Self-Compacting Concrete (SCC): Understanding the J-Ring Test for Workability

What Is Self Compact Concrete?

Making concrete structures without vibration has been done in the past. For example, the placement of concrete under-water is done by the use of tremie without vibration.

Shaft concrete and mass concrete may be successfully placed without vibration. But the above examples of concrete are normally of lower strength and difficult to obtain consistent quality. Modern application of SCC (self-compacting concrete) is focussed on high performance, better and more reliable, and uniform quality.

List of Test Methods for Workability Properties of Self Compacting Concrete (SCC).

1. Slump flow by Abrams cone.

2. T_{50 cm} Slump flow

3. J-ring

4. V-funnel

5. V-funnel at T₅ minutes

6. L-box

7. U-box

8. Fill-box

9. GTM Screen Stability Test

10. Ouimet

In this article, we are discussion & Procedure Slump Flow Test  

What Is J-ring Test?

J-ring test denotes the passing ability of the concrete.

The equipment consists of a rectangular section of 30 mm x 25 mm open steel ring drilled vertically with holes to accept threaded sections of reinforcing bars 10 mm diameter 100 mm in length.

The bars and sections can be placed at different distances apart to simulate the congestion of reinforcement at the site.

Generally, these sections are placed 3 x maximum size of aggregate.

The diameter of the ring formed by vertical sections is 300 mm and height 100 mm.

J-ring Test?

Equipment of J-ring Test.

Slump Cone 

The usual slump cone having a base diameter of 200 mm, top dia. 100 mm, and height 300 mm are used.

Base Plate For J-ring Test

A stiff base plate square in shape is 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

J Ring For J-ring Test

J-ring-rectangular section 30mm x 25mm planted vertically to form a ring 300 mm dia generally at a spacing of 48 ± 2mm

Trowel

This tool is used to place cement mortar.

Scoop

This use in QC department for the material.

Measuring tape

To measure the length.

Procedure of the J-Ring Test.

1. About 6 liters of concrete is needed for the test.
2. Moisten the inside of the slump cone and base plate.
3. Place the J-Ring centrally on the base plate and the slump cone centrally inside the J-ring.
4. Fill the slump cone with a scoop.
5. Do not tamp. Simply strike off the concrete level with a trowel.
6. Remove all surplus concrete.
7. Raise the cone vertically and allow the concrete to flow out through the J-ring.
8. Measure the final diameter in two perpendicular directions.
9. Calculate the average diameter.
10. Measure the difference in height between the concrete just inside J-Ring bars and just outside the J Ring bars.
11. Calculate the average of the difference in height at four locations in mm.s.
12. Note any border of mortar or cement paste without coarse aggregate at the edge of the concrete.
13. The acceptable difference in height between inside and outside should be between 0 and 10 mm.

Calculations of J-Ring Post

The J-ring flow spread SJ is the average of diameters d_max and d_perp, SJ is expressed in mm to the nearest 5 mm.

SJ = ( d_max + d_perp) /2  = _________ mm

The J-ring blocking step BJ is calculated as,

BJ = (Δhx1+ Δhx2+ Δhy3+ Δhy2) / 4 -Δh0

Where Δhx1 and Δhx2 are height differences between the lower edge of the straight rod and the concrete surface in the x-direction.

Δhy1 and Δhy2 are height differences between the lower edge of the straight rod and the concrete surface in the y-direction (perpendicular to x as shown in the figure).

Δh0 is the height difference between the lower edge of the straight rod and the concrete surface at the central position.

BJ = ________ mm

Calculate the difference between slump flow and J ring flow

Results of J-Ring Post

J-ring flow spread SJ of self compacting concrete = _________ mm

FAQs on Self-Compacting Concrete (SCC) and J-Ring Test

What is Self-Compacting Concrete (SCC)?

Self-Compacting Concrete (SCC) is a type of concrete that can flow and fill the formwork without the need for mechanical vibration. It is known for its high performance, better reliability, and uniform quality compared to traditional concrete.

Why is SCC used?

SCC is used to achieve higher performance and more reliable and uniform quality in concrete structures. It is particularly useful in complex structures with dense reinforcement and in applications where vibration is not feasible.

What are the common test methods for SCC workability?

The common test methods for assessing the workability properties of SCC include:

1. Slump flow by Abrams cone
2. T50 cm Slump flow
3. J-ring
4. V-funnel
5. V-funnel at T5 minutes
6. L-box
7. U-box
8. Fill-box
9. GTM Screen Stability Test
10. Ouimet

What is the J-Ring Test?

The J-Ring test measures the passing ability of SCC, indicating how well the concrete can flow through obstructions such as rebar without segregation.

What equipment is required for the J-Ring Test?

The equipment required for the J-Ring test includes:

1. Slump cone
2. Base plate with concentric circles
3. J-Ring with rectangular sections
4. Trowel
5. Scoop
6. Measuring tape

What is the procedure for conducting the J-Ring Test?

The procedure for the J-Ring test involves:

1. Preparing about 6 liters of concrete.
2. Moistening the slump cone and base plate.
3. Placing the J-Ring and slump cone centrally on the base plate.
4. Filling the slump cone with concrete without tamping.
5. Striking off the excess concrete.
6. Lifting the cone to allow the concrete to flow through the J-Ring.
7. Measuring the final diameters and height differences of the concrete spread.
8. Calculating the flow spread (SJ) and blocking step (BJ).

How is the J-Ring flow spread (SJ) calculated?

The J-Ring flow spread (SJ) is the average of the maximum diameter (dmax) and the perpendicular diameter (dperp) of the concrete spread. It is expressed in millimeters to the nearest 5 mm.

How is the J-Ring blocking step (BJ) calculated?

The J-Ring blocking step (BJ) is calculated by averaging the height differences between the concrete surface and the lower edge of the straight rod at four locations, minus the central position height difference.

What is the acceptable height difference in the J-Ring test?

The acceptable difference in height between the concrete just inside and just outside the J-Ring bars should be between 0 and 10 mm.

What results are obtained from the J-Ring Test?

The results of the J-Ring test include the J-Ring flow spread (SJ) and the J-Ring blocking step (BJ), which indicate the passing ability and flow characteristics of the SCC.