Geopolymers are exclusively mineral nature and are considered an alternative to materials based on Portland clinker, whose production accounts for about 5% of anthropogenic CO 2 emissions in the world. The geopolymer cement concrete (GCC) may be prepared from natural oxide-aluminosilicates such as metakaolin (MK), or synthetic, such as fly ash (FA) together with active silica contained in the rice husk ash (RHA). The fracture properties of the Portland cement concrete (PCC) with 25 MPa and 50 MPa, and of three different geopolymeric concretes with the same strength Classes were determined for comparative analysis. The aim of this study is to provide support to begin the use of geopolymers in the reinforced concrete precasting Industry. Three-point bending tests of notched beams with a/d (notch depth/beam depth) of 0.5 from RILEM TC80-FMT Recommendations were used to determine the critical values of K, G, R and J-integral for crack propagation under mode I. The results showed that the geopolymeric concretes exhibit similar mechanical behavior and fracture properties higher that those determined in PCC for the same strength class.

The addition of certain pozzolanic materials to Portland cement significantly changes the properties of the hardened matrix. If it has too high content of blast furnace slag, as the case of blast furnace Portland cements (BFPC), the early and late compressive strengths can be severely delayed or reduced. The objective this work was to investigate the potential of alkali-activation of BFPC and metakaolin (MK) blends by different types and contents of alkali-activators. The results clearly showed the influence of the MK pozzolanic activity and the type and content of activator used, in the development of compressive strengths of BFPC-MK blends. Microstructural analysis by SEM/EDS, DSC and XRD shown that the consumption of portlandite and the extra formation of C-S-(A)-H phases are the main positive effects registered. However, MK also promotes the formation of ettringite and unstable hydrated calcium aluminate phases, which, with the course of hydration, undergo a change in structure and volume loss, contributing to the reduction of final strengths. Content of 25% MK and 7.5% Na2SiO3 provided the best mechanical strength. The microstructures formed showed greater formation of ettringite, however there was also a reduction in portlandite and massive formation of C-S-H and C-S-(A)-H products.

The addition of certain pozzolanic materials to Portland cement significantly changes the properties of the hardened matrix. If it has too high content of blast furnace slag, as the case of blast furnace Portland cements (BFPC), the early and late compressive strengths can be severely delayed or reduced. The objective this work was to investigate the potential of alkali-activation of BFPC and metakaolin (MK) blends by different types and contents of alkali-activators. The results clearly showed the influence of the MK pozzolanic activity and the type and content of activator used, in the development of compressive strengths of BFPC-MK blends. Microstructural analysis by SEM/EDS, DSC and XRD shown that the consumption of portlandite and the extra formation of C-S-(A)-H phases are the main positive effects registered. However, MK also promotes the formation of ettringite and unstable hydrated calcium aluminate phases, which, with the course of hydration, undergo a change in structure and volume loss, contributing to the reduction of final strengths. Content of 25% MK and 7.5% Na2SiO3 provided the best mechanical strength. The microstructures formed showed greater formation of ettringite, however there was also a reduction in portlandite and massive formation of C-S-H and C-S-(A)-H products.

O presente trabalho é um estudo preliminar das potencialidades de emprego de metacaulins obtidos a partir da calcinação controlada de rejeitos de beneficiamento de caulins comerciais, na produção de geopolímeros para aplicações estruturais. Os resultados de caracterização mostraram composições químicas similares, mas diferenças significativas de granulometria entre os seis tipos de rejeito estudados. Análises por microscopia eletrônica de varredura (MEV) e difração de raios X (DRX) foram realizadas para investigar a morfologia das partículas, confirmar as composições química e mineralógica e verificar se a calcinação foi capaz de amorfizar a estrutura da caulinita. As amostras calcinadas foram comparadas entre si e com uma amostra de referência e usadas como precursor aluminossilicato em uma formulação padrão, tendo sua consistência em estado fresco e a resistência à compressão no estado endurecido determinadas. Os resultados destacaram apenas duas amostras calcinadas consideradas em conformidade com o padrão, embora se considere que o beneficiamento por moagem e a calcinação por tempo mais longo conduza à resultados mais promissores.

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