Post Contents

## 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.** A 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 on the concrete cube at the point of failure by the **cross-section are**a of the cube **(15x15x15 cm)** on which **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 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 Test and Their Procedure**

## Compressive Strength of Concrete Formula

The following is** the compressive strength of 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** depending upon the **size of aggregate **is used for** concrete making**. For most of the **concrete works **cubical moulds 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** specimen **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 curing or 28 days curing. **

The **Load on the cube** should be applied **gradually** at the** rate of 140 kg/cm2 per minut**e till the **specimen fails.** Load at the **failure of a cube** divided by **area of specimen **gives the co**mpressive 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 specimen**s are 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 laye**r using a** tamping rod **(steel rod **16mm diameter** and 60cm long, **bullet-pointed** at lower end) The **top level of **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 water** must be at** 27+-20 C.**

**Concrete Cube Test Procedure**

**Remove**the**concrete cube**from water after**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 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 **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 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**.

**Standard Compressive Strength of Concrete at 7 days and 28 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**. These values of concrete percentage with respect to the days are considered to be standard, as per the **standard codes. **Also**,** it is much easier to examine concrete with respect to these standards. Hence we test the concrete compressive strength at 7, 14, and 28 days.

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

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

As per the standards, 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 gains 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 M20 grade of concrete compressive strength of concrete at 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.

## Watch Video: Concrte Cube Test Procedure & Calculation

**You Might Also Like:**

supportcivilthis blog is really helpful for me .i have website and i provide civil engineering subjects handwritten notes on supportcivil.com

once again thanks

ClanzaAzieIwant to learne more in steel bar

Keep ReadingThis makes clearer sense than other people…

Asha RenukaVery Informative

PCTEThe post helped me a lot to learn more about the Compressive strength of concrete tests. Keep sharing such useful information.

Bhushan MahajanCompressive Strength of Concrete