Even after significant technological advancements in concrete production — automated batching and dispatching, GPS systems, chemical admixtures, high-tech mixers, finger-tip management and real-time cost analysis — management of waste concrete from returns and washout continues to challenge the industry. Producers grapple with managing waste concrete, avoiding environmental penalties, and returning reclaimed materials back into mixes without compromising quality.

To this end, Knelson Concrete Systems provides continuous process capabilities by integrating the engineering principles of slurry management into existing batching and production. A continuous process thereby consumes 100 percent of waste concrete without negative impact on production and quality, company engineers note. In day-to-day operations, the Knelson process follows seven basic steps to provide control over the recovery and reuse of waste material:

Washout

The system allows drivers to quickly rinse and discharge their drum contents and leave the washout area promptly. It is a simple, fast, and wide-open method, which is also user-friendly and safe.

Aggregate separation and recovery

The CRS uses a specially designed aggregate classifier, developed for use in concrete recovery, allowing the producer a clean split of the aggregates very close to #200 mesh.

Hydration stabilization

The wash water is supplied by process water collected from the yard and dosed with hydration stabilizer at all times. The stabilizer suspends hydration at the moment of washout and maintains stabilization for a user-defined period until reuse.

Slurry management

The CRS monitors and adjusts system settings for automatic management of slurry density and temperature. The process is adapted to meet the immediate needs of the individual producer, but can be adjusted to changing conditions with the touch of a button.

Process automation

All functions of the system controls are automated to reduce or eliminate hands-on management. The design of the automation is intended to simplify user interface for the driver and batcher alike. Once the system settings are in place, the process will maintain itself.

Reuse

The system automatically delivers slurry of a constant density and temperature to a small, agitated storage tank at the batch plant. This tank holds a just-in-time volume of slurry that is controlled by the batch computer for use as mixing water.

Quality control

Water and solids compensation can be written into mix designs to allow for maximum benefit from the use of the slurry. By modifying mix designs and adjusting slurry densities through controlled water blending, the producer can set up various configurations for batch management. Generating slurry that is consistent from batch to batch, the CRS contributes to the strength and finishability of the end product.

The CRS offers an integrated controls package to manage all aspects of recovery and reuse of waste concrete. Company officials note that waste material once considered a liability now potentially serves as value-added inventory directed to production, thereby eliminating waste management practices and costs. The complexities of reusing what was once a waste product are now reduced to clear and attainable goals, they add.
— Knelson Concrete Systems, 888/456-3576, www.concreterecovery.com