There are projects that contain a thousand cubic meters of concrete and if the engineer does not carefully plan the checkpoints and routes of the concrete mixers, it might create a delay in pouring the concrete and eventually create a problem in the concrete itself.
In addition, the potential worst case scenario is the failure of the slump test for concrete when it arrives at the checkpoint, due to delays in the concrete's arrival as well as the time of checking the slump of the concrete.
Now, in order to avoid such issues, the proper steps to check the slump of concrete are discussed below.
Here are seven steps to properly check the slump of concrete.
The engineer will collect the delivery note of the concrete from the driver of the truck mixer when it arrives at the checkpoint. And he or she will make sure that the delivered concrete matches the design mix of the concrete to be poured.
Extra care must be applied in receiving the concrete on site. Sometimes there is a nonconformance of the delivered concrete—that was what I experienced in one of our projects.
Read Also: 7 Types of Concrete Test
If truck mixers have arrived at the checkpoint, the drum of the truck mixer should be rolled before taking the amount of concrete for cube or cylinder sample. Rolling the drum again will properly mix the concrete.
This is to ensure an equal distribution of the concrete constituents in the concrete mix.
Make sure to use the wheelbarrow to get a sample of fresh concrete, as the concrete will not drop at an unacceptable height. Clean the wheelbarrow with water, making sure there is no dirt stuck to the surface basin of the wheelbarrow so that the concrete will not absorb unnecessary materials.
Position the wheelbarrow at the point where the concrete will fill exactly in the center.
It is necessary to check the temperature of the concrete as per specifications, in order to control the workability of the concrete. The concrete may have an immediate shrinkage due to high temperature.
Once the fresh concrete is in the wheelbarrow, place the probe of the thermometer through the concrete, making sure that the probe is sunk properly so that no ambient temperature will be taken, which could result to a false result.
A fresh concrete of more than 30 degrees Celsius may be rejected. Therefore, extra care is recommended during concrete batching.
Read Also: Concrete Curing How it is Done
In order to ensure a good flow of the concrete, the technician who does the slump should ensure the slump tray is cleaned so that it will not provide a false result in the slump test. Dampen the table tray before placing the slump cone.
Make sure that the table tray is at the same level.
Place the slump cone on the table tray and the technician should stand firmly on the pins of the cone to make it temporarily rigid, and will not move during the placing and tamping of the concrete.
Fill the slump cone with fresh concrete in 3 layers, and tamp each layer with a 16mm diameter round bar in 25 blows. Ensure that during tamping, the round bar does not go through the bottom layer when tamping at the second layer so that it will not go beyond the required no. of blows for each layer.
Measure the slump after tamping and leveling the concrete on the top of slump cone. The required height of the slump varies, depending on the concrete design mix. The slump determines the workability of the concrete. The higher the slump, the greater the workability of the concrete.
Workability simply means the concrete is capable being molded, compacted and transported without segregation.
The above steps must be followed in order to avoid compromising the quality of the concrete delivered on site and ultimately to prevent the rejection of the concrete.
In addition, the potential worst case scenario is the failure of the slump test for concrete when it arrives at the checkpoint, due to delays in the concrete's arrival as well as the time of checking the slump of the concrete.
Now, in order to avoid such issues, the proper steps to check the slump of concrete are discussed below.
Here are seven steps to properly check the slump of concrete.
1. Collect the concrete delivery note
The engineer will collect the delivery note of the concrete from the driver of the truck mixer when it arrives at the checkpoint. And he or she will make sure that the delivered concrete matches the design mix of the concrete to be poured.
Extra care must be applied in receiving the concrete on site. Sometimes there is a nonconformance of the delivered concrete—that was what I experienced in one of our projects.
Read Also: 7 Types of Concrete Test
2. Roll the drum of the concrete mixer
If truck mixers have arrived at the checkpoint, the drum of the truck mixer should be rolled before taking the amount of concrete for cube or cylinder sample. Rolling the drum again will properly mix the concrete.
This is to ensure an equal distribution of the concrete constituents in the concrete mix.
3. Take the fresh concrete with wheelbarrow
Make sure to use the wheelbarrow to get a sample of fresh concrete, as the concrete will not drop at an unacceptable height. Clean the wheelbarrow with water, making sure there is no dirt stuck to the surface basin of the wheelbarrow so that the concrete will not absorb unnecessary materials.
Position the wheelbarrow at the point where the concrete will fill exactly in the center.
4. Take a temperature check of the fresh concrete
It is necessary to check the temperature of the concrete as per specifications, in order to control the workability of the concrete. The concrete may have an immediate shrinkage due to high temperature.
Once the fresh concrete is in the wheelbarrow, place the probe of the thermometer through the concrete, making sure that the probe is sunk properly so that no ambient temperature will be taken, which could result to a false result.
A fresh concrete of more than 30 degrees Celsius may be rejected. Therefore, extra care is recommended during concrete batching.
Read Also: Concrete Curing How it is Done
5. Clean the slump tray or table tray
In order to ensure a good flow of the concrete, the technician who does the slump should ensure the slump tray is cleaned so that it will not provide a false result in the slump test. Dampen the table tray before placing the slump cone.
Make sure that the table tray is at the same level.
6. Place the fresh concrete in the slump cone
Place the slump cone on the table tray and the technician should stand firmly on the pins of the cone to make it temporarily rigid, and will not move during the placing and tamping of the concrete.
Fill the slump cone with fresh concrete in 3 layers, and tamp each layer with a 16mm diameter round bar in 25 blows. Ensure that during tamping, the round bar does not go through the bottom layer when tamping at the second layer so that it will not go beyond the required no. of blows for each layer.
7. Measuring the slump
Measure the slump after tamping and leveling the concrete on the top of slump cone. The required height of the slump varies, depending on the concrete design mix. The slump determines the workability of the concrete. The higher the slump, the greater the workability of the concrete.
Workability simply means the concrete is capable being molded, compacted and transported without segregation.
The above steps must be followed in order to avoid compromising the quality of the concrete delivered on site and ultimately to prevent the rejection of the concrete.
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