Unique types of cements for desired performance in a given environment are being manufactured by changing the chemical composition of the OPC or by using additives, or by using different raw materials.
Some of the types of cements available in the market are the following:
Fast-hardening Portland cement (IS:8041)
This type of cement has a high lime content and can be obtained by increasing the C3S content, but it is normally obtained from OPC clinker by finer grinding (450 m2/kg). Check the Portland cement guide here
The basis of the application of rapid hardening cement (RHC) is the hardening properties and heat emission rather than the setting speed.
This allows for the addition of a little more plaster during fabrication to control the rate of setting.
Quick-hardening cement reaches the same strength in one day that ordinary cement can achieve in 3 days.
However, it is subject to high shrinkage and the water requirement for its workability is higher.
The cost of quick-hardening cement is about 10 percent more than ordinary cement.
Concrete made with this type of cement can be safely exposed to frost as it matures more quickly.
Properties
| Initial setting time | 30 minutes (minimum) |
| Final setting time | l0 hours (maximum) |
| compressive strength 1 day | 16.0N/mm2 |
| compressive strength 3 days | 27.5N/mm2 |
Quick Hardening Portland Cement Uses
It is suitable for road and bridge repair and when load is applied in a short period of time.
High Alumina Cement
This is not a type of Portland cement and is made by fusing 40% bauxite, 40% lime, 15% iron oxide with a little bit of iron oxide and silica, magnesia, etc, at a very high temperature.
The alumina content should not be less than 32%. The resulting product is finely ground.
The main ingredient of the cement is monocalcium aluminate CA which interacts with water to form dicalcium octahydrate hydroaluminate and aluminum oxide hydrate.
2(CaO.AL2O3.10H2O) + H2O = 2CaO.Al2O3.8H2O + 2Al(OH)2
The dicalcium hydroaluminate gel consolidates and the hydration products crystallize. The rate of consolidation and crystallization is high, which leads to a rapid gain in strength.
Since C3A is not present, the cement has a good resistance to sulfates.
Properties of high alumina cement
It does not have a fast setting : Initial (minimum) setting time is 30 minutes, even up to 2 hours. Final setting time should not exceed 600 minutes.
It reaches strength in 24 hours, high early strength, high heat of hydration and resistance to chemical attack. The compressive strength after one day is 30.0 N/mm2 and after 3 days it is 35.0 N/mm2.
After setting and hardening, there is no free hydrated lime as in ordinary Portland cement. The fineness of the cement should not be less than 225 m2 / kg.
The cement should not have expansion greater than 5 mm.
High Alumina Cement Applications
It is resistant to the action of fire, sea water, acid water and sulphates and is used as refractory concrete, in industries and is widely used for precast concrete.
It should not be used in places where the temperature exceeds 18 ° C.
Supersulfated portland cement (IS:6909)
This type of cement is made by crushing or intimately mixing a mixture of not less than 70 percent granulated blast furnace slag, calcium sulfate, and a small amount of grade 33 Portland cement.
In this cement, the tricalcium aluminate that is susceptible to sulfates is limited to less than 3.5 percent.
Sulfate-resistant cement can also be produced by adding additional iron oxide before firing; this combines with the alumina that would otherwise form C3A, instead forming C4AF which is unaffected by sulfates. S
It is used only in places with temperatures below 40 ° C. The water resistance of supersulfate Portland cement concretes is higher than that of common Portland cements due to the absence of free calcium oxide hydrate.
In supersulfate Portland cements, the latter is bound by slag to calcium hydroaluminates of low solubility and calcium hydrosilicates of low basicity, while Portland cement concretes carry a large amount of free hydrated calcium oxide that can wash out and weaken them.
Supersulfate Portland cement has good frost and air resistance, but is less strong than Portland cement concrete because low-basicity hydrosilicates show a greater tendency to deform from fluctuating humidity and resist the combined action of water and frost less effectively.
Properties of supersulfated portland cement
It has little heat of hydration and is resistant to chemical attacks, particularly sulphates. The compressive strength should be as follows:
72 ± 1 hours 15 N/mm2
168 ± 2 hours 22 N/mm2
672 ± 4 hours 30 N/mm2
It must have a fineness of 400 m2 / kg. The expansion of the cement is limited to 5 mm. The initial setting time of the cement should not be less than 30 minutes and the final setting time should not be more than 600 minutes.
Uses of Super Sufated Portland Cement
Supersulfated Portland cement is used for purposes similar to ordinary Portland cement. But due to its higher water resistance property, it should be preferred in hydraulic engineering installations and also in constructions intended for service in humid environments.
RCC pipes in groundwater, concrete structures in sulphurous soils, sewers carrying industrial effluents, concrete exposed to concentrated sulphates of weak mineral acids are some of the examples of this cement.
This cement should not be used in construction exposed to frequent freeze-thaw or wet-dry conditions.
Sulfate resistant portland cement (IS:12330)
In this type of cement, the amount of tricalcium aluminate is restricted to an acceptably low value (5). Not to be confused with supersulfated cement.
It is made by crushing and intimately mixing together calcareous and clayey and/or other materials containing silica, alumina, and iron oxide. Materials burn at clinking temperature. The resulting clinker is ground to produce cement.
No post-combustion material is added except gypsum and no more than one percent of the air entraining agents are added.
Properties of sulfate resistant portland cement
The specific surface of the cement must not be less than 225 m2 / kg. The expansion of the cement is limited to 10 mm and 0.8 percent, when tested with the Le-chatelier method and the autoclave test, respectively.
Setting times are the same as ordinary Portland cement. The compressive strength of the cubes should be as follows.
72 ± 1 hours 10 N/mm2
168 ± 2 hours 16 N/mm2
672 ± 4 hours 33 N/mm2
It must have a fineness of 400 m2 / kg. The expansion of the cement is limited to 5 mm. The initial setting line of the cement should not be less than 30mm and the final setting time should not be more than 600mm.
Applications and uses of cement
This type of cement can be used as an alternative to pozzolanic cement or Portland slag cement under normal conditions.
However, its use is restricted when the prevailing temperature is below 40 ° C.
The use of sulfate resistant cement is particularly beneficial in conditions where the concrete is exposed to the risk of deterioration due to sulfate attack; concrete in contact with soil or groundwater containing an excess of sulphate, as well as concrete in seawater or directly exposed to the sea coast.
Slag portland cement
This type of cement is made by the intimate grinding of a clinker mixture of Portland cement and granulated slag with the addition of gypsum or calcium sulfate, or by an intimate and uniform mixture of Portland cement and finely ground granulated slag.
Slag is a non-metallic product made up essentially of glass containing silicates and aluminosilicates of lime and other bases, as is the case with blast furnace slag, which is developed simultaneously with the ironin a blast furnace or in an electric cast iron furnace.
Granulated slag is obtained by further processing the molten slag by quenching or by cooling it with water or steam and air.
The slag component in the cement varies between 25 and 65 percent.
Properties of portland slag cement (IS: 455)
The chemical requirements for Portland slag cement are the same as those for Grade 33 Portland cement.
The specific surface of the slag cement should not be less than 225 m2/kg. The expansion of the cement should not be more than 10 mm and 0.8 percent when tested with the Le Chatelier method and the autoclave test, respectively.
Initial and final set times and compressive strength requirements are the same as for ordinary Grade 33 Portland cement.
Uses of portland slag cement
This cement can be used in all places where OPC is used. However, due to its low heat of hydration, it can also be used for mass concreting, eg dams, foundations, etc.
Low temperature portland cement (IS: 12600)
To limit the heat of hydration of low heat Portland cement (LHC), the tricalcium aluminate component in the cement is minimized and a high percentage of dicalcium silicate and tetracalcium aluminum ferrite are added.
The heat of hydration should not exceed 272 and 314 J/g after 7 and 28 days respectively. The rate of force development is slow, but the maximum force is the same as OPC.
To meet this requirement, the specific surface area of cement is increased to approximately 3200 cm2/g.
Properties of low temperature portland cement
Less heat is generated during the setting of low-heat Portland cement. When tested with the Le Chatelier method and the autoclave test, the expansion should not be more than 10 mm and 0.8%, respectively.
The minimum initial setting time must not be less than 60 minutes and the final setting time must not be more than 600 minutes.
The compressive strength should be as follows.
72 ± 1 hours 10 N/mm2
168 ± 2 hours 16 N/mm2
672 ± 4 hours 35 N/mm2
Uses and applications
It is more suitable for high-mass concrete works, such as dams, large raft foundations, etc.