cementitious ratio is limited to 0.32 due to the use of a super plasticizer, as well as due to air entrainment which is always required in Canada. So this is a typical CANMET mix, and the next slide shows the properties.
The bleeding with this mix ranges from very low to negligible due to the very low water content of this type of concrete, and also due to the obstruction of channels of flow, you don't expect bleeding on the surface. One of the negative side effects of this is, that you have to take proper care to prevent plastic shrinkage cracking. There are a lot of benefits to this material, but you will also have to learn about the negatives, what is the flip side of the coin. The flip side of the coin is you don't have the luxury of too much bleed water. The construction workers cannot take a coffee break and go away until the sheen is gone, and then come back and finish it. Because there is no sheen to go away, there is no bleed water at all, so you have to be aware of that.
Next slide. With the CANMET mix, the setting time is somewhat longer because remember, the cement content is less that 300 pounds here, and it is the cement that hydrates very, very quickly. It is the hydration of cement that forms calcium silicate hydrate, and as these fibers of calcium silicate hydrate grow, they tend to weave into each other and give you the time of set and strength. So if the cement content is low, naturally the time of set will be slow. But in general, the experience both from the laboratory and the field mixture is that high volume flyash concrete does not show unacceptable retardation in setting time, and demonstrates enough strength development to produce adequate strength at one day. They have obtained 10 MPa (1,500 psi) strength at one day in many of these mixes.
Next slide. Another very important advantage of flyash in concrete is the reduction of thermal cracking. Well known structural engineers who have been in the business for a long time, Professor T.Y. Lin, Professor Ben Gerwick, from their field experience can tell you that many of the problems in concrete are due to thermal cracking. Heat of hydration impacts are usually only considered in mass concrete, such as massive dams. But even in structures which are much less massive, only two or three feet thick, it is massive enough to accumulate enough heat of hydration to cause thermal cracking. So CANMET did a study on 10 foot x 10 foot x 10 foot cubes with a high volume flyash mix. Using this mix the temperature rise was only 35 degrees C compared to 65 degrees C in the control mix using only portland cement. This is a very significant advantage for the durability of concrete because thermal cracking would reduce the watertightness.
The typical compressive strengths that we get with this mix (see figure 2.6) is 8-10 MPa at one day, 35 MPa at 28 days, about 43 MPa at 91 days, and about 55 MPa at one year.
Next slide. Very important from the standpoint of sustainable development is the durability of structures. A lot of structural damage, especially in reinforced concrete, occurs due to the corrosion of steel. There is an ASTM test, rapid chloride penetration test ASTM C1202, where at 28 days 500 to 2,000 coulomb rating was found for the CANMET mixes (see figure 2.7). There is a table showing that anything less than 2,000 coulombs is a very low permeability concrete, so the permeability to CO2, and to chlorides which are responsible for the corrosion of steel is very low in the high volume flyash concrete. And this coulomb rating continues to improve, because many flyash particles react very slowly, pushing the coulomb value lower and lower.
A field test was undertaken by the University of Toronto. Preliminary data is shown in the next slide (courtesy of Professor Michael Thomas). In ten years you can see that the chloride penetration is negligible at about 1 inch depth of cover if you have 50% flyash in the concrete mix. It is an ongoing study in a tidal zone exposed to sea water, with 25 MPA concrete.
The next slide shows another advantage, this is based on a study by Professor Schiessl at the University of Aachen. In Europe they are very much concerned about dumping of industrial by-products because of the potential for ground water contamination. Flyash contains very small amounts of toxic elements, so they wanted to find out about the potential for the leaching of elements such as zinc, chromium, etc. Schiessl and his coworkers found out in the study that flyash concrete is very effective at immobilizing even externally added heavy metals in mortars. Test B is not a very good test, test C is the correct test for mortars and concrete, it is called the tank test and is a leach test on uncrushed specimens. They introduced into the mix, 185 mg of zinc per kg of mix. Then in the leach test they could only leach out 0.09 mg in 56 days. So it's not only that flyash concrete would prevent outside ions from getting in, but it also keeps whatever is in the concrete all tied up, it will not permit it to get out. If you have a toxic metal that has been immobilized by using flyash in concrete, rest assured that it will stay there. In the case of chromium from 53 mg of added chromium, only 0.15 mg could be leached out from the flyash mortar specimens.
Next slide. So this is the mix for the future. In the future, because of so many of these advantages, and much concern about sustainable development, we'll have not only portland cement in the concrete mix, we'll have silica fume and other pozzolans. And in this witches brew a super plasticizer, an air entraining admixture, or other chemical admixtures may be incorporated. This is the future.
Let me go back to a few more transparencies and then I'll finish. I mentioned the ASTM C1202 which is based on AASHTOis T277 test. A 1,000 to 2,000 coulombs current flow in a 6 hour test is a rating of low chloride permeability (see figure 2.8). This is usually a portland cement concrete with less than a 0.4 water cement ratio. If you want very low permeability, less than 1,000 coulomb rating, this is typical of an internally sealed pore system such as with a latex modified concrete. Such low permeability ratings can be obtained with ternary cement blends which I will discuss next.
Chloride Permeability Ratings per AASHTO T-277
Charge Passed
coulombs
Chloride Permeability
Typical of:
> 4000
High
Portland Cement Concrete
W/C > 0.6
2000 - 4000
Moderate
Portland Cement Concrete
0.4 < W/C < 0.6
1000 - 2000
Low
Portland Cement Concrete
W/C < 0.4
Thursday, July 8, 2010
advance cementitious material
Advanced cementitious materials
Dr.V.V.Deshmukh
Introduction :
Recent years have seen the development of many new advances in cementitious materials as ceramic like materials formed as the result of chemical reactions occurring at or near ambient temperatures. These new advances have occurred as a result of manipulating the microstructure and controlling the chemistry or both, of cements. These advances have led to the development of new families of high performance cementitious materials including very high strength materials. Some of these materials cross the boundaries of what has been defined as traditional cementitious materials, and the term chemically bonded ceramics has been used to classify these new materials. CBCs are defined at or near ambient temperatures. These new novel cements or CBCs follow the general rules of behavior of cementitious materials in certain respect The strength of hardened paste increases as the ratio of water to cement is reduced. Because the residual porosity, its distribution and the excess uncombined molecular water are responsible for most of the limitations on the properties of conventional hardened cement paste. Many attempts have been made to reduce the amount of water used in processing. The situation has changed beginning in about 1970 as new approaches have led to the development of more advanced cement matrix composites.
1) Densification by pressure and heat
The bonds limiting the strength of cement paste are normally thought to be weak van der waals forces Before 1970,the potential strength of cement paste at theoretical density had never been approached because considerable porosity (20 to 30% or more total porosity) always remain after complete hydration of cement. Following this research resulted in achieving very high strengths by warm pressing. Compressive strengths up to 650 Mpa (compared to more typical 30 Mpa) tensile strength up to 68 Mpa and values of youngs modulus up to 40 Gpa were attained. Enormous increases in strength resulted from the removal of most of the porosity and the generation of very homogenous fine microstructure with porosity's as low as 2%.
2) Micro defect free cement.
The warm pressed cements discussed in the previous section were successful but not easy to produce in large amounts due to the high pressure used. The next step was to develop more easily processed materials. .Another innovation was the engineering of a new class of high strength materials, the MDF cement. MDF refers to the absence of relatively large voids or defects which are usually present in conventionally mixed cement paste because of entrapped air and inadequate dispersion. In the MDF process 4 to 7% of one of several water soluble polymer is added as a rheological aid to permit cement to be mixed with very small amount of water., subsequent high shear mixing produces a plastic cohesive mixture which can be shaped by extrusion or other forming technique and which sets in times ranging from minutes to hours. The highest strength materials have been prepared with calcium aluminate cement. Control of the particle size distribution for optimum particle packing was also considered important for generating strength. A final processing stage in which entrapped air is removed by applying modest pressure or heating at 80 0C resulted in a paste that is free of large defects. with excellent mechanical properties. Very low porosity's were achieved <1% as well as flexural strength of 150 Mpa. compressive strength of 300 Mpa and a young’s modulus of 50 Gpa. When MDF material is exposed to moisture, the polymer phase which MDF cement where constitute 30% on a volume basis, swells and softens. This property of MDF cement has restricted the use of its in application where water is used.
3) DSP and other densely packed systems
An important class of new materials termed DSP (Densified systems containing homogeneously arranged ultrafine particles) was first elucidated in detail by Bache The new class of materials is defined as materials with matrix comprising of 1) Densely packed particles of a size ranging from 0.5 to 100micron usually cement 2) Homogeneously arranged ultra-fine particles ranging in size from 50 A0 to 0.5 microns usually silica fume, arranged in the spaces between the larger particles. The combination of densely packed silicafume and cement was found to benefit for a combination of reasons
1) The silica particles are smaller than even the finest cement produced by grinding and therefore pack more easily into the spaces between the cement particles.
2) The silica particles are spherical in shape
3) The particles are chemically less reactive than cement, which eliminates the problem of too rapid hardening encountered with very fine cement
4) Finally with added dispersing agents a low water requirement may be achieved.
Numerous investigations have contributed to the understanding of the effects of fine particles in densely packed cementitious materials. With 15% silica fume replacement of cement thwere are 2000000 particles of silica fume for each grain of portland cement in a concrete mixture. Concrete containing 5 to 15% silica fume have high compressive strengths up to 100 Mpa flexural strength up to 12 Mpa and young’s moduli (up to 34 Gpa)and have very low permeability to water (10-9 um).The microstructure of the critical interfacial zone between cement paste and the aggregates in concrete is more dense and uniform than when conventional pastes are used and the bond between paste and other embedded materials such as aggregates and fibers appears to be improved. The most striking results have been found with silica fume substituted pastes and DSP systems. Compressive strengths of up to 270 Mpa or higher with young’s moduli up to 80 Gpa were achieved in preparations with up to 20 to 25% silicafume at a water to solid ratio of 0.12 to 0.22 through mechanical compaction. Such materials are used to resist mechanical erosion in impeller screws for moving coal and fly ash and in flooring to industrial area. This material retains a compressive strengths of 300 Mpa up to about 500 0c and 200 Mpa at about 700 0C.
Silica fume hydration reactions.
Properly dispersed silica fume particles when used in propertions to replace up to 10 % of cement significantly reduces the bleeding and segregation of the mixtures and may be used in higher proportions. Silica fume contains particles as fine as 0.1 microns or less which partially dissolve in saturated Ca(OH)2 solution in a time as early as 5 to 15 minutes, and a SiO2 rich hydrates is deposited in layers or films on the silica fume particles. Despite the early rapid reaction much silica fume is remained for later slow reaction. The fume particles play an important role in various composites when they surround each cement grain, densifying the matrix, filling the voids with the strong hydration products and improve the bonding with aggregates, and reinforcing materials such as fibers. Silica fume by reacting with alkali also affords a protection against the alkali aggregate type reaction occurring between a cement pore solution and glass fiber.
Particle packing in concrete.
The Toufar/Aim model of dry particle has been verified as adequately modeling the dry packing of mixers of powder, each with a different size distribution. Typically in the model ,materials with three different size distributions may be mixed .Furthermore, the characterization of the size distribution can be modeled by a commonly used procedure describe by Rosin-Rammler. Input to this PC-based algorithm consists of the experimentally determined tap density of each component and the characteristic diameter of the distribution as described by D in Rosin-Rammler fitting equation. The results of applying this algorithm to concrete systems have provided the mathematical basis for formulating concrete mixtures which were developed through field experience in the concrete placement. Its applications should prove useful in monitoring the quality of concrete in the design stages and to maximize performance.
Discussion and summary
The particle packing and hydration reactions in DSP cement pastes are responsible for the fine microstructural development. These complex reactions involve phase solubility ,accelerating and retarding effects of a multiphase, multiparticle size distribution material, and surface effects at the solid-liquid interface. This particle packing combined with chemical reaction is extremely important for developing strength. The initial degree of dispersion of cement and fume in the paste strongly influences the development of the final hardened paste microstructure. The ultra fine particles can fill the intergranular interstices and produce a dense paste structure. Reflected in a high strength. Superplasticizers should be used to minimize the water demand and adequately disperse the fine particles, resulting in dense products with fine pore size, very low permeability and low ionic diffusivity. Despite the rapid early hydration, much silica fume remains unreacted until a later stage. Physical and chemical characteristics together influence the hydration kinetics. Silica fume ordinaraly accelerates the early portland cement hydrtion, largely because of its very high surface area, increasing the heat development and resembling a high early strength cement. Fume also disperses the hydration product, provides for deposition of C-S-H and there by fills the pore interstices with fine hydration products. The mechanical properties of some highstrength DRC -type materials have been summarised in table given below
Dr.V.V.Deshmukh
Introduction :
Recent years have seen the development of many new advances in cementitious materials as ceramic like materials formed as the result of chemical reactions occurring at or near ambient temperatures. These new advances have occurred as a result of manipulating the microstructure and controlling the chemistry or both, of cements. These advances have led to the development of new families of high performance cementitious materials including very high strength materials. Some of these materials cross the boundaries of what has been defined as traditional cementitious materials, and the term chemically bonded ceramics has been used to classify these new materials. CBCs are defined at or near ambient temperatures. These new novel cements or CBCs follow the general rules of behavior of cementitious materials in certain respect The strength of hardened paste increases as the ratio of water to cement is reduced. Because the residual porosity, its distribution and the excess uncombined molecular water are responsible for most of the limitations on the properties of conventional hardened cement paste. Many attempts have been made to reduce the amount of water used in processing. The situation has changed beginning in about 1970 as new approaches have led to the development of more advanced cement matrix composites.
1) Densification by pressure and heat
The bonds limiting the strength of cement paste are normally thought to be weak van der waals forces Before 1970,the potential strength of cement paste at theoretical density had never been approached because considerable porosity (20 to 30% or more total porosity) always remain after complete hydration of cement. Following this research resulted in achieving very high strengths by warm pressing. Compressive strengths up to 650 Mpa (compared to more typical 30 Mpa) tensile strength up to 68 Mpa and values of youngs modulus up to 40 Gpa were attained. Enormous increases in strength resulted from the removal of most of the porosity and the generation of very homogenous fine microstructure with porosity's as low as 2%.
2) Micro defect free cement.
The warm pressed cements discussed in the previous section were successful but not easy to produce in large amounts due to the high pressure used. The next step was to develop more easily processed materials. .Another innovation was the engineering of a new class of high strength materials, the MDF cement. MDF refers to the absence of relatively large voids or defects which are usually present in conventionally mixed cement paste because of entrapped air and inadequate dispersion. In the MDF process 4 to 7% of one of several water soluble polymer is added as a rheological aid to permit cement to be mixed with very small amount of water., subsequent high shear mixing produces a plastic cohesive mixture which can be shaped by extrusion or other forming technique and which sets in times ranging from minutes to hours. The highest strength materials have been prepared with calcium aluminate cement. Control of the particle size distribution for optimum particle packing was also considered important for generating strength. A final processing stage in which entrapped air is removed by applying modest pressure or heating at 80 0C resulted in a paste that is free of large defects. with excellent mechanical properties. Very low porosity's were achieved <1% as well as flexural strength of 150 Mpa. compressive strength of 300 Mpa and a young’s modulus of 50 Gpa. When MDF material is exposed to moisture, the polymer phase which MDF cement where constitute 30% on a volume basis, swells and softens. This property of MDF cement has restricted the use of its in application where water is used.
3) DSP and other densely packed systems
An important class of new materials termed DSP (Densified systems containing homogeneously arranged ultrafine particles) was first elucidated in detail by Bache The new class of materials is defined as materials with matrix comprising of 1) Densely packed particles of a size ranging from 0.5 to 100micron usually cement 2) Homogeneously arranged ultra-fine particles ranging in size from 50 A0 to 0.5 microns usually silica fume, arranged in the spaces between the larger particles. The combination of densely packed silicafume and cement was found to benefit for a combination of reasons
1) The silica particles are smaller than even the finest cement produced by grinding and therefore pack more easily into the spaces between the cement particles.
2) The silica particles are spherical in shape
3) The particles are chemically less reactive than cement, which eliminates the problem of too rapid hardening encountered with very fine cement
4) Finally with added dispersing agents a low water requirement may be achieved.
Numerous investigations have contributed to the understanding of the effects of fine particles in densely packed cementitious materials. With 15% silica fume replacement of cement thwere are 2000000 particles of silica fume for each grain of portland cement in a concrete mixture. Concrete containing 5 to 15% silica fume have high compressive strengths up to 100 Mpa flexural strength up to 12 Mpa and young’s moduli (up to 34 Gpa)and have very low permeability to water (10-9 um).The microstructure of the critical interfacial zone between cement paste and the aggregates in concrete is more dense and uniform than when conventional pastes are used and the bond between paste and other embedded materials such as aggregates and fibers appears to be improved. The most striking results have been found with silica fume substituted pastes and DSP systems. Compressive strengths of up to 270 Mpa or higher with young’s moduli up to 80 Gpa were achieved in preparations with up to 20 to 25% silicafume at a water to solid ratio of 0.12 to 0.22 through mechanical compaction. Such materials are used to resist mechanical erosion in impeller screws for moving coal and fly ash and in flooring to industrial area. This material retains a compressive strengths of 300 Mpa up to about 500 0c and 200 Mpa at about 700 0C.
Silica fume hydration reactions.
Properly dispersed silica fume particles when used in propertions to replace up to 10 % of cement significantly reduces the bleeding and segregation of the mixtures and may be used in higher proportions. Silica fume contains particles as fine as 0.1 microns or less which partially dissolve in saturated Ca(OH)2 solution in a time as early as 5 to 15 minutes, and a SiO2 rich hydrates is deposited in layers or films on the silica fume particles. Despite the early rapid reaction much silica fume is remained for later slow reaction. The fume particles play an important role in various composites when they surround each cement grain, densifying the matrix, filling the voids with the strong hydration products and improve the bonding with aggregates, and reinforcing materials such as fibers. Silica fume by reacting with alkali also affords a protection against the alkali aggregate type reaction occurring between a cement pore solution and glass fiber.
Particle packing in concrete.
The Toufar/Aim model of dry particle has been verified as adequately modeling the dry packing of mixers of powder, each with a different size distribution. Typically in the model ,materials with three different size distributions may be mixed .Furthermore, the characterization of the size distribution can be modeled by a commonly used procedure describe by Rosin-Rammler. Input to this PC-based algorithm consists of the experimentally determined tap density of each component and the characteristic diameter of the distribution as described by D in Rosin-Rammler fitting equation. The results of applying this algorithm to concrete systems have provided the mathematical basis for formulating concrete mixtures which were developed through field experience in the concrete placement. Its applications should prove useful in monitoring the quality of concrete in the design stages and to maximize performance.
Discussion and summary
The particle packing and hydration reactions in DSP cement pastes are responsible for the fine microstructural development. These complex reactions involve phase solubility ,accelerating and retarding effects of a multiphase, multiparticle size distribution material, and surface effects at the solid-liquid interface. This particle packing combined with chemical reaction is extremely important for developing strength. The initial degree of dispersion of cement and fume in the paste strongly influences the development of the final hardened paste microstructure. The ultra fine particles can fill the intergranular interstices and produce a dense paste structure. Reflected in a high strength. Superplasticizers should be used to minimize the water demand and adequately disperse the fine particles, resulting in dense products with fine pore size, very low permeability and low ionic diffusivity. Despite the rapid early hydration, much silica fume remains unreacted until a later stage. Physical and chemical characteristics together influence the hydration kinetics. Silica fume ordinaraly accelerates the early portland cement hydrtion, largely because of its very high surface area, increasing the heat development and resembling a high early strength cement. Fume also disperses the hydration product, provides for deposition of C-S-H and there by fills the pore interstices with fine hydration products. The mechanical properties of some highstrength DRC -type materials have been summarised in table given below
Monday, July 5, 2010
EFFECT OF ADDITIVES ON COMPRESSIVE STRENGTH OF CEMENTIOUS GROUT
The comparative study using all possible additives tried for cost optimisation or improvement in properties is given in above table.The metakeoline with proper calsination gives promising results
The activity of flyash 
Mumbai Pune Express Highway
Repair of Bridge decks of Bumbai-Pune express highway using ACCMARG Technology of ACC-LTD.
The Mumbai-Pune Express highway is the first modern expressway in the country. The ministry of surface transport during the seven five year plan identified this corridor as amongst the three most congested national highway corridors and proposed it to be developed as part of national expressway system.
The 100 kilometer long stretch that winds up the hill and literally flies over the twin hill station resorts of Lonavala and khandala 600 m up in the western ghats. It continues its impressive routes into the inland plateau towards Pune The views while travelling up the western ghats looking towards mumbai are quite spectacular. The number of civil engineering structures on this express way are
Underpass 26
Overpass 20
Major bridges/viaducts :6
Minor bridges :21
Box/slab culverts :81
Cart tracks/pedestrian crossing :33
Railway bridges :2
Interchanges :4
It is indeed a pleasure ride to reach Pune in two hours from Mumbai using the express way. Such a marvel piece of work in the history of Indian road was not with out few blemices.
The 75 mm thick reinforced concrete wearing course over bridge decks was cracking. The cracking was may be due to many reasons. There were many articles in news paper stating the reasons of cracking. The problem of cracking was more severe at bridge decks at Khandala,kune and kusgaon.These threee bridge decks of roughly 60,000 square meter were cracking and there were potholes on the decks even before one year of opening the traffic.
The MSRDC the main body responsible for building the Mumbai-Pune express highway approached ACC to give solution to this severe problem. The ACC at that time has developed ACCMARG technology which can exclusively used for resurfacing of damaged concrete and bituminous roads.The same was used to solve the problem.
ACCMARG TECHNOLOGY
ACCMARG technology can be described as a semi flexible surfacing process consisting of open graded asphalt concrete filled with a special cement grout. The joint less wearing surface is approximately 30 to 100 mm thick applied to an existing asphalt or concrete pavement. The primary use of ACCMARG on road surfaces to provide protection against fuel spillage and resistant to abrasion and rutting. ACCMARG has been applied to various types of pavements in India. These includes bridge decks, road intersections. roads sections etc. The material has been tested in and around Mumbai on several high trafficed roads. Based on the experience to date ACCMARG pavement can withstand abrasive action from heavy vehicles, heavy point loads and pavement deterioration from fuel spills.
MATERIALS AND CONSTRUCTION
The open graded bituminous macadam mixture is similar to a porous bituminous course and is placed using standard paving techniques. The mix design procedure is used to determine the optimum bitumine content. The aggregate gradation is part of the ACCMARG technology. With a bitumine content of about 4% and rolling the surface with a predetermined number of passes produces a surface with 25-30% voids. The air voids content is critical since the grout canot penetrate the mix if sufficient voids are not present.
After laying the porous bituminous mix it is allowed to cool only then is the grout introduced into the voids.The grout is composed of a proprietary material of ACC which is wet mixed and poured onto the open graded bituminous surface.The excess grout is squeezed out by brooming the surface.
PROCEDURE OF CONSTRUCTION.
The ACC’S expert team visited L&T site at Lonawalla on 25 th December 2002.The three bridge decks at Khandala, Kune and Kusgaon were damaged and around 60000 sq meter area covering all the three bridge decks were to be repaired using ACCMARG technology
The badly cracked concrete panels were removed and fresh concrete panels were laid. The rest of the panels with surface cracks and before damaging further were used as such for ACCMARG placement.
.M/S Lonawalla construction limited which is local party who has supplied the aggregates to L&T for their concrete making has been finalized for bituminous macadam placement. The general requirement of mixing and placing the open graded macadam includes requirements of aggregates, bituminous binder, hot mix asphalt plant, surface preparation, spreading and compacting of porous bitumen macadam. The asphalt mixture is of two component mixture as given in Table-1
Table-1:Asphalt mix proportion.
Material Proportion
Bituminous material 3.7-4.3%
Aggregate 95.8-96.2%
M/S Lonawalla construction has used bituminous of 60/70 grade as per penetration test from BPCL. The aggregates used were from Chakan area 30km away from Lonawalla .The aggregates used are of following specifications.
Test VALUE
Water absorption 1.6%
Aggregate impact value 24.75%
Aggregate abrasion value 29.8%
There was a challenge to ACC team to execute ACCMARG laying job in two months time without stopping the vehicular traffic. The job started from the right carriage way of Kune bridge which is 430 meters long and 11 meters wide. Out of two lanes of right carriage way one lane was kept open for traffic and the other was used for ACCMARG laying. Fourty eight hours were required for ACCMARG placement with curing period of 36hrs.
The concrete surface is cleaned and emulsified bitumen Hincol is used as tack coat and 30 mm hot bituminous macadam is placed using paver.The mixing,spreading and finishing should be a continuous operation.Not more that two hours should be elapse between porous asphalt is mixed and the time of completion of rolling.During tack coating and the paving work only traffic necessary for the execution of the paving work was allowed on asphalt base course pavement. The paved bituminous macadam is rolled with 10 ton steel wheel roller to obtained 25-30% voids. The thickness of bituminous macadam and necessary camber is monitored at regular interval.
Mixing and pouring of grout.
The M-60 grout was made using ACCMARG dry powder and water at ready mix concrete plant of L&T situated at Kusgaon few kilometers away from the site. The grout was brought to the site in transit mixers. Grout mixing, pouring and spreading was a continuous operation. Not more than three hour should elapse between water is added to the mix and the time of completion..The ACCMARG pavement is cured for further 32 hrs and open to traffic. After completion of write carriage way left carriage way was completed by similar fashion.
ACCMARG laying at Khandala which is 670 meter long and 11 meter wide amd Kusgaon which is 1090 meter long and 15 meter wide were completed. The entire job is copleted by second week of march.In case of Kune and khandala decks the ACCMARG 30mm thick is laid expansion joint to expansion joint with taper near the joints.In case of kusgaon deck the expansion joints were raised by 30 mm by welding the circular metal bar to the existing expansion joints and then 30 mm ACCMARG is laid throughout.
The job was completed in time and handed over to client L&T. This experience has proved ACCMARG as unique wearing course material for bridgedecks .
The Mumbai-Pune Express highway is the first modern expressway in the country. The ministry of surface transport during the seven five year plan identified this corridor as amongst the three most congested national highway corridors and proposed it to be developed as part of national expressway system.
The 100 kilometer long stretch that winds up the hill and literally flies over the twin hill station resorts of Lonavala and khandala 600 m up in the western ghats. It continues its impressive routes into the inland plateau towards Pune The views while travelling up the western ghats looking towards mumbai are quite spectacular. The number of civil engineering structures on this express way are
Underpass 26
Overpass 20
Major bridges/viaducts :6
Minor bridges :21
Box/slab culverts :81
Cart tracks/pedestrian crossing :33
Railway bridges :2
Interchanges :4
It is indeed a pleasure ride to reach Pune in two hours from Mumbai using the express way. Such a marvel piece of work in the history of Indian road was not with out few blemices.
The 75 mm thick reinforced concrete wearing course over bridge decks was cracking. The cracking was may be due to many reasons. There were many articles in news paper stating the reasons of cracking. The problem of cracking was more severe at bridge decks at Khandala,kune and kusgaon.These threee bridge decks of roughly 60,000 square meter were cracking and there were potholes on the decks even before one year of opening the traffic.
The MSRDC the main body responsible for building the Mumbai-Pune express highway approached ACC to give solution to this severe problem. The ACC at that time has developed ACCMARG technology which can exclusively used for resurfacing of damaged concrete and bituminous roads.The same was used to solve the problem.
ACCMARG TECHNOLOGY
ACCMARG technology can be described as a semi flexible surfacing process consisting of open graded asphalt concrete filled with a special cement grout. The joint less wearing surface is approximately 30 to 100 mm thick applied to an existing asphalt or concrete pavement. The primary use of ACCMARG on road surfaces to provide protection against fuel spillage and resistant to abrasion and rutting. ACCMARG has been applied to various types of pavements in India. These includes bridge decks, road intersections. roads sections etc. The material has been tested in and around Mumbai on several high trafficed roads. Based on the experience to date ACCMARG pavement can withstand abrasive action from heavy vehicles, heavy point loads and pavement deterioration from fuel spills.
MATERIALS AND CONSTRUCTION
The open graded bituminous macadam mixture is similar to a porous bituminous course and is placed using standard paving techniques. The mix design procedure is used to determine the optimum bitumine content. The aggregate gradation is part of the ACCMARG technology. With a bitumine content of about 4% and rolling the surface with a predetermined number of passes produces a surface with 25-30% voids. The air voids content is critical since the grout canot penetrate the mix if sufficient voids are not present.
After laying the porous bituminous mix it is allowed to cool only then is the grout introduced into the voids.The grout is composed of a proprietary material of ACC which is wet mixed and poured onto the open graded bituminous surface.The excess grout is squeezed out by brooming the surface.
PROCEDURE OF CONSTRUCTION.
The ACC’S expert team visited L&T site at Lonawalla on 25 th December 2002.The three bridge decks at Khandala, Kune and Kusgaon were damaged and around 60000 sq meter area covering all the three bridge decks were to be repaired using ACCMARG technology
The badly cracked concrete panels were removed and fresh concrete panels were laid. The rest of the panels with surface cracks and before damaging further were used as such for ACCMARG placement.
.M/S Lonawalla construction limited which is local party who has supplied the aggregates to L&T for their concrete making has been finalized for bituminous macadam placement. The general requirement of mixing and placing the open graded macadam includes requirements of aggregates, bituminous binder, hot mix asphalt plant, surface preparation, spreading and compacting of porous bitumen macadam. The asphalt mixture is of two component mixture as given in Table-1
Table-1:Asphalt mix proportion.
Material Proportion
Bituminous material 3.7-4.3%
Aggregate 95.8-96.2%
M/S Lonawalla construction has used bituminous of 60/70 grade as per penetration test from BPCL. The aggregates used were from Chakan area 30km away from Lonawalla .The aggregates used are of following specifications.
Test VALUE
Water absorption 1.6%
Aggregate impact value 24.75%
Aggregate abrasion value 29.8%
There was a challenge to ACC team to execute ACCMARG laying job in two months time without stopping the vehicular traffic. The job started from the right carriage way of Kune bridge which is 430 meters long and 11 meters wide. Out of two lanes of right carriage way one lane was kept open for traffic and the other was used for ACCMARG laying. Fourty eight hours were required for ACCMARG placement with curing period of 36hrs.
The concrete surface is cleaned and emulsified bitumen Hincol is used as tack coat and 30 mm hot bituminous macadam is placed using paver.The mixing,spreading and finishing should be a continuous operation.Not more that two hours should be elapse between porous asphalt is mixed and the time of completion of rolling.During tack coating and the paving work only traffic necessary for the execution of the paving work was allowed on asphalt base course pavement. The paved bituminous macadam is rolled with 10 ton steel wheel roller to obtained 25-30% voids. The thickness of bituminous macadam and necessary camber is monitored at regular interval.
Mixing and pouring of grout.
The M-60 grout was made using ACCMARG dry powder and water at ready mix concrete plant of L&T situated at Kusgaon few kilometers away from the site. The grout was brought to the site in transit mixers. Grout mixing, pouring and spreading was a continuous operation. Not more than three hour should elapse between water is added to the mix and the time of completion..The ACCMARG pavement is cured for further 32 hrs and open to traffic. After completion of write carriage way left carriage way was completed by similar fashion.
ACCMARG laying at Khandala which is 670 meter long and 11 meter wide amd Kusgaon which is 1090 meter long and 15 meter wide were completed. The entire job is copleted by second week of march.In case of Kune and khandala decks the ACCMARG 30mm thick is laid expansion joint to expansion joint with taper near the joints.In case of kusgaon deck the expansion joints were raised by 30 mm by welding the circular metal bar to the existing expansion joints and then 30 mm ACCMARG is laid throughout.
The job was completed in time and handed over to client L&T. This experience has proved ACCMARG as unique wearing course material for bridgedecks .
Sunday, July 4, 2010
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