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.
Bibliometric analysis of studies involving e-waste: a critical review de Albuquerque, Carlos Alberto; Mello, Carlos Henrique Pereira; de Freitas Gomes, José Henrique ...
Environmental science and pollution research international,
09/2021, Letnik:
28, Številka:
35
Journal Article
Recenzirano
The correct destination of waste is an essential factor for sustainable development. Electronic waste, which is very toxic, is the type of waste with the highest rate of increase in its generation. ...For these reasons, the amount of research on this topic increases year by year, as shown by the literature review carried out by this study. This review aims to identify the main characteristics and proposals of the main study on electronic waste and verify how Brazil is inserted globally in the research on e-waste. Another objective is to suggest a path for researchers who want to start research on e-waste by identifying the keywords most used in the analyzed articles. The results evidenced that the most published countries on the subject are China, the USA, and India. Brazil is in a position of little prominence concerning its research production on the subject. Most of the central studies we analyzed use case study and literature review as the research method. Among the 44 articles analyzed, only one proposed a destination for e-waste. It highlights the need for more research focusing on the environmentally correct destination of e-waste. A good way to start a search on electronic waste is to use the keywords identified in this study, especially those used most frequently in the analyzed articles.
The addition of Superabsorbent Polymer (SAP) decreases the effect of autogenous shrinkage present in pastes, mortars, and concretes. In this study we investigated the influence of the addition of SAP ...in self-compacting cement paste mixtures. Eighteen 5 × 10 cylindrical specimens were molded in all, three for each mixture (CPII base, CPII 0.15%SAP/600μm, CPII 0.15%SAP/800 μm, CPV base, CPV 0.15%SAP/600 μm, CPV 0.15%SAP/800 μm). Two types of cement were tested, CP II-Z and CP V-ARI with 0.15% of weight replaced per two diameters of SAP (600 μm and 800 μm). The samples followed the standards required. Mini slump tests were carried out in the fresh state, and uniaxial compressive strength, elastic modulus, specific mass, absorption, and air content in the hardened state after 28 days. The results obtained show the SAP is high indicated to replaced cement in small % of weight i/to fresh and hardened paste. Likewise, the group mix n° 3 composed of CPII 0.15% of SAP with 800 μm diameter presented the best result.
The inadequate disposal of household appliances by consumers and industries have annually been generating enormous amounts of polymeric waste (PW). So, the interest in reuse of PW in civil ...construction has increased. The production of new cementitious materials, such as concrete with PW, proves to be a promising solution to inappropriate disposal of this waste. In this study, self-compacting concrete (SCC) was developed with partial replacement of the coarse aggregates by polymeric waste (PW) from the recycling of refrigerators. In the SCC reference mixture, Portland cement, silica fume, sand, gravel and superplasticizer were used. The study also grouped the gravel as replaced by 5%, 10%, 15% and 20% of PW. In order to analyze the samples, the following tests were used: spreading, viscosity, passing ability, compressive strength, tensile strength, microstructure, modulus of elasticity, specific gravity, absorption, voids index and electrical resistivity. The SCC found showed adequate homogeneity and viscosity, staying within the normative parameters. The mechanical resistance was above 20 MPa; specific mass between 1870 to 2260 kg/m3; modulus of elasticity ranged from 34 to 14 GPa; and electrical resistivity between 319 to 420 ohm.m. Due to the mechanical resistance, the SCC with PW can be used for structural purposes and densely reinforced structures such as pillars, beams and foundation elements.
Self-compacting concrete (SCC) is an innovative type of concrete that does not require vibration for compaction; however, it needs attention in relation to the control of thermally generated cracks, ...due to the hydration heat generated mainly during the curing process in pieces with large concrete volume. In this study we investigated the addition of Superabsorbent Polymers (SAP) as internal curing elements in self-compacting mortar (SCM), as well as its thermal and mechanical characteristics, looking to obtain the optimal proportion of materials in a way that is useful as the basis of self-compacting concrete use, focusing on large volume structures. This work stands out for studying an alternative for shrinkage control, in an unconventional cementitious composite, highlighting the thermal analysis of the mixture. In the experimental program, laboratory trials were conducted using self-compacting mortar with the addition of 0%, 0.1%, and 0.2% of SAP either for CPII-E-32 and CPV-ARI and with samples undergoing both dry and submerged curing. Among the results obtained, the reduction of variation in temperature in samples with added SAP stand out, and it is possible to presume it as being a viable way of mitigating the temperature spikes in large volume concrete parts. By contrast, the compression and tensile tests indicated a reduced strength, except in the tensile trial on the CPII-E-32, which the addition of SAP resulted in an increase in strength.
•Optimization of the use of industrial waste of different natures in cementitious mortars.•Artificial neural network together with response surface for dynamic characterization of cementitious ...mortars.•Natural frequency increase in mortars with polyurethane waste.•Foundry sand with polyurethane are able to increase the damping of cementitious mortars.
Although many studies have reported on the application of experimental, statistical, numerical, and computational tools to composite structures, few have focused on the use of analysis of variance (ANOVA) to analyze experimental data and Artificial Neural Network (ANN) as a technique to predict the modal responses of Portland cement mortars. In this study, by means of DOE and ANN the modal responses of portland cement mortars with polyurethane waste and foundation sand from exhaustion were investigated. The tests were performed by means of free vibration and the analyzed responses were natural frequency and damping factor. The experimental results indicated that the combined PU and FES waste can significantly change the natural frequency and damping of the mortars. This change, when compared to the reference samples, can reach an increase of 11.6% or decrease of 21.7%, depending on the percentage of waste used. The ANN trained with the experimental data showed a high correlation to predict the experimental results.
The utilization of wastes from demolition in civil construction in self compacting concrete (SCM) has the potential to reduce both the environmental impact and financial cost. In this context, this ...article aims to verify the behavior of the incorporation of recycled aggregates of civil construction in the mix designs of self-compacting mortar (SCM) in replacing cement, presenting as an interesting alternative to natural raw materials. This study used the EMMA® software to optimize the choice of percentages of fine recycled aggregates when replacing cement. The proportions chosen were 0%, 5%, 15%, and 25%, through the analysis of the granular packing curve of the respective mix designs. The proportion of 0% has in its composition cement, metakaolin, sand, superplasticizer (SP) and water. The parameters obtained, through tests in the fresh state of the mini-slump and mini-funnel V, certified the samples as SCM. The compressive strength and flexural tensile strength tests in the hardened state demonstrated a reduction in mechanical properties of the material with cement replacement. It is concluded that the waste used brick and ceramic can be added in replacement to the cement in SCM without significant loss of properties in the fresh and hardened state.
resumo: A utilização de resíduos de demolição da construção civil em concreto autoadensável (CAA) tem o potencial de reduzir o impacto ambiental e o custo financeiro. Nesse contexto, este artigo tem como objetivo verificar o comportamento da incorporação de agregados reciclados da construção civil nos traços de argamassas autoadensáveis (AAA) em substituição ao cimento, apresentando-se como uma alternativa interessante às matérias-primas naturais. Este estudo usou o software EMMA® para otimizar a escolha das porcentagens de agregados reciclados finos ao substituir o cimento. As proporções escolhidas foram 0%, 5%, 15% e 25%, através da análise da curva de empacotamento de partículas dos respectivos traços. A proporção de 0% tem em sua composição cimento, metacaulim, areia, superplastificante (SP) e água. Os parâmetros obtidos, por meio de testes no estado fresco do mini-slump e mini-funil V, certificaram as amostras como AAA. Os ensaios de resistência à compressão e a tração na flexão no estado endurecido demonstraram redução nas propriedades mecânicas do material com a substituição do cimento. Conclui-se que os resíduos usados de tijolo e cerâmica podem ser adicionados em substituição ao cimento na AAA sem perda significativas de propriedades no estado fresco e endurecido.
Self-compacting concrete is still little used in Brazil and in the world. This is due to the lack of studies on the subject and the difficulty in obtaining an ideal mixture proportion. The ...performance of studies in this area is of great importance to increase knowledge and increase the visibility of this concrete in the market. In this context, this article presents a contribution to self-compacting concrete mixture design using the virtual packing aggregates method. EMMA software has been used. Four SCC mixtures were analyzed in which the M1 mixture composed of 100% natural sand. Mixtures M2, M3 and M4 with partial replacement of fine aggregate by metallic, ceramic and rubber residues respectively. The good results obtained indicate that the methodology presented in this study for SCC mixture design was effective thus avoiding several mixtures steps.
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