Reuse of fines from ready-mix concrete washing slurries

Abstract

Concrete waste slurries coming from the washing of concrete mixer trucks in the manufacture of ready-mix concrete generate high costs and environmental impacts. In this work, we examined the consumption of raw materials, water, and generation of wastes for three Brazilian ready-mix concrete plants (that used different waste management strategies). The reuse of concrete slurry fines was also investigated in new concretes considering the waste management scenarios, production and operational costs. The strategy to recover fresh concrete provided the best scenario since it reduced significantly operational costs, despite the inclusion of new production cost, i.e. the hydration stabilizer additive. The replacement of sand with 1 vol.% concrete slurry provided adequate rheological conditions for concretes, when the water content increased up to 6 wt.% or added 0.3 % m.c. of polycarboxylate-based additive. The marginal increase in the production cost can also be compensated by the reduction of the disposal operational costs. The reuse strategy was not enough for the total elimination of concrete fines, requiring market diversification (e.g. pre-cast concrete products); but fines availability can be very limited.