Use of recycled water from mixer truck wash in concrete: Effect on the hydration, fresh and hardened properties

This work investigated the effect of using recycled water (RW) from mixer truck wash on the properties of pastes and concretes containing partial and total replacement of potable water. The fresh properties (rotational rheometry for pastes and slump for concretes, both at 0 and 60 min), hydration (isothermal calorimetry and TG) and compressive strength (at 3, 7 and 28 days) were evaluated. The results showed that the solid particles and high alkalinity of RW increased the viscosity of the pastes by up to 11% and the yield stress by up to 25% (both for 100% RW), also reducing the slump of the concretes. However, the flowability losses from 0 to 60 min were lower in the RW-containing mixtures. TG and calorimetry indicated that the RW enhanced the cement hydration at early ages, resulting in compressive strengths 8 and 16% higher than those of the reference (average of RW-containing concretes), respectively at 3 and 7 days. At 28 days, the reference concrete presented the greatest strength because of the lowest amount of water required to reach the desired flowability. Nevertheless, all concretes containing RW showed 28-days strength compatible with the reference, reaching 94% and 92% of it respectively for 50% and 100% RW. Finally, a brief discussion on the potential for RW reuse in concrete plants is presented. (C) 2019 Elsevier Ltd. All rights reserved.