Healing Mechanism Investigation of Self-Healing Concrete by Microencapsulated Calcium Nitrate

Durability of reinforced concrete structures depends highly on the integrity of the concrete which protects the structure from the environment. However, concrete is a brittle material and as such it is prone to cracking which allows for detrimental agents to penetrate the structure and produce early deterioration. Embedding microcapsules with chemical healing agents in concrete materials for self-healing applications as well as implementing SMAs as reinforcement of concrete structures for self-closing of cracks are both state-of-the-art techniques with enormous potential for enhancement of concrete infrastructure durability. In this work, both techniques are combined as an alternative for superior self-healing of cracks in concrete materials to prevent early deterioration of structures. The objective of this study was to evaluate the mechanism and effectiveness of microcapsules with encapsulated calcium nitrate on self-healing of unreinforced and reinforced (Steel and SMA) cement mortar. To fulfill this objective, short term healing efficiency (up to 28 days) of unreinforced and reinforced (Steel and SMA) mortar beam specimens with calcium nitrate containing microcapsules were evaluated under different environmental conditions (dry, water submerged, and wet and dry cycles) at different microcapsule dosages. Specimens were cracked by three-point bending test and evaluated during the healing period by light microscopy and Ultrasonic Pulse Velocity (UPV) test. Cracks analyzed ranged from 13 to 387 μm. Water submerged healing conditions yielded the best self-healing results followed by wet and dry cycles. Dry healing conditions did not enable appreciable healing, thereby suggesting the need of external moisture conditions for proper functioning of the self-healing mechanism proposed. Moreover, SMA reinforced specimens (with and without microcapsules) presented an enhanced healing performance at early stages of the healing process likely due to the self-closing effect. Furthermore, the general tendency of healing results suggested that the combination of microcapsules and SMA favored self-healing. Lastly, the healing products generated in cracks were investigated under ESEM-EDS to assess their chemical nature. The overwhelming majority of healing products were identified as likely calcium carbonate in the form of calcite crystals, and a limited quantity of gel-like healing products of possibly CSH chemical nature were also identified

Evaluation of the Performance and Cost-Effectiveness of Engineered Cementitious Composites (ECC) Produced from Region 6 Local Materials

The project objective is to develop cost-effective Engineered Cementitious Composites (ECC) with locally available ingredients in Region 6 to address the deficiencies observed in ordinary concrete materials. The study explored the utilization of two types of river sands (coarse and fine), two types of PVA fibers (long and short), four levels of cement replacement with Class F fly ash, and the implementation of recycled crumb rubber in the performance of ECC materials. A total of 24 mix designs were prepared and evaluated in compression, tension, and bending to assess its mechanical properties. Furthermore, the cracking characteristics of the materials produced were evaluated to assess the durability potential of these composites. Lastly, the cost of each mix design and the feasibility of ECC implementation in transportation infrastructure were assessed. The experimental results showed that implementing crumb rubber and/or increasing contents of fly ash in the mixtures produced a positive impact in the ductility of the materials. However, a tradeoff between ductility and strength was observed. Furthermore, the utilization of the different types of sand evaluated in this study produced minor effects in the mechanical properties of ECCs evaluated. The properties of the materials developed in this study were exceedingly superior than that of regular concrete. It was concluded that ECC materials are promising for the future of transportation infrastructure

Determination of the Optimal Parameters for Self-Healing Efficiency of Encapsulated bacteria in Concrete Simulated Subtropical Climate

Concrete is a remarkable construction material. However, its low tensile strength makes it prone to cracking, which negatively affects its durability. To address this issue, bacterial concrete has been implemented as a self-healing alternative due to its capability to seal microcracks through microbial-induced calcium carbonate precipitation (MICCP). In this study, a bacterial strain (i.e, Bacillus Pseudiformus) was encapsulated through three different methods: encapsulation through hydrogel beads, vacuum impregnation on lightweight aggregates, and attachment to cellulose nanocrystals. Furthermore, three precursor types were used, magnesium acetate, calcium lactate, and sodium lactate were implemented. Compressive strength tests and flexural strength tests were performed on mortar specimens to characterize their mechanical properties. Once the crack was induced, samples were subjected to 28 days of wet/dry cycles in which the corresponding crack width was monitored. At the end of this period, the beams were retested to determine the strength recovery of the specimens. The results showed that the specimen groups in which calcium lactate was added to the cementitious matrix displayed the highest values in compressive strength. In terms of flexural strength, no major difference was found among the specimens. Moreover, the flexural strength recovery of the specimens did not show any significant difference as well. In terms of the healing efficiency, the sample that displayed the best results was the one containing calcium lactate as a precursor along with bacteria and yeast extract encapsulated in hydrogel beads. In addition, scanning electron microscopy (SEM) along with x-ray energy dispersive spectroscopy (EDS) was performed on the cracked specimens to characterize the healing products. Furthermore, a scale study was performed on concrete samples to determine the long-term implications of adding encapsulated bacteria along with calcium lactate and yeast extract in concrete

Determination of the Optimal Parameters for Self-Healing Efficiency of Encapsulated bacteria in Concrete Simulated Subtropical Climate

Concrete is a remarkable construction material. However, its low tensile strength makes it prone to cracking, which negatively affects its durability. To address this issue, bacterial concrete has been implemented as a self-healing alternative due to its capability to seal microcracks through microbial-induced calcium carbonate precipitation (MICCP). In this study, a bacterial strain (i.e, Bacillus Pseudiformus) was encapsulated through three different methods: encapsulation through hydrogel beads, vacuum impregnation on lightweight aggregates, and attachment to cellulose nanocrystals. Furthermore, three precursor types were used, magnesium acetate, calcium lactate, and sodium lactate were implemented. Compressive strength tests and flexural strength tests were performed on mortar specimens to characterize their mechanical properties. Once the crack was induced, samples were subjected to 28 days of wet/dry cycles in which the corresponding crack width was monitored. At the end of this period, the beams were retested to determine the strength recovery of the specimens. The results showed that the specimen groups in which calcium lactate was added to the cementitious matrix displayed the highest values in compressive strength. In terms of flexural strength, no major difference was found among the specimens. Moreover, the flexural strength recovery of the specimens did not show any significant difference as well. In terms of the healing efficiency, the sample that displayed the best results was the one containing calcium lactate as a precursor along with bacteria and yeast extract encapsulated in hydrogel beads. In addition, scanning electron microscopy (SEM) along with x-ray energy dispersive spectroscopy (EDS) was performed on the cracked specimens to characterize the healing products. Furthermore, a scale study was performed on concrete samples to determine the long-term implications of adding encapsulated bacteria along with calcium lactate and yeast extract in concrete