Building Materials

Interview Questions on Building Materials

BRICKS

  1. Composition of brick earth –

Silica or Sand 50-60%– Prevent Shrinkage, Cracking and wrapping but too much quantity can make the brick brittle.

Alumina or Clay 20-30%– It make the brick earth plastic and provide the brick its hardness.

Lime and Oxide of Iron – Malt the sand grains and bind the clay particle when heated. Iron oxide provide the brick its red color.

Magnesia – Small quantity desirable but excess makes the brick yellow.

  • Burning Temperature – 800-10000C
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  • Strength of 1st Class, 2nd Class and 3rd Class, Jhama bricks – 10.5N/mm2  7.5 N/mm2 5.5 N/mm2
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  • Water absorption – First Class < 20% (Preferable below 15%) 2nd Class < 22% 3rd Class < 25%
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  • Frog Size and Its position in masonry – 100x40x 10-20 mm

Frog acts as a key to the joint of brick and mortar.  

  1. Stones used in civil engineering and their strength –

Granite – Abutment and Pier of Bridge,

Stand Stone – Ashlar Masonry

Marble – Floor and Ornamental Work.

  • Why bricks are soaked before their use in brick masonry?

Dry brick absorb water and to prevent water getting absorbed from mortar and for better bonding with cement sand mortar.

  • Points to be supervised during brick masonry. –

No continuous vertical joint should be formed.

For brick masonry brick should be sufficiently wet before use.

Maximum height of construction should be limited to 1.5 m.

Verticality should be checked.

Proper curing should be done.

SAND

  1. Types- River Sand, Nallah Sand, Artificial Sand etc.

Sizes- Fine Sand, Medium Sand, Coarse Sand

Uses – Cement mortar, fine aggregate of concrete, Soil improvement, Plinth filling.

Bulking of sand The phenomenon of increase in volume of sand due to moisture in sand particle.

It’s Value – The volume may increase up to 45% corresponding to the water content of about 4.6%

What is FM of Sand – It’s an index number representing the size of sand particle.

FM -2.2-2.6 Fine Sand, 2.6-2.9 – Medium Sand, 2.9-3.2 Coarse sand.

 What does it indicate, what are their values?

It indicate the average size of the sand particles.

CEMENT

  1. Chief Ingredients – Limestone or Chalk (Calcareous materials), Shale or Clay (Argillaceous materials),
  2. Calcination temperature – 13000C – 15000C
  3. Bogue’s compounds –

Tricalcium Silicate – 3CaO.SiO2 (C3S)

Dicalcium Silicate – 2CaO.SiO2 (C2S)

Tricalcium Aluminate – 3CaO.Al2O3 (C3A)

Tetracalcium Aluminoferrrite – 3CaO. Al2O3 .Fe2O3 (C4AF)

Their functions – Tricalcium Silicate and Di Calcium Silicate are the two most important compound of cement responsible for strength development. Average C3S content is 45% and C2S is 25%. C3A flash set and to prevent flash set retarder like gypsum is added to the cement.C4AF is relatively inactive compound. C3S hardens early and develops early strength. C2S hydrates slowly and contribute to ultimate strength. C2S hydrate are much superior to C3S hydrate.

  • The Types of Cement and their uses in different locations –

Ordinary Portland cement – General purpose construction.

Portland Pozzolana Cement – Marine and hydraulic construction and mass concrete constructions.

Rapid Hardening Cement – Where formwork to be removed early, road repair works and in cold weather condition.

Portland Slag Cement –Underground construction and marine construction and at coastal regions and in mass concrete structure.

Sulphate resisting Cement – Concrete in foundation and basement where soil contains sulphates, fabrication of pipes, construction of sewage treatment plant and in marine environment.

Quick Setting Cement – Grouting operations.

Low Heat Cement – Mass concrete such as dams.

Super Sulphated Cement –Foundations where chemically aggressive condition exist marine environment and sewage pipe.

Coloured Cement –Decorative purposes.

Hydrophobic Cement – Remote locations where more storage time is required.

  • Initial Setting and Final Setting Time –

30 min 600 min for OPC.

  • What is 53 Grade Cement – Strength of the cement at 28 days is not less than 53N/mm2. (Tested as per IS 4031-1988)
  • How is cement tested at site –

Appearance of the cement should be greenish grey there should not be any lumps in the cement bags.

Smooth feeling is obtained in good cement when we take between our fingers.

If we insert our hand inside a bag of cement it should feel cool.

When a hand full of cement is thrown inside a bucket of water it should float sometime before sinking.

A cake made with stiff paste of cement when kept inside water for 24 hours should retain its shape and attain some strength.

  • Weight and volume of one Bag of cement – 50 kg weight and 0.0347 cum volume.
  1. How much temperature and heat are generated when cement is mixed with water?

After 7 days – 89-90 cal per gram.

After 28 days – 90-100 cal per gram.

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