know about portland cement ,history,hydration,manufacturing, new cement technology, types,uses

1. Portland Cement
Portland cement,binding material in the form of a finely ground powder, usually gray, that
is manufactured by burning and grinding a mixture of limestone and clay or limestone and
shale.
History
Portland cement, arguably one of mankind’s most important manufactured materials, was
invented and patented by Joseph Aspdin from Leeds in 1824. Aspdin produced cement by
heating powdered limestone mixed with clay in a furnace,and grinding the resulting clinker
to a powder. He called the product “Portland Cement” because of its resemblance, when set,
to Portland stone, a type of stone quarried on the Isle of Portland. Aspdin’s cement was
improved in 1843 by his son William, by vigorous heating and using better grinding
equipment to handle the hard clinker. To this day, Portland cement is still the most commonly
used cement around the globe
Chemical composition
Portland cement is made up of four main compounds: tricalcium silicate
(3CaO · SiO2), dicalcium silicate (2CaO · SiO2), tricalcium aluminate (3CaO · Al2O3), and
a tetra-calcium aluminoferrite (4CaO · Al2O3Fe2O3). In an abbreviated notation differing from
the normal atomic symbols, these compounds are designated as C3S, C2S, C3A, and C4AF,
where C stands for calcium oxide (lime), S for silica , A for alumina , and F for iron oxide.
Small amounts of uncombined lime and magnesia also are present, along with alkalies and
minor amounts of other elements
Hydration
The most important hydraulic constituents are the calcium silicates, C2S and C3S. Upon
mixing with water the calcium silicates react with water molecules to form calcium silicate
hydrate (3CaO · 2SiO2 · 3H2O) and calcium hydroxide (Ca[OH]2). These compounds are
given the shorthand notations C–S–H (represented by the average formula C3S2H3) and CH,
and the hydration reaction can be crudely represented by the following reactions:2C3S + 6H =
C3S2H3 + 3CH2C2S + 4H = C3S2H3 + CH During the initial stage of hydration, the parent
compounds dissolve,and the dissolution of their chemicalbonds generates a significant amount
of heat. Then, for reasons that are not fully understood, hydration comes to a stop. This
quiescent, or dormant, period is extremely important in the placement of concrete Without a
dormant period there would be no cement trucks; pouring would have to be done immediately
upon mixing.
Following the dormant period (which can last severalhours), the cement begins to harden, as
CH and C–S–H are produced. This is the cementitious material that binds cement and concrete
together. As hydration proceeds, water and cement are continuously consumed. Fortunately,
the C–S–Hand CH products occupy almost the same volume as the original cement and water;
volume is approximately conserved,and shrinkage is manageable.

2. Although the formulas above treat C–S–H as a specific stoichiometry, with the formula
C3S2H3, it does not at allform an ordered structure of uniform composition. C–S–H is actually
an amorphous gel with a highly variable stoichiometry. The ratio of C to S, for example, can
range from 1:1 to 2:1, depending on mix design and curing conditions.
Manufacture of Portland Cement
Cement is usually manufactured by two processes:
 Wet Process
 Dry Process
The two processes are fundamentally similar, except for the fact that in the wet process the
raw materials are ground with water before they are fed into the kiln. All though there was
little difference in efficiency between the two processes,the wet process had the
disadvantages of CO2 emission and more fuel consumption to evaporate the water in the
slurry. This made most cement manufactures prefer the dry process to wet process.
Dry process
1.Mixing of raw material
The first step in the manufacture of portland cement is to combine a variety of raw ingredients
so that the resulting cement will have the desired chemical composition. These ingredients
are ground into small particles to make them more reactive,blended together, and then the
resulting raw mix is fed into a cement kiln which heats them to extremely high temperatures.
Since the final composition and properties of portland cement are specified within rather
strict bounds, it might be supposed that the requirements for the raw mix would be similarly
strict. As it turns out, this is not the case. While it is important to have the correct proportions
of calcium, silicon, aluminum, and iron, the overall chemical composition and structure of the
individual raw ingredients can vary considerably. The reason for this is that at the very high
temperatures in the kiln, many chemical components in the raw ingredients are burned off and
replaced with oxygen from the air. Table 3.3 lists just some of the many possible raw
ingredients that can be used to provide each of the main cement elements.
Calcium Silicon Aluminium Iron
Limestone Clay Clay Clay
Marl Marl Shale Iron ore
Calcite Sand Fly ash Mill scale
Aragonite Shale Aluminum ore
refuse
Shale
Shale Fly ash Blast furnace dust
Sea Shells Rice hull ash

3. Cement kiln dust Slag
The ingredients listed above include both naturally occurring materials such as limestone and
clay, and industrial byproduct materials such as slag and fly ash. From Table 3.3 it may seem
as if just about any material that contains one of the main cement elements can be tossed into
the kiln, but this is not quite true. Materials that contain more than minor (or in some cases
trace) amounts of metallic elements such as magnesium, sodium, potassium, strontium, and
various heavy metals cannot be used, as these will not burn off in the kiln and will negatively
affect the cement. Another consideration is the reactivity, which is a function of both the
chemical structure and the fineness. Clays are ideal because they are made of fine particles
already and thus need little processing prior to use, and are the most common source of silica
and alumina. Calcium is most often obtained from quarried rock, particularly limestone
(calcium carbonate) which must be crushed and ground before entering the kiln. The most
readily abundant source of silica is quartz, but pure quartz is very unreactive even at the
maximum kiln temperature and cannot be used
Grinding and blending prior to entering the kiln can be performed with the raw ingredients in
the form of a slurry (the wet process) or in dry form (the dry process). The addition of water
facilitates grinding. However,the water must then be removed by evaporation as the first step
in the burning process,which requires additional energy. The wet process,which was once
standard, has now been rendered obsolete by the development of efficient dry grinding
equipment, and all modern cement plants use the dry process. When it is ready to enter the
kiln, the dry raw mix has 85% of the particles less than 90 £gm in size.
2.Burning
The next step in the process is to heat the blended mixture of raw ingredients (the raw mix) to
convert it into a granular material called cement clinker. This requires maximum
temperatures that are high enough to partially melt the raw mix. Because the raw ingredients
are not completely melted, the mix must be agitated to ensure that the clinker forms with a
uniform composition. This is accomplished by using a long cylindrical kiln that slopes
downward and rotates slowly
This description refers to a standard dry-process kiln as illustrated in Figure 3-2. Such a kiln
is typically about 180 m long and 6 m in diameter, has a downward slope of 3-4%, and rotates
at 1-2 revolutions per minute.
The raw mix enters at the upper end of the kiln and slowly works its way downward to the
hottest area at the bottom over a period of 60-90 minutes, undergoing severaldifferent
reactions as the temperature increases. It is important that the mix move slowly enough to
allow each reaction to be completed at the appropriate temperature. Because the initial
reactions are endothermic (energy absorbing), it is difficult to heat the mix up to a higher
temperature until a given reaction is complete.
Dehydration zone (up to ~ 450˚C): This is simply the evaporation and removal of the free
water. Even in the “dry process” there is some adsorbed moisture in the raw mix. Although
the temperatures required to do this are not high, this requires significant time and energy. In
the wet process,the dehydration zone would require up to half the length of the kiln, while the
dry process requires a somewhat shorter distance.
Calcination zone (450˚C – 900˚C): The term calcination refers to the process of
decomposing a solid material so that one of its constituents is driven off as a gas. At about
600˚C the bound water is driven out of the clays, and by 900˚C the calcium carbonate is
decomposed, releasing carbon dioxide. By the end of the calcination zone, the mix consists

4. of oxides of the four main elements which are ready to undergo further reaction into cement
minerals. Because calcination does not involve melting, the mix is still a free-flowing
powder at this point.
Solid-state reaction zone (900˚ - 1300˚C): This zone slightly overlaps, and is sometimes
included with, the calcination zone. As the temperature continues to increase above ~ 900˚C
there is still no melting, but solid-state reactions begin to occur. CaO and reactive silica
combine to form small crystals of C2S (dicalcium silicate), one of the four main cement
minerals. In addition, intermediate calcium aluminates and calcium ferrite compounds
form. These play an important role in the clinkering process as fluxing agents, in that they
melt at a relatively low temperature of ~ 1300˚C, allowing a significant increase in the rate of
reaction. Without these fluxing agents,the formation of the calcium silicate cement minerals
would be slow and difficult. In fact,the formation of fluxing agents is the primary reason
that portland (calcium silicate) cements contain aluminum and iron at all. The final
aluminum- and iron-containing cement minerals (C3A and C4AF) in a portland cement
contribute little to the final properties. As the mix passes through solid-state reaction zone it
becomes “sticky” due to the tendency for adjacent particles to fuse together.
Clinkering zone (1300˚C – 1550˚C): This is the hottest zone where the formation of the
most important cement mineral, C3S (alite), occurs. The zone begins as soon as the
intermediate calcium aluminate and ferrite phases melt. The presence of the melt phase
causes the mix to agglomerate into relatively large nodules about the size of marbles
consisting of many small solid particles bound together by a thin layer of liquid (see Figure
3-3). Inside the liquid phase, C3S forms by reaction between C2S crystals and
CaO. Crystals of solid C3S grow within the liquid, while crystals of belite formed earlier
decrease in number but grow in size. The clinkering process is complete when all of silica is
in the C3S and C2S crystals and the amount of free lime (CaO) is reduced to a minimal level
(<1%).
Cooling zone: As the clinker moves past the bottom of the kiln the temperature drops rapidly
and the liquid phase solidifies, forming the other two cement minerals C3A (aluminate) and
C4AF (ferrite). In addition, alkalis (primarily K) and sulfate dissolved in the liquid combine
to form K2SO4 and Na2SO4. The nodules formed in the clinkering zone are now hard, and
the resulting product is called cement clinker. The rate of cooling from the maximum
temperature down to about 1100˚C is important, with rapid cooling giving a more reactive
cement. This occurs because in this temperature range the C3S can decompose back into C2S
and CaO,among other reasons. It is thus typical to blow air or spray water onto the clinker
to cool it more rapidly as it exits the kiln.
3.Grinding of clinker
Once the nodules of cement clinker have cooled, they are ground back into a fine powder in a
large grinding mill. At the same time, a small amount of calcium sulfate such as gypsum
(calcium sulfate dihydrate) is blended into the cement. The calcium sulfate is added to
control the rate of early reaction of the cement,as will be discussed in Section 5.3. At this
point the manufacturing process is complete and the cement is ready to be bagged or
transported in bulk away from the plant. However,the cement is normally stored in large
silos at the cement plant for a while so that various batches of cement can be blended together
to even out small variations in composition that occur over time. Cement manufacturers go
to considerable lengths to maintain consistent behavior in their cements over time, with the
most important parameters being the time to set,the early strength development, and the
workability at a given water content.

5. 4.Storageand packaging
The grinded cement is stored in silos, from which it is marketed either in container load or
50kg bags.
Wet Process
The raw materials are firstly crushed and made into powdered form and stored in silos. The
clay is then washed in washing mills to remove adhering organic matters found in clay.
The powdered limestone and water washed clay are sent to flow in the channels and transfer to
grinding mills where they are completely mixed and the paste is formed, i.e., known as slurry.
The grinding process can be done in ball or tube mill or even both. Then the slurry is led into
collecting basin where composition can be adjusted. The slurry contains around 38-40% water
that is stored in storage tanks and kept ready for the rotary kiln.
Variations of Portland Cement

6. Portland cement that is used for most construction purposes. Other modified varieties of
Portland cement are also manufactured in order to meet various specific construction
purposes/requirements.
Sulphate-Resisting Portland Cement: The presence of heavy sulphate content in ground
water causes damages such as cracking, scaling and expansion to concretes. The use of
sulphate-resisting Portland cement prevents the sulphate from entering the concrete thereby
enhancing its longevity.
White Portland Cement: This type of cement is intended for use in architectural purposes
where white coloured concrete is desired. This differs from the grey cement primarily in
colour. The white colour is attained by controlling the use of ferrite, that which gives cement
its characteristic Grey colour.
Rapid-Hardening Portland Cement:This is similar to ordinary Portland cement,except
that its particles are more finely ground to facilitate quick reaction with water. It is used when
fast strength growth of forms or structures is required.
LowHeat ofHydration Portland Cement: This type of cement develops strength at a
slower rate than other cement types. This cement is used in huge concrete structures such as
dams. These are produced upon specific requests for large projects.
Types of Portland cement
The ASTM has designated five types of Portland cement, designated Types I-V. Physically
and chemically, these cement types differ primarily in their content of C3A and in their
fineness. In terms of performance,they differ primarily in the rate of early hydration and in
their ability to resist sulfate attack. The generalcharacteristics of these types are listed in
Table
Type Classification Characteristic Applications
Type I General purpose Fairly high C3S content for
good early strength
development
General construction
(most buildings,
bridges, pavements,
precast units, etc)
Type II Moderate sulfate resistance Low C3A content (<8%) Structures exposed to
soil or water containing
sulfate ions
Type III High early strength Ground more finely, may
have slightly more C3S
Rapid construction, cold
weather concreting
Type IV Low heat of hydration (slow
reacting)
Low content of C3S (<50%)
and C3A
Massive structures such
as dams. Now rare
Type V High sulfate resistance Very low C3A content
(<5%)
Structures exposed to
high levels of sulfate
ions
White White color No C4AF, low MgO Decorative (otherwise
has properties similar to
Type I)

7. The differences between these cement types are rather subtle. All five types contain about
75 wt% calcium silicate minerals, and the properties of mature concretes made with all five
are quite similar. Thus these five types are often described by the term “ordinary portland
cement”,or OPC.
Types II and V OPC are designed to be resistant to sulfate attack. Sulfate attack is an
important phenomenon that can cause severe damage to concrete structures. It is a chemical
reaction between the hydration products of C3A and sulfate ions that enter the concrete from
the outside environment. The products generated by this reaction have a larger volume than
the reactants,and this creates stresses which force the concrete to expand and
crack. Although hydration products of C4AF are similar to those of C3A,they are less
vulnerable to expansion, so the designations for Type II and Type V cement focus on keeping
the C3A content low. There is actually little difference between a Type I and Type II cement,
and it is common to see cements meeting both designations labeled as “Type I/II”. The
phenomenon of sulfate attack will be discussed in much more detail in Sections 5.3 and 12.3,
but it should be noted here that the most effective way to prevent sulfate attack is to keep the
sulfate ions from entering the concrete in the first place. This can be done by using mix
designs that give a low permeability (mainly by keeping the w/c ratio low) and, if practical,
by putting physical barriers such as sheets of plastic between the concrete and the soil.
Type III cement is designed to develop early strength more quickly than a Type I
cement. This is useful for maintaining a rapid pace of construction, since it allows
cast-in-place concrete to bear loads sooner and it reduces the time that precast concrete
elements must remain in their forms. These advantages are particularly important in cold
weather,which significantly reduces the rate of hydration (and thus strength gain) of all
portland cements. The downsides of rapid-reacting cements are a shorter period of
workability, greater heat of hydration, and a slightly lower ultimate strength
.Type IV cement is designed to release heat more slowly than a Type I cement, meaning of
course that it also gains strength more slowly. A slower rate of heat release limits the
increase in the core temperature of a concrete element. The maximum temperature scales
with the size of the structure, and Type III concrete was developed because of the problem of
excessive temperature rise in the interior of very large concrete structures such as
dams. Type IV cement is rarely used today, because similar properties can be obtained by
using a blended cement.
White portland cement (WPC) is made with raw ingredients that are low in iron and
magnesium, the elements that give cement its grey color. These elements contribute
essentially nothing to the properties of cement paste, so white portland cement actually has
quite good properties. It tends to be significantly more expensive than OPC,however, so it is
typically confined to architectural applications. WPC is sometimes used for basic cements
research because the lack of iron improves the resolution of nuclear magnetic resonance
(NMR) measurements.
Advancement in Portland Cement
While cement production has traditionally been focused on OPC,composite and blast furnace
slag cements have been developed and are now a central part of the cement-type portfolio of
producers. At the same time Portland limestone and Portland pozzolanic cements have gained
importance, especially in regions where slag or fly-ash are not available. In the global context
of cost reduction and CO2 constraints, cement producers strive to lower the clinker content in
their cements. Limits are given by cement performance, so that product quality of the final

8. concrete may not be impaired. shows the different cements types and their calcium oxide,
silicon dioxide and aluminium/iron oxide content.
The reduction of clinker levels in cement predominantly takes into account well-tried and
tested main constituents. While the global availability of latent hydraulic and pozzolanic
materials of industrial origin is certainly limited, a special focus is on cements with high
limestone content.This is basically an extension of the current cement standards as they have
been developed worldwide and certainly provide opportunities for the future. As an example,
research is performed in the context of the European standard with the main focus on strength
development and durability of the concrete produced.shows the range of current cement types
standardised in Europe today and the extension that is currently under research. In any case,
the production of cements with extended use of well tried and tested constituents certainly
requires excellent quality assurance mechanisms as they have been successfully implemented
in the cement industry. In addition, the inherent characteristics of cement production
guarantee large volume flows and good homogenisation resulting in constant product quality.
1.Dry kilns With multistage pre-heater and Pre-calcination
Multistage preheaters and pre-calciners make use of the waste heat from the kiln and clinker
cooler to pre-heat and pre-process the kiln feed, and thereby allow for considerable energy
savings. Whenever economically feasible a wet process kiln can be converted to a state-of-the
art dry process production facility that includes either a multi-stage preheater,or a multi-stage
pre-heater and a pre-calciner. Such transformations are usually feasible for new plants and
major upgrades. Kiln systems with five cyclone preheater stages and precalciner are
considered standard technology for ordinary new plants.
2.Replacing Vertical shaft kilns
For vertical shaft kilns (VSK), which are commonly used in China, switching over to a new
and more efficient suspension preheater/precalciner kiln system offers the main energy
efficiency opportunity. Such replacements may only be feasible when coupled with capacity
expansions.
3. Kiln shell Heat Loss Reduction
The use of better insulating refractories can reduce heat losses. Refractory choice is the
function of insulating qualities of the brick and the ability to develop and maintain a coating.
The coating helps to reduce heat losses and to protect the burning zone refractory
bricks. The use of improved kiln-refractories may also lead to improved reliability of the
kiln and reduced downtime, reducing production costs considerably, and reducing energy
needs during start-ups. Structural considerations may limit the use of new insulation
materials.
4.Proper sealing and Seal Replacement
Seals are used at the kiln in- and out-let in order to reduce unintended air entry to, or escape
from, the kiln. Leakage at the kiln outlet can both lower the combustion efficiency of the
burner and increase heat losses and are thefore of particular importanceAir leakage can be
controlled by employing an appropriate seal - common types include pneumatic, lamella-, and
spring-type seals. Although seals can last up to 10,000 to 20,000 hours, regular inspection
may be needed to reduce leaks..

9. 5.Combustion systemimrovement
Improved combustion systems aim to optimize the shape of the flame, the mixing of
combustion air and fuel and reducing the use of excess air. Different techniques have been
developed to this effect. For rotary kilns, one of such technique, the Gyro-Therm technology
improves gas flame quality while reducing NOx emissions. The technology can be applied to
gas or gas/coal dual fuel burners. The Gyro-Therm burner uses a patented "precessing jet"
technology. The nozzle design produces a gas jet leaving the burner in a gyroscopic-like
processing motion. This stirring action produces rapid large scale mixing in which pockets of
air are engulfed within the fuel envelope without using high velocity gas or air jets. Besides
reducing energy consumption, the technology is reported to help reduce NOx emissions by 30
to 70%, and increase productivity by more than 5%.
5.Cement with Pozzolana
Pozzolana are defined as substances of siliceous or silico-aluminous composition. Finely
ground pozzolanic materials react in the presence of water at normal ambient temperature
with dissolved calcium hydroxide (Ca(OH)2) to form strength-developing calcium silicate
and calcium aluminate compounds. In general, the use of a pozzolana as a main constituent of
cement is possible if the content of reactive silicon dioxide amounts not less than 25% by
mass. Often a differentiation is made between natural pozzolana and natural calcined

10. pozzolana. The production of cements with pozzolana as a main constituent involves the
pre-treatment of the pozzolana like crushing, drying and grinding and the intergrinding or
mixing of the cement clinker with the pozzolanic material. The use of pozzolana as a main
constituent can lead to better workability of the concrete due to a better grain size distribution
as well as to higher long term strength and improved chemical resistance.
6.High Efficiency Separator
Separators and classifiers send larger particles so that they can be sent back to mill for further
grinding. Separators or classifiers with higher efficiency separate larger particles more
accurately and thereby reduce over-grinding and decrease mill energy consumption. By
replacing the external separator to ball mills with higher efficiency external separators,energy
consumption in the mill can be reduced and mill capacity can be increased.
7.Vertical Roller Mills For Finishing Grinding
Ball mills, that are commonly used for finish grinding, have high energy demands,
consuming up to 30-42 kWh/t clinker depending on the fineness of the cement.
Complete replacement of ball mills by vertical roller mills (VRMs) with an integral
separator – as opposed to the use of VRMs as pre-grinding to ball mills – is regarded as
a breakthrough. Use of VRM in finish grinding combines grinding and high efficiency
classification and improves both energy efficiency and productivity.According to MIIT
of China, instability of material bed, vibration in the mill mill, serious wear of grinding roller
and grinding disc, and product quality issues can be encountered when VRMs are used for
finish grinding, and further improvements in these areas are necessary. This technology is
considered to be suitable for new installations as well as for those undertaking major upgrades.
The penetration rate of this technology in Chinese market is reported to be 5% in 2012. This
figure is expected to reach 30% during the twelfth five-year development period. Plants
interested in this technology are advised to carefully consider logistical aspects of
maintenance and parts replacement by technology providers.
8.Emerging Grinding Technologies
There are emerging grinding technologies such as ultrasonic comminution and plasma
comminution. Ultrasonic comminution transfers the energy needed for crushing to the
material by acoustic pulses. This approach was introduced in 2003. Two counter-rotating
disks with special aerodynamic surfaces generate ultrasonic pulses, which due to their small
pulse duration exert pressure waves on the particles which are pulverized very efficiently. The
results from first tests with granulated blast furnace slag of different origins were promising,
but future research remains necessary. The scaling up to industrial dimensions in particular is
an open question. The system has been tested for slag grinding in model scale only. Plasma
comminution is performed in a liquid by using shock waves. The application is tested on
semiconductor materials.
9.High Efficiency Fans For Preheaters
Older generation, low-efficiency, high energy-consuming pre-heater fans can be replaced
with a high efficiency fan resulting in electricity saving.
10.High Pressure Press Rollers

11. In a high-pressure roller press, two rollers pressurize the material up to 3,500 bar, improving
the grinding efficiency dramatically and significantly reducing energy consumption.
High-pressure roller presses are most often used to expand the capacity of existing grinding
mills, and are found especially in countries with high electricity costs or with poor power
supply.This technology is considered to be suitable for both for raw materials grinding and
for finish grinding of cement, as well as ultrafine grinding of blast furnace slag. In China,the
penetration rate of this technology was expected to reach 80% during the eleventh five-year
development period – requiring an investment of 1 billion RMB and holding a potential to
reduce energy consumption by 800 GWh (NDRC,2008. p.49).
11.Cement suspension preheater calcining technology with Highsolid-gas Ratio
A High solid-gas ratio preheater system provides for two parallel twin series of air (laden with
the solid materials) streams,making solid-gas ratio per unit doubled or more for each
preheater,so that the heat consumption of clinker production tends to be close to the
theoretical thermal consumption. The Preheater system is set as a combined multi-level series
of five preheater cyclones in the framework of 2-2-2-2-1, in which gas from each of the five
cyclones flows evenly through each stage of parallel dual series preheater,all the powder
alternately step-wise fed into preheater cyclones from one series to another series,and
solid-gas ratio of the preheater cyclone increased to about 2.0, so that it significantly
improves the heat exchange efficiency of the total preheater system and reduces the exhaust
gas temperature at the preheater exit.
An “External Circulation Calciner” system of high solid-gas ratio adopts a "bypass outside"
approach, in which a certain amount of solid materials exit from the calciner and return to the
calcining furnace, so that large particles of insufficient calcining rate continue to calcine
repeatedly through the high furnace temperature and the more intense heat release area by the
second, third or even fourth times, so that it can increase the calcination rate of material
exiting from the Calciner, reduce the thermal load of the rotary kiln, greatly improve the kiln
production of per unit volume, simultaneously strengthening the thermal stability of
precalciner, and finally reducing harmful gas emissions
According to NDRC,the main technical indicators of this technology include the following
 exhaust gas temperature from Kiln inlet is less than 260 ℃;
 heat energy consumption for clinker making is below 2.85 GJ/t-clinker
(680Mcal/t-clinker);
 power consumption is less than 56kHh/t-clinker;
 operating rate of kiln system is greater than 90%;
 NOx and SO2 contents in exhaust gas are less than 200ppm and 50ppm, respectively
(NDRC,2011. p.36)
Necessities for new technologies
All cements have to fulfil the requirements on durability, strength development, early strength
development, workability, cost and environment. Depending on the cement composition,
these criteria can be fulfilled to different degrees. It is in the hands of the producer to optimise
the different cement types with respect to these categories. The consumer will choose the

12. appropriate cement type for the dedicated construction. Especially for new cements to be
developed in the future, durability is one of the essential requirements. The question of
carbonation resistance,resistance against chloride penetration, only to give a few examples,
must be complied with. In temperate climates durability aspects to a high degree are also
determined by frost-thaw resistance.
Among constituents that might not have developed to their full potential as cement
constituents, calcined clays could play an important role. It is known that these materials
exhibit pozzolanic properties. However,the calcination process is pretty much determined by
the origin and the composition of these clays. Typically, calcination temperatures are in the
range of 700-850°C. Availability on a global scale is good, although in some countries clays
are not available at all.
Future cements
In the literature, quite a few reports are given with respect to new types of cements on a
research scale. Celitement, for example, is based on calcium silicate hybrid phases.
Production is foreseen by hydro-thermal synthesis and by reactive milling of lime in a silicon
component. The Ca/Si ratio is lower than OPC clinker, consequently CO2 emissions and
energy requirements might be lower. However,it is currently much too early to give any
estimation about the future potential of this binder with respect to durability, production cost
or even the technical potential for relevant substitution of current cements.
Novacem has reported a cement based on magnesium oxide and hydrated magnesium
carbonates. According to Novacem,the raw material is based on magnesium silicates which
are digested and subsequently carbonated at elevated temperature and pressure. While
magnesia-based cements have been known for a long time, it is an open question whether in
the end Novacem will provide sufficient durability to substitute relevant amounts of today's
cement. Novacem indicates that significant research has to be done, but has made significant
progress to date.
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