In July last year, the Victorian Government launched a report that found the state’s demand for quarry resources for infrastructure construction is set to double by 2050.
The report – Extractive Resources in Victoria: Demand and Supply Study 2015-2050 – from the Victorian Minister for Resources Wade Noonan, identified that the region’s projected population growth and urban development over the coming decades will drive demand for nearly 90 million tonnes of stone, sand, clay and other materials, annually. This is up from the 46 million tonnes required in 2015.
Despite the rising demand in virgin quarry resources, government, industry and research institutes are tackling the issue head on, not just in Victoria but nationwide.
Crushed glass, recycled rubber and other waste streams are being explored as replacement for virgin quarry resources in road construction. Researchers from Swinburne University of Technology are even investigating used coffee grounds as a supplementary material in a pavement subgrade (Roads & Infrastructure Magazine June/July 2016).
The advent of recycled materials in pavement construction is stemming not just from researchers and contractors, but from plant and machine manufacturers too, including Wirtgen Group companies Benninghoven and Kleemann.
Greg Astill, General Manager – Mineral Technologies for Wirtgen Australia, says reclaimed asphalt pavement (RAP) is one recycled material stream in pavement construction that is increasing in value.
“Not only for what it can save in asphalt production costs, but think about all the energy that goes into the upstream manufacture of aggregate and what can be saved by reducing that effort,” he says.
The increase in RAP usage has also given rise to the number of asphalt plants incorporating continuous use of RAP above 30 per cent into their capabilities.
Mr. Astill says to consistently achieve 30 per cent RAP and above, asphalt plants need to ensure correct material processing so that mix designs aren’t compromised, and also to extract the maximum benefits from the recycled aggregate.
He says when the pavement mix is laid, it is already set to a design specification, so the goal of the plants reusing that material is to ensure the same properties of the aggregate is retained.
Benninghoven asphalt plants are designed with high RAP production in mind, with specific features designed to handle increased and varying RAP qualities.
This includes multiple RAP bins for proportioning fractioned materials, elevated heating of virgin aggregate, ability to maintain production outputs without decline, and emission control.
According to Mr. Astill, to get the most out of RAP it should be processed into a granular material prior to reintroduction into the asphalt manufacturing process. “Fractioning RAP into sizes is about bringing greater control and flexibility to the design and manufacturing process,” he says. “The processed RAP used in recycled hot mix asphalt should be as coarse as possible and the fines minimised.
“The primary advantage of fractionating RAP is that having stockpiles of different RAP sizes provides more flexibility in meeting asphalt mix design requirements.”
While Benninghoven plants are optimising the processing of RAP, Wirtgen Group’s Kleemann range of crushers and screeners are designed with this precise fractioning of RAP in mind.
Darren Booth, Area Sales Manager – Western Region at Kleemann, says reduced aggressive RAP crushing – or controlled crusher speed – is recommended to minimise coarse aggregate fracturing and prevent fine generation. “It is not an uncommon practice to use a combination of crushing and screening devices to prepare RAP for reintroduction to the mixing process,” says Mr. Booth. “Wirtgen, through its Kleemann product range, has provided both the crushing and screening machines to a number of asphalt producers and contractors.”
The MR130Z Evo II impact crusher has been specifically designed around products such as RAP and building demolition waste. Generally, impactors are an aggressive form of crushing, but Mr. Booth says the MR130 can reduce its rotor speed to a level that minimises the fracturing of the aggregate which is already encased in valuable bitumen.
Several features of the impactor assist in RAP production, including an efficient pre-screen and scalping facility where the already sized product will bypass the chamber, preventing wear and unnecessary impact and reduce the production of fines.
In addition to a high volume hopper, the impact crusher has a large impactor feed opening, which reduces the need to break up slabby pavement before processing.
“The secondary screen has a very large surface area allowing maximum throughput at the given aperture size. Any oversize is sent back to the impactor for a re-crush, also helping reduce fines.” says Mr. Booth.
The efficient screening of the on-board SSU reduces the need to process the material again and reduces handling, which, in turn, reduces costs.
“Likewise, health and safety is paramount, so the impactor is all about operator safety and has many safe and time-saving features to assist them.”
Mr. Booth says the features of Kleemann’s MR130Z Evo II impact crusher work hand-in-hand with the manufacturer’s Mobile Classifier Screens – MS952 and MS953.
The MS952 (double deck) and MS953 (triple deck) are screening plants used for many applications, including sand, soil and aggregate processing. “They are also very efficient in processing RAP into its fraction sizes and in recovering the RAP from contaminated RAP stockpiles,” adds Mr. Booth. “During the process of removing the pavement via a profiler, or less conventional methods like excavators, there may be a lot of oversized and irregular shaped materials that cannot be directly introduced to the RAP system.”
These types of portable screens are able to work independently of the crusher and it’s not unusual for a full stockpile to be screened and the oversize returned for secondary treatment at a later time.
By screening the stockpile and having the correct screen media installed, the MS952 or MS953 will separate the profilings into the preferred aggregate sizes and remove oversize material.
“The MS953 is highly mobile and easy to transport. Set up times are quick and easy meaning the operator can start production pretty quickly,” says Mr. Booth.
The screens also have the ability to screen two separate aggregate fractions, in addition to the oversize reject material going to a separate stockpile.
Additionally, the remote control functions allow the operator to control the MS953 from the safety of the excavator or front-end loader.
Mr. Astill says Western European countries have traditionally incorporated high RAP into their asphalt manufacture processes, and Australia is doing the same with the capabilities made possible with Benninghoven and Kleemann products.
“In looking at those countries where RAP inclusion in asphalt mixes can routinely exceed 50 per cent, the story is clear around aggregates for asphalt – if treated correctly our quarries of tomorrow are the customers’ existing roads.”