RESUMO
This work analyzes the effect of the presence of 5 wt.% of solid sodium salts (Na2SO4, Na2CO3, and Na2SiO3) on calcium sulfoaluminate cement (CSA) hydration, addresses hydration kinetics; 2-, 28-, and 90-d mechanical strength, and reaction product microstructure (with X-ray diffraction (XRD), and Fourier transform infrared spectroscopy, (FTIR). The findings show that the anions affect primarily the reactions involved. Ettringite and AH3, are the majority hydration products, while monosulfates are absent in all of the samples. All three salts hasten CSA hydration and raise the amount of ettringite formed. Na2SO4 induces cracking in the ≥28-d pastes due to post-hardening gypsum and ettringite formation from the excess SO42- present. Anhydrite dissolves more rapidly in the presence of Na2CO3, prompting carbonation. Na2SiO3 raises compressive strength and exhibits strätlingite as one of its reaction products.
RESUMO
The addition of natural fibers used as reinforcement has great appeal in the construction materials industry since natural fibers are cheaper, biodegradable, and easily available. In this work, we analyzed the feasibility of using the fibers of piassava, tucum palm, razor grass, and jute from the Amazon rainforest as reinforcement in mortars, exploiting the mechanical properties of compressive and flexural strength of samples with 1.5%, 3.0%, and 4.5% mass addition of the composite binder (50% Portland cement + 40% metakaolin + 10% fly ash). The mortars were reinforced with untreated (natural) and treated (hot water treatment, hornification, 8% NaOH solution, and hybridization) fibers, submitted to two types of curing (submerged in water, and inflated with CO2 in a pressurized autoclave) for 28 days. Mortars without fibers were used as a reference. For the durability study, the samples were submitted to 20 drying/wetting cycles. The fibers improved the flexural strength of the mortars and prevented the abrupt rupture of the samples, in contrast to the fragile behavior of the reference samples. The autoclave cure increased the compressive strength of the piassava and tucum palm samples with 4.5% of fibers.
RESUMO
This study investigated the reactivity properties of self-leveling hybrid alkali-activated cements, such as ordinary Portland cement (OPC) and its residual precursors, coal bottom ash (BA), and rice husk ash (RHA). Due to the relatively low reactivity of BA, binary mixes were produced with OPC using contents of 2.5â»30% in the treated BA samples. Furthermore, ternary mixes were prepared in proportions of 25%, 50%, and 75% with RHA as a replacement material for the OPC (mix with 90%:10% BA:OPC). For all of the mixes the spreading behaviors were fixed to obtain a self-levelling mortar, and dimensional changes, such as curling and shrinkage, were performed. Mortars with 30% OPC reached a compressive strength of 33.5 MPa and flexural strength of 7.53 MPa. A scanning electron microscope (SEM) and X-ray powder diffraction (XRD) were used to indicate the formation of N-A-S-H and a (N,C)-A-S-H gel, similar to the gel with trace of calcium. The best performance was achieved when the binary mix produced 10% OPC. A hybrid mortar of OPS-BA presented 10 times lower susceptibility to curling than an OPC mortar. The results showed that both ashes reduced the shrinkage and curling phenomena.
RESUMO
An experimental study was conducted to investigate the potential use of phosphogypsum (PG) to produce self-leveling underlayments. The study was designed in two stages. Initially a phosphoanhydrite (PA) was produced by heating phosphogypsum at temperatures of 350 °C, 450 °C, 550 °C, and 650 °C. Two periods of heating were applied (2 and 4 h). The formation of anhydrite was determined by thermogravimetric analysis (DTA-TG) and confirmed by X-ray diffraction (XRD). The results show that anhydrite II was obtained at temperatures above 450 °C, and at higher calcination temperatures the PA solubility was lower. In the second stage of this research, the PA was used in self-leveling underlayments as the main binder in the ternary system comprised of calcium sulfate, calcium aluminate cement, and Portland cement. Self-leveling mortar screeds produced using PA (550 °C/4 h) and PA (650 °C/4 h) showed the best performance in terms of mechanical strength and no degradation was observed after immersion and immersion-drying tests. The formation of ettringite, identified by scanning electron microscopy (SEM), may have contributed to these results. Morphological changes were studied using the scanning electron microscopy (SEM) technique.
RESUMO
O grande volume de resíduos de construção e demolição (RCD) gerados no país levou o Governo Federal a desenvolver algumas ações; entre elas, pode-se citar a criação da Resolução n° 307 do CONAMA, que estabelece diretrizes, critérios e procedimentos para a gestão dos resíduos da construção civil nos municípios. Com o objetivo de auxiliar os municípios de pequeno porte no atendimento a essa legislação, desenvolveu-se um sistema de apoio ao gerenciamento desses resíduos, implementado por meio de um programa computacional (software). O sistema, composto de três estágios, com uma interface interativa e acessível, fornece primeiramente ao usuário as informações referentes aos RCDs necessárias para sua utilização. No segundo estágio, com base nessas informações, o usuário realiza a coleta de dados em campo e alimenta o sistema, que fornece um diagnóstico da situação atual dos RCD no município. No terceiro e último estágio o sistema fornece ao usuário alternativas/propostas de gestão dos RCD tais como a previsão da quantidade de pontos de entrega voluntária a ser instalado no município, possíveis destinações finais dos RCD de acordo com a classe e a quantidade gerada, caracterização do programa de informação ambiental e base, textos técnicos, entre outros. Nesse momento, o referido sistema encontra-se em processo de avaliação/atualização para implementação e disponibilidade de utilização.
The large amount of construction and demolition (C&D) waste generated in the country led the federal government to develop some actions, among them, it is possible to quote the creation of the resolution 307 of CONAMA, that establishes guidelines, criteria and procedures for the management of civil construction waste in the cities. With the goal of assisting the small cities in the attention to the legislations it has been developed a system of support to the management of the wastes implemented by means of a software. The system, composed by three stages, starting with a interactive and accessible interface, gives the user the informations about RCD needed to the utilization of it. In the second stage, with those informations, the user makes the collection of data in the field and feeds the system that gives a situation diagnosis in the RCD's of the city. In the third and last stage the system provides the user alternatives/proposals of management of the RCD's such as delivery points quantity predicition to be installed in the city, possible final destinations of the RCD'S in agreement with the class and generated quantity, characterization of the environmental information program and base, technical texts, and others. In this point, the referred system finds in process of evaluation/update for implementation and availability of utilization.
RESUMO
Este trabalho desenvolve um modelo, baseado em técnicas exploratórias de dados e de estatística multivariada, que permite identificar as variáveis mais relevantes associadas ao sucesso da implementação de programas de reciclagem de resíduos de construção e demolição (RCD) nos municípios brasileiros. Os resultados da pesquisa mostraram que existem diferenças marcantes entre as cidades que implantaram programas de reciclagem de RCD e aquelas que não implantaram. As variáveis mais significativas encontradas foram: percentual de funcionários de nível médio que trabalham na prefeitura, renda média anual do município, percentual de domicílios com água, existência de programas de coleta seletiva de lixo, programas de incentivo para geração de trabalho e renda e existência de áreas de recepção de entulhos, a maioria relacionadas à gestão municipal.
This work develops a model, based on exploratory data analysis and multivariate statistics, to identify the regional variables that most contribute to the success in the implementation of construction and demolition waste (CDW) recycling programs in Brazilian cities. The results showed noteworthy differences between cities that had implemented programs of CDW recycling and those that did not. The most significant variables were the number of mid-level education employees in the city hall, the city annual average income, the percentage of household water supply connections, the existence of programs of selective domestic waste collection, programs to stimulate work and income and areas of waste deposition. Most of the variables are related to city administration.
