Abstract
The current paper presents the results of an experimental study on the application of calcium carbonate precipitation bacteria as a new approach to repairing damaged concrete when exposed to high temperatures. To do so, cylindrical and cubic concrete specimens were initially exposed to heat in a furnace for 1 h, after reaching two different temperatures of 600 and 800 °C. A heat rate of 5.5 °C per minute was used to achieve the target temperatures. Then, two types of bacteria, namely Sporosarcina pasteurii and Bacillus sphaericus, with cell concentration of 107 cells/mL, were utilized externally, to repair the thermal cracks, enhancing the mechanical properties and durability of the damaged concrete. The efficiency of the bacterial remediation technique was then evaluated through compressive strength, ultrasonic pulse velocity (UPV), and electrical conductivity tests on the control specimens (unexposed to heat), and those exposed to high temperature with or without bacterial healing. The experimental results demonstrate that the compressive strength of the test specimens exposed to temperatures of 600 and 800 °C decreased by about 31–44% compared with the control ones. However, compared to those damaged at 600 and 800 °C, the compressive strength of specimens repaired by the S. pasteurii and the B. sphaericus showed increases of 31–93%. This increase is associated with the precipitation of calcium carbonate in the deep and superficial cracks and pores of the damaged specimens. Furthermore, the ultrasonic pulse velocity of the specimens subjected to bacterial remediation had a significant increase of about 1.65–3.47 times compared with the damaged ones. In addition, the electrical conductivity of repaired specimens decreased by 22–36% compared with the damaged specimens.
Highlights
Composed of a mixture of Portland cement, water, and aggregates, concrete is one of the most commonly used construction materials, whose consumption increases all over the world
After adding type I bacteria and filling high heat-induced surface and deep cracks, the compressive strength of the repaired samples increased by 93% and 33% compared with the damaged and control samples of the same series, respectively
By adding type II bacteria and repairing damaged samples with calcium carbonate deposit, the compressive strength of the repaired samples increased by 52% and 6% compared with the damaged and control samples of the same series, respectively (Figure 4)
Summary
Composed of a mixture of Portland cement, water, and aggregates, concrete is one of the most commonly used construction materials, whose consumption increases all over the world. The affordability and availability of its ingredients have made concrete one of the most crucial building materials. The composite is reinforced with internal steel rebars to compensate for the disadvantages. Factors such as low tensile strength of concrete, concrete structure exposure to high thermal stresses, structural design errors, chemical attacks, and exposure of the structure to overloading can form cracks in reinforced concrete members [1,2,3,4]. The cracks may not pose a severe danger to the structure in the early days, with the development and increase
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