Concrete & Asphalt Reuse: How Halton Paved The Way To Savings

K. Cliff Chan

Two key components of construction debris have found a new home on the road. The Halton Landfill, Halton, Ontario, has recycled an 11,800 cubic yard pile of concrete and asphalt by crushing and re-using it for, among other things, access road construction.

In 1995, the landfill, which serves 330,000 residents and is owned and operated by the regional municipality of Halton, hired Guelph, Ontario-based Cox Construction to crush a large stockpile of concrete and asphalt rubble. The company had nine weeks to finish the project, with working hours limited to 7:30 a.m. to 5 p.m. The operation also was set up at least 1,800 feet from neighboring homes.

All equipment was inspected to identify potential hazards prior to operation.

Special attention was given to:

* proper guarding for pinch points;

* proper guarding for fall, especially near the crushing chamber;

* availability of personal protective equipment such as hard hats, eye and hearing protection and safety footwear;

* emergency communication set up, such as radio and cell phone; and

* maintenance requirements and lockout procedure.

The crushing was completed in approximately five days using a primary jaw crusher and triple roll reductioneer secondary crusher, manufactured by Cedar Rapids, Iowa-based Cedar Rapids Inc.

A hydraulic excavator manufactured by Caterpillar Inc., Peoria, Ill., knocked down the stockpile, while a Cat loader fed the rubble to the crusher.

The material was then sized by a triple-deck screener while a magnet extracted steel bars. The product on the conveyor belt was sprinkled with water to minimize dust.

The 2-inch minus gravel was produced first, followed by 1-inch minus gravel, and the materials were separated into separate stockpiles.

To keep noise at a minimum, operations were carried out more than 1,800 feet away from neighbors, and hours were limited to 7:30 a.m. to 5 p.m.

The 2-inch gravel was used for landfill access road construction, while the 1-inch gravel was used for compost pad repair and construction. Two local municipal road departments used the 1-inch gravel for road shoulder repairs.

Crushing the landfill rubble was cheaper than buying gravel from a quarry - $52,000 vs. $89,000 (both in U.S. dollars and include sales tax).

The 42 percent cost saving is significant. Even without a tipping fee, the crushing cost was much lower than that of purchased gravel. Several area asphalt or concrete plants are charging $15 to $30 (U.S.) per truckload. A tipping fee would have offset the crushing cost further.

Here are a few tips from this experience:

* Avoid recycling reinforced concrete because large piles of steel are difficult to handle. However, even if you do not accept reinforced concrete, some steel may slip through inspection, such as concrete pieces with steel mesh or rebar or fence pole foundations with steel pole segments. In any event, the contractor's equipment should be required to be able to handle residue steel. The steel pile should be removed quickly before getting too big to handle.

* Workers picking up the finished gravel must keep the gravel from sliding onto the loader since a stockpile can be more than 35 feet tall. If space is available, the steep slope on a stockpile can be knocked down using a hydraulic excavator or dozer. However, this must be done very carefully to avoid roll-over.

* C&A rubble should be separated when it is received to improve product quality. Asphalt tends to crumble more quickly and create more fines. Crushed asphalt also is softer and can bind together, inhibiting drainage. If drainage is a concern, use pure concrete.

* Limit the size of the concrete pieces to less than 2-feet-by-2-feet to help crushing.

* Plan for enough space for the finished product stockpiles, in case there are more than one size needing separation. Since the crusher is not mobile, its articulated conveyor belt will create a stockpile close to the operation.

It is viable for a landfill to start a C&A recycling program. In addition to financial gain, Halton also reduced its demand for virgin gravel materials from local quarries, which is regarded by some as a non-renewable resource.

Careful planning is necessary before a rubble stockpile is created to ensure good product quality, operational efficiency and safety.