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Autor(a/res): Maria Ernestina Alves Fidelis, Romildo Dias Toledo Filho, Flávio de Andrade Silva, Viktor Mechtcherine, Marko Butler, Simone Hempel
Resumo: In this work the degradation mechanisms of concrete reinforced with natural jute textile are discussed. Double-sided pullout tests were performed on specimens reinforced with polymer-coated and uncoated jute fabrics. To obtain a composite with an enhanced durability performance a matrix with partial replacement of the Portland cement by metakaolin was used. Before testing, the specimens were subjected to accelerated aging conditions. After a curing period of 28 days in water the samples were exposed to a temperature of 40 °C and a relative humidity of 99% over 28, 56, 90, 180 and 365 days. Microstructural analyses were performed to evaluate the degradation of the jute yarn and the fiber-matrix interphase using an environmental scanning electron microscope. Thermogravimetric analysis was carried out in order to evaluate the calcium hydroxide content. The pullout results showed that coated fabrics formed a stronger bond than did the uncoated. For ordinary Portland cement matrix the maximum fiber pullout force decreased up to 85% after six months of accelerated aging. In the MK matrix the degradation process was retarded substantially. Polymer coatings improved the bond between fiber and matrix and reduced fiber degradation.
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Autor(a/res): LAO Júnior; DL Araújo; RD Toledo Filho; EMR Fairbairn; MAS Andrade
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Autor(a/res): Edgar Bacarji, Romildo Dias Toledo Filho, Leonardo Mendes Naves
Resumo: The main objective of this work is to present the technical viability of Self Compacting Concretes (SCC) containing by-products from crushed coarse aggregate production. For this purpose, a vast characterization of these by-products was made; six mixtures of SCC were produced using two different aggregates: granite and mica schist. The binder/dry aggregate (b/agg) ratio by mass was 1:3. The following properties were analyzed: compressive strength, direct tensile strength, flexural tensile strength and splitting tensile strength. Granite presented the best mechanical performance. The replacement of natural sand by granite sand generated concretes with the same level of compressive strength and caused an increase in tensile strength values. The incorporation of silica fume into concrete with granite produced an increase of 17% in compressive strength. So, the use of these by-product materials can provide a technically feasible solution that is also consistent with the aims of sustainable development and preservation of the environment.
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Autor(a/res): Dimas Alan Strauss Rambo, Flávio de Andrade Silva, Romildo Dias Toledo Filho, Neven Ukrainczyk, Eddie Koenders
Resumo: The effect of elevated temperatures on basalt textile reinforced calcium aluminate cementitious composite is reported. After being exposed for 1 h at various constant temperature levels, samples were tested in hot as well as after cooling down at room temperature conditions (termed as residual tests). Targeted constant temperatures considered varied from 25 up to 400 °C, representing the range that affects the main dehydration of hydration products present in the matrix. The residual mechanical response of basalt fabric at similar temperature ranges was also measured. Thermogravimetry and X-ray diffraction analysis were used to study phase changes as a function of temperature. Scanning electron microscopy (SEM) was used to study damage processes in the fiber–matrix interfaces. Results indicate that the tensile strength of composites in residual conditions is higher than that in hot conditions. This traced back the mechanism that the fabric-coating visco-elastic/plastic interface changes with temperature, which affects the textile-cementitious adhesion properties. When the composite was tested in hot conditions, a much more aggressive loss of the load-carrying capacity was observed. With increasing temperature, the hot tests, showed a significant reduction in tensile strength, elastic modulus and strain capacity. Ultimate direct tensile strength values obtained under hot condition were, on average, 50% lower than the residual ones.
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Autor(a/res): C. M. A. Fontes, R. D. Toledo Filho, M. C. Barbosa
Resumo: Sewage sludge originated from the process of treatment of wastewater has become an environmental issue for three main reasons: contains pathogens, heavy metals and organic compounds that are harmful to the environmental and human health; high volumes are daily generated; and shortage of landfill sites for proper disposal. This research deals with the viability study of sewage sludge utilization, after calcination process, as mineral admixture in the production of concrete. High-performance concretes were produced with replacement content of 5% and 10% by weight of Portland cement with sewage sludge ash (SSA). The influence of this ash was analyzed through physical and mechanical tests. Analysis showed that the mixtures containing SSA have lower values of compressive strength than the reference. The results of absorptivity, porosity and accelerated penetration of chloride ions, presents that mixtures containing ash showed reductions compared to the reference. This indicates that SSA provided refinement of the pore structure, which was confirmed by mercury intrusion porosimetry test.
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