Abstract A great variety of silica and alumina-rich materials have been investigated in the production of alkaline activated binders (or geopolymers) with low environment impact, e.g. low CO2 emissions. Geopolymer mortars and concretes may be more environmentally friendly if not only Portland cement but also natural aggregates (sand, gravel) are replaced with waste materials. This article presents results of geopolymers made with tailings from the iron mining industry. The geopolymer matrices are composed of metakaolin (MK) activated with a sodium silicate + sodium hydroxide solution. Two different iron ore tailings replaced a natural quartz aggregate in the geopolymers’ formulation. The hardened properties assessed were compressive strength, water absorption, apparent density and porosity. Scanning electron microscopy (SEM) and x-ray micro computed tomography (µ-CT) were used to assess the changes in the microstructure when the tailings were incorporated into the geopolymers. Results show that the employment of iron ore tailings is not detrimental to the mechanical strength of geopolymers; however, geopolymers containing those alternative aggregates may present higher water absorption and porosity, and durability studies are required.

Geopolymers may be described as solid and stable synthesized aluminosilicate materials, whose properties are generally believed to provide a superior durability behavior. The work in hand presents the results of an experimental investigation on the thermomechanical behavior of geopolymer matrices composed by metakaolin (MK), silica fume (SF) and blast furnace slag (BFS). The alkaline activator solution consisted of sodium silicate and sodium hydroxide. The use of different aggregates was also investigated, by replacing natural sand with chamotte. Samples were submitted to different temperatures at predetermined intervals to a maximum of 1000ºC. Compression tests were performed, before and after the exposure to elevated temperatures. X-ray diffraction, thermal analysis (TGA and DTA) and scanning electron microscopy (SEM) were used to investigate the microstructural characteristics of the studied materials. The results showed that the presence of BFS in the geopolymer mixture significantly increases its mechanical response. However, the incorporation of SF presents inferior behavior in regular conditions and when exposed to elevated temperatures. The replacement of sand with chamotte results in higher compatibility above 500ºC, when a better tolerance to extreme environmental temperature conditions was observed.

A Análise de Ciclo de Vida (ACV) é um método que inclui a compilação e avaliação das entradas, saídas e dos impactos de um produto ao longo do seu ciclo de vida. Os resultados desta análise são utilizados para escolher alternativas favoráveis para uma aplicação específica. Este artigo utilizou as ferramentas de ACV, apoiada pelo software Umberto, para comparar o processo de obtenção de concretos de cimento Portland com o de concretos geopoliméricos, obtidos da ativação alcalina de aluminossilicatos. O impacto ambiental foi avaliado considerando 1 m³ de cada concreto, sendo (i) as emissões de CO2 (kg CO2/ m³) e (ii) a demanda energética (MJ/m³) as variáveis para determinar o potencial sustentável de ambos materiais. O objetivo principal foi avaliar se os concretos geopoliméricos são mais sustentáveis do que os concretos tradicionais. Os resultados obtidos mostraram que o consumo energético é reduzido em 45,8% na produção do concreto geopolimérico, quando comparado à produção do concreto de cimento Portland de desempenho mecânico equivalente. Com relação às emissões de CO2, o concreto geopolimérico reduz as emissões em 72,4%, em comparação ao concreto tradicional de cimento Portland CPII. Assim, o primeiro se mostra uma alternativa a ser considerada, na produção de materiais de construção de menor impacto ambiental.

The Life Cycle Assessment (LCA) method comprises the compilation and evaluation of inputs, outputs and environmental impacts of a product during its life cycle. The results of this analysis are used to select alternative products or processes for a particular application. This paper compared the process of making Portland cement concrete and Geopolymer concrete, the latter obtained from the alkaline activation of aluminosilicates. The CO2 emissions (kg CO2 / m³) and energy demand (MJ / m³) for the production of 1 m³ of both concretes were used to determine the sustainable potential of these materials. The main objective was to assess whether geopolymer concrete is more sustainable than traditional Portland cement concrete. The results showed that geopolymer concrete reduces energy consumption by 45.8%, compared with Portland cement-based concrete, and has a similar mechanical performance. In addition, the use of geopolymer concrete reduces CO2 emissions by 72.4%, when compared with traditional CP-II Portland cement concrete. Hence, Geopolymer is an alternative material with lower environmental impact that should be considered in the production of sustainable building materials.

The work described in this paper is related to the effect of adding carbon nanotubes (CNT) on the mechanical properties of polymer-cement composites. A full factorial design has been performed on 160 samples to identify the contribution provided by the following factors: polymeric phase addition, CNT weight addition and water/cement ratio. The response parameters of the full factorial design were the bulk density, apparent porosity, compressive strength and elastic modulus of the polymer-cement-based nanocomposites. All the factors considered in this analysis affected significantly the bulk density and apparent porosity of the composites. The compressive strength and elastic modulus were affected primarily by the cross-interactions between polymeric phase and CNT additions, and the water/cement ratio with polymeric phase factors.

Steatite is a mineral which has been employed in the carving of elements in facades of Brazilian historical buildings and churches since the 17th century. Over the years, many of those historical buildings suffered the consequences of weathering with a current need for restoration. Recently a special cement-based mortar containing additions of fine powder waste from mineral extraction of steatite has been developed in Brazil, as a composite material for restoration of steatite elements. However, the incorporation of steatite waste reduces the flexural strength of the mortar and compromises the restoration of elements where gravity imposes tensile stresses. The addition of carbon fibres may overcome this issue and increase the flexural strength of the cement-steatite composite mortar. This work investigates the effect of carbon fibre addition on the bulk density and flexural strength of compacted precast cement-steatite composites. The results show that the addition of carbon fibres (i) effectively increases the mechanical strength, allowing for a higher amount of steatite powder waste in the mixes; (ii) reduces the weight of the structural elements. This new composite material would help to develop restoration techniques of historical buildings and serve as a disposal route of steatite powder waste in Brazil.