Q&A: Basics of Construction and Demolition (C&D) Recycling

Construction and demolition (C&D) activities generate massive amounts of waste each year. In the United States alone, C&D debris accounts for over 200 million tons disposed annually. Globally, waste from construction makes up around 30% of all landfill waste by volume. This creates substantial environmental and economic burdens.

However, a large portion of C&D waste is recyclable. C&D recycling aims to divert reusable and recyclable materials from landfills to reduce negative impacts. It supports sustainability goals through conservation of resources and reduction of greenhouse gases from landfill disposal. With advanced technologies and management practices, recycling rates for C&D waste can be significantly improved.

Q: How much C&D waste is generated globally each year?

It is estimated that worldwide, Construction and demolition (C&D) activities generate between 1.3 to 2.3 billion tons of waste annually, accounting for approximately 25-30% of solid waste volumes in municipal waste streams. In the United States alone, over 170 million tons of C&D debris is generated yearly based on EPA data. Construction and demolition (C&D) generation rates vary considerably between developed and developing nations depending on local construction practices and demolition activities. Rapid urbanization and infrastructure development in many regions also contributes to rising C&D waste volumes posing significant waste management challenges.

Q: What are Types of C&D Materials?

Construction and demolition (C&D) debris or waste refers to the materials generated during construction, renovation, and demolition activities of buildings and infrastructure. The volume and composition of C&D waste depends on the nature and scale of the construction project. Large amounts of waste are also generated during remodeling or renovation of existing buildings and structures.

C&D debris is largely comprised of wood, concrete, asphalt, gypsum board, metals, plastics, and other materials.

1. Concrete - This typically accounts for the largest portion, often 30-50% by weight. It includes debris from reinforced/structural concrete as well as concrete products like bricks, blocks, and pipes.
2. Wood - Dimensional lumber, plywood, composite boards and wood products constitute 10-20% by weight.
3. Asphalt, roofing materials and other non-wood solid waste.
4. Gypsum drywall or wallboard - Often around 5-10% by weight.
5. Metals - Rebars, steel beams, aluminum, copper and other metals.
6. Plastics - Derived from plastic piping, windows, conduits and various construction materials.
7. Soil, rock, and land-clearing debris from excavation activities.
8. Special wastes - Smaller amounts of hazardous materials like solvents, paints and treated wood.

Q: What are the environmental impacts of landfilling C&D waste?

Simply landfilling large volumes of C&D debris imposes numerous environmental impacts and costs:

1. Significant loss of usable natural resources like aggregates, wood, asphalt and metals that wind up buried in landfills instead of being recycled.
2. Premature exhaustion of limited landfill space since construction and demolition (C&D) has a high specific weight and takes up a sizable portion of disposed waste in many areas.
3. Release of greenhouse gases like methane from decomposing organic waste within landfills, contributing to climate change.
4. Potential groundwater pollution from contaminants in landfill leachate if not managed properly with landfill liners and controls.
5. Air pollution from dust/particulates and toxins during transportation and operation of unregulated dumpsites.
6. Heavy traffic from waste hauling trucks adds congestion and wear-and-tear on local roads.
7. Higher overall waste management costs to taxpayers from wasted value in disposed materials and landfill infrastructure costs.

Q: What are the common process flows of C&D processing?

Here are the details on some key processing steps in construction and demolition (C&D) recycling applications:

1. Feeding:

   Drop chutes and conveyors transport incoming mixed debris to downstream equipment. Vibratory feeders regulate material flow for steady processing.

2. Crushing:

   Jaw, cone and impact crushers are commonly used to size-reduce oversized pieces for separation. Crushers may have multiple stages to achieve various product sizes.

3. Screening:

   Trommel screens, vibratory screens, rotary screens separate crushed material by size into specified fractions like coarse, fine and undersize products suitable for further processing.

4. Scrubbing:

   Drum scrubbers use high-pressure water jets to clean materials by removing dust/coatings and fines before further processing or stockpiling.

5. Washing:

   Log washer style systems combine scrubbing, rinsing and dewatering to purify sand and gravel fractions before shipping to end-markets or further processing.

6. Classifying:

   Air classifiers, hydrocyclones and vibratory equipment segregate specified sizing fractions by density/particle characteristics such as lightweight plastics.

7. Dewatering:

   Belt filters, centrifuges and other processes remove water from washed/classified fractions before conveyance or temporary stockpiling.

8. Sampling:

   Representative material samples are collected from each step and stockpiles for laboratory analysis to ensure quality control.

9. Water recycling:

   Settling ponds, filtration systems and other techniques treat wash plant water for reuse to minimize fresh water needs.

10. Tailings management:

    Non-recoverable fractions comprising fines, unsuitable particles and contaminants are usually landfilled, and such residuals require careful handling for regulatory compliance.

Proper integration of these processing stages enables efficient materials separation, recovery and product delivery from mixed C&D feedstocks.

Q: What are the key benefits of C&D waste recycling?

Some major advantages of recycling C&D debris include:

1. Conservation of natural resources and preservation of raw material sources through reuse of recovered materials.
2. Minimizing the environmental footprint of construction activities by diverting large amounts of waste from landfills and reducing pollution and emissions associated with waste disposal transportation and operations.
3. Economic savings for communities by lowering disposal, processing and transportation costs compared to raw material procurement. Revenue generation is also possible from material sales.
4. Job creation in recycling-related industries like collection, sorting, processing and manufacturing utilizing recycled aggregates, metals, wood and mineral materials.
5. Compliance with landfill diversion mandates and extended usable lifetimes of existing waste facilities relieving need for new expensive landfill developments.
6. Green marketing benefits for construction firms meeting sustainability standards adopted by many developers and governments worldwide.
7. Social awareness raising and stakeholder collaboration supporting circular economy principles with diversion and resource recovery initiatives.

Learn more about how to conduct a waste audit and create a customized construction and demolition (C&D) strategy for your business.