Avaliação da influência de adições minerais e agentes cristalizantes na ocorrência de cicatrização de fissuras em concretos sob cura submersa: estudo de um ano.

Abstract

In this study, two classes of concrete were examined: C30 (addition of blast furnace slag mineral) and C50 (addition of silica fume mineral), each class with three subclasses: a control mixture, one with crystallizing addition A, and another with crystallizing addition B. The objective was to evaluate the potential for healing cracks with initial openings (e0) of up to 500 µm, with and without commercial crystallizing additions, and to identify the main products formed during healing. To this end, the materials and concretes were characterized, and crack healing was evaluated by the healing index (HI) with water percolation tests before the start of the process and at 28, 56, 84, 180, and 365 days. The samples were pre-cracked, measured with an optical microscope, and kept submerged in water for healing until the date of testing. Additionally, chloride ion penetration tests, visual and microstructural analyses were performed. The results showed that the speed of healing is directly related to the e0 of the crack, the curing time, and the availability of carbon dioxide (CO₂). Analysis of the immersion water confirmed calcium carbonate as the main sealing mechanism. The composition of the mixtures influenced the HI and the depth of chloride ion penetration, showing different behaviors among the concrete classes. Cracks with e0 < 200 µm tend to heal completely within a year, while larger cracks heal only partially, with significant limitations for those above 300 µm. The reference mixtures with silica fume (C50) had the highest average HI values, while those with crystallizing additions had variable performance, with results for crystallizing addition A slightly higher than B. The chloride ion penetration test revealed that crystallizing additions can act both in filling the internal region of the matrix and in healing cracks. Microstructural analyses identified phases related to continuous hydration, the formation of calcium hydroxide, calcium carbonate, and other secondary hydration products, such as ettringite and hydrated aluminosilicates, showing that healing involves simultaneous physical and chemical mechanisms. Surface observation proved useful but limited, reinforcing that the effectiveness of the process depends both on the composition of the concrete and on the cracking and curing conditions. Keywords: crack healing; mineral additions; crystallizing addition; water permeability index; submerged curing.