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## What Is **Compressive Strength** of Concrete?

**Compressive strength of Concrete **can be defined as the **ability of mat**erial or structure to **carry** the **loads **on it without any** crack or deflection.** material under** compressive load** tends to reduce the **size**, while in **tension, **size **elongates**.

The compressive **strength **of concrete can be **calculated **by **dividing **the load applied to the **concrete **cube at the point of **failure **by the** cross-section** area of the cube** (15x15x15 cm)** on which the **load was applied.**

The **concrete compressive strength** for normal** construction wor**k varies from **15 MPa (2200 psi) **to **30 MPa (4400 psi)** and more in **commercial **and industrial **structures.**

The **strength of concrete** depends on **factors **such as water-cement ratio, the **strength **of cement use,** quality of concrete** materials, **quality control **during the production of** concrete, **etc.

A **compressive strength **test of **concrete **is performed to check the** compressive strength **of **concrete**. There are various **standard codes** that recommend **concrete cylinde**r or concrete **cube **as the standard **specimen **for the test.

The** American Society** for **Testing Materials** of construction **ASTM C39/C39M** provides **Standard Test Method** for **Compressive Strength** of cube and Cylindrical **Concrete Specimens.**

**Read More: All Cement Tests and Their Procedure**

## Compressive Strength of Concrete Formula

**The following is the compressive strength of the concrete formula,**

**Compressive Strength = Load at failure / Cross-sectional Area of element**

## IS Code For Concrete Cube Test

**Cube Test of Concrete** as per IS Code **IS 516 (1959): Method of Tests for Strength of Concrete ** and **IS 456 2000: Concrete Strength Acceptance Criteria**

**Cube Test of Concrete**

**For cube test of concrete **two types of **specimens **either cubes of **15cm X 15cm X 15cm** or **10cm X 10cm x 10cm**.

It’s **depending **upon the size of **aggregate **used for concrete **making**. For most concrete works **cubical **molds of size**, 15cm x 15cm x 15cm** are commonly **used**.

This** concrete** is filled in the **mould and tempered **properly so as to** minimize **any **air voids **available in **concrete.**

**After 24 hours** these moulds are **opened** and test **specimens **are soaked in** water for curing**.

The **upper surface** of these** specimens **should be made even and **smooth. **This is done by **spreading cement paste** on the whole **area of the specimen.**

These **cubes** are tested by a **compression testing** machine after **7 days **of curing or 28 days of **curing. **

The **Load on the cube** should be applied **gradually** at the** rate of 140 kg/cm2 per minute** till the **specimen fails.** Load at the **failure of a cube** divided by the **area of specimen **gives the compressive** **strength of** concrete**.

**Apparatus for Concrete Cube Test**

- Standard
**Compression testing machine** **Cube mould**of standard size**15 cm x 15 cm x 15 cm**

**Preparation of Concrete Cube Specimen**

The **proportion** and **material **for making these** test **specimens should be taken from the same** concrete used** in the **field**.

**1. Specimen**

**Minimum 9** cubes of 1**5 cm size** Max. **M15** or above

**2.** **Mixing of Concrete for Cube Test**

Mix **the concrete** can be done by **hand** or in a** laboratory batch mixer**

**3.** **Hand Mixing**

Mix the **coarse aggregate**, cement, and** fine aggregate** on a** water platform** until the mixture is** thoroughly** blended and is of **uniform color.**

After that** add water** and** mix it** until the** concrete appears** to be** homogeneous** and of the desired **consistency.**

**4. Pouring Concrete In Cubes**

Clean the **mounds of concrete** and apply oil. Fill the** concrete** in the molds in** 3 layers. Compact each** layer of** mix** with not **less than 35 strokes per layer **using a** tamping rod **(steel rod **16mm diameter** and 60cm long, **bullet-pointed** at lower end) The **top level of the **concrete **cube** and smoothen it **with a trowel.**

**5. Curing of Cubes**

The **cube test specimens** are stored in a **moist air **atmosphere for **24 hours** and after this period the** specimens **are given marking and **removed **from the **molds and kep**t submerged in **freshwater** until taken out for **testing.**

**6.** **Precautions for Tests**

The **water** used for** curing** should be tested every **7 days **and the **temperature of the water** must be at** 27+-20 C.**

**Concrete Cube Test Procedure**

**Remove**the**concrete cube**from the water after the**specified curing time**and clear out**excess water**from the**surface.**- Measure the
**dimension**of the**specimen**to the nearest**2mm.** - Clean the
**test surface**of the**testing machine**. **Place**the**cube sample**in the machine in such a**manner**that the**load shall**be applied to the**opposite sides**of the**cube cast.****Place**the specimen**centrally**on the**base plate**of the machine.**Rotate**the machine’s**movable portion**gently by hand so that it**touches**the**top surface**of the specimen.**Apply the load**gradually to the**cube without shock**and continuously at the**rate of 140 kg/cm2/minute**till the**specimen fails.****Record**the breaking**load and note**any unusual**features**in the**type of failure.**

**Calculations of Compressive Strength**

**Check Compressive Strength of Concrete**

Size of the concrete cube = **15 cm x 15 cm x 15 cm**

Area of the cube sample =**225 cm**^{2}** (22500 mm ^{2})**

The same **calculation **should be done for **28 days **of **compressive strength**

The **maximum load** applied or load at **failure **of cube = **400 KN** (400×1000 N)

Compressive strength = (Load in N/ Area in mm2)=**400×1000/22500 N/mm ^{2}**

= **17.77 N/mm**^{2}

**Percentage of Strength Gain by Cubes In Days**

The** following table** shows the **percentage **gain of **compressive strength **of concrete at **7 days, 14 days, **and** 28 days**

Days | % Gain Strength |

1 Day | 16 % |

3 Day | 30 % |

7 Day | 65 % |

14 Day | 90 % |

28 Day | 99 % |

**Concrete compressive strength gain after 3, 7, 14, and 28 days**

## Compressive Strength of Different Grade of Concrete

**The following table shows the compressive strength of various concrete grades at different ages.**

Grade of Concrete | 1 Day (16%) | 3 Day (30%) | 7 Day (65%) | 14 Day (90%) | 28 Day (28%) |

M 15 | 2.4 | 4.50 | 9.75 | 13.50 | 14.85 |

M 20 | 3.20 | 6.00 | 13.00 | 18.00 | 19.80 |

M 25 | 4.00 | 7.50 | 16.25 | 22.50 | 24.75 |

M 30 | 4.80 | 9.00 | 19.50 | 27.00 | 29.70 |

M 35 | 5.60 | 10.50 | 22.75 | 31.50 | 34.65 |

M 40 | 6.40 | 12.00 | 26 | 36.00 | 39.60 |

M 45 | 7.20 | 13.50 | 29.25 | 40.50 | 44.50 |

## FAQs

**How to Check Compressive Strength of Concrete**

A **concrete Cube Test **is performed to know the Characteristics and **compressive Strength of concrete.** Test for **compressive strength** on concrete is can be** performed **by either using** cube or cylinder.** According to the standards, there are** various codes **that are recommended as the standard **specimen for the test.**

**What is the compressive strength test of concrete?**

The **Compressive strength** **of concrete** is its ability to resist failure in the form of cracks and the fissure when a specific amount of load is acted upon it. Hence higher the value of Compressive Strength higher the value of concrete to resist failure due to acting load.

**How do you measure the strength of concrete?**

Various tests are performed to know the** strength of concrete.** The strength of concrete can also be correlated by knowing its **toughness **value, **durability**, **abrasion** value, **shear **value, etc. For example, Cube Test is performed to know the Compressive strength of concrete by applying pressure on concrete in a** UTM machine**.

**What is the minimum compressive strength of concrete?**

**Minimum Compressive Strength of Concrete: 17300 KN/m2**

As per the standards, the worldwide minimum compressive strength of concrete varies with its grade as well as the nature of construction. However, in a general sense minimum Compressive Strength required is 17300KN/m2.

**Cube Test**

**Compressive strength of concrete** can be defined as the ability of material or structure to carry the loads on it without any crack or deflection. A material under compressive load tends to reduce the size, while in tension, size elongates. It is also known as the Cube test of Concrete in the field.

**Compressive Strength of Concrete at 7 Days**

**Concrete** has the ability to gain 16 percent strength of its total strength in one day, 40 percent in 3 days, 65% in 7 days, 90% in 14 days, and around 99% strength in 28 days. So, for the M20 grade of concrete compressive strength of concrete during the day will be 13 N/mm2.

**Cube Strength of Concrete**

**Compressive strength of concrete** can be defined as the ability of material or structure to carry the loads on it without any crack or deflection. A material under compressive load tends to reduce the size, while in tension, size elongates. It is also known as the Cube test of Concrete in the field.

### After 28 days compressive strength of concrete in psi?

The compressive strength of concrete requires 4000 to 5000 psi at 28 days.

### Watch Video: Concrete Cube Test Procedure & Calculation

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