McLanahan director of engineering Dermot Murphy takes an in-depth look at construction and demolition recycling and how to turn it into a profitable stream for a business.
Construction and demolition (C&D) feed streams are among the most complex and variable in the aggregates and recycling sectors.
Handling them involves dealing with diverse materials from a range of sources and with changing compositions, which can affect key variables such as equipment choice, throughput, and product quality.
However, recovering materials from these streams and processing them with crushing, screening, and washing equipment can unlock valuable revenue for quarrying and aggregates businesses. For businesses to unlock this revenue, they need to understand the key considerations when dealing with C&D recycled materials, so they can design an operational setup that extracts the most from them.
McLanahan director of engineering Dermot Murphy said some key considerations included variability, contamination, moisture content and size distribution of the material.
“Unlike virgin aggregates, C&D is rarely uniform, which creates an opportunity for value recovery but also a challenge for consistent processing,” he said.
“For example, a load dominated with concrete and rebar is going to behave differently than material that is coming from an area with a lot of wood and plastics. If you’re going to be dealing with a lot of concrete, you’re going to want to have your plant set up for that, whereas if you’ve got a lot of lightweight contamination, you want to have your plant set up for that.
“The feed stream of C&D can change daily or by the bucket load, and it can depend on where the material is coming from.”
From a value perspective, the equation for C&D recycling is simple. The material is generated by operators turning waste materials into valuable products like sand and aggregates while reducing costs that would otherwise have been incurred by disposing of the waste.
There is also a sustainability aspect, as this reduces the landfill contributions from quarry and aggregate operators. As the amount of C&D processing has progressed, so too have the applications for recycled materials within the sector. For example, it is not uncommon to see recycled aggregates used in roadbase and backfill applications or washed sands in concrete production. Each C&D stream has its own characteristics that operators need to consider before processing it in the plant. For example, excavation material can contain high fines and clay content, while concrete can contain steel and abrasives. Other C&D streams, such as ready-mix concrete washout, can generate foam and require additional scrubbing and separation to remove fines and clay. These considerations would impact the plant’s design, as a stream like a ready-mix concrete washout could require hydrocycles, thickeners, and a filter press to generate clean water for recirculation throughout the plant.
Murphy said these differences are why it’s important to understand the end goal of selling the material before designing your plant.
“There is value there. You can recover aggregates, and you can recover sand and re-use that back within your products, and it can be done in an efficient method,” he said.
“One of the challenges is the large degree of variability in your feed material, and you need to design your system to be able to deal with that.”
While equipment selection is a significant factor in managing C&D materials, there are several other components that are essential to managing them effectively in a quarrying and aggregates operation.
This includes, in a non-exhaustive list, operator training, early segregation of materials and training in process control and operation.
Murphy said operators are the quarry’s first line of defence against what is put into the plant and potential pain points, such as contaminants. Therefore, it is important that any operator involved in C&D processing be trained in feed recognition so they understand the material and when to process, reject, or quarantine it for further inspection.
It may sound like a small step, but if overlooked, the consequences can be costly and halt production. For example, if a feed material contains a lot of rebar and the plant is not set up to handle it, this can result in the plant being jammed, damaged, and requiring maintenance, leading to unexpected downtime.
If there’s a feed stream with a high concentration of clay fines but the plant isn’t designed to handle them, the fines processor could become overloaded, impacting downstream processing.
“With that constant variability that you can get in C&D materials, it really is down to the operator and the site management to be able to recognise those changes,” he said.
“The operator needs to be able to make those calls and has the ownership and control to do that in regard to how best to deal with that material.”
For primary C&D materials, including concrete, masonry and aggregates, it is important for operations to develop an efficient crushing, screening and washing system. Crushing can help remove contaminants from the C&D feed and reduce its size.
A screening system with magnetic separation capability allows ferrous materials to be removed while materials are sorted, improving material quality and potential value.
A washing system, including log washers and blade mills, can help remove fines from the product, improving its quality.
McLanahan can work with operators to design a plant that incorporates all of these aspects and is tailored to the operator’s specific C&D stream. McLanahan has proven experience in designing solutions with its crushing, screening, and washing equipment to address the variability of C&D feed streams and deliver a marketable end product.
“McLanahan has helped customers produce high-quality products from contaminated materials,” Murphy said.
“We offer a turnkey solution from the front of the plant right to the very back, from crushing to screening to washing, sizing, thickening and filter press, all by ourselves.
“For operators and plant designers, that is really important. It is not about taking one component and putting it in; you need to think about the entire system and how each component interacts with the others. That’s where we can help.”
A key piece of McLanahan’s approach to developing a solution for C&D feed streams is its collaborative work with customers, as well as its modular plant design.
“We work in partnership with our customers to understand what their goals and targets are. They will know their area and market better than we will in regards to the materials that they’re taking on board and the products that they want to achieve,” Murphy said.
“We will work with them to ensure they get the equipment that is best suited to the approach that is required.”
The modular plant design is a key reason why McLanahan has become known for designing efficient plants in the C&D recycling sector. The modular plant enables the customer to scale up the plant as their operation grows in tonnage and productivity.
It also means that the plant itself is tailored by McLanahan for a C&D application, including features such as integrated water management, targeted washing to remove fines, pre-sorting to remove contaminants, and scalping and crushing to improve product quality.
Importantly, Murphy said the modular plant enables customers to handle regulatory changes from environmental protection agencies and other bodies.
“The modular plant does allow you to bolt on additional bits and pieces of equipment relatively easily and integrate additional processes or bolster areas of your plant that need to increase in size,” he said.
For quarry and aggregate operations considering taking on C&D feed streams, working with a proven expert at McLanahan can be beneficial.
“C&D recycling presents significant challenges and substantial opportunities for material recovery and revenue generation,” Murphy said.
“Your success will depend on identifying the feed stream and the valuable materials that can be removed and using best practice process to remove those materials as quickly as possible.
“McLanahan has proven that our equipment can play a role in efficient and reliable C&D recycling operations for our customers.” AB
