Flaxseed gum (FG)-based films were developed with the addition of glycerol as a plasticizer and glutaraldehyde as a crosslinking agent. HCl was added to improve crosslinking and decrease the hydrophilicity of the matrix. Different cellulose nanocrystal (CN) amounts were used as reinforcements in the optimum FG formulation. The crosslinking process at pH 3.5 led to a lower solubility of FG in water (from 100% to 53%) and an increase in thermal stability (from 160 ºC to 209 ºC). FTIR analysis confirmed a reduction in the -OH band due to crosslinking between the hydroxyl groups of FG. A diffuse diffraction pattern was observed for all FG films. The addition of 4% w/w of CN contributed to reduction of water solubility (from 53% to 20.8%) and absorption (from 21.9% to 6.8%). Finally, an improvement was observed in the tensile mechanical properties in the nanocomposites, showing satisfactory results for the proposed formulations, mainly with 8% w/w of CN added to the matrix. Overall, this study demonstrated that FG/CN nanocomposites are promising materials to be use as a sustainable biopolymer for application as bioplastics.

This work studied the properties of lightweight concretes with addition of expanded polystyrene (EPS) for structural walls applications. EPS for being a material produced on a large scale and has low density, produces a large volume of waste. These residues are not reused, especially in Brazil. Given that, in order to perform a comparison of the performance of concrete with adding of EPS in pearls and recycled, it have been manufactured five concrete types, a control without addition of EPS and four other samples with two different percentages of EPS. The mechanical (compressive strength) and physical (density, voids content, absorption by immersion and capillarity) properties were evaluated, and tests were carried out to evaluate the thermal performance of the mixtures studied. The concretes with EPS presented compressive strength less than the reference concrete, however, the absorption for capillarity and thermal properties was better in concretes with EPS. It is concluded that it is feasible to replace the EPS in pearls by recycled EPS, due to the close results found.

Vegetable fibres have been shown to be promising as reinforcement in composites because they are abundant, renewable, and low cost. However, the fibre-matrix interaction can be damaged by dimensional variation of vegetable fibres, due to moisture variations. The alkaline medium of cementitious matrix is aggressive to natural fibres, compromising their durability. The aim of this study was to modify sisal fibres (Agave sisalana) by esterification with acyl chlorides to improve their stability and compatibility with the cementitious matrix in order to optimize the performance and durability of composites. The esterified fibres were characterized by moisture absorption, tensile tests, Thermogravimetric Analysis (TGA), and Scanning Electron Microscopy (SEM) and the composites by bending tests and SEM. The results showed that esterification changed both the morphology and physical properties of sisal fibres. The composite produced using esterified fibres with octanoyl chloride maintained the properties of 28 to 90 days of age, which represented an improvement in the fibre stability compared to natural fibre composite.

RESUMO Estudou-se neste trabalho as propriedades de concretos com adição de fibras vegetais (sisal e rami) e de polipropileno para uso em paredes estruturais. Realizou-se uma comparação do desempenho do concreto com a adição de fibras vegetais e de fibra de polipropileno, a fim de se verificar a possível substituição. Foram avaliadas a retração por secagem restringida, pelo ensaio do anel, além das propriedades mecânicas (resistência à compressão, tração por compressão diametral e módulo de elasticidade) e físicas (massa específica, índice de vazios, absorção por imersão e por capilaridade). Os teores utilizados foram de 0,25 % e 0,5 % para as fibras vegetais e para a fibra de polipropileno o teor de 0,25 %. Em relação à retração restringida foi observado que a adição de 0,25 % de fibras não resultou em incremento do desempenho comparado ao concreto sem adição de fibras. Porém a adição de 0,5 % de fibras vegetais demonstrou resultados satisfatórios, sendo superiores ao concreto de referência. Foi constatado que as propriedades mecânicas dos concretos com adição de fibras, em geral inferiores ao concreto de referência, não sofreram grandes alterações, exceto para o concreto com o maior teor de rami, que não apresentou dispersão adequada das fibras. O concreto com 0,25 % de rami apresentou a maior absorção e índice de vazios, dentre todos os concretos estudados. Em relação à absorção por capilaridade, os concretos com adição das fibras vegetais demonstraram melhor desempenho, ou seja, redução da absorção por capilaridade. Concluiu-se que é plausível a substituição da fibra de polipropileno pelas fibras vegetais, principalmente de sisal.

The quartzite found in rock formations in the Southwestern Minas Gerais - Brazil has been, along the years, explored and commercialized as “coating stone”. The quantity of waste coming from the processing and exploration process, however, is superior to 90% from the extracted product in most of the mining sites, determining a serious environmental passive. This work presents results which can motivate the alternative use of the materials that are dumped on piles of waste. The research involved a petrographic analysis of quartzite occurring in the principal mines of the region; evaluation of aggregates produced in two kinds of crushers; evaluation of the physical and mechanical properties of the rock and evaluation of the physical and mechanical properties of the concrete manufactured with the quartzite aggregate. The results of the technological tests carried out on the rock material were satisfactory and meet all the specifications for the use in concrete. The samples of concrete prepared with the quartzite aggregate presented results of strength similar to the ones manufactured with the aggregate which are used commercially in the region today.

This paper presents a study of the effect of a superabsorbent polymer (SAP) for autogenous shrinkage control on the uniaxial tensile behavior of steel fiber reinforced concrete (SFRC). The use of fibers and SAP potentially increases the durability of the concrete, preventing cracking by autogenous shrinkage and enhancing post-cracking behavior. Furthermore, SAP can provide further hydration for self-healing purposes and improve the ductility of the SFRC. In order to evaluate the effect of the addition of SAP in SFRC, dog-bone SFRC specimens with different dosages of superabsorbent polymers were cast and tested under uniaxial tension. The digital image correlation (DIC) technique was used to understand the effect of SAP on the steel fibers’ crack-bridging mechanisms. Surface strains and crack openings were inferred using the DIC technique. The effect of SAP and fibers on fresh and hardened concrete was individually investigated by flow tests and compressive strength tests. Autogenous shrinkage was measured in plain concrete to investigate the minimum SAP content required to mitigate autogenous shrinkage of 0.3%. The use of 0.3% SAP was also sufficient to reach multiple cracking behavior. This content of SAP completely suppressed the autogenous shrinkage with minimal side effects on compressive strength. An analytical formulation for the tensile behavior of SFRC was developed using the variable engagement model, presenting a mean correlation of R² of 0.97 with the experimental results.