Rapid hardening cement is a type of ordinary portland cement only, except for some variations in its compositions. This results in to change in some of the properties too as discussed later on.
From various types of cements available, rapid hardening cement is the one which hardens and attains strength sooner than any other type of cement.
What is Rapid Hardening Portland Cement?
Rapid hardening cement is a special type of cement, which obtains strength earlier than ordinary portland cement.
According to ASTM, it is termed type-III cement. It is similar to type-I cement (OPC), except for its ability to gain strength faster.
As suggested by the name, RHC hardens faster than OPC. The strength attained by OPC in 3 days is achieved by RHC in just 1 day!
Fineness is the main criteria, which majorly differentiate rapid hardening cement from ordinary portland cement.
RHC has rapid rate of strength development- Why?
Rapid rate of strength development in RHC is due to three reasons, which are discussed below-
- Fineness of grinding
- High C3S content
- Low C2S content
1. Fineness of grinding- The fineness of grinding in RHC is very high (325 m2/kg min.), which means more surface area is exposed to water for hydration of cement resulting in rapid hardening and high heat.
2. High C3S Content- The tricalcium silicate is responsible for early strength and hydrates in the initial phase. This plays a major part in rapid strength attainment of RHC. Up to 70% of C3S Content can be found in RHC.
3. Low C2S Content- The dicalcium silicate is responsible for later hydration and strength. It is in lower amount in RHC.
In today’s time, the fineness of cement from above reasons is a priority distinguishing factor for rapid hardening cement.
Chemical Composition of Rapid Hardening Cement
Rapid Hardening Cement composition is given below:
95-100 % portland cement clinker are used while 0-5 % of minor constituents are present. These can be cementitious materials or filler materials, which can enhance workability or water retention capacity of cement.
Chemical Composition of Rapid Hardening Cement i.e. type-III cement, according to ASTM is given below:
| Maximum Compound Composition | % |
|---|---|
| C3S | 56 % |
| C2S | 19 % |
| C3A | 10 % |
| C4AF | 7 % |
Use of Gypsum in Rapid Hardening Cement
Gypsum is added in OPC at the time of grinding to adjust the setting time of cement and to prevent the flash setting of cement.
The manufacturing of RHC permits addition of more gypsum to counteract the negatives of C3S content in RHC and control the rate of setting.
Characteristics of Rapid Hardening Cement
Physical Characteristics of Rapid Hardening Cement
1. Fineness
It is a measure of size of cement particles.
It is expressed in terms of specific surface of cement.
Specific Surface Area of Rapid Hardening Cement is 325 m2/kg.
2. Setting Time
Setting time of cement is related to plasticity of cement paste.
Initial setting time is the time at which cement paste starts losing plasticity. While final setting time is the time at which the cement loses its plasticity completely.
3. Compressive Strength
It is the compressive strength of cement at the end of 28 days. It is an important measure based on which cement is graded.
4. Density
The bulk density of OPC varies considerably depending on how it is stored and handled as voids are considered in it.
For example, during transportation, cement gets consolidated because of vibration, thus increasing bulk density. Hence, cement quantity should always be specified by weight and not volume.
5. Specific Gravity
Specific gravity of cement does not represent the quality of cement in any way.
Specific gravity of cement is used to calculate mix proportions.
6. Heat of Hydration
Quantity of heat liberated on complete hydration of cement at a given temperature in terms of cal/g of hydrated cement is heat of hydration.
Silicates and alumina present in cement react with water forming a binding material which solidifies to form a hard mass. This reaction of cement with water is called hydration of cement.
As hydration of cement is an exothermic reaction, heat is evolved in the process which is called heat of hydration. It is around 120 cal/g.
Total heat of hydration remains constant for cement. If more heat is released at earlier stages, less heat is evolved later.
About 50 % of total heat is liberated between 1 and 3 days. Around 75 % heat is liberated by 7 days. 83-91 % of the heat is liberated within 6 months.
7. Soundness of cement
Some constituents in cement undergo expansion after the setting of cement. This is an undesirable phenomenon as the expansion of constituents after setting may cause cracks in cement.
The cement exhibiting expansion of its constituents is unsound cement.
For RMC, the Le Chattlier value should not be more than 10 mm while Autoclave value should not be more than 0.8 %.
Chemical Characteristics of Rapid Hardening Cement
1. Lime saturation factor
The minimum lime saturation factor for RHC is 0.66 %.
The maximum lime saturation factor RHC is 1.02 %.
2. Alumina iron ratio
The minimum alumina iron ratio for RHC is 0.66 %.
3. Insoluble residue
The maximum insoluble residue for RHC is 4 %
4. Magnesia
The magnesia content in RHC should not exceed 6 %.
5. Loss on ignition
The loss on ignition should not be more than 5 %.
6. Sulphuric anhydride
Maximum sulphuric anhydride when C3A is less than or equal to 5 is 2.5 %.
When C3A is more than 5, the maximum limit is 3 %.
Properties of Rapid Hardening Cement
The physical and chemical properties of RHC are tabulated below:
Physical Properties of Rapid Hardening Cement
| Physical Properties | OPC | RHC |
| Fineness (min) Specific Surface | 225 m2/kg | 325 m2/kg |
| Soundness (max) Le Chatellier value Autoclave value | 10 mm 0.8 % | 10 mm 0.8 % |
| Setting Time IST (min) FST (max) | 30 min 600 min | 30 min 600 min |
| Compressive Strength 1 day (24 hr) 3 days (72 ± 1 hr) 7 days (168 ± 1 hr) 28 days (672 ± 1 hr) | Nil 16 MPa 22 MPa 33 MPa | 16 MPa 27 MPa – – |
Chemical Properties of Rapid Hardening Cement
| Chemical Properties | OPC | RHC |
| Lime Saturation Factor Minimum Maximum | 0.66 % 1.02 % | 0.66 % 1.02 % |
| Alumina Iron Ratio (min) | 0.66 % | 0.66 % |
| Insoluble Residue (max) | 4 % | 4 % |
| Magnesia (max) | 6 % | 6 % |
| Loss on Ignition | 5 % | 5 % |
Rapid Hardening Cement Specification
The specifications for RHC are mentioned below,
ASTM Standard for Rapid Hardening Portland Cement
RHC is known as type-III cement according to ASTM C 150. Type-III, which is also called rapid hardening cement can be obtained by finer grinding of the type-I cement (OPC).
IS: 8041 – Specifications for RHPC (Rapid Hardening Portland Cement)
IS 8041 specifications for Rapid Hardening Cement:
Physical and Chemical Requirements-
These are mentioned above in Properties of Rapid Hardening Cement.
Storage, Sampling, Testing and Rejection
Storage, sampling, tests and rejection of rapid hardening cement shall be done as laid down in IS 269: 1989 for 33 grade ordinary Portland cement.
Delivery
Cement shall be delivered by packing in the following way-
- Jute sacking bag conforming to IS: 2580
- Multi-wall paper sacks conforming to IS: 11761
- Light weight jute conforming to IS: 12154
- HDPE/PP woven sacks conforming to IS: 11652
- Jute synthetic union bags conforming to IS: 12174
- Composite bag – Approved
Each bag should have net quantity of cement- 50 kg. It can also be available for net quantity of 25 kg.
Marking, Storage, Sampling, Testing and Rejection of Rapid Hardening Cement is done in the same way as OPC. Their specifications can be found here- IS Specifications for OPC
Rapid Hardening Cement Pros and Cons
The advantages and disadvantages of rapid hardening cement are discussed below,
Advantages of Rapid Hardening Cement
- It enables us to load member earlier as rapid hardening cement obtains strength earlier
- It permits early formwork removal so the formwork can be freed earlier and used elsewhere
- It enables construction at lower temperatures
- It facilitates construction under water
- The total construction time can be reduced
- RHC has shorter curing period
- It is quite durable cement
- Safe frost exposure is possible as RMC matures quite early
- It has slightly higher ultimate strength than OPC
Disadvantages of Rapid Hardening Cement
- Mass concreting is not possible as it has high heat of hydration resulting in to cracks due to thermal contractions
- Large structural sections can’t be constructed due to same reason
- It exhibits large shrinkage due to difference in inner and outer temperature
- RHC requires more water for workability requirements comparatively
- Storage and supply of RHC is challenging as even meagre amount of moisture in atmosphere can result in to flash setting of cement
Rapid Hardening Cement Uses
- RHC is used in pre-fabricated concrete construction
- Early stripping of formwork can be done so it can be reused
- RHC is suitable for cold weather concreting
- It is useful for road or bridge repairs as they need early strength
- Fast track construction of structure is feasible so they can be put in to service sooner
- In cold weather places, time for controlled curing is reduced by use of RHC
Applications of Rapid Hardening Cement
- RHC is suitable in cold weather concreting as it has rapid rate of strength development. RHC attains early maturation which leads to early strength. This reduces its vulnerability to frost damage.
- In situations where quick construction is required, rapid hardening cement is a great option.
- The basis of application of rapid hardening cement are its hardening ability and higher heat emission instead of its setting time
- For roads that can’t be closed for longer period of time, quick repair and strength attainment is needed to bear load application in such short period of time
Cost of Rapid Hardening Cement
Many properties of rapid hardening cement are similar to ordinary Portland cement. Type-III cement is akin to type-I cement except for the fineness and hardening properties.
Due to stricter grinding requirements for rapid hardening cement, the cost of RHC is higher than that of OPC. The cost of RHC is about 10% higher than that of OPC.
Key Takeaway
Definition– It is one that gains strength earlier as compared to OPC.
Composition: Its composition is similar to OPC except for C3S and C2S proportions
Manufacture:the manufacturing process resembles that of OPC, however, the clinkers are ground finer.
Characteristics:
Physical Characteristics–
| Characteristics | RHC |
|---|---|
| Fineness (min) | |
| Specific Surface | 225 m2/kg |
| Soundness (max) | |
| Le Chatellier Value | 10 mm |
| Autoclave value | 0.8 % |
| Setting Time | |
| IST (min) | 30 min |
| FST (max) | 600 min |
| Compressive Strength (min) | |
| 1 day (24 hr) | 16 MPa |
| 3 days (72 ± 1 hr) | 27 MPa |
Chemical Characteristics–
| Characteristic | RHC |
|---|---|
| Lime Saturation Factor | |
| Minimum | 0.66 % |
| Maximum | 1.02 % |
| Alumina Iron Ratio (min) | 0.66 % |
| Insoluble Residue (max) | 4 % |
| Magnesia (max) | 6 % |
| Loss on Ignition (max) | 5 % |
Uses/Applications: This is useful for any fast track construction projects as it attains strength very early. This also ensures early stripping of formwork for reuse.
Cold weather concreting is feasible as its high rate of heat of hydration counteract the frost action and the fast hardening rate also reduces time for controlled curing.
Storage: The storage of RHC is challenging as even a meager amount of moisture in the air can set off flash setting.
FAQ
How to make rapid hardening cement?
Rapid Hardening Cement is manufactured in the same way as OPC is Manufactured. But
the grinding of clinkers is done in a much finer way. Additionally, C3S content is more than
that of OPC.
What is rapid hardening cement?
Rapid hardening cement is a type of ordinary portland cement only, except for some
variations in its compositions. This results in to change in some of the properties. The
strength attained by RHC in 1 day is the same as that achieved by OPC in 3 days.
Where we use rapid hardening cement?
Rapid hardening cement is used for fast track constructions, cold weather concreting as
well as repair of roads and bridges. This is because RHC attains strength much earlier
than other types of cement.
Why rapid hardening cement is used?
Rapid hardening cement is used because of its early strength gaining properties,
hardening ability, and higher heat of hydration.
How does rapid hardening cement work?
High strength of rapid hardening cement is due to its fineness. Finer cement particles
provide more specific surface for water to react to. This increases the hydration of cement
liberating more heat of hydration in the early stages. Consequently, the hardening of
cement is quickened.
Besides, it has high C3S content. C3S hydrates in the initial stage while C2S hydrates later
on. Thus increasing C3S content facilitates early strength gain in RHC.
Why rapid hardening cement should not be used for mass concrete?
Rapid hardening cement should not be used for mass concrete because of its high rate of
heat of hydration. due to the high content of C3S, which hydrates in the initial stage high
heat is emitted.