ASTM guidelines place limits on what gray water can contain but no insight into how to reuse the water in production. This absence of guidelines causes a problem as the producer tries to address customer performance requirements and daily production demand.
The Holy Grail of recycled water reuse is a batch panel that adjusts mix designs according to the amount of cement and water in slurry.
Most batching systems are not designed to analyze the recycled water and then adjust mix designs accordingly. The computer system controlling the water has to account for the fact that solids in the water are "robbing" water from the mix design. Adding complexity to the problem is the constantly changing level of solid material in the water due to both the addition of solid material through the recycling process and the hydration process.
One Texas supplier has succeeded in recycling water through batching controls. Lattimore Materials Co. (LMC) and Command Alkon collaborated to develop a comprehensive compensation system that considers two water sources that contain solid material, ASTM C 94 limits, variable specific gravity values for the solid material in the water, and changes in aggregate moisture.
Any batch panel software must be able to measure the specific gravity of the recycled water—using a hydrometer and an automated density meter—and make sure that the total amount of water in the mix design does not exceed 50,000 ppm. The batch panel and software that LMC uses are designed to allow the producer to manually input a specific gravity reading of the slurry water or use an inline density meter for automatic input of the value. In both cases, the computer takes the specific gravity reading and is able to convert to a ppm level that complies with either ASTM or customer expectations.
To this end, the Slurry Compensation software package uses one primary screen for input data and the other two screens for batching and verification.
The article includes ASTM C 94 Table 3: Optional Chemical Limits for Wash Water.