Important Notes - Cement & Concrete

 Important Notes

Building material Civil Engineering

Content on this page

• About OPC, 
• Standard IS code for RCC, 
• Ultrasonic pulse velocity test for concrete, 
• Slump test, 
• Slump value, 
• Steel and its content, 
• Workability, 
• Different Type of slump, 
• Admixtures and its example, 
• Water used in RCC, 
• Plasticizer, 
• Soundness test etc.

The approximate composition of iron oxide in ordinary Portland cement is about _____   0.5% to 6%

Oxide and its Percentage Content On Ordinary Portland cement

CaO                60 - 67

Si02                17 - 25

Al2O3                03 - 08

Fe2O3                0.5 - 6.0

MgO                0.1 - 4.0

Alkalies               0.4 - 1.3   (K2O, Na2O) alkalies

SO3                1.3 - 3.0

In India, concrete mix design for RCC is carried out using IS _______ code.     10262

The various Indian Standard code related to cement and concrete test, mix design, etc.

IS 10070 – 1982: Specification for machine for abrasion testing of coarse aggregates

IS 10079 – 1982: Specification for cylindrical metal measures for use in tests of aggregates and concrete

IS 10086 – 1982: Specification for moulds for use in tests of cement and concrete

IS 10262 – 2009: Guidelines for concrete mix proportioning

IS 10510 – 1983: Specification for vee-bee consistometer

IS 10850 – 1984: Specification for apparatus for measurement of water retaintivity of masonry cement

IS 10890 – 1984: Specification for planetary mixer used in tests of cement and pozzolana

IS 11262 – 1985: Specification for calorimeter for determination of heat of hydration of hydraulic cement

Ultrasonic pulse velocity test of concrete:

It is a non-destructive test. The ultrasonic pulse velocity method as described for green concrete can also be used to determine the strength of hardened concrete. The flaws, quality of concrete, reinforcement, moisture content, temperature of concrete materials etc. affect the pulse velocity and suitable adjustments should be made in evaluating the concrete strength. Ultrasonic pulse velocity test is not used to measure the strength of wet concrete.

Quality of concrete and pulse velocity:

General condition        Pulse velocity(m/sec)

Excellent    Above        5000

Good                             4000-5000

Questionable                3000-4000

Poor                              2000-3000

Workability:

The ease and homogeneity with which a freshly prepared concrete can be mixed, placed, compacted and finished are called workability.

For low workability concrete, the most suitable test is either Vee-bee Consistometer test or Compaction factor test.

As mentioned, its a complex property which involves many factors concerning the good workable concrete. To test the freshly mixed concrete workability, the following tests are usually performed on field and lab.

• Slump test
• Kelly ball test
• K slump test
• Vee bee consistometer test
• Flow table test.
• Compaction factor test

Important Points:

For highly workable concrete, the most suitable test is a flow table test.

For medium workable concrete, slump cone test is favourable.

J-Ring Test is conducted to check whether the given concrete sample is self-compacting concrete or not.

Slump test

A slump test is the simplest test to determine the workability of concrete, involves low cost and provides immediate results.

It is used to measure the consistency/plasticity of the concrete mix.

IS 456 has given the following values of slumps for different workability of concrete.

Slump Test

Degree of        Workability	Slump value  in mm
Very low	Less than 25
low	25-75
medium	50-100
high	75-100
very high'	100 – 150

It can be defined as the difference between the height of the concrete before removing slump cone (mould) and height of the concrete after removing of slump cone as measured during concrete slump test.

Different types of slump

Collapse slump: 

In this case, fresh concrete collapses completely. The mix is too wet or high workability mix, slump test isn’t appropriate for such mix.

Shear Slump: 

If one-half of the cone slides down in an inclined plane, it is called a shear slump. It is an indication of the lack of cohesion of the mix. Again perform the experiment to avoid a shear slump.

True Slump: 

Mix has high stiff consistency. In a true slump concrete just subsides shortly and more or less maintain the mould shape. This type of slump is most desirable.

Zero Slump:

 If concrete maintains the actual shape of the mould, it is called zero slumps which represent stiff, consistent and almost no workability.

Flow table test of concrete to test workability of concrete

Flow table test of concrete:

As the name suggests, in this test the workability of concrete is determined by examining the flowing property of concrete.

Flow table test of concrete also determines the Quality of Concrete concerning its consistency, cohesiveness and the proneness to segregation.

As there are two methods to find the flow value of concrete which one is outdated. Here we are explaining the new method of flow table test. This new flow table test is covered with BS 1881 part 105 of 1984 and DIN 1048 part I.

Apparatus of Flow Table Test:

Flow table made of metal having thickness 1.5mm and dimensions 750mmx 750mm, tamping rod made of hardwood, Scoop, Centimeter Scale, Metal Cone or mould (Lower Dia = 20cm, upper Dia = 13 cm, Height of Cone = 20cm). The middle portion of flow table is marked with a concentric circle of dia 200mm to place a metal cone on it. A lift handle

The more details about Flow table is depicted in the below image go through it if required.

Procedure of flow table test:

• Prepare concrete as per mix design and place the flow table on a horizontal surface.
• Clean the dust or other gritty material on Flow table and Sprinkle a hand of water on it.
• Now place the metal cone at the middle portion of the flow table and stand on it.
• Pour the freshly mixed concrete in the mould comprising two layers; each layer should be tamped with tamping rod for 25times. After tamping the last layer, the overflowed concrete on the cone is struck off using a trowel.
• Slowly, lift the mould vertically up & let concrete stand on its own without any support.
• The flow table is raised at the height of 12.5mm and dropped. The same is repeated for 15times in 15secs.
• Measure the spread of concrete in Diameter using centimetre scale horizontally and vertically. The arithmetic mean of the two diameters shall be the measurement of flow in millimetres.

Formula for Flow value of concrete:

• Flow value of concrete = (D1+D2)/2

---

Air entrained concrete 

        is made by mixing a small quantity of air entraining agent or by using air entraining cement.

These air entraining agents incorporate millions of non-coalescing air bubbles, which will act as flexible ball bearings and will modify the properties of plastic concrete.

Properties improved are:

Workability,

 segregation, 

bleeding 

and finishing quality of concrete.

Types of air entraining agents used in concrete are: 

Natural wood resins, 

Animal 

and vegetable fat oils 

etc.

Property of water used for making concrete:

a) As per IS 456:2000 Ph of water is > 6 and water used for mixing and curing shall be clean and free from injurious amounts of oils, acids, alkalies, salts, sugar, organic materials, or other substances that may be deleterious to concrete or steel.

b) Natural water or freshwater rarely contains more than 2000 ppm of dissolved solids and is generally suitable for making concrete.

c) Water contaminated with industrial wastes, but free of suspended solids is also suitable at low concentrations for making concrete.

d) Much larger contents of the impurities, in natural water can be tolerated except for the alkali carbonates and bicarbonates which may have significant effects even less than or equal to 2000 ppm.

e) Other inorganic impurities of possible industrial origin, that may be detrimental at moderate concentrations are sulfides, iodides, phosphates, arsenates, borates, and compounds of lead, zinc, copper, tin, and manganese are adversely affected.

Soundness Test:

The soundness of cement may be determined by two methods, namely Le-Chatelier method and autoclave method.

Expansion of cement is measured/computed by soundness test. Soundness means the ability to resist volume expansion and it is indication durability.

The unsoundness in cement is due to the presence of an excess of free lime than that could be combined with acidic oxide at the kiln.

The Le-Chatelier test detects unsoundness due to free Lime only. This method of testing does not indicate the presence and after effect of the excess of magnesia.

As per Indian Standard specification, if the content of magnesia is greater than 3% in cement then Autoclave Test is performed which is sensitive to both Lime and Magnesia.

For quality control of Portland cement, the test essentially done is

1) Le Chatelier Test: 

This test is used to measure the soundness of OPC due to lime. Lime & Magnesia are two primary compounds responsible for the soundness of cement.

2) Blaine Air Permeability:

 It is used to measure the fineness of the cement.

4) The Vicat Apparatus: 

It is used to measure setting time and consistency of concrete.

5) Tensile (Briquette) Testing Machine: 

It is used to measure the tensile strength of the concrete.

As per IS 1077:1992, clause 4.1:

The common burnt clay bricks shall be classified on the basis of average compressive strength. As per the code bricks are classified based on its designation from 35 to 3.5.

Where, Class designation 35 represents average compressive strength of 35 N/mm2.

Similarly, Class designation 10 represents average compressive strength of 10 N/mm2.

As per IS 1077: 1992, clause 7.3, 

The rating of efflorescence shall not be more than 'moderate' up to class 12·5 and 'slight' for classes higher than 12.5.

The common burnt clay bricks shall be classified on the basis of average compressive strength as given by

Class designation Avg compressive strength not less than (N/mm2)

35                         35

30                         30

25                         25

20                         20

17.5                        17.5

15                         15

12.5                         12.5

10                         10

7.5                         7.5

5                         5

3.5                         3.5

 

Cement

Cement is important for construction activity like building houses, factories, bridges, roads, airports, dams and for other commercial establishments.

This industry requires bulky and heavy raw materials like limestone, silica, alumina and gypsum. 

Coal and electrical power are needed for production and rail for transportation.

When cement is mixed with water, it becomes hard over a period of time. This is called the setting of cement.

Gypsum is usually added to cement to prevent early hardening or “flash setting”, allowing extended working time. 

Gypsum is added in cement to increases setting time of cement.

Some other type of admixtures:

Plasticizers

Plasticizers are a mixture of organic and inorganic substance which permits the reduction in W/C ratio at the same workability or ensure higher workability at the same W/C ratio.

Example:

 lignosulphate, polyglycol ester, carbohydrates, hydroxylated carboxylic acid 

superplasticizer

superplasticizer is the same as that of plasticizer in terms of their action but in chemical reaction they are different

Example: 

modified lignosulphonate, sulphonated malanie formaldehyde ( SMF ), sulphonated napthalene formaldehyde

Retarders

Retarders are the admixture that slows down the chemical reaction of hydration so that concentration can remain plastic and workable for more duration in comparison to the concentration in which retarders not added.

Example: 

Gypsum, calcium sulphate, tartaric acid, starch, sugar cellulose

Accelerators

These are the admixture which increase the rate of gain of development of strength in concrete.

Example: 

calcium chloride, silicates, flousilicate etc.

Air-entraining admixture

These are the type of admixtures that entrapped million of an air bubble in between the voids of the aggregate, which act as the flexible wall bearing that slips pass over each other thereby modified the properties of concrete with respect to workability, frost action, seggregation, bleeding.

Example: 

Natural wood resin, plant and animal fatty oil, stearic acid, oleic acid, hydrogen peroxide, aluminium powder

Thermoplastic

The material that softens when heated above the glass transition temperature or melting temperature and becomes hard after cooling is called thermoplastic.

The different types of thermoplastic are 

Acrylonitrile Butadiene Styrene (ABS),

Acetals, Acrylics, 

Cellulosics, Fluorocarbons, 

Polyamides, 

Polycarbonates, 

Polyethylene (PE),

Polypropylenes (PP), 

Polystyrenes, 

Polyvinyl Chloride (PVC) 

and Vinyls.

Polyvinyl chloride (PVC):

This insulating material is a synthetic compound. It is obtained from the polymerization of acetylene and is in the form of white powder. For obtaining this material as cable insulation, it is compounded with certain materials known as a plasticizer which are liquids with high boiling points.

Advantages:

It has high insulation resistance

Good dielectric strength

Mechanical toughness over a wide range of temperatures, hence used in the manufacture of plumbing pipes and furniture

This type of insulation is preferred over VIR in extreme environmental conditions such as in cement factories or chemical factories.

The physical property of steel such as ductility, elasticity, strength, etc are influenced by the following three factors:

i) carbon content

ii) the presence of impurities

iii) heat-treatment process

The usual composition of steel should be:

Element                Desirable/Allowable Proportion

Carbon                    0.10 to 1.1%

Silicon                    0.30 to 0.40%

Sulphur                    0.02 to 0.1%

Phosphorous            below     0.12%

Manganese            0.3 to 1.00%

There are 3 methods of Ferro cementing are as follows :

Closed Mould system :

• Several layers of meshes are tied together against the surface of the mould which holds them in position while mortar is being filled in. The mould may be removed after curing or may remain in position as a permanent part of a finished structure.

If the mould is to be removed for reuse, releasing agent must be used.

Integrated Mould system :

• Using minimum reinforcement any integral mould is first to be considered to act as a framework. On this mould layers of meshes are fixed on either side and plastering is done onto them from both sides. Precaution should be taken to have firm connection between the mould and the layers filled in later, so that finished product as a whole integral structural unit.

Armature Method :

• In this method the skeleton steel is welded to the desired shape on either of sides of which are tied several layers of stretched meshes. This is strong enough, so that mortar can be filled in by pressing for one side and temporarily supporting from the other side

It provides a reliable protection. It is used to add vivid colours and durability to small crafts.

Composition of Ordinary Portland cement:

1. Lime: 62% – 67%

2. Silica: 17% – 25%

3. Alumina: 3% – 8%

4. Calcium Sulphate: 3% – 4%

5. Iron Oxide: 3% – 4%

6. Magnesia: 1% – 3%

7. Sulphur: 1% – 3%

8. Alkalis: 0.2% – 1%

From the above, the maximum percentage of chemical ingredient of cement is of lime.

Lime-Cement Mortar:

Also known as Gauged mortar.

It is made from cement and lime.

The advantages of lime-cement mortar are increased Water retentivity, workability, bonding properties and frost resistance.

This mortar gives good and smooth plaster finish and is used in buildings.

Mix proportions are given below-