Influência da carbonatação no comportamento de ligante ternário com cinza volante e MgO reativo para produção de compósito leve

Abstract

The search for reductions in CO2 emissions is a recurrent theme in the development of construction materials, given the significant contribution of the cement industry to the production of greenhouse gases. Improvements in the composition of cementing materials have been developed with the replacement of materials that are aggressive to the environment by more sustainable materials. In this context, several authors address the use of reactive magnesium oxide (MgO) as an alternative to clinker in the composition of new cements. The use of the oxide associated with carbonation curing has shown satisfactory results in terms of strength gain and durability. The present work aims to evaluate the properties of a binder with different levels of replacement of Portland cement by compositions of reactive magnesium oxide and fly ash to evaluate the viability of the material to produce lightweight composite. Initially, pastes were cured in an environment with a high concentration of CO2 and then, mechanical, physical, and mineralogical properties were evaluated. After selecting the paste with the best performance, a light composite was produced, which compressive strength was evaluated at 28 days. After carbonation of the composite, carbon sequestration was evaluated through thermal analysis. Pastes with replacement of Portland cement by reactive MgO showed superior compressive strength (up to 24%) - when associated with CO2 curing - compared to the reference mix with the same water/binder ratio. The estimated CO2 intensity (kg.m-3/MPa) of binders with 30% MgO and 30%MgO + 20%CV represented, respectively, 83% and 69% of the value of the paste without replacement. Carbonation was also shown to be an efficient process in mitigating shrinkage of pastes containing MgO. The performance of the lightweight composite did not reflect the results obtained in paste, given the accelerated formation of carbonates and the low dissolution of magnesium hydroxide, which inhibited the carbonation reaction. It is concluded that the use of MgO to replace Portland cement in binders subjected to carbonation is promising and viable from an environmental point of view. However, improvements are suggested in order to intensify the benefits of using MgO.