Efeito da porosidade, da morfologia superficial e do fíler carbonático na carbonatação de compósitos cimentícios reforçados com fibra de celulose

Abstract

Since the Industrial Revolution, humanity has intensified greenhouse gas emissions primarily carbon dioxide (CO2) stemming from sources such as the burning of fossil fuels. In the construction industry, cement is the primary source of carbon emissions. During Portland cement manufacturing, specifically the clinkerization stage, a decarbonation process occurs wherein the decomposition of calcium carbonate releases carbon dioxide. Furthermore, the fossil fuels used to heat the kiln also contribute to carbon emissions. Aiming to mitigate the environmental impacts of the construction industry, carbon capture via the carbonation process in cellulose fiber-reinforced cementitious composites (fiber-cement) specifically in board form—emerges as a promising mechanism. Due to their slender profile and large surface area, these boards can serve as carbon reservoirs; additionally, there is no concern regarding steel depassivation, as these boards typically rely on natural or artificial fibers for stabilization. Thus, understanding how to maximize carbon capture in these boards can help the construction sector become more eco-efficient. The general objective of this research is to analyze the kinetics of CO2 uptake in cellulose fiber-reinforced cementitious composites by varying their morphological characteristics and incorporating a carbonate filler (acting as a nucleating agent), while observing the resulting impacts on the composite’s properties and eco-efficiency. To achieve this, cellulose fiber-reinforced cementitious boards were produced and cut into prismatic specimens (16 x 4 x 1.5 cm) representing the following variations: a reference specimen (fiber-free); a porous specimen (fiber-cement with a porous flat surface); a rough specimen (surface with modified geometry); and a specimen incorporating a carbonate filler (with the addition of carbonate filler as a mineral admixture). To evaluate the effects of varying surface morphology and adding carbonate filler, the compositions were subjected to a carbonation process. The specimens were kept at a temperature of approximately 25 °C, 70 % humidity, and a 5 % CO2 concentration; samples were subsequently collected after 0, 1, 3, 7, and 14 days of carbonation. Natural carbonation was also carried out over the same periods to compare the two methods (natural vs. chamber carbonation). Following carbonation, the specimens underwent physical-mechanical testing, as well as assessments of carbonation indicators, eco-efficiency, and carbonation shrinkage. The study concluded that incorporating 6 % cellulose improved carbon capture, a result linked to increased porosity. For samples with modified surface areas, carbon capture results were like those of smooth-surfaced samples; this was attributed to the roughness formation process, which reduced porosity and consequently lowered CO2 absorption, though these samples achieved good eco-efficiency indicators and generally performed better than other samples. Samples with added carbonate filler also demonstrated good carbon capture performance, comparable to that seen with increased porosity. Regarding mechanical properties, adding 6 % cellulose reduced flexural strength by 46.64 % an expected outcome given the higher porosity whereas formulations incorporating carbonate filler or featuring a rough surface yielded values like those of samples with 3 % cellulose.