Proposed Changes to VicRoads Specification for Aggregate for Bituminous Sealing

BRUCE McCLURE, CMPA’s General Manager reports on proposed changes by VicRoads to their Section 831 – Aggregate for Sprayed Bituminous Surfacing Specification.

VICROADS is proposing a number of changes to their Specification Section 831 – “Aggregate for Sprayed Bituminous Surfacing”. These changes, if implemented, will impact on those members who produce sealing aggregate. Following discussion with a number of members who are involved with the production of sealing aggregate, the CMPA has responded to VicRoads with comments and suggestions.

The main changes proposed relate to the “Testing and Acceptance of Aggregate” section of the specification. The changes proposed include an increase in lot size, changes to unsound and marginal stone, flakiness index and grading including specified size and tolerances (specifically for the size 7 mm aggregate). Some of the other changes proposed will rationalise the text and make the section easier to understand and work through.

The CMPA understands VicRoads concern is particularly with the 7 mm aggregate. In some instances the material being supplied under the current specification contains too much material at the lower end of the grading curve. Th s has resulted in issues for the contractors using the aggregate on sealing projects with problems such as bitumen flushing arising.

One of the major concerns expressed by Members with the proposed tightening of the specified particle size distribution limits for 7mm aggregate is that there will be an adverse impact on the production rate or yield of 7 mm aggregate produced per tonne of source rock crushed. The reality is that a production rates reduction and a consequential increase in potentially non marketable 5mm minus yield will increase the cost base for some Members in the order of at least 25% on 7mm product.

The obvious consequence of the above is that material production cost will increase considerably and there may be more waste products to be dealt with.

It has been also suggested by CMPA members that the revised specification could adopt a ‘single array of compliance criteria’, rather than the ‘individual’ and ‘mean of lot’ model currently specified.

VicRoads proposed revised criteria for individual tests under the current model of ‘individual’ and ‘mean of lot’ criteria, could be adopted to apply to all tests under a ‘single criteria’ model.

As such, the single criteria values would be a compromise between the existing specification and VicRoads proposed changes. Changing to an ‘individual criteria’ model would bring the VicRoads specification in line with the current Road Traffic Authority (RTA) specification in New South Wales.

The photograph above highlights the differences between the current VicRoads and the RTA specification requirements for size 7 aggregate, at the small side of the respective particle size distribution envelope.

Another change proposed is the increase of the size of a lot. VicRoads is effectively proposing to change the size of a lot to 500 tonnes (and up to 1000 tonnes with Superintendent approval).

Three test samples are required and compliance based on the mean of the lot sample results. Increasing the lot size to 500 or 1000 tonne may be advantageous for some of the bigger quarries but a 500 or 1000 tonne lot may represent for some quarries, in excess of 5 or 10 days production respectively.

The concern is that samples and results obtained at the commencement of a 1000 tonne lot may not be representative of the aggregate produced to complete the 1000 tonne lot. Due to the size of a 1000 tonne lot, it is also possible that in small quarries the production of a 1000 tonne lot may not be continuous. Many small rural quarries alternate between the production of crushed rock and aggregate.

The objective in increasing lot size is surely to reduce the amount of tests required to demonstrate compliance. Consequently a number of members have suggested that VicRoads adopt a procedure similar to the RTA where only one test is required for a lot size up to 250 cubic metres (300 – 375 tonne).

Adopting this removes concerns with increasing the lot size to 1000 tonne and also removes the need to retain the ‘individual’ and ‘mean of lot’ criteria model. It is considered that a quarries contractual risk would be minimised by adopting the above.

A further change proposed by VicRoads is to remove the Acceptance of Aggregate “Reduced Rate” Formula that is currently in the specification. The CMPA supports this initiative. Industry should not encourage these type of existing clauses to be utilised as a means of dealing with the supply of ‘non compliant’ product.

Typically, quarries today do not have direct contract with VicRoads and therefore our industry shouldn’t facilitate a process that enables our customers to negotiate with VicRoads regarding reductions in payment/s for the supply of aggregate. The reduction formula is a hangover from the past when VicRoads purchased aggregate directly from quarries and also performed QC testing through their own laboratories.

With the proposed changes to the unsound stone and marginal stone, flakiness index, average least dimension and the grading for the 7 mm, a number of members suggested that VicRoads may consider allowing the use of granite and river gravel as Class A aggregate.

To allow their use VicRoads may also need to consider additional testing relating to strength, adhesive and Polished Stone Value qualities of the stone and this was not seen as a disincentive by Members.

A number of CMPA Members have expressed concern with the current lack of engineering knowledge being used when specifying the quarry product to be used on different projects by state, and local government authorities.

In many instances VicRoads sealing contracts typically specify Class A aggregate for all roads, irrespective of projected traffic volume or road classification. It is considered that VicRoads should encourage and educate their own staff and local municipalities to specify the appropriate class of aggregate applicable to traffic volume and road classifications.

Many municipalities for example blatantly follow VicRoads specifications without any consideration of the possible options available and savings in material and funds. VicRoads should discourage the simple specification of Class A aggregate for all roads, where Class B or even Class C may be suitable. This step could result in considerable savings to the authorities involved and consequently, to the tax and rate payers who actually pay the costs.

The CMPA will be meeting with VicRoads shortly to discuss the proposed changes to Section 831 and there will no doubt be the need to seek further comments from Members as discussions progress. The CMPA will report back to our Members and give an up date on these proposed changes in future editions of Sand and Stone.

Many thanks to Craig James, E. B. Mawson & Sons Pty Ltd for the photograph of the 7mm grading samples.

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