J-RING TEST FOR SELF COMPACTING CONCRETE

 The test is used to determine the passing ability of the concrete. Passing ability of SCC is defined as the ability of concrete to flow under its own weight to completely fill all spaces within the formwork. It is applicable for laboratory use in testing different concrete mixtures for passing ability or can be used in the field as a quality control test. It is typical to also perform a slump flow test with the J-ring test.

The principle of the J-Ring test may be Japanese, but no references are known. The J-Ring test itself has been developed at the University of Paisley.

It is applicable for laboratory use in testing different concrete mixtures for passing ability or can be used in the field as a quality control test. It is typical to also perform a slump flow test with the J-ring test.

The J-Ring can be used in conjunction with the Slump flow, the Orimet test, or eventually even the V-funnel. These combinations test the flowing ability and (the contribution of  the J-Ring) the passing ability of the concrete. The Orimet time and/or slump flow spread are measured as usual to assess flow characteristics. The J-Ring bars can principally be set at any spacing to impose a more or less severe test of the passing ability of the concrete. After the test, the difference in height between the concrete inside and that just outside the J-Ring is measured. This is an indication of passing ability, or the degree to which the passage of concrete through the bars is restricted.

ASSESSMENT OF TEST:-

 These combinations of tests are considered to have great potential, though there is no general view on exactly how results should be interpreted. There are a number of options – for instance it may be instructive to compare the slump-flow/J-Ring spread with the unrestricted slump-flow: to what extent is it reduced?

 Like the slump-flow test, these combinations have the disadvantage of being unconfined, and therefore do not reflect the way concrete is placed and moves in practice. The Orimet option has the advantage of being a dynamic test, also reflecting placement in practice, though it suffers from requiring two operators.

Figure : the J Ring used in conjunction with the Slump flow

EQUIPMENT:-

 * Mould without foot pieces, in the shape of a truncated cone with the internal dimensions 200 mm.

* Diameter at the base, 100 mm diameter at the top and a height of 300 mm.

* Base plate of a stiff non absorbing material, at least 700mm square, marked with a circle.

* Showing the central location for the slump cone, and a further concentric circle of 500mm. 

* Diameter 

* Trowel

* Scoop

* Ruler

* J-ring a rectangular section (30mm x 25mm) open steel ring, drilled vertically with holes.

* In the holes can be screwed threaded sections of reinforcement bar (length 100mm, diameter 10mm,

* Spacing 48 +/- 2mm)

PROCEDURE:-

* About 6 litre of concrete is needed to perform the test, sampled normally.

* Moisten the base plate and inside of slump cone,

* Place base-plate on level stable ground.

* Place the J-Ring centrally on the base-plate and the and the slump-cone centrally inside it and hold down firmly.

* Fill the cone with the scoop. Do not tamp, simply strike off the concrete level with the top of the cone with the trowel.

* Remove any surplus concrete from around the base of the cone.

* Raise the cone vertically and allow the concrete to flow out freely.

* Measure the final diameter of the concrete in two perpendicular directions.

* Calculate the average of the two measured diameters. (in mm).

* Measure the difference in height between the concrete just inside the bars and that just outside the bars.

* Calculate the average of the difference in height at four locations (in mm).

* Note any border of mortar or cement paste without coarse aggregate at the edge of the pool of concrete.

CALCULATIONS:-

Calculate the average of the two measured diameters. (in mm). 

Measure the difference in height between the concrete just inside the bars and that just outside the bars. 

Calculate the average of the difference in height at four locations (in mm). Note any border of mortar or cement paste without coarse aggregate at the edge of the pool of concrete. 

INTERPRETATION OF RESULT:-

It should be appreciated that although these combinations of tests measure flow and passing ability, the results are not independent. The measured flow is certainly affected by the degree to which the concrete

movement is blocked by the reinforcing bars. The extent of blocking is much less affected by the flow characteristics, and we can say that clearly, the greater the difference in height, the less the passing

ability of the concrete. Blocking and/or segregation can also be detected visually, often more reliably than by calculation.

 Note:- The results of the J-Ring are influenced by the combination method selected and results obtained with different combinations will not be comparable.

REFERECE :-

EFNARC, Association House, 99 West Street, Farnham, Surrey GU9 7EN, UK