The ‘Clayprocess’ helps raise Plasticity Index

ROB BURNS, Managing Director, Claypro (Australia) Pty Ltd reports on how the “Clayprocess” can help raise Plasticity Index.

IN 2004 the reconstruction and duplication of the Calder Highway at Malmsbury was under way. Hanson’s Axedale Quarry had successfully tendered and won supply of Road base materials to the project, the Vicroads project specification called for a Plasticity Index (PI) of 4 + or – 1 for it‘s Class 1 Road base.

Hanson Quarries Axedale had a Road base with a PI of 2 to 3 but without an additive could not meet the 4 PI requirement.

Hanson Quarries Axedale manager Mr Peter Dunlop whilst wanting to meet the specification, did not want to add a high PI sand because of the alteration to the grading on the bottom end and also because if the additive was not consistent the threat of a nonconforming product being supplied carrying claims against the supplier.

During a meeting at Burns Resources Clay Mine between Peter Dunlop, John Jobson (Senior Engineer for Vicroads) and Rob Burns, John recommended trying Burns Resources clay if it was fine enough to mix.

Claypro was at this stage, milling Axedale ball clay to -75 micron for ceramics and refractories. Claypro Australia Pty Ltd had been established in 2001 to vertically integrate with Burns Resources and value add to the Axedale ball clay which had been previously supplied as a crude clay to the pottery, ceramic, refractory and brick manufacturers.

Axedale Ball Clay is secondary kaolin renowned in the pottery and ceramic industries for plasticity and green strength and has been used in these applications for almost one hundred years.

The “Clayprocess” consists of pre breaking -40ml clay, drying it, and then passing the clay through an air swept high speed impactor with control of the air flow for particle size reduction and classification.

The clay powder is then separated from the airstream via dust collectors. The processed clay is then either bagged in 20kg paper bags, 1200kg bulk bags or dense phased transferred to silos for load out into bulk pressure tankers.

A test conducted at Hanson’s lab that day amazed the participants, 1% Claypro mixed/blended like a dye, evenly coated the crushed rock. Further testing showed that 1% claypro had increased the PI from 2 to a factor of 4. The PI is an important property in flexible pavement materials, it indicates a range of moisture content over which the fine particles (less than 0.45mm) behaves plastically, a PI that is too high will cause issues with pavement stability, particularly under dynamic loads whilst a PI that is too low will result in a pavement material that lacks cohesiveness and may result in unraveling and/or uncompacting of that particular course.

The majority of natural pavement materials sourced within Victoria are unable to meet Vicroads PI requirements, whilst also meeting the requirements for swell, grading envelopes and CBR. Claypro is the solution, when mixed into Class 1 paving material at low percentages has demonstrated to have positive effects on the PI and permeability properties, while having minimal affect on the swell, grading envelopes and CBR of such materials this positive affect can be attributed to Claypro having a very high PI and a very small particle size.

Hanson’s Manager, Peter Dunlop installed equipment for dosing Claypro to their pug mill at the rate required, usually between 0.75% and 1%, this was achieved via load cells, weigh belt, and PLC.

The most common method used for the addition of Claypro is a 150mm auger with variable speed from bulk silo to pug mill or conveyor belt and with testing; a ratio for the feed rate can be ascertained.

The claypro has a bulk density of approximately0.75, aerates easily and will flow very easily in this state but if left static will tend to hangup but with aerators fluidizes immediately.We are pleased to assist with proven systems for this additive.

Claypro has helped not only Hanson Quarries Axedale to attain PI requirements but also Barro Mountain View at Point Wilson for Geelong bypass, Barro Seymour for the Nagambie bypass, Fulton Hogan and Holcim Tynong for the Pakenham bypass and Fulton Hogan Tylden for the Calder Freeway.

The Author would like to thank for their contribution to this article; Peter Dunlop (former manager Hanson Quarry Axedale) and Tim Dunlop BEng(Civil), MIEAust.

For more information contact Rob Burns, Managing Director, Claypro (Australia) Pty Ltdon 03 5449 3970 or at clay_pro@bigpond.com

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