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What is Cement?

Cement is a fine, soft, powdery substance, made from clinker ,a mixture of elements found in natural materials such as limestone, clay, sand and/or shale. When cement is mixed with water, it can bind sand and gravel into a hard, solid mass called concrete. Cement is usually grey. White cement is also available, but is usually more expensive.
1. Cement mixed with water, sand and gravel, forms concrete.
2. Cement mixed with water and sand, forms cement plaster.
3. Cement mixed with water, lime and sand, forms mortar.

What is the contribution of constituents of Clinker in Cement?

Clinker

% Constituents

Significance

C3S

45%-75%

Responsible for Early Strength(Contributes the strength of cement up to 28 days)

C2S

7%-32%

Facilitate Latter Strength( Responsible for Progressive Strength)

C3A

0%-13%

Improved concrete resistance to acidic corrosion and erosion effect.

C4AF

0%-18%

Imparts optimum shade to the cement.

What is Portland cement?

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.

What are the different types of Portland cement?

Though all Portland cement is basically the same, five types of cement are manufactured to meet different physical and chemical requirements for specific applications:

  • CEM I  portland cement with a maximum of 5% minor additional constituents – also known as ordinary portland cement or OPC.
  • CEM II portland cement containing varying additions of secondary materials, i.e. fly ash, pozzolana, slag, silica fume, or limestone
  •  CEM III blast furnace cement
  • CEM IV pozzolanic cement
  • CEM V composite cement

What is blended cement?

  • Blended cement is obtained by either intergrading pozzolanic material or slag with clinker along with Gypsum or by blending ground pozzolana or slag with Portland cement. They are also termed as Portland Composite Cements.

What is the difference between Portland cement (OPC) & Portland Composite Cement?

The basic type of cement is called Ordinary Portland Cement (OPC), which bears an ASTM C-150 CEM 1 coding, and usually composed of approximately 95% Portland clinker & 5% Gypsum.
Composite (or blended) Cement contains, besides Portland Clinker and Gypsum, one or more of the following mineral components:
A latent hydraulic component: e.g. Pulverized Fuel Ash (PFA) or Fly Ash (Class C).
A pozzilonic Component: e.g. natural pozzolana, Fly Ash (Class F)
An inert component: e.g. limestone, which usually do not have any real participation in the chemical hydration process and is produced by grinding (separate or compound) or blending of the constituents.

What are the advantages of using Portland Composite Cement over OPC?

In Portland Composite Cement its filler material Fly Ash/ Slag reacts with the free lime (Ca (OH) 2 )generated by cement hydration to form cement-like compounds C-S-H gel, which contribute to strength, impermeability and sulphate resistance .It also contributes to workability, reduced bleeding and controls destructive expansion from alkali-aggregate reaction. It reduces heat of hydration thereby controlling temperature differentials, which causes thermal strain and resultant cracking n mass concrete structures like dams.

Why is the color of PPC sometimes different from OPC?

The colour of PPC comes from the colour of the pozzolanic material used. PPC containing fly ash as a pozzolana will invariably be slightly different color than the OPC.

What is the difference between ASTM & European Standards?

The European cement standard, EN 197, sometimes appears on project specifications. EN 197 cement Types CEM I, II, III, IV, and V do not correspond to the cement types in ASTM C 150, nor can ASTM cements be substituted for EN specified cement without the designer's approval. EN 197 Type CEM I is a portland cement and CEM II through V are blended cements. EN 197 also has strength classes and ranges (32.5, 42.5, and 52.5 MPa). There is no direct equivalency between ASTM and other cement standards of the world because of differences in test methods and limits on required properties.

How the strength of Cement designated?

Compressive Strength or Cement is designated through the PSI stands for "Pounds per Square Inch," and is the common unit of measurement for pressure or in MPa or N/mm2. That means the maximum load recorded per cross-sectional area of Cement-Sand mortar specimen at 28 days.

What is the elaboration of the - BDS EN 197 – 1: 2003 CEM-II/B-M(S-V-L), 42.5 N

What test methods are available to determine the 'Physical Properties' of Cement?

  • Test for Compressive Strength of Cement Mortar
  • Determination of Normal Consistency of Cement.
  • Determination of Initial Setting Time & Final Setting Time of Cement.
  • Fineness Test of Cement.

Define the term 'Compressive Strength', Setting Time & Normal Consistency of Cement?

Compressive Strength of Cement:
Compressive strength is the capacity of a material or structure to withstand axially directed pushing forces. It provides data (or a plot) of force vs deformation for the conditions of the test method. When the limit of compressive strength is reached, brittle materials are crushed.

The most common strength test, compressive strength, is carried out on a 50 mm (2-inch) cement mortar test specimen. The test specimen is subjected to a compressive load (usually from a hydraulic machine) until failure

 

Setting Time of Cement:
Cement, when mixed with water, forms slurry which gradually becomes the less plastic with the passage of time & finally a hard mass is obtained. In this process, a stage is reached when the cement paste is sufficiently rigid to withstand a definite amount  of pressure. Cement at this stage is said to have set & the time required to reach this stage is termed ‘Setting Time’
The term ‘’initial setting time’’ indicates the beginning of the  setting process of cement paste when cement paste starts losing its plasticity.
The term ‘’Final setting time’’ is the elapsed between the moment the water is added to cement & the time when paste completely lost its plasticity and attained sufficient stability to resist certain definite pressure.

Normal Consistency of Cement
The amount of water content that brings the cement paste to a standard condition of wetness is called ‘’normal consistency’’.

What are the reasons for slow or fast setting of concrete or mortar?

Slow or fast setting normally depends on the nature of cement. It could also be due to extraneous factors not related to the cement. The ambient conditions play an important role. In hot weather, the setting is faster, in cold weather, setting is delayed Some types of salts, chemicals, clay, etc if inadvertently get mixed with the sand, aggregate and water could accelerate or delay the setting of concrete.

What controls the setting time of cement?

Setting time of cement is being controlled by the Gypsum (CaSO4 .2H2O) that is actually added to clinker prior to finish grinding. Gypsum controls the C3A compound when water is being added to cement.

What is the difference between setting time and curing time?

Setting time is the time for a specimen of cement to attain a specified degree of rigidity while curing time is the time required for the maintenance of satisfactory moisture content and temp. of the cement specimen so that desired properties develop.

What test methods are available to determine the 'Physical Properties' of Cement?

  • Test for Compressive Strength of Cement Mortar
  • Determination of Normal Consistency of Cement.
  • Determination of Initial Setting Time & Final Setting Time of Cement.
  • Fineness Test of Cement.

What is the Standard Specification of Physical Properties of Cement?

Standard Requirement of  Physical Properties of Cement

Parameters

American Standard

European Standard

 OPC Cement,  ASTM C 150

PCC Cement,ASTM C595

EN-197-1

Compressive Strength Test -Period

Testing Specimen are crushed 3,7 & 28 days

Testing Specimen are crushed 3,7 & 28 days

Testing specimen are crushed after 2 & 28 days

Compressive Strength  Standard requirement

3 days

7 days

28 days

3 days

7 days

28 days

2 days

0

28 days

Psi

Psi

Psi

1760

2740

4060

1800

2900

3620

1450

0

6162.5

Setting Time Standard

Initial = min 45 minute

Initial = min 45 minute

Initial = min. 60 min

Final = max 375 minute

Final = max 420 minute

Final =  max. 720 min

Finness Standard (Sq.m/Kg)

280

280

Not Specified

What makes the cement gray?

The Iron (Fe2O3) content of cement is responsible for the color change. The lower the Iron (3.0%) the lighter its color, vice-versa.

Can we distinguish the brand of cement by its analysis alone? By its color?

We cannot directly distinguish the brand of cement by its analysis or color. However, we can use the analysis just to compare if the cement is ours or not (case to case basis).

Can we gauge the quality of cement by looking at its color? What causes the change in color of cement?

We cannot gauge the quality of cement by just looking at its color. The color of cement is governed by its C4AF content. The higher C4AF the darker cement will be. There is no governing specification for color. The quality of cement can only be gauge after you see the complete physical and chemical characteristics.

WHow do we know if the cement is adulterated or not? What test is required?

Adulteration can be checked by determining its IR (Insoluble Residue) and Loss In Ignition (LOI). Adulteration in cement by adding dust or other materials other than clinker will increase the IR to above 0.75% and increase the LOI to above 3.0%.

What makes high quality cement?

A high quality raw materials plus a high quality process will definitely produce a high quality product.

What are the factors that affect the quality of cement during storage?

The factors that affect cement quality during storage are temperature and humidity conditions, storage time, composition of clinker and gypsum, and fineness of cement. Since cement is a moisture sensitive material, keeping it dry will retain its quality indefinitely A high quality raw materials plus a high quality process will definitely produce a high quality product.

What are the causes of Cement hardening in bags?

Basically, cement hardening in bags occur due to improper handling and storage - moisture is being absorbed.

How should cement be stored?

Precautions that must be taken in the storage of Portland cement are given below in a series of DON'Ts.

  • Do not store bags in a building or a godown in which the walls, roof and floor are not completely weatherproof.
  • Do not store bags in a new warehouse until the interior has thoroughly dried out.
  • Do not be content with badly fitting windows and doors, make sure they fit properly and ensure that they are kept shut.
  • Do not stack bags against the wall. Similarly, don't pile them on the floor unless it is a dry concrete floor. If not, bags should be stacked on wooden planks or sleepers.
  • Do not forget to pile the bags close together
  • Do not pile more than 15 bags high and arrange the bags in a header-and-stretcher fashion.
  • Do not disturb the stored cement until it is to be taken out for use.
  • Do not take out bags from one tier only. Step back two or three tiers.
  • Do not keep dead storage. The principle of first-in first-out should be followed in removing bags.
  • Do not stack bags on the ground for temporary storage at work site. Pile them on a raised, dry platform and cover with tarpaulin or polythene sheet.