# Concrete Cubes: Compressive Strength of Concrete Cubes

Know about Compressive Strength of Concrete Cubes. The best knowledge of Compressive Strength of Concrete Cubes are must know before using it.

It is most useful construction material which uses in all building.

People also ask about Compressive Strength of Concrete Cubes;

- What is meant by compressive strength of concrete?
- What is a cube test?
- What is the meaning of m20 grade concrete?
- How do you measure the strength of concrete?

Many tests applied on concrete is the most important thing gives an idea of all the characteristics of concrete. For this test, a judge that if Concreting is done correctly or not. The compressive strength of concrete depends on many factors such as water-cement ratio, cement strength, concrete quality of the materials, quality control during concrete production, etc.

Compressive strength test is performed in the cube or cylinder. Several standard codes recommended concrete cylinder or concrete bucket as the standard sample for testing. American Society for Testing Materials ASTM C39 / C39M provides Standard Test Method for Compressive Strength of Concrete Cylindrical Samples,

Cubes of 15 cm x 15 cm x 15 cm or 10 cm x 10 cm x 10 cm depending on the size of the aggregate: cubes to test two types of samples are used. For most work cubes cubes size 15 cm x 15 cm x 15 cm are commonly used.

This concrete is poured into the mold and hardened properly to avoid any gaps. After 24 hours, these molds are removed and the test samples are placed in water to be cured. The upper surface of this sample must be made uniform and smooth. This is done in the cement paste and spread gently over the entire surface of the sample.

These samples are tested using a compression test machine after 7 days or 28 days of hardening curing. The load should be applied gradually at a rate of 140 kg / cm2 per minute until the sample breaks. The breaking load divided by the surface of the sample gives the compressive strength of the concrete.

The test procedures for compressive strength testing of concrete cubes are presented

APPLIANCE: Compression Testing Machine

EXAMPLE OF CUBES PREPARATION: The proportion and material to make these specimens are the same concrete used in the field.

SAMPLE: 6 cubes of size 15 cm of mixture. M15 or higher

MIX: Mix the concrete either by hand or in a laboratory batch mixer

BAG MIXED:

(I) Mix the cement and fine aggregates on an impermeable deck until the mixture is thoroughly mixed and uniformly colored

(Ii) Add the coarse aggregate and mix with cement and fine aggregates until the large aggregate is evenly distributed throughout the lot

(Iii) Add the water and mix until the concrete becomes homogeneous and the desired consistency

SAMPLING

(I) Clean mounds and apply oil

(Ii) for filling concrete into the layered molds about 5 cm thick

(Iii) Pack each layer not less than 35 shots per layer using a grooming rod (steel bars 16 mm in diameter and 60 cm long, balls aimed at the lower end)

(Iv) Level the top surface and smooth with a trowel

HEALING: The test samples are stored in moist air for 24 hours and after that time the samples are labeled and removed from the molds and kept immersed in water until clear.

PRECAUTIONS: Water for hardening should be tested every 7 days and the water temperature should be 27 + -2oC.

PROCEDURE

(I) Remove the sample from the water after a specified cure time and wipe off any excess water from the surface.

(II) Take the sample size to 0.2 m

(III) cleaning the support surface of the test machine

(IV) Place the sample in the machine so that the load is applied to the opposite sides of the cube’s distribution.

(V) align the sample to the center of the base plate of the machine.

(VI) Turn the part gently by hand to touch the top surface of the specimen.

(VII) Apply the load without impact gradually and continuously at a rate of 140 kg / cm2 / min until the sample fails

(VIII) Record maximum strength and note any unusual characteristic of the type of failure.

NOTE: At least three animals must be tested in each selected age. If the resistance of any sample varies by more than 15% of the mean strength, the results of the sample must be rejected. Average of copies giving grinding force of concrete. Requirements for concrete strength.

CALCULATIONS: Cube Size = 15cm x 15cm x 15cm

Sample area (calculated from the average sample size) = 225cm2

Characteristic compressive strength (f ck) at 7 days =

Expected load = fck x Maximum area x f.s

Range to be selected is ………………… ..

A similar calculation is required for 28-day compressive strength

Maximum load applied =……….tones = ………….N

Compressive strength = (Load in N/ Area in mm2)=……………N/mm2 =……………………….N/mm2

REPORT

a) Identification mark

b) Date of test

c) Age of specimen

d) Curing conditions, including date of manufacture of specimen

f) Appearance of fractured faces of concrete and the type of fracture if they are unusual.

**RESULT**

Average compressive strength of the concrete cube = ………….N/ mm^{2} (at 7 days)

Average compressive strength of the concrete cube =………. N/mm^{2} (at 28 days)

**Compressive strength of concrete at various ages:**

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

Age |
Strength per cent |

1 day | 16% |

3 days | 40% |

7 days | 65% |

14 days | 90% |

28 days | 99% |