Navegando por Autor "Schmidt, Wolfram"
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Item Enhancing the eco-efficiency of concrete using engineered recycled mineral admixtures and recycled aggregates.(2020) Carvalho, José Maria Franco de; Fontes, Wanna Carvalho; Azevedo, Carlos Felipe de; Brigolini, Guilherme Jorge; Schmidt, Wolfram; Peixoto, Ricardo André FiorottiNon-conventional densely packed concrete mixtures are proposed and evaluated in this paper using engineered recycled mineral admixtures and recycled aggregates obtained from steel slag, quartz mining tailings, and quartzite mining tailings. High fines content sand-concretes containing coarser- and finer- than-cement recycled powders were designed to obtain blends with broader particle-size ranges and improved packing density. As a result, compressive strength up to 99 MPa, cement intensity up to 2.33 kg/m3 /MPa, and consumption of recycled material up to 95 vol% were obtained. Compressive strengths up to 66 MPa and cement intensity up to 2.34 kg/m3 /MPa were also obtained with the addition of coarse aggregates to such sand-concrete mixtures, with consumption of recycled material up to 96.5%. The results launch new insights on the role of recycled admixtures and aggregates on the mixture design of cement-based composites regarding efficiency improvement and technological performance.Item Influence of high-charge and low-charge PCE-based superplasticizers on Portland cement pastes containing particle-size designed recycled mineral admixtures.(2020) Carvalho, José Maria Franco de; Schmidt, Wolfram; Kühne, Hans-Carsten; Peixoto, Ricardo André FiorottiDesign: and use of engineered recycled mineral ad mixtures obtained from industrial and mineral waste are promising strategies to increase the range of materials suit able for use in cement - based composites. In this work, Portland cement - blended pastes con taining mineral ad mixtures designed for improving particle packing were evaluated in the presence of low - and high - charge poly car boxy late - based super plasticizers. The powders were obtained from basic oxy gen furnace slag, iron ore tailings, quartz mining tailings, and quartzite mining tailings. The zeta - potentials of the particles were obtained via electrophoretic mobility. The flow properties were evaluated by rheological tests per formed in a Couette type rheometer. The hydration kinetics was evaluated by isothermal calorimetry and an adapted method based on the Vicat needle test. The high - charge PCE and the finer mineral ad mixtures produced more stable blends. Coarser mineral ad mixtures led to increased flowability and delayed hydration compared to finer ones. Steel slag powders presented the most significant plasticizer effects, but also the largest set ting de lays and segregation tendency. Quartz – rich superfines reduced the set ting de lays caused by the super plasticizers. In summary, both super plasticizers were effective in improving flow prop er ties, but the high - charge PCE was effective in pre venting segregation in pastes con training mineral ad mixtures coarser and heavier than cement.Item Obtention of eco-efficient cement-based composites using industrial waste.(2019) Carvalho, José Maria Franco de; Peixoto, Ricardo André Fiorotti; Peixoto, Ricardo André Fiorotti; Silva, Guilherme Jorge Brigolini; Schmidt, Wolfram; Damineli, Bruno Luís; Aguilar, Maria Teresa Paulino dePortland cement is the main responsible for the low environmental performance of cement-based composites since its production implies the emission of large amounts of carbon dioxide in the atmosphere. Achieving more eco-efficient concrete, therefore, means an effective contribution to mitigating human-made impacts. The search for less aggressive binders and the partial substitution of Portland cement for supplementary materials of low environmental impact are effective mitigation routes that are explored in this thesis. Concomitantly, the consumption of by-products from other productive sectors as inputs in the production of concrete, besides being an effective way of saving natural resources, provides an adequate destination to environmental liabilities. Thus, as part of the work related to this research, a low environmental impact cement produced entirely with industrial and mining wastes was successfully proposed and obtained. This material presented technological characteristics compatible with belitic cements obtained with conventional materials. In addition, supplementary fine materials socalled Engineered Recycled Mineral Admixtures were designed and produced to partially replace Portland cement and increase the packing density of the fine fraction in cementitious matrices. An extensive characterization program of these materials was conducted, as well as performance evaluation in pastes, mortars and concretes, including rheology, hydration kinetics, cementing properties and mechanical performance. Finally, these materials were used in the production of densely packed concretes, where the great potential of the proposed products in the obtention of cementbased composites with high mechanical strength and/or high eco-efficiency was observed.