PPC AS REPLACEMENT OF OPC

Ordinary Portland cement (OPC)

The cement produced by inter grinding of cement clinker prepared in rotary cement kiln along with 3-5% gypsum only are called as ordinary Portland cement (OPC).

Depending upon the strength requirement OPC is further classified as OPC-33 grade, OPc-43 grade and OPC-53 grade.

The 43 grade OPC is the most popular general purpose cement in the country today. The production of 43 grade OPC is nearly 50% of the total production of cement in the country.

The 43 grade OPC can be used for following applications:

·        General civil engineering construction work

·        RCC works (preferably where grade of concrete is up to M-30)

·        Precast items such as blocks, tiles, pipes etc.

·        Non- structural works such as plastering, flooring etc.

The compressive strength of cement when tested as per IS code shall be minimum 43 MPa.

Conforming IS 8112-1989 the properties of this cement are given:

Setting time-

Initial setting time – 30 minute (min.)

Final setting time – 600 minute (max.)

Compressive strength –

Age	Compressive strength
3 days	23 MPa (min.)
7 days	33 MPa (min.)
28 days	43 MPa (min.)

Portland Puzzolana Cement (PPC) –

The Portland Puzzolana Cement is a kind of Blended Cement which is produced by either inter grinding of OPC clinker along with gypsum and pozzolanic materials in certain proportions or grinding the OPC clinker, gypsum and Pozzolanic materials separately and thoroughly blending them in certain proportions.

Pozzolana is a natural or artificial material containing silica in a reactive form. It may be further discussed as siliceous or siliceous and aluminous material which in itself possesses little, or no cementations properties but will in finely divided form and in the presence of moisture, chemically react with calcium hydroxide at ordinary temperature to form compounds possessing cementations properties. It is essential that puzzolana be in a finely divided state as it is only then that silica can combine with calcium hydroxide (liberated by the hydrating Portland cement) in the presence of water to form stable calcium silicates which have cementations properties. The puzzolanic materials commonly used are:

• Volcanic ash 
• Calcined clay 
• Fly ash 
• Silica fumes

The Indian standards for Portland Puzzolana Cement have been issued in two parts based on the type of puzzolanic materials to be used in manufacturing of Portland Puzzolana Cement as given below:

IS 1489 (Part 1) 1991, Portland Puzzolana Cement – specification (fly ash based)

IS 1489 (Part 2) 1991, Portland Puzzolana Cement – specification (Calcined clay based)
the quality of flyash or calcined clay to be used in manufacturing of PPC is also specified by BIS in the following standards:

IS 3812 1981 – specification for flyash as puzzolana and admixture
IS 1344 1981 – specification for calcined clay puzzolana
In view of the availability of good quality fly ash in abundant quantity, the use of calcined clay based puzzolana cement is progressively decreasing. The flyash is a waste product of Thermal power Plant which creates disposal problems at Thermal power plant site. The yearly production of flyash in India is about 70 million tonnes per annum. This would increase in future depending upon the new coal based thermal power plants to be installed in the country. The present utilisation of fly ash in production of blended cement in India is meagre.

PPC score better result with ages so it can be complete replace for general uses such as Fly ash is the ash precipitated electrostatically from the exhaust fumes of coal fired power station. The fly ash particles are spherical and are generally of higher fineness than cement so that the silica is readily available for reaction. As per IS 3812: 1981 the percentage of silica and alumina should be minimum 70% and maximum loss on ignition 12%. Much superior quality fly ash is available from Indian thermal power plants than specified in IS code.

The Portland Pozzolana Cement makes concrete more impermeable and denser as compared to Ordinary Portland Cement.

The long-term strength (90 days and above) of Pozzolana cement is better compared to OPC.

The Portland Puzzolana Cement is ideally suited for the following construction.

-Hydraulic structures
-Mass concreting works
-Marine structures
-Masonry mortars and plastering
-Under aggressive conditions.
-All other application where OPC is used.

The compressive strength of PPC as per BIS code at present is equivalent to that of 43 grade OPC.

The PPC being manufactured by ‘India Cements Ltd’ meets the strength requirements of 53 grade.

Setting time –

·        Initial setting time – 30 minute (min)

·        Final setting time – 600 minute (min)

Compressive strength –

Age	compressive strength
3 days	16 MPa
7 days	22 MPa
28 days	33 MPa

Advantages:

PPC has certain distinct advantages over OPC, as listed below:

·        Low heat of hydration reducing chances of surface cracks

·        Longer setting time making it more workable than OPC

·        Ultimate strength higher than OPC

·        Lower porosity imparting the concrete more water tightness

·        Waste utilization making it more environmental friendly buildings, factories, warehouses etc.

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