Various aspects of concrete construction, rehabilitation and recycling result in the production of a considerable amount of waste material in the form of water with high pH as well as dissolved/suspended solids. Disposal of this material can be costly, adding to the cost of infrastructure construction and rehabilitation. Fortunately, this wastewater and suspended/dissolved solids can be used in the production of new concrete. Many modern ready-mix plants incorporate these materials in their water-recirculation systems, but the only measurements generally made on the water are for specific gravity (index of refraction). While the use of recycled waste water and fines are known to frequently have an accelerating effect on new concrete mixtures, specific gravity measurements provide little information other than the approximate amount of waste material in the recirculation system. This presentation will cover the results of detailed characterization of waste concrete fines obtained from a variety of sources including both concrete truck washout facilities and pavement diamond-grinding operations. Characterizations include index of refraction, conductivity (to differentiate dissolved from suspended solids) and pH. All of these measurements are suitable for use with on-line (continuous-reading) sensors for eventual implementation in concrete ready-mix plants. Results are also presented that correlate actual early and long-term strength measurements to the characterizations of the waste fines at various concentrations.
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