Avaliação de parâmetros físico-químicos na produção de geopolímeros constituídos por vidro vulcânico e silicato de sódio alternativo

Abstract

The Portland cement industry is responsible for generating about 7% of global CO2 emissions. Several studies have sought the development of alternative binders with performance comparable to Portland cement, with a production less aggressive to the environment and that can meet the demands of consumption. Geopolymer cements have shown potential to meet these requirements, being composed of two main elements: the precursor material and the alkaline activator, which, when homogenized, initiate the process of dissolution and rearrangement of SiO2 and Al2O3. The precursor material may originate from industrial waste or natural pozzolans, which have a majority composition in Al and Si in an amorphous state; however, the use of commercial sodium silicate to produce the alkaline activator greatly increases the CO2 emissions and the incorporated energy of the material. Geopolymer materials exhibit satisfactory mechanical properties and durability, but certain associations of constituent factors may cause instability in terms of resistance over time or make the material susceptible to efflorescence upon contact with water. Thus, the main objective of this work is to evaluate the influence of physical and chemical parameters on the mechanical and durability behavior of the geopolymers constituted by volcanic glass and residual sodium silicate produced from rice hull ash. Mechanical tests were performed and, based on the results, a mathematical model was developed to describe the mechanical behavior of the cement paste by varying the combination of four factors (silica modulus, molarity, solution/binder ratio and curing temperature), development of resistance over time at the ages of 1, 7, 28, 63 and 91 days. It was also verified high expansibility of the material when in contact with water and complementary tests were carried out to determine the origin of the deterioration of the samples: X-ray diffraction, X-ray fluorescence, petrographic and thermogravimetric analysis. The cement pastes presented mechanical behavior compatible with the wide variety of functions attributed to Portland cement in civil construction, with a maximum resistance of 181,8 MPa. Based on the statistical analysis, the combination with Ms = 2, Mol = 12 mol, SAgl = 0,45 and Temp = 20ºC presented the best mechanical performance considering initial and final strength development, with continuous resistance gain over the period analyzed. There is evidence that the origin of the water-limiting durability is related to the insufficiency of reactive alumina in the precursor material (volcanic glass) that may result in the formation of unstable gels. In general, the material presents mechanical potential for use in civil construction, however its complete degradation in the presence of moisture generates the need to perform tests to verify its durability, in addition to deepening the knowledge regarding the origin of the expansion mechanism.