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RESUMO: O objetivo deste é determinar o percentual de substituição de cimento por resíduos de mármores/granitos (RMG) das marmorarias na fabricação de concreto autoadensável (CAA). A metodologia adotada foi a realização de vários ensaios laboratoriais: de caracterização; das propriedades reológicas, mecânicas, físicas e químicas do CAA. Foram aplicados dois superplastificantes, sulfonado e polimérico. Os agregados foram caracterizados por ensaios de granulometria, massa específica; massa unitária em estado solto; e massa unitária em estado compactado. Os RMG foram submetidos a ensaio de massa específica e análise de Fluorescência de Raios X. Como ensaios reológicos foram realizados: Espalhamento, T500, Funil V e Caixa L; e Ensaios de Resistência à Compressão e à Flexão, Absorção, Índice de Vazios, Massa Específica e análise de Reação Álcali Agregado (RAA), no estado endurecido. Os resultados mostraram-se eficazes com até 30% de substituição do cimento por RMG. No estado fresco esse CAA atendeu aos requisitos da NBR 15823 (ABNT, 2010), se comportando como concreto adequado para utilização nas aplicações correntes. No estado endurecido apresentou resistência à compressão de 35 MPa e resistência à flexão de 7,0 MPa, satisfazendo a NBR 15805 (ABNT, 2010), podendo também ser utilizado na produção de pavimentos de concreto e assim contribuindo para a redução de resíduos espalhados nas empresas, diminuição de danos ao meio ambiente e trazendo economia para a obtenção de CAA.

The present research aimed to study the replacement of ordinary Portland cement (OPC) by metakaolin (MKL) and silica extracted from rice husk ashes (SRHA) in binary mixtures. To investigate the pozzolanic reactivity, thermal and microstructural analyses were performed in binary mixtures. To understand the physical effect of these blends, the packaging density was calculated according to the model of compressible packaging (MCP) and the compatibility/saturation levels of superplasticizers was studied with cementitious materials. Considering the substitution levels adopted, the results indicated that the paste with 40% of MKL provided a total consumption of calcium hydroxide to 28 days; however, the packaging density of the particles was reduced, while the compressive strength was maintained. The addition of 16% of SRHA in binary mixtures showed partial consumption of calcium hydroxide; nevertheless, this effect, together with the physical effect, led to an increase in the compressive strength for the same age.

In Brazil, the sludge generated in water treatment plants (WTPs) has no economic value and since it is composed of silicon and aluminum oxides, it can be used in the production of geopolymers - alternative binders . Sisal fibers are renewable natural resources and relatively inexpensive. With such materials, a geopolymeric composite was produced, and was evaluated for its durability, flexural strength and microstructure. Durability was assessed through accelerated aging (10 wetting and drying cycles). While the reference composite (0 cycles) reached strength values of about 15 MPa in the flexural test, the aged composite reached the strength of 11 MPa, which indicated good durability to wetting and drying cycles. Samples that were naturally aged for 3 years were evaluated using stereomicroscopy. Considering that there was little degradation in the fibers of the composite, it follows that this material could be used in the manufacture of durable roofing sheets.

Water treatment plants (WTP) in the City of Manaus, Brazil, generate tons of sludge daily, which are then disposed of in landfills and main watercourses, particularly two important Amazonian Rivers: the blackwater Negro River and the pale sandy-colored water Solimoes River. Because WTP-based sludges are rich in silicon and aluminum, they have been employed in the synthesis of geopolymers - alkaline activated inorganic polymers consisting of silicate and aluminosilicate chains. This paper reports the results of a geopolymeric synthesis process in which calcined sludge was explored as a source of silica and alumina. In this research, a laboratory testing program was developed to characterize the waste material generated from a water treatment plant in Manaus, whose intake water is influenced by the above referred rivers. Sample preparation involved kiln drying at 110 °C for 8 h, grinding in ball mill for 2 h, and calcination at 750 °C for 6 h. The calcined sludge was used as precursor, and potassium hydroxide added as activating alkali. Two geopolymers, one from each sludge source, were prepared following identical procedures. The chemical, compositional, morphological, thermal and mechanical properties of the fresh and hardened geopolymers were characterized. The geopolymers reached uniaxial compressive strengths of over 50 MPa at 28 days. Calcination conveyed more refined properties to the sludge-based geopolymers, akin to metakaolin-based geopolymers. The results presented herein support the technical feasibility of geopolymer synthesis in the lab scale.

Este trabalho teve como objetivo caracterizar um subproduto do processo de tratamento de agua, visando inseri-lo na cadeia produtiva da construcao civil. Tal subproduto foi gerado em uma estacao de tratamento de agua (ETA), que realiza a captacao de agua bruta do Rio Negro e, eventualmente, do Rio Solimoes. Para adequar a agua desses mananciais aos padroes de potabilidade brasileiros, executa-se na ETA uma serie de processos fisico-quimicos, os quais acarretam a geracao do residuo designado lodo de ETA. Visando identificar possiveis aplicacoes tecnologicas para o referido residuo, fez-se uma pesquisa bibliografica pertinente. Desse modo, constatou-se que esse tipo de subproduto necessita de beneficiamento previo a utilizacao. Sendo assim, para tornar o lodo de ETA estudado uma materia-prima apropriada, submeteu-se o mesmo a procedimentos de secagem, moagem e calcinacao. Antes e apos tais procedimentos, suas caracteristicas foram determinadas por meio de Fluorescencia de Raios X (FRX), Difracao de Raios X (DRX), Termogravimetria (TG), dentre outras tecnicas. Os resultados das caracterizacoes evidenciaram que mais de 80% da composicao do lodo de ETA calcinado corresponde a oxidos de silicio e aluminio. Acreditase que, apos o beneficiamento, o lodo tornou-se uma materia-prima economica e ambientalmente sustentavel, podendo ser utilizado como substituto parcial de argilas, na producao de materiais cerâmicos; substituto parcial de cimento Portland, em pastas, argamassas e concretos; aditivo mineral ou pozolana artificial; precursor ou agregado geopolimerico. Palavras-chave: lodo de ETA, residuo, construcao civil, Rio Negro, Rio Solimoes.

Composites of high mechanical performance reinforced by fibers need a well set arrangement of them in the matrix so that under reinforcement which they can be submitted, a desirable performance can be shown. Thus, the cement composite studied has a cement matrix which received a reinforcement made by arumã fibers, shaped in bidirectional frames distributed in three layers. Arumã is a typical plant from the Amazon, species from the genus Ischnosiphon polyphyllus, part of the family Marantaceae. This study had the purpose of assessing the cement composites mechanical behaviour from the bending tests in four points and puncture tests in sheets which were supported by the four edges. Having presented mechanical results, a numerical simulation was made through the SAP2000 NonLinear® software, with the aim to obtain a numerical computational model able to represent the composites behaviour up to the point where the loading reaches the greatest amount. The numerical results present a good correlation with those obtained in the experimental tests.

The kinetics of vegetable (sisal) fiber degradation and the mechanisms responsible for deterioration of continuous sisal fiber cement composites are presented in this paper. Two matrices were used: one with 50% partial cement replacement by metakaolin (PC–MK) and a reference matrix having as binder only Portland cement (PC). The durability performance of the composite systems is examined and the mechanisms for the significant delay in the fiber degradation when the total amount of calcium hydroxide is reduced from the matrix discussed. The composites were subjected to 5, 10, 15, 20 and 25 cycles of wetting and drying and then tested under a four point bending load configuration in order to determine the flexural behavior and cracking mechanisms with progressive aging. Furthermore, composites stored under controlled lab conditions were tested under bending load at ages ranging from 28 days to 5 years. Fibers extracted from the aged composites were subjected to thermal analysis, Fourier transform infrared spectroscopy and microscopical observations in order to evaluate the changes in chemical composition and microstructure. Two fiber degradation mechanisms were observed in the PC composites: fiber mineralization due to the precipitation of calcium hydroxide in the fiber cell and surface and degradation of cellulose, hemicellulose and lignin due to the adsorption of calcium and hydroxyl ions. The degradation process occurs rapidly and after 10 cycles of wetting/drying a quite expressive modification in the flexural behavior is observed. The residual mechanical parameters after 25 cycles were the same as those observed in the unreinforced matrix. For the PC–MK composite fiber mineralization was not observed due to the low content of CH in the matrix.

Lignocellulosic fibers present several advantages over synthetic fibers, such as low cost and biodegradability. In this work the tensile mechanical behavior of as-received and surface treated curaua fibers was analyzed. Mercerization and three different enzyme surface treatments were used. The tensile stress data were analyzed using the Weibull statistical distribution, and SEM was used to characterize the surface modifications caused by the treatments. The results show that mercerization causes an increase of the deformation capacity of the fibers. This result was attributed to the removal of hemicellulose, and to an increase of mobility of the internal fibrils. The increase of NaOH concentration at the alkali solution affects both the surface characteristics and the tensile properties. Solutions with more than 5%wt NaOH degraded the fibers. The enzyme treatments increase the tensile mechanical properties, but also increase their brittleness.

Sisal fiber–cement composites reinforced with long unidirectional aligned fibers were developed and their physical–mechanical behavior was characterized in the present study. Flat and corrugated sheets were cast by a manual lay-out of the fibers in a self-compacted cement matrix and compressed with a pressure of 3 MPa. Direct tensile and bending tests were performed to determine the first crack, post-peak strength and toughness of the composites. Drying shrinkage, capillary water absorption and water tightness tests were performed to characterize the physical properties of the composites. To ensure the composite durability, the ordinary Portland cement matrix was modified by adding metakaolin and calcined waste crushed clay brick to consume the calcium hydroxide generated during Portland cement hydration. The durability of the newly developed composite was determined through accelerated aging conditions using the hot-water immersion test. The developed material presented a multiple cracking behavior under bending, even when subjected to 6 months of hot-water immersion under 60 °C. Scanning Electron Microscopy was used to investigate the micro-structure of the composites before and after aging.

This paper presents an experimental research on the durability performance of compression molded sisal fiber–cement mortar laminates (SFRML). To obtain a material with enhanced performance, the used methodology was to replace the Portland cement (PC) by calcined clay (metakaolin and calcined waste crushed clay brick) in order to produce a matrix totally free of calcium hydroxide (CH). The content of calcium hydroxide in the matrix was determined by thermal analysis. SFRML were then produced using both a PC and a CH-free PC-calcined clay matrix and the composites were submitted to accelerated aging through cycles of wetting and drying. The durability of the SFRML was investigated by determining the effects of accelerated aging on the microstructures and flexural behavior of the composites. The results indicate that the newly developed CH-free matrix avoided the fiber embrittlement process keeping the toughness in time even after 100 cycles of wetting and drying.

To design building elements using sisal fibre reinforced mortar composites, the stress-strain curves of the composites both under tensile and compression load is needed. In this study short sisal fibre-cement based composites were developed and their stress-strain behaviour under compression characterized experimentally. The composites consisted of two mortar matrices, one self-compacting and one of normal consistency, reinforced with randomly distributed short sisal fibre (25 and 50 mm long) in volume fractions ranging from 2% to 6%. Based on the experimental results a compressive constitutive law for the composites was proposed based on the damage theory developed by Mazars (1986). This theory was used to model the ascending branch of the stress-strain curve and a damage parameter associated to the fibre-reinforcing index is proposed to allow the modelling of the post-peak behaviour of the composites. The modified model was then validated using results available in the literature. The experimental results obtained in the study indicated that the addition of short sisal fibres to cement matrices tends to reduce its elastic modulus, peak stress and strain and to increase its toughness. However, the use of a self-compacting matrix allowed better sisal fiber dispersion and composites with superior performance were obtained. The modified analytical model was able to predict with good accuracy the ascending and descending branch of the stress-strain curves of the sisal fiber-mortar composites and allowed evaluating the effect of fibre reinforcing index on material damage. In the ascending branch, an increase in the damage from 40% to 70% is recorded for fiber volume ranging from 2 to 6%. In the descending branch, on the other hand, the variation of fiber volume allowed a reduction of the damage from 65% to 60%.