Abstract
Concrete structures placed in aggressive aqueous environments are vulnerable to degradation. Majority of studies have linked structural failures to the ingress of deleterious ions into the cement matrix. Some microbial activities may accelerate the penetration of harmful materials into the cement matrix and hence cause pronounced deterioration. This work reports a laboratory-simulated study carried out to determine the extent of chloride ingress in cement mortars exposed to Acidithiobacillus thiooxidans. Test prisms were cast from Portland pozzolana cement (PPC) and ordinary Portland cement (OPC) with water-to-cement ratio maintained at 0.5. Acidithiobacillus thiooxidans bacterial solution of concentration 1.0 × 10 7 cell/mL was used to prepare microbial mortar prisms, whereas distilled water was used to prepare the control mortar prisms. The test prisms were subjected to porosity and accelerated chloride ingress after 28th day of curing. Compressive strength was determined after the 2nd, 7th, 28th, and 56th days of curing. Apparent diffusion coefficients (Dapp) were estimated from the solutions to Fick’s second law of diffusion. After the 56th day of curing, the microbial-treated mortars exhibited a significant reduction in compressive strength. The resultant percentage decrease in compressive strength was 30.74% and 19.88% for OPC and PPC, respectively. Further, microbial-treated mortars demonstrated both high porosity and chloride ingress as compared to the control test mortars. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses showed the formation of new deleterious products in the microbial-exposed mortars.
Highlights
Concrete is used in different environments for construction and placement of various structures
While recent studies have focused primarily on the microbial deterioration of concrete structures, the effect of bacteria in providing a suitable environment for ingress of other deleterious materials into the concrete matrix has been relatively ignored. is work sought to investigate the contribution of Acidithiobacillus thiooxidans in accelerating the chloride ingress in cement mortars
PANalytical XRF equipment model Epsilon3XLE was used in this experiment. 0.900 g of each test cement was accurately weighed in a platinum crucible and mixed with 9.000 g of lithium tetraborate as a flux. e resultant mixture was fused in an M4 gas fusion unit for a period of 17 minutes to form a glass bead. e formed glass beads were kept in a desiccator to cool before transferred into the XRF unit for analysis
Summary
Concrete is used in different environments for construction and placement of various structures. E successive reaction of the formed biogenic acid with the concrete constituents results in the formation of expansive and low strength products [13]. E formed secondary gypsum further contributes to the deterioration of the hardened Portland cement paste through loss of stiffness and strength, expansion, and cracking of the concrete structure. According to Jensen, a microbial attack on concrete microstructure may reduce its expected service life to less than 100 years [19] Even though it is a well-known fact that composite inhabitants of microorganisms flourish well in sewer setups, the recent view that links concrete corrosion to the action of bacterial production of biogenic sulphuric acid remains broadly acknowledged. While recent studies have focused primarily on the microbial deterioration of concrete structures, the effect of bacteria in providing a suitable environment for ingress of other deleterious materials into the concrete matrix has been relatively ignored. is work sought to investigate the contribution of Acidithiobacillus thiooxidans in accelerating the chloride ingress in cement mortars
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