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 Casting | Strength Gain |

Day 1 | 16% |

Day 3 | 40% |

Day 7 | 65% |

Day 14 | 90% |

Day 28 | 99% |

As possible plainly see the concrete benefits its strength quickly til 7^{th} & 14^{th} Days. Progressively increases from there after that. Therefore we canât 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 testÂ 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 Concrete | Minimum compressive power N/mm2 at seven days | Specified characteristic compressive power (N/mm2) at 28 times |

M15 | 10 | 15 |

M20 | 13.5 | 20 |

M25 | 17 | 25 |

M30 | 20 | 30 |

M35 | 23.5 | 35 |

M40 | 27 | 40 |

M45 | 30 | 45 |

### 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 Â° celsius Â± 2

- After 24 hours take away the specimen from the mould.

- Keep carefully the specimen submerged under fresh water at 27 Â° 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 theÂ load at the rate of 140kg/cm
^{2}each and every minute till the cube collapse.

- The utmost load of which the specimen breaks is taken as aÂ compressive load.

## Calculation

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

Cross sectional Area = 150mm X 150mm = 22500 mm2 or 225 cm^{2}

Believe the compression load will be 450 KN,

Compressive Strength = (450000 N / 225)/9.81 = **204Â kg/cm ^{2}**

**Note** â?1 kg is add up to 9.81 N

## Observation Result (Lab Report)

Details | Samples | ||

Specimen 1 | Specimen 2 | Specimen 3 | |

Compressive Load (KN) | 375 KN | 425 KN | 435 KN |

Compressive Strength (Kg/Cm2) | (375000/225) / 9.81 = 170 kg/cm | (425000/225) / 9.81 = 192.5 kg/cm | (435000/225) / 9.81 = 197.0 kg/cm |

Average Compressive Strength | = (170+192.5+197)/3Â = 186.5 Kg/cm |

##### Notes

- The aforementioned experiment ought to be conducted at the temperature of 27Â° celsius Â± 2Â°.

- 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 |

1-5 | 1 |

6-15 | 2 |

16-30 | 3 |

31-50 | 4 |

51 and above | 4 and something additional sample for every additional 50 m3 |