WHAT IS CEMENT ?

  • A finely ground grey powder.

  • An inorganic compound of calcareous and argillaceous materials.
  • Used in combination with sand, aggregates, water and admixtures to get a versatile and economical construction material called "concrete".
  • It is the main compound which binds all ingredients and gives strength to the concrete.

BASIC PRECAUTIONS FOR STORAGE OF CEMENT

Portland cement is a finally ground material. It therefore readily absorbs moisture even from the atmosphere. It is essential to protect it from dampness during storage. Lack of proper care may cause setting of cement or reduction in its strength due to partial setting.

Following precautions must be takes in storing cement.

  • Cement should be stored in dry weather tight place that is properly ventilated.
  • Cement should not be placed directly on floor but on wooden platform or planks.
  • Cement should be placed at some distance from the walls to avoid moisture penetration.
  • Cement bags should not be piled to a height exceeding 2 m.
  • The strength of cement will decrease on long time storage.

WHICH CEMENT TO USE ?

Of late, the consumer is confronted with a wide variety of cement in the market and has to make a choice. In the market, we have Ordinary Portland Cement ( OPC ) and the blended cement either as PPC or slag cement. Even in Ordinary Portland Cement, we have gradations as 43 grade and 53 grade.

DEFINITION OF OPC

Cement can be defined as the bonding material having cohesive & adhesive properties which makes it capable to unite the different construction materials and form the compacted assembly. Ordinary/Normal Portland cement is one of the most widely used types of Portland cement.

COMPOSITION OF OPC

The chief chemical components of ordinary Portland cement are:

  • Calcium
  • Silica
  • Alumina
  • Iron

USES OF OPC (ORDINARY PORTLAND CEMENT):

It is used for general construction purposes where special properties are not required. It is normally used for the reinforced concrete buildings, bridges, pavements, and where soil conditions are normal.

It is also used for most of concrete masonry units and for all uses where the concrete is not subject to special sulfate hazard or where the heat generated by the hydration of cement is not objectionable. It has great resistance to cracking and shrinkage but has less resistance to chemical attacks.

TESTS ON ORDINARY PORTLAND CEMENT

  • Fineness test
  • Soundness test
  • Setting time test
  • Strength tests

    • Compressive strength test
    • Tensile strength test
    • Flexural strength test
  • Specific gravity test
  • Consistency test
  • Heat of hydration test
  • Loss of ignition test

ENVIRONMENTAL IMPACT OF ORDINARY PORTLAND CEMENT:

There are lots of environmental impacts of Cement on our ecology. One of the major problems is emission of CO2 from the Cement industry. It is found that world yearly 1.6 billion tons production of cement covers 7% of carbon dioxide's yearly production.

As CO2 is harmful for human health and also for the wild life. It causes many respiratory problems like asthma, bronchitis, and nasal infections.

  • Produces highly durable and sound concrete due to very low percentage of alkalis, chlorides, magnesia and free lime in its composition.
  • Almost negligible chloride content results in restraining corrosion of concrete structure in hostile environments.
  • Significant saving in cement consumption while making concrete of grades M15, M20, M25, M35 and pre-cast segments due to high strength.

WHICH CEMENT IS BETTER OPC CEMENT OR PPC CEMENT ?

  • Well, both types of cements have got merits of its own.
  • OPC is pure type cement releasing heat energy at a faster rate & the chances of shrinkage cracks are higher.
  • PPC is low heat cement in comparison to OPC requiring lesser degree of immediate post concrete setting curing.
  • OPC is not suitable for hot weather conditions.
  • PPC is suitable for adverse weather conditions.
  • OPC cannot be used for thick & massive elements.
  • PPC is to some extent suitable for thicker elements.
  • Temperature controls are better conducted on PPC.

PORTLAND POZZOLANA CEMENT (PPC CEMENT)

The Portland Pozzolana Cement is a kind of Blended Cement which is produced by either intergrinding 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.

The Portland Pozzolana 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.

Portland cement is composed of calcium silicates and aluminate and aluminoferrite It is obtained by blending predetermined proportions limestone clay and other minerals in small quantities which is pulverized and heated at high temperature - around 1500 deg centigrade to produce 'clinker'. The clinker is then ground with small quantities of gypsum to produce a fine powder called Ordinary Portland Cement (OPC). When mixed with water, sand and stone, it combines slowly with the water to form a hard mass called concrete.

PPC - PORTLAND POZZOLANA CEMENT

Portland Pozzolana Cement (PPC) is obtained by either intergrinding a pozzolanic material with clinker and gypsum, or by blending ground pozzolana with Portland cement.

Nowadays good quality fly ash is available from Thermal Power Plants, which are processed and used in manufacturing of PPC. Higher durability of concrete structure due to less permeability of water.

  • More resistance towards the attack of alkalies, sulphates, chlorides, chemicals.
  • Better work ability.
  • Low heat of hydration.
  • Due to high fineness, PPC has better cohesion with aggregates and makes more dense concreteness.
  • Comparative lower Water-Cement ratio provides an added advantage for the further increase of compressive strength of the concrete.
  • Better surface finish.

PORTLAND SLAG CEMENT

This is a slag-based blended cement that imparts strength and durability to all structures. It is manufactured by blending and inter-grinding OPC clinker and granulated slag in suitable proportions as per our norms of consistent quality. PSC has many superior performance characteristics which give it certain extra advantages when compared to Ordinary Portland Cement

WHAT IS SPECIAL ABOUT PSC ?

Compared to OPC, PSC imparts some important additional advantages

  • Reduction in free lime leaching.
  • Ultimate higher strength.
  • Improved workability, reduced bleeding as well as segregation and corrosion.
  • Denser, less permeable concrete, and mortar.
  • Better resistance to sulphates, chlorides, and CO2 and alkali-aggregates reaction.
  • Less heat, reduced plasticity and drying shrinkage.
  • Increased static modulus of elasticity.
  • Increased serviceability with less deflection of members and micro cracks and reduced cost of construction and maintenance.

WHAT ARE THE MAJOR ADVANTAGES OF BLENDED CEMENTS (PPC/PSC)
OVER OPC/GRADED CEMENT ?

  • Continuous increase in strength with time
  • Increased resistance against sulphate attack
  • Improved workability
  • Better cohesiveness of fresh concrete
  • Reduced heat of hydration and thermal cracking
  • Reduced corrosion of concrete
  • Better water tightness
  • Reduced Alkali - Silica reaction
  • Better resistance to mild acidic water and aggressive environment
  • Low drying shrinkage

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