Good morning everyone, today we are going to discuss a next-generation of cement that

is Calcium Sulfoaluminate cement-based Binder.

We will look into its properties and applications.

As we all know that Concrete is the most used man-made material in the world.

So it is obvious that we need to look into the carbon footprint of Portland cement, which

is the binding phase of Concrete.

And we know that five to seven percent of global CO2 emission is attributed to Portland

cement manufacturing.

Primarily it is due to the calcination of limestone which is used to manufacture Portland

cement.

So, how can we reduce carbon dioxide footprint of Portland cement?

And we know that most of it is arising from the calcination of limestone.

There are conventional ways of reducing CO2 emission like increasing energy efficiency

by optimising processes and we can also increase the cementitious additions into cement.

We have been doing that for a while, like adding slag, fly ash, limestone.

Also we can think about substituting fuels, we can think about more environmentally friendly

fuels.

But we need to think of non conventional ways if we really want to significantly reduce

the CO2 emissions during the Portland cement manufacturing.

So here is the graph which compares the CO2 emission of individual phases present in Portland

cement and compares it with, so let us look into the CO2 emission of various phases does

not in Portland cement.

C3S has the highest CO2 emission followed by C2S, C3A and C4AF.

Now if we compare it with calcium aluminate,right, which is the main phase of calcium aluminate

cement, the carbon dioxide footprint is quite low.

And C4A3S, which is calcium Sulfoaluminate phase, main phase of CSA based cements is

the least among all these phases.

We know that very high kiln temperature is used to manufacture Portland cement, roughly

around thousand and four fifty degrees Celsius temperature is used.

But to make calcium Sulfoaluminate cement, we need to go only to thousand and two fifty

degrees Celsius.

So we can cut down the kiln temperature by two hundred degrees Celsius.

In addition to that we need less grinding energy because the calcium Sulfoaluminate

cement clinker is more porous.

So all these advantages lead to reduction in CO2 emissions and energy requirement.

So, what is calcium Sulfoaluminate Belite cement?

It comprises of Ye'elimite, also called C4A3S, Calcium Sulfoaluminate, Belite as you know

also present in Portland cement.

But it has a lot of Calcium Sulphate and Calcium Aluminate Ferrite, C4AF.

So, this phase C4A3S is the main phase of CSA cement, it was patented by Alexander Klein

in nineteen sixties at the University of California Berkeley, but the goal was to achieve shrinkage

compensation in concrete.

At that time the focus was shrinkage compensation by inducing expansion in concrete.

We will look into that in the later slides.

Also important thing to note is you don’t need different kinds of raw materials.

It is the same what is used to make Portland cement.

So limestone, clay, bauxite and gypsum is used to make this Calcium Sulfoaluminate cement.

But the kiln temperature has to be around thousand and two fifty degrees Celsius.

So if you look into cement, the CSA clinker has roughly seventy five to ninety percent

in clinker, rest is calcium sulphate.

It is important to look into what exists.

So these are the existing CSA based products.

In USA, I think there are three companies now which make this CSA cement Buzzi CSA cement,

Komponent by CTS company and the Royal White cement company makes CSA cement.

Obviously the application is different, sometime they sell it as a rapid set cement, sometimes

they sell it as zero shrinkage cement, that depends.

In Europe see that this Primekss, a company based in Latvia, it does not sell cement per

se but itself concrete products.

They sell it zero shrinkage concrete products.

In China this company has been manufacturing for decades actually.

So, Oreworld Trade Co.

So these are the existing products on the market, okay, it is good to know that there

is something which exists which is based on CSA cement.

Now we will look into hydration of calcium Sulfoaluminate based cement.

So we know that Ye'elimite, so I will use Ye'elimite and calcium Sulfoaluminate at the

interchangeably, so Ye'elimite which is C4A3S can hydrate just in presence of water and

gives monosulphate.

You have mono sulphate and aluminum hydroxide, also called gypsite.

Now, when there is the presence of gypsum, you have a formation of Ettringite, okay.

And again you will have aluminum hydroxide.

Now, when there is enough lime in the system, which may be the case when you have C2S, enough

of C2S in CSA cement or it is used with Portland cement, which we will see later in a few slides.

You have only Ettringite forming, so no aluminum hydroxide, okay.

Now as you all know that C2S can react with water and form CSH, right, calcium silicate

hydrate.

And the C2S can also react with this aluminum hydroxide which is coming from these two reactions

and form stratlingite.

So these are the possible reactions which may take place depending on obviously composition

of CSA cement.

Although C4AF is in minor amount but it can also hydrate in presence of gypsum and form

Ettringite.

So these reactions are important to always look into.

And we know that whenever we have formation of Ettringite, the reaction can be expensive.

Okay, we will come down to this point later.

How can be leverage this expansion in making concrete durable.

So, here is the study done by Zhang and Glasser in early two thousands, shows like, if you

look into the hydration products, Y axis we have hydration products and what happens when

you increase the amount of gypsum, right.

We know that when there is no gypsum, you will have formation of monosulphate.

But as you increase the amount of gypsum, you form a AFT phase or Ettringite, that is

what it is showing basically.

So with the increase in gypsum you see AFT phase is increasing.

But beyond a point, like here in this case we see this thirty percent limit, you will

have excess gypsum, okay.

Also we see formation of aluminum hydroxide.

So this study was done on this particular type of cement, here is the phase composition,

you have forty eight percent of Ye'elimite, twenty seven percent of C2S, very small amount

of Anhydrite, right.

Also I would like to point out that it depends, what is a form of your calcium sulphate.

It could be in form of anhydrite, could be in form of gypsum and dihydrite, could be

in form of hemi-hydrite.

So the dissolution kinetics of these individual phrases will also influence the hydration

of Ye'elimite.

Again, if you look into now phase content, right, so you start with Ye'elimite , particularly

Ye'elimite, suppose this clinker had anhydrite, some Belite.

So, with that, as the reaction proceeds, you see reaction of Ye'elimite, right.

And what is important to note is just in like four days, hundred hours,right, roughly most

of the Ye'elimite is reacted.

So it tells us that the reaction is fast and we can expect reaction to complete in seven

to ten days completely.

And as Ye'elimite is decreasing in amount, we see increase in the amount of Ettringite.

Again that will depend upon the amount of anhydrite or gypsum.

And depending on the C2S content, we can also see a presence of stratlingite, as we have

seen earlier in one of the slides, C2S can react with aluminum hydroxide and form stratlingite.

So here basically the data points, discrete data points are the measurements and the solid

lines, solid and dashed lines the simulated plot using thermodynamic modelling.

So, now we know that Gypsum plays a big role, depending on the amount of gypsum we can either

form monosulphate or ettringite or both of those, right.

So Chinese researchers have developed this formula.

Basically what it says is like based on this M, M is the molar ratio of gypsum to Ye'elimite,

we can develop different types of cements.

Rapid hardening cement, high-strength cement, spans of cement, self stressing cement, right.

So basically if M is from one point five to two point five, the cement will be expansive.

That means there will be increase in volume, okay.

And self stressing system, you have significant expansion that leads to significant compression,

we will come back to it.

But the important point to note is this M plays a big role in governing the volume change,

okay.

So, this conventional way of looking into the shrinkage cracking of the Portland cement

concrete, right.

What happens, you have a fresh concrete, dries and due to restrain there is a tensile stresses

developed.

And that the stress exceeds strength, there is cracking.

Now in CSA concrete, if you want to leverage the expansion, right, suppose you are trying

to formulate mix which expands, what happens, this expansion will lead to some compression,

right, and that compression can then counteract the themselves stresses developed due to shrinkage.

So what I mean, like in self stressing system, in earlier slides, you have the residual compression,

the level of compression will be higher than just expansive system.

So, now if we look into this typical shrinkage versus time plot, in Portland cement we see

some level of shrinkage, right.

It could be five hundred to six hundred microns, micro strain depending on the drying conditions.

But in the expansive systems based on CSA, because of this expansion at early-age, basically

we are reducing the net shrinkage, right.

So the net, there is a reduction in net shrinkage when you CSA cement as an expansive agent.

So the point is, we know that there are advantages in terms of reducing CO2 footprint, right,

less limestone is needed to make this cement, kiln temperature is two hundred degrees Celsius

lower than what you use for Portland cement, the grinding energy is low.

And also by leveraging this early age expansion, we can make this cement shrinkage resistant,

right.

So it can be used to address both issues sustainability and durability.

Now we will go over early age and hydration properties, hardened properties of CSA based

binders.

We will look into fresh properties, how does it compare with conventional concrete based

on Portland cement.

We will look into mechanical properties, also we will look into early-age volume change.

We will also look into how do we model this early-age volume change, okay.

Eventually we will see one application.

So here is like, if you make a concrete using CSA cement because of the formation of Ettringite

crystals, there is a loss in slump.

And if you compare with OPC, right, when you have a CSA in the system, there is a significant

loss in slump.

And obviously in this study no admixture was used initially.

But we see that when you use a retarder, right the CSA with the retarder, you can reduce

this slump loss, right.

And this is the conventional retarder which people use for Portland cement.

And also I would like to point out, this study was done in which like eighty, only fifteen

percent of OPC was replaced.

So it was OPC CSA blend.

And the CSA cement which was used in the study had this phase composition twenty percent

Ye'elimite, thirty five percent C2S, Belite, and calcium sulphate in all forms was around

forty percent.

So we see that there is a loss in workability but can be reduced.

Now if you want to examine, we can use isothermal calorimetry to look into this closely.

So here is the rate of heat evolution in three different binders.

zero percent CSA corresponds to plain OPC, right, now what happens when you add CSA,

fifteen percent CSA, thirty percent CSA?

Now if you zoom out this region, what happens in early few hours, we see that in OPC we

see a dormant period, right, which is very useful when you have to transfer the concrete

by some time.

But in the cement, when you have CSA, you have a shorter dormant period, right.

Again, in the study, no chemical admixture was used.

And as you increase the amount of CSA, we can see the further reducing the dormant period.

This study was published in two thousand and seven addressed this, addressed the issue

of this shorter dormant period by adding citric acid, right.

Citric acid basically what you can see that is a good retarder for CSA cement.

As you increase the amount of citric acid in this system CSA, you are delaying the peak,

right.

Again, so this isothermal calorimetry is a good tool to look into this early-age hydration

kinetics, right.

Now we know that, okay, in the system with three percent retarder, we have delayed the

hydration by four to six hours, okay.

So this is only one example, there are other examples also.

So there are ways you can retard the CSA, the hydration of CSA cement.

Now, since Gypsum is integral part of this the cement what happens sometimes, it is important

to calculate the optimal Gypsum.

We all know that optimal Gypsum for Portland cement is roughly around three to five percent,

right.

So, again isothermal calorimetry can be used to determine this optimal Gypsum.

So, you see 1st this peak, it is because of Gypsum depletion.

When the Gypsum is depleted, this C4A3S or Ye'elimite hydrates very fast and releases

a lot of heat.

Same phenomena happens in Portland cement when you are run out of Gypsum, your C3A can

hydrate, right, very fast and their reaction way, so you want to control that.

So you see that as we increase the amount of Gypsum, right, we are basically delaying

this peak and basically the optimal Gypsum is a content beyond which the isothermal calometry

curve does not change, right.

It is more clear in the later one, if you see the right plot, so the peak, initial gypsum

depletion peak is here and when we add five percent of Gypsum, you see it here, then beyond

that we do not see any change.

So it tells you that, okay, so the optimal Gypsum for this cement is around eight percent,

okay.

Similar thing also can happen when you have mineral admixtures, right.

So, here is the example, what happens, when you have Portland cement, you have CSA cement

and class C fly ash and class F fly ash.

So depending on the chemistry you will see very different behaviour.

So you notice that this shoulder occurring only in the mix where you have class C fly

ash, right.

So as we saw earlier, usually any shoulder after the main peak can be attributed to gypsum

depletion, okay.

Now if you want to verify, is it because of only gypsum depletion, what you can do, you

can simply add additional Gypsum, that’s what we saw here.

So, with five percent additional Gypsum, you delay this peak and eventually add fifteen

percent, we do not even see that peak, okay.

So it was confirmed that this peak was due to the depletion of Gypsum.

Now what caused that depletion?

So class C fly ash basically has C3A tricalcium aluminate.

So that also competes for your Gypsum.

So obviously if you compare with the class F fly ash which does not have C3A, you will

see early depletion of Gypsum in the mix with class C fly ash.

So if we look into this ternary diagram, where we put all sulphates in one corner, like in

the form of Ye'elimite and calcium sulphates, you can combine C4A3S and calcium sulphate,

here is C2S, silicate phase, right and ferrite phase, C4AF.

So, it gives a very good idea like where do you want to be, right.

You do not want to be in this region because you do not have enough C2S, you do not have

enough binding phase, right.

So if you are somewhere here, that means the product you have has low durability.

Also if you are somewhere here, so very far away from C4A3S corner, that means you have

a very small amount of C4A3S, the hardening will be slow, right.

So this just gives you an idea about the sweet spot you want to be in, right.

If you want normal hardening, you want to be somewhere here, if you want rapid hardening,

you want to be somewhere here, right.

Now coming back to the strength, right, the strength of CSA concrete, at least in the

study was comparable to Portland cement concrete, and many researchers, many studies have reported

that.

So, here is the Portland cement concrete and twenty eight days compressive strength, right.

When you just replace OPC with CSA, in this case the replacement was fifteen percent,

small increase but I would say that we can get comparable strength to Portland cement

concrete.

Further, you can also look into the effect of these mineral admixtures, right.

What happens when you add class F Fly ash, class C Fly ash and Silica fume.

Obviously these are the mineral admixtures, take time to hydrate, right the pozzolanic

reaction is slow.

So this is twenty eight days strength, although it is little bit lower, we expected to be

higher if we test it at later ages.

Again, now coming back to other mechanical properties.

If you look into the tensile strength, right, zero percent CSA again corresponds to plain

OPC, seven percent OPC means ninety three percent OPC, seven percent CSA.

So with that age you see increase in strength, right.

So, hydration is occurring and pores are being filled, so you see continuous increase in

strength.

For OPC with CSA, the system also except in the system when you have thirty percent CSA.

So what happens, when you add lot of CSA, like in this case you got thirty percent CSA,

there was a cracking because there was a lot of expansion which took place that led to

this drop, right.

But again the hydration is happening, right, so your cracks are being filled and then you

see again strength increase, right.

Same behaviour we see when we try to monitor the modulus, dynamic modulus, right.

So you can see increase in dynamic modulus for all other systems, except thirty percent

CSA at early-age.

But then because of this continuous hydration, which fills the pores, cracks, right, you

see increase in strength.

But in general, comparable strength, right, will look into this, seven days comparable

strength of OPC CSA cement paste.

And here I would like to mention that this study was done on paste and not concrete.

Also it is important to look into the pore solution, right because the pH of pore solution

dictates a lot of things like corrosion for an example.

CSA cement have lower pH than OPC, but you can see that, at least in the study they reported

around twelve point six to seven pH, right.

I have not seen any study where it was lower than twelve basically, right.

So, yeah it is lower than OPC but not very low, right, to cause corrosion.

This was the study done when CSA was replaced, right.

So you say a zero percent CSA is OPC, we see like thirteen point three two four, the pH

in the range of thirteen point three two four at the end of seven days, okay.

As you increase the amount of CSA, there is a reduction in pH.

But even at thirty percent CSA, what we see that around thirteen pH, okay.

So yes, reduction in pH with increasing CSA cement but it is not too low.

Look into the microstructure, right, we know that there is a formation of Ettringite and

the crystal.

And a lot of formation of Ettringite and we see that there is a lot of crystal needle

extractions, right.

This was the, this was, these are the micrographs seven-day old sample, right.

So, we see a lot of needle structures in both.

Now it is important to look into, because this is it, this is the phase that is giving

you expansion, right.

If you have a lot of Ettringite, you will see expansion.

And we will come, I will look into this, we want expansion just enough to contract shrinkage,

right.

So it is important to look into factors which influence early-age expansion, right.

How can we quantify?

How can we predict basically?

So we know that Gypsum to Ye'elimite ratio is one of the factors governing early-age

expansion, right.

When you do not have enough Gypsum, you will not have expansion.

Then amount of Ettringite, obvious choice, right.

Degree of super saturation with respect to Ettringite is also an important factor.

Okay, so it depends, this is, what is the saturation level of your sulphates, right.

And these can be estimated, if we know the composition of pore solution and using thermodynamic

modelling we can calculate the degree of saturation.

Apart from these chemical factors, we need to also pay attention to stiffness of the

cementitious matrix, right.

It is like, if you compare a stone versus rubber, same amount of expansion happening

in rubber will cause greater expansion, right, compared to stone.

So we need to pay attention to the stiffness of the cementitious matrix.

Now if you look into early-age expansion, here again we are seeing the effect of CSA

addition, right.

It is also important to capture this expansion very early on, a lot of conventional way of

measuring expansion or shrinkage is relying on the one-day Datapoint.

You know, so you cast your sample demould it after twenty four hours, right.

But we know that C4A3S starts reacting immediately and you have formation of Ettringite, you

will see expansions occurring within twenty four hours.

So it is very important to capture that.

For that we can use this corrugated tube, right, which allows you to take measurements

immediately after casting.

So basically you fill your tube with cement slurry and using this gauge you can monitor

the change in length, right.

And what is important is then you can cast the parallel samples, the prisms which you

do and then add this data, okay.

But here is an evidence that the expansion occurring twenty four within twenty four hours

is not insignificant, right.

So depending on your CSA content, you may have significant expansion occurring within

twenty four hours.

Obviously as we increase the amount of CSA cement, we see increase in expansion, right.

And order of magnitude difference, zero percent CSA is OPC, plain OPC, when you add seven

percent CSA n order increase, fifteen percent n order increase, right, thirty percent CSA,

the samples cracked, right.

Because we saw that earlier in mechanical properties also, there was a reduction in

tensile strength and dynamic modulus and samples cracked, okay.

So expansion within twenty four hours is not insignificant, one thing to note.

And there are ways to capture that.

Now, we look into the hydration of Ye'elimite, right, because that is what is causing the

expansion and that is what leads to the formation of Ettringite, monosulphate and other phases.

So here again, comparing the four different samples OPC and sample with CSA.

So you see presence of Ye'elimite, right, why?

It gives you peak at around twenty three point four degree in XRD.

And you can see that as you increase the amount of CSA, this peak is more intense, right.

This is picture at one-day, what happens in one day.

So you still have underrated Ye'elimite after one day, right.

But now if you look at seven days, right, basically Ye'elimite is consumed, there is

no Ye'elimite, right.

So all Ye'elimite has reacted and led to the formation of Ettringite, right.

And in addition to Ettringite, you have other phases like mono sulphate also, right.

And hemi-carbonate may form depending on the conditions.

So important thing to note is that in seven days, the hydration of Ye'elimite is complete.

Now, depending on the use of mineral admixtures.

We saw earlier that in isothermal calorimetry, that class C fly ash behave differently, right

because there was the Gypsum depletion in class C fly ash.

So, the effect of that on expansion is also, is shown here basically.

So when you have class C fly ash in system, the expansion was less compared to the plane

system.

But when you have class F fly ash, the expansion, there was increase in expansion, right.

It again ties back to isothermal calorimetry data.

So these other techniques can be used to understand what is happening, what is the cause of this

expansion behaviour, right.

Again here we see that within twenty four hours, the expansion of occurring twenty four

hours within twenty four hours is not insignificant.

So we all want to predict the expansion depending on the phase completion.

We want to know like how much it system will expand, right.

So this we have already seen when you had class C, class F, this is a plot shown in

the earlier slide.

Now we know that class C fly ash, again going back to isothermal calorimetry, we found that

when we added the Gypsum, the shoulder peak disappear, right.

So, that led to again this increase in expansion.

When you had fifteen percent Gypsum, you see increase in expansion, twenty percent, further

increase.

So this is one of the ways to mitigate this loss in expansion.

Suppose you, your target is to achieve a level of expansion, right, suppose you want to,

suppose you have class F fly ash, you want your system to expand as class F fly ash but

you have class C fly ash, then you can add Gypsum basically.

You know that there is going to be Gypsum depletion in class C fly ash, so we can add

Gypsum and get that expansion back.

And when we try to calculate this calcium, available calcium sulphate, right, we can

calculate that based on the stoichiometry, we can calculate how much calcium sulphate

is available for the hydration of Ye'elimite, right.

And we saw that it was very interesting to that, it was a very nice correlation basically.

So the system which expanded most, as you see has the highest amount of calcium sulphate

available for Ye'elimite.

These are the simple calculations you can do to predict or compare two systems, right.

Because we know that Ye'elimite is reacting with calcium sulphate and forming Ettringite,

that is causing expansion.

So this availability of calcium sulphate can also give you an idea about the expansion.

Since we are talking about the expansion, it is important to look into the mechanism,

right, what is that causing this expansion, what is the origin of it.

So, long time ago, Taber did a very interesting experiment in nineteen sixteen, where he had

a salt in its saturated solution, right and you put weight on it.

Then what happens, when this, due to evaporation yours salt your saturated solution will become

supersaturated.

And that led to the growth in Crystal and that lifted the weight.

The simple experiment tells us that the super saturation gives rise to crystallization stress.

This test was done long time back and we can calculate this crystallization stress, okay.

So what does super saturation do?

Here are the two systems, the low and high super saturation.

First of all we see that super saturation can be linked to the curvature, right.

And we see when you have high super saturation, it allows crystals to grow in smaller pores.

High super saturation means higher curvature, higher curvature means lower radii, right.

So when you have high super saturation, that means your crystals can form in smaller pores.

But when you have low super saturation, that will not happen.

So these two schematics depict that, right.

In high we see the pores being filled, right, the smaller pores being filled.

Now, this maximum crystallization stress can be calculated, right, if we know the super

saturation.

This gives us the upper bound of the stress.

So, if we know the composition of pore solution, and we know the concentration of various ionic

species, we can calculate the saturation index for any phase.

In this case it was calculated for Ettringite, which is the expansion causing phase.

So, you write the what is the ion activity product.

Because the super saturation gives the ratio of ion activity product and solubility product.

So, now if you know these concentrations, right, using any thermodynamic modelling software,

you can calculate the ion activity, right.

And basically this GEMS is a software, relies on the minimization of Gibbs free energy can

give you saturation index of individual face.

But the input is concentration, right.

And we see here now that what happens as you increase the amounts of CSA, you see the increase

in super saturation.

So we saw that super saturation gives rise to crystallization stress.

So when you have higher fraction of CSA, you see increase in saturation index of Ettringite.

People have been relating expansion to just Ettringite content.

But the correlation is very weak.

If you look into any problem related to sulphate attack, delayed Ettringite formation, even

in this case when you have early-age expansion.

So you see these are the data points, each data point is one mix, right.

But same Ettringite content if it is plotted this way, like when you normalize it by capillary

porosity, you see better correlation right.

We will come back to this point why we did this.

But same thing if we know the volume fraction of Ettringite and we know capillary porosity,

that correlation improves.

So, here are some factors which influence the expansion.

We saw this again, SC, I mean, this volume, Ettringite volume fraction in capillary pores

can also be called SC and the relation is, correlation is better.

And there is a good correlation between saturation index and expansion.

Increase in saturation index leads to increased in expansion.

What is interesting here is what we saw is elastic modulus, right.

It is very important to pay attention to the stiffness of the matrix.

A matrix which is less stiff will expand more, right.

So as you increase the elastic modulus, you see reduction in expansion.

Now, there are simple ways, obviously there are a lot of assumptions like matrix being

isotropic and homogeneous, right, or elastic.

We can estimate the tensile stresses.

This is a case of cylindrical pores basically.

And for plain stress condition, what you can calculate is average hydrostatic tensile stresses,

right.

Just to clarify this point, in cylindrical pores we are assuming these are the crystals

right here causing these stresses, right.

So the Sigma C is the maximum crystallization stress from thermodynamics, right.

Now, based on the volume fraction of crystals, you can estimate this, average hydrostatic

tensile strength.

Using poromechanics also we can relate this stress to this Sc factor.

We talked, there was, we saw also very like better correlation of expansion with the SC

factor, we can calculate the tensile stress.

So, now what happens when we try to plot?

So, here is a graph compares the tensile stresses for spherical pores, cylindrical pores, poromechanics,

like these are the three models used to predict the tensile stresses.

And here is the tensile strength, right.

So basically the thirty percent CSA, right, you can see that your, we are saying significant

amount of tensile stress, they exceed strength, right.

So, these are simplistic models but can be useful to predict, so, all models in this

case enables the prediction of failure, especially at high dosage of CSA, that is what we also

verified experimentally, right, when we measure the length change, we saw cracking in the

sample with thirty percent CSA.

Now, question comes, how to design shrinkage compensating concrete.

If you want to design concrete, where you want to leverage early-age expansion due to

the formation of Ettringite, how can you do that?

So this is a guide, this is from American concrete Institute 223R, guide for the use

of shrinkage compensating concrete exists.

And in that also they mention type K cement basically, it is a blend of OPC, Ye'elimite

and calcium sulphate, right.

So, how do you do it?

Basically first we anticipate the shrinkage of concrete, right, based on the experience

of the local area.

Depending on where you are, what are the conditions, right, you know what is the member shrinkage,

right.

So you know suppose this is the shrinkage, particular region, right.

Now this is a curve where you can get based on the percentage of reinforcement, right,

based on the percentage of reinforcement you can calculate how much maximum restraint,

how much expansion you want in the maximum in the restraint concrete prism, right.

So, based on this area you can calculate the maximum expansion in restraint concrete prism.

And how do you do this concrete prism test?

It is basically according to ASTM878, you have this reinforcing bar, right.

You pour your concrete, right, and then measure the early-age expansion.

So basically in this case we are seeing the expansion from point zero percent point zero

six percent, right, depending on what you have.

But then, again you can calculate it if you are somewhere here and your percentage of

the enforcement is here, then you would like to be here, so you want expansion, your expansion

of your concrete prism, restraint concrete prism somewhere here.

So, this is a guide, right, you can use it.

Now will look into the small scale versus large-scale.

Small-scale test, when you do this concrete prism test, right, it compares, you have seen

similar plot before, so this is a conventional concrete, when you do not have any expansion

agent, right.

There is a shrinkage of the order of six hundred in this case six hundred to seven hundred

micro strain.

And you add the calcium Sulfoaluminate cement, see this early-age expansion and the net shrinkage

is close to zero.

But because of this restraint, right, now if you look into the strain level in slab,

the degree of restraint is different, it is high, right.

Although we see some difference but we are not seeing like zero net shrinkage, right.

There is a difference, like OPC is here, we are able to reduce the net shrinkage.

So that is why it is important to pay attention to the degree of restraint, level of, percentage

level of your reinforcement in the slab, when you want to predict.

Now, coming back to the application of CSA base binder, this was a field application

done using OPC CSA cement in Illinois, where two decks were cast side-by-side.

You see normal deck with Portland cement and when we replace Portland cement with CSA,

right.

And what was interesting to see that the deck with CSA did not crack in early-age.

So, there was no cracking, no sign of shrinkage cracking, right.

So it was a successful implementation of CSA concrete.

This is the deck pour, the concrete was fluid, workable, no issue.

So again this was a blend of OPC and CSA cement.

And there was no issue in terms of pouring it in heavy reinforced areas, right.

So, in summary CSA cement can be formulated as expansive or non-expansive cement system

based on users requirement.

If you want to reduce your shrinkage, then you would, you will leverage the early-age

expansion, okay.

And successful field application of the OPC CSA concrete demonstrates its role in enhancing

both sustainability and durability, right.

And the major applications of this cement include in bridge decks, concrete slabs, self-levelling

floors, grouts, repair materials, pressure pipes, etc.

So where we stand now in terms of research?

So, now we need to think about the manufacturing of the CSA based cement using industrial byproducts,

because that will drastically reduce the cost, okay.

Also durability of CSA based concrete against carbonation, corrosion and acid attack is

an active area of research.

As we see the rheology is very important, how can we come up with the new chemical admixtures

that can control the workability of the CSA based cement.

So these are the future possible areas of research.

That, thank you for your attention.