Análise da carbonatação em concretos com LC³ para diferentes classes de agressividade ambiental

Abstract

The Portland cement manufacturing process is highly polluting, with high CO2 emissions, due to the burning of fuel and the limestone decarbonation process. One of the solutions adopted to control the environmental impacts generated in the cement manufacturing process, regarding CO2 emissions, is the replacement of Portland cement with supplementary cementitious materials (SMCs). In this context, Limestone Calcined Clay Cement (LC³) emerged as a low-carbon cement in cement industries around the world, presenting itself as a cement option produced through the mixture of limestone filler, calcined clay, clinker, and gypsum in established proportions, replacing conventional Portland cement. However, in this type of cement, all calcium hydroxide (CH) is consumed during the hydration phase, which makes it more vulnerable to carbonation. Therefore, this research evaluated the durability of concrete with LC³, for different classes of environmental aggressiveness, using accelerated carbonation tests. To conduct this research, LC³ was used, replacing 50% of the CPV-ARI clinker with metakaolin, limestone filler and gypsum, and varying the water-cement factor of the mixtures, aiming to meet the environmental aggressiveness classes established in the Brazilian standard of procedures for reinforced and prestressed concrete structures. The properties of concrete were investigated in the fresh state, through consistency testing, and in the hardened state, through tests of axial compression resistance, static modulus of elasticity, tensile strength, water absorption by immersion, and resistance to concrete carbonation the accelerated carbonation method. Results demonstrated a reduction in the workability of concrete with the reduction of the water/cement factor to meet the environmental aggressiveness classes defined in the standard, demanding an increase in the amount of superplasticizing additive, and an inverse relationship between the water/cement factor and the resistance axial compression in the hardened state. The values of axial compression resistance showed a large increase after 28 days, increasing between the ages of 28 days and 90 days in environmental aggressiveness classes 1, 2, 3, and 4, by 38.46%, 31.17%, 40, 52%, and 55.20%, respectively. A similarity was observed between the results of compressive strength and tensile strength by diametral compression at 28 days of age. Regarding the resistance to carbonation of concrete, using the accelerated carbonation method, a greater depth of carbonation, at 63 days of exposure to CO2, was found in concretes in which a higher water/cement factor was used, due to the increase in concrete porosity.