## What is Compressive Strength

Compressive strength of concrete is how much load it can take without cracking. In general Construction the compressive strength of concrete varies from 15Pa to 30Pa and higher for commercial and industrial use.

Compressive strength of concrete depends on many factors such as water-cement ratio, cement strength, quality of concrete material, quality control during the production of concrete, etc.

## How to find out compressive strength of concrete

We make concrete cubes and then apply compressive load on these cubes until it fails, thatâ€™s it. Depending on size of aggregates used we use either 15cm x 15cm x 15cm mould OR 10cm x 10cm x 10cm mould of these two 15cm cube is most commonly used.

Concrete mixture is poured into these moulds, compacted to remove any air. After 24 hrs moulds are removed and concrete cubes are dipped in water curing tank.

After 7 days or 28 days we test these concrete cubes on a compression testing machine. Load should be applied gradually at the rate of 140 kg/cm2 per minute till the Specimens fails. Load at the failure divided by area of specimen gives the compressive strength of concrete.

## Compressive Strength of Concrete at various ages

The strength of concrete increases with age. The table shows the strength of concrete at different ages in comparison with the strength at 28 days after casting

Age | Strength Percent |

1 day | 18% |

3 days | 40% |

7 days | 65% |

14 days | 90% |

28 days | 99% |

**Compressive Strength of Different Grades of Concrete at 7 and 28 Days**

Grade of Concrete | Minimum Compressive Strength N/mm2 at 7 days | Specified Characteristic Compressive Strength N/mm2 at 28 days |

M15 | 10 | 15 |

M20 | 13.5 | 20 |

M25 | 17 | 25 |

M30 | 20 | 30 |

M35 | 23.5 | 35 |

M40 | 27 | 40 |

M45 | 30 | 45 |

Now that you know what compressive strength of concrete is and how to calculate it the next step is to learn how to design concrete mix yourself.

I highly recommend you try out Concrete Mix Design app with this you can create design mixes without doing any calculations

Concrete Mix Design Google Play Link: Click here to download

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