Rheological And Mechanical Performances Of Concrete Manufactured By Using Washing Water Of Concrete Mixing Transport Trucks

Abstract

The paper deals with the study of rheological and mechanical properties of concretes manufactured by using wash waters as partial replacement of drinking water. Concretes were manufactured by using only water utilized to wash concrete mixing transport trucks. Three different wash waters, with solid residue amount in the range 0.13% - 5.5% by mass were used. The waters were directly sampled in an innovative beton wash system. 30 and 35 concrete grades were manufactured. The superplasticizer dosage was adjusted in order to attain a slump value of 210 mm (8.3 in.) at the end of the mixing procedure. The workability and workability loss up to 60 minutes were also evaluated. The compressive strength at 1, 7 and 28 days was measured on cubic specimens. At 60 minutes, fresh water was added to compensate slump loss (retempering procedure) and a second series of cubic specimens was taken to evaluate compressive strength penalization. Suspended solids in wash water strongly influences the workability retention: the higher the solid content, the lower the workability loss over time and, hence, the water demand to compensate the slump decrease. At the same w/c ratio, the presence of solid particles in wash water causes an increase in the early compressive strength. A modification of the aggregate grading curve, consisting in reducing the sand fine fractions, should be considered, to manufacture concretes comparable to traditional ones.