Recycled crushed concrete specs in Queensland: MRTS05 and CBR

Most people meet this topic the same way: a drawing or a schedule calls up a subtype like 2.3, someone asks whether recycled crushed concrete can be used against it, and nobody in the room is certain. The answer sits in one document, the Queensland Department of Transport and Main Roads specification MRTS05 Unbound Pavements, and it is more readable than its reputation suggests. This is an explainer of what that specification says, what the subtype numbering actually means, and what to ask a supplier for so the material you receive can be proven against the spec on your job. It is not a claim about any particular product, including ours.

Queensland used to specify recycled material separately, and now does not

Until fairly recently, recycled pavement material in Queensland was specified under its own document, MRTS35 Recycled Materials for Pavements, published in 2010. Natural and quarried materials sat under MRTS05. Splitting them across two documents created a procurement problem: recycled material had to be called up deliberately and separately, so on most jobs it simply was not called up at all. Uptake stayed low, partly on that procurement friction and partly on a general perception that recycled material was inferior to virgin material.

The research programme that changed this was NACOE project P94, Optimising the Use of Unbound and Stabilised Recycled Pavement Materials in Queensland. NACOE is the National Asset Centre of Excellence, a joint programme between TMR and the Australian Road Research Board. P94 ran over three years and covered a literature review, laboratory evaluation of recycled materials sourced in Queensland, and a dissemination stage. On the strength of the earlier stages, TMR consolidated MRTS05 into a single specification covering natural, quarried and recycled materials. The current issue at the time of writing is MRTS05 Unbound Pavements, July 2022.

The practical effect is that a specifier no longer has to choose a recycled document over a natural one. They nominate a material type and subtype, and the material is judged on whether it meets the requirements, whatever it was made from.

How the material types map to what you are buying

The second digit of the subtype is a CBR number

This is the part that saves the most confusion on site. Once a type is nominated, the digit after the decimal point is not a grading or a product name. It maps directly to a minimum California Bearing Ratio, and the ladder is the same across Types 2, 3 and 4.

So a schedule calling up 2.3 is asking for a Type 2 material with a soaked CBR of at least 45. A schedule calling up 3.1 is asking for a Type 3 material with an unsoaked CBR of at least 80, from a certified quarry source. Two jobs can quote the same number and mean quite different things, because the type in front of the decimal point carries the source and certification requirements while the digit after it carries the strength.

The soaked and unsoaked distinction matters more than it looks. A soaked CBR is the harder test, because the sample is saturated before it is loaded. Type 2, the type that expressly admits recycled material, is the one specified on soaked CBR. That is worth knowing before anyone assumes recycled material was given an easier gate.

What CBR to expect from recycled crushed concrete

The honest answer is that no specification publishes a number for this, and anyone who quotes you one without a test report is guessing. CBR is a property of a particular material as produced, graded, compacted and moisture-conditioned, not a property of the category it belongs to. Feed cleanliness, the grading you screen to, compaction effort and moisture at test all move the result. Two stockpiles of crushed concrete from the same city can test differently.

What the research supports is the general position rather than a specific figure. The P94 laboratory work concluded that recycled materials show performance similar to natural and quarried materials, which is the finding that justified consolidating the specification in the first place. P94 also produced a useful placement note: for the recycled blends tested, performance held across degree of saturation levels in the range of about 65 to 80 percent, with the best performance where the degree of saturation was kept below 70 percent. In plain terms, moisture control at placement does real work on how recycled material behaves, and that is a construction control rather than a supply one.

What to ask your supplier for

If a job nominates an MRTS05 type and subtype, the conversation with any supplier, recycled or quarried, should cover the same short list:

• The exact type and subtype the material is being offered against, written down rather than implied.
• Current CBR test results against that subtype, and confirmation of whether they were soaked or unsoaked.
• Grading results against the particle size distribution envelope your contract nominates.
• For a recycled blend, the recycled percentage by mass, because passing or failing the 70 percent line changes which requirements apply.
• For Type 1 and Type 3, evidence of the quarry certification the specification requires for the coarse component.
• Who is holding the testing frequency, and what happens if a batch falls outside the nominated subtype.

The reason to ask rather than assume is straightforward. A specification is a set of requirements and a testing regime, not a label. Material earns a subtype by being tested against it on the job it is going into.

Where this leaves recycled crushed concrete

It leaves it in the same queue as everything else, which is the point of the change. MRTS05 no longer treats recycled material as a separate category to be argued for; it sets requirements and lets any material that meets them be used. Plenty of civil work also sits outside a TMR pavement schedule entirely, on hardstands, pads, laydown areas, access tracks and general fill, where the relevant question is fitness for the application rather than a nominated subtype. On those jobs the specification is still worth reading, because it gives you a shared vocabulary for describing what you actually want.

We crush clean concrete, brick, rock and reclaimed asphalt on site and set the screens to the product a job needs. We do not hold a job's material out as pre-certified to an MRTS05 subtype, because a subtype is proven by testing against the contract it is placed under. Where a spec is in play, tell us before the machine starts so the crush and screening are set to suit and the testing can be arranged around it.

For the grades that come off a crush and where crews use each one, see our recycled aggregate and road base range.

To estimate how much product a stockpile will yield before you plan the layers, use the material calculator.

For how a crush is set up and run on a live site, read about on-site concrete crushing.

If you have a spec in front of you and you want a straight read on whether an on-site crush can be set up to suit it, call 0401 803 662 or send the schedule through.