No abstract

Microbial-induced calcium precipitation (MICP) has shown adequate potential to act as a healing product through Calcium Carbonate (CaCO3) precipitation inside cracks. This work studies the self-healing capability of conventional concrete incorporating two dosages of Bacillus subtilis encapsulated in diatomaceous earth and a liquid solution consisting of a combination of Bacillus, denitrifying, and photosynthetic bacteria. The two bacterial agents used are commercial or industrial products from other sectors. For these mixes, disks of size ϕ100×50 mm were pre-cracked at the age of 21 days by splitting test until reaching residual cracks of 100 to 450 µm. At the age of 28 days, self-healing was promoted during 28 days in three exposures, continuous water immersion at 20°C, a high humidity environment at 20°C and 95% of relative humidity, and 7 days immersed in water at 20°C and 21 days in the high humidity environment. Self-healing was analyzed with water permeability by comparing the results before and after healing. Afterward, chlorides’ penetration was performed to study the possible healing protection on cracked disks compared to uncracked reference disks. As a result, after 7 days of immersion in water, the mixes with bacteria presented acceptable healing results. Some healed cracks could also significantly reduce the penetration of chlorides towards the interior of the concrete matrix.

Self-healing is the capability of a material to repair its damage autonomously. Ultra-High-Performance Fiber Reinforced Concrete (UHPFRC) has potentially higher self-healing properties than conventional concrete because of its lower water/binder content and controlled microcracking due to the high fiber content. This work uses a novel methodology based on the permeability to evaluate autogenous selfhealing of UHPFRC and enhanced self-healing, incorporating several additions. To this purpose, one UHPFRC was selected and modified to include alumina nanofibers in 0.25% by the cement weight, nanocellulose (nanocrystals and nanofibers), in a dosage of 0.15% by the cement weight, and 0.8-1.6% of a crystalline admixture. The results obtained show that the methodology proposed allows the evaluation of the self-healing capability of different families of concrete mixes that suffered a similar level of damage using permeability tests adapted to the specific properties of UHPFRC.

Self-healing is defined as the capacity of a material to repair internal damage without any external intervention. In the case of concrete, this process can be autogenous, which is the natural capacity of the material. Ultra-High-Performance Fibre Reinforced Concrete (UHPFRC) has a high self-healing potential due to its high binder content with a low w/b ratio and its crack pattern with multiple micro cracks. This paper describes two UHPFRC water reservoirs, which were designed to minimise the volume of concrete used. The design is made of ribbed thin walls where shrinkage cracks are likely to happen. The objective of this work is to study the autogenous healing capability of this concrete in these cracks. The two water reservoirs have internal dimensions of 1.30×0.75×0.70 m³ and with 20 mm thickness in the centre of the walls. These walls displayed cracks (w < 100 μm), which were produced just after casting. Both reservoirs were filled with water, showing apparent water leakage. The cracks were monitored for 30 days, analysing pictures taken with an optical microscope. The results show that UHPFRC is able to heal autogenously under the conditions in this work, recovering completely the water tightness required for the water reservoirs.

Self-healing is defined as the capacity of a material to repair internal damage without any external intervention. In the case of concrete, this process can be autogenous, which is the natural capacity of the material. Ultra-High-Performance Fibre Reinforced Concrete (UHPFRC) has a high self-healing potential due to its high binder content with a low w/b ratio and its crack pattern with multiple micro cracks. This paper describes two UHPFRC water reservoirs, which were designed to minimise the volume of concrete used. The design is made of ribbed thin walls where shrinkage cracks are likely to happen. The objective of this work is to study the autogenous healing capability of this concrete in these cracks. The two water reservoirs have internal dimensions of 1.30×0.75×0.70 m³ and with 20 mm thickness in the centre of the walls. These walls displayed cracks (w < 100 μm), which were produced just after casting. Both reservoirs were filled with water, showing apparent water leakage. The cracks were monitored for 30 days, analysing pictures taken with an optical microscope. The results show that UHPFRC is able to heal autogenously under the conditions in this work, recovering completely the water tightness required for the water reservoirs.