Steps in slurry processing
Throughout the slurry handling process, it is important to understand that the ultimate responsible party for the waste is the waste generator, who will be the site owner.
Planning
The planning of slurry management should always be focused on developing a plan which allows for safely managing the slurry, both for people (see section 6.3) and the environment.
In most cases, the owner of the facility, generator of the concrete slurry, transporter and dumpsite or landfill owner all hold the responsibility of the concrete slurry waste.
Keeping this in mind, a possible outline that includes the steps to be taken in the planning of slurry management can be as follows:
- Establish the general requirements for the job and clearly identify them in the contract.
- Check the specific regulations in the area/region/country where the work is to be carried out. It should be noted that there are some countries where this issue is highly regulated.
- Determine who is responsible for the collection, handling, and disposal of slurry. It must be noted the slurry generator should always be responsible for the slurry.
- Select the approved dumpsite, determine where it is located, its hours and fees, and if there are any special handling or testing requirements. Ensure the dumpsite is aware of the waste type.
- Investigate if there is water available on the job site.
- Determinate if the slurry will be treated and if the water will be recycled for use in the project.
- Set up the collection system.
- Determinate if the ‘slurry controls’ will interfere with other work, job site access, or the safety of workers.
Collection and handling
Slurry must be never disposed of in the public sewer. If it was allowed to flow along drainage pipes, it would create a water blockage.
It must be ensured that the slurry will not run into a storm drain, as it will negatively affect the oceans or lakes, causing serious harm, including death to the aquatic life. Even if there is not a storm drain present, concrete must never be left to dry at the jobsite, as the wind will spread the slurry particles over grass, lakes, streams, and ocean. It can even mix into the air we breathe.
In some countries, these practices are punished with large fines.
In this sense, there are several options to collect and handle the slurry. The easiest way to keep time and costs to a minimum is to consult with an expert in concrete slurry management.
Dewatering systems typically keep costs to a minimum while reducing the waste stream volume which reduces the hauling and disposal required.
Thick paste slurries can be diluted with water to help the concrete slurry processor adequately extract, pump or relocate the concrete slurry. Flocculants can be used to accelerate the settling time in recycling the water by quickly separating the solids.
Always try to recycle the maximum amount of water possible. While carrying out the job, access to the worksite should be restricted as needed to minimize hazards associated with the water/slurry and/or respirable crystalline silica exposure.
Auto scrubbers, mops, and pressure washers can be used to clean up a job site. Some chemicals are available to help in the clean-up of dried concrete or dried slurry by softening or solubilizing the cement to allow it to release the bond from the surface so it can be easily cleaned off the surface or removed with no abrasive methods.
Furthermore, it must be taken into account that while handling the slurry generated, it must be ensured that operators use enough water in order to have always a saturated slurry. Otherwise, it will start drying and silica dust will spread all around, generating dangerous risks.
Testing and disposal
The slurry should always be tested to determine what substances are in it so that disposal can be made according to the characteristics of those substances, especially if any of them are considered hazardous.
Such testing must be performed on the slurry, as the previous testing of the concrete is not valid.
Although many legislations do not require it, it is a good practice, because in the drilling and sawing processes, more substances can be added.
In this regard, the most common testing required are:
- pH testing
- TCLP Testing
- Air Monitoring
- Paint Filter Test (PFT)
- Sulphur Test
The slurry can be solidified and treated as solid waste. It must be disposed of in an approved waste site according to the characteristics of the substances contained, paying special attention to the typical presence of hazardous substances will require the review of the landfill or dumpsite owner or owner’s representative.
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