Sustainability and durability of concrete produced with CO 2 beneficiated reclaimed water

Wash water is generated as a by-product of ready mixed concrete production. The water can be reclaimed to be used as mix water in new concrete. The properties, durability and sustainability of concrete produced using high solids reclaimed water, subjected to a novel CO 2 (carbon dioxide) treatment, as mix water was examined. A simulated reclaimed water with a specific gravity of 1.10 was used as a partial (44%) replacement for mix water in concrete production. A comparison was made between reference concrete, batches made with untreated reclaimed water, and reclaimed water treated with CO 2 to either a low or high CO 2 uptake. The treatment mineralized CO 2 at 5 and 20% by weight of the cement in the reclaimed water solids. The mix designs either included the reclaimed water slurry as a replacement for the mix water or further incorporated a reduction to the virgin binder in proportion to the added reclaimed water solids. The compressive strength was improved with the use of both untreated and treated wash water; it is suggested that the improvements are attributable to cementitious properties of the solids, improved particle packing in the binder phase and an effective reduction of the water to binder ratio. A suite of testing (including RCPT, bulk resistivity, bulk diffusion, abrasion, freeze/thaw, salt scaling, drying shrinkage, carbonation, and corrosion) demonstrated that the durability was not affected by the incorporation of the treated reclaimed water. The treated slurry batches had a 10–11% improvement in the carbon index (kg CO 2 embodied/MPa of strength) for the low treatment and 13–14% for the high treatment.