California dreaming

By |  February 1, 2014

Meeting the state of California’s aggregate needs over the next 50 years means coming to terms with alternative processing methods.

Aggregate reserves are dwindling in California and unable to supply current demands. This, coupled with global pressures to be greener and more sustainable, means there are some tough choices ahead for the aggregates industry in the United States.

recycled aggregates

This is a recycling operation on the Isle of Wight. Recycling initiatives throughout Europe are changing the way the construction and aggregates sector is thinking and operating.

One company making a change is CDE Global. According to the company’s chairman, Tony Convery, recently released information from the California Geological Survey (CGS) forecasts a continuing shortage of permitted aggregate resources in California. According to the CGS, California has a resource to meet about one-third of aggregate demand over the next 50 years.

“Aggregate is an essential component for commodities such as concrete, asphaltic concrete, plaster and stucco, which means a shortage may affect California’s ability to provide for new construction projects and infrastructure,” Convery says. “Further, transporting aggregate from farther distances results in increased environmental impacts such as [greenhouse gas] emissions, air pollution and traffic congestion.”

California famine
To give an element of scale to these issues, Convery points out that from 1981 to 2010, California consumed, on average, 180 million tons of mixed construction aggregate each year. If that material was transported in 25-ton truckloads, then it represents more than 7.2 million truckloads per year.

“If we are trying to be greener and more sustainable in our approach, with an average 25-mile haul, that amounts to more than 360 million truck miles traveled, almost 47 million gallons of diesel fuel used, and more than 520,000 tons of carbon dioxide emissions produced annually,” he says.

Land-use planners and decision-makers in California are faced with balancing a variety of needs, Convery says. Increasingly, as existing permitted aggregate supplies are depleted, local land-use decisions regarding aggregate resources can have regional impacts that go beyond local jurisdictional boundaries.

CDE Global

The M2500 from CDE Global is seen here processing clay-contaminated material.

In California, for example, 4 billion tons of permitted aggregate reserves lie within the 31 aggregate study areas shown on the California Geological Survey Map Sheet 52. The permitted aggregate reserves are deposits that have been determined to be acceptable for commercial use and extraction and are within existing land banks owned or leased by aggregate-producing companies that have current extraction permits for the mining of aggregate material.

“In light of these constraints, the activity from aggregate companies is increasingly to ask customers to enter into long-term supply contracts to ensure regular and sustained supply,” Convery says. “In addition, shipping materials from greater distances by sea, from outside the state of California, is proving to be more cost effective than over land given the fluctuating cost of fuel and the dwindling local supply.

“With the inability of the state of California to meet its aggregate demand over the next 50 years, is this a symptom of the industry as a whole? Is the aggregates industry in danger of being unable to provide adequate resources for the home market? For the industry to respond, new out-of-the-box thinking is called for, but what would that new thinking be?”

Convery says the type of new thinking that may work in this instance is being successfully employed in the United Kingdom and throughout Europe, where, under European Union legislation, recycling initiatives are changing the way the construction and aggregates sector is thinking and operating.

CDE Global

Each recycling system CDE Global designs is specific to the material being processed.

In Europe, heavy penalties are in force for the disposal of construction waste in open landfills, with new technologies making it possible to process construction and demolition waste into high-value products. The recycling of construction and demolition materials may be the answer that states like California is looking for.

“These problems that have been affecting the aggregates industry in California have to some extent also been affecting the UK and Europe,” Convery says. “The recent downturn in the UK construction sector has resulted in the granting of new permissions for mineral extractions hitting an all-time low. This has resulted in talk of a materials famine over the last couple of years, and with construction now experiencing a positive upturn, new permissions for the extractions of virgin aggregates cannot be granted quickly enough to meet the newly increasing demand. For the first time in history the UK is about to become an aggregates importer.”

UK thinking
CDE Global is a specialist in materials and aggregates washing, manufacturing equipment for pits, quarries and mines that are exported all over the world. A look at what’s happening in Europe may give an insight to the issues California is dealing with and how alternative processes can bridge the Californian aggregates gap.

New legislation from the European Parliament has dictated that by 2020, 70 percent of all construction, demolition and excavated waste material is recycled and processed into high-quality recycled aggregate for use back in the construction industry. This directive has started to change the construction and aggregates industry in the United Kingdom, resulting in a more sustainable and greener initiative.

“With the UK being such a small and densely populated island, there is only so much open cast mining that can be sustained, hence a need for a change in thinking – something that California and other states in the U.S. could benefit from,” Convery says.

One recent example is the approach taken to construction for the 2012 Olympics in London. The demolition of the surrounding infrastructure resulted in recycled materials providing a large portion of all the aggregates used on the construction of the Olympic Park.

What made this possible in the United Kingdom and why would the same approach work in the U.S.? The introduction of washing technologies for the processing of construction, demolition and excavation waste was driven by a desire in the industry to move recycled sand and aggregates up the value chain, Convery says. The dominant treatment method at that time was dry crushing and screening, he adds, but the limitations of this process mean the recycled products are only ever going to find a home in very low value construction applications.

“What does washing construction, demolition and excavation waste do? It results in much higher quality recycled materials with applications in higher value construction such as concrete and asphalt,” Convery says. “This is achieved by the effective removal of the waste silts and minus No. 200 mesh material – in the same way that washing is effective when processing natural sand and gravel, crushed rock, crusher dust and other similar materials.

recycled aggregates

A C&D recycling plant at work.

“The technology that CDE Global has been developing has been successful as a result of the ability of the system to deal with other contaminants that require removal, such as plastics, polystyrene, metals, organics and other construction debris.”

In addition, each recycling system CDE Global designs is specific to the material being processed and configured to deliver the required recycled sand and aggregates to the required specification.

“The way we approach our construction, demolition and excavated waste recycling projects is the same as the way we approach every project – standardized, off-the-shelf equipment just doesn’t do the job when dealing with washing technologies,” Convery says. “This has been the basis on which we have built our business over the last 21 years. A typical CD&E waste recycling system includes a number of different processing phases – a feed arrangement, recycled aggregate screening, aggregate scrubbing, recycled sand washing and product stacking.

“This is all delivered by a modular skid-framed equipment range, which minimizes setup time, minimizes the space required on site and maximizes plant productivity by ensuring the efficient transfer of material between each phase – maximizing material and water retention within the circuit,” he continues.

Global change
On a global basis the extraction of natural sand and gravel is fast becoming an issue with which the aggregates industry needs to contend. The introduction of the banning of river sand mining in many countries around the world is resulting in an increase in the demand for alternative sourced products such as recycled or commercial crushed aggregates. New extraction opportunities are becoming fewer and harder to secure.

“In the past, natural sand and gravel extraction has been the backbone of the aggregate industry,” Convery says. “This is increasingly becoming less of a case.”

Alternative sources of supply get a tick in the box from an environmental point of view with materials like recycled aggregates and, in some cases, manufactured sand coming with positive credentials, he adds. While mining is the traditional method, new thinkers believe mining can damage the eco-system, with extraction methods causing changes to the ground infrastructure, resulting in ground water depletion, which can threaten the availability of fresh water or cause other environmental issues.

From a stability point of view, dredging can also affect other structural entities associated with rivers such as bridges, dams and adjacent roadways, without even taking into consideration the damage to the wildlife eco-structure, Convery says.

“Urban expansion, an increased need for the planet to be greener through environmental constraints and localized legislation, are all making it difficult for the extraction of natural sand and gravel,” he says. “The commissioning of new mines is not as easy as it was in the past. The processes which operators are made to follow before permissions to extract virgin materials are made are becoming more and more difficult, with a high probability that applications may be rejected. This is becoming a global issue, with many countries embracing the need to protect precious stocks and leaving the industry to seek alternative methods of providing quality materials.”

The increasing problems facing many producers are that concrete manufacturers are demanding more of a consistent product, which creates barriers at excavation. In many world regions, the extraction of sand and gravel is either heavily taxed or the extraction is being banned altogether in an attempt to preserve precious virgin reserves.

Alluvial alternatives
The resistance to using alternatives to alluvial sands and gravels for manufacturing construction products is not just specific to the U.S. The United Kingdom is an island of exceptional natural resources, Convery says, and has been self-sufficient in aggregates for hundreds of years.

As a result, the thought was always that only natural materials were appropriate and nothing else will pass scrutiny. Changes in legislation regarding recycling have brought about a step change in processing in Europe, though, and that has resulted in new thinking. Aggregate recycling and manufacturing aggregate through crushing technologies are two increasing alternative supply methods.

In the case of manufactured sands, Convery says testing has found that the overall composition is critical and should include particles from 63 microns up to 4.75 mm in size and should not be excessively rough. Having fine particles in the proper proportions across the gradient spectrum also means it has great strength and is a durable and pure product, which, once refined is cost effective when compared to excavated sand.

Manufacturers of concrete products have also found that by using manufactured sand, the defects found in the manufacturing stage, such as voiding, segregation and honeycombing are significantly reduced. This fact makes a case for this product, which is found to have greater workability and creates a smoother surface finish, Convery says. Product consistency allows a more predictable mix to be produced, and many concrete product manufacturers have found manufactured sand can result in fewer defects.

“So from a purely commercial perspective, manufactured sand is a high-grade product,” he says. “It has balanced physical and chemical properties, has great strength, plus it is a durable and a pure product. What’s more is it can be produced in close proximity to where it is needed, which avoids lengthy and expensive transportation.”

If California is to overcome its aggregates issues over the next 50 years, serious changes in thought are called for. In the next 50 years, Convery says the consumption in that area is likely to be 12 billion tons of aggregates, with permitted reserves currently standing at 4 billion tons. That’s about 5.7 tons per person per year. With California consuming about 180 million tons of material per year, demands are expected to grow as the state’s population expands.

“Because aggregate is a high bulk weight, low unit value product, it makes commercial sense to produce it locally to save adding additional transport cost on to the consumer,” Convery says. “With the processing and washing of construction, demolition and excavated waste material able to recycle up to 90 percent of all material returning it for use in the construction sector close to its area of production, this provides a viable commodity that would be capable of meeting the shortfall in the needs of a state like California.”

Take note
California consumed, on average, 180 million tons of mixed construction aggregate each year between 1981 and 2010.

Photos: CDE Global

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