RESUMO Esse trabalho apresenta um estudo comparativo do comportamento mecânico de vigas pré-moldadas de concreto armado convencional (CCP), fabricadas por uma empresa local e de concretos geopolimérico de metacaulim (CCG) e geopolimérico com 20% de cinza volante e silicato de cinza de casca de arroz (CCG-20CVCCA), como matrizes substitucionais. Os resultados mostraram que os concretos geopoliméricos apresentaram comportamento similar ao do CCP, na mesma classe de resistência do concreto, taxa de armadura e disposição das armaduras no elemento estrutural estudado. O uso das cinzas promoveu aumento do módulo de rigidez à flexão e dos limites de deformação das vigas geopoliméricas, em especial para a CCG-20CV-CCA sob a maior taxa de armadura. Os padrões de fissuração e os modos de ruptura encontrados foram similares àqueles mostrados pelo CCP, com a conclusão, neste estudo de caso, de que as vigas pré-moldadas, como fabricadas pela empresa, foram superarmadas ao longo do bordo superior. Embora o dimensionamento da viga não tenha sido objeto deste estudo, foi mostrado que o concreto geopolimérico pode substituir plenamente o CCP, em concreto armado, abrindo oportunidade de uso dos mesmos códigos de dimensionamento desenvolvidos para este material tradicional.

ABSTRACT This work presents a comparative study of the mechanical behavior of precast concrete beams (CCP), manufactured by a local company and geopolymer concrete of metakaolin (CCG) and geopolymer concrete with 20% of fly ash and rice husk ash silicate (CCG-20CV-CCA), as substitutional matrices. The results showed that the geopolymer concretes presented similar behavior to the CCP, in the same class of concrete strength, reinforcement rate and arrangement in the structural element studied. The use of the ashes promoted an increase of the flexural stiffness modulus and the limits of deformation of the geopolymer beams, in particular for the CCG-20CV-CCA under the highest reinforcement rate. The cracking patterns and failure modes found were similar to those shown by CCP, with the conclusion, in this case study, that precast beams, as manufactured by the company were super-reinforced along the top of the beams. Although the dimensioning of the beam has not been the object of this study, it has been shown that the geopolymer concrete can completely replace the CCP in reinforced concrete, opening up the opportunity to use the same structural design codes developed for this traditional material.

Geopolymeric materials have some unique properties such as early-high compressive strength, durability, resistance to acids and sulfates, ability to immobilize toxic and radioactive compounds, low porosity and high temperature resistance. These materials are strategic for sustainable development and are a suitable alternative to Portland cement. The use of phyllite as a geopolymer precursor is encouraged by its abundance, low cost, and the fact that it is already applied in ceramic industries as a kaolin substitute. The objective of this paper is the physicochemical characterization of geopolymeric resin using two pulverized phyllite rocks as precursors with STEM, XRD and XRF techniques. It was found that both phyllite rocks studied have a high quartz content of approximately 50% (weight), which have a "filler" function in the microstructure of the resin helping stabilize residual tensions after curing. Kaolinite and muscovite minerals are present in up to 40% (weight) and are responsible for the high compressive strength of the geopolymer resins.

Geopolymers are exclusively mineral nature and are considered an alternative to materials based on Portland clinker, whose production accounts for about 5% of anthropogenic CO2 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.