The growing concern over the environmental impacts caused by construction has driven the development of new technologies and processes that can offer the most eco-efficient alternatives to the market. The alkali-activation has emerged as a promising technology for the alternative cements development. This avoids high CO 2 emissions typically associated with Portland cement manufacturing process. In order to seek alternative cements with CO 2 reductions in its production process, seeking to improve industrial waste, this work presents the possibility of using basalt as a raw material for the production of alternative cements. The basalts are found in large quantities in the earth's crust, covering most of Rio Grande do Sul state, and have chemical and mineralogical characteristics favorable to the alkali-activation process, since they have significant amounts of SiO 2 and vitreous material on his matrix. In addition, due to its extraction, they generate large amounts of waste, often in powder form, which are deposited in the yards of mining companies. From this context, the alternative cement production potential of two deposits were evaluated, one belonging to the Caxias Formation (FAB) and other from Gramado Formation (CB), by means of chemical and mineralogical analysis. Concrete Specimens were molded to compression strength analysis, with FAB sample reaching 10,18 MPa, while CB sample reached 5,24 MPa. From the results it can be concluded that the basalts belonging to formations with higher SiO 2 content and glass in its composition shows higher performance to the development of alternative cements with very low CO 2 emissions rate in the production process.

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A utilização da cinza pesada em seu estado bruto em substituição à areia natural em argamassas pode trazer benefícios ambientais e econômicos para os usuários, uma vez que não é necessário realizar processos como queima ou moagem e proporcionar uma destinação para o rejeito. Sendo assim, este artigo visa analisar as propriedades do estado fresco e endurecido de argamassas produzidas com a substituição parcial de areia natural por cinza pesada não beneficiada. A utilização da cinza pesada foi feita em substituição em massa ao agregado miúdo natural nos teores de 0, 20%, 40% e 60%, utilizando uma faixa granulométrica entre 75 µm e 600 µm. Os resultados para o estado fresco mostraram que a com o aumento da porcentagem de utilização da cinza pesada aumentou a demanda por aditivo dispersante para obtenção de argamassas de mesma consistência. No estado endurecido infere-se que a cinza pesada possa ser utilizada em substituição parcial ao agregado natural sem gerar perda no desempenho da matriz cimentícia.

The retarding effects in the hydration of Portland cement caused by organic molecules such as gluconates, sucrose and organic acids are mainly used to setting control required for the production of ready-mix-mortars. Three commercial products, indicated for the control of hydration reactions of Portland cement, were evaluated regarding to maintain the flowability over time of cement pastes containing additions of fine materials (<75μm). The cement pastes were produced with replacement of the cement up to 50% (by weight) by fine materials (d<75μm): basalt filler; fly ash; quartz filler; perlite filler (perlite was replaced by volume). The organic admixtures were used by 0.5 to 1.0% (by weight of cement). Changes in the flowability of the cement pastes over time were evaluated through mini-flow tests and rheometer measurements. The results demonstrate an important reduction in the shear stress of the cement pastes under the effect of the organic molecules, as a consequence of the homogenization of the ionic charges on the surface of the particles. In addition, all organic admixtures at a dosage of 1.0% were able to maintain the flowability for more than 400 hours, however, with gradual reductions of the mini-flow scattering throughout this period, resulting from a probable partial hydration of the cement. The cement pastes with basalt filler showed a faster reduction of flowability over time, which may indicate reactivity between the mineral particles of the filler and the organic molecules. On the other hand, quartz filler contribute to the increase in initial flow. Calorimeter measurements were used to evaluate the interactions between the fine material and the organic molecules confirming that the basalt filler actually reduces the effect of the admixtures.

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