Cement and its type mcq
Identify the correct statements.
- i. Expanding cement is used for filling the cracks
- ii. White cement is mostly used for decorative works
- iii. Portland Pozzolana cement produces less heat of hydration
- iv. High strength Portland cement is produced from the special materials
Cubical aggregate has maximum strength in concrete as it has good packing and strength in all direction.
Rounded aggregate is not suitable for concrete.
Flaky means have less thickness, elongated means having more length. These aggregate can be easily crushed and having a minimum strength.
Reasons:
Generally, in normal concrete loads are taken by aggregates only and cement acts as a binder, therefore, a normal concrete can have maximum strength till the aggregates are not broken.
If the aggregates fail under a load before failure of cement sand matrix. The concrete produced with that aggregates will not achieve the desired strength.
So using flaky and elongated aggregates might lead to failure of concrete and hence should be avoided.
Classification of aggregates on basis of shape –
Rounded aggregates / spherical - Rounded aggregates result the minimum percentage of voids (32 – 33%) hence gives more workability. They require lesser amount of water-cement ratio. They are not considered for high strength concrete because of poor interlocking behaviour and weak bond strength.
Irregular or partly rounded aggregates - Irregular aggregates may result 35- 37% of voids. These will give lesser workability when compared to rounded aggregates.
Angular aggregates -
Angular aggregates result maximum percentage of voids (38-45%) hence gives less workability
Flaky aggregates -
When the aggregate thickness is small when compared with width and length of that aggregate it is said to be flaky aggregate. Or in the other, when the least dimension of aggregate is less than the 60% of its mean dimension then it is said to be flaky aggregate.
Elongated aggregates -
When the length of aggregate is larger than the other two dimensions then it is called elongated aggregate or the length of aggregate is greater than 180% of its mean dimension.
Flaky and elongated aggregates -
When the aggregate length is larger than its width and width is larger than its thickness then it is said to be flaky and elongated aggregates. The above 3 types of aggregates are not suitable for concrete mixing
Important Point:
Split tensile strength(fct) = 0.66 × Modulus of Rupture
Due to the difficulty in applying uniaxial tension to a concrete specimen, the tensile strength is determined by indirect methods.
It is the standard test to determine the tensile strength of concrete indirectly as per IS: 5816-1970
A standard test cylinder of a concrete specimen of 300 mm × 150 mm diameter is placed horizontally between the loading surfaces of the compression testing machine.
The compression load is applied diametrically and uniformly along the length of the cylinder until the failure of the cylinder along vertical diameter.
Modulus of rupture:
It is a measure of the tensile strength of concrete beams or slabs.
Flexure strength of concrete is determined as a modulus of rupture. Flexural strength of concrete/ Bending tensile strength of concrete/Modulus of rupture of concrete (fcr) is given by,
fcr = 0.7×√fck
Compressive strength of concrete:
It is determined by the compressive strength test on a standard 150 mm concrete cube in a compressive testing machine as per IS 516: 1959. The test specimens are generally tested after 28 days of casting and continuous curing.
In USA standard cylinder of height to diameter ratio of 2 is taken. (150 mm diameter, 300 mm height) for determining.
It is observed that the Cube strength of concrete is nearly 1.25 times the cylinder strength.
∴ Split tensile strength <Modulus of rupture < Cylinder strength < Cube strength
2P/πDL < 0.7 √fck < Cylinderstrength <fck
1. Pith : It is the inner most part of tree consist of cellular tissue which is used for nourishment of tree in young age.
2. Sapwood : It is outer annual rings between heartwood and cambium layers. It is the living, outermost portion of a woody stem or branch.
3. Heartwood : It is the dead, inner wood, which often comprises the majority of a stem's cross-section.
4. Cambium Layer : It is a thin layer of sap between sapwood and inner bark.
A good building stone has the following properties:
Percentage of wear in the attrition test should not be more than 3
Specific gravity should be at least 2.7
Coefficient of hardness should be greater than 17
Percentage of water absorption by weight of stone should be less than 5
Toughness index should not be less than 13
Crushing strength should be greater than 100 N/mm2
Chemical composition: The various tests are carried out to determine the chemical constituents of cement. Following are the chemical requirements of ordinary cement as per IS: 269- 1998:
Ratio of percentage of alumina to that of iron oxide: This ratio should not be less than 0.66.
Ratio of percentage of lime to those of alumina, iron oxide, and silica: This ratio is known as the lime saturation factor (LSF) and it should not be less than 0.66 and it should not be greater than 1.02, when calculated by the following formula:
Total loss on ignition: This should not be greater than 4 percent.
Total sulphur content-The sulphur content is calculated as SO3 and it should not be greater than 2.75%.
Weight of insoluble residue-This should not be greater than 1.5%.
Weight of magnesia-This should not exceed 5%.
Note:
As per IS 12269: 2013, the loss on ignition for OPC 53 should not be greater than 4%.
As per IS 8112: 2013, the loss on ignition for OPC 43 & 33 should not be greater than 5%.
Colored cement:
Colored pigment is manufactured by mixing of color pigments (5-10 %) with OPC.
The pigment is mixed in a finest powdered state.
The main modern white hiding pigment is Titanium dioxide. Zinc oxide is a weaker white pigment with some important usages.
Some pigments are toxic, such as those used in lead paint. Paint manufacturers replaced lead white with a less toxic substitute, which can even be used to colour food titanium white (titanium dioxide).
Portland slag cement:
This cement is prepared by mixing granulated blast furnace slag, hard burnt gypsum, and cement clinkers in suitable proportions.
This cement offer:
The heat of hydration of Portland slag cement is lower than OPC. Therefore, this cement can be used in mass concreting.
Higher resistance against the attack of chlorides and sulfate.
Better refinement of pore structure.
Higher water tightness. so this cement can be used in the marine structures.
Rapid hardening cement:
It is the type of cement that developed a higher rate of gain of strength and must not be confused with quick setting cement which only set quickly.
The cement attains the strength at the age of 3 days equivalent to that attained by OPC in 7 days.
This Higher strength in the initial stage is attributed to the higher fineness of the cement and increases the proportion of C3S (specific surface area should not be less than 3250 cm2/gm and C3S is approximate 56%).
Application
Pre-fabricated construction
Cold weather concreting
Emergency repair work
Pavement construction
High alumina cement:
This cement is obtained by fusing a mixture, in suitable proportions, of alumina and calcareous materials and grinding the resultant product to a fine powder. The raw material used for the manufacture of high alumina cement is limestone and bauxite.
The proportion of alumina in the cement must not less than 32% and the ratio of the percentage of alumina to that of lime is in the range of 0.85 to 1.3.
The cement offers a higher initial setting time (3.5 hours) and a lower final setting time (5 hours), hence more time is available to work with the cement along with speedy construction.
The cement can also resist high temperatures.
It can resist the action of acid up to a greater extent.
It also offers a higher rate of gain of strength.
When Water and Cement mix, heat is generated. This process is known as Hydration.
Hydration is a chemical reaction in which the major compounds in cement form chemical bonds with water molecules and become hydrates or hydration products.
Major compounds of cement clinker (also known as Bogues compounds) are:
Tricalcium aluminate (C3A): Celite is the quickest one to react when the water is added to the cement. It is responsible for the flash setting. The increase of this content will help in the manufacture of Quick Setting Cement. The heat of hydration is 865 J/Cal.
Tricalcium silicate (C3S): This is also called as Alite. This is also responsible for the early strength of the concrete. The cement that has more C3S content is good for cold weather concreting. The heat of hydration is 500 J/Cal.
Dicalcium Silicate (C2S): This compound will undergo reaction slowly. It is responsible for the progressive strength of concrete. This is also called as Belite. The heat of hydration is 260 J/Cal.
Tetra calcium Alumino ferrite (C4AF): This is called as Felite. The heat of hydration is 420 J/Cal. It has the poorest cementing value but it responsible for long term gain of strength of the cement.
Non-destructive Tests
Non-destructive tests are used to ascertain the quality of hardened concrete (strength, durability, elastic properties), generally following test are characterized as non-destructive test are:
1. Schmidt Rebound hammer test
2. Ultrasonic Pulse velocity test
3. Penetration method
4. Pull out Test method
5. Radioactive and nuclear test method
Destructive Test
In the case of destructive tests, the concrete specimens (cube, cylinder, etc) are loaded till destruction in the laboratory, and strength properties are determined from the tests. The following test are characterized as destructive test are:
1. Compressive strength
2. Tensile strength
Splitting tensile test
Modulus of rupture test
3. Bond strength
Different type of strength of timber:
Compressive strength:
The compressive strength is found to be the highest when acting parallel to the axis of growth.
The compressive strength perpendicular to the fibers of wood is much lower than that parallel to fibers of the wood.
Tensile strength:
Tensile strength along a direction parallel to the grains is found to have the greatest strength that can be developed under any kind of stress.
Tensile strength parallel to fibers is of the order 80.0 to 190.0 N/cm2.
Shearing strength:
Resistance to shear in across direction is found 3 to 4 times greater than that along fibers.
The shear strength along the fiber is found of the order 6.5 to 14.5 N/mm2.
Explanation:
The strength of timber is the highest parallel to the grains and minimum perpendicular to grains.
Timber:
The wood that is going to use for the building. The structure of the wood is:
Pith:
The innermost central portion or core of the tree is called the pith or medulla.
As the plant becomes old, the pith dies up and decays.
Sap Wood:
Outer annual rings between the heartwood and cambium layer are the sapwood.
It is light in color and weight.
It takes an active part in the growth of the trees.
It does not impart any strength.
Cambium Layer:
A thin layer of sap in between the sapwood and inner bark is referred to as the cambium layer.
It indicates the portion of the sap which is yet to be converted into the sapwood.
Bark:
The Outer protective layer or covering provided around the cambium layer is referred as bark.
Bulking of Sand:
The increase in the volume of sand due to an increase in moisture content is known as the bulking of sand. A film of water is created around the sand particles which forces the particles to get aside from each other and thus the volume is increased.
The increase in moisture in sand increases the volume of sand. The volume increase in dry sand is known as the bulking of sand. Bulking of sand depends on the quantity of moisture in the sand and also the size of the particles. Five to eight percent of the increase in moisture in the sand can increase the volume of sand up to 20 to 40 percent. Again the finer the sand is more will be the increase in volume and the increase in volume will be relatively less for coarser sand.
So, From the figure, We can say that With an increase in moisture content, the bulking of sand First increases to a certain maximum value and then decreases.
Fineness modulus of an aggregate is an indicator of the mean size of particles. The coarser the particle, the higher the fineness modulus.
Type of Sand Fineness Modulus Range
Fine Sand 2.2 – 2.6
Medium Sand 2.6 – 2.9
Coarse Sand 2.9 – 3.2
Resins:
The resin is a natural or synthetic compound that begins in a highly viscous state and hardens with treatment
Many different kinds of resins may be used to create a varnish
Natural resins used for varnish include amber, kauri gum, dammar, copal, rosin, sandarac, balsam, elemi, mastic, and shellac
Varnish may also be created from synthetic resins such as acrylic, alkyd, or polyurethane
Typically, it is soluble in alcohol, but not in the water
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Vee - Bee Consistometer
It is the method used to determine the workability of very dry mixes with low workability.
It measures the time required for complete remoulding of concrete in seconds after placed in the mould with a slump cone.
It is expressed in seconds.
Note:
As slump increases, Vee - bee time decreases, and the compaction factor increases as it becomes easier for concrete to flow.
The degree of workability in Vee - Bee test is classified based on the time taken in seconds as shown below:
Degree of workability Vee - Bee degree (seconds)
Extremely low > 20
Very low 12 - 20
Low 6 - 12
Medium 3 - 6
High 0 - 3
Pointing is the finishing of the joints in brick masonry using either cement mortar (1 (cement): 3 (sand)) or lime mortar (1 (fat lime): 2 (sand)).
Facing is an outer layer or coating applied to a surface like brick wall for protection or decorative purpose.
Guinting is the process of repairing the already damaged concrete surface. In this method, cement is mixed with sand in 1: 3 or any other specified proportion and this mixture is applied over damaged concrete surface with a cement gun under some pressure. By doing so, a highly impervious surface is achieved.
Plastering is the process of covering rough walls and uneven surfaces in with a material, called plaster, which is a mixture of lime or cement and sand along with the required quantity of water.
Efflorescence:
It is a whitish coloured powdered deposition of salts on the concrete surface that is formed due to evaporation of water from the concrete.
It is caused when water soluble salts are present in the concrete material, which comes on to the surface while evaporation of water from the concrete.
These salts are sulphate and carbonate salts of calcium and sodium and can come from bricks, cement, aggregates, water, or admixtures.
The following water soluble salts are generally leads to efflorescence:
Calcium Sulphate (CaSO4), Sodium Sulphate (Na2SO4), Calcium Carbonate (CaCO3), Sodium Carbonate (Na2CO3), etc.
∴ Sulphates and carbonates of sodium, and calcium leads to efflorescence, but not due to those of iron.
Stones
Quarrying is the process of removing the rock, sand, gravel or other minerals from the ground in order to use them to produce materials for construction or other uses.
Natural bed of stone is the plane along which stone can easily be split. It thus indicates the plane or bed on which the sedimentary stone was originally deposited.
Dressing of Stone is the working of quarried stone into the shape and size required for use. This can be necessary as stones obtained from quarrying generally do not have the exact required dimensions or finish.
Seasoning of stone means to expose the stone in the open air for a period of 6 to 12 months. It removes quarry sap and makes the stone-hard and compact.
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