Avaliaçao de propriedades autocicatrizantes de material cimentício contendo silicato de sódio incorporado em microcápsulas biopoliméricas

Abstract

Used as a binder in coatings, structures, reinforcements and restorations, cement is the most relevant product in civil construction. The cement industry is the largest cause of GHG among industrial processes and, without a change in demand or in the production process, it will reach more than 45 bi ton. cumulative CO2 emissions in the year 2100. The durability of the cementitious material is compromised by porosity, permeability, negligible tensile and flexural strengths, and sensitivity to cracking. The permeation of aggressive agents can lead to deterioration of the cementitious material and corrosion of the inserted steel. Small fissures (up to ≈200 μm) can be healed autogenously, but larger ones only with autonomous healing. In view of this, this study evaluated the self-healing capacity of cementitious materials produced with blast furnace Portland cement (CP III), through the incorporation of sodium silicate (SS) in gum arabic/gelatin (MC) polymeric membrane microcapsules. Polynucleated microcapsules were produced, with evidence of SS incorporation in the nuclei, with approximately spherical morphology and monomodal population profile with D [4;3] of 74.9 μm and Span of 0.96. Reference pastes were tested with only water and cement (G-R), with free SS in the mixing water (G-RSS) and with MC incorporating SS (G-MCSS) or water (G-MCA). The free SS in the mixing water and the addition of MC participated as retardants, leading to inferior results in the compressive strength tests on the 3rd day of age. However, at thirty-five days of age, the presence of CMs provided greater compressive and tensile strength in flexion in cleft and cured samples, when compared to similar intact samples, and led to the surpassing of the reference samples. G-RSS always showed the worst results at more mature ages. The moduli of elasticity calculated from the propagation velocities of ultrasonic waves were also in line with the one presented by the hardness test. The presence of free SS or MCs increased the viscosity of the cementitious paste and slowed down the hydration process. During isothermal calorimetry analysis, samples containing 16% of MCSS produced a heat flux about 24% of that produced by G-R when MCSS was washed, and 10% when it was not washed. Such a decrease in heat flow foreshadows an excellent material for applications in high mass volume structures. Absorption tests demonstrated efficiency in sealing cracks in loaded samples containing microcapsules. In both the capillary absorption and open porosity absorption tests, G-RSS had the worst result and the samples containing MCSS or MCA absorbed less water than G-R or were equal to them. The set of results allowed us to conclude that the addition of 16% (v/vcement) of the MCSS additive increased the durability of the hardened paste in addition to improving the mechanical properties of the specimens after cracking.