Material Testing

BASIC COMPONENT (RAW) MATERIAL
SPECIFICATION AND ACCEPTANCE CRITERIA


For preparing concrete, following parent materials should be used.


(1) CEMENT :

Ordinary Portland cement is the most widely used cement for making concrete. 43 Grade & 53 Grade of cement can also be used. On the arrival of cement on the site, the following field tests should be carried out before using it.

  • % Field tests for cement‐
  • Check the weight of the cement bag with a weigh balance. The weight of the bad should not vary more than 2% of the standard weight of the cement bag i.e. 50 kg.
  • Ensure that the original packing of the company is intact.
    Ensure that the company’s brand & grade is as per the order placed.
  • Check the manufacturing date of the cement that is written on the bag, to know how old the cement is. Always use fresh cement for quality concrete (maximum age 4 months).
  • Ensure that there are no lumps by feeling the cement in the bag manually.
  • The cement should feel cool to the hand immersed in the bag.
  • The cement should feel silky smooth when rubbed.
  • Add a handful of cement slowly to a bucket full of water. The cement particles should1 float for some time before sinking.
  • Prepare 5cm x 5cm x 5cm cubes from the cement paste. Keep them immediately water. After 24 hours, the edges of the cubes should remain sharp and should gain in strength.
 

(2) COARSE AGGREGATES :

Aggregates which pass through I. S. sieve of opening of size 80mm and are entirely retained on 4.75mm I. S. sieve, a re known as coarse aggregates.


The size of the particles to be used for concrete depends on the type of work and reinforcement. Coarse aggregates consist of aggregates consist of aggregates such as stone gravel.

  • % ACCEPTANCE CRITERIA
  • Should not be porous, as porous material corrodes the reinforcement.
  • Elongated and laminated particulars are good in shear.
  • Must be clean and free from clay lumps, vegetable and other organic material. Clay/dirt in the aggregate slows down the setting and hardening of cement and reduces the strength.
  • Angular and roughly cubical particulars are ideal.
  • 25mm &12.5m size coarse aggregates are normally used in R.C.C. works.
  • For mass concrete upto 40mm size coarse aggregates can be used.
  • The maximum size of coarse aggregates should be within the limits specified.

 

(3) FINE AGGREGATES


Sand is used as a fine aggregate to fill voids between coarse aggregates, for producing dense concrete. Sand passes through 4.75mm I. S. sieve.


Sand should consist of sharp angular grains of various sizes. Recent studies show that rounded grains too interlock sufficiently, to produce a strong concrete.

  • %ACCEPTANCE CRITERIA
  • Ensure that the sand is river wet or artificially wet (to increase the bulkage).
  • Check if the fineness (type) of the sand supplied is as per the purchase order.
  • Sand should be free from silt, clay, salts, mica and organic material.
  • Sand is generally found to contain some percentage of silt and clay. Maximum 7% of silt and clay may be allowed in sand at construction sites.

MEASUREMENT OF SAND


BULKING OF SAND

  • Damp sand bulks (expands) and occupies more space, than when completely dry. 2% to 5% moisture contents increases, the volume by 10% to 20% or even 30%. Fine sand bulks more than coarse sand.
  • When the moist sand is measured by volume, allowance should be made for bulking.
  • This is necessary to ensure that the amount of sand actually used in concrete is the same as it would have been if dry sand were to be used.
  • The percentage of bulking of sand, due to moisture content, can be calculated by simple field method.
  • Take the sample of moist sand in a glass cylinder of 250ml capacity.
  • Shake the Cylinder and note down the consolidated sand as per reading.
  • Pour water in the cylinder, above the sand level and shake well.
  • Allow the contents to settle. Take the reading for submerged sand.
  • Then percentage of bulking of sand due to moisture can be calculated by using the formula x100-B A B

 

% TEST FOR PRESENCE OF SILT OR CLAY IN SAND BY VOLUM

  • Rub a sample of the sand with we palms. Good, clean sand will not stick to the hand, whereas sand with silt/clay will stick, changing the colour of the palm.
  • Fill half a glass cylinder with sand and pour clean water until the cylinder is full.
  • Shake it vigorously and leave it to settle for about an hour.
  • Clean sand will settle immediately. Any clay will make the water muddy. Clay or silt will also settle gradually above the sand.
  • Add a teaspoon of salt to the water. It will quicken the process and a layer of silt will settle above the sane.
  • Thickness of the silt layer should not exceed the thickness of the sand layer, by 7%
  • If the percentage of the silt is more, the sand needs washing.

 

(4) WATER


Water used for mixing of concrete should be clean, free of oil, alkalis, acids, salts, sugar, organic materials or any other substances, deleterious to concrete and steel. In general, water that is fit for drinking is good for concrete.

 

FIELD TESTS FOR QUALITY OF STEEL BARS

  • The pitch length between the twist should be 8 to 12 times that of the nominal diameter of bar.
  • The diameter of the bar should not vary. For measuring the diameter of bars, Screw Gauge or Vernier caliper should be kept on site.
  • Steel should not be brittle in nature but soft for working. It should not break into pieces during bending.
  • Length of the bar should be between 11 to 12 meters.
  • Steel should not be corroded. This can be checked by the rusting layers on bars and by taking weight of steel bar before and after immersion in water for 24 hours. Loss of weight of steel shows depth of corrosion.
  • In case of ‘TOR’ steel ‘TOR’ mark should be present on each meter length.

 


FIELD TESTS FOR BINDING WIRE

  • Binding wire should be of 16 gauge.
  • It should be soft in working and should not be brittle.
  • When tied, it should not be loosen from it’s position.
  • It should not be corroded.

 

To The Top