Methods and compositions for treatment of concrete wash water

An apparatus for carbonating wash water produced in the production of concrete wherein the wash water comprises cement and/or supplementary cementitious materials (SCM), comprising

• (i) a source of carbon dioxide;
• (ii) a first conduit operably connected to the source of carbon dioxide that runs to a wash water container, a carbonation loop, or both, for delivering a flow of carbon dioxide to the wash water container, the carbonation loop, or both, wherein
• (a) the wash water container contains wash water from a concrete production site;
• (b) the conduit is configured to deliver carbon dioxide to the wash water in the container, the wash water in the carbonation loop, or both, to produce carbonated wash water, and
• (c) the conduit comprises one or more actuators to adjust the flow of carbon dioxide to the wash water in the container, the wash water in the carbonation loop, or both;
• (iii) a system to transport the carbonated wash water to a concrete mix operation where the carbonated wash water is used as mix water in a concrete mix;
• and
• (iv) a control system comprising at least two sensors configured to send information connected to a controller, wherein the controller is configured to process the information from the sensors and to modulate carbon dioxide flow by sending a signal to the one or more actuators based on the information, wherein the sensors are configured to monitor at least two of
• (a) pH of the wash water,
• (b) rate of delivery of carbon dioxide to the wash water,
• (c) total amount of wash water in the wash water container,
• (d) temperature of the wash water,
• (e) specific gravity of the wash water,
• (f) concentration of one or more ions in the wash water,
• (g) age of the wash water,
• (h) circulation rate of the wash water,
• (i) timing of circulation of the wash water,
• (j) appearance of bubbles at surface of the wash water,
• (k) carbon dioxide concentration of the air above the wash water,
• (l) electrical conductivity of the wash water,
• (m) optical characteristics of the wash water.