A Concrete Test
The process of determining the suitability and durability of concrete is termed a concrete test. This test is basically carried out to know the strength of the concrete produced whether it can withstand the proposed structure load or not. A concrete test is one of the important things to carry out in a concrete construction project. The excess of this test is to ensure safety and durability. The concrete test comprises more than 6 types. But for the sake of this article, we will look at the first three type of concrete test as listed below.
- Slump test
- Compaction factor test
- Compressive strength test
- Tensile strength test
- Flexural strength test
- Water permeability test
- Water absorption test
- Rapid chloride Ion penetration test
Slump Test of a concrete
The first test that is carried out on concrete in its production is the slump test. The consistency of a fresh concrete before setting is been determine by this test. It is also used to check the workability and the easy flow of a concrete.
Firstly, a fresh concrete is collected after batching and is been load into apparatus called slump cone or Abrams cone in three layers with each layer been accompany by 25 blows of 16mm rod. After the last blow on the last layer, the cone is leveled with a leveling knife. The cone is been remove immediately after the leveling and placed beside the casted concrete. The difference in the cone height and the casted concrete (slump height) is measured with the aid of a steel tap and a straight edge pole that is put across the concrete and the cone. The difference in the concrete height and the cone height is called the slump value. See diagram below.
Compaction Test of a concrete
After the slump test, the next is the compaction test. the degree of compaction and workability of a concrete produced is been determine by a compaction test. This test is carried out with the aid of an apparatus called a compaction factor machine. The machine comprises of two hoppers that have a gate at their lower ends and a cylinder at the bottom end. See the figure below.
To carried out this test, firstly, the gates at the lower ends of the two hoppers are looked and the upper hopper is loaded with a concrete sample collected from the batch without compacting it. After loading, the gate of the upper hopper is opened for the concrete to flow into the second hopper. When the whole concrete flows from the first hopper into the second hopper, its gate is in turn opened for the concrete to flow into the cylinder. After the flow of concrete into the cylinder, the cylinder is then leveled with a leveling knife and weighed on a weighing balance and its readings are recorded. The recorded value is called the partial compacted value.
Again, the concrete in the cylinder is poured out and reloaded into the cylinder in three layers with 25 blows of 16mm rod on each layer and leveled with the leveling knife after the last blow on the last layer. After that, the cylinder is placed on a weighing balance and its reading is recorded. Finally, with the records, the desire compaction factor value is then calculated using the formula thus:
Compactionfactor = weight of partially compacted concrete/Weight of fully compacted concrete.
Compressive Strength concrete
The third common test carried out on a concrete is compressive strength test. This test is used to determine the ability of the concrete to withstand loading. According to the standard laid down, the test carried out at the due day of the concrete age. The ages of a concrete ranged from 7days to 28days even to 90days depending on the required condition. Furthermore, before carrying out this test, the concrete to be tested will undergo a process called curing.
Curing Process of a Concrete
This is the process of maintaining adequate moisture content and favorable temperature in the concrete after placement to ensure that desire strength and other properties of concrete are obtained. This process can take 7days, 21days, 28days etc., depending on the requirement stated in the design mix. See the figure below.
Testing the Concrete
In testing concrete, concrete cubes are cast using common molds measuring 150mmx150mmx150mm or otherwise specified. After casting, the cubes are demolded and place in water to undergo a curing process for specified ages ranging from 7days, 14days to 28days as the case may be. When these ages are reach, three cubes are taken to the lab for a test using apparatus called concrete crushing machine. See the figure below.
Procedure of compressive strength test of a concrete.
Firstly, When the specified ages are reached, the cubes are taken out of the water and allow to dry. After that, the cubes are weighed with the aid of a weighing balance and recorded. Secondly, each of the cubes is placed in the machine. Thirdly, apply different loads until failure occurred. Finally, when a failure occurs, the value of the load at which failure occurred is recorded. This process is repeated for all the sample cubes at different ages and their respective compressive strength is been calculated using the formula below:
Compressive strength = load x 100 x 9.81/2.2046 x (150 x 150) mm and the unit is (N/mm2)