The influence of sepiolite on the self-healing capability of concrete by means of water permeability

Abstract

This paper investigates the autogenous self-healing capability of conventional concrete (C30/37) mixtures with water encapsulated in sepiolite. Sepiolite was added in two conditions: previously saturated and dry, at a dosage of 5% by the cement weight. Sepiolite is added in substitution for the sand fraction. For these two mixes and a reference mix without sepiolite, disks of size f100x50 mm were produced and were pre-cracked at 28 days of age by splitting test until reaching residual cracks of 300±150 μm. Crack width was measured by using an optical microscope. Self-healing was promoted after pre-cracking in certain exposures: 1) continuous water immersion at 20°C for 56 days, 2) a high humidity environment at 20°C and 95% of relative humidity for 28 days and water immersion for additional 28 days, and 3) pre-saturation for one day and 55 days in a humidity chamber. Self-healing was analyzed with water permeability by comparing the results before and after the healing stage. Afterward, chlorides’ penetration through the healed cracks was evaluated to study the possible protection provided by crack healing. Uncracked specimens were also tested as a reference for chloride penetration. Mixes were characterized by measuring compression strength at 28 days, slump, air content, and fresh density. The results show that water immersion is an adequate way to improve autogenous self-healing. Sepiolite can improve the self-healing capability of concrete with only one day of pre-saturation and then healing in high humidity conditions, especially in mixes with sepiolite introduced in saturated conditions. On the contrary, sepiolite may have resulted in a higher chloride penetration compared to samples without sepiolite.