RESUMEN
The reuse of waste in civil construction brings environmental and economic benefits. However, for these to be used in concrete, it is necessary a previous evaluation of their physical and chemical characteristics. Thus, this study aimed to characterize and analyze the waste foundry exhaust sand (WFES) for use in self-compacting concrete (SCC). Foundry exhaust sand originates from the manufacturing process of sand molds and during demolding of metal parts. It is a fine sand rich in silica in the form of quartz collected by baghouse filter. Characterization of WFES was conducted through laser granulometry, scanning electron microscopy (SEM) in the energy dispersive spectroscopy (EDS) mode, X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG) and derivative thermogravimetry (DTG) techniques. The waste was classified as non-hazardous and non-inert, with physical and chemical properties suitable for use in SCC composition, as fine aggregate or mineral addition. Five mixtures of SCC were developed, in order to determine the waste influence in both fresh and hardened concrete. The properties in the fresh state were reached. There was an increase in compressive strength and sulfate resistance, a decrease in water absorption of self-compacting concrete by incorporating WFES as 30% replacement.
RESUMEN
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 2.25â¯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 20â¯MPa. Finally, full-scale tests showed that it was possible to produce concrete blocks with 100% WFS and strengths compatible to the reference.
Asunto(s)
Materiales de Construcción , Residuos Industriales , Brasil , Fuerza Compresiva , Dióxido de SilicioRESUMEN
The creation of metal parts via casting uses molds that are generally made from sand and phenolic resin. The waste generated after the casting process is called waste foundry sand (WFS). Depending on the mold composition and the casting process, WFS can contain substances that prevent its direct emission to the environment. In Brazil, this waste is classified according to the Standard ABNT NBR 10004:2004 as a waste Class II (Non-Inert). The recycling of this waste is limited because its characteristics change significantly after use. Although the use (or reuse) of this byproduct in civil construction is a technically feasible alternative, its effects must be evaluated, especially from mechanical and environmental points of view. Thus, the objective of this study is to investigate the effect of the use of WFS in the manufacture of cement artifacts, such as masonry blocks for walls, structural masonry blocks, and paving blocks. Blocks containing different concentrations of WFS (up to 75% by weight) were produced and evaluated using compressive strength tests (35 MPa at 28 days) and toxicity tests on Daphnia magna, Allium cepa (onion root), and Eisenia foetida (earthworm). The results showed that there was not a considerable reduction in the compressive strength, with values of 35 ± 2 MPa at 28 days. The toxicity study with the material obtained from leaching did not significantly interfere with the development of D. magna and E. foetida, but the growth of the A. cepa species was reduced. The study showed that the use of this waste in the production of concrete blocks is feasible from both mechanical and environmental points of view.