CONCRETE

• Concrete


  A mixture of cement, water, and aggregates (like sand and gravel) that hardens over time to create a solid, strong substance
• Components of concrete

  • Cement
  • Water
  • Coarse aggregates
  • Fine aggregates
  • Air
  • Admixtures
  • Supplementary cementitious materials
• Types of cement and their uses

  • Ordinary Portland Cement
  • Portland Pozzolana Cement
  • Rapid Hardening Cement
  • Extra-Rapid Hardening Cement
  • Low-Heat Cement
  • Sulfate Resisting Cement
  • Quick Setting Cement
  • Blast Furnace Slag Cement
  • High Alumina Cement
  • White Cement
• Ordinary Portland Cement


  • Made of silicates of alumina and calcium carbonate
  • Used for general construction and most masonry work
• Portland Pozzolana Cement


  • Ground pozzolanic clinker mixed with OPC
  • More resistive to chemical reactions within concrete
  • Suitable for works underground, in water, or in humid environments
• Rapid Hardening Cement


  • Finer ground
  • Greater strength development at an early stage than OPC
  • Often used in prefabricated road work and concrete construction
• Extra-Rapid Hardening Cement


  • Sets and becomes durable faster than OPC and RHC
  • Adding more calcium chloride to RHC
  • Often used in repairing, for concrete drives, and paths and steps
• Low-Heat Cement


  • Lower heat of hydration & needs less water to mix
  • High chemical corrosion resistance and wear and rupture resistance
  • Used in floors and surfaces, dams, and large footings
• Sulfate Resisting Cement


  • Very low heat of hydration
  • Gains strength at a slower rate
  • Reduces the risk of sulfate attack on concrete
  • Used in constructing foundations in soil with high sulfate content
• Quick Setting Cement


  • Sets faster than OPC, but maintains the same strength
  • Beneficial for time sensitive projects, such as underwater structures and in chilly and rainy climates
• Blast Furnace Slag Cement


  • Ground clinker with up to 60% slag
  • Less expensive, but with many same properties as OPC
  • Used for projects where cost concerns are crucial
• High Alumina Cement


  • High compressive strength
  • More flexible and workable than OPC
  • Commonly used in constructions that are exposed to high temperatures, such as workshops, refractories, and foundries
• White Cement


  • Prepared from raw materials that don't include iron oxide
  • More expensive than other cement types
  • Often used in interior and exterior decorative projects
• Concrete slump


  • Measures the consistency of a concrete batch to see how easily the concrete will flow
  • Ensures that the batches of the same concrete are of constant quality and strength
• Types of concrete slump

  • True slump
  • Shear slump
  • Collapse slump
  • Zero Slump
• True slump


  • Concrete just subsides shortly and more or less maintain the mould shape
  • Concrete mixture is cohesive and has good workability
  • Good cement-to-water ratio
  • Most desirable
• Zero slump


  • The concrete retains its shape completely
  • Little to no workability
  • Best used in road construction
  • Low water-to-cement ratio
• Shear slump


  • Top half of the concrete subsides dramatically, leaning to one side
  • Has workability, but low cohesion
  • Too much water
• Collapse slump

  • Doesn't retain its shape at all and completely collapses
  • Water-to-cement ratio is too high
  • Least desirable
• Aggregates


  Important constituents of the concrete, 60-80% of the concrete mix, selected for their durability, strength, and workability
• Classification of aggregates by size


  • Fine aggregate
  • Coarse aggregate
• Fine aggregate types


  • Coarse sand (2.00 mm - 0.5 mm)
  • Medium sand (0.5 mm - 0.25 mm)
  • Fine sand (0.25 mm - 0.06 mm)
  • Silt (0.06 mm - 0.002 mm)
  • Clay (<0.002)
• Coarse aggregate types


  • Fine gravel (4 mm - 8 mm)
  • Medium gravel (8 mm - 16 mm)
  • Coarse gravel (16 mm - 64 mm)
  • Cobbles (64 mm - 256 mm)
  • Boulders (>256 mm)
• Compression strength test


  • Done by breaking cylindrical concrete specimens in a compression-testing machine
  • Results can be used for quality control, acceptance of concrete, strength estimation, etc.
• Flexural strength test


  • Evaluates the tensile strength of concrete indirectly
  • Tests the ability of unreinforced concrete beam or slab to resist failure in bending
  • Done to specify compliance with standard, as an essential requirement for concrete mix design, etc.
• Rebound hammer


  • A non-destructive testing apparatus
  • The rebound of the spring-driven mass is measured after impact
  • Output is called rebound number
  • Assess the in-place uniformity, delineate poor quality regions, and an in place method to test concrete strength
• Ultrasonic pulse velocity test


  • Strength and quality is tested through measuring the velocity of an ultrasonic pulse passing through the concrete
  • Evaluate dynamic modulus of elasticity, estimate depth of cracks, and detect internal flaws
• Fine aggregates

  • when aggregate is sieved through a 4.75 mm sieve, these are the aggregate that passed through
  • they fill the voids in the coarse aggregate and act as a workability agent
• Coarse Aggregate

  • when the aggregate is sieved through 4.75 mm sieve, these are the aggregates that are retained
  • key component in concrete because they give the largest amount of durability and strength
• Tests on Concrete

  • Compression Strength Test
  • Flexural Strength Test
  • Rebound Hammer
  • Ultrasonic Pulse Velocity Test