Compressive Strength of Cement Cubes


Overall Power of a construction such as flexural opposition and abrasion directly is dependent upon the compressive power of concrete.

In accordance with Wikipedia, Compressive Power of concrete means the Characteristic power of 150mm size cement cubes tested at 28 times.

Why do we check at 7,14 & 28 times?

Concrete is really a macro quite happy with Sand, Cement, & Coarse aggregate as its micro-ingredient (Combine Ratio) and benefits its 100% strength as time passes at the hardened condition.

Have a look at the below table.

Concrete Strength Overtime

Days after CastingStrength Gain
Day 116%
Day 340%
Day 765%
Day 1490%
Day 2899%

As possible plainly see the concrete benefits its strength quickly til 7th & 14th Days. Progressively increases from there after that. Therefore we can’t predict the power until the concrete involves that stable state.

Once it attains specific strength at seven days, then we all know (based on the table) only 9% of power going to increase. Therefore at sites, wwe perform test concrete at this interval usually.If the cement fails at 14 days, we shall reject that batching after that.

Compressive Strength Desk of Concrete at 7 & 28 Days

Grade of ConcreteMinimum compressive power N/mm2 at seven daysSpecified characteristic compressive power (N/mm2) at 28 times
M151015
M2013.520
M251725
M302030
M3523.535
M402740
M453045

Objective

To get compressive strength worth of concrete cubes

Required Products & Apparatus

  • 150 mm Cube Moulds (with IS Mark)
  • Electronic Weighing Balance
  • G.I Sheet (TO MAKE Concrete)
  • Vibrating Needle & additional tools
  • Compressions Testing Machine

Procedure

Cube Casting

  • Gauge the dry proportion of substances (Cement, Sand & Coarse Aggregate) according to the look requirements. The Ingredients ought to be sufficient sufficient to cast check cubes
  • Thoroughly mix the dry components to acquire uniform mixture
  • Add design level of water to the dry proportion (water-cement ratio) and mix well to acquire uniform texture
  • Fill the concrete to the mould by using vibrator for thorough compaction
  • Finish the very best of the concrete by trowel & tapped well till the cement slurry involves the very best of the cubes.

Curing

  • Over time the mould ought to be covered with red gunny bag and put undisturbed for 24 hours at a temperature of 27 ° celsius ± 2
  • After 24 hours take away the specimen from the mould.
  • Keep carefully the specimen submerged under fresh water at 27 ° celsius. The specimen ought to be kept for 7 or 28 days. Every seven days the water ought to be renewed.
  • The specimen ought to be taken off the water 30 minutes before the testing.
  • The specimen ought to be in dry condition before conducting the testing.
  • The Cube weight shouldn't be significantly less than 8.1 Kgs

Testing

  • Now place the concrete cubes in to the testing machine. (centrally)
    • The cubes ought to be placed correctly to the device plate (check the circle marks on the device). Align the specimen to the spherically seated plate carefully.

The strain will be axially.

  • Now slowly apply the load at the rate of 140kg/cm2 each and every minute till the cube collapse.
  • The utmost load of which the specimen breaks is taken as a compressive load.

Calculation

Compressive Strength of concrete = Maximum compressive load / Cross Sectional Area

Cross sectional Area = 150mm X 150mm = 22500 mm2 or 225 cm2

Believe the compression load will be 450 KN,

Compressive Strength = (450000 N / 225)/9.81 = 204 kg/cm2

Note �1 kg is add up to 9.81 N

Observation Result (Lab Report)

DetailsSamples
Specimen 1Specimen 2Specimen 3

Compressive Load

(KN)

375 KN425 KN435 KN

Compressive Strength

(Kg/Cm2)

(375000/225) / 9.81

= 170 kg/cm2

(425000/225) / 9.81

= 192.5 kg/cm2

(435000/225) / 9.81

= 197.0 kg/cm2

Average Compressive Strength= (170+192.5+197)/3 

= 186.5 Kg/cm2

Notes
  • The aforementioned experiment ought to be conducted at the temperature of 27° celsius ± 2°.
  • According to IS 516, the average person variation in compressive load shouldn't be a lot more than plus minus 15% of the common value.

Frequency of Sampling

In accordance with IS 456:2000, Minimum frequency of Concrete Sampling

Level of Concrete in Work (M3)Amount of Samples
1-51
6-152
16-303
31-504
51 and above4 and something additional sample for every additional 50 m3

Experiment Video



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