Self-Compacting Concrete Test is slightly different from the tests that are conduction on normal concrete. There are three basic characteristics of self-compacting concrete namely filling ability (flowability), passing ability (free from blocking due to the presence of reinforcement), and resistance to segregation (stability/homogeneity).
Therefore, it is very necessary to carry out field or mock trials to assess these characteristics. Unfortunately, so far not a single test has been devised to confidently measure anyone of these properties.
A number of tests have been developed and used by many organizations but all these tests are elementary in nature and none of the tests have been standardized.
The most commonly used tests are the Slump Flow Test, V Funnel Test, L Box Test, ‘U’ Box Test, and Fill Box Test. In addition to these tests, there are other tests like the ‘J’ ring test, etc.
Read More: Self Compacting Concrete Mix Design
Self Compacting Concrete Test
5 most commonly used self-compacting tests as listed below,
- Slump Flow Test
- V-Funnel Test
- L-Box Test
- U-Box Test
- Fill Box Test
1. Slump Flow Test
This is one of the simplest tests initially developed in Japan for the assessment of underwater concrete. It is the most commonly used test for SCC and gives a good assessment of filling ability.
However, it gives no indication of the ability of the concrete to pass between the reinforcement without blocking but may give some indications of resistance to segregation.
This test can be used at the site to assess the consistency of supply of ready mix concrete, which has been designed after assessment of various characteristics based on the above-mentioned five tests or more..
The method of execution of the Slump Flow Test is illustrated in Figure. The procedure for execution of this test is as follows:
- Position the slump cone at center of the leveled flow table as show in figure.
- Pour the concrete with a scoop from top without any tamping to fill the slump cone completely. Strike off excess concrete.
- Lift the cone vertically without any jerks and allow the concrete to flow freely on leveled surface.
- Note the time required for the concrete to flow 50 cm diameter spread circle. The time is measured from the time lifting cone starts.
- After that measure the average flow diameter of concrete after concrete stops flowing.
- This value in mm is known as slump flow value (mm).
- Slump flow is the mean diameter in two perpendicular directions of the concrete spread after the concrete had stopped flowing. The slump flow time is the time taken for the concrete to spread by 50 cm.
- A high slump flow value indicates greater flowability and lesser resistance to segregation.
- If the time value is observed to be less than the minimum range value specified then it indicates that viscosity is very low leading to segregation.
- If the time value is observed to be more than the maximum range value specified, it indicates very stiff and nonflowable concrete.
- The permissible range of values for slump flow is 650 mm to 800 mm.
2. V-Funnel Test
V-Funnel Test is designed to assess the flowability and also segregation resistance of Self Compacting Concrete. The figure indicates the dimensions of the funnel used and another figure illustrates the method of execution.
The procedure for execution of the test is as follows.
- Position the ‘V’ funnel along with supporting arrangement on firm or level ground.
- Moisten the internal surface thoroughly with a wet sponge and close the trap door.
- Pour the concrete from the top of the funnel without any external efforts either to compact or level it.
- Open the trap door as quickly as possible after filling the funnel without giving any jerk to the test setup.
- Note the time required to empty the funnel completely in seconds, which is T0.
- Repeat the same procedure with only change that the trap door is opened after 5 minutes of filling completely and note the time required to empty the funnel completely in seconds, which is T5.
- As per the present guidelines, T0 from the test should be in the range of 8 to 12 seconds and T5 should be less than 3 seconds over T0.
- If T5 is more than 3 seconds over T0 then there are chances that the SCC mix will segregate.
3. L-Box Test
- L-Box test is used mainly to assess the passing and filling ability of Self Compacting Concrete. The apparatus consists of an “L” shaped rectangular box section.
- Concrete is designed to pass through the obstructions of known clearances. The vertical section is filled with concrete and the gate is lifted to let the concrete flow into the horizontal section through the vertically placed steel bars.
- When the flow stops the height of the concrete h2 at the end of the flow is measured along with height h1 in the vertical box next to the obstruction. T
- he ration h2/h1 is a measure of the passing ability of SCC. The blocking value for SCC should be between 0.80 to 1.0. if the blocking value is less than 0.80 it indicates viscosity is too high. A ratio close to 1, indicates false results.
- Both passing ability and segregation resistance can be detected during the test visually also. If concrete builds a plateau in front of reinforcement bars, concrete has either got blocked or has segregated.
The procedure for performing such a test is as follows:
- Place the L-box on firm/level ground.
- Moisten the internal surface thoroughly and close the trap door.
- Fill the vertical section of the apparatus with concrete completely.
- After a minute lift the gate without any jerk.
- Measure the height of concrete at the obstruction (h1) and at the end of flow (h2)
- With respect to bottom of the ‘L’ box.
- The ratio of h2/h1 as measured above gives the blocking value of SCC.
4. U-Box Test
- This test is used to assess the pass-ability of Self-compacting concrete.
- The equipment is as shown in the figure. This equipment has a ‘U’ shape and an opening with a sliding gate is fixed between the two compartments with vertical steel bars as obstructions.
- Concrete is made to flow through the obstructions and the level difference between the top surfaces of concrete in both the compartments is measured.
The procedure for performing ‘U’ Box test is as follows:
- Place the ‘U’ box on firm/level ground.
- Moisten the internal surface thoroughly and close the central door.
- Fill the concrete in the left compartment completely.
- Wait for a minute and lift the gate without any jerk & let the concrete flow.
- Gently wipe the slurry adhered to the face of the left compartment without disturbing the top surface of the concrete to enhance the visibility.
- Measure the difference of height between the concrete surfaces on either compartment. This difference will evince the self-leveling ability and passing ability of the concrete.
- The permissible range for difference h1-h2is 30mm. a difference of more than 30mm indicates the possibility of blockage with viscosity being on the higher side. If h1-h2 is close to ‘0’, it indicates low viscosity and concrete could easily pass through.
5. Fill Box Test
- This test is used to assess the filling ability of Self Compacting Concrete. The apparatus consists of a transparent rectangular box with a number of obstructions through which concrete is made to flow.
The procedure for conducting this test is as follows:
- Place the apparatus on firm-level support having a height of 1 meter approximately.
- Fill concrete in the box through the funnel provided at the top of the box until it covers the topmost obstacles at the far end of the box.
- Then measure the height of the concrete at both ends so that the volume of concrete-filled can be calculated.
- Compare the net volume of concrete-filled with respect to the volume of the box up to the top of the topmost obstacles, which gives the filling capacity of SCC.
Figures illustrate the execution of this test.
Acceptance Test Criteria For Self compacting concrete:
Typical acceptance test criteria for SCC with a maximum aggregate size up to 20mm are given in the below table.
|Sr. No||Test||Unit||Acceptable Range of Values|
|1||Slump Flow Test||mm||650-800|
|2||V Funnel T0V Funnel T5||Sec. Increase over in sec.||8-12* 0-3|
|3||L Box (h2/h1)||Ratio||0.8-1.0|
|4||U Box (h1-h2)||mm||<30|
|5||Fill Box||%||Min 90 (90-100)|
- If ‘V’ funnel results are less than 8 sec, decrease the water/powder ratio in the mix. If it is more than 12 sec., increase the water/powder ratio.
- It is the time needed in the slump flow test for concrete to spread by 50 cm.
- Typical ranges of values indicate in the above table are based on current knowledge and practice. They have undergone changes with respect to the previous range values.
- Hence, future developments/experience may lead to further modifications in the ranges indicated.
- Values outside these ranges may also be acceptable if it can be demonstrated that satisfactory performance is obtained in the specific conditions, e.g. large spaces between reinforcement, layer thickness less than 500mm, a short distance of flow from point of discharge, very few obstructions to pass through in the formwork, very simple design of formwork, etc.
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