Estudo de viabilidade de concreto estrutural com areia de descarte de fundição e adições minerais: propriedades mecânicas e análise de ciclo de vida

Abstract

The large volume of waste generated by some productive sectors has led researchers to find suitable solutions for their reuse, in order to address technical, economic, social and environmental issues. The high consumption of raw materials by Brazilian industries for the most diverse uses, associated to the principles of sustainable development, leads to research on recycling of materials discarded by industries for the purpose of their rational and safe use in new products or reuse. Sand contaminated with phenolic resin or sand casting discard, generated in the demolding stage of metal parts in the foundry industries, is currently a serious environmental problem facing the industry. Some of this waste has been accumulated in the companies themselves and another part has to be disposed of locally. Related to this context, the present research studied different concrete traces used for the design of a pillar, using two types of mineral additions that are residues (rice husk ash and fly ash), and the high cast casting sand (75%), as well as, combined with natural sand and aggregate, the main environmental impacts caused by each mixture were determined and the best concrete / pillar alternative from the environmental / sustainable and economic point of view was defined. It was concluded that the level of resistance exerted a greater influence on the sustainability of the pillar than the types of materials studied. The ADF presented few differences in physical characteristics compared to river sand but it presented impurities such as clay, saw dust, bentonia etc which causes it to reduce the specific density of the material, creating voids of air in the concrete and this negatively affected the mechanical properties. For the concrete to reach the established fck's it was noticed an increase of cement consumption. This study aimed to use a high percentage of ADF and together with the mineral additions prove the mitigation of these negative effects in the studied concrete without increasing the consumption of cement and thus prove that the ADF can be effectively used in the manufacture of good concrete quality, compatible and sustainable cost and this was proven but only at later ages because the pozzolanic reaction was slow, at 91 days greater resistance was observed than the REF trace. Considering the integration of all analyzed parameters, the best alternative was the 75% ADF and 25% CCA trace and the characteristic resistance level of 40 MPa. The analyzes by unit of compressive strength, by MPa, evidenced an average decrease of 24% in the cost and total environmental impact when the fck rose from 30MPa to 40MPa.