Portland Cement: Composition and Testing

Introduction to BMC

• Portland cement comprises lime, silica, alumina, iron oxide, magnesia, alkalies, and sulphur trioxide.
• The percentages of these constituents typically range from lime at 63% to sulphur trioxide at 1.5%.

Oxide Composition and Function in Portland Cement

• Lime (CaO) controls strength and soundness; excess leads to unsoundness.
• Silica (SiO2) contributes to strength; excess causes slow setting.
• Alumina (Al2O3) promotes quick setting; excess lowers strength.
• Iron oxide (Fe2O3) provides color and acts as a flux; it also enhances the fusion of different ingredients.
• Magnesia (MgO) impacts color and hardness; excess results in cracks and unsound cement.
• Alkalies (Na2O + K2O) present as residues can lead to efflorescence and cracks.
• Sulphur trioxide, if in excess, causes cement to become unsound.

Material Testing

• Fineness is tested using sieve, air permeability, and sedimentation methods to measure grain size.
  • The sieve method employs a 30N sieve.
  • Air permeability uses the Nurse & Balne's method.
  • Sedimentation utilizes the Wanger turbidity method.
  • Air permeability measures fineness as % residue by weight.
• Consistency is determined with a Vicat apparatus to find the required water quantity for normal paste.
• Setting time is assessed to get the Initial Setting Time (IST) and Final Setting Time (FST).
  • OPC IST minimum is 30 minutes.
  • OPC FST maximum is 40 hours.
• Soundness, the Lechatlier test is used for lime, free if greater than 10mm, and autoclave test for lime & magnesia, free if greater than 0.8%, but no test exists for sulphur'.
• Compressive strength is measured on (OPC) mortar cubes at 3, 7, and 28 days.
  • Cube side√50 cm
  • Cement : sand ratio of 1:3
  • Minimum of 3 cubes, and cured between 27 ± 2°C

Cement Compound Properties

• Tricalcium Silicate (C3S) is best for cementing, providing early strength, and resistance to freezing/thawing. It is used in road work and prefabrication.
• Dicalcium Silicate (C2S) contributes to late strength and chemical resistance, and it is used for dams and bridges.
• Tricalcium Aluminate (C3A) leads to flash setting; most responsible for initial setting time (IST), sulphate resistance, and used within concrete.
• Tetracalcium Aluminoferrite (C4AF) generates less heat but has the poorest cementing properties, and is used within concrete.

Cement Types Characteristics

• Rapid Hardening Cement (RHC) gains early strength; used where quick strength development is needed like in repaired roads/bridges.
  • RHC with 2% Cacl2 (accelerator) provides a max of 20 min to mix, transport, finish, etc.
• Extra rapid hardening cementis suitable for special purposes like cold weather repairs.
• Sulphate Resisting Cement is used in sea water structures with C3A at (5%).
• 40° is required for super sulphate cement with C3A < 3.5%.
• High Alumina Cement is made by fusing lime + Bauxite for refractory concrete and exhibits fire/chemical/seawater resistance.
• Low Heat Cement is used in mass concreting, composed of free Zypsum, sets quick but doesn't harden fast itself.
• Quick Setting Cement: contains Zypsum & used in underwater concreting/running water construction.
• Pozzolana Portland Cement (PPC) is made with pozzolanic materials like rice husk or shale.
• Air Entraining Cement: contains agents like oil/fat/wood resin for greater freeze/thaw resistance and improved workability
• Blast Furnace Slag Cement: It is best for marine works & carrying water containing chemicals.

Differentiating Cement Sets

• Flash set involves rapid permanent rigidity with high heat evolution due to increased C3A & decreased Zypsum.
• False set is premature stiffening with no heat, caused by hot clinker or and alkalis.

Properties of Portland Cement

• White & Colored is used for sewage pipes, sulfate-rich soil, flooring, plastering, and ornamental works.

Brick Earth Composition and Excess Effects

• Silica is responsible for brick, hardness, durability, shape, and prevents cracking/warping.
  • Excess silica makes bricks brittle and weak.
• Alumina imparts plasticity for molding. -High alumina implies refractoriness.
• Lime acts as a flux that binds the brick particles together.
  • Excess cracks upon drying/becomes too hard that also causes cracks.
• Iron oxide gives strength,color, durability, and impermeability and helps silica fuse during burning.
  • Gives a dark blue color.
• Magnesia decreases shrinkage and gives a yellow tint.
  • Excess decays bricks.

Harmful Brick Ingredients

• Lime in lumps, absorbs moisture to cause the disintegration of brick.
• Iron pyrite oxidizes, crystallizes, and splits the brick causing discoloration.
• Excessive pebbles/gravel interfere with mixing which causes the bricks to lack uniformity of being weak & porous.
• Excess Alkalies cause bricks to melt/lose shape, leading to efflorescence deposits.
• Organic matter and vegetation cause pores that cause high level of water absorption.
• Sulphur forms a spongy, swollen structure leading to discoloration.

Brick Defects and Prevention

• Over-burning results in a soft, misshapen brick unsuitable.
• Under-burning yields a brick with high water absorption and reduced strength.
• Bloating manifests as a spongy mass due to carbonaceous matter and sulpher.
• Black core is caused by incomplete carbon oxidation during burning.
• Efflorescence appears as white patches due to alkali presence.
• Checks or cracks arise from lime lumps or excess water.
• Spots indicate sulphide presence, harmful for exposed masonry.
• Blisters result from air trapped during moulding.
• Laminations: It forms lamina that produce weak structures.
• Chuffs: It deforms from rain falling on hot bricks.

Qualities of Bricks

• The brick should have a plane, rectangular surface with straight and sharp edges.
• Crushing strength must be 10 MPa (3.5 MPa for common building bricks).
• Made when free from stones, grit, organic matter.
• it should produce a metallic sound when struck
• It should not break if dropped from 1 meter.
• water absorption: when soaked in water for 24 hours, when allowed to dry it should not show deposits of white salts .

Brick Testing Analysis

• Water absorption tests gauge porosity and durability.

  • Submerge brick in water and measure initial and final weights for calculation.

• Compressive strength tests determine the brick's resistance to pressue.

  • In 24hrs, Take 5 brick sample
  • Cover with cement mortar at room temp.
  • Store under damp fiber for 24+hrs
  • then immerse in water for 3 days
  • Brick fails if its too loaded axial at 14MPa/min.

Testing Analysis

• water absorption: measure of porosity based water in take
• convex surface indicates that it does not touch plane in terms its length that gives the warp-age.
• hardness test - scratch brick if unable to, indicates that its more of the hardness.

Special Type Brick (Brick Masonry)

• Full Brick- (Complete piece used for structural wall)
• Queen Closes-(Half brick used for bond)
• 3/4th brick (Three Quarter closes/bat )- for bond
• Squint brick- used as internal ang wall

Manufacturing phase in Brick

• 1. Dry Soil -> then wet (Unsoiling) + Digging -> Cleaning -> weathering by placing in open -> blending adding all the required with other req ing.

Stages of Burning (DOV)

• Starting, its dehydration: removes the moisture at (400 - 500°C)
• oxidation period: (650 - 900°C) - oxidizes the componds - then in high industries, the coal is heated at melting tem and that will for the vitrification at (900 - 1100) - leads to a low melting level

Limestone Breakdown

• Its is 5 step process like mixing lime to CaO + heat and water slaking CaO + water slaking - then its done by water to make more water.
• The slaking and then in it will quick lime as for lime, and after to mix all that then its will for hydraulized to be quick

Stone Testing Analysis

• Crystalline: Test is to dry that rock or stone for some hrs then measure, then again dry that at some °C level , then again measure its weigh, if every thing is fine and repeat that some cycle to give the durability and other things

Preservation/Quality

• if Its has a low attrition value that it is used for heavy and hard use and and the material such is used a high durability as water that low absorption

Process or rock and cement

• Rock is used for the to cut a design the rough, but the cement is use has to be less that will lead the high with of rock strength that will get the sap drying easily. other wise the cement is bad.

Rock Imperatives

• The Rock has different test like the the cutting the crushing: at the at with sand is done to test all required force

Cementing / Building stone:

• They have many test for everything so check in place has to the be high on the use other wise the product is not usable

Quality Control:

• They are three way that they look by color they break and how they sound, and high resistance to cut

Driers:

• These are the are with something in it that makes it stick.

Solvents:

• Are used that makes it thin or a little less hard to put

Base

• Its used from something that to look at to see that what we doing is right

Paint

• Is white or whatever color to looks so its done by the white/loster:

Types Of Paint:

• Cement Paint is for every thing like water or like wall, very to prevent every thing that is out:
• Aluminium Paint: Its can use to look or see every better

Testing Methods

• They use all and is look the type and when things go wrong in it to fix or what

Rock Quality Analysis

• Its when the tree goes under or is not or it broken type with rock and they put more then its goes away

Flaws In Timber

• Knot
• and how they cut at will tell is it good

Cement Testing

• They test the materials that mixed and everything was is up to date and is everything was good to work other wise nothing is good.

Maturity and Test

• Testing the concrete

I hope these study notes are helpful! If you have any other materials you need to study, feel free to send them over.