Abstract
Cement-based materials are subject to degradation during their service life. Most of the structural failures have been associated with corrosion of the rebar due to chloride ingress, alkali aggregate reaction, and/or sulfate attack. Microbial activities, especially in waste water collection points such as sewer lines, may compromise the integrity of concrete structures. This study reports an experimental work carried out to determine the effect of Starkeya novella bacteria species on mechanical and microstructural properties of cement mortars. Mortar prisms were prepared from selected ordinary Portland cement (OPC) and Portland pozzolana cement (PPC) in Kenyan markets. Bacterial solution of 1.0 × 107 cell/mL concentration was used as either mix water, curing media, or both. Distilled water was used to prepare mortar prisms for control samples. Compressive strength was determined after the 7th, 28th, 56th, and 90th day of curing. Scanning electron microscopy (SEM) was tested on both bacterial and control mortar prisms after the 28th day of curing. Both PPC and OPC exhibited significant decrease in compressive strength for bacterial-prepared mortars as compared to controls. SEM analysis showed extreme erosion on the microstructure of the microbial mortars. This was denoted by massive formation of ettringite and gypsum which are injurious to mortar/concrete.
Highlights
Concrete and/or mortar is used globally in large volumes for construction of roads, bridges, sewage systems, and/or railway lines [1]
Most of transport and collection systems such as sewer lines are made of cement mortar/concrete. ese structures are susceptible to degradation due to microbial activities that enable a chemically aggressive environment suitable for degeneration of such structures [4]
Determination of Cement Oxides. e chemical composition of each test cement was determined using X-ray fluorescence technique (XRF). e 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 a 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 and/or mortar is used globally in large volumes for construction of roads, bridges, sewage systems, and/or railway lines [1]. Concrete and/or mortar durability is a key aspect in evaluating the service life of cement-based structures. Exposure of concrete structures into aggressive environment initiates degradation mechanisms that result in failure and/or increased repair expenses of critical civil structures. Most of transport and collection systems such as sewer lines are made of cement mortar/concrete. While a number of studies have been conducted to investigate the effect of chemical sulphuric acid on the degradation of concrete, little attention has been given to degrading microorganisms present in aggressive environments such as sewer systems [7, 8]
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