Concrete Slump test Procedure | Applications | Types | Uses

Hello friends, today in this post you will learn about the Concrete Slump test Procedure, Applications, Types, Uses & detail stepwise procedure. 

So, don't skip to read the post completely. After reading the post, you will completely understand the simple tests of the Compression test on concrete cubes. 

So, let's start with these amazing topic... 

Importance of Slump test are to check the workability of concrete. A good workable concrete has good strength.

What is Workability of Concrete ? 

It is the most important property of concrete due to which, there will be ease to mixed, transported & placed in position within a homogenous state. 

Workability of concrete mainly depends upon the following : quantity of water, aggregate grade as well as the % of fine materials in the mix. 

The following tests can be used to check the workability of concrete :

1. Slump test
2. Compaction factor test
3. Flow test
4. Kelly ball test
5. Vee-Bee consistometer test.
6. K-Slump Test

On site and lab, mainly Slump test  are performed, due to its ease and results. 

As a result, It gives quick result about the workability of concrete.

Slump Test: –

Slump test was very easy to perform this method. But these method, is not suitable for very wet or very dry concrete.
This test can be used as a control test, it is also an indication of the concrete uniformity from batch to batch. 

Repeated batches of the same mix, brought to the same slump.

This will have the same water content and water cement ratio, weights of aggregate, cement and admixtures are uniform and aggregate grading is within acceptable limits.

Apparatus:-

The apparatus required for Slump test are listed below :

a. Mettalic Mould which is in the shape of frustum cone, 

b. tamping rod with bullet end, 

c. Scale or tape for measuring the slump. d.  Metallic sheet for placing Slump & trowel for pouring concrete in the slump.

1. Frustum Cone:- 
Frustum cone has two different diameters one at the top & other at the bottom. The dimensions of Frustum cone is mentioned in below table :-

2. Tamping rod:-
The rod having  Dia of 16mm & bullet end at one side. The height of tamping rod should be 0.6m long.

Slump test Procedure :-

1. Before, starting the test, we should clean the inner surface of Frustum cone & it should be free from moisture content and adherence of any old set concrete.
2. Now, we have to place the Cone on the metallic steel plate or on any smooth surface.
3. We have now to Fill the cone with concrete in four layers each with an approximate height of 1/4th of the mould.
4. Each layer should be tamped 25 times with tamping rod. We have to take care to distribute the strokes evenly on each part.
5. Now after filling the 4th layer, the excess concrete is struck off with the trowel.
6. After the mould completely filled, then the mould removed from the concrete immediately in a vertical direction by raising it slowly and carefully.
7. This allows the concrete to subside. This we know as SLUMP.

Result:-

1. Now, we have to measure the height of the mould & highest point of the slump in mm.
2. The difference between the Height of the mould and highest point of the Subside gives the Slump value.

To learn about the quantity of Cement, sand and aggregate used for Different grades of concrete, click here. 

Slump test values for Different Concrete Mixes:- 

Slump test values for Different Concrete Mixes:- 

Below are the Different Types of Slump in Concrete are listed below :-

1. True Slump :- 

If Concrete Slumps evenly forms a shape same as a mould then we called it as true slump.

2. Shear Slump:-

If half of the slump is slides or falls down then it is called as Shear Slump. 

This is the indication of that concrete is non-cohesive and have characteristics of segregation.

3. Collapse Slump:-

In these case, the c if the whole slump falls down in all directions & does not maintain the shape of mould, then it is called as Collapse slump. 

This Slump formed due to addition of excessive amount of water in concrete to increase the workability.

4. Zero Slump:- 

This test doesn’t suitable for Dry and Stiff concrete. For very Dry & high stiff concrete does not show any difference after removing the mould.

Limitations:-

1. Slump test cannot be performed, if the aggregate used in concrete is above 40mm size.
2. This test is not suitable for very dry & high stiff concrete.

Advantages:-

1. Slump test procedure can be performed in laboratory as well as construction site.
2. Slump test requires less apparatus, when compared with the other tests.
3. Time required for the results will be less as compared to other tests. 

Watch Video of the Slump test of concrete .

Video 1 :

Video 2 :

 

Compressive Strength of Concrete 

Hello friends, today in this post you will learn the Compressive strength test of concrete with calculations & detail stepwise procedure. 
So, don't skip to read the post completely. After reading the post, you will completely understand the simple tests of the Compression test on concrete cubes. 
So, let's start with these amazing topic... 

What is the Compressive strength ?

In general, Compressive strength means the capacity of material or structure to resist or to withstand under compression. 

The Compressive strength of a material means the ability of the material to resist failure in the form cracks as well as the  fissure.

In this test, we apply pushing force on the both faces of concrete specimen and the maximum compression that concrete can withstand without failure is noted.

In Actual, it means the Compressive strength of concrete is also can be defined as the Characteristic strength of 150 x 150 x 150 mm size concrete cubes at 28 days.

Compressive strength of Concrete and its importance :-

As you know that, concrete is a mixture of cement, sand, aggregates & water. As the strength of the concrete depends upon many factors like individual compressive strength of  materials used for manufacturing of concrete such as (Cement, Sand, aggregate), quality of materials used, air entrainment mix proportions, w/c  ratio, curing methods used and temperature effects.

Factors affecting compressive strength of concrete:-

Coarse aggregate:-

Concrete is made from the homogenous mixture by combining the aggregates, cement, sand, water and various other admixtures. But even with proper mixing, there may arise some microcracks due to differences in thermal and mechanical properties of coarse aggregates and cement, which leads to failure of concrete.

Researchers came up with theoretical concepts regarding size of aggregates, which as the size of aggregate being the major contributor of compressive strength. So if the size of aggregate is increased, it will definetely increased compressive strength of concrete.

This theory was later discarded, after performing many experiments proved that greater size of aggregates showed increased strength in initial phases, but it get reduced exponentially.

The major reason for the decrease in the strength was due to the reduced surface area for bond strength between cement mix and aggregates and weaker transition zone.

Air-entrainment:-

Air entrainment in concrete concepts developed by cold countries in order to prevent damages due to the freezing and thawing of water particles in pores of concrete . Later after performing various tests, finally proved that the benefits of air entrainment improves the workability of concrete at lower water/cement ratio.

The desired workability at lower w/c ratio will helps to achieve concrete with the greater compressive strength, these will leads to light concrete with greater compressive strength.

Water/Cement ratio:-

We all know that excess water can cause harm to the strength of concrete. Cement being the major binding material in concrete needs water for hydration process, but in limit (0.20 to 0.25) % of cement content. The excess water will affect on the workability as well as the finishing of concrete.

The excess water is considered harmful because, if the water in the concrete mix dries, it leaves large interstitial spaces among aggregate and cement grains. This interstitial space may cause the cracks during compressive strength testing of concrete.

Why do we test concrete for 7 days, 14 days & 28 days:

As we know that, Concrete gains maximum strength at 28days. In the construction sector great amount of capital is at stake, due to these reason, instead of checking strength at 28 days, we check the strength in terms of concrete strength psi at 7 and 14 days to predict the target strength of construction work.

From the reference of below given table it is clear that, Concrete gains 16 % of its strength within 24 hrs, whereas concrete gains 65% of the target strength on the 7 days of its casting.

On 14 days, the concrete gains 90% of the target strength and thereafter the gain in strength slows down and it takes 28 days to achieve 99% of strength.

We cant judge the strength of concrete until it becomes stable. Also we can't wait for 28 days to determination of the suitability of concrete for construction works.

The maximum strength gain is observed till 14 days, so we test concrete at an intervals of 7 days, 10 days & 14 days and If concrete fails to show results of 90% of its overall strength at 14 days. then that concrete of that batch is rejected.

Compressive Strength of Different Grades of Concrete at 7, 14, 21 and 28 Days :

Compressive strength testing of concrete:-

For determination of Compression test, we require 150 x 150 x 150 mm size concrete cubes on a Universal testing machine or compressive testing machine.

Apparatus

As per IS: 516-1959 Compressive testing machine (2000Kn),15cm×15cm×15cm steel cube moulds or Cylinder having Dia. 15cm and length 30cm.

Below are the Compression test steps:-

Preparing of material for Cube test:
Mixing of concrete:

Required materials must be brought and stored at an approximate temperature of 27 ±3 degree Celsius. Cement must be uniformly mixed with a trowel, no lumps should be present in it.

The ingredients should not be mixed more than 2 minutes and the following pattern must be followed :

1>Calculated water, 2>50% coarse aggregates, 3>fine aggregates, 4>cement, 5>50% coarse aggregates.

The mixing process must be done on the rectangular non-porous pan until a homogenous mix is obtained. 

Dry mixing of fine aggregates and cement>addition of Coarse aggregate with the even distribution>addition of calculated water in batch till consistency is achieved.

Casting of specimen
Compaction
Age of test

The moulds for concrete cubes should be made of cast iron and proper oiling should be done on inner side of each moulds for the easy removal of cubes. The specimen must be cast in 3 layers and properly compacted in order for prevention of honeycombing.

In compaction should be done with the tamping bar, 35 strokes must be done in all parts of a cube for proper compacting. This tamping bar has the dimension of diameter 16mm and length of 0.6m.

The Compressive strength on concrete cubes can be done on 1,3, 7, 14 and 28 days. In some cases, the strength of greater ages is required which is performed after 13 to 52 weeks of casting.

Number of specimens

It is mandatory to have at least 3 specimens for testing from different batches. The mean of compressive strength achieved by this specimen is used to determine actual strength of the batch.

Procedure for Compressive strength of concrete or Cube test  :-

1. Place the prepared concrete mix in the steel cube mould for casting.

1. When the concrete get sets, After 24 hours remove the concrete cube from the mould.

1. Now we have to Keep the test specimens submerged underwater for stipulated time.

1. 
   
   
   
   

1. The specimen must be kept in water for 7, 14 or  28 days and for every 7 days the water is changed.

1. While performing the test, we must Ensure that concrete specimen must be well dried, before placing it on the UTM.

1. We have to also take, the Weight of samples in order to proceed with testing and it must not be less than 8.1 Kg.

1. Testing specimens are placed in the space between bearing surfaces.

1. Important thing to remeber that, we must take Care that to prevent the existence of any loose material or grit on the metal plates of machine or specimen block.

1. The concrete cubes are placed on bearing plate and aligned properly with the center of thrust in the testing machine plates.

1. 
   
   
   
   

1. Also note that, The loading must be applied axially on specimen without any shock and increased manner at the rate of 140kg/sq cm/min. till the specimen collapse.

1. Due to the constant application of load, the specimen starts cracking at a point & final breakdown of the specimen must be noted.

Calculations

Compressive strength of Concrete Formula:

The Compressive strength of specimen can be easily calculated by dividing maximum load carried by the specimen by cross-sectional area of the specimen cubes.

The surface area of specimen: = 150 x 150 = 22500mm² = 225cm²

Assume, The Max compression load noted as 450KN

1 KN = 1000N ; 450KN = 450×100 = 450000N

Compressive Strength of Concrete  = 450000 / 22500 = 20 N/mm² = 203 Kg/cm²

The same calculation is done for the specimen at different ages as stated below:

Important Note: As per IS: 516-1959  Minimum three specimens should be tested at each selected age (that means three specimens at 7 days, three specimens @ 14 days & 28 days) If strength of any specimen varies by more than 15%  of average strength, such specimen should be rejected. 

Results of cube test
Here is the Video Explanation :

Average Compressive strength at 7 days = _____N/mm²

The average Compressive strength at 28 days = _____N/mm².

You can also take reference of below video for better understanding of Compressive strength of concrete :

Also read our Blogs on other cement tests... .

• Soundness test of Cement.

• Fineness test of Cement.

• Initial & Final Setting time of cement

• Specific gravity test of Cement. 

• Compressive strength test of Cement. 

• Field test of Cement or How to check the quality of Cement on site. 

• What Is Cement & Types of Cement Used for Construction works

Also read other Blogs on :

• Compressive Strength of Concrete 

• Schmidt hammer or Rebound Hammer test of Concrete

• Rebound hammer test application, procedure, etc.

• How to estimate compressive strength of Concrete.

• Schmidt Hammer test of concrete.

• Non-destructive test of concrete

Also read : 

Why concrete is tested at 28 days.

WHY DO WE CHOOSE 7, 14 AND 28 DAYS FOR CONCRETE OR COMPRESSION TESTS?

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