5 questions about concrete washout

1. What is concrete washout?

Concrete washout is the excess concrete returned by trucks to the ready-mix yard, which is watered down and discharged during the cleaning process. According to the National Ready Mixed Concrete Association, the average amount of excess concrete per truck per day is 1.5 cubic yards. In some cases, trucks can return to the ready-mix yard at the end of the operating day with full loads that need to be washed out.

2. How has concrete washout traditionally been managed?

Concrete washout has been managed in a variety of ways over the years. Four examples of the most common traditional methods include:

• dumping at a landfill;
• making precast wall blocks or highway barriers;
• dumping on-site, stockpiling and granulizing hardened concrete material; or
• using reclaim systems to dewater solids and recycle excess water.

3. What is wet-processing concrete washout?

This is a more involved process compared with traditional reclaim systems. Wet-processing concrete washout returns valuable aggregate and water back to its original, clean condition. The sand and rocks are washed, scrubbed and separated by size, so they are as clean as they were when they were considered “virgin” aggregate. The reclaimed products are clean enough to be reused in ready-mix production. Water is also recycled and pH-adjusted so it can be reused in ready-mix production. The cementitious fines are isolated and dewatered into hardened filter cakes that can be crushed to produce a fill material and sold, adding to the complete recovery of materials using this process.

4. What are the benefits of wet-processing concrete washout?

Wet processing concrete washout produces high-value products, preserves mining reserves and reduces costs relating to mining, water and hauling of both natural reserves and waste. It increases operational efficiency by reducing turnaround time for trucks to be ready for the next batch and by freeing up operators and yard space associated with wall block production. By recycling water, the process eliminates wash-water disposal problems associated with dumping, eliminating risk of soil or waterway contamination.

There are business opportunities associated with producing marketable lower-carbon concrete through wet processing concrete washout. It helps to meet the demands from sustainably minded customers and investors, helps attract federal/state infrastructure funds and contributes towards Leadership in Energy and Environmental Design certification. An added benefit is avoiding any long-term liabilities associated with soil or waterway contamination through dumping activities.

5. What are the challenges of wet-processing concrete washout?

Truck drivers are often in a hurry and there are various types of ready-mix concrete, so the system has to be durable and adaptable to deal with the variable feed rates and consistency.

The system needs to be easily washed down daily to prevent the buildup of fines on the equipment. Finally, wash-water is caustic and corrosive, so precautions should be taken to protect operators.