Rheological and the Fresh State Properties of Alkali-Activated Mortars by Blast Furnace Slag.

The fresh and rheological properties of alkali mortars activated by blast furnace slag (BFS) were investigated. Consistency tests, squeeze flow, dropping ball, mass density in the hardened state, incorporated air, and water retention were performed. Mortars were produced with the ratio 1:2:0.45 (binder:sand:water), using not only ordinary Portland cement for control but also BFS, varying the sodium content of the activated alkali mortars from 2.5 to 15%. The results obtained permitted understanding that mortars containing 2.5 to 7.5% sodium present a rheological behavior similar to cementitious mortars by the Bingham model. In turn, the activated alkali mortars containing 10 to 15% sodium showed a very significant change in the properties of dynamic viscosity, which is associated with a change in the type of model, starting to behave similar to the Herschel-Bulkley model. Evaluating the properties of incorporated air and water retention, it appears that mortars containing 12.5% and 15% sodium do not have compatible properties, which is related to the occupation of sodium ions in the interstices of the material. Thus, it is concluded that the techniques used were consistent in the rheological characterization of activated alkali mortars.

Novel applications of waste foundry sand in conventional and dry-mix concretes.

The use of waste materials in the building industry is a major challenge for eco-efficient construction. Brazil generates more than 3 million tons of waste foundry sand (WFS) annually, making it one of the largest industrial wastes produced in the country. This work proposes the use of WFS in two novel ways: in conventional concrete by WFS calcination, and in dry-mix concrete for the production of concrete blocks. For the conventional mixture study, mortars with 0, 50 and 100% replacement of natural sand by WFS and calcined WFS (CFS) were produced. The fresh state properties, volumetric variation, cement hydration and 28-days compressive strength of the mortars were evaluated. For the dry-mix concrete study, compositions with two densities (2.20 and 2.25 g/cm3), three cement contents and 0, 50 and 100% WFS in natural sand replacement were produced in the laboratory. Furthermore, concrete blocks of different strength ranges and 0 and 100% WFS in natural sand replacement were produced in a concrete block manufacturing plant for full-scale testing. The results showed that the use of WFS led to reductions in flowability and compressive strength of the mortars, but did not cause expansion as initially expected. In contrast, the use of up to 100% CFS resulted in mortars with flowability and compressive strength similar to those of the reference. WFS calcination removed the pulverized coal and may have formed pozzolanic phases in the clay material. As a result, the CFS presented performance similar to that of natural sand. In dry-mix concrete, the laboratory results showed that the use of 100% WFS resulted in similar strengths to the reference for concretes of up to 20 MPa. Finally, full-scale tests showed that it was possible to produce concrete blocks with 100% WFS and strengths compatible to the reference.