Cement is classified on parameters of strength, grade, and intended use. Portland Pozzolana Cement (PPC) is manufactured by adding Pozzolana (a natural/artificial siliceous/siliceous-aluminous material) to Portland Cement. While most cement suppliers use fly ash, burnt clay or shale may also be used. Such materials do not possess any cementing qualities. When added to portland cement, they react with calcium hydroxide to produce a stable lime that is resistant to chemical damage and moisture. This makes PPC an ideal choice for projects which involve increased exposure to marine water bodies and airborne humidity. OfBusiness offers professional guidance in helping you choose the right cement supplier for your needs.
Every cement supplier generally follows this basic list of ingredients listed below with minor additions or subtractions depending on each situation.
- Puzzolana 45% by weight
- Alite 25% by weight
- Belite 11% by weight
- Tricalcium Silicate 7% by weight
- Gypsum 5% by weight
- Tetracalcium Aluminoferrite 5% by weight
- Sodium Oxide 2% by weight
- Potassium Oxide 2% by weight
There are broadly two types of PPC. Cement containing fly ash as the pozzolana material has been given IS 1489-1 (1991) while a cement supplier using calcined clay receives an IS 1489-2 certification under the Bureau of Indian Standards.
The Manufacturing Process
Crushing and Grinding
Limestone and clay are first crudely crushed at the quarry and then transported to various plants for fine grinding and homogenization. Each cement supplier has its own sources based on the geographical location of the processing plant. What is however important is the proper homogenization of the mixture and its storage. The storage silos use compressed air outlets at the bottom and/or rotating arms to keep the mixture “ignited”.
Clinker Calcination
The mixture is pre-heated to temperatures up to 1000°C where the Calcium Carbonate gets converted to Calcium Oxide. This pre-heated mixture is then raised to temperatures of 1450°C to create clinkers in the mixture.
Final Additions
These clinkers (solid globules) are then cooled, mixed with gypsum, and pozzolanic material and ready for transportation.
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General Properties
The initial setting time of PPC is ~30 minutes and the final setting can take up to 10 hours. Compressive strength across various stages is 13 MPa at 3 days, 22 MPa at 7, and 33MPa at 28 days. The maximum permissible drying shrinkage is 0.15%. PPC has a relatively slower strength development rate as compared to ordinary portland cement but is used for its high tolerance of exposure to water, sulfate, and carbonic acid attacks.
Advantages of PPC
- The insoluble cemented lime created in the process makes the structure impervious to water damage and leakage issues. Cement suppliers stress the use of PPC in marine constructions like docks, dams, shipyards, etc.
- PPC has lower permeability as the water-soluble calcium hydroxide gets used during the process.
- PPC generates lower heat during the hydration process. This decreases the formation of micro-cracks and fissures during the setting process, creating a sturdier structure.
- The addition of fly ash reduces raw material costs making PPC a more economically viable alternative. 25% of the costlier clinker on average gets replaced.
- Prolonged exposure to moisture actually aids in an extended pozzolanic reaction which ultimately surpasses ordinary Portland cement after 90 days.
PPC’s Disadvantages
- Owing to its longer setting time, there is higher room for distortion in the structure initially.
- A lower rate of strength development means it reaches maturity much slower and needs to be monitored longer initially.
- PPC has lower alkalinity, which can endanger structural integrity by corroding steel beams.
- It requires more water during the setting process as the mixture is porous and is mostly fine particles.
Uses of Portland Pozzolana Cement
Most modern hydraulic and marine constructions employ PPC as their primary construction material. A cement supplier may also suggest PPC in highly humid environments. In public infrastructure, PPC is extensively used in making Bridge Piers, thick foundations, canals, and sewerage systems.
Every construction project carries its unique challenges. Taking all factors into account, Ofbusiness provides both professional guidance and delivery right up to your location of choice, at the lowest costs possible. We ensure all our vendors are trusted names in the industry and connect you with the best cement supplier based on your location from the comfort of your home.
