Self-compacting concrete (SCC) is a highly flowable, non-segregating concrete that fills uniformly and completely every corner of formwork by its own weight and encapsulate reinforcement without any vibration, whilst maintaining homogeneity.
A concrete mix can only be classified as self-compacting concrete if the requirements for all below-mentioned characteristics are fulfilled:
- Filling ability (Flowability)
- Passing ability,
- Segregation resistance
So to measure all these parameters following are some of the tests procedure which is recommended by EFNARC.
- Test Methods For Workability of Self Compacting Concrete
- 1. Slump Flow & T50cm Test
- 2. J-Ring Test
- 3. V-Funnel Test and V-Funnel Test at T5 Min.
- 4. L-Box Test Method
- 5. U box test method
- 6. Fill box test method
Test Methods For Workability of Self Compacting Concrete
1. Slump Flow & T50cm Test
The slump flow test is done to assess the horizontal flow of concrete in the absence of obstructions. It is the most commonly used test and gives a good assessment of filling ability. It can be used at the site, the test also indicates the resistance to segregation. When the slump cone is lifted, start the stopwatch and find the time taken for the concrete to reach a 500 mm mark. This time is called T50 time. This is an indication of the rate of spread of concrete.
- The usual slump cone having a base diameter of 200 mm, top diameter 100mm, and height 300mm is used.
- A stiff base plate square in shape having at least a 700 mm side. Concentric circles are marked around the center point where the slump cone is to place. A firm circle is drawn at 500 mm diameter
- A trowel
- Measuring tape
About 6 liters of concrete is needed for this test.
- Place the baseplate on level ground.
- Keep the slump cone centrally on the base plate.
- Fill the cone with the scoop. Do not tamp. Simply strike off the concrete level with the trowel.
- Remove the surplus concrete lying on-base place.
- Raise the cone vertically and allow the concrete to flow freely.
- Measure the final diameter of the concrete in two perpendicular directions and calculate the average of the two diameters. This is the slump flow in mm.
Note that there is no water or cement paste or mortar without coarse aggregate is seen at the edge of the spread concrete.
The higher the flow value, the greater its ability to fill formwork under its own weight. A value of at least 650 mm is required for SCC. In case of severe segregation, most coarse aggregate will remain in the center of the pool of concrete and mortar and paste at the periphery of concrete. If lower T50 time then it indicates greater flowability.
2. J-Ring Test
J-ring test denotes the passing ability of the concrete. It is also a common test method at site The bars and sections in this test can be placed at a different distance apart to simulate the congestion of reinforcement at the site. Generally, these sections are placed 3 times the maximum size of aggregate. The diameter of the ring formed by vertical sections is 300 mm and height 100 mm.
- Slump cone without foot pieces.
- Base plate at least 700 mm square
- J-ring-rectangular section 30mm x 25mm planted vertically to form a ring 300 mm dia. generally at a spacing of 48 ± 2mm.
About 6 liters of concrete is needed for the test.
- Moisten the inside of the slump cone and base plate. P
- lace the J-Ring centrally on the base plate and the slump cone centrally inside the J- ring.
- Fill the slump cone with a scoop, do not tamp. Simply strike off the concrete level with a trowel.
- Remove all surplus concrete.
- Raise the cone vertically and allow the concrete to flow out through the J-ring.
- Measure the final diameter in two perpendicular directions.
- Note any border of mortar or cement paste without coarse aggregate at the edge of the concrete.
If the concrete has a good passing ability then the spread of concrete with the J ring and without the J ring would be the same or typically a max difference of 50mm in the spread will be observed.
3. V-Funnel Test and V-Funnel Test at T5 Min.
V- Funnel test is used to determine the filling ability (flowability) of the concrete with a maximum size of aggregate 20 mm size. The funnel is filled with about 12 liters of concrete, and the time taken for it to flow down is noted. After this, the funnel can be filled with concrete and left for 5 minutes to settle. If the concrete shows segregation, then the flow time will increase significantly.
- Bucket 12 liters
- About 12 liters of concrete is needed for this test, set the V-funnel on firm ground, and moisten it from inside of the funnel.
- Close the trap door and place a bucket underneath and then fill the apparatus completely with concrete no compaction or tamping to be done.
- Open the trap door after 10 sec. and record the time taken for the concrete to flow down. This can be judged when the light is seen when viewed from the top. The whole test is to be performed within 5 min.
Procedure for flow time at T5 min.
- Do not clean or moisten the inside surface of the funnel.
- Close the trap door and refill the V-funnel immediately after measuring the flow time, place the bucket underneath.
- Fill the apparatus completely with concrete without tamping or tapping and then strike off the concrete level with the top by trowel.
- Open the trap door again after 5 minutes and allow the concrete to flow and calculate the time taken for complete discharge. It is called the flow time at T5 min.
This test measures the ease of flow of the concrete; shorter flow times indicate greater flowability. For SCC a flow time of 10 seconds is considered appropriate.
The inverted cone shape restricts flow, and prolonged flow times may give some indication of the susceptibility of the mix to blocking. After 5 minutes of settling, segregation of concrete will show a less continuous flow with an increase in flow time, for V-funnel test the flow time should be between 8 and 12 seconds. for V- funnel flow time at T5 min.+ 3 seconds is allowed.
4. L-Box Test Method
The test assesses the flow of concrete and also, the extent to which the concrete is subjected to blocking by reinforcement it is mostly preferred while underwater concreting to be done
- L box of a stiff non-absorbing material
- About 14 liters of concrete is required for this test, the vertical section is filled with concrete, then the gate lifted to let the concrete flow into the horizontal section.
- When the flow has stopped, the height of the concrete at the end of the horizontal section is expressed as a proportion of that remaining in the vertical section (H2/H1in the diagram). It indicates the slope of the concrete when at rest. This is an indication passing ability or the degree to which the passage of concrete through the bars is restricted.
If the concrete flows as freely as water, at rest, it will be horizontal. Therefore H2/H1 will be equal to 1. Therefore, nearer the test values, the blocking ratio, is to unity, the better the flow of concrete minimum acceptable value of 0.8 is preferred. T20 and T40 time can give some indication of ease of flow, but no suitable values have been suggested.
5. U box test method
The test is used to measure the filling ability of self-compacting concrete. It consists of a vessel that is divided by a middle wall into two compartments This is a simple test to conduct, but the equipment may be difficult to construct. It provides a good direct assessment of filling ability
- U box of a stiff non-absorbing material
- About 20 liters of concrete is needed to perform the test,
- Moisten the inside surfaces of the apparatus,
- remove any surplus water fill the one compartment of the apparatus with the concrete sample leave it to stand for 1 minute.
- Lift the sliding gate and allow the concrete to flow out into the other compartment. After the concrete has come to rest, measure the height of the concrete in the compartment that has been filled, in two places, and calculate the mean (H1).
- Measure also the height in the other compartment (H2) Calculate H1 – H2, which is also known as the filling height, and it should be as low as possible.
If the concrete flows as freely as water, at rest it will be horizontal, so H1 – H2 = 0. Therefore, the nearer this test value, the ‘filling height’, is to zero, the better the flow and passing ability of the concrete.
6. Fill box test method
The test is used to measure the filling ability of self-compacting concrete with a maximum aggregate size of 20mm. It consists of a container (transparent) with a flat and smooth surface, a container is filled with concrete through this filling pipe and the difference in height between two sides of the container is a measure for the filling ability.
Even a concrete mix with a high filling ability will perform poorly if the passing ability and segregation resistance are poor, it is complex and difficult to perform on-site hence not used commonly.
- Fill box of a stiff, transparent, non-absorbing material
- Scoop 1.5 to 2 liter
About 45 liters of concrete is needed to perform the test, Moisten the inside surfaces of the apparatus, remove any surplus water, fill the apparatus with the concrete sample.
Fill the container by adding every 5 seconds one scoop with 1.5 to 2 liters of fresh concrete into the funnel until the concrete has just covered the first top obstacle. Measure after the concrete has come to rest, the height at the side at which the container is filled in two places and calculate the average(h1). Do this also on the opposite side (h2). Calculate the average filling percentage as Average filling
If the concrete flows as freely as water, at rest it will be horizontal, so the Average filling percentage = 100%. Therefore, the nearer this test value, the ‘filling height’, is to 100%, the better the self-compacting characteristics of the concrete.