Portland Pozzolana Cement Manufacturing
What is Portland pozzolana cement? The hydraulic cementitious materials made of Portland cement clinker, pozzolanic material, and a proper amount of gypsum are all called Portland pozzolana cement (PPC cement). It is a kind of blended cement which is manufactured by mixing and fine-grinding silicate cement clinker, pozzolanic material, and gypsum.
Pozzolanic materials contain active silica and aluminum and usually do not have any cementitious properties. But when they are mixed with water and lime at ambient temperatures, they will react with calcium hydroxide to form compounds possessing cementitious properties. The commonly used pozzolanic materials can be classified as natural or artificial:
Natural pozzolanic material: volcanic ash, pumicite, calcined clay, diatomaceous earth, etc.
Artificial pozzolanic material: fly ash, silica fume, rice husk, blast furnace slag, etc.
Their content in Portland pozzolana cement is about 15% ~35%, and gypsum is about 3%-6%.
Portland Pozzolana Cement Properties
- PPC cement needs a long time for curing, and the curing temperature has a significant influence on its strength development. When the temperature is low, the hardening rate becomes slow. While when steam curing or humid heat treatment is used, the hardening is accelerated, so this cement is not suitable for winter construction.
- The initial strength of PPC cement is less, but the final strength is high. This is due to the active silica in the pozzolanic material interacting with calcium hydroxide to produce a large amount of hydrated calcium silicate.
- The water requirement of PPC cement is large because the mixture material is porous and fine particles. The water requirement of standard consistency varies with the type and amount of admixture.
- The setting time of Portland pozzolana cement is relatively long, the initial setting time needs at least half an hour, and the final setting time needs 10 hours at most.
- The drying shrinkage of Portland pozzolana cement should not exceed 0.15%.The fineness of pozzolana cement should not less than 300m2 /kg.
- PPC cement has good compressive strength that can reach 13MPa in 3 days, 22 MPa in 7 days, and 33 MPa in 28 days.
- The hydration rate and hydration heat of PPC cement is low, which is related to the variety and quantity of mixed materials.
- PPC cement has a high resistance to sulfate attack in acid water and carbonic acid environment.
Portland Pozzolana Cement Features
It is environmentally friendly. The material used in the manufacturing process is made of natural recycled waste.
It is economical because 25% of the costly ordinary Portland cement clinker is replaced by cheaper pozzolanic materials.
Portland pozzolana cement is more cost-effective. It gives more volume of mortar than other Portland cement.
It offers all-round durability, has high finesses and better surface finish.
Portland Pozzolana Cement Manufacturing Process
Portland pozzolana cement shall be manufactured by mixing and inter-grinding Portland cement clinker, pozzolanic materials, and gypsum. The manufacturing process is approximately the same as ordinary Portland cement, which can be divided into four processes: raw material crushing, raw material grinding, clinker calcination, and cement grinding.
Raw Material Crushing
Limestone and clay are the main material for Portland cement production. After mining, these raw material stones are unloaded by trucks and sent into crushers for reducing particle size. Then they are piled in a pre-homogenization yard waiting for processing.
Raw Material Grinding
Fine particle size raw materials are fed into the raw mill in a desired proportion for further particle size reduction, then they are stored in silos, meanwhile completing the material blending and homogenization process.
Clinker Calcination
Cement raw meals are sent into a cement rotary kiln to be calcined under a high temperature. After several chemical reactions are produced, some spherical gray particles, what we called clinker, are formed. In cement cooler, these hot clinkers will be cooled to a normal temperature.
Cement Grinding
After cooling, the clinker is mixed with pozzolanic materials and gypsum in a required proportion and then sent to the cement mill for final grinding. The cement powder is usually stored in cement silos, then bagged and stored in the warehouse.
Portland Pozzolana Cement Manufacturing Equipment
In the Portland pozzolana cement manufacturing process, we need a variety of cement equipment. AGICO, as a cement plant supplier in China, offers different cement solutions and cement manufacturing equipment.
AGICO offers Portland pozzolana cement plants from 50-10000 TPD. Please feel free to contact us!
Portland Pozzolana Cement Uses
- Portland pozzolana cement is suitable for concrete works underground, in water, or humid environment, especially for projects requiring impermeability, freshwater resistance, and sulfate corrosion resistance, such as hydraulic structures, marine structures, dam construction, construction near the seashore, sewage disposal construction, etc.
- Because of its poor frost resistance, Portland pozzolana cement is not suitable for low-temperature construction, and nor for the environment subject to freeze-thaw cycles and alternation of drying and wetting.
- Like the ordinary Portland cement, PPC cement is also ideal for general engineering and mass concrete engineering. Due to the large dry shrinkage, it is not suitable for dry areas.
- CCP cement has low early strength so it is ideally suited for general engineering which does not require high early strength.
- PPC cement is available for decoration and artistic structures as its good surface finish.
Comparison of Various Portland Cements
Portland pozzolana cement, portland slag cement, and portland fly ash cement are all made by adding active admixture and an appropriate amount of gypsum based on Portland cement clinker. They are similar in nature and scope of application, so they can be used interchangeably in most cases. However, the physical properties and characteristics of the active admixture are different, which makes the three types of cement have their unique characteristics.
Similarity
Slow setting and hardening, low early strength, and high late strength. The clinker content of the three kinds of cement is small, and the secondary hydration reaction is slow, while their later strength exceeds the ordinary Portland cement of the same grade.
Sensitive to temperature and humidity, suitable for high-temperature curing. When the three types of cement are cured at high temperatures, the hydration of the active mixture and clinker will be accelerated, and the early strength is improved without affecting the development of the later strength. Ordinary Portland cement, although the use of high-temperature curing can improve the early strength, the development of later strength will be affected.
Good corrosion resistance. They have good corrosion resistance and are suitable for the environment containing sulfate, magnesium salt, soft water, etc. However, when the corrosion resistance requirements are high, it is not suitable for the application.
Low hydration heat. The three types of cement have less clinker content and less heat release in hydration therefore they are available in mass concrete works.
Poor frost resistance. Slag and fly ash are easy to bleed to form connected pores. As to pozzolana, it has a large water storage capacity, which will increase the internal pore number. Therefore, the frost resistance of the three types of cement is poor.
Poor carbonization resistance. After hardening, the amount of calcium hydroxide in cement paste stone decreases so the ability to resist carbonation is poor.
Difference
Portland slag cement: Portland slag cement has poor impermeability, large dry shrinkage, and good heat resistance.
- Applicable engineering: concrete engineering with heat resistance requirements.
- Non-applicable engineering: concrete engineering with impermeability requirements.
Portland pozzolana cement: Portland pozzolana cement features good impermeability, large dry shrinkage, and poor wear resistance.
- Applicable engineering: concrete engineering with impermeability requirements.
- Non-applicable engineering: concrete engineering in a dry environment and concrete works with wear resistance requirements.
Portland fly ash cement: Portland fly ash cement has the characteristic of high bleeding ratio, poor impermeability, poor frost resistance, poor wear resistance, and small dry shrinkage.
- Applicable engineering: late loaded concrete works.
- Non-applicable engineering: concrete engineering with impermeability requirements and wear resistance requirements, concrete engineering in a dry environment.
Composite Portland cement: the early strength of composite Portland cement is higher than slag (or pozzolana, fly ash) cement, closes to ordinary Portland cement. It has low hydration heat, good corrosion resistance, impermeability, and frost resistance.
- Applicable engineering: it is more widely applied than ordinary Portland cement, Portland slag cement, Portland pozzolana cement, etc.
