THE VIALIT TEST FOR BITUMEN ADHESION AND COHESION

CONTENTS
The Vialit Pendulum Test
The Vialit Plate Shock Test
New Zealand Chip Seal Testing Procedures

The Vialit Pendulum Test

The Vialit Pendulum Test, simply described, is a test where a metal block is secured to a steel plate with a thin layer of the bitumen from the sample that is being tested. 
This metal block is secured in a testing frame in the path of a "standard " pendulum. The block is then impacted with the pendulum which is in the form of a "hammer". 
The greater the cohesive properties of the bitumen the less far the pendulum will travel after impact. So, a measurement of how far the pendulum travels after impact can be converted in to a cohesion value for the bitumen that is being tested. 

The Vialit Pendulum test is fully specified in :-
Volume 1 : The Specification for Highway Works : Series 900 : Road Pavements - Bituminous Bound Materials
Clause 939
This clause consists of nine pages of details on the test, how it is performed, the apparatus and the information it provides.
The test can be used to determine the cohesive properties of standard bitumen, modified bitumen or even reclaimed binder.

The Vialit Plate Shock Test

The methodology of a Vialit Plate Shock Test is as described in the picture section below, although the photographs are of a method used in New Zealand.

The full description of the procedure as used in Europe can be obtained by purchasing a copy of the standard:-

BS EN 12272-3 : 2003 : Surface Dressing - Test Methods - Part 3 - Determination of binder aggregate adhesivity by the vialit plate shock test method

My opinion is that although not a perfect test, (what is) it seems a very useful procedure, and I do not see why it is not included in the selection of tests provided by materials testing laboratories, it does not seem widely available at the moment. 
As well as determining which aggregates in their natural state will be more suitable for surface dressing, chip sealing, etc., it can also be used to determine what percentage of adhesion agent is necessary to add to the binder  so that adhesion properties are improved to a level where otherwise unacceptable aggregate is able to be used.

I also recall reading a paper in an engineering journal, which unfortunately I cannot find at the moment, where the aggregate chippings had been replaced by a number of standard steel balls so that the adhesive properties of differing standard and modified binders could be determined, independent of the properties/characteristics of the aggregate.
Information on the performance of binders is always useful and should be sort/requested by binder purchasers.

Conversely you could take one source of aggregate, say you most local source of potentially suitable aggregate,  and therefore likely to be your lowest cost source of chippings, and perform the test with a number of different available binders to establish which binder exhibited the best engineering properties in retaining the chippings.
Or, if all binders displayed similar engineering properties, you could determine which binder was the most economic to purchase.

Sampling and testing is always related to the economics of road pavement design and maintenance, but in my opinion it is far better to use the testing procedures that are available in a proactive manner rather than a reactive process to something already done badly, or at unnecessary expense.

New Zealand Chip Seal Testing Procedures
( The pictures  included in the section below belong to ARR-MAZ Products, © 2002  ARR-MAZ Products, and are used with their kind permission, the text is as supplied with the pictures.
I have created the text associated with each picture for those who do not have internet browsers capable of displaying images.)

40 grams of bitumen is spread over a 20cm. x 20cm. steel plate. The bitumen is placed in a water bath to cool. The plate is removed and 100 aggregate chips are placed on the plate (without touching).
The chippings are compacted onto the bitumen covered plate with a 25kg. rubberized roller. The bitumen plate and chips are returned to the water bath.

The plate is inverted on the testing stand and a steel ball is dropped three times onto the plate within ten seconds.
An 85% rate is expected. Chips coated with bitumen are considered passing. Those that fall off and have no bitumen on them are counted as failures.

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