Important Points related to concrete technology

Important Notes related to concrete technology:

• The bond strength between steel and concrete is due to both friction and adhesion.
  • The differences in shrinkage between surface and interior of concrete results in crazing.
  • Construction joints are provided

    where the member is supported by other memberat 18 m apart in huge structuresin concrete wall at sill level of windows

  • An aggregate is said to be flaky if its least dimension is less than 3/5th of mean dimension
     

• Fineness modulus gives idea about mean size of particles in aggregate.
• After casting, an ordinary cement concrete on drying shrinks.

• MPa (N/mm^2) is the unit for standard deviation in concrete mix design. As grade of concrete increases the standard deviation value will also increases.
• The bulk density of aggregates depend upon :

  size and shape of aggregatesspecific gravity of aggregatesgrading of aggregates

• M10 grade of concrete approximates 1 : 3 : 6 mix

• The formation of small patches of plaster swelling out beyond the plastered surface is known as blowing of plaster.
• Curing

  prevents the loss of water by evaporationpreserves the properties of concretereduces the shrinkage of concrete

• Proper proportioning of concrete, ensures

  desired durabilitywater tightness of the structureresistance to water

• Portland slag cement is suitable for mass concreting.

• Blaine’s air permissibility test is used to determine fineness of cement.

• Retarder slows down the chemical reaction of hydration.
• The risk of segregation is more for
  -larger proportion of maximum size aggregate -wetter mix -coarser grading

• Colored cement (white cement) consists of 5 to 10 percentage of pigment.
• The mixture of different ingredients of cement, is burnt at 1400°C
• For ensuring quality of concrete use graded aggregates.
   
• While compacting the concrete by a mechanical vibrator, the slump should not exceed 5.0 cm.

Segregation is the proper distribution of constituent materials of concrete i.e. the materials are showing the separation from each other(means binding property is not followed properly). Hence concrete having segregation property is weak in compressive strength, show poor quality concrete and reduction of desirable properties.

Segregation shows three types of conditions, first— separation of coarse aggregate from concrete, second— separation of cement paste from concrete (also called bleeding) and separation of water from concrete. To avoid Segregation we have to follow some remedial steps like proper mix proportion, by proper handling, transporting, placing, compacting and finishing. We perform some test which gives fair idea of the quality of concrete like Slump test and flow test.

Curing is the process of applying running water to freshly placed concrete to avoid outgoing movement of heat and moisture from concrete structure to gain full strength. If curing is not done properly then cracks may develop at surface of concrete because of removal of water from interior part of concrete hence leaving behind pores which may result in series of cracks.

To stop this process curing is necessary to reduce outgoing of moisture( actual amount of water used while mixing) from concrete member. So that moisture will distribute uniformly inside the concrete member. According to IS 456-2000 or by any other code, for this, use only running water or fresh water free from any heavy particulates, acids or salts.