Avaliação da autocicatrização de materiais cimentícios contendo diferentes concentrações de silicato de sódio incorporado em microcápsulas biopoliméricas.

Abstract

Portland cement concrete, essential in civil construction, faces significant challenges in terms of durability, strength, and repair costs. Additionally, cement production, an energy-intensive process, significantly contributes to CO2 emissions. Cracking of the cementitious matrix is one of the leading causes of deterioration, directly affecting the safety and durability of structures and increasing maintenance costs and demand for cement. Enabling the cementitious matrix to self-heal cracks can reduce these costs and greenhouse gas emissions. This study focuses on autonomous self-healing using 16% (v/v) biopolymeric microcapsules made of gelatin and gum arabic with different concentrations (0%, 10%, and 20% w/v) of sodium silicate as a healing agent (MC.A, MC.SS10, and MC.SS20). The effectiveness of these microcapsules was evaluated in a Portland cement matrix with pozzolan (CP II-Z-32), analyzing their impact on the physical and mechanical properties of the matrix in both fresh and hardened states. In addition to the microcapsule-containing pastes, a reference paste (REF) consisting only of water and cement and a paste with a 1% sodium silicate solution (SS), freely dispersed in the cementitious matrix, were tested. Optical analysis revealed that the microcapsules had a spherical morphology, validating the effectiveness of the adopted production process. Size distribution curves indicated that the MC.A sample had smaller particles, with an average diameter D[4;3] of 40.5 µm, while the MC.SS10 sample had 75.0 µm. The MC.SS20 sample had considerably larger particles, with an average diameter of 194.0 µm. SEM-EDS analysis confirmed sodium silicate's presence in the MC.SS10 and MC.SS20 microcapsules cores. The characterization of the cementitious matrix included rheology tests, isothermal calorimetry, axial compressive strength tests, water absorption determination, void index measurements, and microstructural analysis by SEM-EDS. The rheology test showed the presence of microcapsules, except in the MC.SS20 sample reduced the paste's workability, making it more dense than the REF paste. Calorimetry analysis showed that incorporating microcapsules into cement pastes reduced the maximum heat flow by 54%, 17%, and 16% for the MC.A, MC.SS10, and MC.SS20 samples, respectively, compared to the REF sample. The compressive strength test showed no significant differences in strength gain between the MC.SS10, MC.SS20 and SS samples compared to the REF. The water absorption of the SS, MC.SS10, and MC.SS20 samples increased by 6.6%, 14.0%, and 22.9%, respectively, compared to the REF sample, while the MC.A sample showed a reduction of 12.14% compared to the reference. Finally, SEM-EDS microstructural analysis revealed a heterogeneous distribution of hydration products in the pastes produced. The results reinforce the viability and effectiveness of using sodium silicate-containing microcapsules as carriers for beneficial additives to enhance cement performance, particularly regarding self-healing and early-stage compressive strength.