Soluble Silicates as Additives for Self-Sealing and Self-Healing Concrete
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Soluble Silicates as Additives for Self-Sealing and Self-Healing Concrete L. E. Rendon Diaz Miron1 , M. E. Lara Magaña2 1 Mexican Institute of Water Technology, Jiutepec, Morelos, Mexico 2 marudecori consultants, Cuernavaca, Morelos Mexico ABSTRACT Tensile strength of concrete is limited and therefore is sensitive to crack formation. Steel reinforcement is added to bear the tensile forces; nonetheless, this does not completely omit crack formation. Repair of cracks in concrete is time-consuming and expensive. Self-sealing and self-healing of cracks upon appearance would therefore be a convenient property. We propose a mechanism to obtain self-repair of the concrete by adding soluble silicates (ASS) which will induce a self-sealing and self-healing process catalyzed by natural periods of wet and dry states of the concrete. Self-sealing approaches prevent the ingress of harsh chemical substances which may deteriorate the concrete matrix. This can be achieved by self-healing of concrete cracks (e.g. further cement hydration, calcium carbonate precipitation) and autonomous healing (e.g. further hydration of partially soluble silicates added as healing agents). The autogenous healing efficiency depends on the amount of deposited reaction products (ASS), its solubility (ratio of calcium to sodium silicate), the availability of water, and the crack width (restricted by adding microfibers). The self-sealing efficiency is generally evaluated by measuring the decrease in water permeability and air flow through the crack. The healing efficiency is usually evaluated by testing concrete´s regain in mechanical properties after crack formation; by reloading the cracked and autonomously healed specimen and comparing the obtained mechanical properties with the original ones. Self-sealing and self-healing of concrete gives a broad perspective and new possibilities to make future concrete structures more durable.
INTRODUCTION Actually, concrete already has some self-healing properties; when cracks appear, water enters and reacts with anhydrate cement grains which results in crack healing. However, only small cracks can be healed in this way. Therefore, it is desirable to improve the self-healing efficiency by adapting the concrete matrix [1]. One way would be introducing high amounts of fibers, and then several small cracks appear instead of one large crack. Also concrete combined with superabsorbent polymers, provides immediate crack sealing. Another methodology is to embed encapsulated polymeric agents in the matrix. When cracks appear, the capsules break and the agent are released. Upon contact of both components, they react and the crack is healed. This technique is sometimes combined with CaCO3 precipitation by bacteria. In that case, not only polymers but also bacteria and nutrients are encapsulated and released upon cracking. First the polymer reacts; later the bacteria start to convert the nutrients into CaCO3 crystals which make the polymer structure denser thus sealing the cracks completely. Crack healing by means of bacter
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